Disease Transmission from Companion Parrots to Dogs and Cats: What is the Real Risk?

      Keywords

      Numerous pet caregivers harbor unwarranted concerns regarding the potential of disease transmission from companion parrots to their dogs and cats. Such concerns may result in an overemphasis on testing and treatment for some of these potential pathogens in companion parrots, rehoming of companion parrots, or prevention of the adoption of parrots because of concern over the health of the household dogs and cats. A number of bacterial, viral, fungal, and parasitic diseases are postulated to undergo transmission from parrots to dogs and cats. In reality, transmission of Pasteurella multocida from companion cats to parrots is of greater concern. The following discussion reviews common conditions presumed to undergo such transmission and demonstrates the lack of data to support such concerns.

      Mycobacterium spp

      Infections with Mycobacterium avium or Mycobacterium genavense are not uncommon in psittacine species.
      • Tully T.N.
      • Dorrestein G.M.
      • Jones A.K.
      Handbook of avian medicine.
      • Pollock C.G.
      Implications of mycobacteria in clinical disorders.
      M genavense is an atypical mycobacterium that is an important source of infection in parrots.
      • Pollock C.G.
      Implications of mycobacteria in clinical disorders.
      Rare reports of infection with Mycobacterium tuberculosis or Mycobacterium bovis exist, and such infections probably occur secondary to close contact with infected humans.
      • Pollock C.G.
      Implications of mycobacteria in clinical disorders.
      Mycobacterium spp are ubiquitous in the environment and are found in soil with heavy fecal contamination or other organic debris.
      • Pollock C.G.
      Implications of mycobacteria in clinical disorders.
      Additional sources include surface water or marshy shaded areas.
      • Pollock C.G.
      Implications of mycobacteria in clinical disorders.
      Transmission occurs by ingestion or inhalation of soil or water contaminated by feces or, less commonly, urine, and vertical transmission is also possible.
      • Pollock C.G.
      Implications of mycobacteria in clinical disorders.
      In parrots, the primary site of entry and initial colonization is the gastrointestinal tract.
      • Pollock C.G.
      Implications of mycobacteria in clinical disorders.
      Inhalation may lead to direct colonization of respiratory tract, and focal skin disease secondary to inoculation into mucosal or dermal tissues or by contaminated needles may also occur.
      • Pollock C.G.
      Implications of mycobacteria in clinical disorders.
      There is no apparent gender predilection.
      • Pollock C.G.
      Implications of mycobacteria in clinical disorders.
      Clinically, affected birds demonstrate muscle wasting, loss of subcutaneous and intracoelomic adipose tissue, and poor quality feathers.
      • Pollock C.G.
      Implications of mycobacteria in clinical disorders.
      Initially the bird has a good appetite, followed by anorexia as the disease progresses. Other findings include wasting with increased appetite, poor feather quality, lethargy, weakness, pallor, chronic or intermittent diarrhea, abdominal distension, and rarely, ascites or pericardial effusion.
      • Pollock C.G.
      Implications of mycobacteria in clinical disorders.
      Bone disease is reported to have a wide prevalence (2%–93%) and can result in acute or chronic lameness or a shifting leg lameness.
      • Pollock C.G.
      Implications of mycobacteria in clinical disorders.
      Respiratory disease and reproductive failure are less commonly described.
      Grossly, hepatosplenomegaly is commonly reported.
      • Pollock C.G.
      Implications of mycobacteria in clinical disorders.
      Granulomatous lesions occur in the gastrointestinal tract and liver.
      • Pollock C.G.
      Implications of mycobacteria in clinical disorders.
      Tubercles are white, tan, or yellow.
      • Pollock C.G.
      Implications of mycobacteria in clinical disorders.
      Miliary foci to nodules several centimeters in diameter may occur within the gastrointestinal wall, liver, spleen, and bone but may occur in other viscera.
      • Pollock C.G.
      Implications of mycobacteria in clinical disorders.
      Generalized disease may be associated with diffuse enlargement of affected organs.
      • Pollock C.G.
      Implications of mycobacteria in clinical disorders.
      The gastrointestinal tract is often distended and thickened, and the intestinal mucosa may display a shaggy-carpet appearance.
      • Pollock C.G.
      Implications of mycobacteria in clinical disorders.
      The carpometacarpal and elbow joints are most commonly involved, and the skin overlying joints may be thickened and ulcerated.
      • Pollock C.G.
      Implications of mycobacteria in clinical disorders.
      Granulomas in the lungs or compression of air sacs secondary to hepatomegaly can lead to dyspnea or exercise intolerance.
      • Pollock C.G.
      Implications of mycobacteria in clinical disorders.
      Rare nodules are reported within the infraorbital sinus, nares, and syrinx.
      • Pollock C.G.
      Implications of mycobacteria in clinical disorders.
      Tubercles in the skin are rare, and dermatitis results in diffuse nonpruritic thickening and subcutaneous masses.
      • Pollock C.G.
      Implications of mycobacteria in clinical disorders.
      Infections of the eyelids, nictitating membranes, retrobulbar tissue and pecten, and cornea are also reported in birds.
      • Pollock C.G.
      Implications of mycobacteria in clinical disorders.
      Additional reports of lesions in the oropharynx, larynx, and external auditory canal exist.
      • Pollock C.G.
      Implications of mycobacteria in clinical disorders.
      Reproductive failure due to infection of the adrenal glands, pancreas, and gonads resulting in subsequent endocrine abnormalities have infrequently been reported.
      • Pollock C.G.
      Implications of mycobacteria in clinical disorders.
      Pulmonary necrosis, as well as granulomatous cardiopulmonary arteritis, are less common presentations.
      • Pollock C.G.
      Implications of mycobacteria in clinical disorders.
      Histologically, mycobacterial infections typically present as a granulomatous enteritis, splenitis, or hepatitis with variable intracytoplasmic acid-fast bacteria.
      • Pollock C.G.
      Implications of mycobacteria in clinical disorders.
      Additionally, macrophages within the dermis, mucous membranes, and subserosa of the peritoneum and air sacs are reported.
      • Pollock C.G.
      Implications of mycobacteria in clinical disorders.
      Granulomatous intestinal lesions are associated with expansion of the intestinal villi by diffuse infiltrates of epithelioid macrophages, multinucleated giant cells, fewer lymphocytes, and proliferation of epithelial cells within the glands of Lieberkühn.
      • Pollock C.G.
      Implications of mycobacteria in clinical disorders.
      Infection with M avium typically results in large numbers of acid-fast bacilli, whereas M bovis and M tuberculosis result in small numbers of acid-fast bacilli. In parrots, granulomas do not possess regions of central calcification or extensive necrotic centers.
      • Pollock C.G.
      Implications of mycobacteria in clinical disorders.
      The diffuse form is more difficult to recognize with resultant diffuse infiltration with large foamy histiocytes.
      • Pollock C.G.
      Implications of mycobacteria in clinical disorders.
      In dogs and cats, mycobacterial infections may be caused by a number of different but closely related bacteria. Relevant members of the tuberculosis complex group in dogs and cats include M tuberculosis, M bovis, and Mycobacterium microti.
      • Gunn-Moore D.A.
      Mycobacterial infections in cats and dogs.
      Other mycobacteria that can be potentially pathogenic in cats and dogs include Mycobacterium lepraemurium and opportunistic nontuberculous mycobacteria such as members of the Mycobacterium chelonae-abscessus group, Mycobacterium fortuitum group, Mycobacterium smegmatis group, and others.
      • Gunn-Moore D.A.
      Mycobacterial infections in cats and dogs.
      In general, mycobacterial infections are rare in both cats and dogs. The majority of cases are seen in cats and present as skin lesions.
      • Gunn-Moore D.A.
      Mycobacterial infections in cats and dogs.
      Most infections in dogs and cats are due to M bovis or, in the case of cats, M microti.
      • Gunn-Moore D.A.
      Mycobacterial infections in cats and dogs.
      Infection with M tuberculosis is increasingly rare.
      • Gunn-Moore D.A.
      Mycobacterial infections in cats and dogs.
      Many cases in dogs and cats are subclinical. Infection usually occurs after prolonged exposure, and disease is seen mainly in adult animals.
      • Gunn-Moore D.A.
      Mycobacterial infections in cats and dogs.
      No gender predisposition is seen in dogs, but male cats seem to be overrepresented.
      • Gunn-Moore D.A.
      Mycobacterial infections in cats and dogs.
      Certain breeds seem to be predisposed, including Siamese, Abyssinian, Bassett hounds, and Miniature Schnauzers.
      • Gunn-Moore D.A.
      Mycobacterial infections in cats and dogs.
      Depending on the route of infection, infected dogs and cats may present with systemic signs related to the alimentary or respiratory tract or with localized disease affecting the skin.
      • Gunn-Moore D.A.
      Mycobacterial infections in cats and dogs.
      The usual presentation for tuberculosis in cats is cutaneous.
      • Gunn-Moore D.A.
      Mycobacterial infections in cats and dogs.
      These lesions probably arise from infected bite wounds, local spread, or hematogenous dissemination to the skin.
      • Gunn-Moore D.A.
      Mycobacterial infections in cats and dogs.
      The lesions often involve the face, extremities, tail base, or perineum. Less frequently, lesions involve the ventral thorax.
      • Gunn-Moore D.A.
      Mycobacterial infections in cats and dogs.
      Lesions typically appear as firm, raised dermal nodules. Ulceration may be present, as well as nonhealing wounds with draining tracts. Granulomatous inflammation may extend into adjacent subcutaneous tissues, muscle, and bone. Skin lesions are commonly associated with localized or generalized lymphadenomegaly.
      • Gunn-Moore D.A.
      Mycobacterial infections in cats and dogs.
      On occasion, submandibular or prescapular lymphadenomegaly may be the only clinical finding.
      • Gunn-Moore D.A.
      Mycobacterial infections in cats and dogs.
      When the infection spreads to the lungs, tubercles arise in the lungs and hilar lymph nodes, and affected animals present with weight loss, anorexia, dyspnea, and cough.
      • Gunn-Moore D.A.
      Mycobacterial infections in cats and dogs.
      Additionally, there may be associated sneezing and nasal discharge.
      • Gunn-Moore D.A.
      Mycobacterial infections in cats and dogs.
      Pneumothorax and pleurisy may also occur with pleural and pericardial effusions.
      • Gunn-Moore D.A.
      Mycobacterial infections in cats and dogs.
      Pulmonary cases in dogs have occasionally presented with hypertrophic pulmonary osteopathy.
      • Gunn-Moore D.A.
      Mycobacterial infections in cats and dogs.
      In the alimentary form, tubercles arise in the intestines and mesenteric lymph nodes.
      • Gunn-Moore D.A.
      Mycobacterial infections in cats and dogs.
      Animals often develop intestinal malabsorption and present with weight loss, anemia, vomiting, and diarrhea.
      • Gunn-Moore D.A.
      Mycobacterial infections in cats and dogs.
      Occasionally, tubercles arise in the tonsils.
      • Gunn-Moore D.A.
      Mycobacterial infections in cats and dogs.
      In dogs and cats, a range of clinical signs may develop with disseminated disease including splenomegaly, hepatomegaly, generalized lymphadenomegaly, weight loss, and fever.
      • Gunn-Moore D.A.
      Mycobacterial infections in cats and dogs.
      With bone involvement, lameness may develop. Ocular involvement may result in granulomatous uveitis, retinal detachment, and central nervous signs due to extension along the optic nerve.
      • Gunn-Moore D.A.
      Mycobacterial infections in cats and dogs.
      Mycobacterial conjunctivitis may also be seen alone or associated with more generalized changes.
      • Gunn-Moore D.A.
      Mycobacterial infections in cats and dogs.
      To the authors' knowledge, there are no known published cases of transmission of Mycobacterium spp from parrots to dogs and cats. It is more likely that companion pets acquire such infections from living with infected people or through opportunistic infections from environmental exposure.

      Chlamydophila psittaci

      Chlamydophila psittaci is a zoonotic intracellular bacterial organism that was first reported in humans and psittacine birds in 1895.
      • Tully T.N.
      Update on Chlamydophila psittaci: a short comment.
      Most parrots and over 130 species in other taxonomic orders of birds have been found to be capable of being infected by this agent. The potential host spectrum of C psittaci also includes practically all domestic mammals including humans and many wild mammals, some amphibians, and arthropods. Chlamydophila spp have an intracellular life cycle and are periodically shed by infected birds.
      • Tully T.N.
      Update on Chlamydophila psittaci: a short comment.
      Carriers can shed the organism intermittently and typically do not demonstrate any clinical signs.
      • Tully T.N.
      • Dorrestein G.M.
      • Jones A.K.
      Handbook of avian medicine.
      The organism propagates in the epithelial cells of the respiratory tract and then generalizes to other organs.
      • Schmidt R.E.
      • Reavill D.R.
      • Phalen D.N.
      Pathology of pet and aviary birds.
      Clinical signs of disease are quite variable and are dependent on the virulence of the infecting strain as well as the host. Young birds with an incompletely developed immune system may develop acute systemic infections when exposed to particularly virulent strains of C psittaci. Most commonly, clinical signs noted in psittacine birds may include respiratory and/or gastrointestinal abnormalities. Clinical signs associated with liver disease are not uncommon in psittacine bird species (lime green diarrhea, biliverdinuria). Some birds may occasionally develop central nervous system abnormalities, keratoconjunctivitis, nasal discharge, and in the cockatiel, flaccid paresis and paralysis have been reported. Multisystemic disease can also develop in cockatiels and other species of parrots.
      • Schmidt R.E.
      • Reavill D.R.
      • Phalen D.N.
      Pathology of pet and aviary birds.
      Gross lesions include hepatic and splenic enlargement.
      • Schmidt R.E.
      • Reavill D.R.
      • Phalen D.N.
      Pathology of pet and aviary birds.
      In parrots, infections of the air sacs result in diffuse cloudy opacification with occasional tan-yellow plaques.
      • Schmidt R.E.
      • Reavill D.R.
      • Phalen D.N.
      Pathology of pet and aviary birds.
      Affected livers may have minimal gross changes, but many are enlarged and discolored, containing foci of necrosis.
      • Schmidt R.E.
      • Reavill D.R.
      • Phalen D.N.
      Pathology of pet and aviary birds.
      The spleen may range from dark red to purple, or the spleen may be pale as a result of increased inflammatory infiltrates.
      • Schmidt R.E.
      • Reavill D.R.
      • Phalen D.N.
      Pathology of pet and aviary birds.
      The conjunctiva may be diffusely reddened with serous or purulent exudates.
      • Schmidt R.E.
      • Reavill D.R.
      • Phalen D.N.
      Pathology of pet and aviary birds.
      Histologically, there is a fibrinous air sacculitis.
      • Schmidt R.E.
      • Reavill D.R.
      • Phalen D.N.
      Pathology of pet and aviary birds.
      Within the gastrointestinal tract, infection may result in diffuse mucosal necrosis and a moderate lymphoplasmacytic and histiocytic inflammatory infiltrate.
      • Schmidt R.E.
      • Reavill D.R.
      • Phalen D.N.
      Pathology of pet and aviary birds.
      C psittaci can also result in marrow granulocytic hyperplasia.
      • Schmidt R.E.
      • Reavill D.R.
      • Phalen D.N.
      Pathology of pet and aviary birds.
      Within the liver, there is a mononuclear inflammatory infiltrate, which may be diffuse within the sinusoids.
      • Schmidt R.E.
      • Reavill D.R.
      • Phalen D.N.
      Pathology of pet and aviary birds.
      Many of the macrophages contain green-brown pigment consistent with bile pigment and/or hemosiderin.
      • Schmidt R.E.
      • Reavill D.R.
      • Phalen D.N.
      Pathology of pet and aviary birds.
      Multifocal to confluent hepatic necrosis is also common.
      • Schmidt R.E.
      • Reavill D.R.
      • Phalen D.N.
      Pathology of pet and aviary birds.
      In chronic disease, portal fibrosis and bile duct hyperplasia occurs.
      • Schmidt R.E.
      • Reavill D.R.
      • Phalen D.N.
      Pathology of pet and aviary birds.
      Urinary tract lesions include lymphoplasmacytic and histiocytic interstitial inflammation.
      • Schmidt R.E.
      • Reavill D.R.
      • Phalen D.N.
      Pathology of pet and aviary birds.
      The most consistent lesion seen in the spleen is histiocytosis.
      • Schmidt R.E.
      • Reavill D.R.
      • Phalen D.N.
      Pathology of pet and aviary birds.
      There is hyperplasia of histiocytes of the perivascular sheaths and a diffuse proliferation of plasma cells.
      • Schmidt R.E.
      • Reavill D.R.
      • Phalen D.N.
      Pathology of pet and aviary birds.
      Arthritis and nonsuppurative meningitis may also occur.
      • Schmidt R.E.
      • Reavill D.R.
      • Phalen D.N.
      Pathology of pet and aviary birds.
      There is typically conjunctival necrosis with a lymphohistiocytic infiltrate.
      • Schmidt R.E.
      • Reavill D.R.
      • Phalen D.N.
      Pathology of pet and aviary birds.
      Organisms can be recognized as basophilic punctuate structures within the cytoplasm of macrophages or hepatocytes.
      • Schmidt R.E.
      • Reavill D.R.
      • Phalen D.N.
      Pathology of pet and aviary birds.
      These organisms can be visualized with Gimenez stains and other special stains.
      • Schmidt R.E.
      • Reavill D.R.
      • Phalen D.N.
      Pathology of pet and aviary birds.
      Uncommon conditions associated with chlamydophilosis include otitis media, bursitis, and solitary nephritis.
      • Shivaprasal H.L.
      Unusual cases of Chlamydiosis in psittacines.
      In cats, Chlamydophila felis, previously known as C psittaci, is a primary conjunctival pathogen.
      • Maggs D.J.
      Ocular manifestations of systemic disease.
      Cats may also shed this organism from other nonocular sites as well.
      • Maggs D.J.
      Ocular manifestations of systemic disease.
      Infection with this organism is not documented in dogs.
      To the authors' knowledge, there are no known published cases of transmission of C psittaci from parrots to other domestic animals.

      Salmonellosis

      Salmonella spp are gram-negative bacteria that typically function as primary pathogens in parrots. Salmonella spp are members of the large family of Enterobacteriaceae and are widely distributed geographically.
      • Schmidt R.E.
      • Reavill D.R.
      • Phalen D.N.
      Pathology of pet and aviary birds.
      Some serotypes have been shown to penetrate the mucosal barrier, and noninvasive serotypes result in carrier states.
      • Schmidt R.E.
      • Reavill D.R.
      • Phalen D.N.
      Pathology of pet and aviary birds.
      Salmonella typhimurium is the most common psittacine isolate.
      • Schmidt R.E.
      • Reavill D.R.
      • Phalen D.N.
      Pathology of pet and aviary birds.
      Previously, the disease was a significant problem among wild-caught birds that were closely confined in quarantine stations.
      • Schmidt R.E.
      • Reavill D.R.
      • Phalen D.N.
      Pathology of pet and aviary birds.
      Currently, this infection is more likely to be identified in parrots from aviaries that have a significant rodent problem.
      • Schmidt R.E.
      • Reavill D.R.
      • Phalen D.N.
      Pathology of pet and aviary birds.
      Affected birds typically die suddenly due to septicemia.
      • Tully T.N.
      • Dorrestein G.M.
      • Jones A.K.
      Handbook of avian medicine.
      Clinically, affected birds develop profuse watery diarrhea, polyuria and polydipsia, dyspnea, pneumonia, depression, inappetance, and neurologic signs.
      • Tully T.N.
      • Dorrestein G.M.
      • Jones A.K.
      Handbook of avian medicine.
      The classic lesions of salmonellosis include hepatomegaly, splenomegaly, pneumonia, and a catarrhal to hemorrhagic enteritis.
      • Schmidt R.E.
      • Reavill D.R.
      • Phalen D.N.
      Pathology of pet and aviary birds.
      Gastrointestinal gross lesions include intestinal redness, exudation, and mucosal ulceration to varying degrees of severity.
      • Schmidt R.E.
      • Reavill D.R.
      • Phalen D.N.
      Pathology of pet and aviary birds.
      Gas or fluid distension of the gastrointestinal tract may occur, and there is generally fecal soiling of the feathers of the vent consistent with diarrhea.
      • Schmidt R.E.
      • Reavill D.R.
      • Phalen D.N.
      Pathology of pet and aviary birds.
      Systemic infections with Salmonella spp may result in multifocal white nodules within the hepatic parenchyma (paratyphoid nodules).
      • Schmidt R.E.
      • Reavill D.R.
      • Phalen D.N.
      Pathology of pet and aviary birds.
      Histologically, intestinal necrosis with fibrin and heterophilic infiltrates are suggestive of a bacterial enteritis.
      • Schmidt R.E.
      • Reavill D.R.
      • Phalen D.N.
      Pathology of pet and aviary birds.
      There may be extension of the inflammatory process into the submucosa as well as the tunica muscularis, and crypt dilatation and abscess formation may be seen.
      • Schmidt R.E.
      • Reavill D.R.
      • Phalen D.N.
      Pathology of pet and aviary birds.
      Within the liver, paratyphoid nodules consist of randomly distributed nodular accumulations of histiocytes with fewer numbers of lymphocytes and plasma cells and variable necrosis.
      • Schmidt R.E.
      • Reavill D.R.
      • Phalen D.N.
      Pathology of pet and aviary birds.
      In most cases there is a multifocal to coalescing necrotizing splenitis with nodular aggregates of lymphocytes, macrophages, and heterophils.
      • Schmidt R.E.
      • Reavill D.R.
      • Phalen D.N.
      Pathology of pet and aviary birds.
      Additionally, salmonellosis may result in lymphohistiocytic meningitis, encephalitis, and myelitis, as well as osteoarthritis associated with bacterial septicemia.
      • Schmidt R.E.
      • Reavill D.R.
      • Phalen D.N.
      Pathology of pet and aviary birds.
      Bacteria are not always readily identifiable upon histologic examination, and additional special stains, bacterial culture, or molecular diagnostics may be necessary.
      • Schmidt R.E.
      • Reavill D.R.
      • Phalen D.N.
      Pathology of pet and aviary birds.
      In dogs and cats, infections typically begin with ingestion of organisms in contaminated food or water with subsequent invasion of M cells in the Peyer patches.
      • Marks S.L.
      Enteric bacterial disease.
      Clinical signs in these species are often associated with acute disease characterized by fever, malaise, anorexia, diarrhea, and vomiting.
      • Marks S.L.
      Enteric bacterial disease.
      The diarrhea is often watery or mucoid and can be bloody.
      • Marks S.L.
      Enteric bacterial disease.
      Most animals, though, are asymptomatic, and in rare cases systemic sepsis may occur.
      • Marks S.L.
      Enteric bacterial disease.
      To the authors' knowledge, there are no known published cases documenting disease transmission of Salmonella spp between parrots and dogs and cats.

       Yersinia pseudotuberculosis

      Yersiniosis is rare in parrots and is typically transmitted via the fecal-oral route.
      • Tully T.N.
      • Dorrestein G.M.
      • Jones A.K.
      Handbook of avian medicine.
      Following ingestion, bacteria invade the intestinal mucosa by attaching to and penetrating the mucus layer overlying mucosal epithelial cells then adhere to and colonize intestinal brush border membranes. After penetrating the mucosa, bacteria are phagocytized by neutrophils and macrophages in the mucosa and submucosa. The organisms are able to survive within the cytoplasm of these phagocytic cells and are subsequently systemically spread.
      In parrots, yersiniosis results in acute illness, diarrhea, and general ill health.
      • Tully T.N.
      • Dorrestein G.M.
      • Jones A.K.
      Handbook of avian medicine.
      Weight loss, decreased physical activity, and lethargy may be noted.
      Gross lesions include hepatomegaly, discoloration of the liver, and miliary white spots throughout the liver, kidneys, and spleen.
      • Tully T.N.
      • Dorrestein G.M.
      • Jones A.K.
      Handbook of avian medicine.
      There may be variable associated foci of necrosis with associated accumulations of caseous material and necrotic debris.
      • Schmidt R.E.
      • Reavill D.R.
      • Phalen D.N.
      Pathology of pet and aviary birds.
      Histologically, yersiniosis results in multifocal random foci of necrosis with variable associated accumulations of neutrophils and macrophages with fewer numbers of lymphocytes and plasma cells.
      • Schmidt R.E.
      • Reavill D.R.
      • Phalen D.N.
      Pathology of pet and aviary birds.
      Foci of necrosis may develop associated foci of mineralization and can be variable in size with some foci becoming quite large.
      • Schmidt R.E.
      • Reavill D.R.
      • Phalen D.N.
      Pathology of pet and aviary birds.
      Associated with foci of necrosis, there are large colonies of coccobacilli, which are suggestive of infection with Yersinia spp.
      • Schmidt R.E.
      • Reavill D.R.
      • Phalen D.N.
      Pathology of pet and aviary birds.
      Confirmatory bacterial culture is warranted in such cases.
      Yersinia pseudotuberculosis can be ingested by cats eating infected rodents or birds. The bacteria then infect the gastrointestinal tract, liver, and lymph nodes.
      • Hall E.J.
      • German A.J.
      Diseases of the small intestine.
      Clinically, affected cats demonstrate marked weight loss, diarrhea, anorexia, lethargy, jaundice, and mesenteric lymphadenomegaly.
      • Hall E.J.
      • German A.J.
      Diseases of the small intestine.
      To the authors' knowledge, there are no known published cases documenting disease transmission of Yersinia spp from companion parrots to other companion animals in the household.

      Avian Influenza

      Influenza viruses come in three groups: groups B and C affect humans and rarely birds, whereas group A affects birds and rarely humans.
      • Tully T.N.
      • Dorrestein G.M.
      • Jones A.K.
      Handbook of avian medicine.
      The primary reservoir is thought to be wild aquatic birds.
      • Shivaprasal H.L.
      Unusual cases of Chlamydiosis in psittacines.
      Avian influenza has affected parrots, causing no illness to sudden death.
      • Tully T.N.
      • Dorrestein G.M.
      • Jones A.K.
      Handbook of avian medicine.
      There are no pathognomonic clinical signs for this condition, and clinical signs may vary depending on the age and species, presence of concurrent infectious disease, and environmental factors.
      • Hawkins M.G.
      • Crossley B.M.
      • Osofsky A.
      • et al.
      Avian influenza A virus subtype H5N2 in a red-lored Amazon parrot.
      Affected birds may demonstrate depression, diarrhea, or neurologic signs.
      • Tully T.N.
      • Dorrestein G.M.
      • Jones A.K.
      Handbook of avian medicine.
      Avian influenza virus should be considered as a differential diagnosis for clinical signs of gastrointestinal tract disease in psittacines.
      • Hawkins M.G.
      • Crossley B.M.
      • Osofsky A.
      • et al.
      Avian influenza A virus subtype H5N2 in a red-lored Amazon parrot.
      This virus is rarely seen in parrots, and most psittacine infections occur either in quarantine stations where it was contracted from other birds or has been caused experimentally.
      • Tully T.N.
      • Dorrestein G.M.
      • Jones A.K.
      Handbook of avian medicine.
      Avian influenza virus varies in its pathogenicity, and the serotypes that affect poultry are not usually a great risk to parrots.
      • Tully T.N.
      • Dorrestein G.M.
      • Jones A.K.
      Handbook of avian medicine.
      Gross findings include dehydration and evidence of regurgitation such as occluded nares and feed material on the beak, head, and within the oral cavity.
      • Hawkins M.G.
      • Crossley B.M.
      • Osofsky A.
      • et al.
      Avian influenza A virus subtype H5N2 in a red-lored Amazon parrot.
      The crop may be full of feed material upon evaluation.
      • Hawkins M.G.
      • Crossley B.M.
      • Osofsky A.
      • et al.
      Avian influenza A virus subtype H5N2 in a red-lored Amazon parrot.
      Evidence of vent soiling consistent with diarrhea is also evident.
      • Shivaprasal H.L.
      Unusual cases of Chlamydiosis in psittacines.
      Additionally, hemorrhagic enteritis is a common finding.
      • Hawkins M.G.
      • Crossley B.M.
      • Osofsky A.
      • et al.
      Avian influenza A virus subtype H5N2 in a red-lored Amazon parrot.
      Occasionally, a nonsuppurative meningoencephalitis is identified.
      • Schmidt R.E.
      • Reavill D.R.
      • Phalen D.N.
      Pathology of pet and aviary birds.
      Polymerase chain reaction with matrix gene as target is needed for confirmation of infection.
      • Hawkins M.G.
      • Crossley B.M.
      • Osofsky A.
      • et al.
      Avian influenza A virus subtype H5N2 in a red-lored Amazon parrot.
      Dogs are susceptible to highly pathogenic avian influenza (H5N1) infection. Affected dogs typically develop fever but not fatal disease.
      • Giese M.
      • Harder T.C.
      • Teifke J.P.
      • et al.
      Experimental infection and natural contact exposure of dogs with avian influenza virus (H5N1).
      Contact exposure experiments of influenza virus–infected cats with uninfected dogs did not result in interspecies transmission.
      • Giese M.
      • Harder T.C.
      • Teifke J.P.
      • et al.
      Experimental infection and natural contact exposure of dogs with avian influenza virus (H5N1).
      There is a single report of a domestic cat infected with highly pathogenic avian influenza (H5N1) following ingestion of an infected pigeon carcass.
      • Songserm T.
      • Amonsin A.
      • Jam-on R.
      • et al.
      Avian influenza H5N1 in naturally infected domestic cat.
      Affected cats often demonstrate many of the following: necrotizing pneumonia with hyaline membrane formation, necrotizing and lymphoplasmacytic meningoencephalitis with gliosis, necrotizing myocarditis, necrotizing hepatitis, and necrotizing adrenalitis.
      • Rimmelzwaan G.F.
      • van Riel D.
      • Baars M.
      • et al.
      Influenza A virus (H5N1) infection in cats causes systemic disease with potential novel routes of virus spread within and between hosts.
      The potential for transmission of avian influenza from parrots to cats remains unsubstantiated. The only documented case of bird-to-cat transmission evidently required ingestion of an infected, nonpsittacine carcass. To the authors' knowledge, there are no known published cases of such transmission from birds to dogs.

      Aspergillosis

      Aspergillosis fumigatus is a noncontagious opportunistic angioinvasive fungus that results in acute and chronic respiratory and systemic disease.
      • Dahlhausen R.D.
      Implications of mycoses in clinical disorders.
      A fumigatus is a ubiquitous fungus found in nature and in the companion bird environment. Soil, moldy litter, moldy grain, and bedding material contaminated with feces are common sources of environmental Aspergillus isolates.
      • Dahlhausen R.D.
      Implications of mycoses in clinical disorders.
      Like any infectious disease, the pathogenesis of aspergillosis is a function of interactions between the host, the agent, and the environment. Host factors commonly implicated include immunosuppression, stress, trauma, and toxicoses. Overall, it seems to be uncommon for immunocompetent birds to develop aspergillosis. Stress seems to be a significant contributor to immunocompentency in both wild and captive birds. Some common stressors may include capture, travel, importation, reproductive activity, overcrowding, and excessive human traffic. Host factors that are commonly associated with risk of aspergillosis include malnutrition (hypovitaminosis A), preexisting disease, and prolonged antibiotic or steroid treatments. Agent factors that can have a role in the development of disease include challenge with a large number of spores or increased invasiveness of the organism because of its capability of being highly invasive given the right set of circumstances. Gliotoxins produced by A fumigatus are immunosuppressive (cytotoxic to lymphocytes). Lipopolysaccharide of bacteria, inhaled along with spores of A fumigatus in particulate matter, may reduce pulmonary function and the ability to clear debris from the respiratory tract, potentiating fungal colonization. A fumigatus is unique among other members of the genus for its thermotolerance; it can grow at a wide range of temperatures (20°C–50°C). Environmental factors contribute to risk of disease through chronic exposure to a small number of spores or acute exposure to a massive number of spores. If the environment is conducive to fungal growth and spore production, the stage is set for increased exposure and increased likelihood of disease. Fungal growth and sporulation are promoted by environmental conditions of warmth and high humidity, followed by a drying period. Poor husbandry practices, allowing the accumulation of debris, discarded feed, feces, and litter support fungal growth. Poor ventilation increases the concentration of spores in the environment. Types of bedding frequently implicated in promoting the growth of Aspergillus spp include corncob, walnut shell, and eucalyptus leaves.
      Aspergillus spp thrive in high humidity and warm temperatures.
      • Dahlhausen R.D.
      Implications of mycoses in clinical disorders.
      Immunosuppression, stress, and other factors related to confinement, poor husbandry, malnutrition, preexisting disease, and prolonged use of antibiotics and/or steroids predisposes to disease in companion birds.
      • Dahlhausen R.D.
      Implications of mycoses in clinical disorders.
      Disease is common in overpopulated, poorly ventilated, and dusty environments.
      • Dahlhausen R.D.
      Implications of mycoses in clinical disorders.
      Infection is often a common sequel to other respiratory tract disease.
      • Dahlhausen R.D.
      Implications of mycoses in clinical disorders.
      Predominantly seed diets may result in vitamin A deficiency and subsequent squamous metaplasia of the oral and respiratory epithelium with secondary establishment of fungal growth.
      • Dahlhausen R.D.
      Implications of mycoses in clinical disorders.
      Gray parrots and Pionus species demonstrate increased susceptibility and are commonly represented in the literature.
      • Dahlhausen R.D.
      Implications of mycoses in clinical disorders.
      Localized infections of the nasal passages are common in Amazons.
      • Dahlhausen R.D.
      Implications of mycoses in clinical disorders.
      Parrots may carry spores in their lungs and air sacs without ill effect.
      • Dahlhausen R.D.
      Implications of mycoses in clinical disorders.
      Infection develops because of inhalation of fungal spores or penetration of broken skin and eggshells, resulting in infection of developing embryos during the incubation process.
      • Dahlhausen R.D.
      Implications of mycoses in clinical disorders.
      Disease of the lower respiratory tract, lungs, and air sacs develop typically secondary to the trachea, syrinx, and bronchi being affected.
      • Hawkins M.G.
      • Crossley B.M.
      • Osofsky A.
      • et al.
      Avian influenza A virus subtype H5N2 in a red-lored Amazon parrot.
      Infections may spread from the respiratory tract to pneumatized bone or enter the peritoneal cavity by direct extension through air sac walls.
      • Dahlhausen R.D.
      Implications of mycoses in clinical disorders.
      Vascular invasion and embolism results in systemic spread of the organism.
      • Dahlhausen R.D.
      Implications of mycoses in clinical disorders.
      Clinical disease may be acute or chronic.
      • Tully T.N.
      • Dorrestein G.M.
      • Jones A.K.
      Handbook of avian medicine.
      Acute onset typically results in fatal respiratory disease.
      • Dahlhausen R.D.
      Implications of mycoses in clinical disorders.
      Dyspnea, tail bobbing, cyanosis, lethargy, anorexia, polyuria and polydipsia, sudden death, tachypnea, open-mouth breathing, gurgling respirations and vomiting may occur.
      • Dahlhausen R.D.
      Implications of mycoses in clinical disorders.
      Weight loss is common.
      • Tully T.N.
      • Dorrestein G.M.
      • Jones A.K.
      Handbook of avian medicine.
      Chronic disease results in a change of behavior, reduced level of activity, decreased appetite, exercise intolerance, weight loss even with good appetite, respiratory compromise, and tachypnea and dyspnea late in disease.
      • Dahlhausen R.D.
      Implications of mycoses in clinical disorders.
      Biliverdinuria, polyuria and polydipsia, ascites, regurgitation, diarrhea, and abnormal droppings also occur in chronic disease.
      • Dahlhausen R.D.
      Implications of mycoses in clinical disorders.
      Ataxia and torticollis may occur with involvement of the central nervous system.
      • Dahlhausen R.D.
      Implications of mycoses in clinical disorders.
      Ocular disease may result in blepharospasm, photophobia, severe periorbital swelling, and conjunctival hyperemia.
      • Dahlhausen R.D.
      Implications of mycoses in clinical disorders.
      The time from onset of clinical signs to death may be less than 1 week to 6 weeks.
      • Dahlhausen R.D.
      Implications of mycoses in clinical disorders.
      Acute disease results in whitish mucoid exudates in the respiratory tract and marked congestion of the lungs with thickening of air sac membranes and miliary foci of inflammation within the caudal thoracic and abdominal air sacs and peripheral lung fields.
      • Dahlhausen R.D.
      Implications of mycoses in clinical disorders.
      Abdominal enlargement due to ascites may also occur.
      • Dahlhausen R.D.
      Implications of mycoses in clinical disorders.
      Mycotic tracheitis results in granuloma formation within the trachea, syrinx, and primary bronchi with resultant change in vocalization ability or obstructive airway disease.
      • Dahlhausen R.D.
      Implications of mycoses in clinical disorders.
      Chronic disease results in multiple nodules, which may coalesce into plaques and larger granulomatous lesions.
      • Dahlhausen R.D.
      Implications of mycoses in clinical disorders.
      Adhesions between air sac membranes, lungs, and abdominal viscera are common.
      • Dahlhausen R.D.
      Implications of mycoses in clinical disorders.
      Air sacculitis is the most frequently encountered form of disease with extension to the lungs, most commonly with the posterior thoracic and abdominal air sacs affected.
      • Dahlhausen R.D.
      Implications of mycoses in clinical disorders.
      Chronic rhinitis and sinusitis, distension of the infraorbital sinus, and periobital soft tissue swellings are common.
      • Dahlhausen R.D.
      Implications of mycoses in clinical disorders.
      Unilateral or bilateral nasal discharge that is serous to purulent with rhinoliths and oronasal granulomas and subsequent upper airway obstruction causing wheezing and secondary bacterial sinus infections is common.
      • Dahlhausen R.D.
      Implications of mycoses in clinical disorders.
      Infection of the central nervous system with encephalitic and meningoencephalitic lesions may occur.
      • Dahlhausen R.D.
      Implications of mycoses in clinical disorders.
      Ocular disease is rare and develops secondary to preexisting upper respiratory infection.
      • Dahlhausen R.D.
      Implications of mycoses in clinical disorders.
      Corneal epithelial erosions and stromal necrosis with perforation of the cornea or panophthalmitis with functional loss of eye may develop.
      • Dahlhausen R.D.
      Implications of mycoses in clinical disorders.
      Histologically, infections with Aspergillus spp result in multifocal granulomas primarily in the respiratory tracts of parrots, including the trachea, syrinx, bronchi, lungs, and air sacs.
      • Schmidt R.E.
      • Reavill D.R.
      • Phalen D.N.
      Pathology of pet and aviary birds.
      Lesions consist of multifocal-coalescing variable accumulations of epithelioid macrophages with associated multinucleated giant cells, occasional fibroblasts depending upon the degree of chronicity, and intralesional fungal hyphae.
      • Schmidt R.E.
      • Reavill D.R.
      • Phalen D.N.
      Pathology of pet and aviary birds.
      Fungal hyphae are 2 to 4 μm in diameter with parallel cell walls and septae and demonstrate acute angle dichotomous branching.
      • Schmidt R.E.
      • Reavill D.R.
      • Phalen D.N.
      Pathology of pet and aviary birds.
      Histologically, fungal hyphae of Aspergillus spp are quite characteristic and can be used to diagnose aspergillosis with a degree of confidence.
      • Schmidt R.E.
      • Reavill D.R.
      • Phalen D.N.
      Pathology of pet and aviary birds.
      Aspergillus spp are a common cause of upper respiratory infection in dogs. Canine sinonasal aspergillosis is characterized by colonization and invasion of the nasal passages and frontal sinuses by A fumigatus.
      • Davidson A.P.
      Aspergillosis.
      The disease primarily affects young to middle-aged dogs and is progressive.
      • Davidson A.P.
      Aspergillosis.
      German Shepherds and Rottweilers are at increased risk.
      • Davidson A.P.
      Aspergillosis.
      Colonization and invasion of the nasal mucosa results in destruction and necrosis of the nasal turbinates and often results in frontal sinus osteomyelitis.
      • Davidson A.P.
      Aspergillosis.
      Facial pain, anorexia, sneezing, and mucoid to hemorrhagic nasal discharge and crusting are common.
      • Davidson A.P.
      Aspergillosis.
      Life-threatening epistaxis and secondary meningoencephalitis may occur.
      • Davidson A.P.
      Aspergillosis.
      Disseminated infections typically involve multiple organ systems with no history of nasal or pulmonary involvement.
      • Davidson A.P.
      Aspergillosis.
      Aspergillus terreus, Aspergillus deflectus, Aspergillus flavipes, and rarely A fumigatus have been reported in association with these cases.
      • Davidson A.P.
      Aspergillosis.
      Dissemination occurs following inhalation of spores and subsequent hematogenous dissemination.
      • Davidson A.P.
      Aspergillosis.
      German Shepherds seem predisposed to systemic disease.
      • Davidson A.P.
      Aspergillosis.
      Associated clinical signs are variable and based upon the organ system involved. Uveitis, ophthalmitis, and chorioretinitis may precede the onset of generalized disease.
      • Davidson A.P.
      Aspergillosis.
      The most common clinical signs are bone pain, paraparesis, draining sinus tracts, weight loss, pyrexia, lethargy, muscle wasting, and fever.
      • Davidson A.P.
      Aspergillosis.
      Infections with Aspergillus spp are often associated with immune suppression in the patient.
      • Davidson A.P.
      Aspergillosis.
      To the authors' knowledge, there are no known published cases documenting disease transmission of aspergillosis from parrots to dogs and cats.

       Cryptococcus neoformans

      Cryptococcus neoformans var neoformans is an encapsulated saprophytic fungus with worldwide distribution and is often found in soils contaminated with bird droppings.
      • Dahlhausen R.D.
      Implications of mycoses in clinical disorders.
      This organism rarely causes disease in birds, but disseminated infections have been reported in a green wing macaw, Moluccan cockatoo, thick-billed parrot, and North Island brown kiwi.
      • Dahlhausen R.D.
      Implications of mycoses in clinical disorders.
      Clinical signs are based upon location of the infection. Infections of the respiratory tract may result in dyspnea, tail bobbing, or increased respiratory noise, whereas infections of the digestive tract may result in weight loss, diarrhea, or the passing of whole seed in the feces. Finally, central nervous system infections may result in neurologic signs such as ataxia, disorientation, impaired mutation, or even seizures. Infections may sometimes be inapparent clinically and only diagnosed upon postmortem examination.
      Infection of the respiratory tract, digestive tract, and central nervous system results in necrotic granulomatous lesions and thick, pale gelatinous exudates.
      • Dahlhausen R.D.
      Implications of mycoses in clinical disorders.
      The lower temperature of the upper respiratory tract makes it more susceptible to infection.
      • Dahlhausen R.D.
      Implications of mycoses in clinical disorders.
      Upper respiratory tract involvement may produce facial granulomas that distort the rhamphotheca.
      • Dahlhausen R.D.
      Implications of mycoses in clinical disorders.
      Chronic rhinosinusitis has been reported in a Major Mitchell's cockatoo due to Cryptococcus neoformans var gate with resultant encephalitis and meningitis causing blindness and paralysis.
      • Dahlhausen R.D.
      Implications of mycoses in clinical disorders.
      Histologically, infections with C neoformans does not typically incite much of an inflammatory response because of the thick mucopolysaccharide capsule of the organism.
      • Schmidt R.E.
      • Reavill D.R.
      • Phalen D.N.
      Pathology of pet and aviary birds.
      When present, inflammatory infiltrates consist of macrophages with possibly associated multinucleated giant cells, lymphocytes, and plasma cells.
      • Schmidt R.E.
      • Reavill D.R.
      • Phalen D.N.
      Pathology of pet and aviary birds.
      Organisms may be intracellular or extracellular and are 5 to 7 μm in diameter with a 2- to 3-μm clear capsule, which stains positive with mucicarmine and a central 3- to 4-μm spherical basophilic body. Organisms are numerous and are readily identifiable with fungal stains such as periodic acid–Schiff or silver stains.
      Infection occurs via inhalation of the yeast from the environment and is not considered contagious.
      • Taboada J.
      • Grooters A.M.
      Cryptococcosis.
      Debris and droppings in and around avian habitats, especially pigeon habitats, contain large numbers of yeasts.
      • Taboada J.
      • Grooters A.M.
      Cryptococcosis.
      Lesions consist of either granulomatous inflammation with few organisms or gelatinous masses of organisms with little inflammation.
      • Taboada J.
      • Grooters A.M.
      Cryptococcosis.
      Cats are more commonly affected, and there is no breed, age, or sex predilection noted.
      • Taboada J.
      • Grooters A.M.
      Cryptococcosis.
      Clinical findings are typically associated with upper respiratory, nasopharyngeal, cutaneous, ocular, or central nervous system involvement.
      • Taboada J.
      • Grooters A.M.
      Cryptococcosis.
      The lungs are not typically affected. Upper respiratory signs include bilateral mucopurulent nasal discharge with or without blood. Proliferative lesions result in destruction of the nasal turbinates and tissue overlying the bridge of the nose.
      • Taboada J.
      • Grooters A.M.
      Cryptococcosis.
      Oral ulcerations may occur, and granulomatous chorioretinitis variably with retinal detachment and meningoencephalitis is common.
      • Taboada J.
      • Grooters A.M.
      Cryptococcosis.
      In dogs, disease typically affects young dogs under the age of 4.
      • Taboada J.
      • Grooters A.M.
      Cryptococcosis.
      American Cocker Spaniels, Labrador Retrievers, Great Danes, and Doberman Pinschers are overrepresented.
      • Taboada J.
      • Grooters A.M.
      Cryptococcosis.
      Central nervous system, upper respiratory, ocular, and cutaneous clinical signs are common.
      • Taboada J.
      • Grooters A.M.
      Cryptococcosis.
      The brain is affected in most dogs.
      • Taboada J.
      • Grooters A.M.
      Cryptococcosis.
      The upper respiratory tract is the second most common site with resultant upper airway stridor, nasal discharge, sneezing, epistaxis, or firm swellings over the bridge of the nose.
      • Taboada J.
      • Grooters A.M.
      Cryptococcosis.
      Optic neuritis may result in blindness, and granulomatous chorioretinitis often occurs.
      • Taboada J.
      • Grooters A.M.
      Cryptococcosis.
      The skin is less likely to be affected in dogs.
      • Taboada J.
      • Grooters A.M.
      Cryptococcosis.
      To the authors' knowledge, there are no known published cases documenting disease transmission for companion birds to dogs and cats.

      Histoplasmosis

      Histoplasma capsulatum is an infectious but not contagious fungal organism reported in poultry and zoo parrots only.
      • Dahlhausen R.D.
      Implications of mycoses in clinical disorders.
      The organism is soilborne and endemic in the eastern and central United States.
      • Dahlhausen R.D.
      Implications of mycoses in clinical disorders.
      H capsulatum is commonly associated with fecal material from pigeons and gallinaceous birds.
      • Dahlhausen R.D.
      Implications of mycoses in clinical disorders.
      The organism has the ability to grow within dirt substrates of enclosed aviaries and results in disease similar to Cryptococcus spp.
      • Dahlhausen R.D.
      Implications of mycoses in clinical disorders.
      An initial pneumonia can progress to disseminated disease with formation of necrotic granulomas in multiple organs.
      • Dahlhausen R.D.
      Implications of mycoses in clinical disorders.
      Osteomyelitis and mineralized soft tissue granulomas within the shoulder and antebrachium in a Moluccan cockatoo have been reported.
      • Dahlhausen R.D.
      Implications of mycoses in clinical disorders.
      Histologically, histoplasmosis results in multifocal granulomatous inflammation composed of nodular accumulations of epithelioid macrophages, multinucleated giant cells, and fewer lymphocytes, plasma cells, and heterophils.
      • Schmidt R.E.
      • Reavill D.R.
      • Phalen D.N.
      Pathology of pet and aviary birds.
      Variable numbers of intracellular fungal yeast may be identified within macrophages and multinucleated giant cells. Fungal yeasts are 2 to 4 μm in diameter and spherical with a 1- to 2-μm central basophilic body surrounded by a clear halo that develops because of artifactual shrinkage.
      • Schmidt R.E.
      • Reavill D.R.
      • Phalen D.N.
      Pathology of pet and aviary birds.
      In dogs and cats, this infection typically originates in the lungs and potentially the gastrointestinal tract with subsequent dissemination to the lymphatics, liver, spleen, bone marrow, eyes, and other organs.
      • Taboada J.
      • Grooters A.J.
      Histoplasmosis, blastomycosis, sporotrichosis, candidiasis, pythiosis, and lagenidiosis.
      Cats seem more susceptible to infection than dogs.
      • Taboada J.
      • Grooters A.J.
      Histoplasmosis, blastomycosis, sporotrichosis, candidiasis, pythiosis, and lagenidiosis.
      This organism is not contagious, and infection is via ingestion or inhalation.
      • Taboada J.
      • Grooters A.J.
      Histoplasmosis, blastomycosis, sporotrichosis, candidiasis, pythiosis, and lagenidiosis.
      Following phagocytosis by macrophages, where they grow as facultative intracellular organisms, hematogenous and lymphatic dissemination results in multisystemic disease.
      • Taboada J.
      • Grooters A.J.
      Histoplasmosis, blastomycosis, sporotrichosis, candidiasis, pythiosis, and lagenidiosis.
      In dogs the lungs, gastrointestinal system, lymph nodes, liver, spleen, bone marrow, eyes, and adrenal glands are commonly infected.
      • Taboada J.
      • Grooters A.J.
      Histoplasmosis, blastomycosis, sporotrichosis, candidiasis, pythiosis, and lagenidiosis.
      In cats the lungs, liver, lymph nodes, eyes, and bone marrow are commonly affected.
      • Taboada J.
      • Grooters A.J.
      Histoplasmosis, blastomycosis, sporotrichosis, candidiasis, pythiosis, and lagenidiosis.
      Lesions consist of multiorgan granulomas with intrahistiocytic fungal yeasts.
      To the authors' knowledge, there are no known published cases of transmission of H capsulatum from companion parrots to dogs and cats.

       Cryptosporidium spp

      Cryptosporidium spp are protozoa that function as an intracellular but extracytoplasmic parasite. Transmission occurs via the fecal-oral route. Cryptosporidium infections usually result in disease in immunocompromised birds, more specifically enteritis in small birds such as cockatiels, budgerigars, and lovebirds.
      • Dahlhausen R.D.
      Implications of mycoses in clinical disorders.
      Upper respiratory tract disease is described in birds of prey.
      Histologically, a mild-moderate lymphoplasmacytic proventriculitis with mucosal, glandular, and ductular hyperplasia has been documented.
      • Taboada J.
      • Grooters A.J.
      Histoplasmosis, blastomycosis, sporotrichosis, candidiasis, pythiosis, and lagenidiosis.
      Organisms are described as intracellular but extracytoplasmic and are histologically identified as apical 1-μm spherical basophilic structures intimately associated with the surface of mucosal epithelial cells.
      Cryptosporidium parvum infection in dogs and cats is typically asymptomatic but has been associated with self-limiting diarrhea in cats.
      • Hall E.J.
      • German A.J.
      Diseases of the small intestine.
      In immunocompromised animals, severe hemorrhagic diarrhea has been reported.
      • Hall E.J.
      • German A.J.
      Diseases of the small intestine.
      There are no published cases documenting disease transmission of Cryptosporidium spp from companion parrots to dogs and cats in the same household.

      Giardiasis

      Giardia sp is an intestinal protozoa identified in a number of different species. Morphologically identical cysts are identified in the feces of a number of different species including dogs, cats, and parrots.
      • Messenger G.A.
      • Garner M.M.
      Proventricular cryptosporidiosis in small psittacines.
      Despite their similar morphologic appearance, infectivity studies have demonstrated a lack of cross-infectivity among different species.
      • Messenger G.A.
      • Garner M.M.
      Proventricular cryptosporidiosis in small psittacines.
      • Lindsay D.S.
      Giardia and cryptosporidium: really zoonotic?.
      Giardia lamblia is typically isolated from mammals, whereas Giardia psittaci is recognized in birds.
      • Messenger G.A.
      • Garner M.M.
      Proventricular cryptosporidiosis in small psittacines.
      Giardia spp are an infrequent cause of diarrhea and have been associated with feather-destructive behavior in cockatiels.
      • Tully T.N.
      • Dorrestein G.M.
      • Jones A.K.
      Handbook of avian medicine.
      Giardial organisms may be difficult to identify antemortem because they are typically found in the upper small intestine.
      • Tully T.N.
      • Dorrestein G.M.
      • Jones A.K.
      Handbook of avian medicine.
      Giardiasis often results in minimal grossly visible changes at necropsy, although excessive fluid and mucus and mucosal hyperemia may be noted.
      • Schmidt R.E.
      • Reavill D.R.
      • Phalen D.N.
      Pathology of pet and aviary birds.
      Histologically, lesions range from nonexistent to villous atrophy and lymphoplasmacytic inflammation.
      • Schmidt R.E.
      • Reavill D.R.
      • Phalen D.N.
      Pathology of pet and aviary birds.
      Organisms may be found within the intestinal crypts but can extend the entire length of the villi.
      • Schmidt R.E.
      • Reavill D.R.
      • Phalen D.N.
      Pathology of pet and aviary birds.
      Giardiasis is described as very common in budgerigars, although most infected animals are asymptomatic.
      • Schmidt R.E.
      • Reavill D.R.
      • Phalen D.N.
      Pathology of pet and aviary birds.
      Infection is also common in cockatiels.
      • Schmidt R.E.
      • Reavill D.R.
      • Phalen D.N.
      Pathology of pet and aviary birds.
      In dogs and cats, diarrhea and abdominal discomfort are the most commonly recognized clinical signs.
      • Messenger G.A.
      • Garner M.M.
      Proventricular cryptosporidiosis in small psittacines.
      Infection is typically asymptomatic, and clinical signs range from mild self-limiting acute diarrhea to severe or chronic diarrhea associated with weight loss.
      • Hall E.J.
      • German A.J.
      Diseases of the small intestine.
      Diagnosis is typically made by identification of the characteristic trophozoites or cysts in fecal samples, although ELISA antigen capture assays are also commercially available.
      To the authors' knowledge, there are no known published cases documenting disease transmission of Giardia spp from parrots to companion dogs and cats.

      Summary

      In conclusion, there are a number of bacterial, viral, fungal, and parasitic diseases that are presumed to be transmittable from companion parrots to dogs and cats. Such disease transmission has not been documented to occur; therefore, concerns for such transmission are apparently unwarranted, and pet caregivers should feel comfortable introducing a companion parrot into their household without increased risk of disease to their pet dogs and cats.

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        • Dorrestein G.M.
        • Jones A.K.
        Handbook of avian medicine.
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        • Pollock C.G.
        Implications of mycobacteria in clinical disorders.
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        Mycobacterial infections in cats and dogs.
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        Update on Chlamydophila psittaci: a short comment.
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        Pathology of pet and aviary birds.
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        Unusual cases of Chlamydiosis in psittacines.
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        Ocular manifestations of systemic disease.
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        Enteric bacterial disease.
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        • German A.J.
        Diseases of the small intestine.
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