Parasites of birds (Proceedings)

Avian parasites consist of multiple species including helminthes, protozoa and arthropods.  Included are some of the important parasites that may be found in various avian species.  The likely hood of infection will depend if the birds are pet birds, captive collection, or backyard species.  The listed parasites in this paper are not inclusive but give the major pathogenic producing parasites that may be encounter in veterinary medicine.

Toxoplasma gondii causes toxoplasmosis which is infectious for all birds.  Cats are the definitive host and shed oocysts in their feces.  Clinical signs in affected birds include incoordination, listlessness, seizures, and convulsions. Lesions can range from encephalitis, myocarditis, pneumonia, and splenomegaly. Infected birds can be diagnosed using the modified agglutination test   Necropsy findings include histopath examination and PCR on affected tissues can identify T. gondii as well. Limiting cat access to yard is the most effective prevention and owners should be strongly encouraged to keep cats indoors.   

Baylisascaris procyonis is a roundworm of raccoons and birds are infected by ingesting larvated eggs in the environment.  Dogs can also serve as the definite host for B. procyonis and can shed eggs. The distribution of B. procyonis has been increasing recently.  Larval migrans of B. procyonis can result in numerous neurological impairment clinical signs including encephalitis, circling, seizures, and death.   Necropsy diagnostics include histopath examination and PCR.  Limiting raccoon access to yard and making the areas unattractive to raccoons is the main way to prevent this disease.

Oxyspirura sp. roundworms which lead to eye worm infection have been reported in avian families.  Affected birds generally have swollen conjunctiva and birds are observed scratching their eyes.  The globe can be rendered non function from chronic inflammation.  Infection in birds occurs by eating infected cockroaches so limiting arthropod ingestion is important.  Ivermectin has been useful in treatment of eyeworms.

Avian trichomonosis is caused by Trichomonas gallinae which is a protozoal parasite that primarily affects columbids, birds of prey, turkeys and passerines.  Clinical signs include swollen crop, listlessness, ruffled feathers, and often open mouthed breathing.  Variable lesions can consist of caseous necrosis within the oral cavity and esophagus and less frequently the liver.  The presence of the parasite does not indicate disease given the wide spectrum of virulence.  Transmission of the parasite occurs by direct avian contact or via contaminated food and water.  Gross lesions of trichomonosis are   not pathognomonic.  Other diseases including avian pox, candidiasis, aspergillosis, oral Capillaria spp. infection, and vitamin A deficiency can have similar gross findings.  Testing to confirm infection is conducted by examining the oral swabs via wet mount by light microscopy to observe the undulating swimming motion.  PCR testing is available as well.  Successful treatments in early infections include metronidazole and carnidazole. 

The thread-like nematode, Capillaria contorta can be found in the oral cavity and esophagus of numerous various avian species.  The parasites are slender and long and may be difficult to see grossly.  Lesions are similar to T. gallinae infection.  Birds are infected by ingesting extremely environmentally resistant eggs and as such, treatment without prevention will not stop infection in a flock. Other capillarid spp. can be found in the gastrointestinal tract leading to weight loss.  

Syngamus trachea often referred to as the gape worm often leads to open mouth breathing due to parasite infection of trachea. The parasites are red color and form a “Y” shape in the trachea.  Variable clinical signs can include gaping and gasping, listlessness, and lethargy.  Infected birds can be treated with benzimidazole antihelmentics.

Coccidiosis is an important disease in captive birds. Oocysts are shed in the host's feces and following ingestion by another host, lead to cellular infection.  Anticoccidial compounds fall into two categories including polyether ionophores and enzymatic reaction compounds. Ionophore compounds allow limited cycling of the coccidia in the bird which aids in producing immunity. Variable compounds are available and depending on previous compound use on a particular farm, experimentation may be needed to determine useable compound. Maxiban (narasin/nicarbazin)  is toxic in turkeys.   Live vaccines are available for use in the poultry industry; immunity develops rapidly after exposure, but needs reinfection to reinforce the developing protection.  

The protozoa Histomonas meleagridis is the cause of blackhead and is considered the most important parasitic disease for wild turkeys and is an important cause of mortality for numerous game birds and domestic turkeys.  Recently mortality has been seen in backyard chickens.  Clinical signs include yellow diarrhea, weight loss, and ruffled feathers.  Lesions include target shaped necrotic areas in the liver and ceca are markedly thickened with necrotic material.  On fresh carcasses, histomonads can be observed via wet mounts of swabs from affected organs.  Ring-neck pheasants are the natural host for H. meleagridis however chickens can serve as unapparent carrier for the parasites including the Heterakis nematode that is a vector for Histomonas. For this reason, turkeys, quail, grouse, or chukars cannot be raised in the same areas as chickens or pheasants.  Nitrasone (Histostat7 Alpharma Inc. Clifton, New Jersey) has been used to prevent outbreaks; however, will not be effective once an outbreak has begun. 

Ascardia spp are frequently reported in birds and can interfere with intestinal passage of food.  Ascarids are relatively large and range from 3-6 cm in length in comparison to Heterakis spp. ranging from 0.5-1.0 cm.