AVIAN PARASITES PART I: PROTOZOA

By David Hannon, DVM

Internal parasites in pet birds are rare. The majority of birds which have problems with parasites are either from questionable backgrounds (imported, smuggled, etc.), housed in outdoor aviaries, where they have contact with wild birds, or poor husbandry is practiced in the aviary. Any contact with other animals, especially rodents, insects, or wild birds, puts a pet bird at increased risk for parasite infection. Protozoan parasites are the most commonly seen internal parasites in cage birds.

GASTROINTESTINAL PROTOZOA

These protozoa are single-celled parasites that mainly infect the intestinal tract, but can infect other tissues as well. The most common gastrointestinal protozoa are:

Trichomonas - This organism is transmitted from one bird to another by direct contact with an infected bird or its feces. It is most commonly spread by pigeons and doves. It is most often seen infecting the upper aspects of the GI tract, such as the mouth, esophagus, and crop, but it can be present throughout, and can even infect the liver. It will cause white-to-yellow plaques or build-ups of cheesy material that might occlude the trachea or esophagus, and typically infected birds will have vomiting and diarrhea, and become emaciated. It is easily treatable in its early stages, and can be prevented by avoiding contact with infected birds.

Giardia - This protozoan is more commonly found in pet birds, mainly because birds can be infected from contaminated water. An infected bird may not show any clinical symptoms, and can therefore act as a source of infection for other birds. Typically symptomatic birds will show diarrhea, depression, decreased appetite, recurrent yeast infections, dry skin, and feather picking. It can sometimes be diagnosed on fecal examination, but often more specific tests are needed if it is suspected. There is a drug available that works well against it, and it can be prevented by keeping the aviary clean and dry, limiting contact with other birds or contaminated water.

Hexamita - This organism is commonly spread in pigeon feces, and usually does not cause clinical disease in psittacines unless the birds are maintained in poor conditions. If the bird does become symptomatic, typical signs are chronic diarrhea and weight loss. It is readily treatable.

Coccidia - This organism is commonly found in mynahs, toucans, pigeons, canaries, finches, and lories. There are two species of Coccidia, and typically the organism that infects one species of bird will rarely infect another. Infected birds may be asymptomatic, or show depression, diarrhea, anorexia, melena (blood in the feces), and death. Transmission occurs from one bird to the next by ingestion of fecal-contaminated food or water. It is readily treatable.

Atoxoplasma - This protozoan most commonly causes disease in canaries and other passerines. Adults are usually asymptomatic carriers, while infected juveniles will show depression, anorexia, diarrhea, and death. Mortality rates as high as 80% have been reported in juvenile birds two to nine months old. Besides the GI tract, it can also infect other organs, such as the heart, liver, spleen, and pancreas. It is typically spread by ingestion of food or water contaminated with feces from wild passerines, typically house sparrows. There is no effective treatment at this time.

Cryptosporidium - Although this parasite commonly infects the intestinal tract, it can also cause severe respiratory and urinary tract disease. Clinical signs can range from anorexia, diarrhea, and weight loss, to coughing, sneezing, and difficulty breathing, to excessive urination, to acute death, or the bird may be an asymptomatic carrier. It is transmitted by ingestion or inhalation of sporulated organism (it sporulates when it leaves the body, so that it is protected from the environment). It is very difficult to diagnose, and there is no effective treatment at this time. It is prevented by good hygiene.

HEMOPROTOZOA

These protozoa affect the blood cells, but can sometimes infect other tissues as well. They are usually spread by insect or other arthropod. The most common hemoparasites are:

Hemoproteus - This organism is spread by Hippoboscid flies (louse flies) or Culicoides (biting midges, punkies). It will infect the red blood cells. It is the most common type of hemoparasite, and rarely causes clinical disease, except when the bird is stressed or immune-suppressed, or concurrently infected with another organism. If clinical signs are apparent, they usually consist of anemia, liver disease, or respiratory disease. It can be diagnosed by examining a blood smear, and it is readily treatable.

Leucocytzoon - This organism is spread by Culicoides and black flies. It typically infects white blood cells, but will also infect red blood cells. It is often asymptomatic, but can cause anemia. Other clinical signs reported include enlargement of the liver or spleen, lung congestion, and heart disease. It can also be diagnosed on a blood smear, and readily treated.

Plasmodium - Infection with this organism is also called avian malaria. It has the widest host range of any of the blood parasites, and is typically carried asymptomatically in passerines, which can act as reservoirs for the parasite. Although it is typically spread by mosquitoes, it can also be spread by blood-to-blood contact. Clinical signs most often seen are anorexia, depression, vomiting, and difficulty breathing for a few hours or days prior to death. It has a very high mortality rate in some species. It is treatable if diagnosed promptly. It is best prevented by good mosquito control.

OTHER PROTOZOA

These organisms are typically found in other areas of the body, besides the blood and GI tract. They include:

Toxoplasma - The primary host for this organism is the cat, and the most common source of infection in pet birds is from ingestion of domestic cat feces, but it can also found in undercooked meat products. It is infective to most avian and mammalian species. In birds it typically causes respiratory, liver, cardiovascular, and neurological disease. Diagnosis is difficult, but it is treatable. It is best prevented by limiting exposure to cats and cat feces.

Sarcocystis - The primary host of this organism is the opossum, and transmission occurs secondary to ingestion of opossum feces or fecal-contaminated foodstuff. Roaches can act as transport hosts as well. Clinical signs include acute death, anorexia, diarrhea, weakness, difficulty or rapid breathing, and neurological signs. It is difficult to diagnose, and the available treatment is questionable as to effectiveness. Prevention centers around cockroach and opossum control.