Avian parasites: a common problem (Proceedings)

The normal avian presentation

The first condition a veterinarian must consider when a case presents for abnormal feather loss is whether the feather loss is normal. Not only must a veterinarian consider if the feather loss is normal but if the bird is exhibiting normal preening behavior. Birds are fastidious with their grooming habits. The body is covered with feathers and the feather architecture requires normal preening by the birds to align the feather barbs for normal positioning on the body. During the process of preening molting feathers are naturally removed, often giving the owners the impression that the bird is pulling out the feathers.

Arguably the most difficult avian cases to diagnose are those that involve pathologic feather picking. With a long list of differential diagnoses it is very important to determine the health status of the presenting patient. If the feather plucking condition is determined to be a treatable disease, then a specific therapeutic regime should be prescribed. A recommended workup for this presentation includes a complete history and external physical examination, complete blood count, plasma chemistry panel, fecal examination, parasite examination (flotation and direct), cloaca and choana cultures, radiographs and biopsies (where indicated). Veterinarians must understand that cases where feather loss is involved take an inordinate amount of time when compared to other presenting complaints. Since there will be more time involved with the initial visit, one must consider charging more for this workup, than a routine complaint. One of the most important considerations during the primary workup is the patient history. There are a number of differential diagnoses for generalized feather loss and a standardized patient history form will allow one to take a complete history in a methodical manner, so not to miss evidence that may lead to an eventual diagnosis.

Veterinarians can make a quick determination if the feather loss is generalized or self induced. If the feather loss is self induced, feather loss will occur at body areas where the bird can reach. Feather loss to areas such as the head usually denotes a generalized disease process or cage mate trauma. Differential diagnoses for generalized feather loss include nutritional, infectious and hormonal diseases.

Specific disease conditions that are diagnosed can be treated by therapeutic or surgical means to reduce the trauma a bird inflicts upon itself by pulling out feathers or traumatizing the underlying epithelium. Trying to find a disease cause of feather picking is almost as difficult as identifying a behavioral source. The difficulty in determining a definitive disease diagnosis for feather plucking reinforces the need to follow a history protocol, as defined above, and a routine diagnostic plan for a feather loss presentation.

Focal areas of feather loss are often associated with an underlying tissue mass or granuloma. The underlying mass can usually be detected through palpation of the exposed skin surface. Inspisated abscesses, granulomas, lipomas, xanthomas and squamous cell carcinomas are common diagnoses of focal feather loss in pet avian species. To diagnose the mass a fine needle aspirate is recommended as the first step in identification followed by an excisional biopsy. In most cases once the underlying irritant is removed the patient stops picking.

External parasites

Parasite induced feather picking is a more complex diagnosis than most text books claim. The underlying basis for internal parasite induced feather picking is that pain, stress and general condition of the bird result in the coping mechanism of feather picking. Internal parasites that have been implicated as possible causes of self induced feather loss include tapeworms, giardiasis (cockatiels?) and roundworms. If any of these parasites are identified during a physical examination the patient should be treated. It is debatable if the parasite infestation is in fact the cause of the feather picking or some other measure that is modified during the visit. If nothing else, the bird will be in better health once treated properly for the identified internal parasites. External parasites can cause feather destruction, feather loss and/or excessive preening. Knemidokoptes spp., also known as the scaley leg and face mite is commonly found in budgerigars. Feather loss around the beak and eyes is evident when birds present with this parasite. Hyperkertosis of the facial skin, beak and legs are a result of the dermal irritation to the mite infestation. Dermanyssid and Macronyssid mites are extremely irritating and are often observed as red or black dots moving over the feathers and skin of an agitated avian patient. Dermanyssid and Macronyssid mites are rarely found on pet bird patients.

Intestinal parasites

As with external parasites, internal parsites are uncommon in companion and caged birds. All birds should have direct fecal and fecal flotation examinations as part of a complete health check. Nematodes, as with most of the parasites that affect avian species, commonly infect birds that live in outdoor environments. Ascarids have a direct life cycle, in which simply ingesting eggs can infect a bird, while Capillaria spp. and Syngamus trachea need an intermediate host. Ascarids and Capillaria spp. live in the intestinal tract, while Syngamus trachea are found in the oral cavity and esophagus. Birds infested with intestinal parasites will be depressed and emaciated. In most cases nematode eggs are shed in the feces and are observed in a fecal flotation exam. It is important to treat the bird and, if possible, the environment.

The 2 most common protozoan parasites diagnosed in avian species are Giardia spp. and Trichomonas gallinae. Giardiasis is associated with intestinal tract disease while trichomoniasis presents as white plaques or necrotic masses in the mouth ans esophagus.The treatment of choice for both Giardia spp. and Trichomonas gallinae is metronidazole (Flagyl, G.D. Searle Co., Chicago, IL) 50 mg/kg, q 24 h, PO for 5-10 days.

Atoxoplasma spp., a coccidian parasite primarily affects canaries, finches and mynah birds. The diagnosis is usually determined during a pathology examination of a dead juvenile bird that dies shortly after appearing depressed. The juvenile birds are exposed by their parents which shed the infective oocysts in the feces. Treatment is difficult, therefore it is recommended that disease free birds be used for breeding. Trimethoprim/sulfadiazine (Roche Pharmaceuticals, Nutley, NJ) 100 mg/kg, PO, BID is the recommended treatment for avian coccidian parasitic diseases. Since it may be difficult to treat a large group of caged birds individually sulfachlorpyridazine, (Vetasulid, Solvay) ¼ - ½ tsp/L drinking water for 5-10 days may be used.

Sarcocysits falcatula is the other coccidian parasite commonly diagnosed in companion avian species. This parasite usually is found in aviary birds housed outdoors in breeding flights. The life cycle of Sarcocystis falcatula involves the opossum (Didelphis virginiana) and cockroaches. As with Atoxoplasma spp., Sarcocystis falcatula is usually diagnosed during a pathology examination on a dead bird. The extensive life cycle requirements of the parasite make environmental management extremely important if the owner wants to prevent exposure and infections within an aviary.

Respiratory parasites

The client must be informed when respiratory signs are potentially life-threatening prior to examination or treatment of the bird. Open-mouth breathing, tail bobbing, and abdominal distention may indicate respiratory compromise, and even minimal restraint for examination may cause death.  A quick thorough history, clinical signs and prior knowledge of common respiratory problems associated with species being examined will aid in forming a list of differential diagnoses. Clinical signs associated with upper respiratory disease include open-mouth breathing, change in vocalization, odor from sinus, rhinorrhea, nasal granulomas, exercise intolerance, dyspnea, head-shaking, mucopurulent nasal discharge, inflammed swollen cere stretching of the neck, yawning, epiphora, periophthalmic swellings and plugged nares. Clincial signs associated with lower respiratory disease include tail-bobbing, change or loss of vocalization, labored respiration, wings out, exercise intolerance, open beak breathing, coughing and abnormal sounds on auscultation. The oral cavity and choanal slit is the next area examined. To examine this area an avian speculum is recommended to open the beak of the bird.  Fecal examinations may reveal respiratory tract parasites, including Syngamustrachea, Cyathostomabronchialis, Trichomonas, Capillaria, Atoxoplasma, Cryptosporidium, and Sternostoma spp.

References

Clyde VL and Patton S. Diagnosis, treatment and control of common parasites in companion and aviary birds. Seminars in Avian and Exotic Pet Medicine. 1996; 5: 52-64.