AVIAN PARASITES PART II: HELMINTHS

By David Hannon, DVM

Helminths, or worms, as they are more commonly known, are not as prevalent in birds as protozoa, but they are encountered frequently in avian practice. There are three types of helminths: 1)trematodes (flukes), 2)cestodes (tapeworms), and 3)nematodes (roundworms). Some of these parasites have a direct life cycle, meaning that the eggs or larvae shed by one infected animal are directly infectious to another animal. Others have an indirect life cycle, meaning that the helminth has to go through a period of development in another organism, typically an insect or other arthropod, before it can infect the primary host (your bird). Thus, they best ways to prevent infection and break the life cycle of these parasites are to practice good sanitation and pest control. Keep in mind that many birds act as natural hosts for these parasites in the wild, and can remain asymptomatic as long as the infection is not too severe and the bird is otherwise healthy.

TREMATODES

Flukes - It is rare to find these parasites in birds in North America. Most reported cases come from imported birds. Flukes have an indirect life cycle, and they typically inhabit the liver of infected animals, although a species that lives in the blood vessels has been reported. The most common clinical symptoms are related to liver disease, such as depression, anorexia, weight loss, diarrhea, melena (blood in the stool), anemia, and death. Fluke infections can generally be diagnosed on fecal examination, and they are readily treatable with limited success. Problems can be avoided by purchasing birds from reputable breeders.

CESTODES

Tapeworms - Tapeworms are long flat worms that attach to the inside of the intestinal wall and survive on the passing food. Instead of shedding eggs in the feces, they often shed entire segments of their bodies, which contain thousands of eggs per segment. They are most commonly seen in finches, African greys, cockatoos, and Eclectus, but because tapeworms have an indirect life cycle, it is rare to find them in birds that do not have access to the ground. If the infected bird does have any clinical signs, they will typically have diarrhea, weight loss, and an unthrifty appearance. They are difficult to diagnose on fecal examination unless a segment has ruptured, releasing eggs into the feces. Several drugs are available for treatment.

NEMATODES

Ascarids - These helminths are the most common parasites found in birds that are maintained on the ground. Budgerigars and cockatiels are the most common psittacines that are affected, but they have also been found in pigeons and gallinaceous fowl. These worms have a direct life cycle, so outbreaks are difficult to control if the birds are located in an area that can't be readily disinfected (like dirt substrate). Mild infections may cause malabsorption, weight loss, anorexia, growth abnormalities, and diarrhea, while heavier infections may lead to intestinal obstructions or even death. They are easily diagnosed and readily treatable if the infection is not too severe.

One type of ascarid that normal lives in the intestinal tract of raccoons, call Baylisascaris procyonis, can infect birds if they have exposure to raccoons or their feces. However, in birds, the larvae do not develop into adult worms, but instead they migrate through the tissues and eventually wind up in the brain or spinal cord, where they cause severe neurological disease, and eventually death. This is best controlled by preventing raccoon access to your birds.
Heterakis is another type of ascarid that is usually found in the cecum (a diverticulum of the large intestine) in gallinaceous fowl and anseriformes (ducks, geese, etc.) These parasites are more of a problem for aviculturists who raise pheasants, quail, or poultry on the ground.

Capillaria - These are tiny worms that can infect the GI tract of almost all species of birds. They are most commonly seen in macaws, budgerigars, canaries, pigeons, raptors, and gallinaceous fowl. They have a direct life cycle, and can remain infectious in the environment for several months. Clinical symptoms include diarrhea, melena, weight loss, depression, anorexia, vomiting, and anemia. Because of their invasive nature of this parasite into the walls of the crop, esophagus, and intestine, severe disease can result. They are easily diagnosed and readily treated.

Spirurids - This is a diverse family of nematodes that can infect many different organ systems. Although little is still known about many of them, all are believed to have an indirect life cycle, with an insect or other arthropod acting as the intermediate host. They can be found in the esophagus, crop, proventriculus, ventriculus, intestine, eyes (conjunctival sacs), air sacs, and lungs. They are fairly species-specific parasites, and the clinical symptoms seen and the severity of the disease are dependent upon the organ system infected. Prevention is centered around appropriate pest control.

Syngamus - Also known as "gape worms", these nematodes are rare in companion birds, but common in gallinaceous fowl and anseriformes. Infection in adult birds is rare, but in juveniles the worms can be found in the trachea or primary bronchi. Typical clinical symptoms include, coughing, open-mouthed breathing, head-shaking, dried blood at the commissure of the mouth, and difficulty breathing. If the infection is severe, death can occur secondary to asphyxiation. Earthworms act as the intermediate host, so birds without access to the ground should not be at risk. It can be diagnosed on fecal examination, and can be readily treated.

Filariids - These nematodes all have indirect life cycles, and must be transmitted from bird to bird by a blood-feeding insect (mosquito, etc.) Depending on the species, the adult worms can reside inside the abdominal cavity, air sacs, heart, or eyes, and one species resides under the skin, causing masses typically on the legs and feet. The adults worms produce microfilaria, which circulate in the blood stream until they are picked up by the insect vector for transport to another host. The clinical symptoms are dependent upon the location of the adult worms, but the microfilaria can clog the small vessels of organs, such as the liver, kidney, or spleen, and lead to organ failure. Diagnosis is usually made by examining a blood smear, and treatment involves surgical removal of the adult worms, if possible, and microfilaricides, like those used in dogs to prevent heartworms. They can be prevented by control of blood-feeding insects.