Pet birds can develop many digestive problems, including infections with bacteria, yeast, and parasites. Some of the more common disorders are described below.
Avian Gastric Yeast Infection (Macrorhabdosis)
Avian gastric yeast (Macrorhabdus ornithogaster) is a fungus that often lives in the digestive system of birds. It is more common in small pet birds, such as budgerigars (budgies), parrotlets, lovebirds, cockatiels, and finches.
Macrorhabdosis (infection with Macrorhabdus yeast) can spread from bird to bird if they are in close contact.Birds with weak immune systems are at higher risk of having macrorhabdosis. Common symptoms of macrorhabdosis include ongoing weight loss, regurgitation, weakness, and diarrhea. Droppings might contain undigested seeds or pellets.
Macrorhabdosis kills 10–80% of the birds it affects, depending on the type of bird and the yeast strain. Birds that recover can still shed the organism in their droppings and become infected again.
Fresh bird droppings are examined under a microscope to determine whether the bird is infected by avian gastric yeast. Finding the organisms helps confirm the diagnosis, but the yeast might be present in low numbers or might be shed into the bird's droppings only at certain times, so repeated examination of droppings might be needed to identify the organism.
Treatment of macrorhabdosis aims to decrease the number of organisms and improve the bird’s overall health and ability to digest food properly. Your veterinarian might prescribe specific antifungal medications.
Candidiasis (Thrush)
Candidiasis, or "thrush," is a common infection caused by the yeast Candida albicans, the same organism that causes thrush in human infants. This yeast is widespread in the environment and might be present in small numbers in the mouths of healthy birds. Under certain conditions, though, it can grow out of control and cause disease.
Very young, unweaned birds (still being fed by their parents or by a human caretaker)—especially if they're on antibiotics—are at higher risk of candidiasis because their immune systems are not fully developed. Recently hatched cockatiels are especially at risk. Adult birds that are malnourished, have other illnesses, or have been on antibiotics for a long time can also develop candidiasis. Antibiotics can disrupt the normal bacteria in the digestive system, allowing Candida to multiply.
Candidiasis in birds most often affects the crop (a special outpouching of the esophagus in the neck that is unique to birds), but it can also involve the bird's stomach, intestines, skin, respiratory system, and, rarely, central nervous system and other organs. How severe the infection is depends on the bird’s age and its ability to fight infection. Very young or very ill birds can develop widespread candidiasis that involves the blood, bone marrow, and internal organs.
Candidiasis can cause delayed emptying of a bird's crop, followed by regurgitation, poor appetite, and general signs of illness. Some affected birds develop an obviously swollen crop filled with mucus or undigested food.
Adult birds can have mild, chronic candidiasis with few obvious symptoms. Candida yeast can cause white patches inside the mouth, but a veterinarian must determine whether these patches are due to candidiasis or to another disease. Microscopic examination of droppings, crop contents, or regurgitated material might show the yeast.
Good hygiene is essential for the health of pet birds. Cages, nest boxes, food dishes, and other feeding utensils must be properly cleaned and disinfected.
In chicks with candidiasis, the crop might need to be manually suctioned to remove retained food and mucus. Affected chicks might also need to be given smaller amounts of food more frequently until their crop empties normally. Veterinarians typically also prescribe antifungal medications to clear the infection.
Avian Ganglioneuritis
Avian ganglioneuritis (AG), formerly called proventricular dilatation disease (PDD) or macaw wasting disease (because it was first recognized in macaws), affects nearly all parrot species. The condition is thought to result from an autoimmune reaction triggered by infection with certain viruses and bacteria, including avian bornavirus and Campylobacter bacteria.
AG is an autoimmune infection in which the bird’s immune system is stimulated to produce antibodies (proteins that target and eliminate infectious organisms) that attack not only the virus or bacteria but also the bird’s own nerves (called ganglia). Affected nerves become inflamed and do not function properly. Similar autoimmune diseases occur in people.
There are two main forms of AG, depending on which nerves are affected:
If nerves in the digestive tract are affected, the digestive tract can't contract to digest food normally, and the bird’s stomach (called the proventriculus) becomes enlarged. Birds with this form of AG lose weight (often after a brief period of increased appetite), pass undigested food (especially whole seeds) in their droppings, and might regurgitate. This form of AG is often fatal, because affected birds can't keep food down or maintain their weight.
If nerves to the wings and legs are affected, an affected bird might be unable to stand or perch. Other symptoms might be seizures, tremors, weakness, poor coordination, and blindness, which can occur with or without digestive symptoms.
Infection with avian bornavirus, one cause of AG, can be passed from parents to chicks and can spread between birds that live together or share food and water. The infection is likely spread through contact with infected droppings, but other routes of infection might exist.
Thorough disinfection of the bird's cage and food dishes, along with good ventilation, is recommended to limit the spread of infection. There is no cure for AG, and affected birds must be treated with anti-inflammatory drugs and given foods that are easy to digest for their whole lives.
Avian bornavirus does not survive long in the environment, so good hygiene and exposure to direct sunshine or to artificial ultraviolet (UV) light might help decrease its spread.
Pacheco Disease/Papillomatosis
Psittacine herpesvirus causes Pacheco disease and a condition called internal papillomatosis in parrots.
Pacheco disease involves fatal viral infection and inflammation of the liver, most often in North and South American species such as Amazon parrots, macaws, conures, and hawk‑headed parrots.
Internal papillomatosis can arise in parrots that have survived Pacheco disease. This illness is often triggered by stress, such as introduction of new birds, moving to a new location, recent breeding, or simultaneous illness with other infections. Internal papillomatosis frequently affects groups of birds, especially in breeding colonies.
The virus that causes Pacheco disease and internal papillomatosis in birds spreads through direct contact, airborne particles, and contamination of food or water by droppings. Symptoms include diarrhea, green droppings, low energy, regurgitation, and weakness. Pink, cauliflower‑like growths called papillomas develop on the lining of the digestive tract, anywhere from the mouth to the vent (the opening of the cloaca, which is the saclike end of the digestive tract, to the outside). The mouth and the cloaca are the easiest places to see these growths.
Symptoms of internal papillomatosis in birds depend on where the papilloma growths are located. Growths in the mouth can cause wheezing, difficulty swallowing, and open‑mouth breathing. Growths further down the digestive tract can cause vomiting, poor appetite, and weight loss. Straining to defecate, blood in the droppings, gas, and a foul odor can occur if papillomas are present. Growths might be visible at the vent, if the bird is straining to defecate.
A veterinarian can try to remove papillomas from birds surgically, but they often return. Treatment for these conditions is mainly supportive. There is no permanent cure, but long‑term control with repeated surgical removal and a soft, easily digestible diet is sometimes possible. No commercially available vaccine for papillomatosis is available, but in the case of flock outbreaks, veterinarians have tried making vaccines from affected birds' papilloma growths with variable success in preventing spread of the disease.
Digestive System Parasites
Giardia
Giardiasis is an infection of the digestive system by microscopic Giardia protozoa. It affects many birds but is particularly common in cockatiels. It can also be spread from birds to people.
Birds become infected when they ingest protozoal cysts (the contagious form of the protozoa) shed into the environment in the droppings of other infected birds. Some adult birds that have the parasite do not show obvious symptoms.
Giardia can cause diarrhea, malnutrition, impaired digestion of food, and weight loss. In some birds, especially cockatiels, it causes itching that leads to screaming, feather plucking, and digging at the skin with the beak. (Many other conditions can also cause feather plucking).
Droppings in birds that have giardiasis might be larger than usual and have a fluffy or popcornlike appearance. Infected chicks might be thin, have sparse feathers, and cry excessively for food, and they might die.
To treat giardiasis in pet birds, veterinarians usually prescribe an antiparasitic medication that is given by mouth. It is also critical to thoroughly disinfect the environment to eliminate infectious cysts.
Trichomonas
Trichomoniasis in parrots—called “frounce” in pigeons and doves, and “canker” in birds of prey (hawks and owls)—is caused by the microscopic protozoan Trichomonas gallinae. It is occasionally found in pet birds, especially budgies.
Trichomoniasis causes whitish‑yellow, cheeselike sores to develop inside a bird's mouth, throat, crop, and esophagus. Infected budgies might also salivate and regurgitate.
Trichomoniasis in birds spreads through direct contact (such as parents feeding chicks) or the consumption of contaminated food or water. The treatment is to thoroughly disinfect food dishes and feeding utensils and to give the bird vet-prescribed medications by mouth.
Roundworms
Roundworms can infect the digestive system of pet birds, and wild birds can pass roundworms to parrots kept outdoors.
Birds become infected when they ingest roundworm eggs from contaminated food. Symptoms of infection include weight loss, weakness, and death. In severe infections, the intestines can become blocked with worms.
Veterinarians usually prescribe deworming medications given by mouth to treat roundworm infections. In warm climates, routine deworming is often recommended for birds kept in outdoor cages.
Tapeworms
Tapeworms are now rare in pet birds because the life cycle of a tapeworm requires an intermediate host such as an insect, earthworm, or slug to complete. To spread to birds, tapeworms must pass through this intermediate host, which ingests the parasite and then is eaten by the bird.
Most pet birds today are bred in captivity, rather than being captured in the wild for sale, so they are not exposed to these intermediate hosts like wild birds are. In pet birds, infections with tapeworms are most common in cockatoos, African grey parrots, and finches.
Tapeworms rarely cause symptoms in birds, but segments of the tapeworm’s body might be visible in an infected bird’s droppings.
Pet birds with tapeworms are treated with prescription medications either given by mouth or injected to kill the worms. After being treated, a bird is unlikely to be infected again by tapeworms, unless it is repeatedly exposed to infected intermediate hosts.
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Also see professional content mycotic diseases, viral diseases, and parasitic diseases of pet birds.
