Birds have various digestive disorders, including infections and parasites, that can cause problems. The next section discusses some of the more commonly seen disorders in detail.

Avian Gastric Yeast (Macrorhabdus)

Avian gastric yeast colonizes the digestive tract of birds. Birds that have weakened immune systems are most often infected. The most common sign of infection is chronic weight loss, regurgitation, and/or excessive eating followed by decreased food intake. Droppings may contain undigested seeds or pellets. The percentage of deaths varies from 10 to 80% of affected birds, depending on the species and strain of the yeast. In birds that recover, both relapses and potential shedding of the organism in the droppings are likely.

The goals of treatment are to reduce the number of organisms and improve the general health and immune status of the bird. Your veterinarian may prescribe various medications to achieve this goal. This disease can be transmitted between birds.

Candidiasis (Thrush)

Candidiasis is caused by infection with the yeast Candida albicans. It is the same organism that causes “thrush” in the mouths of human babies. This yeast is common in the environment and may be present in small numbers in a normal bird's digestive tract. It may, however, cause illness under certain conditions. Very young, unweaned birds, especially those on antibiotics, may develop candidiasis due to their immature immune systems. Adult birds on longterm antibiotics or suffering from malnutrition or other illnesses may also develop candidiasis. This occurs because some antibiotics can disturb digestion by killing off beneficial bacteria that normally live in the digestive tract, allowing other organisms, such as the Candida yeast, to overgrow.

Candidiasis most often affects the crop, although the stomach and intestines may be affected as well. It can also affect the skin, respiratory tract, and rarely, the central nervous system and other organs. The severity of infection often depends on the age of the bird and the state of its immune system. A very young or very ill bird may develop an infection that spreads to the blood, bone marrow, and other organs.

Regurgitation of food, lack of appetite, and general signs of illness may be caused by delayed crop emptying caused by candidiasis. Some birds develop a swollen, mucus-filled crop. Adult birds can harbor low-grade candidiasis with few signs of illness. White spots may be present in the mouth if oral Candida is present. A veterinarian can determine whether these white spots are due to candidiasis or another disease.

Good hygiene, including proper cleaning and disinfection of the cage, nest box, and any feeding utensils, is critical to minimize the amount of Candida in the environment. In baby chicks affected with candidiasis, the crop must be emptied more often and smaller amounts fed until the crop begins to function normally again. Your veterinarian may prescribe medications to aid in effectively clearing the infection.

Proventricular Dilatation Disease (Macaw Wasting Disease)

Proventricular dilatation disease, also known as macaw wasting disease, affects not only macaws, but many other species of pet birds. Cockatoos, conures, Eclectus parrots, and many African and Asian species have been infected. The condition appears to be caused by a virus.

Proventricular dilatation disease affects the nerves of the digestive tract and results in stretching of the stomach and lack of normal muscular contractions. Signs include chronic weight loss (often following an initial increase in appetite), the passage of undigested food (most easily recognized when whole seeds are found in the droppings), and regurgitation. Widespread outbreaks are uncommon, but the infection is often fatal.

The transmission of proventricular dilatation disease appears to be by exposure to feces of infected birds, but other routes may exist. Isolation of affected birds is the only way to prevent transmission of the disease to other birds. Disinfection and improved ventilation is recommended and may help reduce transmission.

Isolation or euthanasia of affected birds is necessary in order to prevent transmission to other birds. Treatment with antiviral drugs has not been effective to date, but preliminary trials of drugs that modulate the immune system, the use of anti-inflammatory medication, and feeding a liquid diet show some promise at improving an infected pet bird's quality and length of life.

Papillomatosis

Pink, cauliflower-like growths or tissue thickening called papillomas may occur anywhere from the oral cavity, through the digestive tract, to the cloaca of a bird. The most common, or at least the most readily detected locations, are the mouth and cloaca. Papillomatosis is most likely caused by a herpesvirus that is spread through close contact between birds.

The highest incidence of these growths occurs in green wing macaws, but it is also common in other macaws, Amazon parrots, and hawk-headed parrots. Papillomatosis tends to occur as a flock problem, particularly in breeding colonies of macaws and Amazon parrots.

The signs exhibited depend on where the papillomas occur. Growths in the mouth may cause wheezing, difficulty swallowing, and open-mouth breathing. Papillomas in the gastrointestinal tract may cause vomiting, loss of appetite, and wasting. Cloacal papillomas may look like and be mistaken for a cloacal prolapse (see Disorders and Diseases of Birds: Cloacal Prolapse (Vent Prolapse)). Papillomas may be seen protruding from the vent when the bird becomes stressed or during elimination. Straining to produce stool, blood in the droppings, passing gas, and an abnormal odor to the droppings may occur.

Surgical removal of the papillomas may be attempted by your avian veterinarian, but the growths often recur. There is no permanent cure, but control for many years is possible.

In Amazon parrots, there is a high incidence of liver or bile duct cancer in birds affected with papillomatosis.

Gastrointestinal Parasites

Giardiasis occurs when protozoa (microscopic, single-celled parasites) of the genus Giardia invade the intestines. It most often affects cockatiels, lovebirds, and budgerigars (budgies), although parrots, macaws, cockatoos, and other pet birds may also become infected. Transmission occurs when infected material is eaten, and adult birds may be carriers. Giardia may cause diarrhea, malnutrition, and problems with absorption of nutrients. In some birds, especially cockatiels, Giardia may lead to itching; causing a bird to scream and pull its feathers or dig at the skin with the beak. (Note: many other causes of feather plucking exist that will cause the same symptoms.) With giardiasis, droppings may be more numerous than normal, and have a “popcorn” appearance. If baby birds are infected, they may be thin, with poor feathering, cry excessively to be fed and may die prior to fledging. The veterinarian will most often prescribe a medication taken by mouth (see Routine Care and Breeding of Birds: Giving Medication to Pet Birds).

Trichomoniasis (known as frounce or canker in non-pet bird species) is also the result of infection with a protozoan parasite, Trichomonas gallinae. It is occasionally seen in pet birds, notably budgies. Whitish-yellow lesions resembling cheese or curds stick to the lining of the mouth and throat, crop, and esophagus. Infected budgies may have signs such as increased salivation and regurgitation. Transmission may occur by direct contact (such as infected parents feeding young) or indirect contact (eating contaminated food or water). Treatment requires a medication taken by mouth.

Various types of roundworms occur in the digestive tract of pet birds, and wild birds may transmit certain roundworms to parrots housed outdoors. Transmission occurs when birds eat the roundworm eggs. Signs of infection include loss of condition, weakness, emaciation, and death. In heavy infections, the intestines can become obstructed. The veterinarian will most often prescribe a medication to kill the worms. In warm climates where exposure in outdoor aviaries is likely, a routine deworming with one of these oral medications is often performed.

Tapeworms have become uncommon in pet birds now that most are bred in captivity. These parasites are most common in cockatoos, African Grey parrots, and finches. The tapeworms are transferred from infected animals by an intermediate host that bites the animal or picks up the tapeworm organism from droppings or other discharges and then transfers the infecting parasite to a previously healthy animal. Intermediate hosts for tapeworms are most likely insects and spiders of various types, earthworms, and slugs. Signs of illness are rarely present, but segments of the tapeworm can sometimes be recognized in the droppings of affected birds. Your veterinarian will most often prescribe medication to kill the tapeworms; medicine may be given by mouth or injected into a muscle. Recurrence is rare unless the bird continues to be exposed to the intermediate host.

Last full review/revision July 2011 by Teresa L. Lightfoot, DVM, DABVP (Avian)