Ask the Vet
Drury R., DVM
4/1/91

Q: Psittacosis, Chlamydia, parrot fever throws most breeders, pet owners, pet shops, into total panic of fear and despair. I consider it a fact that a percentage of birds will be carriers but pose very little risk to other birds or humans under normal circumstances. 1) How is the disease diagnosed? 2) What treatment is available? 3) In most cases, will a bird completely recover after treatment? 4) Would you advise breeders of large flocks to treat every few years for psittacosis?

A: Diagnosis: Chlamydia infections in birds are diagnosed by a number of different laboratory tests. Avian practitioners can make a presumptive diagnosis by the physical exam, history, a simple blood test, the CBC (complete blood count), and sometimes an x-ray. However, because a chlamydial infection looks like several other diseases, additional tests are required to confirm an actual infection.

Chlamydia can be grown and isolated in special media at laboratories equipped to do so. Unfortunately the growth period is very long, usually several weeks. By the time the disease is diagnosed, the bird could be dead. Another problem is in getting the live chlamydia to the lab.

There are several antigen ELISA tests which are used to diagnose a bird shedding chlamydia. These tests look for the chlamydia in the nasal or eye secretions or the feces. The antigen ELISA test can also be used on the tissues from a surgical biopsy or a necropsy sample. One problem with these tests is that birds intermittently shed chlamydia and the sample may be taken when the bird was not shedding. Also several antibiotics inhibit chlamydial shedding, giving a false negative test result. The test takes several hours to complete, but many labs run groups of samples together and may only do this on certain days of the week.

Chlamydia can be diagnosed by a type of blood test called serology. When a bird is infected with chlamydia, the immune system produces antibodies to fight the chlamydia. The serology test measures the antibodies. There are several different serology tests offered. Most have some drawback to their universal use. One test may require more blood than a budgie can give, another may need expensive test supplies, and another may not work in certain bird species. European veterinarians have developed a good serology test that works in all species and does not require much blood. This test (BELISA) is offered by the California Avian Lab under a provisional USDA license.

Finally, the disease can be diagnosed at necropsy. Special stains are used on the tissues to identify the chlamydia.

Treatment: For years, chlamydial infections have been treated with tetracyclines. In fact the only government approved treatment is with chlortetracycline medicated feed. This drug has several problems. One is that many birds do not like the taste and won't eat the food. In order to be effective, it needs to be the only food offered, so some birds may suffer malnutrition and get very ill. Chlortetracycline also kills many of the normal gut bacteria in a bird. This can lead to secondary gram negative bacterial infections and yeast infections.

More commonly a new semisynthetic tetracycline called doxycycline is used. This drug is superior to the old tetracyclines for treating chlamydia. It has fewer side-effects and is more effective. It comes as an oral drug and as an injectable drug. Unfortunately the injectable form is marketed in Europe, so it is very expensive when it is available.

There are other drugs that have activity against chlamydia, but they do not seem to effectively treat the disease.

Most birds should completely recover with effective treatment and adequate cleaning of the environment. However this will depend on the species of the bird, the virulence of the chlamydia, the duration of the infection, and the health of the bird before infection. Because chlamydia is highly contagious among birds, it is important to isolate any new additions and have them tested before introducing them to your other birds.

I do not recommend treating large flocks every few years for the infection, unless it is diagnosed in the group. The side-effects of the drug may be detrimental to your prize breeders or to their young. Also, it may be possible to develop a tetracycline or doxycycline resistant chlamydia with inappropriate treatments. The best course of action is to maintain the highest husbandry standards, practice good nutrition, and isolate any new birds.

Human Health Hazard: Because chlamydia is contagious to people and years ago caused several large outbreaks and deaths, it was designated a reportable disease by the public health authorities. Under "normal circumstances" it may pose little risk to healthy people. However, in this day of AIDS and cancer and immune system diseases, we need to be aware of the risk from chlamydia. It can cause disease in people (there were eight confirmed human cases in the state of California last year) and can be severe enough to result in a hospital stay. For those people with immunodeficiencies, it can be a deadly disease. I do believe it poses a significant risk to other birds and if diagnosed, it should be treated.

[Editor's note: I don't want to hog ALL of the fun. I'll leave this for another reviewer! ]