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Chlamydia: A Reclassification

This is very big news and changes much of what we know about this organism and the diseases it causes.

Chlamydia psittaci, the primitive bacterial organism that causes psittacosis (also called chlamydiosis or ornithosis), no longer exists, according to new research. The organism has been reclassified into the genera Chlamydophila. This is very big news and changes much of what we know about this organism and the diseases it causes.

To understand this new information, we need to review some basic scientific data. All plant and animal life has a scientific name composed of two parts; the genus name, capitalized, and the species name, in lowercase letters. The entire name is italicized. Up until now, all of the chlamydial organisms were listed in the same genus, Chlamydia. The species thought to infect birds, which was considered to be transmissible to humans, was in the species, psittaci. The three main chlamydial organisms were: Chlamydia trachomatis, the organism causing a venereal disease in humans, C. psittaci, and C. pneumoniae, causing respiratory disease in humans.

But since new genetic testing has recently been performed, the single Chlamydia genus has been broken up into two different genera (plural for genus); Chlamydia and Chlamydophila. Dr. Karin D. E. Everett, at the University of Georgia, has been instrumental in redefining these organisms. The isolates that had historically been grouped into Chlamydia psittaci are now separate species, which include Chlamydophila pneumoniae, C. psittaci, C. abortus, C. felis, C. suis and others. Each species is generally associated with a particular species of animal, however it appears that many or all of the different Chlamydophila species can infect other species of animals than the one it is primarily associated with. For example, C. felis is considered to be primarily associated with cats, and C. pneumoniae is associated with humans; however, it appears that C. pneumoniae can also infect birds. While C. psittaci can infect and induce disease in most species of free-ranging and domestic birds, it is also able to infect numerous mammals, including (but certainly not limited to) cats, koalas, marine mammals and humans.

What Diagnosis Means
This is very important information for you, your avian vet and human physician to know. Why? Well, it is vital to know which chlamydial organism a human, bird or cat is infected with in order to begin assessing where this infection came from and what the diagnosis means to the human family, aviary or pet store. For example, if a human is infected with Chlamydophila, the physician must then ascertain if it is C. psittaci, C. felis, or C. pneumoniae, or one of the other species, and then through the medical history, the doctor needs to find out if the infected person was exposed to other infected humans, or whether the person has had contact with birds, cats, livestock or other sources of possible infection.

The new classification of Chlamydophila will make us change our thinking about chlamydiosis. Your avian vet must know which tests should be used in each situation to aid in diagnosing chlamydiosis in avian species. Human physicians must be aware of the transmission potential between species, as well.

If a bird is diagnosed with Chlamydophila, it is important to know which species it is infected with, in order to determine the source of infection, if possible. Was it infected by other birds, humans, cats or livestock? Suddenly, this is important information to know. This reclassification of the organism is forcing us to think about this disease in new ways! We used to think that if a single pet bird broke with chlamydiosis after living in a home for six years, that it had to have been chronically infected and that something caused it to become ill years after exposure. Now, we need to look around in a case like this, and try to determine if the bird could have been exposed to and recently infected by an infected human, cat or livestock animal (a pet Vietnamese pot-belly pig, for example).

The standard serology tests (antibody titers) used in humans to diagnose chlamydial infections do not differentiate between the different species of Chlamydophila. The same holds true for the antibody titers that can be run on birds. They do not identify which species of Chlamydophila the bird has. The Infectious Disease Lab at the University of Georgia has developed assays that distinguish between the various species, which will aid the avian veterinarian in identifying potential sources of infection. This will allow the vet to determine which species of Chlamydophila is present in samples from bird or cat patients with suspicious signs.

This new classification of Chlamydia and Chlamydophila also impacts the tests that are usually run to diagnose chlamydiosis in our avian patients. Serology tests, which measure antibodies to Chlamydophila organisms in the blood, are used to aid in the diagnosis of this disease. Chlamydiosis is notoriously difficult to diagnose in a live bird. An avian veterinarian will utilize a combination of the physical exam, medical history, complete blood count, blood chemistry tests, radiographs (X-rays), endoscopy, ultrasonography and/or one or more of the available Chlamydophila tests.

Two titers are currently commonly used in diagnostic testing. The EBA (elementary body agglutination) titer measures an immunoglobulin called IGM, which is usually the first globulin to rise during infection with chlamydiosis, so this test is a good choice for suspected acute infections. Another titer, called the IFA (indirect fluorescent antibody) titer, measures IGG, which rises in the chronic stages of infection, so this test is useful in cases of suspected chronic infection.

An ELISA test is available, which is performed on feces or a cloacal swab, and is an antigen test (meaning it looks for the organism itself). This test is useful in cases where the bird is ill and it is suspected that it could be shedding the organism in the droppings. Another test, a DNA PCR, also is useful if a bird is suspected of shedding the Chlamydophila organism. Using a pooled swab from the choana and cloaca, this test actually looks for segments of the DNA from the organism in the sample. The DNA PCR test can also be used on the blood of a suspect bird, and this test also looks for the DNA of the Chlamydophila organism in the white blood cells. It is the DNA PCR tests that can identify the species of Chlamydophila that the bird is infected with.

The gold standard for diagnosing chlamydiosis is by the identification of the organism on culture. This method uses tissue culture to grow the organism for identification. A positive culture result shows that the Chlamydophila organism was present in the sample. However, a negative culture result does not rule out chlamydiosis, because it is possible for the organism to die in transit to the lab, or for other reasons, it might not grow out in the test medium. This is why culturing is not frequently performed on live birds. If the chlamydial organism is cultured in a sample, to determine the species present, a DNA PCR test must be performed on it, additionally.

The treatments for chlamydiosis have not changed throughout all of these new changes. Research is still ongoing about the classifications of Chlamydia and Chlamydophila. Research is also continuing regarding treatments and varying dosages required for the different species of birds, as well as methods of administration of medications. Avian researchers and avian veterinarians are always striving to provide our avian patients with the most current and accurate information available to best help our companions.

Dr. Margaret A. Wissman, Diplomate, American Board of Veterinary Practitioners, Avian Practice, owns Icarus Mobile Veterinary Service, and with her husband, Bill Parsons, co-owns Small World Zoological Gardens and Sanctuary. She also performs veterinary consultations for Antech Diagnostic Labs part-time. She has lectured worldwide on avian and exotic animal medicine, and has contributed to many avian texts and proceedings. She is active in the Association of Avian Veterinarians. See her Web site at:


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