Chlamydiosis: It's Not What You Think

Anything that you thought that you knew about chlamydiosis fuhgeddaboudit! Much of what we know is no longer valid information. For example A ten-year-old single pet budgie was diagnosed recently with chlamydiosis. We used to think that in the case of a single bird that hadn't been exposed to other birds that developed chlamydiosis must have been a long-term sub-clinical carrier that, for some reason, broke with disease. We now know that that bird might have recently acquired chlamydiosis, from a human or perhaps a cat, ill with chlamydiosis.

In the last several months, amazing new research has turned everything upside-down! As if this disease isn't confusing enough already, now we need to learn new facts about chlamydiosis and unlearn some of the information about how this disease affects our birds and ourselves. Chlamydiosis is also called parrot fever, psittacosis or ornithosis. The primitive bacterial organism responsible for this disease used to be called Chlamydia psittaci. According to latest research, Chlamydia psittaci no longer exists. For you to better understand all of the changes involved with this disease, we must first review some basic scientific information. Scientists use a system called binomial nomenclature to identify all living things, including bacterial organisms. The scientific name is composed of two parts; the genus name, capitalized, and the species name, in lower-case letters, and the entire name is italicized. Up until these changes in the chlamydial organisms were made, all were listed as being in the same genus, Chlamydia. The species of organism thought to infect birds, which was classified as a zoonotic disease (that is, one contagious from birds to humans), was the species, psittaci. Once a genus has been identified in a manuscript the genus name may be shortened to an abbreviation, using the first letter of the genus name, followed by the species name. So, until the recent changes were made, the three main chlamydial organisms were Chlamydia trachomatis, the organism causing a venereal disease in humans, C. psittaci, and C. pneumoniae, one that causes a respiratory disease in humans. There were others, also, that I will not be discussing here.

Since new genetic testing has been performed, the single genus, Chlamydia, has been broken up into two different genera (pleural 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 other 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.

This is very important information for you, your avian veterinarian 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. 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 standard tests used in human medicine, serology tests, that measure antibody titers (that is, measuring the response by a body to a given infectious organism) for 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 (mainly the EBA, elementary body agglutination, and IFA, indirect fluorescent antibody, titers). They do not identify which species of Chlamydophila the bird is infected with. 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 avian vet to determine which species of Chlamydophila is present in samples from avian or feline patients with suspicious signs.

I know that this might all sound confusing. In a nutshell, titers, run on blood samples, cannot differentiate between the many species of Chlamydophila. The titer tests can only tell a physician or veterinarian that a patient has been exposed to one of the Chlamydophila species. Often, a second titer, run about two weeks later, will be necessary to determine if the infection is active (by the titer number rising). To further confuse things, for veterinarians, the two different titers (EBA and IFA) should be run under specific circumstances. To simplify things, the EBA titer should be run on cockatiels and in birds suspicious of having an acute infection. The IFA titer should be run on birds suspected of having a chronic infection. So, regarding titers, it is important that the avian veterinarian select the correct test for a specific bird, based on the history and clinical signs. 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 this bird infected by another bird, or a human, or cat or livestock animal? Suddenly, this is important information to know, whereas before, we thought that all chlamydial infections came from other birds. So, this new classification of the organism is forcing us to think about this disease in new ways.

This new classification of Chlamydia and Chlamydophila also impacts the tests that are usually run to diagnose chlamydiosis in our avian patients. As I have already mentioned, antibody titers may be helpful in diagnosing this disease, which may be notoriously difficult to accurately diagnose in a live bird. An avian veterinarian will use a combination of the physical examination, medical history, complete blood count, blood chemistry tests, radiographs (x-rays), endoscopy, protein electrophoresis, ultrasonography and/or one or more of the available Chlamydophila tests. In addition to the titers available for diagnosing this disease, an ELISA (enzyme-linked immunosorbent assay) test is available, which is performed on feces or a cloacal swab, and it an antigen test, meaning that it looks for the presence of 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. A negative ELISA test result does not rule out chlamydiosis, rather, it just means that the Chlamydophila organism was not present in the droppings. Another test, the DNA PCR, is useful if the bird is suspected of shedding the Chlamydophila organism. Since the organism if found in respiratory secretions and in droppings, a suspected bird can be swabbed, using a pooled swab of the choana and the cloaca. This test actually looks for segments of the DNA from the organism in the sample. A DNA PCR test can also be used on the blood of a suspect bird, and this test also looks for the DNA of the chlamydial organism in the white blood cells. It is the DNA PCR test that can identify the species of Chlamydophila that the bird is infected with. At this point, there is an extra step involved in determining the species of a Chlamydophila, which will probably result in a higher charge for this testing. However, since this information will help in determining where this particular species of Chlamydophila came from, it will be worth it. When your physician or veterinarian chooses a laboratory to perform chlamydiosis testing, it is important that they know if that lab can do the DNA PCR testing to determine the species, if necessary. Since this is new information, it is also very important that physicians and veterinarians acquire a thorough understanding of chlamydiosis as we know it today. Chlamydiosis has always been a reportable disease in some counties and states. In light of this new information, there may be changes in the reporting requirements. This will be something that will need to be determined for the county that you live in.

The Gold Standard for diagnosing chlamydiosis is by the identification of the organism on culture. This method uses tissue culture to grow and then identify the organism by growing it out from a swab. A positive culture shows that the Chlamydophila organism was present in the sample. However, a negative culture result does not rule out chlamydiosis, as 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 which species is present, a DNA PCR test must be performed on it, additionally. The new classification of Chlamydophila will make us change our thinking about chlamydiosis. Your avian vet must know which test should be utilized in each situation to aid in diagnosing chlamydiosis in avian species. Human physicians must be aware of the transmission potential between species, as well. No longer will birds get a bad rap in all cases of chlamydiosis in humans. For now we know that humans may give a bird chlamydiosis as well as birds being able to transmit it to humans.

The treatments for chlamydiosis have not changed throughout all of these new changes. Research is still on-going about the classifications of Chlamydia and Chlamydophila. Research is still continuing regarding treatments and varying dosages 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 clients and patients with the most current and accurate information available to best help our companions.

Cadeusus
Copyright 2006 Margaret A. Wissman, D.V.M., D.A.B.V.P.
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