by Darrel K. Styles, DVM
(Editors note: More accurate tests for psittacosis have been developed since this article was written. And, the genus Chlamydia has been separated into two genera.)
Psittacosis or parrot fever is caused by the bacterium Chlamydia psittaci. This is one of the oldest known diseases of our domestic birds and still causes significant physical and economic loss to aviculturists.
Several species of Chlamydia exist: C. trachomatis, which is a venereal disease of humans that causes pelvic inflammatory disorder in women and is the leading cause of infectious blindness in the world; C. pneumoniae, which is a primary human respiratory pathogen; and C. psittaci, which is an extremely cosmopolitan organism infecting a wide variety of animals including all species of birds, mammals including humans, and even reptiles! This highly nonselective nature is what makes psittacosis such a unique disease and an important zoonotic infection (a disease transferred from animals to humans). We will limit our discussion of C. psittaci to how it can affect our collections and even ourselves.
Chlamydia psittaci is a bacterium, contrary to popular literature you may have read that asserts it is a virus. However, it is a highly specialized bacterium in that, like a virus, it is an obligate intracellular parasite, meaning that it must have an animal host cell in order to grow and reproduce.
For this reason, we cannot culture psittacosis organisms on conventional bacterial media like we would E. coli. Conventional media contains only nutrients and a gel matrix for support. C. psittaci requires cells to grow. Cell culture is a more expensive and complex method of propagating the bacteria, but is the only means available.
The bacteria go through a highly complex method of reproduction and growth which is beyond the scope of this article. Suffice it to say that it results in cell death and may even kill the host.
C. psittaci is easily and casually transmitted by means of secretions, both in the stool and in respiratory secretions where the infection is airborne. Therefore, it is not easily confined like other bacteria.
The organisms survive outside their host in a specialized form called an elementary body. These elementary bodies hold the bacteria in stasis until they either find their way into a host or die. Elementary bodies can persist in the environment for a long period of time, especially when encased in organic material such a feces, but will eventually succumb to desiccation (drying out).
Psittacosis manifests itself differently in each different animal. Even different species of parrots show different signs when infected. For example, when the birds become infected they may immediately begin to show signs. Or the infection may become occult, and the birds can latently hold the disease for long periods of time, even years.
If the birds do become ill, we first typically see the bird display sick bird syndrome. This may quickly be followed by loose lime-green to yellowish stool. What is happening to cause this change in stool appearance? The organism is attacking the liver. The liver becomes somewhat dysfunctional, which causes certain blood pigments to be spilled into the urine. This causes the entire stool to be discolored, and increased urine output causes the loose nature. A component of diarrhea also is included, which further complicates matters.
This scenario is typically observed in Amazon parrots. However, macaws may show strictly respiratory signs. It is hard to say whether this is a function of species or the strain of Chlamydia infecting the bird. Nevertheless, if the infection goes untreated, death or at least severe liver damage often ensues.
The latent nature of psittacosis makes it another candidate for time bombs in our collections. We do not fully understand how this organism can lie dormant for weeks to years without causing disease, and then have a stressful event precipitate an outbreak. The bacteria probably reside in the liver waiting for an opportunity to strike. This occult behavior makes it very hard for us to detect carriers in our flocks or in newly purchased acquisitions.
The lack of reliable testing methods is another difficulty. Chlamydia may be intermittently shed in low numbers making it a difficult disease to detect. I have even heard of an instance where the organism was dormant for up to 5 years in a solitary pet Amazon who succumbed to the disease for no apparent reason. So, this bacterium can cause no illness for a long period of time, then suddenly strike.
Diagnosis and detection is a real problem! Several commercially available tests are on the market. Some of these tests have fair-to-good reliability and some, in my opinion, are not very useful. Many vets use the Kodak sure-cell test kit, which is designed for human C. trachomatis but will react to C. psittaci. This test is particularly useful in that it can be done in the office and is fairly reliable. However, the test typically cannot detect carriers because the organisms must be shed in sufficient quantities for the test to detect them, and carriers typically do not shed sufficient quantities.
Another test, latex agglutination, detects antibodies to psittacosis. But this test has mixed results and will not detect carriers. Other commercially available tests exist, which I cannot mention by name, but give very high degrees of false positive results in my experience. These tests cannot be relied upon, and I do not recommend their use. “Gold standard” tests rely upon culturing the organisms, but unfortunately are only done at the university level.
The oldest means of diagnosis is intuition. Vets experienced in seeing birds with psittacosis will usually be able to diagnosis many cases by the clinical data and patient presentation. In any event, therapy must start immediately and often on a presumptive basis until all the results are in. Fortunately, psittacosis can be treated if the disease is diagnosed early and treated properly. However, treatment is a nightmare for patient and doctor.
Psittacosis is a reportable disease in some states, which means diagnosis requires reporting to a local or state health authority. Therefore, its treatment is mandated by certain federal regulations, sort of. By this I mean that the USDA determined totally empirically that the treatment period for psittacosis must be at least 45 days. This pulled-out-of-the-hat number probably comes from quarantine days, where it took at least 30–45 days to get the results of the Newcastle disease test back from the federal testing labs. The USDA was not really concerned about psittacosis but wanted to ensure that exotic Newcastle disease did not enter the country, because it could devastate the poultry industry. However, to “protect” the public the USDA did require that quarantined birds be treated with tetracycline-treated feed for the duration of the quarantine.
Well, the birds just hate the taste of that medication. Often the station owners just would not put the medicine into the food. Otherwise they would sustain losses due to birds not eating bitter feed. At any rate, most veterinarians comply with these loose guidelines to stay out of malpractice suits and recommend a 45-day treatment period. This makes it stressful for both the bird and the aviculturist, because it is the bird owner who must conduct the bulk of the therapy unless he can afford a very expensive vet bill. Many other vets and I believe that the treatment period is probably less, maybe 10-14 days with the newer long-acting tetracyclines. But we are compelled by federal precedent to recommend the longer period.
Most vets treat with some form of tetracyclines. There are many types, all of which are effective. Some newer drugs are being used in human venereal infections that are effective after only a few doses. These hold great promise for the aviculturist if certain clinical trials now in progress prove effective.
If we are treating a solitary bird or only a few, some people elect to use an oral suspension called doxycycline. This drug is long acting and highly effective against psittacosis. But, it is difficult to get therapeutic doses down the unwilling patient. The drug has a sticky consistency with a raspberry color, which serves to stain both bird and owner in the battle. If the bird does not take the syrup willingly, it can be dangerous to try to force it down once to twice a day depending on the species.
The other option is medicating the birds in their feed. This is the only viable alternative for flock medication and can be conducted in two ways, either feed the drug as a food bolus or pill or purchase pelleted medicated feeds, which are commercially available from a variety of dealers. One can also concoct a homemade mash and incorporate the drug.
However, often birds will refuse the pellets or mash and the aviculturist must battle to get the drug in somehow. Once the treatment is finished, the bedraggled birds must again be treated for the ensuing yeast infections which result because of wiping out the normal bacterial flora.
Aviculturists must be vigilant during the treatment period to make sure birds are eating and not losing too much weight. So, as you can see, medication for psittacosis is an arduous undertaking not without risk. (Ed: I know of one story of small birds starving to death. Although they were ravenous and acting like they were eating the tetracycline-impregnated food, they were actually refusing it while they frantically picked through the food to find something palatable.)
Injectable forms of long acting tetracyclines are used by Canadian and European aviculturists, but they are not available in this country. However, newer drugs offer the hope that we can reduce the duration and frequency of therapy. Even in a very sick bird, if we can initiate tetracycline and supportive therapy early enough, the bird can be returned to virtually a normal state in 48-72 hours, so the drugs are quite effective.
Once the treatment is completed, you have hopefully eliminated the organism and the carrier state. But there is no guarantee. And, because the birds have been infected once does not mean that they cannot be reinfected. Immunity is short lived, probably on the order of 3 months. I had a blue-and-gold macaw that I treated who came back to me 6 months later reinfected. It seems pigeons were daily visitors to his cage and probably served as the vectors.
Also, you can get Parrot Fever. I speak from experience because I have had it twice. If it is not treated effectively, or if exposure is prolonged, it can cause heart problems later in life, due to infection of the heart valves. The symptoms include malaise, joint pain, and fever--like a bad case of the flu only worse. Tetracycline therapy makes you feel much better in about 12 hours. However, it appears large doses are required to infect us. I got my cases after treating large outbreaks in collections or pet shops where the birds were filling the air with psittacosis.
You must be vigilant. Because you own birds, if you experience these symptoms, advise your doctor that you may have been exposed so he can do suitable diagnostics and begin treatment. And you should know that this can be a very serious infection in immuno-compromised individuals and the very young and very old. So don’t treat psittacosis lightly.
Some states even require a quarantine if a large outbreak is detected, which can lead to the closing of pet shops. I recommend to my clients that they close their collections and not sell or accept birds during the treatment period to help eliminate liability. Retesting for effective treatment is always a good idea.
To summarize, hopefully you can detect the organism during the stressful quarantine period. But be aware that it may slip into your collections even born by wild birds. If psittacosis is diagnosed, work with your veterinarian to design a suitable treatment regimen and be aware of its human infective potential.