James Harris, DVM
Many birds carry dormant psittacosis
 Information on psittacosis seems to get increasingly confusing. My question is about carriers. Is it possible for a bird to test positive for psittacosis (using a DNA PCR blood test), be treated for 45 days with doxycyline, and still be a carrier? (That is, still have the psittacosis organisms which could change from inert to active and be shed at anytime?) Would a carrier test positive using the DNA PCR blood test? Obviously, I am concerned because I adopted a bird who did test positive. I have treated her and she will be retested in a few months, but I am concerned she could be a carrier who could infect my other birds in the future.
-- Lynne Page, marduckbud@lycos.com
 The answers to your questions are yes, a bird that has been treated for psittacosis can still be a carrier, and no, a carrier will not necessarily test positive. But your situation may not be as dire as you think. Let me explain.
First, for those not familiar with it, DNA PCR (desoxyribose nucleic acid pollymerase chain reaction) is a biochemical test that identifies an organism from small amounts of its genetic material. The test detects pisttacosis, an infection of birds, humans, and other mammals, by the presence of the organism that causes the disease, Chlamydiophilla psittaci.
Doxycycline, an advanced form of tetracycline, is the treatment of choice for psittacosis. Treatment continued for 45 days usually clears disease symptoms, which may include lime-green droppings, discharges from nostrils and eyes, and a general malaise. Unfortunately, as you've discovered in your readings, psittacosis is a bit more complicated than that.
That's because chlamydia are normal flora in many species of birds, including parrots (it's been identified in 52). They carry the organism, but may never shed it or become ill because of it. As long as a bird remains healthy, with good nutrition and an adequately functioning immune system, the presence of chlamydia is not a problem.
It's when a bird becomes stressed that the chlamydia organisms can multiply and be shed in droppings or from the nostrils or eyes. Sometimes chlamydia overwhelms the shedding bird and the bird becomes clinically ill, showing the classic symptoms of psittacosis. If birds and humans that come into contact with the shedder are in a weakened state, too, they also can become ill.
Here's how the DNA PCR test does - and does not - work. Chlamydia live within cells of tissue. When they become active, they reproduce by breaking out of their host cells and invading others. It is during this time, when the chlamydia are in transit, between cells, that the DNA PCR test can detect their genetic material and medicine can destroy them.
However, no treatment is 100 percent effective. Negative followup tests (assuming they're properly done) mean only one thing: the telltale genetic material of the organism detectable when it's spreading was not found. Negative tests don't mean the chlamydia does not live on within host cells.
So as you can see, the reality is that any bird is capable of carrying chlamydia, shedding it, and becoming ill from it. As long as there are birds there will be chlamydia, and as long as we interact with birds, we can be exposed. The good news is that you can greatly lessen the chances of infection by keeping your bird robust, and humans, unless they are elderly or immune compromised, rarely suffer from anything worse than flulike symptoms.
James Harris, DVM is owner and medical director of the Mayfair Veterinary Clinic in Sandy Bay, Tasmania, Australia. He founded Montclair Veterinary Hospital in Oakland, Calif., and has served as medical director and chairman of the board for the International Bird Rescue Research Center in Berkeley. Dr. Harris' numerous professional honors include California and National Bustad Companion Animal DVM Awards.
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