C. psittaci's ability to mystify us does not end with classification. It can cause disease in humans, other mammals and birds. It can kill a bird in 48 hours or it can survive in birds causing no outward sign of illness, for as long as 10 years. It can be explosively contagious or barely contagious.
It can be destroyed by antibiotics easily or with incredible difficulty. It can be easy to diagnose or extremely frustrating. It can kill baby birds and cause no disease in their parents. It can live outside the body, as well as within. It can be easy to control or almost impossible. It causes massive flock outbreaks one year and none the next.
The incubation period of psittacosis, as well as the degree of clinical illness, adds to our bewilderment. Just how a bird manifests its exposure to the disease depends on host susceptibility and the virulence (strength) of the strain.
Host susceptibility. Some birds, because of their genetic resistance, are less likely to become ill and, consequently, are more likely to develop into carriers. These include pigeons (one study suggests 70 to 90 percent of all wild pigeons are carriers), doves, budgerigars, cockatiels, cockatoos, herons, gulls, hawks, and approximately 100 additional sylvatic species. Other species, such as rosellas, lorikeets, neophemas, mynahs, canaries and some parrots have low natural resistance and are highly susceptible.
Young birds, due to the relatively incompetent immune systems, are subject to neonatal psittacosis with subsequent high mortality. Any factor that stresses a bird will lower its resistance and increase its potential susceptibility and mortality. Egg production, feeding young, weaning, poor management, overcrowding, concurrent infections and molting are just a few of the many things that stress birds.
The individual power of any agent to infect is known as virulence. This power is subject to change, especially as it inoculates birds and is passed out in the stool. Since each gram of stool from diseased birds can infect 10,000 other birds, the agent's power to cause psittacosis becomes very pertinent.
Transmission of C. psittaci is also unsettling. The organism is shed in the nasal secretions and in the stool from infected birds, recovering birds and carriers. Once outside the body, the organism can live for a long period of time, drying to form dust and infecting the susceptible hosts as they breathe. Fecal and oral contamination are especially significant in crowded conditions, as well as in nest boxes. As a general rule, inhaled Chlamydia will cause severe disease, while ingested Chlamydia will tend to develop into carriers.
Transmission through the egg has been experimentally produced in ducks, but as a practical problem, is not documented in psittacines.
Symptoms and Diagnosis
The clinical symptoms can be variable, depending on the species infected, the virulence of the agent, the route of exposure and concurrent stresses. The "typical psittacotic bird" is ruffled, depressed, has labored breathing, nasal and ocular discharge, and is neither eating nor vocalizing. The appearance of lime-green or yellow droppings, especially when the urine component is discolored, is highly suggestive, although not diagnostic, of the malady.
One form of psittacosis seen infrequently manifests central nervous system signs. Tremors, shaking, head twisting and convulsions may be the only symptoms you see. This clinical peculiarity has been recognized in Amazons, African greys and cockatoos. Cockatiels can develop a psittacosis syndrome that causes paralysis of the limbs, and usually dark, tarry stools. Additionally, cockatiels and neophemas (turquoisines, scarlet-chested parakeets) with low-grade infections may seem to have an eye disease resembling a sty.
Diagnosis of chlamydiosis in birds is definitive only if the organism is identified, isolated or causes a predictable physiologic response. The identification of the organism is achieved by stains or a fluorescent antibody test.
Treatment for parrot fever is now much more successful than it once was. Most veterinarians use tetracycline and its derivatives, mainly Vibramycin, to treat sick patients as well as carriers. The antibiotic can be given by intravenous or intramuscular injections, orally or mixed in proper ratios with palatable food. Calcium must be withheld - it binds the tetracycline. Blood levels of tetracycline can be enhanced by citric acid in the birds' drinking water.
Patients in chlamydial crisis need intense, supportive care (heat, isolation, extremely clean conditions, absence from stress, etc.) as well as therapy for concurrent problems. Appropriate lactobacillus, as well as antifungal medications, are essential.
Control and Prevention
Controlling avian psittacosis is best accomplished by keeping susceptible birds away from the infecting agent. Since this little "microvarmit" can remain infective for many months in dried excrement, cleanliness and disinfection are essential. The Chlamydia species is inactivated by quaternary ammonium compounds. These disinfectants should be used to clean cages and wet-mopped on surrounding areas. Eliminating drafts and spraying the area with disinfectants will help keep infectious feathers and dust to a minimum. Birds that have had the disease or are under treatment are fully susceptible to reinfection since the disease does not convey immunity.
In wild birds, psittacosis is controlled naturally by the inability of sick birds to keep up with the flock. Additionally, infective droppings fall to the ground below the trees in which the birds perch. The clinical disease that we see in pets is promoted by confining, crowding, transporting, dietary changes, exposure to other infections and forced exposure to infective excrement…
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