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Avian spirochetosis, an acute septicemic bacterial disease, occurs in various avian species as a result of Borrelia anserina. The spirochete, or spiral shaped bacteria, can be located in the blood of birds that have been infected in the beginning of the disease process. The pathogen is transmitted by a few species of Argas ticks.
In numerous countries, avian spirochetosis was once found to be one of the most serious diseases of the poultry industry. The disease is now pretty much limited to small flocks that are kept to be eaten or sold locally in places where the tick vector has continued to exist. It is commonly found in regions that are temperate or tropical where the biologic vectors are located.
Avian spirochetosis is an acute bacterial disease caused by the spiral shaped bacteria Borrelia anserina, which is transmitted by Argas ticks.
Symptoms of avian spirochetosis will vary in accordance with the virulence of the spirochete. In some cases, there will be no symptoms in the bird. It has been found that young birds are impacted more than older ones. In the disease’s early stages, a green or yellowish diarrhea is often noted.
In infected birds you may observe:
The typical course of the disease is one to two weeks.
Diverse types of B anserina have been found. Recovering from infection from one form of the bacteria will provide immunity against the same or similar types of bacteria for at least a year, however immunity will not be developed against different strains.
The organism that causes spirochetosis, (Borrelia anserina), is a motile spirochete. Argas persicus, a fowl tick, is the most common vector that transmits the B. anserina spirochete, though there are other Argas spp that will transmit the bacteria in different geographic locations. For example, in the western United States, A. sanchezi is a vector that will transmit the bacteria.
When the tick in infected, it can transmit the bacteria each time it feeds (bites) and will keep the infection through the larval, nymphal and adult stages. The incubation period after a tick bite is three to twelve days. Other methods of transmission include:
When examining a bird, larval ticks may be noticed on the underneath side of his wings and evidence of tick bites may be present. To diagnose spirochetosis, the bird’s blood will be tested for the presence of Borrelia. This can be done through darkfield microscopy, Giemsa-stained blood smears or by PCR. Young birds that are infected will often have high numbers of Borrelia for several days while older birds will typically have low numbers that are more challenging to detect and that disappear after 1-2 days. There will likely be high numbers of immature red blood cells as a result of anemia. To test for bacteria in tissues, silver staining can be used.
When looking to treat spirochetosis, there are a few antibacterial agents that are successful. Penicillin derivatives are the most used, however streptomycins, tetracyclines and tylosin are effective as well. When administered when the spirochetes count is low or moderate, the use of antibiotics can be totally effective. Once large numbers of spirochetes are in the bloodstream, upon receiving medication, there may be so much in the way of degradation product that the medication can lead to a higher rate of death than if treatment were not provided.
The typical disease course is one to two weeks. In areas where there is a high infestation of ticks, morbidity can be close to 100% and the mortality rate between 33 and 77%.
When looking to control the spread of the disease it is important to focus on the biological vector; the Argas tick. These ticks have a long lifespan and can survive for a long period of time without a meal. Another challenge is their ability to hide in cracks and crevices and therefore not be eradicated by pesticides.
The next thing to focus on is Immunization. Using local strains of Borrelia, bacterins have been prepared and used to inoculate birds. Inoculation will typically not protect against different serotypes. Fortunately, birds will usually have protective immunity from the same or similar strain after they recover from a natural infection.
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