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Avian Borreliosis

Other Names: Fowl Spirochetosis

Avian borreliosis, also referred to as fowl spirochetosis, is an acute, highly fatal septicemic disease of birds caused by the helical spirochete bacterium, Borrelia anserina. The disease affects a number of avian species, including chickens, ducks, turkeys, geese, pheasants, and game birds. Occurrence of avian borreliosis corresponds with the subtropical and tropical distribution of fowl ticks in the genus Argas, which serve as both the reservoir and primary vector.

The severity of the infection depends on the strain of bacteria. Infection with low virulent strains may be mild or inapparent, when infection with virulent strains causes visible signs of sickness. In infected birds, there is a marked elevation in body temperature that begins shortly after infection and a rapid loss of body weight. Affected birds pass fluid, green droppings containing excess bile and urates, and have increased water consumption. Late in the disease, birds develop paresis or paralysis, become anemic, and are somnolent to comatose.

Diagnosis of Avian Borreliosis

Avian borreliosis is confirmed through laboratory tests which confirm the presence of B. anserina or its antigens in affected birds. Dark-field microscopy is the method of choice for identifying spirochetes in blood. Avian borreliosis can be diagnosed postmortem by finding characteristic lesions in birds with signs consistent with the disease. These include:
  • Spleen: Marked enlargement and mottling of the spleen. However, this may not be present in birds infected with low virulent strains or early in the disease.
  • Liver: The liver is often enlarged and contains small hemorrhages, pale foci, or marginal infarcts.
  • Kidneys: Kidneys are swollen and pale with excess urates distending the ureters.
  • Intestines: Green, mucoid intestinal contents are usually present, and there often are variable amounts of hemorrhage, especially at the proventriculus-ventriculus junction.
  • Heart: Fibrinous pericarditis occurs infrequently.

Treatment Options

Most antibiotics, including penicillin, chloramphenicol, kanamycin, streptomycin, tylosin, and tetracyclines, are effective in treating infected birds.

Clinical Signs

Weight loss
Green diarrhea containing excess bile and urates
Pale comb/wattles (anemia)
Increased water consumption
Paresis or paralysis


  • History
  • Clinical signs
  • Physical exam
  • Lab testing
  • Necropsy


Supportive careIsolate the bird from the flock and place in a safe, comfortable, warm location (your own chicken "intensive care unit") with easy access to water and food. Limit stress. Call your veterinarian.
AntibioticsPenicillin, chloramphenicol, kanamycin, streptomycin, tylosin, or tetracyclines.



Reduce the number of ticks on the property.

Scientific References

Risk Factors

  • Larval ticks on the birds, evidence of tick bites, or presence of ticks in the bird’s environment.
  • Summer months