The causal agent Borrelia anserina is a spiral-shaped organism about 8-30 um in length but commonly 14-15 um long and 0-3 um wide. The organisms are actively motile with serpentile movements. The organisms can be seen by staining with Leishman’s or Giemsa methods or a droplet of blood in dark ground illumination of the microscope. The organism can be grown in developing chicken embryo or a susceptible fowl. There is evidence of existence of different antigenic groups. The organism infects chicks, geese, turkeys, ducks, sparrows and other species of birds.
Transmission: The organism is transmitted from one bird to another by fowl tick, Argas persicus, pigeon tick and occasionally by red raise and rarely by mosquitoes. The disease in a flock, is introduced by infected poultry brought on the farm or possibly from wild birds. During initial stages of infection a septicaemia develops when large number of spirochaetes are present in peripheral blood and ingested by the vectors.
Symptoms: The incubation period following the tick bite varies from 4 to 10 days.The body temperature rises to 430 - 440 C, and is accompanied by depression, cyanosis of comb and wattles followed by jaundice. The faeces are watery, inconsistent and greenish. The mortality rate may be 100 %. The spleen is enlarged with mottled appearance and areas of necrosis.
Diagnosis and control: The disease can be diagnosed by observing the organisms in blood smears or sections of the spleen, liver and kidneys. Live organisms in blood from diseased birds can be seen under dark ground or phase contrast microscopy.
Treatment: Arsenical preparations have been effective when given promptly. Penicillin is very effective at a dose of 15,000 units for an average sized bird. Eradication of ectoparasites, particularly ticks from poultry houses, and hygienic conditions are essential for the control of the disease.
Prophylaxis: Vaccines derived from haemolysed blood or tissue from infected birds and killed with formal saline or phenol, or from formalinized chicken embryos are effective for at least 6 months.