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Other Names: Chicken Malaria

Leucocytozoonosis is a vector-borne, parasitic disease of birds, caused by infection with the blood parasite Leucocytozoon. Chickens are primarily affected by L. caulleryi, L. andrewsi, L. schoutedeni, and L. sabrezi. The parasite is found frequently in chickens in southern and eastern Asia, and the south eastern United States. In one survey, 13.6% of domestic backyard chickens in South Carolina were infected.

L. caulleryi are transmitted by black flies (Simulium) and biting midges (Culicoides) and are known for infection and destruction of the host's red blood cells, resulting in intravascular hemolytic anemia.

Black flies or biting midges will carry the infective sporozoites in their salivary gland, which gets transferred into the bird upon the insect bite. One inside the bird's body, sporozoites travel to the liver, enter hepatocytes and replicate numerous times and migrate to different tissues and organs, such as the brain, spleen, heart, and lungs.

Leucocytozoonosis Clinical Signs

Clinical signs of Leucocytozoonosis varies with age and condition of the host. In young chicks, the disease is usually more severe and progresses very quickly. Signs include loss of appetite, listlessness, rapid breathing, weakness, and sometimes death within 24 hours. When adult chickens are affected, signs of disease usually occur gradually, and are milder. Most affected birds will die a few days after signs develop.

Recovered birds may harbor L. caulleryi in their blood for more than a year. They may also continuously cough and tracheal rales. There is also loss of vigor, and birds often die when under stress. Roosters will show reduced mating.

Clinical Signs

Rapid breathing
Loss of appetite
Anemia (pale comb/wattles)
Increased thirst
Reduced mating in males
Tracheal rales
Loss of vigor
Thickened oral discharge


  • History
  • Clinical signs
  • Physical exam
  • PCR
  • Histopathology

Reported Cases

  • Case 1: Leucocytozoon infection in a Welsh Harlequin Ducks A group of eleven, 6-week-old Welsh Harlequin ducklings hatched in Northern Ontario in late June were housed indoors until approximately 4-5 weeks of age, and then were allowed access to an outdoor enclosure during the day. Other than green watery diarrhea, the ducks were clinically normal. However in mid-August, at six weeks of age, one of the ducks became inappetent and lethargic, exhibited labored breathing, and died overnight. In the following two days, three more ducks died, the last two exhibiting similar clinical signs as the first. In total, the owner lost 5 of the 11 ducks; two recovered following intensive supportive care. Chickens were also maintained on the same property but housed in a separate enclosure and suffered no morbidity or mortality. Pens were cleaned every 1-2 days; feed and water were always available and refreshed daily. Ref


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.
Primaquine0.75-1 mg/kg PO once, used in conjunction with chloroquine (25 mg/kg PO at 0h, then 15 mg/kg at 12,24, and 48h)B Speers
PyrimethamineGiven orally (0.5 mg/kg PO q12h x 14-28 days) or in feed (1 mg/kg feed for 28 days), Supplement with folic acid.B Speers



Fly control

Scientific References

Risk Factors

  • High populations of flies or midges.