Leucocytozoon caulleryi

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Leucocytozoon caulleryi
Kingdom Protista
Phylum Protozoa
Order Haemospororida
Family Leucocytozoidae
Genus Leucocytozoon
Species L. caulleryi

Also Known As: Avian Haematozoa

Causes: Leucocytozoonosis


L. smithi within an erythrocyte, distorting its appearance.

Leucocytozoon caulleryi is a protozoan blood-borne parasite of birds.

This disease is not zoonotic.


Chickens are infected through biting midges, specifically Culicoides arakawae. Other Leucocytozoon species are transmitted by mosquitoes.

Sporozoites are parasitic and can migrate to and affect the liver, spleen, lungs and kidneys, forming schizonts. Schizonts can then release merozoites or secondary schizonts in the endothelial cells of the blood vessels and in essentially any of the viscera. These secondary schizonts have a distinct protective capsule and contain many merozoites.

Gametogony (sexual reproduction) then occurs within the erythrocytes.

Other Leucocytozoon species can invade and replicate within the leucocytes.

Signalment and Distribution

L. caulleryi has been reported in Thailand, India, Taiwan, Japan, Burma, Sri Lanka, the Philippines, Singapore, Malaysia, Indonesia, China, and Korea.[1]

Acute outbreaks of leucocytozoonosis have been reported in chickens, turkeys, waterfowl and wild birds worldwide.

Seasonality is dictated by presence of the insect vectors, so is usually in the Summer in temperate countries such as Japan but is present throughout the year where insects are active year-round such as in Southern Asia.

Clinical Signs

Infections range from subclinical to fatal and mortality can reach 100%. Mortalities are highest in young chicks due to marked haemorrhaging.

Leucocytozoonosis causes anaemia due to haemorrhages from damaged, ruptured blood vessels and affected erythrocytes. This can preset as pale mucous membranes, comb or wattle, petechiation and ecchymoses, lethargy, weakness and neurological signs. Anorexia and diarrhoea often occur and soft, thin, defective eggs with reduced hatchability may be laid by infected hens.

Neurological signs can also be caused by parasite replication and invasion of nervous tissues.


Large, poorly pigmented gametocytes can be identified within the host red blood cells distorting their appearance beyond recognition.

Antibodies and antigens can be detected serologically in serum using agar gel precipitation and ELISA.[2]

On post-mortem, petechial haemorrhage and second generation schizonts are seen in various organs of dead chicks and also in oviducts of infected hens, when analysed histologically.[3] The shell glad of the reproductive tract and oviducts are most severely affected. Schizonts can cause inflammation, oedema and pressure atrophy of surrounding tissues. Granulomatous and lymphocytic lesions are seen in the lungs, heart, brain and peripheral nerves. Large gametocytes can block capillaries of the lungs.


No treatment is usually effective.


Preventative medication with pyrimethamine and sulfadimethoxine in the feed can be used.

Insect vector control is helpful but difficult.

Leucocytozoon caulleryi Learning Resources
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  1. Akiba, K (1970) Leucocytozoonosis of chickens. Natl. Inst. Anim. Quart., 10:131-147
  2. Isobe, T., Suzuki, K (1986) Enzyme-linked immunosorbent assay for detection of antibody to Leucocytozoon caulleryi. Avian Pathology, 15(2):199-211; 14
  3. Nakamura, K., Mitarai, Y., Tanimura, N., Hara, H., Ikeda, A., Shimada, J., Isobe, T (1997) Pathogenesis of reduced egg production and soft-shelled eggs in laying hens associated with Leucocytozoon caulleryi infection. J Parasitology, 83(2):325-327; 11


This article was originally sourced from The Animal Health & Production Compendium (AHPC) published online by CABI during the OVAL Project.

The datasheet was accessed on 1 July 2011.

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