Theileria parva - Microscopic exam; Molecular diagnosis (PCR)

Theileria parva is an intracellular protozoan parasite of the genus Theileria, family Theileriidae. This parasite mainly affects cattle, which causes theileriosis called East Coast Fever, a highly pathogenic disease with an associated mortality of 90-100%. Theileria parva is located in Central and Eastern Africa, specifically in Sudan, South Africa, the Democratic Republic of the Congo, Swaziland, Zimbabwe, Zambia, Tanzania, Kenya and Uganda.

The biological cycle of this microorganism involves a definitive mammalian host and an intermediate host, usually arthropod vectors such as infected ticks (specifically ticks of the genera Rhipicephalus and Hyalomma), which would transmit the infection during their feeding. In addition, infection can also occur by iatrogenic transmission through the blood, for example, in the reuse of needles. Inside the mammalian host, Theileria parva infects erythrocytes. In the erythrocytes, the parasites are visualized round, oval or in the shape of a coma and with a size of 0.5 to 2 μm. The sporozoites of Theileria parva penetrate the lymphatic vascular system and multiply especially in the lymphocytes of the spleen, lymph nodes and liver, where they carry out a complex biological cycle that involves the multiplication of schizonts in leukocytes and piroplasmas in erythrocytes. The forms found in the lymphocytes and occasionally in the endothelial cells in the lymph nodes and spleen, have a circular or irregular shape with a size of 8 to 12 μm. Piroplasmas appear in erythrocytes approximately 10 days after inoculation. When feeding a new tick of the blood of an infected animal, it ingests erythrocytes infected with piroplasmas, and undergoes other stages of its life cycle in the intestine and the salivary glands of the tick vector. 

In affected animals, the incubation period is approximately 10 to 25 days after infection. Symptoms associated with Theileria parva infection may include fever, anorexia, dyspnea, lacrimation, nasal secretions and decay. Due to the rapid spread of the parasite and its aggressiveness, the death of infected animals occurs around 18 to 30 days after infection. Theileria parva infection causes lesions in the lymph nodes, liver, kidneys, lungs, heart, as well as ulcers in the abomasum (or rennet, fourth and last compartment of the stomach of ruminants). In endemic regions, animals that survive generally become lifelong carriers.

Recommended tests for diagnosis:

The diagnosis is based on the microscopic identification of the microorganism in blood smears, antibody detection (ELISA), or molecular diagnostic methods (PCR).

Serological tests, in addition to requiring time for antibodies to develop, allow the Theileria genus to be identified as the cause of the infection but not the species. Due to this, molecular diagnosis is recommended as the most sensitive method for the identification of the Theileria parva species.

Tests carried out in IVAMI:

  • Molecular diagnosis (PCR), to detect DNA from Theileria parva.

Recommended sample:

  • Total blood extracted with EDTA (2 to 5 mL).
  • Lymph node biopsy.

Conservation and shipment of the sample:

  • Refrigerated (preferred) for less than 2 days.
  • Frozen: more than 2 days (only for molecular diagnostic tests).

Delivery of results:

  • Microscopic examination: 24 hours.
  • Molecular diagnosis (PCR): 24 to 48 hours.

Cost of the test: