Theileria orientalis - Microscopic exam; Molecular diagnosis (PCR)

Theileria orientalis is an obligate intracellular protozoan of the genus Theileria, family Theileriidae. This parasite mainly affects cattle, in which it causes benign theileriosis (also known as "Oriental theileriosis" or "bovine anemia due to Theileria orientalis"). Theileria orientalis is located in Australia, Japan and other Asian countries, as well as in Turkey, the United Kingdom, France, Spain and the USA.

The biological cycle of this microorganism involves an intermediate host, usually arthropod vectors such as infected ticks (specifically ticks of the genus Haemaphysalis), which would transmit the infection during feeding, and a definitive mammalian host. In addition, infection can also occur by iatrogenic transmission through the blood, for example, in the reuse of needles. In the interior of the mammalian host, Theileria orientalis infects erythrocytes. The sporozoites of Theileria orientalis penetrate into the lymphatic vascular system and multiply especially in lymphocytes of the spleen, lymph nodes and liver, where they carry out a complex biological cycle involving the multiplication of schizonts in leukocytes and piroplasmas in erythrocytes. Piroplasmas appear in erythrocytes approximately 10 days after inoculation. When feeding a new tick with blood from 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, infection with Theileria orientalis manifests as an anemia of varying severity. Signs and symptoms associated with the disease include transient fever, anemia, tachypnea, depression, weakness, lethargy, jaundice and, occasionally, death. Other signs and symptoms may include exercise intolerance, hematuria, lack of appetite, weight loss and difficulty breathing. In addition, in milk cows there may be a decrease or fall in milk production. There have been cases in which infection by this microorganism causes abortions in late stages. In immunologically intact animals, parasitaemia is generally low and animals recover from infection. However, parasites can remain in the body, sometimes causing a relapse, particularly under stress conditions such as pregnancy, lactation or changes in environmental conditions.

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. Because of this, molecular diagnosis is recommended as the most sensitive method for the identification of the species Theileria orientalis.

Tests carried out in IVAMI:

  • Detection by isolation by cultivation in selective media.
  • Molecular diagnosis (PCR), to detect DNA from Theileria orientalis.

Recommended sample:

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

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: