Theileria annulata (African and Mediterranean theileriosis) - Microscopic exam and molecular diagnosis (PCR)

Information 28-15-2010.

Theileria annulata is an obligate intracellular protozoan of the Apicomplexa class, gender Theileria, family Theileriidae, with a worldwide distribution, transmitted by ticks cause of mortality and significant economic loss in cattle affected, which causes a lymphoproliferative disease characterized primarily by fever , anemia, and jaundice that is fatal when not treated properly. This parasite primarily affects cattle, which causes a disease called tropical Theileriosis or Mediterranean Theileriosis, a disease affecting cattle in areas of the Mediterranean coast of North Africa, extending to northern Sudan, and south of Europe. They are also affected South-East Europe, Middle East, India, China and Central Asia. Although there is a vaccine, it is not completely effective, and gives a short period of protection. Furthermore treatments lead to resistance, and also after infection when the animals recover from it, as carriers may be playing an important role in the transmission to help maintain the life cycle.

The life cycle of this organism involves an intermediate host, arthropod vectors usually infected ticks, particularly ticks of the genus Hyalomma, as in Spain with the species Hyalomma lusitanicum and Hyalomma marginatum, which transmit the infection during their feeding. The Theileriosis is in Spain in the regions where these species of ticks as in the eastern, central and southern regions, and even in some islands of the Balearic archipelago. Ticks transmit the protozoan to the mammal definitive host (cattle). Infection can also occur by iatrogenic transmission through blood, for example in the reuse of needles. Inside definitive host mammal, sporozoites of Theileria annulata penetrate the lymphatic vascular system and especially multiply spleen lymphocytes, lymph nodes and liver, where they perform a complex life cycle involving replication schizonts leukocytes and erythrocytes. Exceptionally, also they reach the bloodstream. By feeding a new tick blood of an infected animal, infected erythrocytes ingested. In the gut of the tick, the merozoites are released during digestion and can lead to the formation of male and female gametes which form a zygote which causes an ookinete able to penetrate into the cytoplasm of cells of the salivary glands tick, where a sporogony occurs with formation of sporozoites. These sporozoites will be inoculated into a mammalian host during tick feeding, thus completing the cycle.

The incubation period of tropical Theileriosis is 1 to about 3 weeks. Pathogenic Theileria annulata phase is the schizont. At the beginning of Theileria annulata infection causes a lymphoproliferative process, and subsequently causes a lymphodestructive disease. The infected animal shows swollen lymph nodes, fever, a gradual increase in respiratory rate or respiratory distress, dyspnea and / or diarrhea, and weight loss. These parasites also destroy erythrocytes, causing jaundice, anemia , and in some cases, hemoglobinuria, leukopenia and lymphopenia. In the later stages, it can be observed bloody diarrhea or diarrhea with blood clots. The most common post-mortem lesions consist inflammatory hypertrophy of lymph nodes, a remarkably enlarged spleen, lung edema, foamy exudate in the trachea, erosions and ulceration of the stomach, and enteritis with necrosis of Peyer's patches. Lymphoid tissues hypertrophy in the early stages of the disease, but if the animal survives atrophy during the chronic phases of the same. When examined histologically, infiltrations of immature lymphocytes in the lung, kidney, brain, liver, spleen and lymph nodes are. Animals recovering from Theileria annulata infections are usually carriers and subclinical infection they may remain for months or years, with the risks inherent to act as a reservoir to perpetuate the life cycle. From the economic point of view they cause a loss of milk production in chronic infections.

Recommended tests for diagnosis:

The diagnosis is based on microscopic identification of the organism in peripheral blood smears or puncture-biopsies of lymph nodes stained with Giemsa or equivalent; in detecting antibodies by immunoenzymatic methods (ELISA); or molecular diagnostic methods (PCR).

Microscopic examination of the problem is its low sensitivity when parasitemia is low, especially in asymptomatic carrier states.

Antibodies have interest only to know the prevalence states, but do not indicate the existence of acute infections. Therefore, they are more useful to know whether there has been infection, or if the animal is a possible carrier. Nor can differentiate the infecting species by cross-species antigen reactions, some of which have no pathogenic significance.

Therefore, molecular diagnosis (PCR) is recommended as the most sensitive for the identification of Theileria annulata method species. These methods are used to diagnose both overt clinical forms, such as carrier states where parasitaemia is low.

Tests in IVAMI:

• Microscopic examination in peripheral blood or biopsy-lymph node biopsies. Not recommended because of its lower sensitivity.

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

Recommended sample:

• Whole blood collected with EDTA (2 to 5 mL).

• Obtained by needle aspirate or biopsy of affected lymph nodes.

Preservation and shipment of sample:

• Refrigerated (preferred) for less than 2 days.

• Frozen: over 2 days (for molecular diagnostic tests only).

Delivery term:

• Microscopic examination: 24 hours.

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

Cost of the test:

• Consult ivami@ivami.com