Theileriosis - Cattle
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Caused By: Theileria parva — Theileria annulata
T. parva and T. annulata in cattle and T. lestoguardi in sheep are the most economically important in domestic ruminants.
Buffalo, both domestic and wild, appear less susceptible to theileriosis.
Native animals also appear to have a higher degree of innate tolerance in endemic areas than those that are imported, even if of the same breed.
Friesians appear particularly susceptible to infection with Theileria species.
Age linked tolerance may make younger calves more tolerant of disease than adults in some areas.
Distribution of disease depends on the presence of tick vectors and thus is primarily in tropical regions. Various species of tick are implicated.
The distribution of theileriosis is increasing all the time.
Asexual reproduction in the host is followed by sexual reproduction within the tick vector. The parasite is then transmitted through the salivary glands of the tick into the mammalian host during bloodfeeding.
In endemic areas, endemic stability is often reached, in which most or all cattle may be infected and be carriers and most ticks are also infected, but young calves gain solid immunity from their immune dams and therefore rarely show clinical disease. This state however takes time to stabilise and will cause significant economic losses in the process.
Ocular signs and masses may develop.
Pruritus and skin lesions/plaques are also seen.
Neurological and reproductive signs may develop in chronic or endemic disease.
The degree of pyrexia, pathogen load and host susceptibility will determine the severity of clinical signs at presentation.
Detection of parasite stages in thin blood smears with Giemsa staining. Schizonts should be looked for in thin smears from lymph node or liver biopsies.
On post-mortem examination, blood is watery and carcasses are icteric and gelatinised. Numerous petechiae may be present within the mucous membranes, gut mucosae and heart. The liver is often pale and friable and the gall bladder distended with dark green bile. Ulcers are often evident in the abomasum of ruminants and are surrounded by haemorrhagic zones. Urine is dark brown due to the presence of bilirubin. Pulmonary oedema may be present.
Indirect Fluorescent Antibody Tests (IFAT) and ELISAs are also available and are useful for identifying carrier animals.
Sporozoites can also be detected within the salivary glands of ticks by staining with methyl-green pyronin and more recently with PCR.
Buparvaquone and Halofuginone chemotherapeutics and/or Tetracyclines are the treatments of choice.
Control of tick vectors and use of tick resistant host species such as zebu cattle in endemic areas is effective but expensive.
Care should be taken when intensively dipping with ectoparasiticides to control ticks as upsurges in other tick borne diseases are not uncommon when programmes are interrupted.
Endemic stability can be encouraged by breeding indigenous or known carrier animals, although these are often still infective for ticks so separation from adult susceptible animals is essential to prevent further spread of disease.
Vaccines are available involving attenuated schizont-infected cells and are the mainstay of tropical theleriosis in endemic countries with highly susceptible cattle breeds.
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The datasheet was accessed on 3 June 2011.
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