Bovine Anaemia - Theileria
Overview
Theileriosis is a tick-borne disease caused by intracellular blood parasites belonging to the Theileria orientalis group (BATOG).
A large number of Theileria spp are found in domestic and wild animals in tick-infested areas of the Old World. The most important species affecting cattle are T Parva and T annulata, which cause widespread death in tropical subtropical areas of the Old World. T leptoquarks, T luwenshuni, and T uilenbergi are important causes of mortality in sheep.
Aetiology
Bush ticks are mainly a cattle parasite but can attach to other mammals including wildlife, birds, livestock (including horses, sheep, goats and poultry) and domestic animals such as dogs and cats. In sheep, bush ticks prefer to attach mainly to body parts not covered by wool.
Transmission
Ticks attached to the cattle is an important factor for transmission.
The most common sites of attachment on cattle are around the tail, on the udder, inside the legs, on the brisket, in the ears, and occasionally on the face and neck.
Although it may cause tick irritation and local reactions in all species, H. longicornis only transmits benign theileriosis to cattle.
Pathogenesis
Theileria uses, successively, WBCs and RBCs for the completion of their life cycle in mammalian hosts. The infective sporozoite stage of the parasite is transmitted in the saliva of infected ticks as they feed. Sporozoites invade leukocytes and, within a few days, develop into schizonts. In the most pathogenic species of Theileria (eg, T Parva and T annulata), parasite multiplication occurs predominantly within the host WBCs, whereas less pathogenic species multiply mainly in RBCs. Development of the schizont stage of pathogenic Theileria causes the host WBC to divide; at each cell division, the parasite also divides. Thus, the parasitized cell population expands and, through migration, becomes disseminated throughout the lymphoid system. Later in the infection, some of the schizonts undergo merogony, releasing merozoites that infect RBCs, giving rise to piroplasms. Uptake of piroplasm-infected RBCs by vector ticks feeding on infected animals is the prelude to a complex cycle of development, culminating in the transmission of infection by ticks feeding in their next instar (trans-stadial transmission).
Factors
In some endemic areas, indigenous cattle have a degree of innate resistance. Mortality in such stock is relatively low but introduced cattle are particularly vulnerable.
Unlike in babesiosis, in theileriasis, there is no evidence of increased resistance in calves
The disease is generally seen when calves are 8-12 weeks old. By about six months of age, immunity develops and it is rare to see disease in calves older than six months and adults who have been resident in the area.
Clinical signs
The disease is known as bovine anaemia. Signs are those associated with
severe anaemia
Lethargy,
Lack of appetite
Exercise intolerance (weak cattle that lag behind the mob if moved).
If forced to run they may stagger and gasp for breath and some may collapse and die.
Their gums will be pale and/or yellow.
Pregnant cows may abort and stillbirths are common.
In dairy cows, a drop in milk production will occur.
Death rates are highest in heavily pregnant cows.
➡️Diagnosis:
Testing of animal blood samples has been demonstrated as an effective detection tool for the main strains of Theileria Orientalis.
Treatment
The drug of choice for Theiliriosis is Buparvaquone (Butalex, Bupralex).
Treatment options for benign theileriosis are limited to supportive care and symptomatic treatment.
Blood transfusion has been performed occasionally on valuable animals. Animals improve the following transfusion but it is expensive and not practical if multiple animals are involved.
Most importantly, stress and movement of affected cattle should be minimised or their reduced ability to transport oxygen throughout the body may lead to collapse. They should be rested, nursed and given high-quality feed. Handling of affected cattle should be avoided where possible; if movement or yarding is necessary, move animals slowly.
Prevention
The most important preventive measure is Tick control.
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