Anaemia in Sheep Caused by Babesia and Theileria Haemoparasites

SIMPLE SUMMARY: Vector-borne diseases are a group of diseases caused by different pathogens, including viruses, bacteria or parasites transmitted by the bite of hematophagous arthropods, and have a direct impact on livestock, especially animals exposed to vector bites. Among these vector-borne diseases, Babesia and Theileria in sheep cause anaemia. Theileria species can infect two types of blood cells, including leukocytes and erythrocytes, while Babesia species infect only erythrocytes. Clinical signs vary in severity from subclinical infection to severe clinical picture with anaemia, depending on different factors such as the immune response developed by the host against the parasite, the parasite load, and the haemoparasites species involved, among others. This review aims to explain the main clinicopathological findings related to these two vector-borne pathogens in sheep, emphasising the pathogenic mechanisms associated with anaemia. ABSTRACT: Piroplasmoses in sheep are caused by vector-borne apicomplexan protozoa, Babesia and Theileria. Different species are responsible for the disease; some species are more pathogenic than others and have a worldwide distribution. In this sense, these causative agents can cause anaemia in flocks. In general, these vector-borne diseases infect small ruminants and cause host-mediated pathology. In the case of Babesia species, a combination of different mechanisms is involved: red blood cell lysis due to intracellular parasite multiplication, activation of biogenic amines and the coagulation system with the possibility of disseminated intravascular coagulation. By contrast, less information is available on the different immunopathogenic mechanisms involved in the development of anaemia in sheep with theileriosis. However, the mechanisms of pathogenic action in theileriosis are similar to those studied in babesiosis. Diagnosis is based on compatible clinical signs, laboratory findings, specific diagnostic tests and the presence of the tick vector. Some of these tests detect the causative agent itself, such as direct identification by light microscopy and molecular analysis. In contrast, other tests detect the sheep’s immune response to the organism by serology. Both diseases pose a significant diagnostic challenge for veterinary practitioners around the world. This review presents the most frequent clinical signs, pathogenesis and clinicopathological findings, diagnosis.