Babesiosis [ba-be-si-o-sis] and Theileriosis [thei-le-ri-o-sis] are caused by Babesia and Theileria species, which belong to the group known as piroplasms. These are pear-shaped organisms that parasitize the red blood cells of vertebrate hosts. They produce a malaria-like disease in livestock, pets and humans. Babesia species can be transmitted transovarially (from a female tick through the egg to the next generation), while Theileria species appear to only be transmitted transstadially (through each stage of the tick’s life cycle). In splenectomised individuals, both Babesiosis and Theileriosis can be fatal.

Babesia divergens is the cause of Red Water Fever in cattle. This disease gets its name from the colour of the animal’s urine, which becomes dark red due to haemoglobin produced by the rupture of red blood cells. Blood in the urine (haemoglobinuria) occurs in most species with Babesiosis. B. divergens has been implicated as the most common agent of human Babesiosis in Europe.

B. major, which also affects cattle, occurs in coastal regions of Britain (Lewis and Herbert 1980).

B. motasi is generally transmitted by Haemaphysalis ticks. It causes severe Babesiosis in sheep and was first identified in Britain from sheep in Wales.

Theileria species do present in Europe but it is generally in tropical regions that large-scale problems occur. T. ovis and T. recondite both occur in the UK (Lewis et al., 1981, and Alani and Herbert, 1988)

Signs & Symptoms

The manifestations of human Babesiosis can range from asymptomatic to severe illness, and can result in death in asplenic, elderly, or immunecompromised individuals.

The incubation period is generally 1-3 weeks, but may be as long as 9 weeks following inoculation from a tick bite. Symptoms may include fever, chills, headache, nausea, vomiting, anaemia, jaundice and blood in the urine.



Diagnostic techniques for human infection are Indirect Immunofluorescent Assay (IFA), examination of Giemsa-stained blood smears and identification of Babesial DNA by Polymmerase Chain Reaction (PCR).

Babesia can be overlooked during microscopic examination of thin blood smears because parasitemia can be sparse early in the course of infection, infecting less than 1% of erythrocytes.



The general recommended therapy for human Babesiosis is a combination of oral Azithromycin and Atovaquone or, in severe cases, IV Clindamycin and oral Quinine. In acute cases of disease with high parasitemia, exchange transfusion can be life saving.



There is currently no vaccine available against Babesiosis.



Other Diseases

Borreliosis (LymeDisease )

Anaplasmosis & Ehrlichiosis


TBE & Louping ill

Disease Transmission

Disease Notification