Transovarial transmission efficiency of Babesia bovis by Rhipicephalus (boophilus) microplus

by 1973- Howell, Jeanne Marie

By Jeanne Marie Howell, D.V.M., Ph.D. Washington State University May 2007 Chair: Donald P. Knowles Babesia bovis is a deadly disease of cattle transmitted by Rhipicephalus (Boophilus) ticks resulting in severe economic losses in vast regions of the world where it is endemic. Infected cattle develop high fever, depression, anemia, and often die. Although essentially eradicated from the U.S. in 1943, a quarantine zone remains along the U.S. border with Mexico. The endemicity of babesiosis in Mexico, in combination with the development of acaracide resistant Boophilus ticks, facilitates the reintroduction of this pathogen into the U.S. The parasite is acquired by feeding adult female Boophilus ticks, and is transmitted transovarially to developing larval offspring as the kinete stage. Infectious sporozoites develop within larval salivary glands and are transmitted when larvae commence feeding on susceptible cattle. The efficiency of female tick acquisition and transovarial transmission of B. bovis is poorly understood. In order to address the risk imposed on U.S. cattle, it is essential to examine the efficiency at which adult female Boophilus ticks acquire blood stages of B. bovis and how efficiently the kinete stage is passed transovarially to developing offspring. These studies were designed to first evaluate the efficiency of B. bovis transmission following acquisition feeding on splenectomized acutely parasitemic cattle, and secondly investigate the efficiency of transovarial transmission following acquisition feeding on spleen intact persistently infected calves. iv