Submitted to: Journal of Clinical Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/4/2006
Publication Date: 2/5/2007
Citation: Howell, J.M., Ueti, M.W., Palmer, G.H., Scoles, G.A., Knowles Jr, D.P. 2007. Transovarial Transmission Efficiency of Babesia bovis Tick Stages Acquired by Rhipicephalus (Boophilus) microplus during Acute Infection. Journal of Clinical Microbiology. 45(2):426-431. Interpretive Summary: The emergence of resistance in Rhipicephalus microplus (the tick which transmits bovine and equine babesiosis) to currently used acaricides is a concern to U. S. Agriculture. Control of bovine babesiosis has depended upon tick control at the southern U. S. border therefore cattle infected with the agents of bovine babesiosis (Babesia bovis and Babesia bigemina) are likely within the U. S. The research reported in this manuscript detailed the efficiency of the tick Rhipicephalus in acquisition and transmission of Babesia bovis at multiple levels of parasite load. The data showed that R. microplus is very efficient in the acquisition and transmission of Babesia bovis from infected cattle.
Technical Abstract: The protozoan parasite Babesia bovis, a reemerging threat to U.S. cattle, is acquired by adult female ticks of the subgenus Boophilus, and is transovarially transmitted as the kinete stage to developing larval offspring. Sporozoites develop within larvae and are transmitted during larval feeding on a bovine host. This study evaluated the efficiency of B. bovis infection within Rhipicephalus (Boophilus) microplus following acquisition feeding on acutely parasitemic cattle. Parasite levels were quantified in blood from experimentally infected cattle, and within hemolymph and larvae derived from acquisition fed female B. microplus. There was a positive correlation between blood parasite levels in acutely parasitemic cattle and kinete levels in hemolymph of adult female Boophilus following acquisition feeding; however, there was no relationship between kinete levels in females and infection rates of larval progeny. Boophilus microplus females that acquisition fed produced larval progeny with infection rates of 12% to 48%. Importantly, larvae derived from replete females with very low levels of kinete infection as demonstrated by microscopy and PCR, had infection rates of 22% to 30% and transmitted B. bovis during a transmission feed. These data demonstrate that although hemolymph infection may be undetectable, transmission to larval progeny occurs at a level which assures transmission to the bovine host.