Submitted to: Journal of Clinical Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 29, 2007
Publication Date: October 15, 2007
Citation: Howell, J.M., Ueti, M.W., Palmer, G.H., Scoles, G.A., Knowles Jr, D.P. 2007. Persistently Infected Calves as Reservoirs for Acquisition and Transovarial Transmission of Babesia bovis by Rhipicephalus (Boophilus) microplus. Journal of Clinical Microbiology. 45(10):3155-3159 Interpretive Summary: Certain ticks which transmit important diseases to domestic livestock are developing acaricide resistance. One of these diseases is caused by a complex parasite (a protozoan) and has been controlled by treating cattle with acaricides before they enter the United States. Because ticks which transmit this diseases (babesiosis) are developing resistance to treatment it is important to know their efficiency in terms of disease transmission. This work showed that certain ticks (Rhipicephalus (Boophilus) microplus are very efficient of transmitting parasites which cause babesiosis regardless of the level of parasite in cattle from which they acquire infection.
Technical Abstract: Babesia bovis is a deadly disease of cattle resulting in severe economic losses in the vast regions of the world where it is endemic. If re-introduced into the United States, babesiosis would cause significant mortality in the naïve cattle population. In order to address the risk to U.S. cattle, it is essential to quantify the transovarial transmission efficiency in adult female Boophilus microplus following acquisition feeding on persistently infected cattle. This study tested the hypothesis that infection rates are the same for larval progeny derived from females fed to repletion during persistent or acute infection. Increasing parasite levels during acute infection correlated with an increasing number of females harboring kinetes detectable in hemolymph (r= 0.9). Percent infected larvae ranged from 0-20% when derived from females fed to repletion on persistently infected calves and from 4-6% when derived from females fed to repletion during acute parasitemia. There was no significant difference in infection rates of larval progeny implying that the risk associated with the introduction of either persistently infected or acutely infected cattle is equal. Parasite levels ranged from 2.4 x 102 to 1.9 x 105 in three day fed larvae derived from females fed to repletion on persistently infected cattle. One group of larvae failed to transmit the parasite suggesting that a threshold level of parasites must be obtained by larval progeny via transovarial transmission in order for larvae to deliver sufficient parasites to infect a naïve host.