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Title: Silencing of a putative immunophilin gene in the cattle tick Rhipicephalus (Boophilus) microplus increases the infection rate of Babesia bovis in larval progeny

Author
item BASTOS, REGINALDO - Washington State University
item UETI, MASSARO - Washington State University
item Guerrero, Felicito
item Knowles Jr, Donald
item Scoles, Glen

Submitted to: BioMed Central (BMC) Parasites and Vectors
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/20/2009
Publication Date: 11/20/2009
Citation: Bastos, R., Ueti, M.W., Guerrero, F., Knowles Jr, D.P., Scoles, G.A. 2009. Silencing of a putative immunophilin gene in the cattle tick Rhipicephalus (Boophilus) microplus increases the infection rate of Babesia bovis in larval progeny. BioMed Central (BMC) Vectors and Parasites. 2(1):57.

Interpretive Summary: The cattle tick Rhipicephalus (Boophilus) microplus is involved in the transmission of the protozoan parasite that causes cattle tick fever, also known as bovine babesiosis. The ticks transmit the parasite transovarially; after feeding on an infected bovine host, female ticks produce infected offspring that transmit the parasite to the subsequent host. Very little is known about how the parasite interacts with its tick vector. Studies of tick genes that affect protozoan infection and the ability of the tick to feed and reproduce can help us to develop a better understanding of this interaction. In this study we used a molecular technique called RNA interference to silence the expression of selected tick genes that had been previously shown to increase their expression in response to tick infection. The silencing of two genes (Spi and Lpc) decreased the ability of the tick to feed and reproduce, but had no significant effect on infection of the larval progeny. However, silencing of another gene (Imnp) decreased the hatching rate and survival of the larval progeny. In a previous study, expression of Imnp increased in response to infection; in this experiment silencing this gene increased the number of larval progeny that were infected. Suggesting that this gene may be involved in the ability of the tick to resist infection with the parasite, thus playing a role in controlling the protozoan infection in tick ovaries and larvae progeny. It is hoped that this type of information will lead to new ways of controlling ticks and the parasites they transmit.

Technical Abstract: Background: The cattle tick Rhipicephalus (Boophilus) microplus is involved in the transmission of the protozoan Babesia bovis, the etiological agent of bovine babesiosis. Interactions between ticks and protozoa are poorly understood and the investigation of tick genes that affect tick fitness and protozoan infection can set the stage for dissecting the molecular interactions between the two species. Results: In this study, RNA interference was used to silence R. microplus genes that had been previously shown to be up-regulated in response to B. bovis infection. The silencing of a putative immunophilin gene (Imnp) in female ticks fed on a calf acutely infected with B. bovis decreased the hatching rate and survival of larval progeny. Interestingly, Imnp was up-regulated significantly in ovaries of R. microplus in response to B. bovis infection and its silencing in female ticks significantly increased the infection rate of the protozoan in larval progeny. The results also showed that the silencing of a putative Kunitz-type serine protease inhibitor (Spi) gene and a putative lipocalin (Lpc) gene decreased the fitness of R. microplus females, but had no significant effect on the infection rate of B. bovis in larval progeny. Conclusion: The silencing of the Imnp, Spi or Lpc genes decreased the fitness of R. microplus females fed on a calf during acute B. bovis infection. The Imnp gene data suggest that this putative immunophilin gene is involved in the defense system of R. microplus against B. bovis and may play a role in controlling the protozoan infection in tick ovaries and larvae progeny.