Seasonal variation in the abundance and distribution of ticks that parasitize Microcebus griseorufus at the Bezà Mahafaly Special Reserve, Madagascar.

At Bezà Mahafaly Special Reserve (BMSR), Madagascar, mouse lemurs (Microcebus griseorufus) are parasitized by multiple species of haemaphysaline ticks. At present we know little about the role ticks play in wild lemur populations and how they can alter interspecies relationships within communities or impact host fitness. In order to better understand these dynamics at BMSR, we examined parasite-host interactions as well as the ecology of mouse lemurs and their infesting ticks, Haemaphysalis lemuris and H. sp. cf. simplex. We show that season, host sex, and habitat influence the relative abundance of ticks on mouse lemurs. Specifically, infestations occur only during the dry season (May-October), are higher in males, and are higher at the study site with the most ground cover and with greater density of large-bodied hosts. Microcebus likely experience decreased susceptibility to tick infestations during the wet season because at that time they rarely if ever descend to the ground. Similarly, male mouse lemurs have higher infestation rates than females because of the greater time they spend traveling and foraging on the ground. During the dry season, Microcebus likely serve as hosts for the tenrec tick, H. sp. cf. simplex, when tenrecs hibernate. In turn, during the wet season when mouse lemurs rarely descend to the ground, other small mammals at the reserve may serve as maintenance hosts for populations of immature ticks. The synchronous development of larvae and nymphs could present high risk for vector-borne disease in Microcebus. This study also provides a preliminary description of the ecology and life cycle of the most common lemur tick, H. lemuris.

Possible role of a cell surface carbohydrate in evolution of resistance to viral infections in old world primates.

Due to inactivation of the α1,3-galactosyltransferase gene (GGTA1, or the α1,3GT gene) approximately 28 million years ago, the carbohydrate αGal (Galα1,3Galß1,4GlcNAc) is not expressed on the cells of Old World monkeys and apes (including humans) but is expressed in all other mammals. The proposed selective advantage of this mutation for these primates is the ability to produce anti-Gal antibodies, which may be an effective immune component in neutralizing αGal-expressing pathogens. However, loss of α1,3GT expression may have been advantageous by providing natural resistance against viral pathogens that exploited the α1,3GT pathway or cell surface αGal for infection. Infections of paired cell lines with differential expression of α1,3GT showed that Sindbis viruses (SINV) preferentially replicate in α1,3GT-positive cells, whereas herpes simplex viruses type 1 and type 2 (HSV-1 and HSV-2) preferentially grow in cells lacking α1,3GT. Viral growth and spread correlated with the ability of the different viruses to successfully initiate infection in the presence or absence of α1,3GT expression. GT knockout (KO) suckling mice infected with SINV strains (AR339 and S.A.AR86) experienced significant delay in onset of disease symptoms and mortality compared to wild-type (WT) B6 suckling mice. In contrast, HSV-2-infected GT KO mice had higher viral titers in spleen and liver and exhibited significantly more focal hepatic necrosis than WT B6 mice. This study demonstrates that α1,3GT activity plays a role in the course of infections for certain viruses. Furthermore, this study has implications for the evolution of resistance to viral infections in primates.