Fatal attraction: lone star ticks (Amblyomma americanum) exhibit preference for human female breath over male breath.

Ticks use a variety of chemical cues to locate hosts, the main cue being carbon dioxide, which is exhaled by hosts. This study sought to experimentally determine whether ticks exhibit preference among human hosts based on host sex, as the chemical components of human male and female breath have been shown to differ. We focused on the lone star tick, Amblyomma americanum, due to its importance as a disease vector in the United States and its active host-seeking behavior. To test the hypothesis that ticks exhibit preference based upon host sex, we conducted a binary choice behavioral bioassay. Male and female human volunteers (n = 20 pairs) breathed into opposite sides of a secured polycarbonate tube containing 10 adult A. americanum and the proportion of ticks that exhibited a host preference was recorded. We found that under controlled conditions, human females attract a significantly larger proportion of ticks than males. Possible mechanisms to explain these results include that (1) female breath contains components that ticks find attractive, and/or (2) male breath contains a repellent chemical component.

Interacting effects of wildlife loss and climate on ticks and tick-borne disease.

Both large-wildlife loss and climatic changes can independently influence the prevalence and distribution of zoonotic disease. Given growing evidence that wildlife loss often has stronger community-level effects in low-productivity areas, we hypothesized that these perturbations would have interactive effects on disease risk. We experimentally tested this hypothesis by measuring tick abundance and the prevalence of tick-borne pathogens (Coxiella burnetii and Rickettsia spp.) within long-term, size-selective, large-herbivore exclosures replicated across a precipitation gradient in East Africa. Total wildlife exclusion increased total tick abundance by 130% (mesic sites) to 225% (dry, low-productivity sites), demonstrating a significant interaction of defaunation and aridity on tick abundance. When differing degrees of exclusion were tested for a subset of months, total tick abundance increased from 170% (only mega-herbivores excluded) to 360% (all large wildlife excluded). Wildlife exclusion differentially affected the abundance of the three dominant tick species, and this effect varied strongly over time, likely due to differences among species in their host associations, seasonality, and other ecological characteristics. Pathogen prevalence did not differ across wildlife exclusion treatments, rainfall levels, or tick species, suggesting that exposure risk will respond to defaunation and climate change in proportion to total tick abundance. These findings demonstrate interacting effects of defaunation and aridity that increase disease risk, and they highlight the need to incorporate ecological context when predicting effects of wildlife loss on zoonotic disease dynamics.

Host-Parasite Associations in Small Mammal Communities in Semiarid Savanna Ecosystems of East Africa.

Despite the established importance of rodents as reservoirs of vector-borne zoonoses in East Africa, there is relatively limited information regarding the infestation parameters and host associations of ectoparasites that vector many such pathogens among small mammals in this region. Between 2009 and 2013, small mammals were live-trapped in the semiarid savanna of Kenya. A subset of these individual hosts, including 20 distinct host taxa, was examined for ectoparasites, which were identified to species. Species of fleas, ticks, mites, and sucking lice were recorded. Based on these data, we calculated host-specific infestation parameters, documented host preferences among ectoparasites, conducted a rarefaction analysis and extrapolation to determine if ectoparasites were adequately sampled, and assessed nestedness for fleas to understand how pathogens might spread in this system. We found that the flea community structure was significantly nested. Understanding the ectoparasite network structure may have significant human relevance, as at least seven of the ectoparasite species collected are known vectors of pathogens of medical importance in the region, including Yersinia pestis, Rickettsia spp., and Theileria parva, the causative agents of plague, spotted fevers and other rickettsial illnesses in humans, and theileriosis, respectively.