Detection of Bartonella spp. and Rickettsia spp. in cat fleas (Ctenocephalides felis) collected from free-roaming domestic cats in southeastern Georgia, USA.

The cat flea (Ctenocephalides felis) is a competent vector of numerous bacterial pathogens in the genera Bartonella and Rickettsia. In the United States, free-roaming domestic cats (Felis catus) increase the risk of exposure to C. felis for humans and their companion animals. In collaboration with a trap-neuter-return program, we collected fleas from 283 feral/stray cats in southeastern Georgia between May and July of 2020. A total of 3,643 flea specimens were collected, and C. felis was the only flea species recovered from all cats sampled. The mean number of fleas per cat host was highest in the month of June when compared to May and July, and higher in juvenile cats (< 1 year) than the adults (≥ 1 year). Real-time PCR assays were used to test a subset of the collected fleas (n = 468) for the presence of Bartonella spp. and Rickettsia spp. DNA. Among those flea pools tested, 35.2% were positive for genus-specific citrate synthase gene of Bartonella, 16.5% were positive for the genus-specific 17-kDa protein antigen gene of Rickettsia, and none were positive for the species-specific outer membrane protein B gene of Rickettsia typhi. The identification of potential flea-borne pathogens was more frequent from the subset of C. felis collected in May, and female cats had more Bartonella-positive fleas and less Rickettsia-positive fleas than male cats. Overall, the present study provides valuable insights into the frequency of C. felis from outdoor community cats in southeastern Georgia, and highlights the possible risk for human exposure to potential flea-borne pathogens.

Reactive oxygen species-mediated immunity against bacterial infection in the gut of cat fleas (Ctenocephalides felis).

Fleas (Order Siphonaptera) transmit numerous bacterial pathogens that cause severe human diseases (e.g., cat scratch disease, flea-borne spotted fever, murine typhus, plague). Because initial entry of these infectious agents occurs while blood feeding, the immune response in the flea gut is considered to be the first line of defense against invading microbes. However, relatively few studies have identified the flea immune molecules that effectively resist or limit infection in the gut. In other hematophagous insects, an immediate immune response to imbibed pathogens is the generation of reactive oxygen species (ROS). In this study, we utilized cat fleas (Ctenocephalides felis) to investigate whether oral infection with a well-known insect bacterial pathogen (Serratia marcescens) induces ROS synthesis in the flea gut, and whether production of ROS provides a defense mechanism against microbial colonization. Specifically, we treated fleas with an antioxidant to limit the number of free radicals in the digestive tract prior to infection, and then measured the following: S. marcescens infection loads, hydrogen peroxide (ROS) levels, and mRNA abundance of ROS signaling pathway genes. Overall, our data shows that ROS levels increase in response to infection in the flea gut, and that this increase helps to strengthen the flea immune response through the microbicidal activity of ROS.

Effects of methylmercury on mosquito oviposition behavior: Maladaptive response to non-toxic exposure.

Animals can modulate their own exposure to environmental contaminants through behavioral plasticity such as diet and habitat choice. However, it remains unclear if behavior also has cascading effects on contaminant exposure across multiple generations. In insects, oviposition site selection is an important behavior females can use to modify offspring contaminant exposure risk. In this study, we use the yellow fever mosquito, Aedes aegypti, to test how methylmercury (MeHg) affects oviposition site selection. We found that mosquito larval development rate and survival were negatively affected at MeHg concentrations ≥100 ppb. Adult females not exposed to MeHg as larvae avoided oviposition sites with high MeHg concentrations (>50 ppb), but MeHg exposure at the larval stage significantly affected this oviposition site selection. Specifically, females raised from larvae exposed to non-toxic MeHg levels (i.e., five-50 ppb) showed a significant increase in preference for oviposition sites contaminated with toxic MeHg concentrations (≥500 ppb), compared to unexposed controls. This maladaptive behavioral response could be because, when conditioned with non-toxic MeHg concentrations, MeHg-associated olfactory cues act as a "supernormal" stimulus during oviposition site selection. Importantly, however, this maladaptive behavioral response is eliminated in female mosquitoes raised from larvae exposed to toxic MeHg concentrations (i.e. 100 ppb), and these mosquitoes showed a significant increase in preference for MeHg uncontaminated oviposition sites, compared to unexposed controls. Thus, in mosquitoes, the magnitude of MeHg exposure in one generation can impact MeHg exposure in subsequent generations by altering oviposition site selection behavior. Our results have broad implications for our understanding of how contaminant-mediated behavioral modifications can feedback on contaminant exposure risk across multiple generations, and consequently how behavior can affect the evolutionary trajectory of organisms inhabiting a heterogeneously contaminated environment.