Mixed infections, cryptic diversity, and vector-borne pathogens: Evidence from Polygenis fleas and Bartonella

Department of Biological Sciences, Vanderbilt University, Nashville, TN 37235, USA, Department of Biology, Georgia Southern University, P.O. Box 8042,Statesboro, GA 30460, USA

^* To whom correspondence should be addressed. Email: patrick.abbot{at}vanderbilt.edu.

	Abstract

Co-infections within hosts present opportunities for horizontal gene transfer between strains and competitive interactions between genotypes, and thus can be a critical element of the lifestyles of pathogens. Bartonella are -Proteobacteria that parasitize mammalian erythrocytes and endothelial cells. They are thought to be vectored by various biting arthropods, such as fleas, ticks, mites, and lice, and are commonly cited as agents of various emerging diseases. Co-infections by different Bartonella strains and species can be common in mammals, but little is known about specificity and co-infections in arthropod vectors. We surveyed the rate of mixed infections of Bartonella in flea vectors (Polygenis gwyni), parasitizing cotton rats (Sigmodon hispidus) in which previous surveys indicated high rates of infection. We found that nearly all fleas (20 of 21) harbored one or more strain of Bartonella, with rates of co-infection approaching 90%. A strain previously identified as common in cotton rats was also common in their fleas. However, another common strain in cotton rats was absent from P. gwyni, while a rare cotton rat strain was quite common in P. gwyni. Surprisingly, some samples were also co-infected with a strain phylogenetically-related to B. clarridgeiae, which is typically associated with felids and ruminants. Finally, a locus (pap31) that is characteristically borne on phage in Bartonella was successfully sequenced from most samples. However, sequence diversity in pap31 was novel in the P. gwyni samples, relative to other Bartonella previously typed with pap31, emphasizing the likelihood of large reservoirs of cryptic diversity in natural populations of the pathogen.