Genetic structure of raccoon roundworm in North America

Background/Question/Methods

Raccoon roundworm (Baylisascaris procyonis) is a nematode parasite that infects raccoons throughout North America. Over 100 birds and small mammals can serve as paratenic, or transport, hosts. In paratenic hosts, this parasite migrates to the brain, among other tissues, and often causes death. Baylisascaris procyonis is zoonotic, and has the potential to migrate to the brain in humans and cause severe neurological damage or death. Reported human infections of B. procyonis are rare, but subclinical infections are presumed to be more common. Despite the potential consequences of infection for humans and paratenic hosts, genetic analyses of B. procyonis have been minimal. Determining the genetics of geographic variation and potential for gene flow in B. procyonis will clarify the ability of this parasite to spread. Many traits of the parasite and its hosts predict high gene flow and reduced genetic structure. This study presents genetic prospecting data to discern the population genetic structure of B. procyonis in North America. Baylisascaris procyonis nematodes were obtained from raccoon hosts sampled throughout major geographic regions of the United States. Mitochondrial sequence data (cox-1) and ten nuclear microsatellite markers were used to identify genetic clusters of B. procyonisin these specimens.

Results/Conclusions

Three factors may reduce population genetic structure of B. procyonis: vagility of raccoon hosts, many paratenic hosts, and resistant eggs that are widespread in the environment. Analyses based on microsatellite markers identified two clusters of B. procyonis, supporting limited genetic structure. Specimens from California were found to be distinct from those collected east of the Mississippi. The F_ST value for California specimens compared to all other specimens was 0.47. This same geographic disjunction was found through phylogeographic analysis of mitochondrial sequence data (cox-1) for similar samples. Six cox-1 haplotypes were identified using the TCS method. Most B. procyonis individuals collected east of the Mississippi shared the most common haplotype, while specimens collected from California had a different haplotype. These clusters are hypothesized to represent separate evolutionary lineages, which may have implications for pathogenicity to paratenic and accidental human hosts.