Prevalence of rats and rodent borne pathogens across post-Katrina New Orleans

Disasters are happening at an increasingly higher rate and intensity a trend that is expected to continue as more humans migrate to coastal urban areas. Disasters, and as importantly, disaster recovery can affect how native and pest populations will recover. My aim was to improve understanding of disease risk by evaluating the socioecological conditions that have shaped commensal rat recovery and distribution, as well as the pathogens they carry, across New Orleans after Hurricane Katrina. I first estimated relative abundance and distribution of commensal rats from rodent trapping conducted between mid-2014 and early-2017 across 96 sites in 10 areas of the city that represent different flooding levels and policy-driven post disaster abandonment. Additional rats were obtained from supplemental sites sampled by the city rodent control board as part of control programs. All Norway rats were then genotyped at 236,971 ddRAD generated SNPs to infer if their abundance was a result of resilience, in-situ population recovery, immigration from un-flooded areas or a combination of them. Blood of all sampled rodents also was tested for the presence of Trypanosoma cruzi, the causative agent of Chagas disease, one of the many zoonotic pathogens rodents can carry and transmit to humans. A total of 1428 rodents, representing 5 species (380 norway rats, 629 roof rats, 394 house mice, 20 cotton rats and 7 rice rats) were trapped across the study area. Roof rats were more abundant and more widely distributed than Norway rats. Overall rat occurrence and abundance were higher in flooded areas with more vacant lots and abandonment. We observed patterns of inbreeding in flooded areas as well as signatures of population structure and limited movement, supporting the hypothesis that Norway rats suffered a population collapse and recovered by in situ reproduction and population growth. T.cruzi was detected in 11% of tested rodents, in all species tested and in all study areas across New Orleans indicating that transmission is local and widespread across the city and thus that exposure risk is much higher than has previously been recognized.