Ranavirus and helminth parasite co-infection in invasive American bullfrogs in the Atlantic forest, Brazil.

Emerging infectious diseases threaten amphibian species across the globe. In Brazil, the American bullfrog (Aquarana catesbeiana) is a highly invasive species that can potentially transmit parasites and pathogens to native amphibians. This is the first assessment of co-infection of Ranavirus and helminth macroparasites in invasive populations of bullfrogs in South America. We collected, measured, and euthanized 65 specimens of A. catesbeiana sampled from 9 sites across three states of Brazil in the Atlantic Forest biome. We collected and identified helminth macroparasites and sampled host liver tissue to test for the presence and load of Ranavirus with quantitative PCR. We documented patterns of prevalence, parasite load, and co-infection with generalized linear mixed models, generalized logistic regressions, and randomization tests. Most individual bullfrogs did not exhibit clinical signs of infection, but the overall Ranavirus prevalence was 27% (95% confidence interval, [CI 17-38]). Bullfrogs were infected with helminth macroparasites from 5 taxa. Co-infection of helminth macroparasites and Ranavirus was also common (21% CI [12-31]). Bullfrog size was positively correlated with total macroparasite abundance and richness, and the best-fitting model included a significant interaction between bullfrog size and Ranavirus infection status. We observed a negative correlation between Ranavirus viral load and nematode abundance (slope = -0.22, P = 0.03). Invasive bullfrogs (A. catesbeiana) in Brazil were frequently infected with both Ranavirus and helminth macroparasites, so adult bullfrogs could serve as reservoir hosts for both pathogens and parasites. However, many macroparasites collected were encysted and not developing. Coinfection patterns suggest a potential interaction between Ranavirus and macroparasites because helminth abundance increased with bullfrog size but was lower in Ranavirus infected individuals. Future studies of bullfrogs in the Atlantic Forest should investigate their potential role in pathogen and parasite transmission to native anurans.

High prevalence and concomitant infection of Ranavirus and Eustrongylides sp. in the invasive American Bullfrog in Brazil.

American Bullfrogs, Aquarana catesbeiana, are invasive anuran species distributed worldwide. One of the adverse impacts that this species causes in native communities is as a reservoir host for pathogens and parasites. Here, we report the coinfection of two pathogenic organisms in A. catesbeiana: Ranavirus and the nematode Eustrongylides. Bullfrogs were collected in the wild in a pond close to the urban area of São Paulo, Brazil. The prevalence of both pathogens was high: 77% were infected with ranavirus with a mean viral load of 1010.3 viral copies, and 100% of the bullfrogs were infected by Eustrongylides sp. with a mean intensity of infection of 13.4 specimens per host. Four host specimens (31%) presented pathological signs that seemed to be related to the Eustrongylides sp. infection, such as internal organs adhered to each other due to high intensity and large size of the nematodes, ulcers, and raw flesh wounds caused by the nematode. The pathogenic and concomitant infections have potential zoonotic implications and raise concerns about human infection risks for Eustrongylides infection. Moreover, such infections may represent an additional level of threat to native communities through the potential shifts in patterns of parasite and pathogen transmission. Future research involving the native anuran community is essential to ascertain whether invasive bullfrogs are attenuating or exacerbating diseases such as ranavirosis and eustrongylidiosis.