Host genetic diversity and body condition influence parasite resistance and clearance in a wild marine mammal population

Host genetic variability can modulate infection resistance, although its role in infection clearance remains unclear. Hookworm disease (Uncinaria sp.) is the leading cause of pup mortality in several otariid species, although the parasite can be cleared through immune-mediated processes. We evaluated the association of host genetic diversity, body condition, and immune response with hookworm resistance and/or clearance in South American fur seal (Arctocephalus australis). Uninfected pups had higher heterozygosity than parasitized individuals, indicating a negative relationship between heterozygosity and the chances of infection. Likewise, pups that died of hookworm infection had lower heterozygosity than those that died of non-infectious causes. Interestingly, once infected, pups that survived hookworm infection had heterozygosities similar to pups that died of hookworm disease. However, pups that cleared the infection had a higher body mass and parasite-specific IgG levels than those that did not recover or died of hookworm disease. Thus, although heterozygosity predicted resistance to and mortality from hookworm infections, it did not affect parasite clearance, which was facilitated by better body conditions and adaptive immune responses. This demonstrates that host genetic variability and host-environment interactions influence disease dynamics, acting at different, well-defined stages of infection.

Methods
The biological data was collected in the South American fur seal breeding colony of Guafo island. The genetic data was processed and analyzed in the "Evolution of Infectious diseases Lab" at Austral University of Chile.