The impact of multiple infections on wild animal hosts: a review

Bordes, Frédéric; Morand, Serge

Fundamentally, the studies on host genetics have mainly focused on MHC gene polymorphism. Investigating the maintenance of host genetic variation through coevolutionary hostÁpathogen interactions, a first prediction hypothesises the existence of a link between high MHC polymorphism and high diversity of parasites (55Á60). In accordance with this prediction, variation at the Human Leukocyte Antigen (HLA) class I genes was found associated with local pathogen richness (57) . Various studies in fish showed that individual hosts harbouring higher parasite species have higher genetic diversity at the MHC genes (55, 61, 62) . However, such pattern was not observed in rodents (60, 63Á65). A low diversity at MHC genes in grey slender mouse opossum was linked to high helminth parasite loads in terms of individual parasite species richness, nematode intensities and prevalence (60) . The authors explained this unexpected pattern by an 'unbalanced situation' scenario, which might be caused by a recent loss of genetic diversity and a lack of resistance alleles (60) . MHC-depleted species was supposed to suffer from higher parasite loads than MHC-diversified species. Interestingly, this prediction was supported in a tropical Asian rat (Leopoldamys sabanus) for which a more diverse MHC IIB allele repertoire was linked to reduced individual helminth species richness (65) . Due to the better body condition observed in rats harbouring higher allele diversity, the authors inferred that individuals harbouring higher polymorphism at MHC level should be more resistant to multiple infections (65) .