African arenaviruses - Coevolution between virus and murid host?

The Arenaviridae is a family of enveloped, negative-stranded RNA viruses which cause severe hemorrhagic fever in humans in areas of Africa and South America. Each arenavirus is generally associated with a single small-mammal host species in which it establishes a chronic infection involving shedding of virus in secretions and excretions. Infection in humans occurs via inhalation of aerosolized virus or ingestion or direct contact with food or fomites contaminated with infectious animal wastes. Genetic analysis shows that known arenaviruses fall into a New-World and an Old-World complex. New-World arenaviruses are associated with species of the rodent subfamily Sigmodontinae and Old-World viruses with the subfamily Murinae. This pattern suggests that an ancestral arenavirus was associated with an ancestral murid rodent before the two subfamilies diverged > 20 million years ago, and that distinct arenaviruses may have coevolved with murid species since that time. If this hypothesis is true, the phylogeny of the arenaviruses should mirror the phylogeny of their rodent hosts. Although the prediction of coincidence of host and virus phylogenies is supported for another group of viruses with murid hosts (the hantaviruses), a comparison of arenavirus and host phylogenies reveals several important inconsistencies. These irregularities may reflect cross-taxon transfer of viruses as well as the relatively incomplete knowledge of the systematics of African and South American murids. Doubtless, many more arenavirus/host associations remain to be discovered within Africa. Continued studies of the relationships among African murids and collaboration between mammalogists and virologists are important to the development of both disciplines.