Experimental Morogoro Virus Infection in Its Natural Host, Mastomys natalensis

Natural hosts of most arenaviruses are rodents. The human-pathogenic Lassa virus and several non-pathogenic arenaviruses such as Morogoro virus (MORV) share the same host species, namely Mastomys natalensis (M. natalensis). In this study, we investigated the history of infection and virus transmission within the natural host population. To this end, we infected M. natalensis at different ages with MORV and measured the health status of the animals, virus load in blood and organs, the development of virus-specific antibodies, and the ability of the infected individuals to transmit the virus. To explore the impact of the lack of evolutionary virus–host adaptation, experiments were also conducted with Mobala virus (MOBV), which does not share M. natalensis as a natural host. Animals infected with MORV up to two weeks after birth developed persistent infection, seroconverted and were able to transmit the virus horizontally. Animals older than two weeks at the time of infection rapidly cleared the virus. In contrast, MOBV-infected neonates neither developed persistent infection nor were able to transmit the virus. In conclusion, we demonstrate that MORV is able to develop persistent infection in its natural host, but only after inoculation shortly after birth. A related arenavirus that is not evolutionarily adapted to M. natalensis is not able to establish persistent infection. Persistently infected animals appear to be important to maintain virus transmission within the host population.

Three arenaviruses in three subspecific natal multimammate mouse taxa in Tanzania: same host specificity, but different spatial genetic structure?

Mastomys natalensis is widespread in sub-Saharan Africa and hosts several arenavirus species, including the pathogenic zoonotic Lassa virus in West Africa. Mitochondrial lineages sub-divide the range of M. natalensis and have been associated with cryptic structure within the species. To test specificity of arenaviruses to hosts carrying these lineages, we screened 1772 M. natalensis in a large area of Tanzania where three mitochondrial lineages meet. We detected fifty-two individuals that were positive for one of three arenaviruses: Gairo, Morogoro, and Luna virus. This is the first record of Luna virus in Tanzania. We confirmed the specificity of each arenavirus to a distinct host mitochondrial lineage except for three cases in one locality at the centre of a host hybrid zone. No arenaviruses were detected in a large part of the study area. Morogoro and Gairo virus showed differences in prevalence (Morogoro virus lower than Gairo virus) and in genetic structure (Morogoro virus more structured than Gairo virus). However, both viruses have genetic neighbourhood size estimates of the same order of magnitude as Lassa virus. While differences in arenavirus and/or host evolutionary and ecological dynamics may exist, Tanzanian arenaviruses could be suited to model Lassa virus dynamics in M. natalensis.