Transmission ecology of Old World Arenaviruses in natural populations of their reservoir hosts
28 January 2019
Campus Drie Eiken, O.05 - Universiteitsplein 1 - 2610 Antwerpen-Wilrijk (route: UAntwerpen, Campus Drie Eiken
Organization / co-organization:
Department of Biology
Herwig Leirs & Jonas Reijniers
PhD defence Joachim Mariën - Faculty of Science, Department of Biology
In West Africa, the multimammate mouse (Mastomys natalensis) is the primary reservoir of Lassa virus, an arenavirus that causes severe haemorrhagic fever in humans. The disease affects between 200.000 and 300.000 people yearly with a fatality rate of 1-2%. Humans get infected by close direct or indirect contact with the rodent or its excretions, which can be through contaminated food or water, direct consumption of the rodent, or inhalation of excretion particles. Because no vaccine for use in humans exists and therapeutic options are limited, rodent control is currently assumed to be the only feasible option to control Lassa fever. However, no solid information exists on how effective rodent control really is or which control strategies would be most effective to reduce spillover. Moreover, Mastomys natalensis also hosts several other arenaviruses such as Morogoro virus, which occurs in rodent populations in Tanzania. Because Morogoro virus is not pathogenic for humans, it is considered a safe substitute for studying closely related but pathogenic arenaviruses like Lassa virus.
In this thesis, we present new insights into how arenaviruses can persist in populations of their reservoir hosts. First, by using Morogoro virus as a model, we show that arenaviruses exhibit several characteristics that can prevent extinction at low rodent densities, such as their avirulent residence and ability to initiate chronic infections in the host. The importance of other characteristics for viral persistence was also suggested (e.g. host manipulation and indirect, sexual or vertical transmission), although they were not investigated in detail. Then, based on the insights derived from Morogoro virus and additional field experiments in Guinea, we developed a mathematical model to predict the effectiveness of rodent control techniques to manage Lassa virus spillover risk to humans. Both field experiments and model simulations suggest that annual rodent elimination is pointless, as M. natalensis will reinvade houses quickly and Lassa virus prevalence will return easily to levels before control. In contrast, the models suggest that continuous elimination or vaccination of rodents are more sustainable approaches, and should be considered by policymakers in combination with other prevention strategies, such as rodent proofing of houses.