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Rainy season Upper Guinea

Ecology and environment 

There is evidence that cases of Lassa fever increase during the dry season, and ecology studies suggest this is because of a restriction of food supply outdoors. However, this rise may not exclusively be related to rodent movement. For instance, this might be related to increased survivability of the virus in lower temperatures, or increases in pre-existing rodent populations within households. However, previous studies have failed to show a correlation between the abundance of infected rodents in houses and the incidence of human Lassa fever cases. Lassa virus was only significantly associated with seasonality amongst rodents trapped in proximal fields. For those trapped insides homes, whilst the population of the rodents had increased, the virus prevalence fluctuated non-significantly.

Resources

Movement patterns of small rodents in Lassa fever-endemic villages in Guinea

The authors investigate in this study the spatial behaviour of M. Natalensis in Upper Guinea. They use to experiments: capture-mark-recapture studies and Rhodamine B. Their findings showed that M.Natalensis moves between houses and proximate fields. This is an important information for rodent control activities that need to be extended from indoors to fields.

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Forecasting rodent outbreaks in Africa: an ecological basis for Mastomys control in Tanzania

This study collected rainfall data preceding historical outbreaks of Mastomys rats in East Africa in order to test the hypothesis that such outbreaks occur after long dry periods. It found that rodent outbreaks were generally not preceded by long dry period and the population dynamics of Mastomys natalensis rats in Tanzania are significantly affected by the distribution of rainfall during the rainy season.

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Diversity and dynamics in a community of small mammals in coastal Guinea, West Africa

This resource investigated three villages in high endemic zones of Lassa fever in Guinea and presents the biodeiversity of the small mammal community identified through standardized trapping in houses, cultivations and forest.

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Fluctuation of abundance and Lassa virus prevalence in Mastomys Natalensis in Guinea, West Africa

This study investigates the link between the ecology of the M. Natalensis and the incidence of Lassa fever in human cases in Guinea. They found that the risk for Lassa virus transmission was present in both rainy and dry season; however the risk increased in the dry season because of the possibility of encountering rodent excreta in the houses.

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Lassa Fever: a rodent-human interaction

This resource examines the sites of interactions between humans and the multimammate mouse, Mastomys natalensis. It presents findings such as new arenaviruses in other African rodents and in snakes, that  argue preferably toward the host-switching concept. The recent emergence in Sierra Leone, the absence of virus positive Mastomys between the two endemic zones and poor virus diversity in the Mano River area also point in the direction of a unique import of Lassa virus from Nigeria to Sierra Leone during the 19th century. This resource also discusses the hypothesis of human displacements through the Atlantic slave trade and its abolition in 1807.

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