Two Novel Arenaviruses Detected in Pygmy Mice, Ghana

Karl C. Kronmann¹

, Shirley Nimo-Paintsil¹, Fady Guirguis, Lisha C. Kronmann, Kofi Bonney, Kwasi Obiri-Danso, William Ampofo, Elisabeth Fichet-Calvet, and Elisabeth Fichet-Calvet.

Author affiliations: US Naval Medical Research Unit No. 3, Ghana Detachment, Accra, Ghana (K.C. Kronmann, S. Nimo-Paintsil, L.C. Kronmann); US Naval Medical Research Unit No. 3, Cairo, Egypt (F. Guirguis); Noguchi Memorial Institute for Medical Research, Legon, Ghana (K. Bonney, W. Ampofo, S. Nimo Paintsil); Kwame Nkrumah University of Science and Technology, Kumasi, Ghana (K. Obiri-Danso); Bernhard Nocht Institute of Tropical Medicine, Hamburg, Germany (E. Fichet-Calvet); Evolutionary Biology Group, University of Antwerp, Antwerp, Belgium (E. Fichet-Calvet)

Abstract

Two arenaviruses were detected in pygmy mice (Mus spp.) by screening 764 small mammals in Ghana. The Natal multimammate mouse (Mastomys natalensis), the known Lassa virus reservoir, was the dominant indoor rodent species in 4 of 10 sites, and accounted for 27% of all captured rodents. No rodent captured indoors tested positive for an arenavirus.

Lassa fever is an arenavirus infection transmitted to humans from rodents in a limited geographic region of western Africa. Nosocomial outbreaks have been recorded in Sierra Leone, Liberia, Guinea, and Nigeria: the countries best known to report Lassa fever (1). Most cases reported in travelers have originated in these 4 countries (2). However, cases have been reported from other countries in the region, including 1 caused by a previously undescribed strain of Lassa virus (LASV) after the case-patient traveled through Ghana (3). In addition, infection of humans with an arenavirus other than LASV has recently been recognized in southern Africa (4).
LASV has a bisegmented genome: the nucleoprotein (NP) and glycoprotein (GP) genes are on the small RNA segment, and the polymerase (L) and matrix protein (Z) genes are on the large RNA segment. LASV circulates in rodent populations even when infections in humans are not occurring, providing a source for subsequent outbreaks among humans.
Arenaviruses have species-specific reservoirs, and studies in Sierra Leone and Guinea found Mastomys natalensis to be the only rodent reservoir for LASV (5,6). In Guinea, M. natalensis abundance and viral prevalence rates in rodents have been associated with LASV seroprevalence among humans (6). Using a risk map model, we selected 10 sites in Ghana to examine rodent populations and arenavirus carriage rates.

The Study

The study was performed in accordance with a protocol approved by the Institutional Review Board of the Noguchi Memorial Institute for Medical Research, and the Institutional Review Board and Institutional Animal Care and Use Committee of the US Naval Medical Research Unit No. 3.

Figure 1

Thumbnail of Lassa virus risk map of Ghana showing 10 numbered study sites adapted from Fichet-Calvet and Rogers, Model 3 (1). Red areas indicate high predicted risk for Lassa fever and green areas indicate low predicted risk. Solid black lines and letters indicate vegetation zones: a) Guinea savanna woodland; b) moist semideciduous forest; c) tropical rainforest.

Figure 1. . . Lassa virus risk map of Ghana showing 10 numbered study sites adapted from Fichet-Calvet and Rogers, Model 3 (1). Red areas indicate high predicted risk for Lassa...

Seven sites were selected from areas of high predicted risk and 3 from areas of low predicted risk (Figure 1). A village was then selected for each site according to 3 criteria: a human population between 500 and 2,000; distance > 20 km from any urban center or major road; and willingness to participate. All field work was scheduled during the rainy seasons of 2010 and 2011, when viral prevalence rates in rodents have been shown to be higher (7).