Rodent-Borne Pathogens in Mastomys Species and Humans in Ghana

Small mammals such as mice and rats are abundant in many regions throughout Sub-Saharan Africa, and some of these have been described as reservoirs for many human pathogens including Lassa fever. Lassa fever is a viral haemorrhagic fever unique to West Africa. Lassa virus, the aetiologic agent of Lassa fever is zoonotic, with Mastomys species as the reservoir. Outbreaks with high fatality rates have been reported in Nigeria and Sierra Leone. It is presumed to exist in West Africa, but there has been little research in most of these countries, despite reports of disease in travellers to Burkina Faso, Cote d’Ivoire, Ghana and Mali. In addition to Lassa virus, some of these small mammals are known to habour other agents such as Hantaviruses, Borrelia crocidurae, Leptospira and Leishmania species. The remarkable expansion of human population has led to increasing contact with these rodents, thereby disrupting their habitats and increasing opportunities for disease transmission. The magnitude of the potential for human disease involving rodent-borne agents in Ghana is largely unknown. A recent risk map was therefore used to select study sites in Ghana in an attempt to help define the burden of some of these pathogens. Small mammals were collected, identified by species and screened for the presence of pathogens during the rainy seasons of 2010 and 2011 from ten communities in Ghana together with 657 human sera from healthy adults living in the same communities (7 predicted high risk and 3 low risk). Sherman collapsible traps were set on three consecutive nights in houses (indoors) and surrounding farmlands (outdoors) totaling 9,269 night traps. In all, 764 small mammals were captured constituting ten genera of seventeen species: Praomys (n=333), Mastomys (n=231), Mus (Nannomys) (n=133), Gerbilliscus (n=6), Crocidura (n=21), Rattus (n=5), Lophuromys (n=3), Lemniscomys (n=2), Taterillus (n=29), and Uranomys (n=1). Of the total captured, 66% were trapped indoors with Praomys daltoni (312/504), the predominant species, followed by Mastomys natalensis (180/504). The pygmy mice, Mus (Nannomys) (130/260) were abundant in the outdoor captures which constituted 50%. There were more Mastomys occurrence in Upper West (n=36), Upper East (n=32) and Northern (n=75) regions than in the southern sector. Whole blood of two rodents (0.3%) Mus (Nannomys) spp. was positive for Arenavirus presence by conventional polymerase chain reaction assay (PCR). All rodent lung tissues were negative for Hantaviruses (Dobrava and Puumala serotypes). Using an in-house enzyme-linked immunosorbent assay (ELISA), human serum showed evidence of Arenavirus antibodies in 34 samples (5.2%). Puumala and Dobrava serotype antibodies were also detected with commercial kit, constituting 11% and 12% respectively. Twenty one percent (21%) of the human serum showed evidence of Leptospira antibodies using SERION ELISA classic test kit. Human exposure to the zoonotic infections studied was observed to cut across all age groups. Seropositivity was highest for anti-LASV at site 7-Eastern region (29%), anti-hantavirus (Dobrava serotype) at site 10-Brong Ahafo region (26%), and anti-Leptospira at site 8-Northern region (19%). Fifty six individuals (21% of positives) had been exposed to more than one of the rodent-borne infections tested, whereas 208 (78%) had been exposed to only one type of infection. Putative rodent reservoirs of the different pathogens found in the human sera were xviii captured in most of the study sites but human exposure could not be linked to their presence in the rodents. This study suggests that 40% of residents in rural farming communities in Ghana have been exposed to at least one rodent-borne disease (Arenavirus, Hantavirus, or Leptospira).

Source: KNUST