High Seroprevalence of Rift Valley Fever and Evidence for Endemic Circulation in Mbeya Region, Tanzania, in a Cross-Sectional Study

Abstract

BackgroundThe Rift Valley fever virus (RVFV) is an arthropod-borne phlebovirus. RVFV mostly causes outbreaks among domestic ruminants with a major economic impact. Human infections are associated with these events, with a fatality rate of 0.5–2%. Since the virus is able to use many mosquito species of temperate climates as vectors, it has a high potential to spread to outside Africa.Methodology/Principal FindingsWe conducted a stratified, cross-sectional sero-prevalence survey in 1228 participants from Mbeya region, southwestern Tanzania. Samples were selected from 17,872 persons who took part in a cohort study in 2007 and 2008. RVFV IgG status was determined by indirect immunofluorescence. Possible risk factors were analyzed using uni- and multi-variable Poisson regression models. We found a unique local maximum of RVFV IgG prevalence of 29.3% in a study site close to Lake Malawi (N = 150). The overall seroprevalence was 5.2%. Seropositivity was significantly associated with higher age, lower socio-economic status, ownership of cattle and decreased with distance to Lake Malawi. A high vegetation density, higher minimum and lower maximum temperatures were found to be associated with RVFV IgG positivity. Altitude of residence, especially on a small scale in the high-prevalence area was strongly correlated (PR 0.87 per meter, 95% CI = 0.80–0.94). Abundant surface water collections are present in the lower areas of the high-prevalence site. RVF has not been diagnosed clinically, nor an outbreak detected in the high-prevalence area.ConclusionsRVFV is probably circulating endemically in the region. The presence of cattle, dense vegetation and temperate conditions favour mosquito propagation and virus replication in the vector and seem to play major roles in virus transmission and circulation. The environmental risk-factors that we identified could serve to more exactly determine areas at risk for RVFV endemicity.

Seroprevalence of Alphavirus Antibodies in a Cross-Sectional Study in Southwestern Tanzania Suggests Endemic Circulation of Chikungunya

“…Map created by use of Manifold System 8.0 software. (C) reproduced from [23] under creative commons license.…”

“…Detection of anti- Alphavirus IgG, anti-Yellow fever virus IgG, anti-dengue 1–4 virus IgG, and anti-West Nile virus IgG on bio-banked samples were performed as described previously for Rift Valley fever virus (RVfV) IgG [23]. A commercially available biochip (Euroimmun, Lübeck, Germany), containing infected and non-infected Vero E6 cells or only non-infected Vero E6 cells (negative control), was used for indirect immunfluorescence testing (IIFT), following a standard protocol.…”

Seroprevalence of Rift Valley fever virus infection in camels (dromedaries) in northern Tanzania

“…The current theory is that RVFV is maintained in aedine mosquito eggs and epidemics occur following an increase in the mosquito population after abnormally heavy rains (Tchouassi et al 2013), which occur classically every 10 years. Evidence of RVFV exposure has been shown to occur in African buffalo (Syncerus caffer) (Evans et al 2008;Bird et al 2008;LaBeaud et al 2011); giraffe (Giraffa camelopardalis) (Bird et al 2008), humans (Swai and Schoonman 2009;Pepin et al 2010;Heinrich et al 2012), cattle (Sumaye et al 2013) and in sheep (Rostal et al 2010;Fafetine et al 2013).…”

High seroprevalence of Rift Valley fever phlebovirus in domestic ruminants and African Buffaloes in Mozambique shows need for intensified surveillance

“…Studies carried out in the central (Zambezia and Manica) and south (Maputo and Gaza) Mozambique between 1996 and 2013, have shown high seroprevalence of RVF antibodies in cattle (7% – 51.6%), goats (11.6% – 25.1%), and sheep 9.2% – 44.2%) [29–34]. The high density of cattle in the herds in relation to goats and sheep may be one of the contributing factors to their greater susceptibility to RVFPV infection [56]. However, it would be important to evaluate the effect of density of animal species on susceptibility to RVFPV infection in Mozambique.…”