Division of Infectious Diseases, Medical Center of the University of Munich, Munich, Germany.
PLoS Negl Trop Dis. 2012;6(3):e1557. doi: 10.1371/journal.pntd.0001557. Epub 2012 Mar 27.
The 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 FINDINGS: We 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.
RVFV 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.
裂谷热病毒（RVFV）是一种虫媒黄病毒。RVFV 主要在牲畜中暴发，对畜牧业造成严重的经济影响。人类感染与这些事件有关，死亡率为 0.5-2%。由于该病毒能够利用许多温带气候的蚊子作为媒介，因此它有很高的传播到非洲以外地区的潜力。
方法/主要发现：我们在坦桑尼亚西南部姆贝亚地区的 1228 名参与者中进行了分层、横断面血清流行率调查。样本选自 2007 年和 2008 年参加队列研究的 17872 人中。使用间接免疫荧光法确定 RVFV IgG 状态。使用单变量和多变量泊松回归模型分析可能的危险因素。我们在靠近马拉维湖的一个研究点发现了 RVFV IgG 流行率的独特局部最大值，为 29.3%（N=150）。总体血清流行率为 5.2%。血清阳性与年龄较大、社会经济地位较低、拥有牛以及与马拉维湖的距离较远有关。植被密度较高、最低和最高温度较低与 RVFV IgG 阳性相关。居住地的海拔高度，特别是在高流行地区的小范围内，与 RVFV IgG 阳性密切相关（每米 0.87，95%CI=0.80-0.94）。在高流行地区的低海拔地区，有大量的地表水汇集。在高流行地区，RVF 尚未在临床上确诊，也未发现疫情。
裂谷热病毒可能在该地区流行。牛的存在、茂密的植被和温带条件有利于蚊子的繁殖和病毒在媒介中的复制，这似乎在病毒传播和循环中发挥了主要作用。我们确定的环境危险因素可以更准确地确定裂谷热病毒流行的风险地区。
