Postepidemic Analysis of Rift Valley Fever Virus Transmission in Northeastern Kenya: A Village Cohort Study

Abstract

BackgroundIn endemic areas, Rift Valley fever virus (RVFV) is a significant threat to both human and animal health. Goals of this study were to measure human anti-RVFV seroprevalence in a high-risk area following the 2006–2007 Kenyan Rift Valley Fever (RVF) epidemic, to identify risk factors for interval seroconversion, and to monitor individuals previously exposed to RVFV in order to document the persistence of their anti-RVFV antibodies.Methodology/FindingsWe conducted a village cohort study in Ijara District, Northeastern Province, Kenya. One hundred two individuals tested for RVFV exposure before the 2006–2007 RVF outbreak were restudied to determine interval anti-RVFV seroconversion and persistence of humoral immunity since 2006. Ninety-two additional subjects were enrolled from randomly selected households to help identify risk factors for current seropositivity. Overall, 44/194 or 23% (CI95%:17%–29%) of local residents were RVFV seropositive. 1/85 at-risk individuals restudied in the follow-up cohort had seroconverted since early 2006. 27/92 (29%, CI95%: 20%–39%) of newly tested individuals were seropositive. All 13 individuals with positive titers (by plaque reduction neutralization testing (PRNT80)) in 2006 remained positive in 2009. After adjustment in multivariable logistic models, age, village, and drinking raw milk were significantly associated with RVFV seropositivity. Visual impairment (defined as ≤20/80) was much more likely in the RVFV-seropositive group (P<0.0001).ConclusionsOur results highlight significant variability in RVFV exposure in two neighboring villages having very similar climate, terrain, and insect density. Among those with previous exposure, RVFV titers remained at >1∶40 for more than 3 years. In concordance with previous studies, residents of the more rural village were more likely to be seropositive and RVFV seropositivity was associated with poor visual acuity. Raw milk consumption was strongly associated with RVFV exposure, which may represent an important new focus for public health education during future RVF outbreaks.

Cross-Sectional Survey of Rift Valley Fever Virus Exposure in Bodhei Village Located in a Transitional Coastal Forest Habitat in Lamu County, Kenya

“…As previously noted in our other surveys, symptoms of poor vision and objective visual impairment were significantly associated with evidence of past RVFV infection. 16 Among our Bodhei study population, a history of sensorial changes (pre-syncope, syncope, or coma) proved to be a significant correlate of anti-RVFV seropositivity among subjects without a history of livestock skinning or birthing exposure, perhaps suggesting a difference in disease manifestations depending on route of exposure. Visual disturbances, retinitis, 12,18 and longterm neurological complications 19 remain less well-known complications of RVFV infection.…”

“…12,16,17 Similarly, animal exposures differed according to gendered rolesmales had overall more live animal contact and butchering exposure, whereas females had more exposure by cooking.…”

Potential for Autoimmune Pathogenesis of Rift Valley Fever Virus Retinitis

“…Recent outbreaks have been documented in Saudi Arabia (2000) and the Horn of Africa (2006)(2007). [3][4][5][6][7][8][9] The most common severe complication of human RVFV infection is retinitis. Retinal complications occur in up to 10% of those affected and can cause lasting loss of vision.…”

“…Serum samples were collected during household-based cluster surveys of residents of Masalani (2008) 5 and Sangailu (2011), North East Province, Kenya, where a RVF epidemic had occurred in 2006-2007. The persons participated in a formal interview regarding demographics, potential viral exposures, their recent symptoms, and their vision.…”

“…5,6 Four groups were available for comparison: 1) persons with retinitis after exposure to RVFV (n = 8); 2) persons without retinitis after exposure to RVFV (n = 9); 3) persons with retinitis and no exposure to RVFV (n = 9); and 4) persons without retinitis and exposure to RVFV (n = 17). This study was approved by the institutional review boards at Case Western Reserve University and the Kenya Medical Research Institute.…”