Transmission Dynamics Of Human Rift Valley Fever Virus In Ijara District, Garissa County, Kenya

ABSTRACT

Rift Valley Fever (RVF) is an emerging viral disease which causes among other problems severe hemorrhagic syndrome, retinitis and meningo-encephalitis in humans. The disease was previously thought to be a disease of animals but it is increasingly developing to be a human health problem. Two human RVF epidemics have previously occurred in Kenya (1997-1997; 2006-2007) each resulting to human deaths. Most RVF outbreaks occur in rural locations where keeping of livestock is the main livelihood of the affected communities. Flooding due to excessive rainfall after a long dry spell allows the breeding of vector mosquitoes. Human beings get infected either through the bite of infected mosquitoes or exposure to infected animal material. The dominant mode of transmission of RVF from animal to human during combined epizootics and epidemics has not been clearly understood. The main objective of this study is to assess the transmission dynamics of RVF in an area where epidemics occur. The survey was done in Gumarey, a rural village and Sogan-Godud, a sub-urban village in Ijara District, Kenya where 248 study participants were randomly selected. Venous blood was then collected from the subjects for the detection of Rift Valley Fever Virus (RVFV) antibodies by IgG Enzyme Linked Immunosorbent Assay (ELISA) testing technique. Rift Valley Fever Virus (RVFV) IgG seropositivity was used as the primary measure for RVFV exposure. Animal and non- animal exposure factors were then determined against RVFV IgG seropositivity. Subjects were clinically examined for ophthalmological disorders by an Ophthalmologist. A structured questionnaire was used to collect relevant data while observations were made on the homesteads. Mosquito sampling was done by use of Centers of Disease Control (CDC) Light Traps. A total of 12252 mosquitoes were collected. The morphological identification was confirmed by Polymerase Chain Reaction (PCR). The mosquito RVF viral infection rates were also confirmed by PCR. The Geographical Positioning System (GPS) of the households under study was recorded by Etrex GPS machine. Overall anti-RVFV seropositivity by IgG was 13%. Increased IgG seropositivity was found among older male persons and evidence of interepidemic RVFV transmission was detected. In location analysis, participants who resided from Gumarey were 4 times more at risk of RVFV than those residing from Sogan Gudud (P=0.001;Odds Ratio: 3.8). Gumarey village reported more animal exposures than Sogan Gudud. The results also showed significant association between eye disease and seropositivity (P=0.003) and the most common causes of eye disease in seropositive persons were visual impairments and retinal lesions. Disposal of animal fetus, birthing, skinning, butchering and milking were highly associated with seropositivity (p=0.0001). In total 22% of the mosquito pools tested by PCR were positive for RVFV. A geospatial map showing seropositive households by clusters was constructed for both villages. The study highlights the variability in exposure and anti-RVFV seropositivity between villages and also emphasizes the impact of age, gender, location and animal husbandry in RVF transmission. The results show the potential of future outbreaks in Ijara District. Public health education could be used to prevent transmission of RVF and avert possible epidemics