Epidemiological Investigation of a Rift Valley Fever Outbreak in Humans and Livestock in Kenya, 2018

Abstract

On the last week of May of 2018, a community-based syndromic surveillance system detected mass abortions and deaths of young livestock in northeastern Kenya. Two weeks later, Rift Valley fever (RVF) was confirmed in humans presenting with febrile illness and hemorrhagic syndrome in the same region. A joint animal and human response team carried out an investigation to characterize the outbreak and identify drivers of disease transmission. Here, we describe the outbreak investigation and findings. A total of 106 human cases were identified in the months of May and June 2018: 92% (98) and 8% (8) of these cases occurring in the northern and western regions of Kenya, respectively. Seventy-six (72%) were probable cases, and 30 (28%) were laboratory confirmed by ELISA and/or PCR. Among the confirmed cases, the median age was 27.5 years (interquartile range = 20), and 60% (18) were males. Overall, the case fatality rate was 7% (n = 8). The majority of the confirmed cases, 19 (63%), reported contact with livestock during slaughter and consumption of meat from sick animals. All confirmed cases had fever, 40% (12) presented with hemorrhagic syndrome, and 23% (7) presented with jaundice. Forty-three livestock herds with at least one suspect and/or confirmed animal case were identified. Death of young animals was reported in 93% (40) and abortions in 84% (36) of livestock herds. The outbreak is indicative of the emergence potential of RVF in traditionally high-and low-risk areas and the risk posed by zoonosis to livestock keepers.

Serological evidence of single and mixed infections of Rift Valley fever virus, Brucella spp. and Coxiella burnetii in dromedary camels in Kenya

“…Outbreaks of Rift valley fever have been frequently reported in Kenya since the first detection of the virus in 1931[ 45 , 46 ]. Traditionally, cattle, sheep and goats are considered to be the species of interest during RVF outbreaks but emerging evidence shows camels play a significant epidemiological role during epizootics [ 14 , 47 , 48 ]. Our study found a positivity rate of 14% which is lower than previously reported rates of 57% and 21% from two studies conducted in 2007 [ 15 , 48 ].…”

“…Our study found a strong association between Brucella and Coxiella co-exposure exposure and camels above five years. This can be explained by the increased likelihood of exposure to the two pathogens over time due to their endemicity [ 14 , 53 ]. Intra-herd correlation coefficient values are key in calculating sample sizes for multistage sampling [ 54 ].…”

“…Similarly, camels play an important but underappreciated role in the epidemiology of RVFV, one of the pathogens with the highest exposure levels in Kenyan camels [8]. In addition to the high prevalence rates, high camel mortality rates during RVF outbreaks in Kenya and the association of camels with confirmed human RVF cases are indicative of role of camels in the epidemiology of the virus [14][15][16].…”

High Real-time Reporting of Domestic and Wild Animal Diseases Following Rollout of Mobile Phone Reporting System in Kenya

“…The effectiveness of application was demonstrated in 2018 when KABS detected a RVF outbreak that affected livestock and humans across three counties. [21] Disease surveillance in the domestic animal sectors in Kenya and SSA has been primarily paper-based, whereas the wildlife sectors rarely conducted routine disease surveillance and reporting. Therefore, the roll out of KABS in the wildlife sector represented a major milestone and an opportunity for detecting and responding to diseases before spillover to livestock and humans.…”

Using cross-species vaccination approaches to counter emerging infectious diseases

“…In Kenya, the Zoonotic Disease Unit, a national entity co-led by medical and veterinary epidemiologists for the purpose of zoonotic disease surveillance, may provide an exemplar framework through which vaccine programmes to tackle endemic/epidemic zoonoses can be implemented 73 . For instance, through extant surveillance for key disease syndromes in livestock, the most recent Rift Valley fever outbreak in Kenya was detected in humans within a fortnight of confirmed livestock cases 74 . In such a scenario, Rift Valley fever vaccination could be implemented among susceptible animals (licensed vaccines are already available) and humans (when a vaccine is available) within a radius in proximity to the initial cases.…”