A Countrywide Seroepidemiological Survey of Rift Valley Fever in Livestock, Uganda, 2017

Abstract

In 2016, an outbreak of Rift Valley fever was reported in the Kabale District in Uganda for the first time in 48 years. Three human cases were confirmed by polymerase chain reaction, and subsequent serological investigations revealed an overall IgG seropositivity of 13% in humans and 13% in animals. In response to this reemergence, we designed a countrywide survey to determine the seropositivity of anti-Rift Valley fever virus (RVFV) IgG antibodies in livestock. Samples were collected from 27 districts and tested for RVFV anti-IgG antibodies. A total of 3,181 livestock samples were tested, of which 54.4% were cattle (1,732 of 3,181), 34.3% were goats (1,091 of 3,181), and 11.3% were sheep (358 of 3,181). Overall RVFV seropositivity was 6.9% (221 of 3,181). Seroprevalence was greater in cattle (10.7%) compared with goats (2.6%) and sheep (2.0%), among females (7.5%) compared with males (5.2%), and among adults (7.6%) compared with juveniles (4.9%) and nurslings (6.4%). Exotic breeds and animals with a history of abortion or stillbirth also had greater odds of RVFV seropositivity. Animals grazed under tethering and paddocking had greater RVFV seropositivity compared with animals that grazed communally, and livestock in the western and eastern regions had the greatest seroprevalence. In a multivariate regression model, animal species (odds ratio [OR], 6.4; 95% CI, 3.5–11.4) and age (OR, 2.3; 95% CI, 1.4–3.6) were associated significantly with RVFV seropositivity. This study could be important in developing risk-based surveillance for early outbreak detection to limit the spread of RVFV in both human and animal populations.

Exploring community-based reporting of livestock abortions for Rift Valley Fever surveillance in Uganda: A pilot study

“…Regarding brucellosis, goats had the highest prevalence than cattle. These findings align with previous research conducted in Uganda and Keny (Birungi et al, 2021;Kabami, 2023;Ndumu et al, 2021;Nyakarahuka et al, 2018aNyakarahuka et al, , 2023aNyakarahuka et al, , 2023bNyakarahuka et al, , 2023cNyamota et al, 2023;Tumusiime et al, 2023b).…”

“…Multiple reports/samples taken from the same farm could have skewed distribution towards cattle, or it may be that farmers were more likely to report cattle due to their value. Previous studies in Uganda (Nyakarahuka et al, 2018(Nyakarahuka et al, , 2023a(Nyakarahuka et al, , 2023c and neighbouring countries like Kenya (Hassan et al, 2020;Muturi et al, 2023) have also found surprisingly low rates of reports of abortions in sheep. However, the small number of sheep included in the study, means we could not measure the (relative) risk of infection infection in this species.…”

“…However, the first laboratory confirmed cases from animals and humans were not reported until 2016 from Kabale District (Shoemaker et al, 2019). Since then there have been sporadic RVF outbreaks in different parts of the country and these have been investigated by Ministry of Health (MoH) and Ministry of Agriculture, Animal Industries and Fisheries (MAAIF)’s surveillance departments (Aceng et al, 2023; Birungi et al, 2021; Kabami, 2023; Nyakarahuka et al, 2018a, 2023c, 2023a; Tumusiime et al, 2023a, 2023c). However, RVF surveillance is typically only carried out responsively after outbreaks that have already led to the loss of human lives or livestock.…”