Longitudinal seroprevalence of Crimean-Congo hemorrhagic fever virus in Southern Uganda

Abstract

Crimean-Congo hemorrhagic fever (CCHF) is a tick-borne disease endemic to many regions of Africa, the Middle East, Southeast Asia and the Balkans. Caused by the CCHF virus (CCHFV), CCHF has been a recognized cause of illness in Uganda since the 1950s and recently, more intensive surveillance suggests CCHFV is widely endemic within the country. Most surveillance has been focused on the Ugandan cattle corridor due to the risk of CCHFV exposure associated with livestock practices. Here we evaluated the seroprevalence of CCHFV in several Southern Ugandan communities outside the cattle corridor combined with longitudinal sample sets to measure the immune response to CCHFV for up to a decade. Interestingly, across three community types, agrarian, trading and fishing, we detected CCHFV seroprevalence in all three but found the highest seroprevalence in fishing communities. We also measured consistent CCHFV-specific antibody responses for up to a decade. Our findings support the conclusion that CCHFV is widely endemic in Uganda and highlight that additional communities may be at risk for CCHFV exposure.

Keywords: Africa; CCHF; Uganda; antibodies; seroprevalence.

Figure 1.

Seropositivity of CCHFV in Southern Uganda. Map of Uganda with highlighted Masaka region where RCCS study samples were collected. CCHFV seropositivity map by community type (circle = fish landing site, triangle = agrarian, square = trading; black = 0%, yellow = 1-4%, orange = 5–7%, red = >7%).

Figure 2.

Antibody responses to CCHFV are lifelong. (a) Longitudinal CCHFV IgG antibody endpoint titres of the 51 positive individuals with sera collected between July 2014–March 2023, RCCS rounds 16–20 respectively. Each box represents 1 individual titled by their sample number and colour coded to their CCHFV-specific IgG endpoint titre. *Sample numbers 479 and 197 were weakly positive at round 19 cross-sectional testing, which may explain the low or negative titres longitudinally. (b) The fitted line is the antibody titre decay data of all individuals simultaneously using a mixed-effect regression approach. Available longitudinal sample sets of seropositive individuals by number of rounds are as follows- 1 round:6 individuals, 2 rounds:10 individuals, 3 rounds:9 individuals, 4 rounds:11 individuals, 5 rounds:15 individuals. (c) Sera was evaluated for neutralization against authentic CCHFV strain UG3010. VN titres are reported as the reciprocal of the last dilution to show no cytopathic effect. P value calculated with Welch’s t-test. ** P < 0.01.

Figure 3.

Household contact network stratified by fish landing site, agrarian, and trading community households. Of the 52 household contacts tested, 5 were seropositive for CCHFV IgG antibodies. 1 household had 2 index positive individuals. Line = household contact connection. Red shape = positive household contact. Filled shape = index positive household member from 1,199 sample set. Empty shape = negative household contact.