A retrospective sero-epidemiological study on rift valley fever in cattle in Uganda between 1997 to 2009

Abstract

Surveillance on Rift Valley fever (RVF) in cattle was conducted in Uganda, with a view to ascertaining whether the RVF virus circulated in bovine undetected during the period 1997 to 2009. Four hundred eighty (480) frozen bovine sera collected in 1997, 1998, 2000, 2001 and 2005 were tested using both RVF IgG and IgM ELISA performed in parallel. Additional 685 bovine sera collected in 2006 and 2007 were tested using the Virus Neutralization Test (VNT). A further 232 and 296 bovine sera collected in 2008 and 2009, respectively, were tested using IgM ELISA. The findings revealed a prevalence of anti-RVF virus IgG antibodies in cattle ranging from 0.0 - 2.5% across districts and 0.0 – 2.6% across years (1997 – 2005), without significant differences across districts or years. Meanwhile the prevalence of anti-RVF virus IgM antibodies in cattle ranged from 0.0 – 6.3% across districts and 0.0 – 2.6% across years (1997-2009). Cattle sampled in Kumi district were 7 times (Odds Ratio (OR) 7.0: 95% CL, 1.8-26.9) more likely to be seropositive than those from other districts. Furthermore, cattle sampled in 2008 were 3.4 times (OR 3.4: 95% CL 1.0-10.1) more likely to be seropositive than during other years. Regarding analysis of anti-RVF virus neutralizing antibodies, cattle from Apac district were 3.6 times (OR 3.6: 95% CL 1.9-6.7) more likely to be seropositive than those from other districts. In addition, cattle from large herds (> 100) were 5 times (OR 5.0: 95 CL 2.3 – 10.8) more likely to be seropositive than those from small herds (0-50). Arungi farm in Apac district had a higher likelihood (OR 4.0: 95 CL 1.8-9.3) to have seropositive cattle. The majority of the 685 cattle (90%) had low titres (> 1: 10) of neutralizing antibodies while few (10%) had high titres, ranging from 1:10 to > 1: 80. In conclusion, the study revealed evidence of low level circulation of the RVF virus in cattle in Uganda in certain districts and farms, especially during certain years (2008) when flooding occurred.

Keywords: IgG; IgM; RVFV neutralizing antibodies; Cattle; Uganda