Seroprevalence and Molecular Detection of Rift Valley Fever in Sheep, Gezira state, Sudan (2017-2019)

Abstract

Aims: Livestock is the largest subsector of the Sudanese domestic economy and is a growing contributor to exports. Rift Valley fever (RVF) is an economically important arthropod-borne virus disease in Africa, primarily affecting sheep, goats, and cattle. RVF causes paramount loss in sheep industry in Sudan. The objective of this study was to detect RVF in sheep. Methodology: Five hundred and fifty-six sheep blood Serum from inoculated animals was collected from six study areas in the Gezira (Sudan)was evaluated for the presence of neutralizing antibodies using the diagnostic kit (ID. Vet.) for detecting antibodies directly against the RVFV nucleoprotein (NP) in serum and Reverse transcription (RT)-Polymerase Chain Reaction (PCR) protocol was used as standard test to diagnose and confirm RVFV among studied animals. Results: The ELISA test indicated that the highest Seroprevalence was found at Shikaira (38%), while samples from Albasabeir, Wad alnaem and Umalqura tested positive for antibodies against RVFV by 15%, 10% and 9% respectively. The lowest Seroprevalence found at Wad anor and Shabona (5% and 2%). The overall seroprevalence was 14.2% in the study sites, there is no significant difference among the six study sites with respect to seroprevalence. The Rt-PCR provided more sensitive and specific detection of RVFV in serum samples (sensitivity= 95% specificity = 80%). Conclusion: The results from this study showed the presence of anti-RVFV antibodies in all   study sites, suggesting that RVFV is actively circulating among sheep in Gezira state. The high seroprevalence of RVFV infection in Gezira state indicates its endemicity. Test validation using ROC analysis was able to distinguished between ELISA (actual class) and the PCR (predicted class) and the AUC = 0.79 which indicate that the PCR is gold standard test. Thus Rt-PCR used in the present study is reliable to detect precisely the M segment of RVFV and it is valuable for Wide area survey, among both sheep and Aedes spp. Targeting the prevailing genotypes of RVF-M segment, especially at high-risk areas and as a confirmatory test that should be considered by reference laboratories in the region.