Spatial distribution of non-clinical Rift Valley fever viral activity in domestic and wild ruminants in northern Tanzania

Abstract

Rift Valley fever (RVF) is an acute zoonotic viral disease of domestic ruminants in mainland Africa and Madagascar. The disease may exist in non-clinical form in apparently health animals. This study was designed to investigate the existence and spatial distribution of non-clinical form of RVF virus (RVFV) activity in wild and domestic animals in six districts in northern Tanzania. A retrospective cross-sectional study involved testing a total of 285 and 100 serum samples from domestic ruminants and wildlife species, respectively. The samples were subjected to IgG and IgM enzyme-linked immunosorbent assay (ELISA) as well as to the Real-time Polymerase Chain Reaction (RT-PCR). Based on ELISA test, the  seroprevalence of RVF-specific IgG antibodies was: African buffalo (40.9%,
n=22), African elephant (33.3%, n=3), cattle (11.8%, n=93), sheep (11.3%, n=97) and goats (8.4%, n=95). Two serum samples from goats tested positive for IgM. All samples tested were RVFV-negative based on RT-PCR test. The highest intravillage sero-prevalence of IgG was observed in two villages (Kimotorok and Lormorije) of Simanjiro district. Domestic ruminants from herds that were located at an elevation below 1000m were at higher risk (OR=2.32, 95% CI 1.05 – 5.16, p=0.04) of RVFV infection. Findings of the current study indicate existence of a wide range of  domestic and wildlife hosts which could serve as potential reservoirs of RVFV during inter-epidemic period. This calls for adoption of one health approach in responding to RVF epidemics as well as during implementation of RVF controlling measures with the ultimate goal of eradicating RVF in Tanzania.

Key words: Rift Valley fever, inter–epidemic period, seropositivity, spatial
distribution, ruminants, Tanzania.