Serological evidence of Rift Valley fever virus infection among domestic ruminant herds in Uganda

Deo B Ndumu,Jackson Kyondo,Jesca Nakayima,Edward Miller,Kariuki M Njenga,Mary Nanfuka,Jean-Paul Gonzalez,Fred Monje,Eugene Kidega,Rose Ademun,Chris Rutebarika,Francisco Veas,Barnabas Bakamutumaho,Dan Tumusiime,Stephen Balinandi,Robert Downing,Eugene Arinaitwe,Natascha Meunier

doi:10.1186/s12917-021-02867-0

Abstract

BackgroundPrior to the first recorded outbreak of Rift Valley fever (RVF) in Uganda, in March 2016, earlier studies done until the 1970’s indicated the presence of the RVF virus (RVFV) in the country, without any recorded outbreaks in either man or animals. While severe outbreaks of RVF occurred in the neighboring countries, none were reported in Uganda despite forecasts that placed some parts of Uganda at similar risk.The Ministry of Agriculture, Animal Industry and Fisheries (MAAIF) undertook studies to determine the RVF sero-prevalence in risk prone areas.Three datasets from cattle sheep and goats were obtained; one from retrospective samples collected in 2010–2011 from the northern region; the second from the western region in 2013 while the third was from a cross-sectional survey done in 2016 in the south-western region. Laboratory analysis involved the use of the Enzyme Linked Immunosorbent Assays (ELISA). Data were subjected to descriptive statistical analyses, including non-parametric chi-square tests for comparisons between districts and species in the regions.ResultsDuring the Yellow Fever outbreak investigation of 2010–2011 in the northern region, a total sero-prevalence of 6.7% was obtained for anti RVFV reacting antibodies (IgG and IgM) among the domestic ruminant population. The 2013 sero-survey in the western region showed a prevalence of 18.6% in cattle and 2.3% in small ruminants. The 2016 sero-survey in the districts of Kabale, Kanungu, Kasese, Kisoro and Rubirizi, in the south-western region, had the respective district RVF sero-prevalence of 16.0, 2.1, 0.8, 15.1and 2.7% among the domestic ruminants combined for this region; bovines exhibited the highest cumulative sero-prevalence of 15.2%, compared to 5.3 and 4.0% respectively for sheep and goats per species for the region.ConclusionsThe absence of apparent outbreaks in Uganda, despite neighboring enzootic areas, having minimal restrictions to the exchange of livestock and their products across borders, suggest an unexpected RVF activity in the study areas that needs to be unraveled. Therefore, more in-depth studies are planned to mitigate the risk of an overt RVF outbreak in humans and animals as has occurred in neighboring countries.

Highlights

Prior to the first recorded outbreak of Rift Valley fever (RVF) in Uganda, in March 2016, earlier studies done until the 1970’s indicated the presence of the RVF virus (RVFV) in the country, without any recorded outbreaks in either man or animals
This paper examines three different sets of data with the aim of illuminating the serological status of domestic ruminant populations due to possible exposure to the RVF Phlevovirus, in the absence of overt outbreaks, in high-risk areas of northern, western and south-western regions of Uganda
The first dataset of 75 sera specimens collected from cattle and small ruminants obtained during the investigation of a Yellow Fever outbreak of 2010/2011 in Agago and Kitgum districts showed an overall RVF antibody sero-prevalence of 6.7%; species sero-prevalences in this region were 4.7% in cattle and 9.4% in small ruminants for the two districts combined; both immunoglobulin G (IgG) and immunoglobulin M (IgM) antibodies to the RVF virus were detected at the time

Summary

Introduction

Prior to the first recorded outbreak of Rift Valley fever (RVF) in Uganda, in March 2016, earlier studies done until the 1970’s indicated the presence of the RVF virus (RVFV) in the country, without any recorded outbreaks in either man or animals. Before the disease emerged in Egypt in 1977, with severe epizootics in humans and animals [7], RVF was known to occur only in Eastern and Southern Africa. In 1979, the disease emerged on the island of Madagascar [9] as well on the Arabian Peninsula in 2001 [10] This dramatic extension was hypothesized to be associated with the trade routes and movements of viraemic animals [11]

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