Identification of Bunyamwera and Possible Other Orthobunyavirus Infections and Disease in Cattle during a Rift Valley Fever Outbreak in Rwanda in 2018.

Marie Fausta Dutuze,Manassé Nzayirambaho,Angelique Ingabire,Solange Uwituze,Rebecca C Christofferson,Isidore Gafarasi

doi:10.4269/ajtmh.19-0596

Abstract

.In 2018, a large outbreak of Rift Valley fever (RVF)–like illness in cattle in Rwanda and surrounding countries was reported. From this outbreak, sera samples from 157 cows and 28 goats suspected to be cases of RVF were tested to confirm or determine the etiology of the disease. Specifically, the hypothesis that orthobunyaviruses—Bunyamwera virus (BUNV), Batai virus (BATV), and Ngari virus (NRIV)—were co-circulating and contributed to RVF-like disease was tested. Using reverse transcriptase-polymerase chain reaction (RT-PCR), RVFV RNA was detected in approximately 30% of acutely ill animals, but in all cases of hemorrhagic disease. Seven cows with experienced abortion had positive amplification and visualization by gel electrophoresis of all three segments of either BUNV or BATV, and three of these were suggested to be coinfected with BUNV and BATV. On sequencing, five of these seven cows were conclusively positive for BUNV. However, in several other animals, sequencing was successful for some but not all segments of targeted viruses BUNV and BATV. In addition, there was evidence of RVFV–orthobunyavirus coinfection, through RT-PCR/gel electrophoresis and subsequent Sanger sequencing. In no cases were we able to definitely identify the specific coinfecting viral species. This is the first time evidence for orthobunyavirus circulation has been molecularly confirmed in Rwanda. Furthermore, RT-PCR results suggest that BUNV and BATV may coinfect cattle and that RVFV-infected animals may be coinfected with other orthobunyaviruses. Finally, we confirm that BUNV and, perhaps, other orthobunyaviruses were co-circulating with RVFV and contributed to the burden of disease attributed to RVFV in Rwanda.

Highlights

The samples were put into 2-mL Eppendorf tubes and kept in −80°C, and subsequently, the samples were shipped to Louisiana State University where they were tested for Rift Valley fever virus (RVFV) and Bunyamwera virus (BUNV), Batai virus (BATV), and Ngari virus (NRIV) as described in the following paragraphs
Twelve goats were positive to RVFV, whereas 44 cattle were positive to RVFV via reverse transcriptase-polymerase chain reaction (RT-PCR)
Of those that were positive for RVFV, 26.7% had signs of hemorrhagic disease, whereas 82.1% presented with abortion

Summary

Introduction

The group of viruses commonly referred to as bunyaviruses have caused diseases of zoonotic and economic importance globally since the beginning of the twentieth century.[1,2,3,4] In Africa, Rift Valley fever virus (RVFV) was first identified and characterized in 1912 and further detected as the etiological agent of an epizootic outbreak in Kenya in 1930.5–7 Rift Valley fever virus is a vector-borne virus that causes disease in humans, livestock, and wildlife ruminant species.[1,6,8,9] In animals, it is clinically characterized by abortions and stillbirths, hepatitis, and hemorrhagic fever in severe cases.[8,10,11] In humans, the mild form is characterized by a self-limiting febrile illness, but individuals may progress to severe disease manifesting as hemorrhagic fever, encephalitis, vision loss, and conjunctivitis.[8,12,13,14,15,16,17,18] These clinical manifestations are common in many diseases caused by bunyaviruses.[2,19,20] RVFV has a broad range of identified vectors consisting of mosquitoes, ticks, and flies, the primary vectors are Aedes spp. and Culex spp. mosquitoes.[21,22,23,24,25,26,27,28] Rift Valley fever virus consistently circulates in domestic ruminants and human populations throughout different countries of Africa and the Arabian Peninsula where it causes significant outbreaks associated with livestock mortality, associated economic losses, and human mortalities.[1,7,29,30,31,32,33,34] The virus is maintained during interepidemic periods by transovarial transmission in Aedes mosquitoes, and the resurgence of outbreaks is facilitated by periodic rainfall and flooding due to the intertropical convergence of air currents from southern and northern hemispheres which leads to a seasonal emergence of infected Aedes mosquitoes.[27,35].

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Conclusion