Rift Valley Fever in South Sudan, Uganda and Gambia


On 28 December 2017, the Ministry of Health of South Sudan reported a suspect viral hemorrhagic fever cluster to the WHO. The initial cluster involved three deaths in Thonabutkok village, Yali Payam, Yirol East county with 7 December 2017 as the earliest date of onset. The putative index case was a 30-year-old female from Thonabutkok village in Yirol East county. Her illness started on 7 December 2017 with fever, headache, neck pain and sudden nose, gum, and injection site bleeding. She reported to a health facility the same day where she was admitted in maternity ward since she was pregnant. After 8 days of treatment with no improvement, she moved to a private clinic for 4 days where she was treated for malaria and typhoid fever. On 19 December 2017, since the illness worsened, she requested to return home and she died at home the same day.

On 14 January 2018, the Ministry of Health of South Sudan notified to the WHO the suspicion of a new human case of Rift Valley Fever (RFV). It involved a young 14-year-old girl from Arwa Village in Yrol Westcounty with no apparent linkages with the cases already reported in December in the Yirol East county.

Possible cases suggesting a zoonotic hemorrhagic illness, as abortions in goats and sheep, deaths/disease in goats and cows, wild bird die-offs, have been reported in association with this cluster of human infections.


Up to 28 January 2018 new suspect RVF cases have been reported in East Yirol county, but since that date no new alerts in all the areas under surveillance were notified. However, reports of illness and death in livestock are still rampant in the outbreak area where, on 31 January 2018, the disease was observed in Acigoor village close to the Thonabutkok village, in 4 goats, one of which aborted and two had nose bleeding.

Up to the 2 February 2018, a total of 26 suspect RVF human cases have been reported in Eastern Lakes State. Out of the 26 suspect human cases, three human cases have been confirmed, three died and were classified as probable cases with epidemiological linkage to the three confirmed cases, 4 were classified as non-cases following negative laboratory results for RVF, and 16 are still classified suspect cases due to pending or partial laboratory sample testing.


During the second week of January 2018, 7 human samples were collected and sent to Uganda Virus Research Institute (UVRI) for testing: 6 samples were from close contacts (asymptomatic) and the 7th sample was obtained from the new suspect case in Yirol West county. The first batch of seven human samples initially tested negative on 10 January (by PCR) for Ebola, Marburg, CCHF, RVF and Sosuga viruses. Follow up serological testing showed one sample had high RVF IgM and IgG and another two samples had high RVF IgG titres. A second batch of 11 human samples were taken and shipped to UVRI. Serological testing is pending. Moreover, a total of 7 samples from animals (2 sheep, 2 goat, and 3 cattle) were shipped to UVRI for testing. Test results showed that one cow was positive for RVF infection (RVF IgG).


The overall coordination of investigation and response activities is currently coordinated by a multi-sectoral taskforce that is meeting weekly at the national level and sub-national (Yirol East) level.


The outbreak summary can be view at the following address:



In August 2017, Uganda’s Ministry of Health reported the presence of the disease in three countries districts (of Kiboga, Buikwe and Mityana), with 5 confirmed RVF cases.

A joint National Rapid Response team has been dispatched to the affected districts to handle the situation. Rift Valley fever virus is endemic in Uganda, and human cases occur sporadically in the country. The above report and the previous one in November 2017 make no mention of cases of RVF in domestic animals in the area where the human cases occurred. Farmed animals are the main reservoirs and amplifiers of RVF virus. RVF outbreaks very often involve significant numbers of ill and dead small ruminant animals and abortions. It is odd that no small ruminant animal cases are mentioned (unless the animals had been vaccinated previously and are immune) in conjunction with clusters of human infection.

In addition, on 3 January 2018, the Ministry of Health of Senegal notified the WHO of one case of RVF reported from a hospital in Dakar. On 29 December 2017, the Institute Pasteur of Dakar analyzed the blood sample of a 52-year-old man, resident in the Gambia, and the result was positive for RVF on IgM testing. Previous PCR testing were negative for RVF and other arboviruses.

A multidisciplinary team from the Centre of Health Emergency Operations of the Ministry of Health of Senegal carried out a case investigation. Enhanced RVF surveillance in the animal population and community RVF sensitization have been implemented in the country. Outbreaks of RVF are uncommon in Gambia. The last documented human case of RVF in the Gambia was reported in 2002. There is currently no indication of risk of a major RVF outbreak in the Gambia, Senegal, or Guinea-Bissau.

Rift Valley fever is a major zoonotic disease caused by a virus of the genus Phlebovirus of the family Bunyaviridae. The virus affects various animal species (buffaloes, camels, cattle, goats, and sheep) and can pass to humans either by direct contact through blood and/or body fluids during slaughter and/or abortion, or indirectly through mosquitoes biting.

Heavy rainfall, causing flooding and mass emergence of RVF vectors as Aedes and Culex spp. mosquitoes, is closely associated with RVF outbreaks. Uncontrolled movement of livestock can increase the risk of spread of the disease to new areas.

The virus can persist for a long time in some areas, maintained in Aedes vector mosquitoes that deposit eggs in seasonally flooded areas, where those eggs are transovarially infected with the virus. Adult female mosquitoes coming from infected eggs can transmit the virus during their first blood meals. Eradicating the virus from these areas is not possible with current technology. Rift Valley fever can cause trade restrictions and important economic losses due to high mortality and abortion rates among infected livestock. Integrated control measures that address both human and animal health are therefore necessary (e.g. preventive animal vaccination, vector control, control of animal movements, educational campaigns for populations at risk).


Daniela Morelli

National Reference Centre for Risk Analysis
Armando Giovannini

Paolo Calistri

Statistics and GIS
Annamaria Conte


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