Rift Valley Fever outbreak in Kabale district, March-April 2016: The first reported human outbreak in Uganda
Authors: Henry Kyobe Bosa1,2 , Steven Kabwama Ndugwa1, Robert Majwala1, Alex R. Ario1, Daniel Kadobera1, Robert Downing2, Noah Kiwanuka3, Hannah Kibuuka4 , Julius Lutwama2: 1Public Health Fellowship Program, 2Uganda Virus Research Institute, 3Makerere University School Of Public Health, 4Makerere University Walter Reed Project
In what appears to be a new emerging viral infection in Uganda, two non-fatal human confirmed Rift Valley Fever Virus (RVFV) infections were reported in Kabale district, Southwestern Ugandan in March-April 2016. These are the first reported human cases of RVF in Uganda following a suspected spillover of a missed RVF outbreak among livestock in the region. There was no clear epidemiological link between the two cases as noticed in the apparent modes of transmission. This outbreak highlights the potential of zoonotic diseases crossing the livestock-human interface to cause diseases in humans. We recommend acute febrile illness sentinel surveillance in abattoirs as a proxy for RVF transmission in this district for early detection of RVF in humans.
Introduction: On 7th March 2016, the Uganda Ministry of Health received a report of a suspected case of viral hemorrhagic fever (VHF) in Kabale Regional Referral Hospital, Kabale district South West Uganda. Two cases were subsequently confirmed as Rift Valley Fever Virus (RVFV) by Reverse Transcriptase Chain Reaction (RT-PCR) at Uganda Virus Research Institute, Entebbe. A subsequent RVF sero-survey in 1051 domestic animals in Kabale and the neighboring districts showed strong evidence of RVF IgG seroprevalence in cattle (27%), goats (6.5%) and sheep (5.7%). Prior to the current outbreak, no reported RVF human cases had been reported in Uganda. Here we report the findings of an epidemiological investigation on the extent of the
outbreak in the human population and identification of sources of infection and the risk factors in order to inform interventions for controlling the outbreak.
Methods: We defined a suspect RVF case as acute onset of fever (>37.5oC) in Kabale district resident? and a negative malaria test and at least two of the following symptoms: headache, muscle or joint pain and plus any gastrointestinal symptom. A confirmed case was a suspected case that is laboratory confirmed by detection of RVF nucleic acid by RT-PCR or demonstration of serum IgM or IgG antibodies by ELISA. We actively identified cases by visiting affected communities, abattoirs and reviewing of clinical records in.
Results: Between 10th March to 23rd April 2016, we identified 24 suspect cases including two confirmed cases.
Confirmed cases: The dates of onset of symptoms for a 56-year old schoolboy and the 42-year old butcher were February 13th and 18th 2016 respectively. Infection of the index case appears to be vector-borne transmission as opposed to meat handling in the second case. There was no clear epidemiological link between the two cases.
A records review in 10 health centers in the vicinity of the area where the primary case originated also did not reveal any noticeable increase in number of acute febrile illnesses, hemorrhagic manifestations, central nervous system or ocular lesions. Similarly, there were no reported similar symptoms among other abattoir workers in the area. Three weeks prior to onset of symptoms of the primary case, 3 cow abortions within the same week were reported in a nearby farm. That, in addition to multiple successive goat first- trimester abortions from October 2015 in the nearby farms.
Conclusion : We report the first two independent cases of hu- man RVF infections in Uganda in a small-scale outbreak. These observed human cases appear to have been a random spillover of a RVF outbreak among the livestock population into the human population that manifested largely as first trimester abortions in goats stocks in the area. The progression and the extent of this outbreak appear to have been self-limiting
The high RVF sero-prevalence among most of the susceptible domestic animals in the area shows the likelihood of similar spillovers and sustained vectorial transmission in the human population to be high. Human RVF infections appear to be an
emerging disease in Uganda with paucity of information on transmission and spectrum of clinical manifestations ranging from: asymptomatic presentation to hemorrhagic manifestations and neuro-ocular lesions and lasting complications to potential death. This is coupled with infrequent nature of the outbreaks requires deeper understanding.
Zoonotic disease surveillance at the human-livestock interface is key for early identification of RVF from livestock. Acute febrile illness sentinel surveillance amongst abattoir workers in the area is recommended for detection of RVF transmission in humans in this setting
