WHO | Oropouche virus disease

On September 30, 2020, the Regional Health Agency of French Guiana (ARS) reported the first detection of the Oropouche virus (OROV) in French Guiana. On September 22, 2020, the Pasteur Institute in Cayenne (a member of the French National Reference Laboratory for Arboviruses) informed the France IHR National Contact Point of seven laboratory-confirmed cases of Oropouche virus infection in the village of Saül. These cases were identified after clinical trials of an unusually large number of dengue-like diseases in the village. Between 11 August and 25 September, 37 clinically compatible cases of Oropouche virus disease were identified in Saül. Serology results for dengue, chikungunya, and zika were negative, and seven of the nine cases showed positive OROV by reverse transcriptase polymerase chain reaction (RT-PCR).

Among 37 clinically compatible cases, most cases are male (60%) and the mean age is 36 years (range 3-82 years). The most common age range is 15 to 54 years (19 cases), followed by 0 to 14 years (10 cases). The peak of cases was recorded in mid-September, however, an investigation into the outbreak of the epidemic is still ongoing.

The village of Saül is remote and surrounded by the Amazon rainforest. The village can only be reached by Saül Airport and is approximately a 45-minute flight from Cayenne.

It is a popular hiking destination, and the official population of Saül is 150 people. However, due to a drastic reduction in the frequency of flights to and from Saul during the COVID-19 pandemic, it is estimated that the population living in Saul during August-September is between 50 and 80 people. Therefore, given the 37 clinically compatible cases, the OROV attack rate in this village could be up to 70%. So far, no COVID-19 cases have been reported in Saul.

Public health response

Public health measures planned or ongoing include the following:

• An entomological research mission planned for the epidemiological week ending October 3, 2020;
• Request for entomological expertise from the Pasteur Institute of French Guiana;
• Preventive messages aimed at locals, tourists and other visitors passing through Saül;
• Convening an expert committee to discuss the implementation of a strategy for entomological and virological surveillance of arboviruses and a study of vector competences for areas not yet affected.

WHO risk assessment

This is the first detection of the Oropouche virus in French Guiana. Therefore, the population is very sensitive. To date, there is no evidence of direct human-to-human transmission of the Oropouche virus. Cases of Oropouche virus infection have been reported in other countries in the Americas region, so the relevant vector, Culicoides paraensis flies are present in the region as well Culex quinquefasciatus which can also be a vector. However, the extent to which they are present in French Guiana needs to be further determined. Given the geographical distribution of other relevant vectors in the Americas region, cases can be identified in other countries. The WHO Regional Office for America and the Pan American Health Organization continue to monitor the epidemiological situation based on the latest available data.

With the current COVID-19 pandemic, there is a risk of disrupting access to health care due to the burden on the health system and health workers associated with COVID-19 and reduced demand due to demands for physical distancing or community reluctance.

Another aspect to consider given the current COVID-19 pandemic is the ability of local laboratories and national reference laboratories to process samples for arboviruses due to excessive demand in COVID-19 sample processing and the absence of commercial diagnostic kits. As of October 12, French Guiana has reported 10,144 COVID-19 cases and 69 deaths.

WHO advice

Given its clinical presentation, Oropouche fever should be included in the clinical differential diagnosis for other common vector-borne diseases in the American region (e.g., malaria, dengue, chikungunya, zika, yellow fever). The WHO recommends vaccination against yellow fever at least 10 days before the trip for all international travelers aged nine months going to French Guiana. French Guiana requires a yellow fever vaccination certificate for travelers older than one (1) year.

The proximity of human-resident fly vector breeding is an important risk factor for OROV infection. Prevention strategies are based on measures to control or eradicate pinnipeds and personal protection measures. Vector control measures rely on reducing fly populations by eradicating farms, including good agricultural practices. This can be achieved by reducing the number of natural and artificial water-filled habitats that support fly larvae, reducing adult fly populations around at-risk communities. Personal protection measures rely on the prevention of fly bites by means of mechanical barriers (mosquito nets), insect repellents, bumper-treated clothing and mosquito repellents. Chemical insecticides such as deltamethrin and N, N-diethyl-meta-toluamide (DEET) have been shown to be effective in controlling Culicoides and Culex species.

Oropouche fever is caused by the Oropouche virus (OROV), a single-stranded RNA virus that is part of Peribunyaviridae a family, found to be circulating in Central and South America and the Caribbean. Viral circulation is suspected to include both an epidemic and a sylvatic cycle. In the sylvatic cycle, primates, sloths, and perhaps birds host vertebrates, although the final vector of arthropods has not been identified. In the epidemic cycle, humans are the reinforcing host and OROV is transmitted primarily by stabbing Culicoides paraensis a fly. Direct human-to-human transmission of the virus has not been documented. Oropouche fever causes dengue-like symptoms, with an incubation period of 4-8 days (range: 3-12 days). Symptoms include sudden onset of fever, headache, myalgia, rash, joint pain, and vomiting. The disease usually lasts 3-6 days. Brief recurrence of symptoms can occur in up to 60% of cases. Aseptic meningitis is an uncommon complication. In the United States, OROV attacks have been reported in rural and urban communities in Brazil, Ecuador, Panama, Peru, and Trinidad and Tobago, and now in French Guiana.

References

• Romero-Alvarez D, Escobar LE. Oropouche fever, a new disease from America. Microbes are contagious. 2018; 20 (3): 135-146.
• Sakkas H, Bozidis P, Franks A, Papadopoulou C. Oropouche fever: a review. Viruses. 2018; 10 (4): 175. Published April 4, 2018. Doi: 10.3390 / v10040175. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5923469/
• Travassos da Rosa JF, de Souza WM, Pinheiro FP, et al. Oropouche virus: Clinical, epidemiological and molecular aspects of a neglected orthobunyavirus. Am J Trop Med Hyg. 2017; 96 (5): 1019–30.