WHO | Mayaro virus disease

On October 13, 2020, the French health authorities officially reported 13 laboratory-confirmed cases of Mayaro fever in French Guiana, France.

In September 2020, the Pasteur de la Guyane Institute (IPG) (member of the French National Reference Laboratory for Arboviruses) identified two cases of Mayaro virus infection (MAYV) confirmed by a polymerase reverse transcriptase chain reaction (RT-PCR) and one probable case found positive for Mayaro. antibodies. The cases showed dengue-like symptoms and joint pain, and RT-PCR tested negative for dengue.

This unexpected diagnosis led to a further retrospective search of additional cases of Mayar fever among patients with dengue-like symptoms who tested negative for dengue. The polymerase reverse transcriptase chain reaction was performed on samples collected between July 15 and September 15 in laboratories located mainly in the Cayenne area. These blood samples were collected from patients with dengue-like symptoms, who tested negative for dengue within five days of the onset of symptoms. In total (including first detections and retrospective screening) IPG RT-PCR identified 11 cases of Mayar fever from 79 samples tested. These cases were recorded on September 21, 2020.

The Pasteur de la Guyane Institute in Cayenne reported two additional confirmed cases of Mayaro fever on October 2 and October 8, 2020, resulting in a total of 13 confirmed cases among 97 tested samples between July 15 and early October. The onset of symptoms for 13 confirmed cases ranged from 18 July to 29 September 2020. Of the 13 confirmed cases, 11 lived in the urban coastal area, including nine from the Cayenne area (Cayenne: 1, Rémire: 4, Matoury: 4) , one from Kourou and one from Montsinery-Tonnegrande. Only two cases lived in a rural / sylvatic area, both in Roura (including one in the village of Cacao, located further inland). The age of these cases ranged between 11 and 68 years (median = 40 years), and the male to female ratio was 1.2: 1.

The Mayaro virus (MAYV) has been known to circulate in French Guiana since 1998, but the number of detected MAYV RT-PCR via IPG between 2017 and 2019 ranged from 1 to 3 confirmed cases per year, detected from 150 up to over 600 samples tested each year. According to the MAYV test criteria, blood samples were collected within 5 days of the onset of dengue-like symptoms and were found to be negative for dengue virus.

Therefore, the detection of 13 confirmed cases in less than 3 months is unusual. Furthermore, MAYV is mainly transmitted through the sylvatic cycle, and transmission in urban areas is sparsely described. It is therefore atypical that 11 of the 13 (85%) identified cases of Mayar fever resided in an urban area.

MAYV vector (Hemagogue mosquito species) is also a vector of the yellow fever cycle of the yellow fever virus and is present in wild or rural habitats in the Americas and the Caribbean. MAYV was isolated from other mosquito genera, including Culex,,Mansonia ,, Aedes,, Psorophora , i Sabethes .

Epidemiological research is ongoing, in particular to document the travel history of the cases and to determine whether the infections are infected in forest areas or can be suspected of transmission through the urban cycle.

Public health response

Public health measures planned or ongoing include the following:

• Entomological research and entomological expertise from IPG;
• Convening an expert committee to discuss the implementation of the strategy for entomological and virological surveillance of arboviruses and the vector competence of areas not yet affected;
• Vector prevention: Public health measures to keep human exposure to mosquitoes to a minimum to prevent the spread of viruses and thus diseases;
• Information to the community on transmission risk and ways to reduce the risk of vector exposure, either in rural areas or at home in suburban areas or those bordering rural areas.

WHO risk assessment

MAYV was first isolated in Trinidad and Tobago in 1954. However, a retrospective study showed evidence of MAYV infection in sera collected during canal construction in Panama and Colombia between 1904 and 1914. Since then, cases have been reported in Central America and South America , especially in the regions around the Amazon Basin, with some cases reported by travelers in the academic literature. These cases affected individuals from Canada, France, Germany, the Netherlands, Switzerland, and unidentified parts of North America.

Although some studies suggest MAYV transmission in urban areas, most of the epidemics described in the last decade in America have been recorded among residents of rural communities in the Amazon region of Brazil, Bolivia, Peru, and Venezuela. Most human cases have occurred among people working or residing in tropical rainforests. The reservoir for MAYV is unknown, but some studies have reported virus isolation or high levels of antibodies in host vertebrates, such as non-human primates.

Changes in the natural environment, deforestation, urbanization, and mining result in increased interactions between host and vector populations and show the potential of MAYV to re-emerge in new areas and re-emerge in existing areas.

Mayaro fever is a zoonosis transmitted by mosquitoes and caused by the Mayaro virus (MAYV), an arbovirus of the genus Alphavirus, family Togavirus. MAYV transmission is mainly maintained through a sylvatic cycle involving non – human primates and Hemagogue mosquitoes. Cases in humans have been linked to recent exposure to humid forest environments inhabited by these vectors.

In the initial stage, Mayaro fever presents as a nonspecific clinical picture like other arboviral diseases (dengue, chikungunya, Zika). The incubation period ranges from 1 to 12 days. The disease is only limited, lasting 3 to 5 days, with permanent arthralgia that may remain for weeks or months; however, as with other alphavirus infections, MAYV can create serious complications, such as intermittent fever, neurological complications, myocarditis, and even death.

Due to the generic nature of arbovirus symptoms, misdiagnosis can occur. MAYV cases may not be detected due to a lack of awareness in the medical community.

Diagnostic testing for MAYV is not widely available, and little is known about MAYV outside of endemic areas. Imported cases can be clinically misdiagnosed as dengue, Zika, Chikungunya. In endemic regions, coinfection with other arboviral diseases may also misdiagnose MAYV.

The risk of international expansion appears to be small at this stage, but cannot be ruled out if an urban transmission cycle is shown to be in place.

In the urban coastal area around Cayenne, there is a risk of additional cases if the transfer occurred in a suburban forest. The most likely sites of infection are still under investigation.

The risk of spreading nationally cannot be ruled out as the virus circulates over a larger area, outside Cayenne and the surrounding area. Investigations are currently underway to identify the affected areas.

With the global circulation of the current COVID-19 pandemic, there is a risk of disruption of 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 in light of the current COVID-19 pandemic is the ability of local laboratories and national reference laboratories to process samples due to excessive demand in COVID-19 sample processing, with a continuous dengue epidemic and localized outbreak of Oropouche virus (see DON released Oct. 13). Furthermore, due to the unavailability of commercial diagnostic kits, Mayaro diagnostic capacity rests solely on the national reference laboratory. As of October 18, 2020, French Guiana has reported 10,268 cases of COVID-19 and 69 deaths.

WHO advice

Given the prevalence of the main vector involved in transmission in rural areas of the Region and in light of the recent detection of cases of Mayar fever in new geographical areas, the WHO encourages Member States to take action to detect cases and inform healthcare professionals about it, so consider Mayar fever part of the differential diagnosis. arboviruses such as chikungunya, dengue, Oropouche, yellow fever and Zika. Considering a similar clinical presentation for Mayaro fever with that of other arboviruses, such as dengue, chikungunya, Oropouche, yellow fever, and zika, Mayaro fever surveillance could be integrated with existing arbovirus surveillance.

Surveillance, MAYV diagnosis, and vector control are the three main pillars in terms of disease prevention. Mayar prevention depends on controlling mosquito bites and, consequently, human-vector contact. In case of Hemagogue and Aedes vector, whose peak activity coincides at the beginning or end of the day, personal protection measures should be encouraged and promoted. Control of mosquito breeding sites by reducing resources can be enhanced by community engagement and social mobilization.

The WHO does not recommend any travel and / or trade restrictions for French Guiana based on available data on this event.

References

• PAHO / WHO Epidemiological Alert. Mayaro fever – an outbreak situation in America. May 1, 2020. Available here
• Mayaro virus in Latin America and the Caribbean, special report, Pan American Journal of Public Health, 2020. Available here
• Mayaro virus fever in French Guiana: isolation, identification and seroprevalence. Available here
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