Mayaro Virus Infections in European Field Researchers in the Remote Amazon Rainforest, French Guiana, 2024

Mayaro virus (MAYV), an alphavirus found in Latin America related to the chikungunya virus, is transmitted primarily by sylvatic Hemagogus mosquitoes. Sporadic cases have been reported in French Guiana, with notable outbreaks occurring in 2020. In this study, a cluster of MAYV infections observed among European researchers in French Guiana in early 2024 is described. The study included individuals who stayed at the Nouragues Nature Reserve between January 1 and February 28, 2024. The case definitions were based on clinical symptoms and virological tests (polymerase chain reaction or IgM serology). Complementary investigations in asymptomatic exposed individuals were also conducted. Six European individuals developed acute fever, polyarthralgia, headache, or rash. Polymerase chain reaction testing was used to confirm two cases, and serology was used to identify two probable cases. Symptoms resolved within weeks for most, but two cases had chronic arthralgia that lasted more than 3 weeks. In addition to the six symptomatic individuals, 13 people stayed for more than one night at the scientific station, and all were asymptomatic. Five of them underwent anti-MAYV IgM serological testing between 4 and 8 weeks after their stay, and all results were negative. Entomological investigations had revealed Hemagogus janthinomys, a MAYV vector, in the area just a few months before. The cluster highlights the potential for sylvatic MAYV outbreaks among visitors to the Amazon rainforest. These findings highlight the need for greater awareness of MAYV symptoms and the potential for underdiagnosis.