Mayaro Virus

Mayaro virus (MAYV; species Alphavirus mayaro) is an enveloped, positive-sense, single-stranded RNA arbovirus belonging to the genus Alphavirus within the family Togaviridae. Placed antigenically within the Semliki Forest antigenic complex alongside chikungunya virus, Ross River virus, O'nyong-nyong virus, and its closest Neotropical sister species, Una virus, Mayaro virus is the etiological agent of Mayaro fever, an acute febrile and arthritogenic zoonosis endemic to the humid tropical forests of South and Central America. In nature, the virus circulates within an enzootic rainforest canopy cycle connecting diurnal tree-hole mosquitoes—most notably Haemagogus janthinomys—with arboreal non-human primates, sloths, and forest rodents.

First isolated in 1954 from the blood of febrile forest workers in southeastern Trinidad, Mayaro virus is distributed throughout the Amazon, Orinoco, and Tocantins-Araguaia river basins, as well as the Guiana Shield and the Chocó-Darién moist forests. Because its clinical presentation of sudden fever, maculopapular rash, and persistent peripheral polyarthralgia closely resembles chikungunya and dengue fever, human infections are frequently misdiagnosed during seasonal arboviral outbreaks across northern and central South America.

The 1954 Trinidad Isolations

Mayaro virus was discovered between August and September 1954 by Charles R. Anderson, Wilbur G. Downs, and colleagues at the Trinidad Regional Virus Laboratory in Port of Spain. While investigating acute febrile illnesses among forestry laborers near Mayaro County in southeastern Trinidad, the team inoculated serum samples from five symptomatic patients intracerebrally into suckling Swiss mice. All five inoculations yielded antigenically identical viral strains, with the prototype (TRVL 4675) designated Mayaro virus.

In April 1955, Otis R. Causey and O. M. Maroja at the Belém Virus Laboratory (Instituto Evandro Chagas) isolated identical strains during an outbreak of febrile illness along the Guamá River east of Belém, Pará, Brazil. Subsequent serosurveys across Brazil, Suriname, Guyana, Colombia, Venezuela, Peru, and Bolivia confirmed widespread enzootic circulation across lowland South American rainforests.

Placement in the Semliki Forest Complex

The International Committee on Taxonomy of Viruses (ICTV) classifies Mayaro virus as Alphavirus mayaro within the genus Alphavirus, family Togaviridae. Although endemic to the Americas, Mayaro virus and its sister taxon Una virus cluster within the Old World-like Semliki Forest antigenic complex rather than the New World encephalitic alphaviruses, reflecting an ancient introduction and radiation of arthritogenic alphaviruses into Neotropical forest ecosystems.

Icosahedral T = 4 Capsid and Envelope Glycoprotein Spikes

The mature Mayaro virion is a spherical, enveloped particle 68 to 70 nanometers in diameter with T = 4 icosahedral symmetry. Cryo-electron microscopy reconstructions reveal an outer shell of 240 copies each of transmembrane glycoproteins E1 (~47 kDa) and E2 (~47 kDa), which form E1–E2 heterodimers assembled into 80 trimeric surface spikes. E2 mediates attachment to host receptors—including the adhesion molecule MXRA8 and heparan sulfate proteoglycans—while E1 houses a hydrophobic class II fusion loop. Following clathrin-mediated endocytosis, endosomal acidification dissociates the E1–E2 heterodimer and drives E1 homotrimerization and membrane fusion, releasing the nucleocapsid core (240 copies of capsid protein C bound to genomic RNA) into the cytosol.

Positive-Sense RNA Genome and Polyprotein Processing

The Mayaro virus genome is a single-stranded, positive-sense RNA molecule 11.4 to 11.5 kilobases in length, flanked by a 5' methylated cap (m⁷GpppA) and a 3' polyadenylated tail. Two open reading frames are separated by a non-coding junction containing an internal 26S subgenomic promoter:

Phylogenetic analyses of E1/E2 envelope sequences and complete genomes divide Mayaro virus into three evolutionary lineages across South America:

• Genotype D (Widely Disseminated): Encompasses the 1954 Trinidad prototype and strains circulating throughout the pan-Amazonian and Orinoco basins, including northern and central Brazil, Peru, Colombia, Venezuela, Bolivia, French Guiana, Suriname, and Guyana.
• Genotype L (Limited): Concentrated in north-central Brazil, especially Pará State and adjacent municipalities of the eastern Amazon and Tocantins basins, diverging from Genotype D by 15 to 19 percent at the nucleotide level.
• Genotype N (New): Identified in 2010 from febrile surveillance cohorts in Loreto and Madre de Dios in the Peruvian Amazon, forming an intermediate clade sister to the D/L split.

The Canopy Cycle: Haemagogus janthinomys and Non-Human Primates

Across the Amazon and Orinoco basins, Mayaro virus is maintained in an arboreal sylvatic cycle analogous to jungle yellow fever. The principal enzootic vector is Haemagogus janthinomys, a diurnal, acrodendrophilic mosquito that oviposits in water-filled tree holes high in the rainforest canopy (15 to 30 meters above ground). During timber harvesting, land clearing, hunting, or road construction, Haemagogus janthinomys descends to ground level to bite humans along disturbed forest margins.

Arboreal non-human primates serve as the primary vertebrate amplifying hosts, developing high-titer viremia sufficient to infect blood-feeding canopy mosquitoes. High seroprevalence and viral isolations occur across howler monkeys (Alouatta seniculus, Alouatta belzebul, Alouatta caraya), marmosets and tamarins (Callithrix and Mico spp.), capuchin monkeys (Sapajus apella), and squirrel monkeys (Saimiri sciureus), with sloths (Choloepus and Bradypus spp.), marsupials, agoutis, and forest birds acting as secondary hosts. Field isolations have also been recorded in Psorophora ferox, Sabethes chloropterus, Coquillettidia venezuelensis, and Aedes serratus, while laboratory competence assays show that urban Aedes aegypti and Aedes albopictus can transmit the virus above threshold oral blood-meal titers of 10⁵ PFU/mL.

In humans, Mayaro virus infection causes Mayaro fever after a 3- to 12-day incubation period, presenting with abrupt fever (39–40 °C), retro-orbital headache, myalgia, maculopapular rash, and symmetric polyarthralgia of the wrists, ankles, and small joints that can persist for several months.

Because Mayaro virus co-circulates with chikungunya, dengue, Zika virus, and Oropouche virus, laboratory diagnosis relies on two stage-specific methods:

1. Molecular Detection (Days 1–5): RT-qPCR targeting the nsP1 or E1/E2 genes provides species-level identification during acute viremia, distinguishing Mayaro virus from Una virus and chikungunya.
2. Serological Differentiation (Day 6 Onward): IgM capture ELISA (MAC-ELISA) detects antibodies after day 5, but cross-reactivity within the Semliki Forest antigenic complex requires a plaque reduction neutralization test (PRNT₈₀ or PRNT₉₀) demonstrating a fourfold or greater neutralizing titer differential against Mayaro virus.

How is Mayaro virus distinguished from Una virus in the laboratory?

Although Una virus is the closest Neotropical relative of Mayaro virus inside the Semliki Forest complex, the two species diverge by ~25 percent across their nucleotide genomes and occupy distinct ecological niches (arboreal Haemagogus–primate transmission for Mayaro versus ground-level Psorophora transmission for Una). Multiplex RT-qPCR primers targeting nsP1 or E2 differentiate the two viruses during acute viremia, while convalescent serology uses parallel PRNT₉₀ neutralization panels.

Why are logging and forest-edge settlements major risk factors for Mayaro virus spillover?

The primary vector, Haemagogus janthinomys, feeds on non-human primates in the upper rainforest strata. When logging or agricultural clearing opens the canopy, tree-hole breeding habitats and microclimatic gradients shift downward, bringing infected female mosquitoes into direct contact with forestry workers and peri-rural residents.

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2. Powers, A. M., Aguilar, P. V., Chandler, L. J., et al. (2006). "Genetic relationships among Mayaro and Una viruses suggest distinct patterns of transmission." The American Journal of Tropical Medicine and Hygiene, 75(3), 461–469. https://doi.org/10.4269/ajtmh.2006.75.461
3. Auguste, A. J., Liria, J., Forrester, N. L., et al. (2015). "Evolutionary and ecological characterization of Mayaro virus strains isolated during an outbreak, Venezuela, 2010." Emerging Infectious Diseases, 21(10), 1742–1750. https://doi.org/10.3201/eid2110.141660
4. Acosta-Ampudia, Y., Monsalve, D. M., Rodríguez, Y., et al. (2018). "Mayaro: an emerging viral threat?" Emerging Microbes & Infections, 7(1), 163. https://doi.org/10.1038/s41426-018-0163-5
5. Diagne, C. T., Bengue, M., Choumet, V., Hamel, R., Pompon, J., & Missé, D. (2020). "Mayaro virus, a neglected arbovirus in South America: from molecular biology to epidemiology and pathogenesis." Viruses, 12(8), 889. https://doi.org/10.3390/v12080889