Peru Emerges as a Genetic Hub for Mayaro virus
Mayaro virus is no longer a quiet sylvatic pathogen moving only at the edge of surveillance. In Peru, sequencing and phylodynamic reconstruction now place the country inside a broader transmission network for this neglected alphavirus, with multiple lineages circulating, diverging, and dispersing across South America at different speeds. The clinical significance is straightforward: when an arbovirus produces fever, rash, and prolonged arthralgia yet often resembles other febrile illnesses, missed detection becomes routine unless diagnostics are built for low viral loads and brief viremia.
The investigation examined 1,000 whole blood specimens from patients with acute febrile illness seen at six health facilities between September 2023 and October 2024. Unbiased metagenomic sequencing and target-enriched sequencing found Mayaro virus in 5 people, or 0.5% of the cohort, with one complete genome and four partial genomes. Those sequences showed 99% nucleotide identity to a Peruvian strain from 2018 and fell within genotype D. Two Peru-derived sequences grouped with a Colombian sequence at the root of one subclade, while another patient sequence clustered in a separate branch with a similar pattern. The topology points to either endemic evolution within Peru or repeated introductions from neighboring countries, especially Colombia.
One sentence captures the diagnostic challenge: low-level Mayaro viremia can fall below the reach of sequencing workflows designed for broader pathogen discovery.
A Dual-Target PCR Pulled a Missed Case Out of the Background Noise
To recover cases missed by sequencing, investigators built a new quantitative reverse transcription PCR assay with two targets in conserved regions of the nonstructural protein 1 gene, both read in the Cy5 channel. The assay performed well across a 10-fold dilution series, with linearity from 107 to 101 copies per reaction, an R2 of 0.99, and 90% efficiency. Analytical sensitivity reached approximately 4 copies per reaction. An internal control monitored extraction and amplification, which is essential for a field where specimen quality and low RNA abundance can easily distort results.
Re-screening the same 1,000 specimens on the Abbott m2000 platform confirmed the 5 positives already found by sequencing and identified 1 additional PCR-positive case that NGS had missed. That extra detection was associated with a cycle threshold above 28, consistent with the limits of target-enrichment sequencing at very low copy number. In practical terms, the assay did not merely duplicate the sequencing workflow; it extended detection into the gray zone where early or waning infection would otherwise vanish from the dataset.
The difference between a surveillance signal and a false negative often comes down to how much viral RNA remains in blood when the patient arrives.
Phylodynamics Trace Repeated Seeding Events Across South America
The broader evolutionary analysis pushed the story far beyond a single Peruvian outbreak. Using a Gaussian Markov random field prior, the temporal reconstruction placed the origin of Mayaro virus around 1886, with the major genotype split occurring in 1897 for genotype L and 1912 for genotype D. The estimated evolutionary rate was 2.6 × 10−4 substitutions per site per year. The cluster that included Trinidad and Tobago emerged around 1954, aligning with the first reported human case and supporting the calibration of the time-scaled tree.
Peru stood out repeatedly. Multiple Peruvian clusters appeared at different times, mostly 40 to 49 years ago, including one cluster that emerged around 2010 and another whose ancestor circulated around 2007. Bayesian Skyride analysis showed rising genetic diversity from about 1925 until 2005, followed by a sharp decline as several genotype L strains disappeared. Diversity then stabilized, likely after newer genotype D strains took hold. This pattern fits a landscape of replacement rather than simple persistence, with one lineage set fading while another expands into its place.
The geographic reconstruction was even more striking. The root of Mayaro virus emergence lay in Brazil, followed by two main dispersal routes. One stayed mostly in Brazil before reaching Haiti. The other moved from Brazil to Peru and then expanded further through Brazil, Trinidad and Tobago, Venezuela, Haiti, and Bolivia, with multiple exportation events into Central America. Those findings place Brazil and Peru at the center of lineage movement across the region.
Lineage 3 Spread Faster Than Lineage 2 and Reached More Countries
Phylowave analysis identified three distinct lineages in the dataset. Two arose in the 1930s and 1940s, while the most recent emerged in the late 1950s. Lineage 1 appears to have been pushed toward extinction. Lineages 2 and 3 alternated in frequency and showed comparable genetic fitness, but they moved differently across the continent. Lineage 1 began in Brazil, spread to Trinidad and Tobago, and was later detected in a bird sample from Louisiana. Lineage 2 emerged in Brazil and diversified mainly in Brazil, Haiti, and Peru. Lineage 3 originated in Peru and then spread to Bolivia, Venezuela, Brazil, and Colombia, consistently tracing back to Peru as the source.
Continuous phylogeographic analysis gave the dispersal story a measurable shape. Lineage 2 first spread in the late 1940s through the early 1970s, mostly within Bolivia and Brazil, then accelerated in the late 1990s and early 2000s toward Venezuela, French Guiana, and Haiti. Lineage 3 appears to have entered Peru around the late 1970s and expanded outward from the early 1990s onward. Its median mean branch dispersal velocity was 40.24, compared with 10.85 for lineage 2, meaning lineage 3 spread about four times faster. Faster movement through susceptible mosquito and human populations could help explain rising regional case reports and makes surveillance in Peru more urgent.
Mayaro virus remains a neglected arbovirus without a licensed vaccine or specific antiviral therapy. In that setting, molecular diagnosis is not a laboratory luxury; it is the only reliable way to separate Mayaro from the many other causes of acute fever in endemic settings. The new dual-target PCR improves that position by capturing low-level infections and variants that sequencing alone can miss. Even so, the study is bounded by the availability of samples and sequence density across the region, which means the true scale of lineage movement is still larger than the current map can show.