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Evidence of Ongoing Transmission of Zika Virus in Mérida, Mexico
James T Earnest1, Karina Jacqueline Ciau-Carillo2, Oscar D Kirstein1
1Department of Environmental Sciences, Emory University, Atlanta, Georgia.
Abstract:
Since the Zika virus (ZIKV) pandemic in 2015-2017, there has been a near absence of reported cases in the Americas outside of Brazil. However, the conditions for Aedes-borne transmission persist in Latin America, and the threat of ZIKV transmission is increasing as population immunity wanes. Mexico has reported only 70 cases of laboratory-confirmed ZIKV infection since 2020, with no cases recorded in the Yucatán peninsula. Here, we provide evidence of active ZIKV transmission, despite the absence of official case reports, in the city of Mérida, Mexico, the capital of the state of Yucatán. Capitalizing on an existing cohort, we detected cases in participants with symptoms consistent with flavivirus infection from 2021 to 2022. Serum samples from suspected cases were tested for ZIKV RNA by polymerase chain reaction or ZIKV-reactive IgM by ELISA. To provide more specific evidence of exposure, focus reduction neutralization tests were performed on ELISA-positive samples. Overall, we observed 25 suspected ZIKV infections for an estimated incidence of 2.8 symptomatic cases per 1,000 persons per year. Our findings emphasize the continuing threat of ZIKV transmission in the setting of decreased surveillance and reporting.
Insights
Active Zika virus (ZIKV) transmission is occurring in Mérida, Mexico, despite low reported cases. This study detected ZIKV infections in a local cohort, highlighting ongoing risks from this mosquito-borne flavivirus.
Area of Science:
- Virology
- Epidemiology
- Public Health
Background:
- Zika virus (ZIKV) transmission has been minimal in the Americas since 2015-2017, with few cases reported outside Brazil.
- Persistent Aedes-borne transmission conditions and waning population immunity in Latin America pose an increasing ZIKV threat.
- Mexico reported limited ZIKV cases since 2020, with none in the Yucatán peninsula, suggesting underreporting.
Purpose of the Study:
- To investigate active ZIKV transmission in Mérida, Yucatán, Mexico, despite the lack of official case reports.
- To detect and confirm ZIKV infections within a symptomatic cohort in the region.
- To estimate the incidence of symptomatic ZIKV cases in an area with presumed low surveillance.
Main Methods:
- Utilized an existing cohort in Mérida, Mexico, to identify participants with flavivirus-like symptoms from 2021-2022.
- Tested serum samples for ZIKV RNA via polymerase chain reaction (PCR) and ZIKV-reactive IgM antibodies using ELISA.
- Performed focus reduction neutralization tests (FRNT) on ELISA-positive samples for specific ZIKV exposure confirmation.
Main Results:
- Identified 25 suspected ZIKV infections among symptomatic individuals in the cohort.
- Estimated an incidence of 2.8 symptomatic ZIKV cases per 1,000 persons per year.
- Provided evidence of active ZIKV transmission in Mérida, contradicting official surveillance data.
Conclusions:
- Zika virus continues to pose a threat in Latin America, even in areas with low reported cases.
- Decreased surveillance and reporting may obscure the true burden of ZIKV infections.
- Active ZIKV transmission necessitates continued vigilance and robust public health monitoring in regions like Yucatán.
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