Co-Circulation of All Four Dengue Viruses and Zika Virus in Guerrero, Mexico, 2019.

A clinical and entomological investigation was performed to identify flavivirus infections in humans and mosquitoes in impoverished areas of Guerrero, a coastal state in southwestern Mexico. A total of 639 patients with acute febrile illness and 830 resting female mosquitoes in low-income communities of Guerrero in 2019 were tested for evidence of flavivirus infection. Sera were collected from all patients and screened at a dilution of 1:20 by plaque reduction neutralization test (PRNT) using dengue virus (DENV)2. A total of 431 (67.4%) patients were seropositive. Sera from a subset of seropositive patients (n = 263) were tested for flavivirus NS1 by enzyme-linked immunosorbent assay. Forty-eight (18.3%) sera contained viral antigen. All NS1-positive sera were titrated and further tested by PRNT using DENV-1 to -4, St. Louis encephalitis virus, West Nile virus, and Zika virus (ZIKV). Seven patients were seropositive for DENV-1, five patients were seropositive for DENV-2, one patient was seropositive for DENV-3, and two patients each were seropositive for DENV-4 and ZIKV. The remainder had secondary flavivirus infections or antibodies to an undetermined flavivirus. Comparative PRNTs were also performed on 60 randomly selected NS1-negative sera, identifying patients seropositive for DENV-2, DENV-3, and ZIKV. The entomological investigation yielded 736 Aedes aegypti and 94 Culex quinquefasciatus that were sorted into 183 pools and 20 pools, respectively. Mosquitoes were assayed for flavivirus RNA by RT-PCR and Sanger sequencing. DENV-2 RNA was detected in three pools of A. aegypti. In summary, we provide evidence for the concurrent circulation of all four DENVs and ZIKV in Guerrero, Mexico. The public health authorities reported no cases of DENV-3, DENV-4, and ZIKV in Guerrero in 2019 and thus, we provide evidence of under-reporting in the region.