Surveillance for Zika in Mexico: naturally infected mosquitoes in urban and semi-urban areas

Abstract

Zika cases have been reported in 29 out of the 32 states of Mexico. Information regarding which mosquito species might be driving Zika virus transmission/maintenance in nature must be regularly updated. From January 2017 to November 2018, mosquitoes were collected indoors and outdoors using the CDC backpack aspirator in urban and semi-urban areas with evidence of mosquito-borne disease transmission. 3873 mosquito pools were tested for Zika infection using the CDC Trioplex real-time RT-PCR. For each collected specie, maximum likelihood estimator of infection rate (MLE) was estimated. Results showed 492 mosquito pools positive for Zika virus RNA. The majority of the positive pools were Aedes (Stegomyia) aegypti (Linnaeus) (54.6%, MLE = 19) (males and females) and Culex (Culex) quinquefasciatus (Say) (19.5%, MLE = 16.8). For the first time, ZIKV infection was detected in Ae. (Georgecraigius) epactius (Dyar and Knab) (MLE = 17.1), Cx. (Melanoconion) erraticus (Dyar and Knab) (MLE = non-estimable), Culiseta (Culiseta) inornata (Williston) (MLE = non estimable), and Cs (Cs.) particeps (Adams) (MLE = 369.5). Other detected species were: Ae. (Stg.) albopictus (Skuse) (MLE = 90.5), Cx. (Cx.) coronator s.l. (Dyar and Knab) (MLE = 102.8) and Cx. (Cx.) tarsalis (Coquillett) (MLE = 117.2). However, our results do not allow for the incrimination of these species as vectors of ZIKV. Routine surveillance should start to consider other mosquito species across the taxonomic spectrum of the Culicidae.

Keywords: Arbovirus; Culicidae; mosquito-borne diseases; vector control.

Figure 1.

Distribution map summarizing where human and mosquito ZIKV infections have been detected in Mexico. Stars indicate the 16 surveyed states in this study. Infections in both humans and mosquitoes have been detected in 14 states (Baja California Norte (1), Baja California Sur (2), Tamaulipas (7), San Luis Potosí (13), Jalisco (14), Estado de México (19), Guerrero (24), Puebla (25), Veracruz (26), Oaxaca (27), Chiapas (28), Tabasco (29), Campeche (30) and Yucatán (31)), shown in dark red. Human cases alone have been detected in 13 states (Sonora (3), Coahuila (5), Nuevo León (6), Durango (9), Zacatecas (10), Nayarit (11), Aguascalientes (12), Michoacán (18), Guanajuato (16), Querétaro (17), Hidalgo (20), Morelos (22) and Quintana Roo (32)), shown in orange. Two states showed infected mosquitoes but no infected humans (Chihuahua (4) and Mexico City (21)), shown in yellow. Tlaxcala (23, in green) was the only state without infected humans or mosquitoes.