Chikungunya Virus in Febrile Humans andAedes aegyptiMosquitoes, Yucatan, Mexico

Chikungunya virus (CHIKV) was isolated from 12 febrile humans in Yucatan, Mexico, in 2015.One patient was coinfected with dengue virus type 1.Two additional CHIKV isolates were obtained from Aedes aegypti mosquitoes collected in the homes of patients.Phylogenetic analysis showed that the CHIKV isolates belong to the Asian lineage. C hikungunya virus (CHIKV; family Togaviridae, genusAlphavirus) is transmitted to humans by Aedes spp.mosquitoes (1,2).The virus is the etiologic agent of chikungunya, an acute febrile illness that is often accompanied by debilitating arthralgia.Historically, CHIKV has been restricted to the Eastern Hemisphere, but in 2013, the virus was reported in the Western Hemisphere during a large outbreak in the Caribbean region.CHIKV spread rapidly to South America, Central America, Mexico, and the United States.The Pan American Health Organization estimated that >1.7 million suspected and laboratory-confirmed cases of chikungunya have occurred in the Western Hemisphere (http://www.paho.org/hq/index.php?option=com_topics& view=readall&cid=5927&Itemid=40931&lang=en).CHIKV was isolated in Mexico from a patient from Jalisco in whom symptoms developed in May 2014 shortly after the patient returned from the Caribbean region (3).The first autochthonous case was reported in October 2014 after CHIKV was isolated from a patient in southeastern state of Chiapas (4).CHIKV-infected Aedes aegypti mosquitoes and additional chikungunya cases were identified in Chiapas later in 2014 (5,6).To our knowledge, no reports of CHIKV in any other states in Mexico have been published.In this study, we tested febrile patients in the state of Yucatan and mosquitoes temporally and spatially associated with these patients for CHIKV infection. The StudyWe obtained written informed consent from all patients who participated in the study or their legal guardians.The study population was composed of patients who came to hospitals or clinics in Yucatan during August-October 2015 with chikungunya-like illness.These patients were referred to the hematology laboratory at the Hideyo Noguchi Research Center (Merida, Yucatan, Mexico).A patient was considered to have chikungunya-like illness if he or she had fever and arthralgia.Travel history of each study participant was recorded, and any patient who had traveled outside Yucatan in the past 30 days before disease onset was excluded from the study.Blood was collected from the cephalic vein of each patient, dispensed into a vacutainer tube (BD Diagnostics, Franklin Lakes, NJ, USA), and centrifuged.Serum was collected and stored at -80°C.Resting mosquitoes were collected from the homes of each study participant by using Centers for Disease Control and Prevention (Atlanta, GA, USA) backpack-mounted aspirators.Each house was examined once, and collections were made between 9:00 am and noon.All rooms were inspected, particularly dark areas (i.e., underneath furniture, in closets, and in curtains).Backyards were also searched, particularly shaded areas (i.e., pet homes, tool sheds, and underneath vegetation).Mosquitoes were transported alive to the laboratory and identified on chill tables by using morphologic characteristics (7).Female mosquitoes were sorted into pools of <10 and homogenized in phosphate-buffered saline (pH 7.2) by using a mortar and pestle.Male mosquitoes were discarded.An aliquot of each serum sample and mosquito homogenate was filtered and inoculated onto subconfluent monolayers of Ae. albopictus (C6/36) cells in 25-cm 2 flasks.Cells were incubated for 7 days at 28°C.Second and third blind passages were performed in C6/36 and African green monkey kidney (Vero) cells, respectively.Vero cells were incubated for 3-7 days at 37°C in an atmosphere of 5% CO 2 .Cells were scraped from flasks after each passage and centrifuged at 10,000 × g for 10 Chikungunya Virus in Febrile Humans and Aedes aegypti Mosquitoes, Yucatan, Mexico1804