Endemic Venezuelan Equine Encephalitis in Northern Peru Table 1. Classification of the Venezuelan equine encephalitis (VEEV) complex of alphaviruses Transmission Equine Subtype Variety Species pattern virulenceb Location I AB VEEV Epizootic Virulent Central, South, North America C VEEV Epizootic Virulent South America D VEEV Enzootic Avirulent Central, South America II III E F A B VEEV Mosso das Pedras Everglades Mucambo Tonate Enzootic Enzootic Enzootic Enzootic Enzootic Variable Unknown Avirulent Avirulent Unknown Central America, Mexico Brazil Southern Florida South America South, North America C Enzootic Unknown IV Pixuna Enzootic Unknown V Cabassou V Enzootic Unknown VI Rio Negro Enzootic Unknown aSource: The Arboviruses: Epidemiology and Ecology (9). bVirulent strains produce high viremia titers and generally >50% death rates in horses experimentally infected. Peru Brazil French Guiana Argentina Vector Mammalophilic mosquitoes Mammalophilic mosquitoes Culex (Mel.) ocossa, panocossa, pedroi, adamesi, vomerifer Cx. (Mel.) taeniopus Unknown Cx (Mel.) cedecei Cx (Mel.) portesi Unknown (Tonate), bug (Bijou Bridge strains from N. America) Unknown Unknown Unknown Unknown human isolates belonged to the Panama ID genotype (9). Lack of detection of the Colombia/Venezuela genotype in the Iquitos area during 1993 through 1995, when the Panama genotype was repeatedly isolated, suggested that the Colombia/Venezuela genotype had been replaced by virus strains from Panama. Because the Colombia/ Venezuela VEEV genotype is believed to give rise to epi- zootic viruses through mutations of the E2 envelope glycoprotein (15–18), disappearance of this genotype from the Iquitos area could have important public health implications. Since 1995, 75 VEEV strains have been isolated from mosquitoes, humans, and sentinel hamsters in Peru. We determined the genetic relationships among strains isolat- ed from 1995 through 2002 and compared them with other VEEV strains isolated from the Americas. Our results indi- cate that the VEEV subtype ID Colombia/Venezuela geno- type continues to circulate in Iquitos but may infect people at a lower rate than the Panama genotype. We also demon- strated that a recent subtype III isolate is genetically dis- tinct from the subtype IIIC strain isolated in 1971 (12). This strain, which we propose as subtype IIID in the VEE complex, and both subtype ID genotypes cause human febrile disease in the Iquitos area. Methods Study Sites VEEV isolates were obtained from several locations in Peru. The main study site was centered around Iquitos, a city of 300,000 people on the Amazon River in the Department of Loreto (Figure 1). The major occupations of the inhabitants are housekeeping, teaching, military work, agriculture, fishing, and tourism. The climate is tropical, with a mean annual temperature of 27.5°C and mean annual precipitation of 2.7 m (4). Virus Isolates The VEE complex isolates included in this study are shown in Table 2. These viruses were provided by the University of Texas Medical Branch World Health Organization Collaborating Reference Center for Arboviruses, the United States Army Medical Research Institute of Infectious Diseases, and the U.S. Naval Figure 1. Map of Peru showing the geographic distribution of the Venezuelan equine encephalitis virus (VEEV) complex isolates included in the study. Numbers in parenthesis indicate the number of isolates compared to the total number of febrile cases during the year. ID, IAB, IIIC, IIID correspond to VEEV subtypes isolated dur- ing the indicated year. Emerging Infectious Diseases • www.cdc.gov/eid • Vol. 10, No. 5, May 2004 881