From March to July 1990, an epidemic of classical dengue caused by dengue types 1 and 4 (DEN-1 and DEN-4) occurred in Iquitos and the surrounding area of the department of Loreto in the Amazon region of Peru (Figure 1). A smaller outbreak was reported in Tarapoto in the neighboring department of San Martin. Although cases were reported in Peru during 1953-1955 and in 1958 (1), the epidemic in 1990 was the first laboratory confirmation of indigenous transmission of dengue in Peru. This report summarizes the preliminary findings of the epidemiologic investigation by the Peruvian Ministry of Health (MOH) and the U.S. Naval Medical Research Institute Detachment (NAMRID), Lima, Peru, which conducted special studies and laboratory confirmation of cases in persons seen at the Peruvian Naval Medical Center, Iquitos, Peru.

The first cases in Iquitos occurred in late March 1990. Common manifesta tions included fever, headache, and musculoskeletal pain. A case was subsequently defined according to major and minor criteria (e.g., fever, headache, and musculoskeletal pain and rash, ocular pain, and adenopathy). Predominant manifestations were fever, headache, and malaise (Table 1). Hemorrhagic manifestations, such as bleeding gums, were noted in 6.5% of patients with clinical dengue; no cases of shock syndrome were documented.

Acute-phase blood samples were collected at the Naval Medical Center from patients whose illness met the case definition for dengue. A total of 158 blood specimens were inoculated into cultures of C6/36 mosquito cells and Vero (African green monkey kidney) cells; 58 viral isolates were obtained. Based on indirect fluorescent antibody (IFA) tests, 24 of these isolates were identified as DEN-1 and seven as DEN-4. Identification of the remaining 27 viral isolates is pending. Of 43 paired serum samples analyzed by IFA and hemagglutination inhibition (HI) antibody tests, fourfold or greater rises in antibody to DEN-1 occurred in eight and to DEN-4 in 26; in eight persons, similar increases occurred to both DEN-1 and DEN-4 (HI antibody titer greater than 10,240).

Five of 20 pools of mosquitoes (approximately 25 females per pool) collected with human bait or dry ice in or near Iquitos during the first 3 weeks of the outbreak yielded DEN-1 virus. However, only two of the five pools comprised Aedes aegypti. The remaining three pools comprised Culex amazonensis, Aedeomyia squamipennis, and an undetermined Sabethes species.

A random survey based on a grid plan of houses in early May 1990 indicated that approximately 25% of the 305,000 residents of Iquitos had a febrile illness during the 60 days before the survey. Based on this finding, an estimated 76,000 persons in Iquitos may have experienced a dengue-like illness at that point in the epidemic.

Control measures during the epidemic were constrained by limitations in the availability of medical workers and equipment for spraying insecticide. However, public announcements using local radio, television, and newspapers provided information about the prevention of mosquito breeding. Reported by: E Colan, MD, J Escamilla, PhD, I Phillips, JT Need, PhD, Naval Medical Research Institute Detachment, US Navy, Lima, Peru. M Rodriguez, L Vasquez, MD, LJ Seminario, MD, Dept of Epidemiology, Ministry of Health of Peru, Lima, Peru. Dengue Br, Div of Vector-Borne Infectious Diseases, Center for Infectious Diseases; Global EIS Program, International Br, Div of Field Epidemiology, Epidemiology Program Office, CDC.

Editorial Note

Editorial Note: In the 1990 epidemic in Peru, although mosquito pools containing species other than Ae. aegypti yielded dengue virus, it is not possible to determine whether other species were actually involved in dengue transmission. Two possibilities exist: 1) one or two mosquitoes of the three other species had taken blood meals from viremic persons but were not involved directly in dengue transmission, or 2) body parts of infected Ae. aegypti mosquitoes were inadvertently mixed with the other three species during processing.

Ae. aegypti, the epidemic vector of dengue, was declared eradicated from Peru in 1958 (1). In October 1984, reinfestations were detected in Iquitos by MOH officials. In 1985, MOH officials reported a house index (i.e., the percentage of houses inspected that had larval Ae. aegypti) of 10%; by 1988, the index had increased to 26%. Serum specimens collected from a random sample of 1015 persons in coastal, mountain, and jungle areas of Peru during 1985-1987 were analyzed by the Evandro Chagas Institute in Belem, Brazil, for HI antibodies to DEN-1, DEN-2, DEN-3, and DEN-4 antigens. Of the 1015 persons tested, DEN-4 antibody was detected in two (0.2%); in both cases, antibody titers were low, and all samples were negative to the other three dengue serotypes (NAMRID, unpublished data).

Dengue appears to be increasing in the Americas, particularly in South America (2,3). Although the outbreak in Peru began as one was concluding in Caracas, Venezuela (4), the origin of the outbreak in Peru has not been established. Iquitos is a thriving, commercially active city with daily river and air traffic from Brazil, Venezuela, and Colombia. Surveillance and control programs are needed to minimize morbidity and mortality from dengue epidemics.

References

1. Ministry of Health. Guidelines for the prevention and control of dengue. Lima, Peru: Ministry of Health, General Office for Epidemiology, 1990.

2. CDC. Dengue and dengue hemorrhagic fever in the Americas, 1986. MMWR 1988;37:129-31.

3. CDC. Dengue epidemic--Ecuador, 1988. MMWR 1989;38:419-21.

4. Pan American Health Organization. DHF outbreaks in Venezuela. Epidemiol Bull 1990:1117-9.

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