International Notes Dengue -- Americas, 1983

After the relatively high level of epidemic dengue activity in the Americas in 1981 and 1982, most countries reported only low-level or sporadic transmission in 1983 (1,2). Notable exceptions were Colombia, El Salvador, and Mexico, all of which experienced large epidemics in 1982. All had significant, although somewhat smaller, outbreaks in 1983 as well.

Colombia reported 4,977 cases in 1983, compared with over 6,000 cases in 1982. Two serotypes, dengue 1 and dengue 4, were isolated from patients' sera in 1983, and both were probably responsible for some outbreaks. Additionally, serologic data obtained by the arbovirus laboratory, Instituto Nacional de Salud, Bogota, Colombia, suggest that dengue 2 and dengue 3 may still be transmitted in some areas of the country; if so, Colombia is the first country in the region to have simultaneous transmission of all four dengue serotypes. In El Salvador, 3,243 cases were reported in 1983, compared with over 5,000 in 1982. The 1983 epidemic began in late June and early July in San Salvador. By late August, cases were reported from most areas of the country, but the largest outbreak occurred in the eastern region bordering Honduras. Although the serotypes of all outbreaks were not known, dengue 4 virus was isolated by CDC from patients in San Salvador. The epidemics in Mexico have previously been reported (3,4).

Barbados, Haiti, Jamaica, and Trinidad experienced small dengue outbreaks in 1983. In Jamaica, dengue 2 predominated, although serologic evidence from U.S. travelers suggested that dengue 4 was still active as well. Dry weather was probably responsible for limiting transmission. In Haiti, the outbreak was apparently limited to the city of Belladere and the surrounding area on the border with the Dominican Republic. Dengue 1 virus was isolated, confirming earlier serologic evidence of this serotype occurring among medical missionaries working in Haiti. Despite the epidemic dengue activity in Haiti, relatively few cases were confirmed in the Dominican Republic in 1983. Dengue 4 activity remained high in Trinidad throughout 1983, with peak transmission from July through October. This serotype was isolated by the Caribbean Epidemiology Centre laboratory from 115 cases, compared with only four dengue 2 isolates in 1983. In Barbados, dengue 4 was active early in the year, but no isolations were made from April through September. Another virus isolate was made in October, but travel history on the patient was not available.

Following 2 consecutive years with major epidemics (dengue 1 in 1981 and dengue 4 in 1982), Puerto Rico experienced little confirmed dengue activity in 1983. Dengue 4 virus was isolated only once in 1983 (January), but serologic evidence confirmed sporadic transmission of that serotype throughout the year.

Overall, 25,216 dengue cases were reported in the Americas in 1983, compared with approximately 50,000 in 1982 (Table 1). As in 1982, however, all countries probably underreported dengue, and some countries failed to report at all. For example, Barbados, Haiti, Jamaica, and Trinidad all probably had many more cases of dengue than were reported (Table 1). On the other hand, many of the more than 2,522 cases reported in Puerto Rico were probably not really dengue.

Dengue 4 was the predominant virus in the region again in 1983, but dengue 2 also had a wide distribution (Figure 1). There was renewed activity of dengue 2 in the western part of the region (Jamaica and Mexico). Dengue 1 transmission was confirmed only in Colombia, Haiti, Honduras, and Mexico. However, all four types were introduced into the region, as evidenced in the United States (Table 1, Figure 1).

Clinically, dengue illness in the Americas in 1983 was of the classical type. There were apparently no cases of confirmed dengue hemorrhagic fever (DHF) in the region. However, health authorities in Colombia reported several cases of fatal hemorrhagic disease that were not confirmed as either dengue or yellow fever. Confirmed cases of dengue associated with encephalitic signs were observed in the Dominican Republic. Reported by Pan American Health Organization, Washington, DC; Caribbean Epidemiology Centre, Port-of-Spain, Trinidad; Dengue Br, Div of Vector-Borne Viral Diseases, Center for Infectious Diseases, CDC.

Editorial Note

Editorial Note: The frequency of epidemic dengue in the Americas has increased greatly in the past decade. Regional epidemics caused by dengue 1 and dengue 4 have occurred since 1977. Additionally, a major epidemic of DHF caused by dengue 2 occurred in Cuba in 1981, where over 10,000 patients were hospitalized with DHF, and 159 deaths occurred (case-fatality ratio of 1.6%) (5). The increased dengue activity in the region, along with transmission of multiple serotypes in many countries, is similar to the early stages of the establishment of DHF as a major health problem in Southeast Asia in the early 1960s.

This severe disease is not presently widespread in the Americas. Except for Cuba, only sporadic cases of confirmed fatal dengue have occurred or been reported from other countries of the region (Jamaica, Puerto Rico, Surinam, and Trinidad).

Two major factors potentially responsible for the increased epidemic activity are increased frequency of air travel and lack of effective mosquito control in most countries of the region. The result is repeated introduction of new dengue strains and serotypes into areas where Aedes aegypti coexists with humans. Prevention of epidemic dengue can best be achieved by improved surveillance and more effective public and private mosquito control efforts.

References

1. CDC. Dengue surveillance summary, No. 11. San Juan Laboratories, CDC. April 1983.

2. CDC. Dengue surveillance summary, No. 17. San Juan Laboratories, CDC. February 1984.

3. CDC. Dengue--Mexico, El Salvador, Honduras. MMWR 1983;32:586-8.

4. CDC. Dengue--Mexico, 1983. MMWR 1984;33:203-4, 209-10.

5. CDC. Dengue--Cuba. MMWR 1981;30:317.

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