International Notes Dengue Type 1 in Mexico

During the past 3 months, health authorities in Mexico have reported cases of dengue-like illness from scattered locations. Serologic evidence from the Instituto de Salubridad y Enfermedades Tropicales in Mexico City suggested the virus was dengue type 1. More recently, transmission has increased with outbreaks reported from Apatzingan and Huetamo in Michoacan State and Culiacan in Sinaloa State on the west coast of Mexico, and from Veracruz, Cordoba, and Tierra Blanca in Veracruz State on the east coast (Figure 1). In the latter state, dengue has moved north and scattered cases have been reported recently from cities in the Tampico area.

An investigation of the outbreak in Cordoba, Veracruz, began in July 1982. Acute-phase serum specimens were taken from 18 patients with a dengue-like illness and sent to the San Juan Laboratories, CDC, for virus isolation. In subsequent visits, paired specimens were obtained from 16 additional patients and were also sent to the same laboratory for virologic and serologic testing.

The first acute-phase specimens were inoculated into Toxorhynchites mosquitoes. Three viruses were isolated and tentatively identified as dengue type 1 by type-specific monoclonal antibodies on mosquito brain tissue. This serotype was confirmed by complement fixation (CF) using antigen prepared from the bodies of infected mosquitoes.

Serology has been completed on the second group of specimens received. Ten of 16 paired specimens (62%) showed a greater than or equal to 4-fold rise in dengue hemagglutination-inhibition (HI) antibodies between acute- and convalescent-phase specimens. Seven of these 10 patients had HI antibody titers compatible with primary dengue infection and follow-up serology by CF suggested that all were probably due to dengue type 1 virus. Four more dengue type 1 viruses were isolated from these specimens. The virus(es) responsible for the outbreaks in Michoacan and Sinaloa States are unknown at this time.

Because of the potential northward movement of dengue on Mexico's east coast, active virologic surveillance for dengue has been implemented in the Texas border towns of Brownsville and Laredo. Texas State Health Department health centers in each city will take five to 10 acute-phase serum specimens from suspected dengue cases each week and will send them to the San Juan Laboratories for virus isolation. In addition, health authorities in other border communities have been alerted to the possibility of increased dengue-like illness.

Entomological surveillance has also been intensified in Texas. Detailed surveys to determine the relative abundance and the breeding sites of Aedes aegypti will be undertaken in Brownsville, Laredo, Eagle Pass, and Corpus Christi. At this time, no implementation of virologic surveillance in other gulf coast cities is planned, but health authorities should be aware of the potential introduction of dengue from Mexico and the Caribbean (1-3). Reported by L Cabrera-Coello, MD, Subdirector de Vigilancia y Epidemiologia, Secretaria de Salubridad y Asistencia, FP Miranda, E Zorrilla, MD, Instituto de Salubridad y Enfermedades Tropicales, Mexico City, Mexico; T Betz, MD, Texas State Health Dept; Vector-Borne Viral Diseases Div, Center for Infectious Diseases, CDC.

Editorial Note

Editorial Note: Dengue type 1 outbreaks were widespread in Mexico in 1979 and 1980 (4). Since then, only sporadic transmission has been reported. Dengue types 1, 2, and 4 have been responsible for major epidemics in other parts of the Caribbean basin during the past 12 months (1-3). There is no evidence that either dengue type 2 or 4 is currently being transmitted in Mexico.

During 1980, epidemics of dengue were reported in several cities in northeastern Mexico (4). In August of that year, indigenous transmission of dengue virus in the United States was documented for the first time since 1945 (5). A total of 21 locally transmitted cases of dengue type 1 were confirmed in Texas from August to November 1980. For reasons not fully understood, however, transmission remained sporadic in Texas that year.

Because the principal vector mosquito, A. aegypti, is currently widespread in Texas border cities and in other major gulf coast urban areas, health authorities in these cities and states should be aware of the potential of dengue transmission in the United States.

References

1. CDC. Dengue fever in Puerto Rico--1981. MMWR 1982;31:103-4.

2. Pan American Health Organization. Program for dengue elimination and Aedes aegypti eradication in Cuba. Epidemiological Bulletin--PAHO 1982;3(1):7-10.

3. CDC. Dengue Surveillance Summary, No. 3. San Juan, PR: San Juan Laboratories, CDC.July 1982.

4. Pan American Health Organization. Dengue in Mexico and in the United States, 1980. Epidemiological Bulletin--PAHO 1981;2(1):9-11.

5. CDC. Dengue--Texas. MMWR 1980;29:451.

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