Hurricane Andrew crossed south Florida on August 24, 1992, entered the Gulf of Mexico, and struck the Louisiana coast on August 26. In Florida, an estimated 25,000 housing units were destroyed and 37,000 severely damaged in a 200,000-acre area in the southern portion of Dade County; in Louisiana, an estimated 25,000 housing units were destroyed or severely damaged by the storm, primarily in the coastal sections of the 36-parish disaster area. Initial assessment of the disaster areas indicated a need for vector surveillance and control (1). This report summarizes actions to assess and alleviate mosquito-related problems in Florida and Louisiana.

Persons residing in the affected areas or returning after the initial evacuation were exposed to high densities of mosquitoes (e.g., because of damage to door and window screens and lack of electricity to run air conditioners). In addition to being a nuisance that hampered recovery efforts (e.g., repair and reconstruction crews were unable to work during early morning and late afternoon/early evening hours), this exposure increased the potential for mosquito-transmitted diseases among recovery workers and displaced residents, and secondary bacterial infections of mosquito bites among children were reported in both states. Florida

Dade County Mosquito Control monitored morning and evening mosquito landing rates at 27 sites beginning September 1. On September 2, carbon dioxide-baited encephalitis vector survey (EVS) traps were placed at eight locations and monitored daily by the U.S. Navy Disease Vector Ecology and Control Center. Aedes taeniorhynchus and Culex nigripalpus were the predominant mosquito species in the area. Daytime landing rates of nuisance mosquitoes in early September exceeded 20 per minute in sampling sites near coastal sections of the disaster area. During the 50 days following the hurricane, 659,458 acres in Dade County were treated by aerial application of mosquito-control insecticides, resulting in substantially reduced landing rate counts. For example, after one application to 99,000 acres on September 11, landing rates in the area were reduced from an average of 14.3 mosquitoes per minute to 0.4 mosquitoes per minute, and EVS trap collections decreased from an average of 550 Ae. taeniorhynchus per night to 20 per night.

Mosquito-based surveillance for St. Louis encephalitis (SLE) was conducted from September 8 through October 15; 28,369 specimens (primarily Cx. nigripalpus) in 402 pools were tested by antigen capture enzyme-linked immunosorbent assay (ELISA). No SLE viral antigen was detected.

The presence of competent mosquito vectors (Ae. aegypti and Anopheles quadrimaculatus) and of recent immigrants from the Caribbean Islands and Latin America raised the possibility of dengue and malaria transmission in Florida. Because mosquito-based surveillance for SLE is unable to detect these diseases, fliers with information on identification and reporting of dengue and malaria were distributed to health-care workers in the area. No dengue or malaria cases were reported to the Florida Department of Health and Rehabilitative Services. Louisiana

The disaster area in Louisiana comprised 36 parishes. Nine were considered candidates for a large build-up of nuisance mosquitoes or for transmission of mosquitoborne pathogens because early surveillance indicated that large numbers of mosquitoes were appearing in urban and suburban areas with large human populations. Emergency mosquito surveillance programs were established in eight of the 36 parishes, and existing surveillance programs in three parishes were augmented.

Densities of nuisance mosquitoes were estimated with carbon dioxide-baited CDC light traps and landing/biting surveillance conducted by the parish mosquito-control districts. The number of telephone complaints received by health departments or vector-control agencies were also used to assess mosquito biting activity. The most common nuisance species collected were Psorophora columbiae, Cx. salinarius, Psorophora ferox, and Ae. sollicitans. During the 36 days following the hurricane, approximately 788,000 acres were treated by aerial and ground application of mosquito-control insecticides by the cooperating parish mosquito-control programs and private mosquito-control contractors. Pretreatment and posttreatment surveillance indicated immediate but short-term reductions in nuisance mosquitoes.

Before and after the storm, the Louisiana Department of Health and Hospitals and the Louisiana Mosquito Control Association reported no eastern equine encephalitis (EEE) or SLE virus activity in their wild bird sampling program, indicating that transmission of arboviral disease was unlikely following the hurricane. Carbon dioxide-baited CDC light trap collections after the storm were processed for virus detection by the state public health laboratory; 2738 mosquitoes (131 pools) of known or suspected vector species (Culiseta melanura, Coquillettidia perturbans, Cx. pipiens quinquefasciatus, and Cx. salinarius) were tested for the presence of EEE and SLE viruses. No arbovirus activity was detected.

Reported by: M Nelms, Dade County Mosquito Control, Miami; US Navy Disease Vector Ecology and Control Center, Naval Air Station, Jacksonville; WR Opp, Florida Dept of Agriculture and Consumer Svcs; Florida Dept of Health and Rehabilitative Svcs. MM Yates, East Baton Rouge Mosquito Abatement and Rodent Control; GM Stokes, Mosquito Control Contractors, Inc, Iberia Parish, New Iberia; BB Broussard, Vermilion Parish Mosquito Control, Abbeville; CL Meek, Louisiana State Univ and Louisiana Mosquito Control Association, Baton Rouge; MJ Keppinger, Louisiana Dept of Agriculture and Forestry; C Anderson, HB Bradford, B Savoie, L McFarland, DrPH, State Epidemiologist, Office of Public Health, Louisiana Dept of Health and Hospitals. Federal Emergency Management Agency, regions 4 and 6. US Air Force 910th Airlift Group, Youngstown Air Reserve Station, Vienna, Ohio. Medical Entomology/Ecology Br, Div of Vector-Borne Infectious Diseases, National Center for Infectious Diseases, CDC.

Editorial Note

Editorial Note: In Florida, Dade County nuisance mosquito-population densities after the storm were at approximately normal levels for that time of year, and mosquito species collected were routinely found in large numbers in the area (Dade County Mosquito Control Program, unpublished surveillance data, 1992). Increased human exposure to mosquitoes in the Florida disaster area occurred primarily because of the extensive damage to housing, and mosquito densities that were tolerable before the storm were unacceptable when human exposure increased. In the affected Louisiana parishes, storm-associated rainfall substantially increased nuisance mosquito populations, and displaced persons were exposed to higher than usual mosquito densities. In East Baton Rouge Parish, landing rate indices were 212 times higher than the September averages for 1983-1991, and light trap indices following the storm were 2.1 times higher than normal in Iberia Parish for 1980-1991.

Federal assistance for emergency vector surveillance and control is available when a disaster is declared and when one or more of the following conditions are met* (2): 1) transmission of human or animal disease is in progress or is deemed imminent, 2) reconstruction efforts are substantially hampered by large populations of nuisance species, 3) normal functioning of communities in the disaster area is substantially disrupted, or 4) the large nuisance populations place additional stress on the human population. Mosquito-transmitted pathogens were not detected in either disaster area, and emergency mosquito control was primarily intended to provide relief from high mosquito densities that hampered recovery efforts. Surveillance after control measures were implemented indicated that mosquito populations had decreased markedly.

Although Cx. nigripalpus, the vector of SLE virus, is present in Dade County, SLE virus activity in the area is historically low (Florida Department of Health and Rehabilitative Services, unpublished surveillance data). SLE virus activity throughout Florida and Louisiana was low before and after the hurricane, and the potential for SLE virus transmission in the area was low. SLE virus surveillance was initiated because of the increased exposure of the displaced residents and recovery workers to mosquito bites.

In 1989, emergency arbovirus surveillance following Hurricane Hugo was based on virus isolation in cell culture, and all mosquitoes collected were identified and tested. Turnaround time was 2-3 weeks using this protocol. Following Hurricane Andrew, surveillance programs in both disaster areas tested only known vector species using antigen capture ELISA techniques; with this protocol, results were available in 3-6 days. This substantial improvement in turnaround time should enable timely detection and response to a mosquitoborne disease in emergency situations (CDC, unpublished data, 1990).

References

1. CDC. Rapid health needs assessment following Hurricane Andrew --

Florida and Louisiana, 1992. MMWR 1992;41:685-8.

2. CDC. Centers for Disease Control emergency response plan, 1990. Atlanta: US Department of Health and Human Services, Public Health Service, 1990.

• Federal Emergency Response Plan (Public Law 93-288, as amended April 1992).

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