August 22, 2003

WEST NILE VIRUS: BEWARE OF MOSQUITOS BEARING GIFTS
By Dr. Saul Wilen

A number of human diseases are spread by mosquito vectors. Included are Dengue fever, Malaria, Yellow fever, West Nile virus and filariasis. Some mosquitoes are great travelers. However, much depends on the travel accommodations. The mosquito is hardy and enterprising, ready to use every opportunity. The development of the airplane in the 20th century provided mosquitoes with the opportunity to spread to all "corners of the earth." If the mosquito cannot get there as an adult, it sends an egg or a larva.

The spring and early summer rains of 2003 have enhanced the breeding grounds for mosquitoes. The rainfall has also made it harder to control them because pesticides become diluted with each new cloud burst. The cool wet weather has delayed the development process with more time for growth through the larval stage into the adult form. The result is bigger and hungrier mosquitoes by the time the weather gets hot and dry and they begin to fly. This has been the case this summer.

Mosquitoes are able to deliver potentially deadly diseases like West Nile virus. The virus is spread to mosquitoes that have bitten infected birds. West Nile virus is a flavivirus. Other flaviviruses cause Yellow fever and Dengue fever. Most mosquitoes live only through the summer, but females of some species, including the most common carrier of West Nile virus (Culex pipiens), can survive through the winter and lay eggs in the spring.

Though West Nile virus was first found in Uganda in 1937, its progression in the United States, identified first in New York in 1999, has generated great interest and concern. The initial failure of U.S. health officials to quickly identify the West Nile virus exposed weaknesses in America's ability to detect emerging infectious diseases that occur elsewhere and are then transported to the United States. It was presumably carried to the United States from Europe or the Middle East by an infected traveler, bird, or disease-bearing mosquito. In that year only four states were affected, with 62 cases and seven deaths. By 2002, West Nile was present in 40 states. There were 4,156 cases and 284 deaths making the U.S. outbreak of West Nile Encephalitis the largest reported in the world.

West Nile has proven to be extremely aggressive and versatile. The CDC (Centers for Disease Control) has been surprised at the speed of transmission in 2003, with more and more human infections diagnosed weekly. These cases are broadly dispersed and occurring earlier than last year. The elderly are the most vulnerable to infection and complications.

The virus affects more than 130 species of birds, and is carried by at least 36 types of mosquitoes making widespread transmission possible. Migrating birds (the main wildlife host for the virus) have carried the disease quickly across the U.S. West Nile virus is expected to occur in every place where people coexist with a natural reservoir (birds) and the insect (mosquito) intermediary. No medical treatment or vaccine presently exists. The rapid spread of this disease in only three years raises significant questions, and serious problems to be evaluated and solved now. Since 1999, health officials have tried -- mosquito spraying and other control efforts, public information messages and disease detection programs.

CDC is recommending in the states where the virus has been found, the use by the public of mosquito repellents containing DEET, removing standing water, repair of screens, clothing that protects by covering the arms, legs, and midriff, and to avoid the times of day (morning and evening) when mosquitoes are most active. Communities need to work to prevent mosquitoes from biting and breeding.

A CDC spokesperson in early August, 2003, stated, "There may be no way to prevent the virus from spreading and there is no way to predict which areas it will strike hardest." This points up major issues that are similarly raised when considering bio-terrorism, including prevention strategies and predictability of occurrence. Applications based on these experiences will support modeling approaches and analysis of the data that relate to bio-terrorism and terrorism prevention.

Dr. Saul B. Wilen is president and CEO of International Horizons Unlimited (www.intlhorizons,com, 210-692-1268), a national consultation and resources consortium based in San Antonio. Dr. Wilen has a background in medicine and education, and is a recognized authority in prevention strategies, problem solving, systems dynamics and informatics.