As if organized mosquito control doesn’t have enough responsibility protecting public health and well-being from natural mosquito pests and mosquito-borne pathogens, another responsibility may include being among the first responders to a potential bioterrorism attack using infected mosquitoes. Although some might believe that it is unlikely that infected mosquitoes would serve as a vehicle for such an attack in the U.S., I refer readers to the recent book by Jeffrey A. Lockwood (Lockwood, J.A. 2009. Six Legged Soldiers: Using Insects as Weapons of War. Oxford University Press. 377pp.) that serves as an alarm to the very real potential of such a threat to the U.S. in this era of low tech terrorist attacks.

Lockwood does an excellent job reviewing the use of insects as weapons and to spread terror and panic to adversaries throughout history. However, it is Lockwood’s review of modern attempts to use insects as agents of bioterrorism that is certainly more instructive and with consequences for mosquito control. Did you know that during the past 60 years the U. S. has been the leader in actual programs to use mosquitoes to deliver pathogens? Lockwood’s review of this is chilling.

A common thread among attempts to use insect vectors to deliver pathogens in modern times has been the use of Aedes aegypti as the theoretical vector of choice. Indeed Ae. aegypti was the U.S’s. “golden child,” as Lockwood terms it, for entomological warfare programs. This program reached its zenith in the 1950s with projects like “Operation Big Buzz” in 1955. This U.S. military operation consisted of rearing more than one million Ae. aegypti, maintaining the adults for 2 weeks to simulate operational conditions for releasing mosquitoes. About a third of these uninfected mosquitoes were actually released by aerially dropping them on rural Georgia. Human volunteers assessed the resulting biting rates and reported that the mosquitoes were able to find human hosts about 0.5 mile downwind from the release site. Similar types of experiments with Ae. aegypti followed for the next several years, many of them are still classified.

There were releases in 1956 in Savannah Georgia. Consider the Avon Park Experiment(s) from 1956-58. Yes, this is Avon Park Florida, where in one experiment the military released 200,000 Ae. aegypti from aircraft employing a bagging system with uninfected mosquitoes in paper bags that were dropped from the air. Other Avon Park experiments where Ae. aegypti were dispersed from planes, helicopters, and ground devices are summarized elsewhere (Cole, L.A. The Eleventh Plague: The Politics of Biological and Chemical Warfare. 284 pp). It was reported that Ae. aegypti dispersed more than two miles two days after release from a helicopter. It was also reported that these mosquitoes entered all types of buildings and that many people were bitten. Operation Bellweather in 1959 consisted of 52 different experiments testing the effects of weather on vector behavior including host location. One experiment showed that Ae. aegypti would take 40 blood meals for every 100 Ae. aegypti released from volunteers seated on the perimeter of a 30 foot diameter circle. Another experiment showed that biting activity dropped from about 200 feet from a central release point, and Lockwood makes the startling comment that this means a single release could likely saturate an area equivalent to 3 football fields. Anyone familiar with Ae. aegypti behavior should not be surprised at these results. Mosquito control workers, medical entomologists, and public health workers are all too familiar with the extreme human host seeking ability and biting activity of Ae. aegypti. These features of Ae. aegypti are among the reasons it is considered so efficient as a natural pathogen vector to humans, and could be such an efficient virus delivery vehicle as a weapon.

Since the 1960s attention focused on the use of mosquitoes as potential weapons and preparations to mitigate their use as weapons have declined considerably. National defensive programs, including those in the U.S., place greater emphasis on delivering aerosolized pathogens. Lockwood believes this is due to the fascination with high tech weaponry that would be required for aerosolized Volume 9, Issue Number 3 15 May/June 2009 pathogens, some of which are normally vector borne pathogens, like yellow fever, Venezuelan equine encephalitis, eastern equine, etc. I tend to agree with Lockwood’s thesis. There is no doubt that employing aerosolized pathogens and dispersing them on a population center has the capability to approach the effects of weapons of mass destruction (See Mangold, T. & Goldberg, J. 2000. Plague Wars: The Terrifying Reality of Biological Warfare. St. Martin’s Press, 336 pp.). Indeed the “developed” countries with national scientific infrastructure and resources have focused on such strategies which employ high tech resources to create sophisticated biological weapons. Protecting against the low tech strategies that might be considered by terrorist groups, including the use of infected mosquitoes, has been largely ignored in recent years. Any nation using an aerosolized pathogen that causes mass numbers of infections would certainly be an act of war and would likely require a sophisticated weapon and delivery system. Such an attack would present difficult challenges for a bioterrorist group having limited ability to obtain quantities of such agents, and limited means to deliver them. However, terrorists used our own passenger airlines as weapons on 9-11.

Lockwood points how cheaply mosquitoes such as Ae. aegypti could be used in a simultaneous release in several cities that would create a large number of cases and spread fear and panic in the U. S. In 1981 the U.S. Army Test and Evaluation Command report “An Evaluation of Entomological Warfare as a Potential Danger to the United States and European NATO Nations” compared the economics of two theoretical biowarfare attacks. Though the mosquito attack with yellow fever was less costly than the attack with aerosolized tularemia bacteria, the mosquito attack was deemed too unpredictable because of vector movement. Lockwood quotes the reports finding that the total cost of a mosquito attack on Washington DC with yellow fever infected mosquitoes would be less than just the planning costs of an aerosol attack. Leave it to bureaucrats to detail the actual costs of a theoretical attack in detail. The total for the mosquito attack in 1981 was $10,473! Planning ($547), agent production ($9,066), munitions acquisition ($500), weapon deployment ($360), and like any government budget this included travel and per diem estimates for covert agents! How low-tech can one get?

What would be the U.S. response to a large scale attack on several cities using Ae. aegypti and yellow fever virus? With foreknowledge of such an event, what can be done to prevent it, or mitigate the effects? Clearly there is a role for organized mosquito control. However, what is this role? What is the role of organized mosquito control to prevent an attack if there is foreknowledge? To mitigate an attack while it is ongoing? To mitigate an attack after human cases begin appearing? What are the lines of authority? I would assume that immediately upon learning of such an event, the government’s Homeland Security apparatus would take charge, including law enforcement, particularly the FBI. What then are the lines of authority for organized mosquito control? What plans would be put into place? Who, when, and how would potential responders in mosquito control be requested, ordered, and instructed to respond? I do not have any answers to offer. However, I do advise that as medical entomologists and organized mosquito control professionals we need to ask the right questions, get some answers, and have some plans in place.

The UF IFAS Florida Medical Entomology Laboratory, The Whitney Laboratory, UF Emerging Pathogens Institute, and the USDA ARS Center for Medical and Veterinary Entomology is planning a workshop within the next few months to address the issues I have raised. Florida with its history and resources has a great deal to offer to the entire nation in providing a plan and protection. Florida mosquito control will be an essential component as first responders. We need to attend to this now.

Walter J. Tabachnick - Retired
Florida Medical Entomology Laboratory
University of Florida IFAS, Vero Beach, Florida

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