Editor Gratz et al. (1) advocate the disinsection of aircraft flying from airports in tropical disease endemic areas into nonendemic areas. The authors reflect WHO's position in recommending the use of pyrethroid insecticides on the basis of efficacy, cost-effectiveness, and absence of adverse health effects to humans. Vector-borne diseases are global public health issues and their control is essential, but it is erroneous to state that the recommended pyrethroid insecticides are not of toxicological concern and are safe to use around humans.
The health effects of pyrethroids include dermal paresthesia, exacerbation of pre-existing asthma and, at high doses, excitatory neurotoxicity (2). Airline passengers may not associate the adverse effects they experience with pesticide exposure aboard aircraft because they are unaware of the exposure and do not recognize the signs and symptoms of pesticide-related illness, and several hours may elapse before the onset of symptoms (3). Children may be especially susceptible to such adverse effects.
WHO's statement (4) that pyrethroids on aircraft are unlikely to precipitate pre-existing diseases contradicts existing literature. Studies suggest that asthmatic patients respond to inhalation exposure to pyrethroids with airway hyper-responsiveness and that even "low irritant" aerosols may trigger nose and eye symptoms (5).
The California Department of Health Services (CDHS) conducts ongoing surveillance of occupational pesticide illness. Pyrethroid pesticides accounted for 119 of 776 (15%) occupational pesticide illness cases reported in 1998 and 1999 (6). Adverse health effects of pyrethroids were dermatological (22%), ocular (34%), respiratory (19%), gastrointestinal (69%), and neurological (73%). During this two-year period, permethrin, a pyrethroid recommended for aircraft disinsection, accounted for 16 cases (13%) of occupational pyrethroid illnesses reported.
CDHS has received reports of occupational illnesses among flight attendants. While dermal uptake of pyrethroids is low (2), exposure in an enclosed environment may enhance absorption by dermal exposure, inhalation, and ingestion. Furthermore, the half-life of pyrethroids may be prolonged by the absence of ultraviolet light aboard aircraft. Flight crew may have significant acute inhalation and dermal exposures because they are physically active and touch many surfaces during the course of their work. Both staff and passengers who fly frequently may incur significant cumulative exposures.
Solvents and other inert ingredients in pesticide formulations may contribute to the adverse effects of pyrethroids (5). There is little toxicological information available about these ingredients but, rather than constituting evidence that health effects are nonexistent, the absence of data identifies gaps that need to be filled prior to encouraging the continued practice of aircraft disinsection by pyrethroid application, especially while passengers and crew are on board.
With ample evidence to demonstrate that exposure to pyrethroid pesticides may result in adverse health effects, especially among sensitive subpopulations, there is insufficient information to determine that aircraft disinsection as currently practised is safe. We believe that reconsideration of the use of pesticides as described by Gratz et al. is warranted, in order to ensure the safety of passengers and crew while preventing transmission of vector-borne diseases through air travel.n
Rupali Das, Public Health Medical Officer
Occupational Health Branch
California Department of Health Services and
Assistant Clinical Professor Division of Occupational and
Department of Medicine
University of California, San Francisco, USA
tel: (510) 622-4406
James Cone, Chief
Occupational Health Branch
California Department of Health Services
Patrice Sutton, Research Scientist
Public Health Institute
Funding for work described in this letter was provided by the US National Institute for Occupational Safety and Health, the US Environmental Protection Agency, and the State of California.
Conflicts of interest: none declared.
1. Gratz NG, Steffen R, Cocksedge W. Why aircraft disinsection? Bulletin of the World Health Organization, 2000, 78: 9951004.
2. Ray DE. Pesticides derived from plants and other organisms. In: Hayes WJ, Laws ER, eds. Handbook of pesticide toxicology, Vol. 2. San Diego, Academic Press, 1991.
3. He F et al. Clinical manifestations and diagnosis of acute pyrethroid poisoning. Archives of Toxicology, 1989, 63: 5458.
4. Report on the Informal Consultation on Aircraft Disinsection. Geneva, World Health Organization, 1995 (unpublished document WHO/IPCS/ 95.51).
5. Salome CM et al. The effect of insecticide aerosols on lung function, airway responsiveness and symptoms in asthmatic subjects. European Respiratory Journal, 2000, 16: 3843.
6. CDHS. Sentinel Event Notification System for Occupational Risk: occupational pesticide poisoning California, Year 3. San Francisco, California Department of Health Services, 2001 (unpublished document).