Letters

Disinsection of aircraft

Editor – While agreeing with Gratz et al. (1) that vector-borne diseases are a global public health issue and that their control is essential, Das et al. (2) question the safety of aircraft disinsection as recommended by the World Health Organization to prevent spreading malaria and other vector-borne diseases by aircraft and to aircraft personnel and passengers. All chemicals are toxic, and it is very important to be aware of risks related to exposure to them. It is therefore valuable to question present practices and seek better and less harmful ones, as advocated by Das and coworkers. However, their letter contains some inaccuracies that need to be corrected so that the discussion on aircraft disinsection continues on a sound basis.

Pyrethroids are among the safest pesticides: no long-term or serious health effects have been observed after decades of very extensive use worldwide. Pyrethroids do not accumulate in the body and have not caused long-term adverse effects in experimental animals. Toxicity of chemicals depends on the dose. The duration of exposure among aircraft personnel is very short because of the short time of use and the rapid exchange of air in the aircraft. The cumulative exposure of passengers and crew is thus considerably less than that of, say, agricultural workers. Permethrin, for example, has been and still is extensively used as an anti-lice agent; it is applied directly onto the skin, even in children, without reports of serious adverse effects. Pyrethroids are also very widely used as household pesticides — here, too, the exposure is likely to be much higher than in aircraft, where the ventilation is much faster than in any residential buildings.

No "exacerbation of pre-existing asthma" due to exposure to pyrethroids, mentioned by Das et al., has been documented. Specifically, such a phenomenon is not mentioned in the reference they give to support this notion, which is a well-regarded handbook on toxicology of pesticides (3).

According to Das et al., WHO's view that use of pyrethroids on aircraft is unlikely to precipitate pre-existing diseases contradicts existing literature. To support this claim, they write: "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." This claim is based on a single study (4), in which permethrin or phenothrin (the only chemicals that WHO recommends for aircraft disinsection) were not tested. Exposure in the study was very heavy, effects were marginal and were only observed after exposure to commercial aerosols — where the total amount of pyrethrins was less than that of other active ingredients (piperonyl butoxide or N-octylbicycloheptene dicarboxamide) — while no significant effects on lung function or airway responsiveness were observed after similar exposure to an aerosol containing pyrethroids only; a low-irritant aerosol (i.e., an aerosol containing pyrethroids but no other active components) specifically did not trigger significant symptoms. The WHO-recommended aerosol does not contain piperonyl butoxide or N-octylbicycloheptene dicarboxamide, which would appear to be responsible for the marginal effects in the cited study.

In order to support the view that pyrethroids are toxic, Das et al. provide statistics on occupational illnesses ascribed to pesticides from reports of the California Department of Health Services. While this information is interesting, it does not shed light on the toxicity of permethrin or phenothrin or, in fact, of any pyrethroids in humans and certainly not after the very low exposure of passengers or crews on aircraft. In fact, it is surprising that the number of cases linked (with no causality proven) to pyrethroid use is only 15% of all pesticide incidents, considering the very widespread use of pyrethroids and the fact that the general conception of their harmlessness is likely to lead to careless use and thus to high exposure.

At present, there is no information that would contradict WHO's advice that aircraft disinsection is necessary when there is a risk of vector spread (5) and that permethrin and phenothrin, when used for this purpose in accordance with WHO recommendations (2), are safe. It is equally clear that any use of pesticides for public health purposes — such as pyrethroids for aircraft disinsection — should only be encouraged when they are effective against spreading a serious disease. It is also well known that pyrethroids may cause irritation and other skin effects, which are annoying but of short duration and without serious consequences, and that these effects can and should be minimized by keeping the exposure in aircraft disinsection to a practical minimum. Pyrethroid pesticides are available which have far fewer local adverse effects (e.g. etofenprox); tests should be carried out to determine their efficacy and suitability for aircraft disinsection. Above all, passengers and aircraft crews should be informed of the serious health risks of not disinsecting aircraft.

Antero Aitio¹

Conflicts of interest: none declared.

1. Gratz N, Steffen R, Cocksedge W. Why aircraft disinsection? Bulletin of the World Health Organization 2000;78:995-1003.

2. Das R, Cone J, Sutton P. Aircraft disinsection. Bulletin of the World Health Organization 2001;79:900-1.

3. Ray DE. Pesticides derived from plants and other organisms. In: Hayes WJJ, Laws ERJ, editors. Handbook of pesticide toxicology. San Diego (CA): Academic Press; 1991. p. 585-636.

4. Salome CM, Marks GB, Savides P, Xuan W, Woolcock AJ. The effect of insecticide aerosols on lung function, airway responsiveness and symptoms in asthmatic subjects. European Respiratory Journal 2000;16:38-43.

5. International Programme on Chemical Safety (IPCS). Report of the Informal Consultation on Aircraft Disinsection, Geneva, 6–10 November 1995. Geneva: World Health Organization; 1995. Unpublished document WHO/PCS/95.51.

¹ Medical Officer, International Programme on Chemical Safety, World Health Organization, 1211 Geneva 27, Switzerland (email: aitioa@who.int).