Report of the 2nd WHOPES Working Group meeting. WHO/HQ, 22−23 June 1998

Overview

Dr Zaim also emphasized that the main objective of the WHOPES testing/evaluation of insecticides is to study the properties of the products and their impact on the vector and/or pest population. Therefore, safety, determination of the application dose, residual activity on different surfaces, efficacy in different ecological settings, ease of application, acceptability, resistance assessment and cost-effectiveness are the main objectives of the programme. Epidemiological studies are only carried out where appropriate.

Dr Zaim informed the Group that the two compounds under the review by the Scheme have been reviewed for safety by the WHO/ILO/UNEP Joint Meeting on Pesticide Residues (JMPR). The International Programme for Chemical Safety (IPCS) has classified, by hazard, the technical products of the two compounds in Class II “moderately hazardous”, with acute oral LD50 (mg/kg of body weight) of 250 and 79 for cyfluthrin and alphacypermethrin, respectively . It should however be noted that the final classification of any product is based on the formulation and thus the above-mentioned formulations of the two compounds are classified as “products unlikely to present acute hazard in normal use”.

Dr Zaim informed the Group that the tentative diagnostic concentration has been established by WHOPES for cyfluthrin and alphacypermethrin as 0.15 and 0.05%, respectively, using WHO standard test tubes and one hour exposure. More detailed studies, however, are needed to determine the diagnostic concentration for wider range of mosquito vector/pest species, to establish an accurate discriminative concentration.

Dr Zaim emphasized that pyrethroid resistance has already been reported in several major mosquito vectors and pests of public health importance (e.g., An. albimanus, An. gambiae, An. sacharovi, An stephens and Cx. quinquefasciatus) in which insensitive sodium channels (kdr) and monooxygenases have been the resistance mechanisms involved and which confer cross resistance to a wide range of pyrethroids, including cyfluthrin and alphacypermethrin. Hence, careful monitoring of pyrethroid resistance and their judicious use should be promoted.

The Meeting was attended by 8 scientists. Professor H. Townson was appointed as Chairman and Dr C. Lengeler as Rapporteur. The meeting was convened in plenary sessions at WHO/HQ in Geneva 22-23 June 1998, and the reports of the WHOPES supervised trials, published literature on the two compounds, as well as the reports submitted by the national disease and vector control programmes were fully discussed and recommendations on the use of the above-mentioned products were made.