Indiscriminate use of agro-verinary pesticides and susceptibility status of xenopsylla cheopis (family: pulicidae) in plague endemic foci in Tanzania

Abstract

The control of rodent-borne fleas, which play major role in the transmission of plague, is the mainstay of plague control. The application of chemical insecticides forms the most powerful and widely used control measure. The reliability and continued use of this approach however is threatened by the development of resistance. The excessive use of agro-veterinary pesticides is increasingly associated with the development of resistance in different arthropods; however, such possibility has not been explored in flea vectors of plague in Tanzania. This study identified injudicious uses and/or malpractices which potentially enhance exposure of flea vectors to agro-veterinary insecticides and emergence of resistance thereof. Furthermore, the study assessed susceptibility status of major plague flea vector, Xenopsylla cheopis, to commonly used agro-veterinary and public health pesticides. The study was conducted in Lushoto and Mbulu districts, northern Tanzania, both of which are active plague foci. About 91% of the respondents in Lushoto and 93% respondents in Mbulu reported using agricultural pesticides during the cropping season. Excessive and injudicious use of agricultural and veterinary pesticides was common across the study districts. Most of the farmers reported applying agricultural pesticides for up to four times per a cropping season. The three out of fourteen most commonly used agricultural pesticides in Lushoto were master kinga72WP (mancozeb 640g/kg+ cymoxanil 80g/kg) (44%), suracron720EC (profenos 500g/l EC) (25.3%) and Sumo 5EC (lambda-cyhalothrin) (18.7%). The three out of seventeen most commonly used agricultural pesticides in Mbulu were Dursban 50W (Chlorpyrifos) (29%), Duduban 450EC (Cypermethrin 10g/lt+chloropyrifos 35g/lt) (18%) and Dursban+farmerzeb (Chlorpyrifos 48%, Mancozeb 80%WP). Cybadip (Cypermethrin) (≥45%) and paranex (alphacypermethrin) (≥13%) were the two most commonly used veterinary pesticides across the districts. Moreover, the susceptibility of Xenopsylla cheopis, originating from wild population in Mbulu was assessed against nine different agro-veterinary and public health pesticides via contact bioassays. The percentage mortality after exposure to recommended doses of eight insecticides tested was strongly suggestive of resistance (100% 24 h mortality, 93 - 96%). The fleas confirmed resistance to lambdacyhalothrin and carbaryl, with 90% mortality. The reference ‘susceptible’ colony Xenopsylla Cheopis was fully susceptible (100% 24 h mortality) to all tested insecticides. Similarly, the field Xenopsylla Cheopis was fully susceptible (100% 24 h mortality) to 5× and 10× the recommended doses of all insecticides indicating low resistance intensity. Conclusively, this study identified a suite of injudicious uses and/or malpractices; excessive use of agricultural chemicals, maluse of agro-veterinary chemicals as well as poor adherence to the application and safety procedures, all of which potentiate contamination of environments/surfaces and exposure of the chemicals to fleas thereof. Furthermore, the study indicates resistance in the wild population of Xenopsylla cheopis from Mbulu district. As such, flea vector populations across Lushoto and Mbulu districts are putatively under intense risk of resistance development, thus warranting further studies across plague endemic areas in country to understand distribution of the resistance, involved resistance mechanisms; and confirm the contribution of agro-veterinary insecticides