Insecticide‐treated cattle for tsetse control: the power and the problems

Abstract

Trypanosomiasis control increasingly involves financial input from livestock owners and their active participation. If control is carried out on smaller scales than in the past, methods such as aerial and ground spraying and sterile insect techniques will have reduced application. There will be increased reliance on trypanocidal drugs, and bait methods of tsetse control--where flies are attracted to point sources and killed. If drug resistance develops, cheap and simple bait methods offer the only means of disease control that might be applied, and paid for, by stockowners themselves. The methods have been effective in some circumstances, but not in others, and it is important to understand the reasons for the successes and the failures. Analysis is presented of the results of two Tanzanian tsetse control campaigns involving the use of insecticide-treated cattle. Between 1991 and 1996, following the introduction of widespread dipping in the Kagera Region, trypanosomiasis declined from >19000 cases to <2400 and deaths from >4000 to 29. On four ranches in the region, tsetse have been almost eliminated and trypanosomiasis prophylaxis is no longer used. Similarly aggressive use of pyrethroids on Mkwaja Ranch in Tanga Region has not had such dramatic effects. Tsetse and trypanosomiasis are still common, despite high levels of prophylaxis and the deployment of approximately 200 odour-baited targets. The difference in the results is attributed to a combination of the much smaller area covered by treated animals at Mkwaja, a greater susceptibility to re-invasion and a more suitable habitat for the flies. A better understanding of the dynamics of the use of insecticide-treated cattle is needed before we can predict confidently the outcome of particular control operations.

Conflict of interest: use of pyrethroids and amidines against tsetse and ticks in zoonotic sleeping sickness endemic areas of Uganda

“…This shift in reservoir dynamics has presented an opportunity to integrate bovine and zoonotic trypanosomiasis control through mass cattle treatments and farmer-driven vector control. Trypanocidal drugs eliminate all bovine trypanosomes including the zoonotic pathogen Trypanosoma brucei rhodesiense from the animal, while application of synthetic pyrethroid-based acaricide (insecticides that kill insects and arachnids, including both ticks and tsetse) turn cattle into moving tsetse traps or ‘live bait’ [9,24-26]. Since tsetse preferentially feed on the legs and belly of cattle, synthetic pyrethroids at dip concentration can be applied to only these sites on the animal - the so-called ‘restricted application protocol’ or RAP.…”

Protection of confined cattle against biting and nuisance flies (Muscidae: Diptera) with insecticide-treated nets in the Ghanaian forest zone at Kumasi

“…Lower flanks, belly, and legs constitute the predilection sites for many hematophagous insects. In areas of high vector densities or particular host preferences, the impact of livestock treatments on vector populations and, hence, disease prevalence can be mediocre and ephemeral Hargrove et al 2000;Okiria et al 2002). Moreover, since treatments with pouron solutions are barely affordable and treatments with spray formulations prove cumbersome because of scarcity of water and lack of appropriate infrastructure, the farmers sometimes tend to substitute pyrethroid applications by more affordable control methods, like using old motor oil or household disinfectants, jeopardizing successful vector control (Hlatshwayo and Mbati 2005).…”

Is the Even Distribution of Insecticide-Treated Cattle Essential for Tsetse Control? Modelling the Impact of Baits in Heterogeneous Environments

“…Areas 0–12 km and 19–22 km from the front were poor habitat, with mortality being double the standard. Scenario W is roughly comparable to Mkwaja cattle ranch in Tanzania (5.8°S, 38.7°E), where the invasion source was a game park, from which an imaginary transect went first through mostly grassland, then through a wild wooded area where cattle seldom grazed, before going through grassland again and then onto the very poor habitat of sisal estates [15], [16].…”

“…Second, the control measures have not always been applied at the same time and intensity throughout the operational area, so that residual pockets of infestation remain, as in the early aerial spraying operations in Botswana [11] and some of the ground spraying in Zimbabwe [14]. The difficulty of even cover can be particularly serious when control is based on pyrethroid-treated cattle since the animals available for treatment are often distributed patchily, due to the animals' need for adequate grazing and water [15], [16]. This is unfortunate since the cattle treatment is by far the most economical method of control [3], [17].…”