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The objective of this study was to assess the effect of an insecticide-treated net on the density of insects of veterinary and medical importance (Dipterids) inside and in the surroundings of zero-grazing cattle enclosures by measuring fly and mosquito densities through three different trapping methods. The effect of the insecticide-treated net fence on anophelines was also investigated because of their role as malaria vectors
As experimental setup, four similar sites were chosen for the construction of four pens. These were built approximately half a kilometer from each other and were all near a small water course surrounded by dense vegetation. Six black zebu bulls of comparable size were chosen as experimental animals and remained within the pens throughout the trial. Pens were denominated as A, B, C and D; pen A served as the negative control pen with no animals and no netting; pen B with two zebu bulls was surrounded by an untreated net (100 cm height); pen C with two animals had no netting, and pen D also with two animals was protected by a deltamethrin impregnated net (100 cm height). The trial was performed for six weeks during the months of October and November 2005. For the entomological monitoring three insect catching methods were applied: mono-conical traps, odor-baited traps (BG-SentinelTM Trap) and human landing catch (HLC) with volunteer human baits in order to determine the mosquito biting rates. The caught insects were then counted and identified. Anopheline mosquitoes were dissected to assess parity. Serological identification of malaria infected mosquitoes was conducted by the KCCR through ELISA and sporozoite rates were determined. In addition, monthly biting rates (MBR) and entomological inoculation rates (EIR) were calculated. The annoyance caused by biting and nuisance flies was monitored twice weekly by digital photos of selected animal body regions and thirty-second video recordings of each animal. Weekly means of counted flies and recorded defensive movements were calculated per animal.
In and around pen D (treated net) the results showed a consistently low catch of insects with all catching methods, as well as a considerable reduction (70-80%) of nuisance and animal disturbance. Animals appeared calmer and displayed an undisturbed fodder intake whereas in other pens the nuisance and biting flies created significant annoyance. Most mosquitoes caught with the HLC method were caught in pen B (untreated net) demonstrating that an untreated net provides no protection. Many mosquitoes were caught with the HLC method in pen A (negative control), possibly due to the absence of animals as alternative host to divert the insects from the human catcher. It is acknowledged that animals can be protective against malaria – a circumstance commonly known as zooprophylaxis. The BG SentinelTM trap (without black light) caught distinctly fewer mosquitoes than the HLC method and was considered unsuitable for catching anophelines. However, it proved to be valuable for catching biting midges (Ceratopogonidae) and sand flies (Phlebotominae). Analysis of malaria transmission parameters (MBR, SR, EIR) revealed slight differences among experimental pens.
Studies should be continued over a longer time period to determine if the use of insecticide-treated nets surrounding animal enclosures influences malaria transmission. Furthermore, the impact on weight gain and milk yield should be evaluated. Cost efficiency of using insecticide-treated net fences by African farmers must be estimated. Considerable benefits for livestock keepers both in intensive as well as in traditional farming systems (nomadic grazing economy) are likely to be obtained.