warmwell.com is very grateful for the informed comment here (in italics) by Sabine Zentis
Reducing the chances of bluetongue infection
Livestock Technical | 10 October, 2007
WHILE the difficulty of keeping bluetongue midges away has been well publicised, Schering-Plough veterinary adviser Paul Williams has reiterated the fact that there are some steps farmers can take to reduce the chances of animals becoming infected.Products on the market in Germany (Pyrethroids and their derivates) have been tested in the lab and the pharmaceutical companies claim there is a proven (repellent and knock-down) effect on culicoides midges.But it has to be noted that the products have been tested by scientists paid for by the respective companies and not by independent labs so the outcome of this tests are, at least, biased.In addition, there are different members of the culicoides family suspected as competent vectors and so far it is not clear which culicoides have been used in the lab. There might be differences in the effect on the different culicoides. This trials haven't been done in the field so factors like rain, humidity and animal behaviour are not included.From our own experience the use of these products might have only a very small effect on vector attack rates.
He said some simple husbandry changes and practical midge control measures could help break the livestock infection cycle.
�It may be difficult on some farms, but you must try to reduce vector access to susceptible livestock.
�If you can house livestock during times of maximum midge activity � which is from dusk until dawn � you will significantly reduce biting rates and the potential likelihood of infection.So far vector surveys have been conducted using blacklight traps as it was assumed that the midges are active during the darker hours. Weather patterns during August/September indicate that some vectors must be active during daytime hours, especially when days are cloudy and overcast. It is known that vectors follow cattle and sheep inside so leaving animals outside i.e. in windy fields will reduce the risk of infection more than housing.
�In addition, protecting livestock housing openings with fine mesh netting or coarser material impregnated with insecticide may also help.�This will be a technical problem, how can animals and people enter buildings covered in mosquito nets ? In addition, the widespread use of insecticides will kill other insects as well, can pollute watercourses and from the US it is known that excessive use of Permethrine has led to selection of resistent sof insects.
He also said tackling potential midge breeding grounds and using pour-on insecticides approved for use on sheep and cattle could reduce the risk of infection to some degree.
�Midges that carry the virus usually breed on animal dung and moist soils, either bare or covered in short grass.Potential midge habitats are everywhere (this species has survived for millions of years ) so where to start ? The moment you have spread your muck heap the next generation of vectors might hatch in horse manure on the farm next door and as we can't prevent the rain from falling drying off all moist or wet patches on a farm is impossible. Some vectors are known to lay their eggs close to wooded areas into decomposing leaves, unless one plans to concrete the whole country this isolated measures won't have any influence on vector numbers.
�Turning off taps, mending leaks and filling in or draining damp areas will all help dry up breeding areas. And dung heaps and straw bedding should be removed at least weekly to break the immature midge breeding cycle,� he said.How is this to be done ? Farmers usually have a routine of working fields and using manure ,moving dung heaps around a farm every other week is not a feasible option.
�The Defra technical review on bluetongue maintains that targeted use of synthetic pyrethroids � such as deltamethrin � applied weekly in and around animal housing and directly onto the target animals should be effective as a practical disease defence strategy.�See above, from the experience in our region the use of these products only had a very minimal, if any effect on infections.The use of Ivermectin or Avermectine is an option to be considered. As a side effect, these chemicals are known to have a negative effect on dung beetles and organism so they might affect the survival rate of dung breeding midges as well. In addition, if animals are showing clinical signs treatment with one of the products will kill for at least 2 weeks midges biting the infected animal and thus might reduce transmission rates.The problem is the vast amount of culicoides, there are gazillions around and because of their numbers these measures don't work satisfactoraly
However, Mr Williams did stress the importance of consulting a vet first as use of insecticides in that way would be �off label� and meat withdrawal periods would need modification.My private view :The whole insecticide exercise gave people the feeling to do at least SOMETHING but the use as a means to prevent Bluetogue is questionable. We did it all from as early as April, pour on, ear clips containing deltamethrine, Ivermectine but with approx. 20% of animals clinically affected and an unknown number of subclinically infected animals I don't see this as a big success.It is a Don Quixote fight....
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