By Alfred Nyakinda
Wildlife resources, aside from attracting foreign exchange through tourism, also offer opportunities for combating diseases found in different parts of Africa.
This has been the case in the fight against African Animal Trypanosomiasis, also known as nagana, which continues to render large segments of fertile land on the continent unusable for livestock farming.
Control of tsetse flies which spread the disease causing pathogen has been found to be possible through the use of repellents derived from wild animals such as the waterbuck, with zebras also showing promise in this area.
“We found that the crude skin odor of zebra was effective in reducing field trap catches of savannah tsetse flies, like the known tsetse repellent, WRC (waterbuck repellent). Previous research has shown that zebras, although present in tsetse habitat, are usually avoided by these flies,” states a recent study by researchers from the International Centre of Insect Physiology and Ecology (icipe), and University of Pretoria, South Africa.
Repellent collars containing synthetic waterbuck blends, which have been developed by icipe, protect against tsetse and other biting flies, with the potential to reduce disease incidence by over 90 percent and enable farmers to raise livestock in tsetse infested areas.
According to icipe, reducing tsetse flies with synthetic insecticides over large areas is impossible. Furthermore the frequent dosage of animals with drugs has resulted in the disease-causing pathogen developing resistance, while the disease continues to be present in the environment through infected wildlife.
As a result, control of nagana is increasingly employing specific traits of the pest in developing control measures.
This includes using data from the genome sequencing of the fly, published in 2014, which has revealed new information and presented alternative approaches to controlling the pest.
Scientists now know that tsetse flies, unlike other insect disease vectors such as mosquitoes, have a reduced ability to respond to odours from plants as they exclusively feed on blood and have lost the receptors for sensing sugar, instead possessing an increased capacity for detecting carbon dioxide.
Using information gathered about the parasite, Icipe, whose scientists were involved in the genome sequencing of the tsetse fly, have developed different techniques for reducing its harmful impact.
These include the NGU series of traps, named after the Nguruman icipe field station in Kenya, which exploit the fly’s reliance on odour and visual cues to find hosts.
The traps attract the flies using their blue colour and odour baits, and black panel triggers a landing after which the odour further lures them into a plastic cage where the heat of the sun kills them.
This method alone, however, is not suitable for pastoralists as their nomadic lifestyle requires a mobile means of protecting their livestock from tsetse flies.
The collars and traps can be used together in a ‘push-pull’ system, given this name because the repellent pushes the flies away from the animals while the traps pull them into killing containers.
The results of adopting this system have included significant weight gains among cattle in affected areas, enabling farmers to make use of land previously rendered unfavourable for livestock,
In addition protected cows have been found to produce up to twice as much milk and protected bulls are able to plough as much as three times more land daily.
The study notes this preference of certain hosts extends to other parasites that feed on blood, with the anopheles mosquito avoiding chickens and the brown dog tick avoiding the beagle breed of dog, and adds that the skin odors of these animals are are being exploited for their potential to control the flies.
The new repellent developed from zebras, will contain fewer ingredients and could be produced at lower prices than the current waterbuck repellent, as well as having the potential to be longer lasting.
The researchers also mentioned that zebra stripes, which have been suggested to contribute to tsetse flies frequently avoiding them, would have a limited effect as they are only visible to the flies up to a distance of 5 to 10 metres. Beyond this, the zebras appear to be uniformly grey to the flies due to the limitation of their compound eyes.
Despite this, the authors suggest that new deterrent techniques using odour and visual elements in combination are worth exploring.