By Wanjohi Kabukuru – New research published by an international research team in Proceedings of the National Academy of Sciences (PNAS) and using a new and intensive combination of approaches has found two genes that may prove of vital importance to the lives and livelihoods of millions of farmers in a tsetse fly-plagued Africa.
ILRI estimates that the annual economic impact of “nagana,” (officially known as African animal trypanosomiasis), stands at US$4–5 billion.
The research which merged a range of high-tech tools and field observations, sought to find biological answers to protection from a single-celled trypanosome parasite that causes both African sleeping sickness in people and the wasting nagana disease in cattle.
Tsetse fly carries the trypanosomes parasites which cause both sleeping sickness in humans, and the similar disease, nagana in cattle. Trypanosomiasis is endemic in much of Africa. Both nagana and sleeping sickness are fatal without treatment and quick interventions. Alphonce Laveran won the 1907 Nobel Prize for medicine for outlining his strategies for controlling sleeping sickness and nagana. While many countries in the continent have put in place measures to combat tsetse flies the reservoir of parasites in wild populations of wildlife such as antelope and buffaloes is large, and the disease remains difficult to control.
It is estimated that courtesy of increased surveillance and control in the last 13 years (1998-2009) sleeping sickness in people has dropped from 300,000 to 30,000. In that duration it has killed more than half of those infected.
“The two genes discovered in this research could provide a way for cattle breeders to identify the animals that are best at resisting disease when infected with trypanosome parasites, which are transmitted to animals and people by the bite of infected tsetse flies,” said senior author Steve Kemp, a geneticist on joint appointment with the Nairobi-based International Livestock Research Institute (ILRI) and the University of Liverpool.
According to disease mapping scientists and economists at ILRI the tsetse fly belt across Africa, stretches from “Senegal on the west coast to Tanzania on the east coast, and from Chad in the north to Zimbabwe in the south. Annually the disease renders millions of cattle too weak to plow land or to haul loads, and too sickly to give milk or to breed, before finally killing off most of those infected. This means that in much of Africa, where tractors and commercial fertilizers are scarce and prohibitively expensive, cattle are largely unavailable for tilling and fertilizing croplands or for producing milk and meat for families. The tsetse fly and the disease it transmits are thus responsible for millions of farmers having to till their croplands by hand rather than by animal-drawn plow.”
This international research on the hereditary norms of disease resistance research brought together scientists from the Africa, Europe and Asia. It was led by scientists from the Nairobi-based ILRI , universities of Liverpool, Manchester and Edinburgh, and drew the input of researchers from other institutions in Britain, Ireland and South Korea.
For the first time the international team that made this breakthrough did so by amalgamating multiple ranges of genetic approaches. Hitherto this had been done in isolation and separately.
“This may be the first example of scientists bringing together different ways of getting to the bottom of the genetics of a very complex trait,” says Kemp. “Combined, the data were like a Venn diagram overlaying different sets of evidence. It was the overlap that interested us.”
The key informant of the research was a hump less West African breed called the N’Dama. Much of African cattle especially the Boran breed are susceptible to disease-causing trypanosome parasites. N’Dama, on the other hand is not seriously affected by the disease as it was domesticated in Africa some 8,000 or more years ago and as such has had time to evolve resistance to the parasites.
Even though the N’Dama is a valued asset in the continent’s endemic regions it is characteristically small in size and produces less milk. However its disease resistant attributes is what many farmers would want transmitted to more productive breeds. N’Dama disease resistant gene has been the ‘Holy Grail’ for international livestock geneticists for more than 20 years.
Genetic approaches to distinguish differences between the West African N’Dama, and Boran cattle, which come from Kenya, in East Africa were used at intervals to look for differences in those sequences between the two breeds. The Edinburgh team conducted gene expression analyses investigating differences in genetic activity of the two cattle breeds after sets of animals of both breeds were experimentally infected with the parasites. The ILRI group tested selected genes in the lab. Finally, they looked at the genetics of cattle populations from all over Africa.
“We believe the reason the N’Dama do not fall sick when infected with trypanosome parasites is that these animals, unlike others, have evolved ways to control the infection without mounting a runaway immune response that ends up damaging them,” said lead author Harry Noyes, of the University of Liverpool. “Many human infections trigger similarly self-destructive immune responses, and our observations may point to ways of reducing such damage in people as well as livestock.”
According to Kemp this new research which advances our understanding of genes that allow Africa’s N’Dama cattle to fight animal trypanosomiasis buttresses the importance of maintaining as many of Africa’s indigenous animal and breeds as possible.