Gene clues to African cattle disease

Scientists studying the tsetse fly-borne disease "sleeping sickness" and a devastating version found in cattle say they have found two genes that may in future help rescue the livelihoods of millions of farmers in Africa.

In a study in the Proceedings of the National Academy of Sciences (PNAS) journal, the researchers said the genes should help cattle breeders identify animals that can resist the disease, as well as shedding more light on the human form, "African sleeping sickness," caused by the same parasite.

The World Health Organisation estimates that around 30,000 Africans a year get sleeping sickness, although numbers have fallen sharply in the past decade due to better control measures. It is found in 36 sub-Saharan African nations and is caused by the trypanosome parasite which is transmitted by tsetse fly bites.

Although the parasite is best known for sleeping sickness, which in its advanced stages causes sleep disturbance and can be fatal if left untreated, experts say its highest toll in terms of human welfare is from sick, wasting cattle and farming productivity losses.

Huge economic impact

The annual economic impact of African animal trypanosomiasis, known locally as "nagana," a Zulu word meaning "to be depressed," has been estimated at $4 to $5 billion (about R28 billion – R35 billion).

"The two genes discovered in this research could provide a way for cattle breeders to identify the animals that are best at resisting disease," said Steve Kemp, a geneticist working on the study at both the Nairobi-based International Livestock Research Institute (ILRI) and the University of Liverpool.

The study was led by scientists from ILRI and from Britain's Liverpool, Manchester and Edinburgh universities, and also involved other researchers in Britain, Ireland and South Korea.

The researchers said they drew on the fact that while the humped cattle breeds characteristic of much of Africa are susceptible to disease-causing trypanosome parasites, a humpless West African breed called the N'Dama is not seriously affected.

Valuable animal

This makes N'Dama a valued animal in Africa's endemic regions, although the breed tends to be smaller, produce less milk, and be less docile than its bigger, humped cousins, they said.

The scientists used a range of genetic approaches, including analysing differences in genetic activity in the tissues of the two cattle breeds after animals were experimentally infected with the parasites. They also analysed the genetics of cattle populations from all over Africa.

The vast amounts of data collected were brought together with powerful new analytical tools.

"Combined, the data were like a Venn diagram overlaying different sets of evidence (and) it was the overlap that interested us," Kemp said in a statement about the work.

The scientists said that with this new knowledge, breeders could screen African cattle to find animals with more disease resistance and seek to combine this genetic trait with other important traits like high productivity and drought tolerance.

If further research confirms the significance of the genes in disease resistance, a breeding program could develop a small breeding herd of disease-resistant cattle in the next 10 to 15 years, the scientists said, and this could then be used over the next decades to breed animals for African regions.

Using genetic engineering to achieve the same disease-resistant breeding herd, an approach still in its early days, may be done in four or five years, Kemp said.

(Reuters Health, May 2011)

Read more:

Malaria, Cholera and parasites

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