Bill & Melinda Gates Foundation

Parasite Page-Turner: Africa’s Battle with a Cattle Killer Takes New, Unexpected Turns

February 03, 2014

An unusual story is unfolding in Africa, where the battle against a cattle-killing disease called East Coast fever is quickly becoming a cliff-hanger.

It’s the story of a tick-borne parasite that first appeared in southern Africa with diseased cattle imported from the east coast of Africa at the turn of the 20th century. It now kills a million or more cattle a year in Africa and causes annual losses of more than $300 million. But it has other compelling plot lines.
 
 In wealthy countries, this kind of livestock threat would be a major problem. In countries like Kenya, South Sudan, Tanzania, Uganda, and Zambia, East Coast fever is more often a tragedy because, for millions of Africans, cattle are still the central family asset.It’s a story about hunger and poverty and the central role of livestock in the diets, economies and cultures of developing countries. And it’s a story about a creative group of scientists waging a decades-long battle against East Coast fever and coming up with novel solutions, like a vaccine made of ground-up infected ticks. 

The latest installment is just now being written. So far, it involves many of these same scientists launching a consortium last week at my institute, in Nairobi, Kenya, funded by the Bill & Melinda Gates Foundation. This consortium is devoted to making a new and better vaccine for the disease, one that involves a compelling plot twist, as it could link the fate of poor livestock keepers in Africa to that of cancer and malaria victims the world over.

The central protagonist in this drama is a single-celled parasite called Theileria parva that’s carried by a common tick and now threatens the lives of tens of millions of cattle in Africa, with the more productive breeds proving particularly vulnerable. The parasites, injected into cows via a tick bite, quickly penetrate the animals’ white blood cells and cause them to divide uncontrollably. Most infected animals succumb to the cancer-like disease within three to four weeks.

In wealthy countries, this kind of livestock threat would be a major problem. In countries like Kenya, South Sudan, Tanzania, Uganda, and Zambia, East Coast fever is more often a tragedy because, for millions of Africans, cattle are still the central family asset.
 
 Trade, lending and bequeathing of cattle remains culturally vital in many communities, essential for marriage and funerals, and helping people recover from drought and other shocks.A cow’s daily milk and occasional meat can provide most of the protein and micronutrients a poor family needs to stay healthy. Bovine muscle pulls ploughs where no tractors exist. Cattle manure fertilizes croplands where commercial fertilizers are out of reach. And the trade, lending and bequeathing of cattle remains culturally vital in many communities, essential for marriage and funerals, and helping people recover from drought and other shocks.

Knowing that for many Africans the loss of even a single cow can be devastating, an international group of livestock scientists have worked for years to defeat East Coast fever. Their biggest breakthrough occurred decades ago when scientists at the East African Veterinary Research Organization (now the Kenya Agricultural Research Institute) successfully made a vaccine by cultivating and then grinding up ticks infected with the East Coast fever parasite. This first-generation vaccine prevents severe infections and is estimated to have saved some 620,000 cows from untimely death.

But as welcome as this vaccine is, it remains expensive for African herders and smallholder farmers. It requires constant refrigeration and trained personal to deliver and is difficult to make (taking more than a year to produce a single batch).

Members of the new consortium are now pursuing a second-generation vaccine that is cheaper, safer and easier to use. Success, however, is going to require working at the frontiers of vaccine science.
 
 This novel approach has the attention of both malaria and cancer researchers. If it protects animals from disease, malaria researchers could use the information generated in similar “one-two punch” vaccines under development for malaria.Their goal is to produce a vaccine that, like most human or animal vaccines, stimulates production of antibodies, which will kill any parasites in the cow’s bloodstream. The twist is that these scientists are also aiming for something much harder: a vaccine that simultaneously provokes production of “killer cells” that will target and destroy the cow’s parasite-infected white blood cells, which are invisible to the antibodies.

This novel approach, made possible by very recent advances in genomics and the biological sciences, has the attention of both malaria and cancer researchers. If it protects animals from disease, malaria researchers could use the information generated in similar “one-two punch” vaccines under development for malaria. And cancer researchers could accelerate their efforts to enlist these same killer cells to eliminate cancerous cells in human patients.

Clearly, a lot is riding on the outcome of this story—particularly as the narrative now involves conflict-ridden South Sudan, where the disease is now endemic and threatens to spread to the troubled Central African Republic to the west and the great cattle-keeping communities of Ethiopia to the east. As work on the new vaccine gets under way, many are hoping the scientists manage to provide a happy ending.

 
  • Tags Livestock, Vaccines
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