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ILRI’s Philip Toye VOA interview on East Coast fever, and the benefits of co-parasitic infections

Typical mixed crop-livestock farming of western Kenya

ILRI-Wellcome projects have investigated the disease pathogens circulating in both people and animals in the communities outside the border town of Busia, Kenya, where smallholders mix crop growing with livestock raising (photo credit: ILRI/Pye-Smith).

Voice of America’s Joe DeCapua interview Phil Toye, a scientist with the International Livestock Research Institute (ILRI), about a paper published this week in Science Advance.

‘East Coast fever kills one cow every 30 seconds in Africa, causing 300 million dollars in annual losses. But a new discovery could lead to an effective and much cheaper way to prevent the disease by pitting one form of parasite against another.

Listen to VOA’s De Capua and ILRI’s Phil Toye report on new East Coast fever research.

‘Philip Toye said, “East Coast fever is a major burden for millions of poor people in Africa whose existence depends on healthy cattle.”

‘It’s restricted to east, central and southern Africa. And in those countries it’s the most important constraint to livestock productivity. It affects particularly the better breeds of cattle. It’s a lethal disease. It can kill up to 90-95 percent of a susceptible herd. And death usually occurs in about two to three weeks.’—Phil Toye

‘Toye, a principal scientist at ILRI, the Nairobi-based International Livestock Research Institute, said the parasitic disease is spread by ticks and has “devastating consequences if not controlled.”

‘He said, “The means of control at the moment – pesticides – just to reduce the tick burden – is expensive and it requires continual application. And, of course, there are also environmental effects there.”

‘Currently, cattle can be inoculated against East Coast fever. It’s been shown to reduce calf mortality in some areas from about 50 percent to less than three percent.

‘Toye said,”There is a vaccine available, which involves inoculating essentially the live parasite, but at the same time giving a long-acting antibiotic, which means the animal experiences the infection, but not the disease to any great extent. But they do develop a very strong immunity to the disease. So, it’s a very effective vaccine. It’s very safe when administered correctly, but it’s complex to produce and it is expensive.” . . .

‘The potential new prevention method is based on a study of co-infections done in Western Kenya. . . .

‘They discovered that the co-existence of parasites in calves appears to be a good thing in the East Coast fever zone.

‘“The most important pathogen out in that area is Theileria parva, which causes East Coast Fever. If calves were infected at the same time as they got Theileria parva with a related organism called Theileria mutans or Theileria valifera – these so-called low pathogenic Theileria – then the odds of their dying of East Coast fever was significantly reduced. And that’s the basis of the paper, which is being published,” he said. . . .

‘Some speculate the findings could be applied to other parasitic diseases, including malaria. Two parasites cause malaria, but one – Plasmodium falciparum – is much more deadly than the other – Plasmodium vivax. A 1996 study suggests that people in the South Pacific, who have a genetic mutation making them susceptible to the less deadly parasite, may be protected against Plasmodium falciparum.’

Read the whole article, and listen to the interview by Joe DeCapua on Voice of America: Co-infections may protect cattle,  20 Mar 2015.

Read the news release about this publication on the ILRI News Blog: Fighting fire with fire: New study shows co-parasitic infections of cattle protect the animals from lethal disease, 21 Mar 2015.

Read the paper in Science Advances: African parasite that spreads poverty by killing cattle tamed by its less lethal cousins, 20 Mar 2015.

Many individual hosts are infected with multiple parasite species, and this may increase or decrease the pathogenicity of the infections. This phenomenon is termed heterologous reactivity and is potentially an important determinant of both patterns of morbidity and mortality and of the impact of disease control measures at the population level. Using infections with Theileria parva (a tick-borne protozoan, related to Plasmodium) in indigenous African cattle [where it causes East Coast fever (ECF)] as a model system,we obtain the first quantitative estimate of the effects of heterologous reactivity for any parasitic disease. In individual calves, concurrent co-infection with less pathogenic species of Theileria resulted in an 89% reduction in mortality associated with T. parva infection. Across our study population, this corresponds to a net reduction in mortality due to ECF of greater than 40%. Using a mathematical model, we demonstrate that this degree of heterologous protection provides a unifying explanation for apparently disparate epidemiological patterns: variable disease-induced mortality rates, age-mortality profiles, weak correlations between the incidence of infection and disease (known as endemic stability), and poor efficacy of interventions that reduce exposure to multiple parasite species. These findings can be generalized to many other infectious diseases, including human malaria, and illustrate how co-infections can play a key role in determining population-level patterns of morbidity and mortality due to parasite infections.

Researchers from the Universities of Edinburgh, Glasgow, Pretoria and Nottingham, the Roslin Institute and ILRI contributed to the study, which was funded by the Wellcome Trust.

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