Scientists uncover secrets of parasite transmission in livestock


Scientists at the University of Liverpool and the Wellcome Trust Sanger Institute have furthered understanding of the transmission of two parasites that are responsible for millions of pounds of lost production to the UK farming industry.

Researchers at the University’s School of Veterinary Science and Institute of Infection and Global Health have uncovered regions of the genome of two closely related parasites of cattle and sheep that demonstrate how subtle variations in some genes have enabled these pathogens to adopt highly successful transmission strategies. The results are anticipated to lead to new approaches to control infection in livestock.

The discovery was made by studying the genomes of two closely related parasites, Toxoplasma gondii and Neospora caninum. These microscopic pathogens that live inside cells are important causes of disease in UK livestock, but one of them, called Toxoplasma, can also affect humans where infection can result in abortion or birth defects during pregnancy.

The research team discovered that despite the genetic material of the two parasites being very similar, there were a small number of changes in key genes that control how the parasite interacts with cells. In the case of Toxoplasma these differences appear to be associated with its ability to infect an extraordinarily wide range of animals, including humans. This is in contrast to Neospora, which cannot infect humans and is restricted mainly to cattle and other farm animals.

Professor Jonathan Wastling, project director at the University, said: “We were investigating these two parasites because they represent a big problem for the farming industry and in the case of Toxoplasma – for public health too. However, they are also genetically very closely related, but show very different features – such as human infectivity in the case of Toxoplasma.”

The research team also aimed to discover the mechanism by which Neospora can be transmitted from cow to calf during pregnancy as understanding this may help the development of new ways to prevent the disease spreading further in the UKs cattle population.

Dr Adam Reid, who led the genome analysis at Sanger, said: “The remarkable thing about the two genomes is just how similar they were – which made the job of hunting for the differences a little easier.”

The team then investigated how the absence of some of these genes alters the way the parasite interacts with the cells. The breakthrough came when the team discovered that the loss of one gene in particular in Neospora meant that the parasite could no longer suppress an important component of the host immune response making the parasite less virulent.

Professor Wastling said: “The fact that Neospora has lost key virulence factors might be thought of as a good thing because it should cause less disease. It appears, however, that it might be the loss of these genes that has resulted in Neospora becoming so well adapted to cattle and has developed the ability to be passed down the generations from cow to calf.”

Neospora causes abortion and birth defects in cattle and it represents the most important cause of infectious abortion in dairy cows, costing the UK farming industry millions of pounds a year.

Professor Sandy Trees, Emeritus Professor at Liverpool, said: “The reason why Neospora is such a difficult disease to deal with by farmers is that it can be passed silently down the generations and suddenly appears – causing widespread disease.”

It is hoped that this discovery will enable a more successful approach to vaccine design for both parasites and lead to better outcomes for both humans and animals.

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