Subtle differences can lead to major changes in parasites

Mar 22, 2012
Groups of genes which are different between the parasites and how they relate to particular parts of the cell. [DOI:10.1371/journal.ppat.1002567]

Researchers have found the subtle genetic differences that make one parasite far more virulent than its close relative.

They looked at the evolution of these parasites and found that although their genome architecture still remains similar, the two split from their 28 million years ago, approximately four times longer than the human-gorilla split.

is arguably the most successful parasite. It can spread to any cell type in any warm blooded . It can cause blindness and . Alternatively, the Neospora parasite can infect far fewer hosts. It is a veterinary pathogen and causes a high number of abortions in cattle, costing the UK farming industry millions of pounds a year. The parasites, though different, are closely related.

"The question we wanted to answer was; what causes this difference in between Toxoplasma and Neospora?" explains Dr Adam Reid, first author from the Wellcome Trust Sanger Institute. "We used genome sequencing to probe the parasites for differences that might underlie the way they spread and how they have diverged."

The team found that a gene that helps the Toxoplasma pathogen to evade the host's immune system and enter the cell, is missing from neospora. The lack of this single gene means Neospora cannot evade the in mice and may not be able to evade the immune response in other species. This could explain why Neospora has a more limited host range.

"Our results do not imply that Toxoplasma has in some way gained the gene, but that Neospora has actually lost the gene," says Professor Arnab Pain, senior author from the Wellcome Trust Sanger Institute. "We speculate that the loss of this gene in Neospora may be an adaptive change. Reducing Neospora's virulence may increase its chance of survival in the ."

The team also found that although the between the two parasites are minor, there is a significant difference in the number of surface proteins found in both parasites. Neospora has more surface proteins, nearly twice as many as Toxoplasma, but fewer are active. Although this is difficult to interpret, the researchers hypothesise that a larger number of proteins are needed to restrict the parasite's host range.

"We were investigating these two parasites because they represent a big problem for the and in the case of Toxoplasma – for public health too," says Professor Jonathan Wastling, senior author from the University of Liverpool.

"Collectively, our results indicate that the ecological niches occupied by both parasites are influenced by subtle, adaptive, genetic changes. This project is an excellent example of how humans and animal medicine can learn from each other to provide better outcomes for both"

The next step for the team is to examine the genomes of other parasites within the same family as Toxoplasma and Neospora to better characterise the function of the genes and surface proteins. By deciphering which of these surface proteins are involved in the cell invasion process, it may be possible to develop vaccines for both of these parasites

Explore further: Discovery of nanotubes offers new clues about cell-to-cell communication

More information: Reid et al 'Comparative genomics of the apicomplexan parasites Toxoplasma gondii and Neospora caninum: Coccidia differing in host range and transmission strategy' Published online in PLoS Pathogens, DOI:10.1371/journal.ppat.1002567

Related Stories

Protein helps parasite survive in host cells

Dec 29, 2010

Researchers at Washington University School of Medicine in St. Louis have learned why changes in a single gene, ROP18, contribute substantially to dangerous forms of the parasite Toxoplasma gondii. The an ...

'Promiscuous parasites' hijack host immune cells

Sep 20, 2011

Toxoplasma gondii parasites can invade your bloodstream, break into your brain and prompt behavioral changes from recklessness to neuroticism. These highly contagious protozoa infect more than half the wo ...

How Toxoplasma gondii gets noticed

Jan 19, 2009

Researchers provide insight into how Toxoplasma gondii, a common parasite of people and other animals, triggers an immune response in its host. The report will appear online on January 19th in The Journal of Experimental Medicine. ...

Do parasites evolve to exploit gender differences in hosts?

Feb 28, 2012

Some disease-causing parasites are known to favor one sex over the other in their host species, and such differences between the sexes have generally been attributed to differences in immune responses or behavior. But in ...

Recommended for you

Fin regenerative capability abates during aging

23 hours ago

Regenerative processes are the reason why wounds can heal and injured tissues can regrow. Some flatworms, salamanders and fishes even have the ability to completely rebuild whole bodily parts. In contrast, ...

Why human egg cells don't age well

Jul 01, 2015

When egg cells form with an incorrect number of chromosomes—a problem that increases with age—the result is usually a miscarriage or a genetic disease such as Down syndrome. Now, researchers at the RIKEN ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.