Featured Research

from universities, journals, and other organizations

How mice survive infection by virulent Toxoplasma parasites

Date:
October 29, 2013
Source:
Instituto Gulbenkian de Ciência (IGC)
Summary:
One of the commonest parasites in the world is Toxoplasma gondii. Toxoplasma can infect most warm-blooded animals, including humans, and causes significant damage to the unborn child if a woman becomes infected for the first time during pregnancy. The natural cycle of the organism depends on cats and on mice. Infection by Toxoplasma normally doesn't kill the animal, but there are some "virulent" strains that kill mice only a few days after infection.

Laboratory mouse.
Credit: Roberto Keller, IGC

One of the most common parasites in the world is Toxoplasma gondii. Toxoplasma can infect most warm-blooded animals, including humans, and causes significant damage to the unborn child if a woman becomes infected for the first time during pregnancy. The natural cycle of the organism depends on cats and on mice. Infection by Toxoplasma normally doesn't kill the animal, but there are some "virulent" strains that kill mice only a few days after infection. Jonathan Howard, researcher at the Institute for Genetics, University of Cologne and at the Instituto Gulbenkian de Ciência, and his team have now found a mechanism that allows some mice to survive infection by the virulent strains. These findings offer an explanation for the evolution of parasitic strains with different levels of virulence.

The sexual reproduction of this parasite occurs only in cats and result in the release of enormous numbers of toxoplasma eggs in their feces. These get eaten by grazing animals such as sheep or chickens but also by small wild animals such as mice. Upon infecting these animals, the parasite normally settles down in cysts in brain and muscle and can wait for many months until another animal eats its host. When mice are eaten by a cat the toxoplasma completes its cycle. In the case of virulent strains of Toxoplasma, the outcome of the infection results in the rapid death of the mouse which can be bad for the parasite, because if the mouse dies from the infection before being eaten by a cat the parasite cannot complete its cycle and is eliminated. Virulent strains should therefore be at a disadvantage and die out. But the presence of these virulent strains in nature show that somehow there must be a mechanism to keep them.

The story depends on the balance that needs to be reached between the virulence of a parasite and the resistance of its host, if both parties are to survive. If the resistance is too weak, the host dies rapidly. When laboratory mice are infected with a non-virulent strain of Toxoplasma a group of proteins from the immune system of the mouse, the IRG proteins, disrupt the intracellular vesicles where parasites are located, killing most of them and saving the mouse's life. The surviving parasites become dormant as cysts in brain and muscle. Virulent parasites inactivate the IRG proteins of laboratory mice, which therefore die of the infection. Howard's team discovered that IRG proteins from many strains of wild mice differ from the laboratory strains, and cannot be inactivated by virulent strains. These wild mice are extremely resistant to virulent Toxoplasma strains. The high resistance of the mouse balances the high virulence of the parasite. As a result, the infected mice survive long enough for the parasites to make cysts and survive in a dormant state, allowing time for the mouse to be caught and eaten by a cat, and therefore for the parasite to be propagated.

Jonathan Howard explains these findings in the light of evolution: "We think there is probably a kind of arms race going on out there. Toxoplasma needs to infect mice efficiently because they are such good vectors to cats, but mice have exploited IRG proteins to create a resistance mechanism. The better the IRG resistance mechanism, the stronger the Toxoplasma virulence mechanism has to become. But why are not all mice as resistant as possible? We suspect that maintaining a highly resistant IRG system might be costly for the individual, though we do not know why. In fact, the IRG system has disappeared in several vertebrate groups perhaps because they are not important vectors for Toxoplasma. The maintenance of the highly developed IRG system in the mouse probably tells us that this species is an evolutionarily significant host for T. gondii."

The experimental work for this study was conducted at the Institute for Genetics, University of Cologne where Jonathan Howard has worked since 1994. In 2012 he became Director of the Instituto Gulbenkian de Ciência, where this research is continued. This research was funded by the Deutsche Forschungsgemeinschaft (Germany) and the International Graduate School in Development Health and Disease (University of Cologne, Germany).


Story Source:

The above story is based on materials provided by Instituto Gulbenkian de Ciência (IGC). Note: Materials may be edited for content and length.


Journal Reference:

  1. J. Lilue, U. B. Muller, T. Steinfeldt, J. C. Howard. Reciprocal virulence and resistance polymorphism in the relationship between Toxoplasma gondii and the house mouse. eLife, 2013; 2 (0): e01298 DOI: 10.7554/eLife.01298

Cite This Page:

Instituto Gulbenkian de Ciência (IGC). "How mice survive infection by virulent Toxoplasma parasites." ScienceDaily. ScienceDaily, 29 October 2013. <www.sciencedaily.com/releases/2013/10/131029171659.htm>.
Instituto Gulbenkian de Ciência (IGC). (2013, October 29). How mice survive infection by virulent Toxoplasma parasites. ScienceDaily. Retrieved September 23, 2014 from www.sciencedaily.com/releases/2013/10/131029171659.htm
Instituto Gulbenkian de Ciência (IGC). "How mice survive infection by virulent Toxoplasma parasites." ScienceDaily. www.sciencedaily.com/releases/2013/10/131029171659.htm (accessed September 23, 2014).

Share This



More Plants & Animals News

Tuesday, September 23, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Will Living Glue Be A Thing?

Will Living Glue Be A Thing?

Newsy (Sep. 23, 2014) — Using proteins derived from mussels, engineers at MIT have made a supersticky underwater adhesive. They're now looking to make "living glue." Video provided by Newsy
Powered by NewsLook.com
Raw: Tiger Kills Man at India Zoo

Raw: Tiger Kills Man at India Zoo

AP (Sep. 23, 2014) — A white tiger killed a young man who climbed over a fence at the New Delhi zoo and jumped into the animal's enclosure on Tuesday, a spokesman said. (Sept. 23) Video provided by AP
Powered by NewsLook.com
Cat Lovers Flock to Los Angeles

Cat Lovers Flock to Los Angeles

AFP (Sep. 22, 2014) — The best funny internet cat videos are honoured at LA's Feline Film Festival. Duration: 00:56 Video provided by AFP
Powered by NewsLook.com
Washed-Up 'Alien Hairballs' Are Actually Algae

Washed-Up 'Alien Hairballs' Are Actually Algae

Newsy (Sep. 22, 2014) — Green balls of algae washed up on Sydney, Australia's Dee Why Beach. Video provided by Newsy
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
 
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:  

Breaking News:

Strange & Offbeat Stories

 

Plants & Animals

Earth & Climate

Fossils & Ruins

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:  

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile iPhone Android Web
Follow Facebook Twitter Google+
Subscribe RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins