Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Researchers decipher cause of parasite’s worldwide spread

17.01.2003


Research at Washington University School of Medicine in St. Louis reveals that a unique combination of genes inherited less than 10,000 years ago allows the parasite responsible for toxoplasmosis to infect virtually all warm-blooded animals.



Parasite life cycles are complex and thought to develop over long periods with their hosts. This study reveals that parasites sometimes adapt rapidly to new hosts, indicating that host-parasite relationships may not always represent stable, long-term associations.

"Our findings raise the possibility that other parasites may also radically change their lifestyle by a similar mechanism and hence present new threats of infection" says study leader L. David Sibley, Ph.D., associate professor of molecular microbiology. The work is published in the Jan. 17 issue of the journal Science.


About 35 million people in the United States - and up to a quarter of the world’s population - are thought to be chronically infected with Toxoplasma. However, only people with weakened immunity typically develop severe toxoplasmosis, a potentially serious disease that can lead to birth defects, brain inflammation and vision problems. The infection usually is acquired by accidentally swallowing spores from contaminated soil, water, cat litter or objects that have had contact with cat feces. The infection also can be acquired from eating raw or partially cooked meat, especially chicken, pork, lamb or venison.

While eating infected meat easily spreads Toxoplasma from animal to animal, related parasites have highly restricted life cycles and require that a specific carnivore eat a specific herbivore for transmission to occur.

Toxoplasma also is unusual in that worldwide there are only three main strains, whereas related parasites typically have many distinct strains. Research has shown that the three strains are highly similar genetically and arose from a single mating event between two parent parasites. In the present study, members of Sibley’s laboratory, working closely with colleagues at Cambridge University and the University of Georgia, determined how long ago that mating event occurred. They first estimated the rate at which mutations arise in Toxoplasma. They then sequenced a select set of genes from the three strains to determine how many mutations were present. That data, along with estimates of the mutation rate, indicate that the three strains arose from a common ancestor no more than 10,000 years ago.

"That’s the blink of an eye in evolutionary time," says Sibley.

During that blink, however, the new strains managed to infect a wide range of animal species and spread worldwide, suggesting that they had undergone some fundamental change. To explain how that happened, Sibley and his colleagues hypothesized that the parasite’s life cycle had been altered, facilitating much more efficient spread.

The investigators compared the young strains to less common, older strains of Toxoplasma. They found that the young strains have a heightened ability to infect animals that have eaten the cysts that form in the meat of infected animals. Normally such tissue cysts are infectious only to a single species of animal, typically a carnivore that serves as the definitive host where sexual replication occurs. The ability of the young Toxoplasma strains to bypass this restriction allows them to infect many different hosts, where they again form cysts and reproduce asexually.

"Direct oral infectivity after eating tissue cysts is seen only in Toxoplasma and this trait is exemplified by these young strains," says Sibley. "This strongly suggests that the unique combination of genes passed along during that one mating event endowed the three young strains with an ability to more effectively spread throughout the food chain."

The findings demonstrate that changes in the infectiousness of parasites can occur not just through new mutations but also through a reshuffling of existing genes.

"This was a big surprise," says Sibley. "We have always appreciated that genetic recombination could cause subtle changes in an organism, but this is an extreme change: It produced a completely new lifestyle and removed a major barrier to infection."

Sibley and his colleagues now are studying genetic differences between the young and old strains of the parasite to learn more about how the newly derived strains can infect so many hosts.

"If one wanted to make a vaccine against this parasite, those genes and their products might be good ones to target," says Sibley.


###
Su C, Evans D, Cole RH, Kissinger JC, Ajioka JW, Sibley LD. Recent expansion of Toxoplasma through enhanced oral transmission. Science, Jan. 17, 2003.

Funding from the National Institute of Allergy and Infectious Diseases, the Biotechnology and Biological Sciences Research Council And the Burroughs Wellcome Fund supported this research.

Darrell E. Ward | EurekAlert!
Further information:
http://medinfo.wustl.edu/

More articles from Life Sciences:

nachricht Multi-institutional collaboration uncovers how molecular machines assemble
02.12.2016 | Salk Institute

nachricht Fertilized egg cells trigger and monitor loss of sperm’s epigenetic memory
02.12.2016 | IMBA - Institut für Molekulare Biotechnologie der Österreichischen Akademie der Wissenschaften GmbH

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Novel silicon etching technique crafts 3-D gradient refractive index micro-optics

A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.

Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...

Im Focus: Quantum Particles Form Droplets

In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.

“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...

Im Focus: MADMAX: Max Planck Institute for Physics takes up axion research

The Max Planck Institute for Physics (MPP) is opening up a new research field. A workshop from November 21 - 22, 2016 will mark the start of activities for an innovative axion experiment. Axions are still only purely hypothetical particles. Their detection could solve two fundamental problems in particle physics: What dark matter consists of and why it has not yet been possible to directly observe a CP violation for the strong interaction.

The “MADMAX” project is the MPP’s commitment to axion research. Axions are so far only a theoretical prediction and are difficult to detect: on the one hand,...

Im Focus: Molecules change shape when wet

Broadband rotational spectroscopy unravels structural reshaping of isolated molecules in the gas phase to accommodate water

In two recent publications in the Journal of Chemical Physics and in the Journal of Physical Chemistry Letters, researchers around Melanie Schnell from the Max...

Im Focus: Fraunhofer ISE Develops Highly Compact, High Frequency DC/DC Converter for Aviation

The efficiency of power electronic systems is not solely dependent on electrical efficiency but also on weight, for example, in mobile systems. When the weight of relevant components and devices in airplanes, for instance, is reduced, fuel savings can be achieved and correspondingly greenhouse gas emissions decreased. New materials and components based on gallium nitride (GaN) can help to reduce weight and increase the efficiency. With these new materials, power electronic switches can be operated at higher switching frequency, resulting in higher power density and lower material costs.

Researchers at the Fraunhofer Institute for Solar Energy Systems ISE together with partners have investigated how these materials can be used to make power...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

ICTM Conference 2017: Production technology for turbomachine manufacturing of the future

16.11.2016 | Event News

Innovation Day Laser Technology – Laser Additive Manufacturing

01.11.2016 | Event News

#IC2S2: When Social Science meets Computer Science - GESIS will host the IC2S2 conference 2017

14.10.2016 | Event News

 
Latest News

UTSA study describes new minimally invasive device to treat cancer and other illnesses

02.12.2016 | Medical Engineering

Plasma-zapping process could yield trans fat-free soybean oil product

02.12.2016 | Agricultural and Forestry Science

What do Netflix, Google and planetary systems have in common?

02.12.2016 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>