Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

A genetic identity card for Plasmodium populations to improve control strategies

09.11.2007
WHO figures show that malaria currently affects between 300 and 600 million people in various parts of the world. Several malaria-hit regions are experiencing an advance of the disease owing to the parasite’s increasing resistance to most antimalarial drugs.

Any increase in efficacy of medical treatments, with optimal limitation of resistance, requires that scientists unravel the evolutionary strategies of the enemy they are fighting. One of the research leads involves prior determination of the population genetic structure of Plasmodium falciparum.

This work was recently accomplished by a joint team of researchers from the IRD and the CNRS (2). Dissections were conducted on over 10 000 mosquitoes of the species Anopheles gambiae and Anopheles funestus, two of the principal malaria vectors in Sub-Saharan Africa. The work was done simultaneously on two sites in Cameroon and one Kenyan site, all three strongly infected by malaria. This large-scale investigation resulted in the isolation of 746 Plasmodium falciparum oocysts from the gut of 183 infected mosquitoes.

Two years previously, a preliminary study carried out in Kenya by the same team solely on A. gambiae, had yielded 600 oocysts from 145 infected mosquitoes caught in 11 different localities. The oocyst of the parasite provided the researchers with a means of access to the diploid phase of the microorganism, containing all its genetic information. Up to then, nearly all studies aiming to determine the genetic structure of Plasmodium populations were elaborated with parasite samples taken from humans. However, that kind of genetic analysis results in several points of bias. With samples collected from humans, scientists can work only on the haploid phase of the parasite cycle during which only one example of each chromosome is present.

Therefore they cannot measure the rate of association and organization between genes within populations. Moreover, in the zones where malaria is endemic, infected individuals are bitten regularly by mosquito vectors. Consequently, there is a high frequency of infection of one subject by several Plasmodium falciparum with different genotypes. Monoinfected patients, the only ones that can be selected for a pertinent genetic analysis, are therefore too rare to enable scientists to obtain representative results.

Assays on short sequences of DNA located on the 14 chromosome pairs of the parasite genome enabled the IRD and CNRS team to draw up quite a detailed genetic identity card of the different populations studied. They revealed an extremely high rate of genetic diversity but also a considerable overall rate of inbreeding, approaching 50%. This high level of inbreeding can be explained by the existence of a process of self-fertilization, selfing (3), combined with a non-random genotypic distribution of parasite oocysts in the mosquito vector guts. The set of data corroborated those acquired in Kenya in 2005.

They confirmed the persistence of a strong population genetic structure of Plasmodium between mosquito vectors, associated with a reproduction regime combining genetic mixing and selfing. A genetic identity card of Plasmodium falciparum populations could help improve malaria control strategies. The use of mathematical models that take into account genetic information about parasite infection foci could then feasibly predict the changes occurring in genes involved in drug resistance. Therapies could then be targeted according to the evolution dynamics of Plasmodium populations with the aim of controlling parasite populations while minimizing resistance development.

This study also proved that the parasite’s overall reproduction strategy is the same in the two vector species investigated. One of the approaches envisaged by the international scientific community for limiting morbidity from malaria would entail the progressive eradication of its principal vector Anopheles gambiae. To achieve this some research teams envisage the introduction into the wild of mosquitoes modified genetically to render them incapable of transmitting the parasite to humans. However, seeing that Plasmodium can use a number of different vectors, neutralizing just one, albeit one of the most dangerous, runs the risk of weakening only slightly the efficiency of the parasite’s reproduction strategy which could then merely switch to the other available vectors.

Grégory Fléchet - DIC

(1) Plasmodium’s life-cycle is set off as soon as a female Anopheles mosquito containing a form of the parasite called the sporozoite in its salivary glands bites a human. Once in the blood circulation, some of these parasites can develop into a sexually predetermined form: the male and female gametocytes. The mosquito ingests these gametocytes when it takes a second blood meal. They then migrate into its digestive tube where they give rise to male and female gametes. A process of fertilization ensues which produces the oocyst.

(2) This research programme was conducted with the aid of the Kenya Medical Research Institute, the ‘Organisation de control contre les endémies en Africa Centrale’, the French Ministry of Higher Education and Research and the Institute of evolution and the University of California.

(3) Self-fertilization, or selfing, results from the fusion of a female gamete and a male gamete originating from one and the same parasite genotype and therefore from the same individual.

Grégory Fléchet | alfa
Further information:
http://www.ird.fr/fr/actualites/fiches/2007/fas276.pdf

More articles from Health and Medicine:

nachricht Study points to new drug target in fight against cancer
19.09.2019 | Rice University

nachricht Researchers develop tumour growth roadmap
19.09.2019 | Universität Leipzig

All articles from Health and Medicine >>>

The most recent press releases about innovation >>>

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

Im Focus: 'Nanochains' could increase battery capacity, cut charging time

How long the battery of your phone or computer lasts depends on how many lithium ions can be stored in the battery's negative electrode material. If the battery runs out of these ions, it can't generate an electrical current to run a device and ultimately fails.

Materials with a higher lithium ion storage capacity are either too heavy or the wrong shape to replace graphite, the electrode material currently used in...

Im Focus: Stevens team closes in on 'holy grail' of room temperature quantum computing chips

Photons interact on chip-based system with unprecedented efficiency

To process information, photons must interact. However, these tiny packets of light want nothing to do with each other, each passing by without altering the...

Im Focus: Happy hour for time-resolved crystallography

Researchers from the Department of Atomically Resolved Dynamics of the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) at the Center for Free-Electron Laser Science in Hamburg, the University of Hamburg and the European Molecular Biology Laboratory (EMBL) outstation in the city have developed a new method to watch biomolecules at work. This method dramatically simplifies starting enzymatic reactions by mixing a cocktail of small amounts of liquids with protein crystals. Determination of the protein structures at different times after mixing can be assembled into a time-lapse sequence that shows the molecular foundations of biology.

The functions of biomolecules are determined by their motions and structural changes. Yet it is a formidable challenge to understand these dynamic motions.

Im Focus: Modular OLED light strips

At the International Symposium on Automotive Lighting 2019 (ISAL) in Darmstadt from September 23 to 25, 2019, the Fraunhofer Institute for Organic Electronics, Electron Beam and Plasma Technology FEP, a provider of research and development services in the field of organic electronics, will present OLED light strips of any length with additional functionalities for the first time at booth no. 37.

Almost everyone is familiar with light strips for interior design. LED strips are available by the metre in DIY stores around the corner and are just as often...

Im Focus: Tomorrow´s coolants of choice

Scientists assess the potential of magnetic-cooling materials

Later during this century, around 2060, a paradigm shift in global energy consumption is expected: we will spend more energy for cooling than for heating....

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Optical Technologies: International Symposium „Future Optics“ in Hannover

19.09.2019 | Event News

Society 5.0: putting humans at the heart of digitalisation

10.09.2019 | Event News

Interspeech 2019 conference: Alexa and Siri in Graz

04.09.2019 | Event News

 
Latest News

On the trail of self-healing processes: Bayreuth biochemists reveal insights into extraordinary regenerative ability

23.09.2019 | Life Sciences

New method for the measurement of nano-structured light fields

23.09.2019 | Life Sciences

Clarification of a new synthesis mechanism of semiconductor atomic sheet

23.09.2019 | Materials Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>