Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

A possible ancient origin for tuberculoses in Casablanca

23.11.2004


Each year tuberculosis kills about three million people in the world. In particular it is responsible for the death of more than one-third of HIV- infected people, who prove particularly susceptible owing to a decline in immune defences. The agent responsible is a bacterium of the species Mycobacterium tuberculosis, also termed Koch’s bacillus, after the scientist who discovered it in 1882.



Molecular epidemiology has proved valuable for understanding the transmission and control of tuberculosis, thanks to the development of different methods of characterization of the M. tuberculosis genome. However, little genetic data is currently available in the countries of the South, where this disease is often a major public health problem. In Morocco, tuberculosis incidence is still high, with about 30 000 new cases are recorded each year, in spite of a level of HIV infection that remains of quite low concern and the application since 1991 of a WHO strategy called DOTS (2). Researchers from the IRD and their scientific partners (1) studied the genetic diversity and structure of a Moroccan population consisting of 150 strains of the species M. tuberculosis. These strains come from 150 pulmonary tuberculosis infected subjects living in Casablanca, the country’s economic capital, which on its own accounts for one-fifth of all tuberculosis cases declared in Morocco.

Two independent and complementary molecular genotyping techniques were applied to the specimens collected. The first used generalist genetic markers which allow analysis of the genetic diversity of the population considered, but also comparison of the genetic diversity of the pathogenic species M. tuberculosis with that of other microorganisms. The second, which is the most recent technique used for characterizing the M. tuberculosis genome, calls on specific markers of this mycobacterium, adapted to the identification of the different strains isolated.


The statistical analyses performed on the basis of data obtained concerning the population studied shows that it has a clonal structure: its constituent strains behave and evolve overall like natural clones that are stable with time.

Moreover, analysis of the genetic profiles of the different strains revealed a large genetic diversity in the population (3). This result was unexpected, because the populations of M. tuberculosis coming from high-incidence countries, as in Morocco, generally show a low degree of polymorphism. The polymorphism that did occur was seen between the strains of one and the same district of the city of Casablanca, between strains collected the same year and often between those resulting from the same infected family. The population studied consequently consisted of many circulating clones.

The results taken overall suggest that there is an ancient origin of tuberculosis in Casablanca. No one genetic profile was numerically dominant. Therefore transmission of the disease would be effected by reactivation of pre-existing, latent, strains rather than by recent transmissions of novel strains. The fact that several genetically different strains can affect the members of a single family shows that contamination, in this context of high incidence, can also be exogenous, the disease being contracted outside the family home. Important pieces of information on the biological, clinical and epidemiological behaviour of this mycobacterium, especially in terms of identification and treatment of different sources of contamination, have thus been contributed.

No genetic study had previously been conducted in Morocco on M. tuberculosis populations. The work performed on the sample collected at Casablanca therefore provided the first indices for understanding tuberculosis transmission in this area. Such molecular epidemiology investigations, conducted in other towns and villages of Morocco, and in other countries where the disease is endemic, favour an overall approach to the transmission dynamics of tuberculosis. This is vital if effective control measures of this disease are to be deployed.

Marie Guillaume – DIC

(1) The joint CNRS-IRD research unit Génétique et Evolution des Maladies Infectieuses (Genetics and Evolution of Infectious Diseases) has worked in tandem with the INSERM Laboratory of Molecular Mechanisms of Bacterial Pathogenesis at the Lille Pasteur Institute. Sample collection and the epidemiological survey were conducted in conjunction with the Mycobacteria Department of the Morocco Pasteur Institute at Casablanca.

(2) DOTS: Directly observed Treatment Short-course. This strategy for tuberculosis control was implemented in Morocco in 1991, with the following main objectives: application of the standard short chemotherapy course (6 months) for all new microscopically positive cases of pulmonary tuberculosis; treatment of all the other forms of tuberculosis once the diagnosis established; maintenance of vaccination cover using BCG at over 90 % in newborns. These different objectives involve the permanent commitment of government authorities in tuberculosis control and the necessity for regular, consistent supply of high-quality medicines.

(3) Moreover, this diversity appears highly significant when compared with that of other species of microorganism (bacteria, yeasts, protozoans) that evolve on the same clonal model. M. tuberculosis has a greater genetic diversity than the 4 species of Leishmania tested (average values are 0.48 as against 0.14; 0.07; 0.19 and 0.14). The value obtained for M. tuberculosis (0.48) is close to that of Saccharomyces cerevisiae (0.42) and Candida albicans (0.51).

Marie Guillaume | alfa
Further information:
http://www.ird.fr

More articles from Health and Medicine:

nachricht GLUT5 fluorescent probe fingerprints cancer cells
20.04.2018 | Michigan Technological University

nachricht Scientists re-create brain neurons to study obesity and personalize treatment
20.04.2018 | Cedars-Sinai Medical Center

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: Molecules Brilliantly Illuminated

Physicists at the Laboratory for Attosecond Physics, which is jointly run by Ludwig-Maximilians-Universität and the Max Planck Institute of Quantum Optics, have developed a high-power laser system that generates ultrashort pulses of light covering a large share of the mid-infrared spectrum. The researchers envisage a wide range of applications for the technology – in the early diagnosis of cancer, for instance.

Molecules are the building blocks of life. Like all other organisms, we are made of them. They control our biorhythm, and they can also reflect our state of...

Im Focus: Spider silk key to new bone-fixing composite

University of Connecticut researchers have created a biodegradable composite made of silk fibers that can be used to repair broken load-bearing bones without the complications sometimes presented by other materials.

Repairing major load-bearing bones such as those in the leg can be a long and uncomfortable process.

Im Focus: Writing and deleting magnets with lasers

Study published in the journal ACS Applied Materials & Interfaces is the outcome of an international effort that included teams from Dresden and Berlin in Germany, and the US.

Scientists at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) together with colleagues from the Helmholtz-Zentrum Berlin (HZB) and the University of Virginia...

Im Focus: Gamma-ray flashes from plasma filaments

Novel highly efficient and brilliant gamma-ray source: Based on model calculations, physicists of the Max PIanck Institute for Nuclear Physics in Heidelberg propose a novel method for an efficient high-brilliance gamma-ray source. A giant collimated gamma-ray pulse is generated from the interaction of a dense ultra-relativistic electron beam with a thin solid conductor. Energetic gamma-rays are copiously produced as the electron beam splits into filaments while propagating across the conductor. The resulting gamma-ray energy and flux enable novel experiments in nuclear and fundamental physics.

The typical wavelength of light interacting with an object of the microcosm scales with the size of this object. For atoms, this ranges from visible light to...

Im Focus: Basel researchers succeed in cultivating cartilage from stem cells

Stable joint cartilage can be produced from adult stem cells originating from bone marrow. This is made possible by inducing specific molecular processes occurring during embryonic cartilage formation, as researchers from the University and University Hospital of Basel report in the scientific journal PNAS.

Certain mesenchymal stem/stromal cells from the bone marrow of adults are considered extremely promising for skeletal tissue regeneration. These adult stem...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Invitation to the upcoming "Current Topics in Bioinformatics: Big Data in Genomics and Medicine"

13.04.2018 | Event News

Unique scope of UV LED technologies and applications presented in Berlin: ICULTA-2018

12.04.2018 | Event News

IWOLIA: A conference bringing together German Industrie 4.0 and French Industrie du Futur

09.04.2018 | Event News

 
Latest News

Structured light and nanomaterials open new ways to tailor light at the nanoscale

23.04.2018 | Physics and Astronomy

On the shape of the 'petal' for the dissipation curve

23.04.2018 | Physics and Astronomy

Clean and Efficient – Fraunhofer ISE Presents Hydrogen Technologies at the HANNOVER MESSE 2018

23.04.2018 | Trade Fair News

VideoLinks
Science & Research
Overview of more VideoLinks >>>