Friday, September 23, 2005

Mycobacterium Tuberculosis and migrations out of Asia

The following two abstracts deal with the dispersal of Mycobacterium Tuberculosis out of eastern Asia to other parts of the world.

The second abstract is focused specifically on the demographic history of Madagascar.

Paul Kekai Manansala

Genome Res. 2005 Sep 16;

Origin and primary dispersal of the Mycobacterium tuberculosis Beijing genotype: Clues from human phylogeography.

Mokrousov I, Ly HM, Otten T, Lan NN, Vyshnevskyi B, Hoffner S, Narvskaya O.

Laboratory of Molecular Microbiology, St. Petersburg Pasteur Institute, St. Petersburg, 197101, Russia.

We suggest that the evolution of the population structure of microbial pathogens is influenced by that of modern humans. Consequently, the timing of hallmark changes in bacterial genomes within the last 100,000 yr may be attempted by comparison with relevant human migrations. Here, we used a lineage within Mycobacterium tuberculosis, a Beijing genotype, as a model and compared its phylogeography with human demography and Y chromosome-based phylogeography. We hypothesize that two key events shaped the early history of the Beijing genotype: (1) its Upper Palaeolithic origin in the Homo sapiens sapiens K-M9 cluster in Central Asia, and (2) primary Neolithic dispersal of the secondary Beijing NTF::IS6110 lineage by Proto-Sino-Tibetan farmers within east Asia (human O-M214/M122 haplogroup). The independent introductions of the Beijing strains from east Asia to northern Eurasia and South Africa were likely historically recent, whereas their differential dissemination within th! ese areas has been influenced by demographic and climatic factors.

Infect Genet Evol. 2005 Oct;5(4):340-8.

A study of spoligotyping-defined Mycobacterium tuberculosis clades in relation to the origin of peopling and the demographic history in Madagascar.

Ferdinand S, Sola C, Chanteau S, Ramarokoto H, Rasolonavalona T, Rasolofo-Razanamparany V, Rastogi N.

Unite de la Tuberculose and des Mycobacteries, Institut Pasteur de Guadeloupe, Morne Joliviere, BP 484, Pointe-a-Pitre Cedex, F97165 Guadelouge, France.

Despite well-developed tuberculosis (TB) control policies in Madagascar, the incidence of TB remains high and is estimated at about 100 new cases per 100000 inhabitants. This paper describes genetic characteristics of TB bacilli in Madagascar. Using an international spoligotyping database, SpolDB4, we also attempted to identify the origin of strains circulating in Madagascar. DNA polymorphism of 333 Mycobacterium tuberculosis complex isolates was assessed. A total of 301 isolates belonging to 60 spoligotyping-defined clusters were found, whereas 32 isolates harbored orphan patterns. By comparison with the international database, we identified a new genetic group of closely genetically related M. tuberculosis strains which we suggested to be specific from Madagascar. Most of them belonging to the East-African-Indian (EAI) superfamily of strains that are responsible for 14% of total TB cases (shared types ST1514-1525). These strains are closely related to the most prevalen! t shared type ST109, whose distribution is mainly confined to Madagascar. The observed distribution of genotypes shows that principal genetic group 1 strains (EAI, Beijing, CAS, Afri, "Manu") is high (35.4%) suggesting an ancient evolutionary history of tuberculosis in Madagascar, in relation to the origin of peopling and the demographic history.