EVOLUTION OF PATHOGENS
by Acad. Vladimir SERGIEV, Director of the Ye. I. Martsinovsky Institute of Medical Parasitology and Tropical Medicine, I. M. Sechenov Moscow Medical Academy, Russian Academy of Medical Sciences (RAMS)
Last year, in 2006, our magazine told you about the selective effect of microorganisms on the evolution of the human genome, and about the impact of pathogens - viruses and bacteria - on the destinies of nations and civilizations. But what about changes in the pathogenic agents themselves? How do they survive in spite of the constant struggle waged against them?
ORIGINATION OF CLONES
Today we have clearly traced the formative course of certain pathogenic agents responsible for mass diseases of man. In many instances the causes of such diseases can be blamed on his social activities. Like, for example, the renaissance of the ТВ bacterium Mycobacterium tuberculosis.
Primarily soil mycobacteria became obligate parasites in the intestine of animals and birds and, consequently, came to be transmitted by the fecal-oral mode among populations of warm-blooded animals and fowl. Man, the Homo sapiens, came in touch with this pathogen about 5 thousand years ago in the process of domestication of cattle, sheep and goats. Consuming milk, Caucasoids developed an ability of lactolysis - that is to digest milk and milk products by means of corresponding enzymes - not only in childhood but also in adult years (unlike representatives of the other races losing this ability in puberty). Indirectly this factor contributed to the emergence of a human-adapted pathogenic species, as seen in the high affinity of DNA contained in the human and bovine types as well as in the fact that from among other ТВ mycobacteria (not counting in M. tuberculosis), man is susceptible only to the bovine pathogen, M. bovis.
Parasitizing in man, the originally animal pathogen mutated and acquired specific characteristics to become what is now kn ... Read more