A study of the skeletons of 200 generations of humans has shown how pathogens adapt to reproduce. The research results are published by the journal PLOS ONE.
Ancient bacteria mutated to better infect ancient humans. At the same time, in an effort to infect as many new hosts as possible, bacteria have reduced their influence on humans. Scientists decided to explain why this is happening. In addition, associate professor of archeology Maciej Henneberg, Ph.D. Tegan Lucas of Flinders University and female Ph.D. Kara Holloway-Q of Deakin University analyzed data from 70,000 ancient skeletons to learn more about the spread of ancient diseases. Scientists have used bone marks as hallmarks of infection. The research results are published in PLOS ONE.
“Pathogens can kill or invade a human host without causing death. This ensures their survival, reproduction and distribution. Tuberculosis, treponematosis and leprosy are common chronic infectious diseases in which the host does not die immediately, ”explains Professor Henneberg, a renowned anthropologist.
Recall that treponematoses are non-venereal infectious diseases caused by spirochetes, bacteria indistinguishable from the pale spirochete (Treponema pallidum), which causes syphilis.
These are chronic infections such as endemic syphilis, yaws and pinta, which are found in specific geographic areas.
All three diseases – tuberculosis, treponematoses and leprosy – are considered prime examples of the co-evolution of pathogens and human hosts. They span over 200 generations.
The prevalence of each of these three diseases is decreasing as a result of joint adaptation. It is a mutually beneficial process for the disease and the human host. In the last 5,000 years, before the advent of modern medicine, signs of tuberculosis on skeletons have become less common, and the incidence of leprosy in bones in Europe has decreased since the end of the Middle Ages. At the same time, signs of infection with treponematoses in North America decreased, especially in recent years before contact with the invading Europeans.
Research shows whether microbes become more transmissible, but less deadly, over time so that they can continue to spread.
From an evolutionary point of view, it makes sense for a pathogen to cause less harm to the host on which its survival depends. This is why high transmission levels decrease over time. An illustrative example is the mass infections with leprosy, tuberculosis and syphilis in the past, scientists explain.