http://www.digitaljournal.com/science/from-jungle-to-city-the-move-affects-the-immune-system/article/457696

From jungle to city, the move affects the immune system

Posted Feb 16, 2016 by Tim Sandle
The move from living in rural settings to cities altered human exposure to certain microorganisms. In turn this residential shift appears to have impacted upon immune function.
Scenery at York
Scenery at York
Overtime, as human society became urbanized, this increased the range of human-associated microorganisms people became exposed to. At the same time, the population of outdoor, environmental microorganisms that people come across has decreased. New research suggests the interplay, over many years, between environmental exposure to microorganisms has affected how the immune system has developed and how it is passed through generations.
This change also brings with it a higher risk of "modern diseases," the researchers argue in their study report. The types of environmental bacteria seen in homes today probably contribute to various immune and metabolic disorders, including asthma to obesity. It should be noted that such diseases require a balance of social, environmental and biological factors to come together.
The finding is based on analysis of the microbiome (the totality of microorganisms and their genetic interactions within a given niche) of people who live in U.S., Puerto Rico, Brazil, and Peru. In Brazil and Peru, the people lived in villages and small towns.
The researchers also examined the types of bacteria found on walls and floors in each of the dwellings, from the urban high rises in the U.S. to a small Peruvian village. They found noticeable differences. For instance, human related bacteria were found in small towns and cities, whereas bacteria associated with outdoors, such as soil organisms, were found in the villages and rural settings.
It was also of interest that the researchers found higher levels of bacteria associated with the human mouth and gut in bathrooms and bacteria associated with food in kitchens.
The study authors did not make any direct connection between the microbial profile and disease, or alterations over time. Much of this is implied, although it does support research around the hygiene hypothesis. To make direct medical links, other researchers will need to examine these associations further.
The research was carried out by the NYU Langone Medical Center. The research has been published in the journal Science Advances, in a paper titled “Walls talk: Microbial biogeography of homes spanning urbanization.”