Exploring ancient tuberculosis transmission chains

Date:
March 10, 2022
Source:
Max Planck Institute for Evolutionary Anthropology
Summary:
Tuberculosis (TB) is the second most common cause of death worldwide
by an infectious pathogen (after Covid-19), but many aspects of
its long history with humans remain controversial. Researchers
found that ancient TB discovered in archaeological human remains
from South America is most closely related to a variant of TB
associated today with seals, but surprisingly these cases were
found in people who lived nowhere near the coast. This implies that
these cases were not the result of direct transmission from seals,
and instead one, or more, spillover events were likely to be the
primary drivers of human infection.



FULL STORY ========================================================================== Nearly one quarter of the world's population is suspected to have been
exposed to the bacterium responsible for tuberculosis, a disease that
accounts for the highest global mortality from a bacterial infection. TB's global distribution was once viewed as support for its emergence deep
in our past, where it was thought to have evolved in Africa tens of
thousands of years ago and became distributed throughout the world
following migrations with its host. Its ability to infect a number of
mammalian species also make it a highly adaptable pathogen.


========================================================================== Analyses of ancient TB genomes have stirred up controversy about when
this host-pathogen association began and precisely how TB became globally distributed. A 2014 study led by research teams at the University of
Tu"bingen and Arizona State University reported on three ancient TB
genomes from coastal Peru, which revealed aspects of its history that
were incompatible with prevailing assumptions on TB's origins.

First, rather than identifying one of the well-characterized
human-associated strains of the pathogen, the team identified a
comparatively rare strain that today infects mostly marine mammals such as seals and sea lions (pinnipeds). In addition, their data suggested that TB
was a much younger disease than previously thought, having emerged only sometime in the last 6000 years. "At the time, we assumed that TB made
its way from Africa to the Peruvian coast through travel with infected
seal populations," comments Kirsten Bos of the Max Planck Institute
for Evolutionary Anthropology who co-led the new study. "We assumed
the source of the infection in Peru had been a zoonosis from seals. It
was not clear, though, if the specific TB infection we identified in
the three people was a local phenomenon restricted to the area, or
whether its distribution was broader." TB is an infection well known
to specialists in bone lesions and pathology.

Paleopathologist Jane Buikstra of Arizona State University has extensively studied human skeletal remains across the Americas, and clear cases
of TB infection are easily identified across the continents in the
pre-contact period. "We've known for decades that a form of TB infection
was present in the western coast of South America through the study of
human remains. Now, with 21st century scientific advances, ancient DNA
is the best tool available to investigate the relationships between
the TB manifestations we observe osteologically in different parts of
the Americas." In a study published this week in Nature Communications,
the team reports on three new cases of pre-contact era South American TB,
this time from human remains that come from inland archaeological sites,
two of which are situated in the highlands of the Colombian Andes. All
three people were infected with the marine-associated strain of TB,
thus making a simple zoonosis from seals unlikely.

TB's entry into South America through human exposure to infected seals is
still the strongest hypothesis, but how TB was subsequently distributed
on land remains an open question. Lead authors AAshild Vaagene and Tanvi
Honap are confident that these new cases present strong evidence that
the TB variant currently found in seals was once able to travel long
distances on land. "The TB bacterium can infect numerous mammalian
species, so there are many candidates for its terrestrial dispersal,
including humans themselves," says Vaagene. "Vast trade networks may
have played an important role in transporting the pathogen from the
coast." Honap adds that "recovering ancient TB DNA in animal remains
from the pre-contact era Americas may one day allow us to explore the transmission chains responsible for bringing this marine variant so
far inland." Anne Stone of Arizona State University who specializes in
the evolutionary history of TB and co-led the current study, sees the new results as an opportunity for deeper exploration into the ecology of the disease in the Americas before the colonial period. "It's an exciting time
in ancient DNA research, as we can now look at genome-level differences in these ancient pathogens and track their movements across continents and
beyond. For TB, the open question is how widespread the seal-associated
strain was in human populations of the Americas prior to its replacement
by the more virulent strains that arrived with the Europeans."

========================================================================== Story Source: Materials provided by Max_Planck_Institute_for_Evolutionary_Anthropology. Note: Content may
be edited for style and length.


========================================================================== Journal Reference:
1. AAshild J. Vaagene, Tanvi P. Honap, Kelly M. Harkins, Michael S.

Rosenberg, Karen Giffin, Felipe Ca'rdenas-Arroyo, Laura Paloma
Leguizamo'n, Judith Arnett, Jane E. Buikstra, Alexander Herbig,
Johannes Krause, Anne C. Stone, Kirsten I. Bos. Geographically
dispersed zoonotic tuberculosis in pre-contact South American
human populations. Nature Communications, 2022; 13 (1) DOI:
10.1038/s41467-022-28562-8 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/03/220310115054.htm

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