August 21, 2014

Tuberculosis is 6,000 years old

... and sea mammals (not Europeans) introduced it to the New World.

Nature (2014) doi:10.1038/nature13591

Pre-Columbian mycobacterial genomes reveal seals as a source of New World human tuberculosis

Kirsten I. Bos et al.

Modern strains of Mycobacterium tuberculosis from the Americas are closely related to those from Europe, supporting the assumption that human tuberculosis was introduced post-contact1. This notion, however, is incompatible with archaeological evidence of pre-contact tuberculosis in the New World2. Comparative genomics of modern isolates suggests that M. tuberculosis attained its worldwide distribution following human dispersals out of Africa during the Pleistocene epoch3, although this has yet to be confirmed with ancient calibration points. Here we present three 1,000-year-old mycobacterial genomes from Peruvian human skeletons, revealing that a member of the M. tuberculosis complex caused human disease before contact. The ancient strains are distinct from known human-adapted forms and are most closely related to those adapted to seals and sea lions. Two independent dating approaches suggest a most recent common ancestor for the M. tuberculosis complex less than 6,000 years ago, which supports a Holocene dispersal of the disease. Our results implicate sea mammals as having played a role in transmitting the disease to humans across the ocean.



andrew said...

There are individuals with genetic affinities to Peru, Japan and NE Asia in 1000 year old Peruvian tombs. These individuals could have been pre-Columbian vectors of TB from Asia. If there is an affinity to seal varieties, this may have come from these formerly circumpolar area new arrivals who would likely have had major seal consumption in circumpolar areas rather than directly from seals.

AW said...

The phylogenetic tree in the paper clearly shows that the seal strain is derived from the Amerindians.
Also, the Amerindian strain is so different from that of other Old World H. sapiens strains that it is difficult to imagine that Africans passed it on to seals which then crossed the Atlantic, mutated the strain making it different to the original African one and then passed it on to Native Americans.
The most parsimonious explanation is that it evolved separately in America and then infected seals there.

ron quiroriano said...

Well, this paper has me somewhat puzzled, as a previous work shows that tb was widespread in north American bovine species during the late Pleistocene.

I am aware that infectious diseases jump species, but usually only among species that have close contact, such as pigs and pig farmers. They also can jump species when they share a natural intermediary vector like ticks or mosquitoes.
To me it seems the thing bovines and pinnepeds have in common is homo sapiens.
The habitats of these two divergent species never converge to the point that tb would naturally pass to pinnepeds from bovines, unless Hss was the vector.

saphorr said...

@ron quiroriano: the last paragraph of the paper does address the evidence of TB in older archaeological material.

Such caveats are of paramount importance considering the many investigations that report on members of the MTBC identified in skeletal samples that predate our inferred MRCA, or American material from periods that predate our proposed time of MTBC entry. Such claims could only be reconciled with what we propose here if (1) the rate heterogeneity or horizontal gene transfer is obscuring our dating analysis, perhaps as a result of human population expansions which increase the availability of susceptible hosts and allow selection to operate more quickly, (2) the pathogens identified in the earlier archaeological material are in fact not members of the MTBC, but rather are ancestral forms that have since undergone replacements, or (3) certain techniques for MTBC identification in archaeological material lack specificity.

ron quiroriano said...

@Saphorr, I was only able to read the abstract, thanks for posting that paragraph.
But it is ridiculous, "2) the pathogens identified in the earlier archaeological material are in fact not members of the MTBC, but rather are ancestral forms that have since undergone replacements, or (3) certain techniques for MTBC identification in archaeological material lack specificity."
So all of the well defined skeletal markers for identifying tb infections, such as those on the skeltons they sampled are wrong?. Their arguments just don't make sense, and as Austin pointed out in his reply the seal specific strain is downstream of the Peruvian human strain.

LivoniaG said...

In 2013, evidence of Tuberculosis was identified in a large percentage of human remains (up to +30%) from three LBK sites in modern Germany.

Tests were performed to confirm the presence of the MTBC pathogens. Even if those strains were "ancestral" the symptomatic consequences gave all the appearance of being the same.

Unless the disease identified in LBK completely disappeared, tuberculosis is not 6000 years old. All this time estimate suggests is that something is wrong with such time estimates.

“In this study, 118 individuals from three sites in Saxony-Anhalt (Germany) dating to the Linear Pottery Culture (5400-4800 BC) were examined macroscopically to identify TB related bone lesions...

Rib lesions, however, are not specific indicators of TB as they can also be caused by other diseases; so additional investigations were undertaken using histology and micro-CT scans to say more about the disease process.

Supplementary molecular analyses indicate the presence of pathogens belonging to the Mycobacterium tuberculosis complex in individuals of all sites."

Nicklisch N, Maixner F, et al., Rib lesions in skeletons from early neolithic sites in Central Germany: on the trail of tuberculosis at the onset of agriculture.