A post-Thanksgiving story of leptospirosis

I'm about half way through 1491, a book that gives readers a view of the Americas before Columbus showed up.  It also describes the devastating impact that foreign infectious diseases had on the native population as Europeans explored the New World.

One chapter tells the story of Tisquantum (Squanto), who lived in the village of Patuxet, one of the many Indian communities thriving along the coast of New England at the time.  In 1614 Thomas Hunt, a British slave trader, kidnapped Tisquantum and other Indians and shipped them to Spain.  Fortunately, Tisquantum was rescued by Spanish priests before he could be sold.  After convincing the priests to let him return home, he left for London, where he learned English while staying at a shipbuilder's home, and eventually made his way back to North America.  As he sailed down the New England shoreline in 1619 on a British ship, he realized that the world familiar to him had vanished.  A mysterious disease had wiped out 90% of the population of coastal New England.  When he arrived at his home village of Patuxet, he found it deserted.  Tisquantum was soon captured and sent to Massasoit, the leader of the Wampanoag confederacy, which encompassed Patuxet.  Massasoit did not trust Tisquantum because of his recent association with the British, yet he would later use him as a translator in a negotiation that turned out to be a pivotal event in American history.

The epidemic had been blamed at one time or another on smallpox, the plague, yellow fever, typhus, and hepatitis.  As I've mentioned before, a recent analysis has added leptospirosis to the list of suspects.  The symptoms and signs of leptospirosis match those reported from first-hand accounts of the mystery ailment.  Here's a post on the Slate website about the epidemic.  I'm glad to see that the story is getting attention from popular news sites.

Leptospirosis can be deadly, but could it account for the devastating 90% motality rate of the 1616-1619 epidemic?  A hypervirulent strain of Leptospira or genetic susceptibility of the Indians could be an explanation.  However, the authors of the study thought that the most critical factor was the Indian lifestyle, which brought them into repeated contact with Leptospira in the environment.  The Europeans who fished nearby were spared because they did not engage in activities that exposed them to Leptospira.  Therefore, only the Indians contracted the illness, according to the hypothesis.

Figure 3 from Marr and Cathey, 2010.

Whatever its cause, it's hard to overstate the significance of the epidemic.  Prior to 1616, the New England native communities traded with the Europeans and even welcomed them for brief stays.  However, all attempts by the foreigners to establish permanent settlements were fiercely resisted.  Coastal New England was well defended by the large native population.  The Wampanoag confederacy became especially hostile towards the Europeans after having their citizens abducted.

By the time the Mayflower landed in Patuxet (Plymouth) in December of 1620, the thinking of the Wampanoag had changed.  Their depleted population was vulnerable to attack by their longtime enemies to the west, the Narragansett, who remained untouched by the epidemic.  To forestall an attack, Massasoit felt that the best course of action was to form an alliance with the Pilgrims rather than expel them.  In the spring of 1621, with Tisquantum serving as the translator, Massasoit arranged a peace treaty with the Pilgrims.

Reference

Marr J.S. & Cathey J.T. (2010). New hypothesis for cause of epidemic among Native Americans, New England, 1616–1619, Emerging Infectious Diseases, 16 (2) 281-286. DOI: 10.3201/eid1602.090276

Related post

• Did spirochetes kill off the Indians in Massachusetts before the Mayflower landed?

Looking for the syphilis spirochete in ancient bones

PCR is a powerful tool that has been used to detect microbial DNA in human remains unearthed by archaeologists.  This approach has helped reveal when and where infectious diseases such as tuberculosis and the plague have afflicted human populations in the past.  With the controversy raging over the question of whether the syphilis spirochete was present in Europe before Columbus sailed to America, one would think that scientists would have tried PCR to detect Treponema pallidum DNA in skeletal remains.  Well, they have, but in almost every case they failed to detect T. pallidum DNA, even in bones bearing the lesions of syphilis.  The problem is that adults who die in the later stages of syphilis do not have many T. pallidum spirochetes in their bones.

On the other hand, spirochetes are relatively abundant in the bones of infants afflicted with congenital syphilis.  Therefore the skeletal remains of the very young may be a better source for detection of T. pallidum DNA by PCR.  As reported in their recent PLoS One article, Montiel and colleagues looked for T. pallidum DNA in skeletal remains gathered from a 16th-17th century crypt in Spain.  The investigators found four infant bones with lesions that were consistent with congenital syphilis.  Since there were two left humeri (specimens ELS551 and ELS558 in the image below), the bones must have belonged to at least two newborns.

Figure 1 from Montiel et al., 2012.  Source.

The PCR reactions were conducted on specimens from both newborns in each of three different laboratories.  Two segments along the T. pallidum chromosome were targeted.  One lab targeted the arp gene, the second lab targeted the 5' UTR of the 15 kDa lipoprotein gene, and the third targeted both sequences.  All attempts but one led to the generation of PCR products.  To confirm that they derived from T. pallidum sequences, the PCR products were either analyzed by restriction digestion or cloned and sequenced.  The 5' UTR of the lipoprotein gene was critical to this effort because its sequence can be used to distinguish the syphilis spirochete from the other disease-causing treponemes.  The PCR products from both newborns turned out to have the Eco47III restriction site that is unique to the syphilis spirochete among modern treponemes.  The molecular analysis therefore supported the diagnosis of congenital syphilis in the two long-deceased infants.

The investigators took special precautions to minimize the risk of contamination, which is always a concern of paleomicrobiologists running PCR reactions.  For example, the experiments were done in laboratories in which Treponema-containing samples had never been handled.  The investigators even excluded positive controls from their PCR reactions.

Scientists are still not certain whether congenital syphilis can be correctly diagnosed by examining bone pathology alone (see pp. 102-103 of this paper for a nice discussion of this issue).  The PCR method will therefore aid scientists wishing to identify skeletal remains afflicted with congenital syphilis.  It also gives paleomicrobiologists hope that PCR methods will help answer the centuries-old question about the origin of syphilis.

References

Montiel R, Solórzano E, Díaz N, Álvarez-Sandoval BA, González-Ruiz M, Cañadas MP, Simões N, Isidro A, & Malgosa A (2012). Neonate human remains: a window of opportunity to the molecular study of ancient syphilis. PloS one, 7 (5) PMID: 22567153

Bouwman, AS, & Brown, TA (2005). The limits of biomolecular palaeopahology: ancient DNA cannot be used to study venereal syphilis Journal of Archaeological Science, 32, 703-713 DOI: 10.1016/j.jas.2004.11.014

Related posts

• Still no solid evidence for the Old World origin of syphilis
• The origin of syphilis: a phylogenetic approach

Still no solid evidence for the Old World origin of syphilis

The first recorded syphilis epidemic flared up in war-torn Naples in 1494, only two years after Columbus discovered the New World.  From there syphilis spread throughout Europe.  Ever since then, controversy has raged about the origin of syphilis.  A popular belief is that Columbus's crew got infected in the New World and brought the spirochete back to Europe, where they transmitted the disease to others while serving as mercenaries during the first Italian War.  The competing pre-Columbian hypothesis asserts that syphilis was always present in the Old World yet wasn't recognized until 1494.

Among the treponemes, Treponema pallidum subspecies pallidum, the agent of syphilis, is the only one that's sexually transmitted.  Other treponemal diseases include yaws and endemic syphilis, each caused by a genetically distinct subspecies of Treponema pallidum.  The exuberant immune response to T. pallidum during the tertiary stage of treponemal disease leaves marks on the bones.  Historical cases of treponemal disease can therefore be identified by looking for these skeletal lesions.  Diagnosing treponemal infection in this way is tricky because a number of diseases cause similar lesions.  Nevertheless, bone deformities specific to treponemal diseases do exist, most famously the worm-eaten appearance of caries sicca.  Unfortunately, skeletal lesions cannot be used to reliably distinguish syphilis from the other treponemal diseases, so I will be speaking of treponemal disease instead of syphilis when discussing the skeletal evidence.

The findings of treponemal lesions in pre-1492 skeletal remains from the Old World would upend the Columbian hypothesis.  A number of claims of pre-Columbian treponemal lesions on Old World skeletons have appeared in the scientific literature, with some garnering widespread media attention.  One example is the findings from the excavation of an English friary at Hull Magistrate's Court, which was a subject of an episode of the PBS series Secrets of the Dead.  Skeletal remains from four individuals unearthed at the site had evidence of treponemal disease.  The site where the bones were found was dated to 1300-1450.

The Syphilis Enigma, part 1 of 4


The Syphilis Enigma, part 2 of 4


The Syphilis Enigma, part 3 of 4



The Syphilis Enigma, part 4 of 4


Harper and colleagues recently took another look at the published claims of pre-Columbian treponemal disease in Old World skeletal remains.  Their work came out last month in the Yearbook of Physical Anthropology, the supplement to the Journal of Physical Anthropology  They scrutinized the data in the 54 published reports with a standardized set of criteria for diagnosing treponemal disease and radiocarbon dating the bones.  There were two parts to their analysis.  First, they looked at the description of the skeletal lesions (including photographs, when available) to make sure they were the type caused solely by treponemal diseases.  Second, they looked at method used to date the bones.  In turns out that all 54 reports were flawed in some manner.  In many reports, diagnosis of treponemal disease was based on the types of skeletal lesions that could have been induced by other diseases.  In others, the bones were dated indirectly by archeological methods instead of directly by radiocarbon dating the bones.  Or worse, details of the dating method were sometimes omitted.

Among the 11 specimens for which the diagnosis of treponemal disease was deemed to be correct by the authors, two were dated by radiocarbon methods to the pre-Columbian years.  The time of death for the two individuals were 1424-1479 for a specimen unearthed in Safed, Israel and 1426-1486 for one dug up at the Church of St. Helen-on-the-wall in York, England.  At first glance, these specimens appear to undermine the Columbian hypothesis.  However, radiocarbon dating assumes that the ratio of ¹⁴C ("new" carbon, which decays at a known rate) to ¹²C ("old" carbon) remains constant in the environment and by extension living things, which exchange carbon with the environment by eating and breathing.  Slight deviations of the ratio may throw off the calculated date by hundreds of years.  One factor that must be accounted for is the "marine reservoir effect," which could skew the isotope ratio in humans who consume seafood.  The problem is that water near the surface mixes with deeper water, which reflects the higher proportion of old carbon from the material coming off the ocean floor.  The carbon in the air does not mix quickly enough with the carbon in the water to equalize the carbon ratios.  Therefore, marine organisms do not contain the same carbon ratio as land organisms.  Humans who consume seafood will have a slightly lower proportion of new carbon than expected, making bones from seafood consumers appear older than they really are if no correction is made.  When the correction is made for the marine reservoir effect, the new dates for the specimens become 1424-1953 for the Safed specimen and 1421-1669 for the St. Helen-on-the-Walls specimen.  An additional three Old World specimens were dated to the pre-Columbian period by radiocarbon dating, corrected for the marine reservoir effect.  However, the specimens lacked lesions specific for treponemal disease.  In sum, proper dating of the skeletal remains revealed that none of the Old World skeletons bearing treponemal marks could have originated from the pre-Columbian era.  There is still no convincing evidence for the Old World origin of syphilis.

So can we now reject the pre-Columbian hypothesis?  The authors make an interesting comment about this.

The trope that absence of evidence is not the same as evidence of absence will be invoked by some. While it is true that a working hypothesis may be falsified at any time, at what point does the absence of skeletal evidence of pre-Columbian treponemal disease in the Old World become compelling? After all, the best proof of a theory is failure to disprove it, and we find that despite intense research interest, credible evidence disproving the Columbian Hypothesis is lacking.

The "intense research interest" includes past examination of tens of thousands of skeletons in continental Europe and North Africa and 50,000 in England alone, with none yielding convincing evidence of pre-Columbian treponemal disease.  The authors do point out that skeletal remains from vast regions of sub-Saharan Africa and Asia have not been well-studied.  For this reason, it may be too soon to lay the pre-Columbian hypothesis to rest.


ACKNOWLEDGEMENTS:  A big thanks to Molly Zuckerman for alerting me to her group's work and for sending me the article.

References
Harper, K.N., Zuckerman, M.K., Harper, M.L., Kingston, J.D., & Armelagos, G.J. (2011). The origin and antiquity of syphilis revisited: an appraisal of Old World pre-Columbian evidence for treponemal infection American Journal of Physical Anthropology, 146 (S53), 99-133 DOI: 10.1002/ajpa.21613

von Hunnius, T.E., Roberts, C.A., Boylston, A., & Saunders, S.R. (2006). Histological identification of syphilis in pre-Columbian England American Journal of Physical Anthropology, 129 (4), 559-566 DOI: 10.1002/ajpa.20335

Related posts by other bloggers

• Revisiting Syphilis in the Old World in Bones Don't Lie
• The French Disease, the Italian Disease, the Christian Disease--the New World Disease? in The Loom

Related posts in Spirochetes Unwound

• The origin of syphilis: a phylogenetic approach