Category Archives: Palaeopathology

Domestication of the donkey

An international group of researchers has found evidence for the earliest transport use of the donkey and the early phases of donkey domestication, suggesting the process of domestication may have been slower and less linear than previously thought.

Based on a study of 10 donkey skeletons from three graves dedicated to donkeys in the funerary complex of one of the first Pharaoh’s at Abydos, Egypt, the team, led by Fiona Marshall, Ph.D., professor of Anthropology at Washington University in St. Louis, and Stine Rossel of the University of Copenhagen, found that donkeys around 5,000 years ago were in an early phase of domestication. They looked like wild animals but displayed joint wear that showed that they were used as domestic animals.

“Genetic research has suggested African origins for the donkey,” said Marshall. “But coming up with an exact time and location for domestication is difficult because signs of early domestication can be hard to see. Our findings show that traces of human management can indicate domestication before skeletal or even genetic changes.”

The previously unpublished research was presented in “Domestication of the Donkey: New Data on Timing, Process and Indicators” in the March 10 online edition of the Proceedings of the National Academy of Sciences.

Domestication of the donkey from the African wild ass was a pivotal point in human history. It transformed ancient transport systems in Africa and Asia and the organization of early cities and pastoral societies.

The research team examined the 5,000-year-old Abydos skeletons along with 53 modern donkey and African wild ass skeletons. Analysis showed that the Abydos metacarpals were similar in overall proportions to those of wild ass, but individual measurements varied. Mid-shaft breadths resembled wild ass, but mid-shaft depths and distal breadths were intermediate between wild ass and domestic donkey.

Despite this, all the Abydos skeletons exhibited a range of wear and other pathologies on their bones consistent with load carrying. Morphological similarities to wild ass show that despite their use as beasts of burden, donkeys were still undergoing considerable phenotypic change during the early dynastic period in Egypt. This pattern is consistent with recent studies of other domestic animals that suggest that the process of domestication is slower and more complicated than had been previously thought.

Source: EurekAlert!

Know Your Pathology: Treponematosis

Treponematosis is “a chronic or subacute infection caused by microorganisms called spirochetes of the genus Treponema. On the basis of clinical and geographic variation, the infection is divided into four types: pinta, yaws, bejel (or endemic syphilis) and venereal syphilis” (Aufderheide and Rodríguez-Martín, 1998: 154). There is debate about whether these are different diseases caused by different bacterial species within the genus, or whether they are different clinical manifestations of infection by one species, Treponema pallidum (Aufderheide and Rodríguez-Martín, 1998: 154):

  • Pinta is the most geographically restricted of the four syndromes. It is limited to the tropical regions of America, from Mexico to Ecuador. Treponema carateum is responsible for the disease;
  • Yaws or frambesia affects especially those populations with a low level of hygiene in tropical or subtropical humid areas. It is caused by Treponema pertenue;
  • Bejel (endemic syphilis or non-venereal syphilis) is present in rural populations in temperate and subtropical non-humid regions, and caused by Treponema pallidum endemicum;
  • Venereal syphilis is the most ubiquitous of the four syndromes, occurring primarily in urbanised populations in all geographic regions. It is caused by Treponema pallidum pallidum.

Except for pinta, which does not involve bone, the other syndromes produce nearly identical lesions upon the skeleton (Steinbock, 1976: 94). These lesions represent a late stage that marks the generalised spread of bacteria within the body. Inflammatory changes of a mainly destructive nature occur within the skeleton, although considerable repair and regeneration can often also be demonstrated. Venereal syphilis may be either congenital or acquired, congenital syphilis being transmitted in utero via the infected mother. The most severe of the forms, it is characterised not only by inflammatory changes in most tissues of the body, but also by the affection of arterial circulation and the nervous system (Roberts and Manchester, 1995: 151).

The gross bone destruction, called a gumma, is not dissimilar to non-specific osteomyelitis. However, treponemal osteomyelitis is accompanied by extensive regeneration. Consequently, the bone becomes much altered in appearance. The frequency of bone involvement ranges from about 3-5 percent of all cases of yaws to 10-12 percent of all cases of venereal syphilis, with endemic syphilis lying somewhere between the two. In yaws the most commonly affected bone is the tibia, resulting in the distinctive ‘sabre shin’, with the other bones only being affected to a lesser extent, the skull in particular being infrequently involved. Skull involvement is also uncommon in endemic syphilis, but may result in extensive destruction of the nasal and jaw regions. As with yaws, the ‘sabre shin’ shape is often seen, the tibia again being the most commonly affected element (Roberts and Manchester, 1995: 152).

As with the other previously described treponemal diseases, the tibia is the most commonly affected element of venereal syphilis, but multiple bone involvement is frequently noted. It may also result in destructive changes of the joints, such as the characteristic ‘Charcot’s joint’. In contrast to yaws and endemic syphilis, the skull is frequently affected, exhibiting a ‘worm-eaten’ appearance called caries sicca (Roberts and Manchester, 1995: 153).The diagnostic criteria most frequently used to establish the presence of treponemal disease in dry bones are by Hackett (1976).

The epidemiology and spread of treponemal disease has been the subject of much debate, with controversy raging over whether a New or Old World origin for the condition was more likely, the transatlantic voyage of Christopher Columbus being a date of great significance to epidemiologists. It is still unclear when, where and how the currently recognised clinical forms developed, and how they are related to one another from an evolutionary standpoint. Identifying the form of treponemal disease from the physical examination of skeletal remains is often impossible, although attempts have been made to make such a differentiation at population level and it is possible that ancient DNA analysis may aid in this (Mitchell, 2003: 122). For example, the causative agent of venereal syphilis, Treponema pallidum pallidum, has recently been extracted from a two hundred-year-old skeleton from Easter Island using a combination of immunological assay and DNA analysis (Kolman et al., 1999). The oldest dated case of treponematosis in the Middle East comes from Israel, and dates to 1290-1420 AD, during the Mamluk period just after the Crusades (Mitchell, 2003). Pre-Columbian dates have also been given for cases from Britain (Mays et al., 2003) and the United States of America (Hutchinson and Weaver, 1998).

Buckley and Tayles (2003) examined a prehistoric Pacific Island sample for diseases such as yaws, leprosy and malaria. Each type of bone change was recorded, with each type of pathological change also being given a numerical code. This code indicated the type of observed change and whether it was primarily osteoblastic activity, osteoclastic activity, or a mixed response. The presence of lesions was identified macroscopically. Diffuse pitting and/or apposition of new bone on the cortical aspect is an indication of osteoblastic activity as a response to an infectious or non-infectious mechanism. Active (unremodelled) or remodelled lesions were coded as such, the authors stating that “active osteoblastic lesions display a fibrous, vascular, porous, and irregular layer of new bone that has a scab-like appearance over the normal smooth cortex”, in contrast to remodelled lesions that “is usually smooth in appearance, and more organised than new woven bone.” Lesions that developed as a result of osteoclastic activity were identified by lytic foci in the cortical bone and/or trabeculae. Distortion of the normal shape, such as diaphyseal bowing, was also noted as pathological (Buckley and Tayles, 2003: 306). These lesions were then placed into either Osteoblastic (OB) or Osteoclastic (OL) grades 1-4 (Buckley and Tayles, 2003: 306-307), which are described in the article, with photographic illustrations of most, but not all, classes. Hackett’s (1976) coding criteria was used for recording classic gummatous caries sicca lesions of the cranial vault (Buckley and Tayles, 2003: 307).

In an attempt to control some of the limitations of estimating lesion prevalence within a population, the prevalence was estimated using both the individual and skeletal element as denominators. An ‘individual’ was defined by the presence of certain bone elements that are most frequently affected by systemic disease. Those selected, with at least one of each being needed, were the femur, tibia, clavicle, ulna and either the hands or feet for the minimum definition of an ‘observable individual’ (Buckley and Tayles, 2003: 308). This selection criteria was not as strict for the sub-adults due to the fact that sub-adult bones are more readily affected by pathological change. This was useful for increasing the sample size given the fragmentary nature of most of the sub-adult skeletons. Therefore, a sub-adult burial that included the tibia and any two other limb bones were included as individuals (Buckley and Tayles, 2003: 310).

Cranial material was recorded for all observable individuals as complete (presence of all cranial elements, whether articulated or fragmentary), partial (presence of some cranial elements, may be missing the frontal), or absent (no cranial material present). A burial was retained as an individual regardless of cranial preservation, however the presence of the frontal bone and a partial or complete naso-maxillary region was deemed ideal (Buckley and Tayles, 2003: 310).

All bones present were included in the analysis using the skeletal element as the indicator of prevalence, whether complete or partial, and from observable individuals or not. Left and right elements were combined to increase the sample sizes and the bones were sub-divided according to age group. It was considered that sex-related distributions of lesions could be best analysed using observable individuals and so were not studied using skeletal element as the denominator (Buckley and Tayles, 2003: 311). One limitation of the current study was the lack of systematic recording of joint pathology, which may have distorted the prevalence of lytic lesions affecting the joints (Buckley and Tayles, 2003: 310).

The status and severity of lesions in observable individuals was assessed; status 1 indicating several bones were affected and all lesions were active at death, status 2 indicating the presence of active lesions, but with some remodelling at the time of death, and status 3 indicated solely remodelled lesions (Buckley and Tayles, 2003: 310-311). In contrast, the lesions assessed by skeletal element were first classified into three main groups: active OB, remodelled OB, or OL. Cranial lesions were considered separately (Buckley and Tayles, 2003: 311).

It was found that more than half of the observable individuals (57 of 101) had post-cranial lesions, with similar prevalence for all age groups and both sexes. Less than one quarter had cranial lesions and the prevalence decreased with age. However, lesions were present in a low proportion of post-cranial elements overall, although the major long bones, especially the tibia, were most frequently affected. The lesions were effectively all active in sub-adults, whilst in adults there was a mixture of active and remodelled lesions (Buckley and Tayles, 2003: 313-316), a diagnosis of yaws being proposed as the most likely to fit the pattern displayed at the site (Buckley and Tayles, 2003: 321).

This methodology seems particularly useful as it does not require any specialist, or expensive equipment, and would be readily adoptable by most osteoarchaeologists. The categories seem a little crude at times, however this is not uncommon with those methodologies based upon macroscopic examination, and the classes do at least provide a baseline for comparison between populations. Better illustration of the various classes, by photographs of all grades for example, would have been useful in order to help decrease inter-observer variation.

It is worth noting, however, that bone lesions caused by treponemal disease are frequently very similar to non-specific bone diseases, particularly in the long bones. The use of polarised light in light microscopy can illuminate elements of the internal bone structure such as the arrangement of collagenous fibres, and this can make visible structures typically built up by different diseases. At the micro-level, telltale signs of treponemal disease are polsters and grenzstreifen (Schultz, 2001: 126).

Polsters are frequently found in the chronic treponemal diseases of the long bones, and consist of “parallel lamellae arranged at the periosteal level in the form of pillow-like newly built bone formations demarcated by periosteal blood vessels developed during the course of the inflammatory process” (Schultz, 2001: 126). These show a homogeneous structure due to the generally slow growth, in contrast to haematogenous osteomyelitis, which has a much more rapid growth pattern, and thus a more irregular structure (Schultz, 2001: 126). ‘Grenzstreifen’ or ‘grenzlinie’ can be observed in chronic treponemal diseases. This is a “very fine line or a narrow, band-like structure that represents the original external surface of the bone shaft (remains of external circumferential lamellae) and newly built lamellae that originate during the first infection of the periosteum due to the pathological process” (Schultz, 2001: 126).

In contrast to leprosy, treponemal diseases such as endemic syphilis include not only alterations in the subperiosteal bone, but also osteoclastic changes in the endosteal bone and the bony trabeculae of the medullary cavity, as well as in the compact bone of the affected elements (Schultz, 2001: 128). Palaeohistopathological analysis can, therefore, be an important tool for diagnosing conditions such as this in archaeological specimens, helping to discount non-specific conditions that are similar at a macromorphological level.

References:

Aufderheide, A. C and Rodríguez-Martín, C. 1998. The Cambridge Encyclopedia of Human Paleopathology. Cambridge: Cambridge University Press.

Buckley, H. R, and Tayles, N. 2003. Skeletal pathology in a prehistoric pacific island sample: issues in lesion recording, quantification, and interpretation. American Journal of Physical Anthropology 122: 303-324.

Hackett, C. 1976. Diagnostic criteria of syphilis, yaws and treponarid (treponematosis) and of some other diseases in dry bone (for use in osteo-archaeology). Berlin: Springer-Verlag.

Hutchinson, D. L, and Weaver, D. S. 1998. Two cases of facial involvement in probable treponemal infection from Late Prehistoric coastal North Carolina. International Journal of Osteoarchaeology 8: 444-453.

Kolman, C. J, Centurion-Lara, A, Lukehart, S. A, Owsley, D. W, and Tuross, N. 1999. Identification of Treponema pallidum subspecies pallidum in a 200-Year-Old skeletal specimen. Journal of Infectious Diseases 180: 2060-2063.

Mays, S, Crane-Kramer, G, and Bayliss, A. 2003. Two probable cases of treponemal disease of medieval date from England. American Journal of Physical Anthropology 120: 133-143.

Mitchell, P. D. 2003. Pre-Columbian treponemal disease from 14th century AD Safed, Israel, and implications for the medieval Eastern Mediterranean. American Journal of Physical Anthropology 121: 117-124.

Roberts, C., and Manchester, K. 1995. The Archaeology of Disease. 2nd Edition. Stroud: Alan Sutton Publishing Ltd.

Schultz, M. 2001. Paleohistopathology of bone: a new approach to the study of ancient diseases. Yearbook of Physical Anthropology 44: 106-147.

Steinbock, R. T. 1976. Paleopathological Diagnosis and Interpretation: Bone Diseases in Ancient Human Populations. Springfield: Thomas Books.

Know Your Pathology: Leprosy

Leprosy, also known as Hansen’s disease, is “a chronic infectious disease of humans, affecting skin, nasal tissues, peripheral nerves and bones caused by Mycobacterium leprae” (Aufderheide and Rodríguez-Martín, 1998: 141). Co-existing with tuberculosis in many regions of the world today, the leprosy bacilli are transmitted either by inhalation or by direct contact into an open wound from an infected individual. Unlike tuberculosis, however, leprosy is not readily communicable. Those who acquire the condition have frequently been in prolonged contact with infected individuals (Larsen, 1997: 104). This perhaps explains the fact that today this is a disease with high rural incidence, clustering in families (Manchester and Roberts, 1989: 267).

Neurotrophic changes are commonly seen in advanced leprosy. Destruction of the sensory nerves with ensuing anaesthesia and circulatory alterations lead to slowly progressive atrophy of terminal phalanges, resorption progressing proximally, even as far as the metapodials in some instances. Severe degenerative arthritis and neuropathic arthropathy, similar to Charcot’s joint, can be seen in weight-bearing joints such as ankles and feet. In addition, the existing anaesthesia facilitates traumatic mutilations and secondary infections  (Ortner and Putschar, 1981: 177). Such paralysis also predisposes the individual to fractures caused by clumsiness or uncoordination (Judd and Roberts, 1998: 53).

If the affected individual has good immunological resistance the disease is confined to the nerves, producing what is known as the tuberculoid form of the disease. If resistance is poor then the lepromatous form occurs. Borderline cases can, and do, occur, however. Skeletal changes occur in both forms, but they are more frequent in the lepromatous form (Waldron, 2001: 101). Disruption of the muscles in the lower limbs and hands, as well as paralysis of the ulnar nerves, results in claw-hand deformities. Whilst such paralysis can be difficult to determine in archaeological specimens, in at least one instance a groove has been identified on the volar surface of the distal end of the proximal phalanx, a lesion also noted in the radiographs of modern patients (Andersen and Manchester, 1987: 78). Similar loss of motor function in the feet leads to the collapse of the longitudinal arch and the development of pes planus, or flat foot. The tensile stress this imparts to the ligaments is likely to be the cause of exostoses found at the sites of attachment (Andersen and Manchester, 1988: 52-54).

Facies leprosa of the skull shows atrophy of the anterior nasal spine, in most cases combined with central atrophy of the alveolar process. This is classified into three degrees (Møller-Christensen and Inkster, 1965: 11):

I° – in which there is a well-defined reduction of the spine;
II°- in which there is an advanced nasal spine atrophy although a distinct but very small nasal spine remains;
III° – in which there is a complete obliteration of the nasal spine.

The atrophy of the maxillary alveolar process and inflammatory changes of the superior surface of the hard palate are also classified into three degrees in a similar manner (Møller-Christensen and Inkster, 1965: 11). Further bone changes are set out in Møller-Christensen (1961).

The deformations associated with advanced leprosy led to sufferers being segregated, especially during the medieval period with theologians portraying the disease as the chastisement of God. The concept of the leper hospital did not really develop until the eleventh century AD, the third Lateran Council issuing orders for the isolation of lepers in 1179 (Rawcliffe, 1995: 14), at which point there was a sudden explosion in the numbers of these institutions. This suggests that either leprosy was becoming more common, that disease generally was becoming more common, or that society was becoming more charitable (Manchester and Roberts, 1989: 268). Alternatively, it may be viewed as part of a wider crusade against heretics, Jews, homosexuals, and anyone else whose behaviour was viewed as suspicious (Rawcliffe, 1995: 14).

The cross-immunity of leprosy and tuberculosis may explain the decline in leprosy towards the fourteenth century when there is a coincident rise in tuberculosis (Manchester and Roberts, 1989: 269). This relationship is not simple, nor universal, and appears to be affected by multiple variables. However, it may be this that explains the burial of two leprous males and tuberculous female from the Iron Age of South East Asia (Tayles and Buckley, 2004: 253).

A study aimed primarily at the epidemiological analysis of leprosy in medieval Denmark devised a simple recording form that allowed them to generate large amounts of data relatively quickly. In this the osteological changes were recorded in seven locations (Boldsen, 2001: 383):

  1. the edge of the nasal aperture;
  2. the anterior nasal spine;
  3. the alveolar process on the premaxilla;
  4. the palate;
  5. subperiosteal exostoses on the fibula;
  6. porotic hyperostosis on the fibula;
  7. the fifth metatarsal

Whilst it is acknowledged that some symptoms are best described as a multi-stage sequence of events, for the sake of simplicity all were recorded simply as 1) present or 2) absent. Zero indicated the condition was unobservable in that skeletal element. This coding could then be analysed using statistical packages to describe the frequency and prevalence of the disease (Boldsen, 2001: 383). Such simplicity does make this recording system easy to apply, and also easy to duplicate by other researchers. Scoring changes merely as present or absent reduces the likelihood of inter-observer error, which, on the whole, is more likely to arise with examples of minor change. It does, however, possibly over-simplify the sequence of many of the symptoms, and has the effect of grouping together all sufferers with the condition regardless of the degree of advancement. This could mean that some more subtle nuances of patterning are lost.

Many skeletal changes are considered characteristic of leprosy, however, others such as tibial periostitis may be caused by several different infections. The identification of Mycobacterium leprae DNA can, therefore, be very useful in confirming a diagnosis (Wilson, 1999: 14), and this is an approach that is becoming more common as the techniques involved in the study of ancient DNA improve. An example of this is a case from Byzantine Israel where the presence of M. lepra was used to differentiate between leprosy and a condition known as Madura foot, or Mycetoma (Spigelman and Donoghue, 2001).

Palaeohistopathological analysis can help to differentiate diseases such as leprosy from other specific infections like treponemal disease and from non-specific conditions. For example in lepromatous periostitis polster-like structures that are rudimentarily developed and relatively flat can be observed, in contrast to those of treponematosis which tend to be well-developed (Schultz, 2001: 126). Furthermore, in contrast to chronic treponemal disease, there are no observable grenzstreifen in chronic leprosy (Schultz, 2001: 128).

References:

Andersen, J. G and Manchester, K. 1987. Grooving of the proximal phalanx in leprosy: a palaeopathological and radiological study. Journal of Archaeological Science 14: 77-82.

Andersen, J. G and Manchester, K. 1988. Dorsal tarsal exostoses in leprosy: a palaeopathological and radiological study. Journal of Archaeological Science 15: 51-56.

Aufderheide, A. C and Rodríguez-Martín, C. 1998. The Cambridge Encyclopedia of Human Paleopathology. Cambridge: Cambridge University Press.

Boldsen, J.L. 2001. Epidemiological approach to the paleopathological diagnosis of leprosy. American Journal of Physical Anthropology 115: 380-387.

Judd, M. A, and Roberts, C. A. 1998. Fracture patterns at the medieval leper hospital in Chichester. American Journal of Physical Anthropology 105: 43-55.

Larsen, C. S. 1997. Bioarchaeology: Interpreting behavior from the human skeleton. Cambridge: Cambridge University Press.

Manchester, K, and Roberts, C. 1989. The palaeopathology of leprosy in Britain: a review. World Archaeology 21 (2): 265-272.

Møller-Christensen, V. 1961. Bone Changes In Leprosy. Bristol: John Wright & Son Limited.

Møller-Christensen, V, and Inkster, R.G. 1965. Cases of leprosy and syphilis in the osteological collection of the Department of Anatomy, University of Edinburgh. Danish Medical Bulletin 12 (1): 11-18.

Ortner, D. J, and Putschar, W. G. J. 1981. Identification of Pathological Conditions in Human Skeletal Remains. Smithsonian Contributions to Anthropology 28. Washington and London: Smithsonian Institution Press.

Rawcliffe, C. 1995. Medicine and Society in Later Medieval England. Stroud: Sutton Publishing.

Schultz, M. 2001. Paleohistopathology of bone: a new approach to the study of ancient diseases. Yearbook of Physical Anthropology 44: 106-147.

Spigelman, M and Donoghue, H. D. 2001. Brief communication: unusual pathological condition in the lower extremities of a skeleton from ancient Israel. American Journal of Physical Anthropology 114: 92-93.

Tayles, N and Buckley, H. R. 2004. Leprosy and tuberculosis in Iron Age Southeast Asia? American Journal of Physical Anthropology 125: 239-256.

Waldron, T. 2001. Shadows in the Soil: Human Bones and Archaeology. Stroud: Tempus Publishing.

Wilson, L. E. 1999. Leprosy in Scotland. Unpublished MA dissertation. University of Leicester.

Yersinia pestis, ancient DNA and the Black Death

Introduction:

The Black Death is the name given to a pandemic which killed up to a third of the European population between 1347 and 1352. Over the next three hundred years this pandemic was followed by further plagues of lesser mortality. These are historically ascribed to bubonic plague whose aetiological agent is the bacterium Yersinia pestis.

Recently, DNA specific for Y. pestis was amplified from 16th and 18th century human teeth believed to be French plague victims (Drancourt et al., 1998) and 14th century French Black Death victims (Raoul et al, 2000). The lead authors of these reports now believe that the consideration of any cause for the Black Death other than Y. pestis is now speculative.

Ancient DNA analysis:

The study of aDNA involves the extraction and analysis of DNA from the remains of organisms preserved as fossils, skeletons or mummified tissues. Studies are hampered by extremely low levels of preservation, often coupled by the presence of much greater levels of modern contaminants. Characteristically only short aDNA fragments can be amplified and easy amplification of longer fragments is an indication that contamination has occurred.

In the case of Y. pestis, fatal infection would not be expected to leave any specific bony changes, so no osteological confirmation is available and any retrospective diagnosis is completely DNA-based. Two studies from the same research group reported the successful extraction and sequencing of Y. pestis-specific DNA retrieved from the dental pulp cavities of plague victims. Findings that pathogen-specific DNA can be recovered from this source in systemically infected animals have led Drancourt et al (1998) to hypothesise that teeth provide a lasting, contamination-free refuge where pathogen aDNA may survive.

Results:

  • Previous extraction techniques are unsuited to preventing bacterial contamination of the DNA extract. Dental enamel is extremely resistant to diagenesis, but may be permeable to contaminating DNA using both the ‘ground’ and the ‘scraped’ methodologies. Encasing teeth in silicone appears to act as a barrier to movement of DNA between the tooth and the gloved hand and this may explain the reduction in contamination with this method.
  • No evidence of surviving Y. pestis DNA was found in this study, despite the examination of a large number of samples from five mass graves, including two well-documented plague pits and several other probable plague-victim burial sites.
  • Previous studies reported successful direct sequencing from ancient teeth. This implies a low-level of contaminating non-Y. pestis bacterial DNA, despite using a dentine extraction method demonstrated to be contamination prone. This raises two questions:
    1. why such levels of contaminating DNA from other bacteria were found in this study, and
    2. why it was not possible to amplify Y. pestis-specific DNA from samples of plague victims that yield what appears to be authentic human DNA.
  • It is possible that diagenetic conditions in the relatively drier and warmer Southern French locations were more conducive to ancient DNA survival than those of north-western Europe. However, aDNA studies have repeatedly demonstrated an inverse correlation between average temperature, humidity and aDNA retrieval. It is, therefore, surprising that warmer locations would be more successful.
  • An alternative environmental variable is groundwater. An inverse correlation has been noted between sample survival and exposure to water. However the ability to amplify host DNA suggests survival is not an issue.
  • A further explanation is that the individuals from whom the samples derive were either infected by a Y. pestis strain lacking the plasmid-located sites for amplification or not infected with Y. pestis (because they were not victims of the Black Death, or because the infection did not seed the pulp cavity, or because the Black Death and subsequent plagues were not caused by Y. pestis). The first hypothesis is unlikely as the plasmid containing the pla gene is a consistent feature of contemporary isolates. The second hypothesis is plausible. There is no guarantee that bacteria causing a systemic infection entered the teeth. It is, therefore, possible that Y. pestis may not have been present in the teeth specimens but that infection by this bacteria caused death. The third hypothesis is controversial, but cannot immediately be discounted.

Reference:

Gilbert, M.T.P, Cuccui, J. White, W, Lynnerup, N, Titball, R.W, Cooper, A and Prentice, M.B. 2004. Absence of Yersinia pestis-specific DNA in human teeth from five European excavations of putative plague victims. Microbiology 150: 341-354.

Know Your Pathology: Calculus

In this edition of ‘Know Your Pathology’, we shall examine the subject of calculus, also known as calcified plaque. This consists of micro-organisms, which accumulate in the mouth, embedded in a matrix partly composed of the organisms themselves and partly derived from proteins in the saliva (Roberts and Manchester, 2005: 71). It accumulates faster when there is a high protein and/or carbohydrate diet favouring an alkaline oral environment (Roberts and Manchester, 2005: 71).

Where crystallites of mineral are deposited in the plaque, the plaque can be mineralised and form calculus (Roberts and Manchester, 2005: 71-71). Two types are commonly seen:

  1. Supragingival calculus (above the gum) is more common and is usually thicker and grey or brown in colour;
  2. Subgingival calculus (below the gum) is often seen on exposed tooth roots and is harder and green or black in colour.

Calculus varies widely in mineralisation, but subgingival calculus is more heavily mineralised (46-83% by colume) than supergingival (16-80% by volume). The minerals include apatite, whitlockite, octacalcium phosphate and brushite, all of which have been found in archaeological specimens (Hillson, 1996: 257). Brushite is prominent during the earlier part of calculus deposition, whilst mature supergingival calculus has more apatite and brushite, and subgingival calculus has abundant whitlockite (Hillson, 1996: 257).

Beneath a Scanning Electron Microscope, it is possible to see that calculus is more heavily mineralised than dentine or cement, but less so than enamel, and that it presents an irregular appearance with layerings, voids and clefts (Hillson, 1996: 257). Outlines of bacteria are presented as voids with mineralised shells – the filamentous forms as 2um diameter tubules, and shorter rods or cocci as globular outlines – and similar outlines have been demonstrated in calculus from English medieval human remains (Dobney and Brothwell, 1986).

Dental reports from some archaeological human populations indicate that calculus was common in all periods (Roberts and Manchester, 2005: 72).

References:

Dobney, K and Brothwell, D. 1986. Dental calculus: its relevance to ancient diet and oral ecology, pp 55-82. In Cuwys, E and Foley, R.A. Teeth and Anthropology. BAR International Series 291. British Archaeological Reports: Oxford

Hillson, S. 1996. Dental Anthropology. Cambridge University Press: Cambridge.

Roberts, C. and Manchester, K. 2005. The Archaeology of Disease. 3rd Edition. Stroud: Alan Sutton Publishing Ltd.

NB: For those looking for past editions of ‘Know Your Pathology’, and so that I can keep track of which topics I’ve covered and which I’ve not, there is now an index.

The Origins of Syphilis

The origin of syphilis has been hotly debated in recent years. Was it already in the Americas by the time of Columbus’ landing, or were he and his men somehow fundamentally linked to its arrival in the New World, are some of the questions typically asked. John Hawks looks at a new paper on just this topic in ‘Syphilis origin pinpointed?‘.

Know Your Pathology: Dental Caries

What is dental caries?

Dental caries is a destruction of enamel, dentine and cement, ultimately leading to the formation of a cavity in the crown or root surface (Hillson, 1996: 269). It is caused by the fermentation of food sugars, especially sucrose in the diet, by bacteria that occur on the teeth in plaque, such as Lactobacillus acidophilus and Streptococcus mutans (Roberts and Manchester, 2005: 65). Carious cavities usually develop in three regions of the tooth (Brothwell, 1981: 153):

  1. on the occlusal (biting) surface, generally in the region of natural fissures;
  2. in the region of the neck (cervical area) of the tooth, either on the lingual (tongue) or labial (lip) side;
  3. in the region of the neck of the tooth, but between the teeth (mesial and distal).

Caries in modern human populations

In living human populations, caries has a characteristic pattern. For all types of carious lesions, molars are most commonly affected, followed by premolars and then anterior teeth. Coronal caries is a disease of children, rising steadily to fifteen years or so of age, and then falling away in early adulthood. It is more common in girls than boys, but earlier dental eruption in girls exposes their teeth to risk for longer (Hillson, 1996: 281-282). Root surface caries also particularly affects the approximal surfaces of cheek teeth, but is a disease of adults (Hillson, 1996: 282). The pattern of caries is similar in members of the same family over several generations, perhaps due to inherited factors, but environmental factors such as dental treatment and diet also have a large role (Hillson, 1996: 282). The clearest single factor in caries is sugar, as shown by the decrease in caries rates during sugar rationing in Japan, Norway and Jersey during the 1939-45 war, which was followed by a rise when normal supplies resumed (Hillson, 1996: 282).

Caries in archaeological populations

Caries was very uncommon amongst fossil hominids, into Palaeolithic and Mesolithic contexts. Nevertheless, there are celebrated examples such as the rampant caries in the Middle Pleistocene skull from Broken Hill, Zambia, and coronal caries has also been noted in Australopithecus and Paranthropus (Hillson, 1996: 282). In European material, there is a an apparent gradual rise from very low caries rates in Palaeolithic to Iron Age contexts, to a rapid rise through medieval and post-medieval times (Hillson, 1996: 282). In parallel, the number of carious teeth per mouth increased, with more pit and fissure caries, less cervical caries, and more children affected. Similar trends have been demonstrated for Egypt and Nubia (Hillson, 1996: 282).

In North America, increased reliance upon maize agriculture is a clear cultural horizon (Hillson, 1996: 283). Several studies have show an increase in caries rate associated with the change from a hunter-gatherer diet to a diet heavy with starch-rich cereal (Hillson, 1996: 283). Similar rises in caries rate have been associated with increased reliance on arable agriculture in South America, South Asia, Egypt and Nubia (Hillson, 1996: 283). Meanwhile, a recent innovative survey of a Mayan population dated to the Classic period in Mexico (AD 250-900) demonstrated that the lowest rate of caries, and the highest rate of ante-mortem tooth loss, occurred in elite males; this correlated with poor oral hygiene and a softer and more refined diet (Roberts and Manchester, 2005: 67).

Caries in animal populations

Caries is an ancient phenomenon in non-human populations. Carious lesions have been reported in Permian fish, as well as mastodon and cave bear teeth. Caries with possible actinomycosis infection has also been noted in the three-toed horse, Merychippus campestris (Rothschild and Martin, 1993: 211-212). They are moderately common amongst wild great apes, particularly chimpanzees, whose diet includes a lot of fruit and, therefore, sugar. Gorillas, which eat considerably less fruit, have much lower caries rates, whereas orangutans seem to occupy an intermediate position (Hillson, 1996: 282).

References:

Brothwell, D. 1981. Digging up Bones. Third Edition. New York: Cornell University Press.

Hillson, S. 1996. Dental Anthropology. Cambridge University Press: Cambridge.

Roberts, C. and Manchester, K. 2005. The Archaeology of Disease. 3rd Edition. Stroud: Alan Sutton Publishing Ltd.

Rothschild, B.M. and Martin, L.D. 1993. Paleopathology: Disease in the Fossil Record. CRC Press: London.