Infectious Disease

These disorders are caused by microorganisms, including bacteria, viruses, rickettsia, fungi, and single-celled protozoan parasites. Invasion by macroorganisms, those visible to the eye, such as worms and insects, constitutes infestation. Modern treatment has altered many diseases and comparison between ancient and modern diseases must keep this fact in mind.

Most infections do not affect the skeleton directly, but the skeleton can be involved indirectly. Childhood infections can result in the production of growth arrest lines or Harris lines in the long bones, resulting in a very rough index of morbidity. Infections that result in anemia cause a secondary hyperplasia of the bone marrow, particularly in the skulls of children. X-rays show a characteristic hair-on-end appearance and the external surface of the bone shows osteoporotic pitting, called porotic hyperostosis. The geographic distribution of this lesion has been shown to overlap that of malaria and these conditions have been linked to sickle cell anemia and thallessemia.

Bone infections, osteomyelitis, mostly bacterial infections, reach the bone by a penetrating injury such as a laceration or open fracture, by the bloodstream from a distant site, or by direct extension from an infection such as a soft tissue or dental abscess or a sinus infection. Mastoiditis has been found in Neanderthal, Nubian,

Egyptian, and American Indian skulls, secondary to middle ear infection. The infected bone becomes necrotic and is surrounded by pus, which may drain to the surface through sinus tracts. Such infections can still be very difficult to treat and may persist for years. Pyogenic osteomyelitis is an ancient disease, having been described in dinosaur skeletons.

An infection with extensive historical documentation is bubonic plague, caused by Yersinia pestis. The black death killed more than a quarter of the population of Europe in the 14th century. Infection is transmitted to humans by the bite of an infected rat flea. The lymph nodes become greatly swollen (bubos), or, under conditions of crowding, transmission is by inhalation, causing a rapidly fatal pneumonia. Sporadic infections still occur, traceable to wild rodents.

A spirochetal disease of significance in human history is syphilis. Advanced acquired disease results in damage to many organs, including the cardiovascular system, skeleton, skin, and upper respiratory tract. Congenital syphilis is passed across the placenta and is characterized by deformities of the teeth, legs, and face. The periostitis of syphilis is quite distinctive, but in archeological material can be impossible to distinguish from yaws.

The origin of syphilis, New World or Old, has long been a point of controversy. One school holds that the varying spirochetal diseases are different manifestations of the same disease in different populations. Some feel that yaws originated in the Pacific, spread to the New World and manifested itself as syphilis when contracted by adult European explorers, while others believe that syphilis was present in the pre-Columbian Old World.

Tuberculosis, caused by an acid-fast bacillus, affects the bone in a certain percentage of cases with destruction of joints as well as bone. Involvement of the vertebral bodies causes collapse and hunchback (kyphosis or Pott's disease). There are good examples from Dynastic Egypt, but not pre-Dynastic, suggesting a possible evolution from the bovine form of the disease, cattle having been domesticated at the beginning of the Dynastic period. Tuberculosis has been found in Europe at about 2000 BC and in a mummy from pre-Columbian America, where pottery figurines with kyphosis are also found.

Leprosy, caused by another acid-fast bacillus, is a disease of considerable historical interest, because of Biblical references and the fact that the characteristic bone changes in the disease were first delineated in a study of medieval skeletons. The primary infection is through the nose, with atrophy of the maxilla in the region of the incisors, with or without loss of teeth, inflammation of the hard palate, and atrophy of the nasal spine, these lesions having been identified by MollerChristiansen in medieval lepers. While leprosy is mentioned in the Old Testament, the earliest skeletal evidence dates only to early Christian era Europe. The disease was certainly common in Europe by medieval times, but most of the lepers were killed off by the bubonic plague.

Although viruses are responsible for a long list of human diseases, there is little evidence of these intracel-lular parasites in paleopathology. A rare example is the mummy of the Pharaoh Siptah, of the 19th Dynasty, which shows a leg deformity characteristic of polio. Smallpox has been diagnosed in the mummy of Ramses V and a mummy of the 20th Dynasty. The effects of viruses on nonimmune populations have been demonstrated repeatedly. Measles, smallpox, and yellow fever have been largely responsible for the decimation of aboriginal populations in America, Australia, New Zealand, and among the Inuit.

Fungi are plants that produce chronic infections in humans. These organisms are often seen in paleopathol-ogy but are invariably postmortem contaminants.

Protozoa are single-celled animals responsible for many infections, primarily in tropical and underdeveloped countries. Evidence of the malaria has been found in Egyptian mummies.

Diseases caused by helminths (worms) are relatively uncommon in temperate climates but have a major impact on tropical and subtropical areas. Worms are classified morphologically as roundworms (nematodes), flatworms, or "tapeworms" (cestodes) and flukes (trematodes). Most helminths have elaborate life cycles often requiring intermediate hosts and almost always involving the ingestion of infective forms, ova or larvae, by the definitive host. The effect on the host is variable. Some parasites cause profound debilitation while others have a more benign course. The latter probably are better adapted to their host, as it is to the advantage of the parasite for the host to be in relatively good health, death of the host meaning at the least a search for a new host, if not death for the parasite as well. The effects of the parasite on the host may bear a roughly inverse relationship to the time that the two genera have been associated.

Parasitic worms and their ova remain well preserved for millennia, and the characteristic ova of a roundworm,

Ascaris lumbricoides, tapeworm, Taenia solium, and blood fluke, Schistosoma hematobium, have been reported in Egyptian mummies, including one case of death due to cirrhosis. Parasitic worms and ova have been seen in European bog bodies and in the New World. Adult hookworms, Ancylostoma duodenale, have been seen in the small intestine of a 1,000-year-old Peruvian mummy.

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