On zoonoses and their relevance to paleopathology • 19 



ticks). Similarly, the survival of tsetse fly in Africa, and thus 

 the transmission of trypanosomiasis, depends on the avail- 

 ability of woodland or savanna. 



There is no doubt that there are many aspects of human 

 disease, past and present, which will continue to benefit from 

 a balanced consideration of zoonoses in relation to other 

 aspects of human health. In an earlier largely agricultural 

 society for instance, can we consider the apparent historic 

 evidence for leprosy without also taking account of the possi- 

 bility of confusion with. say. contagious pustular dermatitis 

 (known as "Orf")? And should one evaluate Burkitt's lym- 

 phoma and other conditions of uncertain etiology without 

 taking into account that they may have resulted from a virus 

 zoonosis? 



In terms of distances over which disease can be intruded 

 into populations, birds are clearly a major group of rele- 

 vance. Even today in Britain, their numbers exceed humans 

 by two to one. and many are migrants. If they don't directly 

 affect human groups, wild birds can transport numerous dis- 

 eases to our domesticates (Keymer 1958). including anthrax, 

 foot and mouth disease, and salmonellosis. The bird- 

 mosquito- Japanese encephalitis link is perhaps one of the 

 more complex epidemiologies in this respect (McClure 

 1963). 



Parasite evolution and disease changes 



Viewing hominid diseases against a broader background of 

 vertebrate diseases provides more opportunity for reflecting 

 on the adaptive evolutionary changes which must have oc- 

 curred in a variety of parasite species. Lambrecht (1967). for 

 instance, provides a convincing reconstruction of the se- 

 quence of events which could have resulted in the intrusion of 

 trypanosomiasis from nonprimate mammals into hominids 

 living in savanna biomes. Eventually, Trypanosoma rhodesi- 

 enseAypt parasites evolved specifically in association with 

 the hominids. Then, in post-Pleistocene times, the early pas- 

 toralists moving south with their livestock were to be se- 

 verely affected by "nagana" in their animals, other trypano- 

 some species transferred by Glossina from reservoirs in wild 

 mammal species. 



A very different evolutionary scheme is needed to explain 

 the difterentiation of mycobacteria causing tuberculosis and 

 leprosy in the vertebrates. While Grmek (1983) suggests that 

 this parasite has a very long history of association with verte- 

 brates, extending p)erhaps over 300 million years, he views 

 the last 25,000 years as a critical period for the differentiation 

 of varieties of tuberculosis and leprosy in mammals. But 

 what ecological or other biological factors are responsible for 

 this late microevolution is not easy to resolve. 



While the differentiation of human pathogenic mycobac- 

 teria has received attention recently, further evidence of the 

 possible rate of change which can occur in that group could 



be provided by paratuberculosis (Johne's disease). So far, 

 only cattle and sheep appear to be infected. In northern Eu- 

 rope, three types have been described, including a distinc- 

 tive Icelandic form (Hungerford 1959). What is interesting 

 from an evolutionary point of view is that the Icelandic vari- 

 ety is only just over fifty years old, the disease carriers hav- 

 ing been imported from Germany in 1933. The disease 

 probably did not exist in the Icelandic sheep population 

 before then, but within the first fifteen years 70,000 had 

 been killed by it on the island (Halpin 1975). Has the dis- 

 ease changed, or are Icelandic sheep sufficiently different 

 ('?genetically-immunologically) to determine the difference, 

 or are environmental factors influencing the manifestation 

 of the disease? 



A major problem in understanding parasite evolution and 

 dispersal from a primary host to other species is that we don't 

 know enough yet about potential host resistance. Shigella, 

 for instance, is restricted in the number of mammal species it 

 normally infects, yet it has been relatively successful in pri- 

 mates (Fiennes 1978). Moreover, the virulence and often 

 fatal nature of human shigellosis, caused by our own evolved 

 pathogen Shigella dysentehae. suggests that it diverged rela- 

 tively recently from the monkey parasite S. flexneri. Could 

 this have been due to the closer association of hominids with 

 a wide variety of other higher primate species as a result of 

 increased hunting during later Pleistocene times? 



Zoonoses in relation to hunting, farming, 

 and urbanism 



During hominid evolution, profound changes have occurred 

 in terms of food resource exploitation and the development of 

 urbanism. This is not the place to enter the debate on the 

 actual antiquity of Pleistocene hunting, but food bone debris 

 and butchery marks certainly suggest that hominids were 

 widely hunting and becoming more closely associated with 

 their prey (including meat processing and skin preparation) 

 by at least half a million years ago. Compared with more 

 herbivorous primates, this closer association with other 

 mammals could have greatly assisted in establishing certain 

 zoonoses in the hominids. 



Psittacosis (i.e., all types of ornithosis), for instance, 

 would have been a potential danger to all those handling birds 

 infected with the causative microorganisms (Beaudette 

 1955). This disease is not restricted to parrots, and indeed 

 pigeons arc now an important reservoir of the infection. An- 

 other condition one could associate with increased hunting 

 would be the tick-borne infection tularemia. Toxoplasmosis 

 could have been a zoonosis of worldwide importance. While 

 cats have probably been the most important group to carry 

 these sporozoans. these days sheep and pigs are commonly 

 infected. Poorly cooked meat would enable the infection to 

 be passed on. In the indigenous South African hunter- 



Zagneb Paleopathology Symp 1988 



