Abstracts

REVIEW

Animal helminths in human archaeological remains: a review of zoonoses in the past

Helmintos animais em vestígios arqueológicos humanos: revisão de zoonoses no passado

Luciana Sianto^I; Marcia Chame^I; Cassius S.P. Silva^I; Marcelo L.C. Gonçalves^II; Karl Reinhard^III; Martin Fugassa^IV; Adauto Araújo^I

^IFundação Oswaldo Cruz, Escola Nacional de Saúde Pública Sérgio Arouca, Rua Leopoldo Bulhões 1480, 21041-210 Rio de Janeiro, RJ, Brasil

^IIUniversidade de Fortaleza, Av. Washington Soares 1321, Edson Queiroz, 60811-341 Fortaleza, CE, Brasil

^IIIUniversity of Nebraska, Lincoln, NE 68588, USA

^IVCONICET, Universidad Nacional de Mar del Plata, Diagonal J. B. Alberdi 2695 - (7600)- Mar del Plata, Argentina

^{Correspondence to:} Correspondence to: Adauto Araújo Fundação Oswaldo Cruz, Escola Nacional de Saúde Pública Sérgio Arouca Rua Leopoldo Bulhões 1480 21041-210 Rio de Janeiro, RJ, Brazil adauto@ensp.fiocruz.br

ABSTRACT

The authors present a review of records of intestinal parasitic helminths from animals in human archaeological remains, reported since the emergence of paleopathological studies. The objective was to relate paleoparasitological findings to geographic, biotic, and abiotic factors from the environment in which the prehistoric populations lived, and understand some aspects related to the process of human dispersion and biological and cultural evolution. Modification of eating habits and the incorporation of new cultural practices are analyzed from the perspective of zoonoses from prehistory to the present day, especially in Brazilian indigenous populations. Three tables identifying the helminths, their natural hosts, dates, and sites of archaeological findings complete this review. In conclusion, various zoonoses known today have occurred since antiquity, and these data, combined with studies on the emergence and reemergence of diseases, could make possible to compose scenarios for the future.

Keywords: Coprolites; Paleoparasitology; Helminthiasis; Zoonoses; Ancient diseases.

RESUMO

São revistos os registros de ocorrência de helmintos intestinais parasitos de animais em vestígios arqueológicos humanos, relatados desde o surgimento dos estudos paleopatológicos. Busca-se relacionar os achados em paleoparasitologia com fatores geográficos, bióticos e abióticos do ambiente em que as populações pré-históricas viviam, e com aspectos do processo de dispersão e evolução biológica e cultural humana. A modificação de hábitos alimentares e a incorporação de novas práticas culturais são analisadas sob o ponto de vista das zoonoses desde a pré-história até a atualidade, em especial em populações indígenas brasileiras. Três tabelas identificando os helmintos, seus hospedeiros naturais, datações e local dos achados arqueológicos complementam esta revisão. Conclui-se que várias zoonoses conhecidas hoje ocorrem desde a antiguidade e que estes dados, combinados a estudos de emergência e reemergência de doenças, podem auxiliar a compor cenários para o futuro.

INTRODUCTION

Parasites of animals may infect humans, and in some cases cause disease. On the other hand, false parasitism is also observed in individuals after eating infected animals with parasite species that are not able to infect humans. Therefore, the eggs pass with feces without causing infection, as recorded in indigenous groups²⁹. In examining archaeological material one has to separate coprolites of human origin from others of animal origin. However, parasitism is a dynamic process, and changes may occur.

The finding of Echinostoma sp. in a mummified body from the pre-Colombian period in Minas Gerais State, Brazil¹¹⁹ can be used as an indication of modifications in the parasite fauna in human groups over time. These modifications reflect possible variations in eating habits among prehistoric human groups, since hunter-gatherers ingested wild animals, thus becoming potential hosts for new parasites over the course of their evolutionary history⁵⁴.

Cases of animal parasites infecting humans were described in Europe, especially in the Neolithic and Medieval periods⁷¹, and in Patagonia in the pre-contact period⁴⁵. Evidence of the ingestion of small animals, consumed whole or in pieces, without cooking, described by REINHARD¹⁰³ in human coprolites, increased the interest in the investigations of animals used for food and as possible transmitters of parasites to humans.

The possibilities for the occurrence of parasitic helminths from wild animals in prehistoric human populations are wide and variable according to the local fauna and different habits and cultures around the world. The absence of many of these species today reflects the change in these parameters, especially since agriculture and domestication^32,54.

Thus, the interest in studying eating habits in past times and the interaction with intermediate, definitive, and paratenic hosts motivated a review of findings of helminths in archaeological material, situating them in time and space, as well as associating them with the living habits of ancient human groups.

The study of parasites in archaeological material has developed extensively in recent decades⁴⁰. Since its emergence nearly a century ago, paleoparasitology has contributed empirical data on the presence of infections and clinical disease conditions among populations that have already disappeared from the Old and New Worlds. This science provides data on the evolution of parasites and their hosts, in addition to helping understand the occupation of territories and retracing migratory paths of prehistoric populations^2,4.

Paleoparasitological findings feature not only specific human parasites, inherited from ancestors, but also those acquired over the course of hominid dispersion and biological and cultural evolution³. Therefore, in paleoparasitology it is very important to know whether the coprolite is of human or other animal origin. Thus, the final diagnosis is based on evidences pointing to a true infection by a parasite or a false parasitism. A zoonosis may have occurred, i.e., a parasite of an animal may also have infected humans, and the paleoparasitologist has to deal with this possibility.

Rudolph Virchow coined the term zoonosis in 1855. Since then, other authors have attempted to define zoonoses and identify their causes, propelled by the early age of bacteriology that furnished data concerning their etiological agents and modes of transmission⁷³. In the 1950s, the World Health Organization (WHO) issued its definition of zoonosis. The official concept (1959), adopted to this day, defines zoonosis as any disease or infection that is naturally transmissible from vertebrate animals to humans^73,88 and vice-versa. This transmission is possible since parasites can occur in hosts over the course of the evolutionary process, that is, there is a parasite specificity that restricts infections, but the latter can occur by evolutionary adaptation in new host species^9,54.

These various possibilities can include an accidental encounter between parasites and new hosts. Such encounters can generate new intraspecific relations (either successful or unsuccessful) and intermediate relations⁹¹. This fact can be exemplified by the sporadic finding of animal helminth eggs in human feces, merely meaning human consumption of some animal infected with the parasite and that the eggs passed through the human digestive tract together with the ingested food, without establishing a relationship and without even causing any damage to his health³⁸.

REINHARD¹⁰² also refers to false parasitism, a relationship in which the parasite's lack of specificity with the individual that consumed it prevents the parasite from completing its biological cycle, developing, or multiplying inside this host; a large quantity of eggs in the feces would indicate true infection. The amount of eggs found in coprolites can vary according to the fragment of the sample used, the taphonomic processes involved, the diversity of parasites in an individual^40,102, environmental factors⁶³, and interaction between parasites that occupy the same habitat and that can express themselves in inter and intra-specific cooperation and/or competition^6,12. COIMBRA Jr. & MELLO²⁹ report the consumption of raw rodent liver by indigenous peoples, in whom Capillaria eggs are eliminated for days, but without infection occurring.

When an animal parasite manages to establish itself in the human body, a true infection occurs, thus a zoonosis, whether or not the parasite succeeds in completing its life cycle. For example, human infection with larvae of Ancylostoma caninum or Toxocara canis, both canine parasites, cause infection and clinical manifestations, but the parasites do not complete their life cycle in the human host¹⁰⁵. Another example is Trichinella spiralis infection. Humans become infected when they eat raw or undercooked meat of infected animals, especially pigs. There are ancient records of T. spiralis infection in Egypt from 3,220 years BP³⁰ (Before Present), Spain in the 19^th century 19 AD¹³ (Anno Domini), and Alaska from 440 ±70 BP¹³⁸. Currently, in addition to T. spirallis, eight other species of the genus have been recorded in humans⁹⁹. Echinococcus granulosus also fails to complete its cycle in humans but has been found in archaeological remains in the USA^79,89,132, Europe^{11,21,100,130,131}, and Middle East^5,137.

In this review we searched only for records of intestinal helminths. The article by GONÇALVES et al.⁵² guided the research. We conducted a search in electronic databases (PubMed, Isi Web of Science, Scopus, Scirus, and Scielo) up to January 2008 and a search in indexing journals. The attempt was to verify all the existing records on paleoparasitology and related sciences that in some way had recorded the occurrence of animal intestinal parasitic helminths in human archaeological remains. We excluded findings of uncertain origin, but false parasitism was considered.

This review is expected to expand the knowledge on the occurrence of animal parasites in humans from an evolutionary perspective, from prehistoric periods, correlating them to the various regions of the world, chronology, and different habits between populations, thus contributing to the studies conducted today among special populations, like indigenous groups in Brazil.

Principal Zoonoses of the Old World (except East and Southeast Asia)

As shown in Table 1, the majority of findings of animal parasites in human archaeological material from the Old World are concentrated in Europe, where numerous latrines provide material for paleoparasitological analyses of practically the entire continent¹⁸.

The first published studies containing zoonotic helminths were by SZIDAT¹²⁴, who found Diphyllobothrium latum eggs in material from Austria dated 1,500 years BP, followed by findings of Dicrocoelium sp. in material from England dated 1,100 AD¹²⁵. In Germany, JANSEN & OVER⁶⁸ found D. latum, Taenia sp., and Fasciola hepatica eggs dated 100 BC - 500 AD. The paleoparasitological findings since then have always shown the presence of zoonotic parasites transmitted mainly by consumption of and/or contact with domesticated animals. The domestication of animals and plants favored an increase in the occurrence of parasitosis among human populations, as exemplified in specific regions. The increase in food production obtained through agriculture favored the agglomeration of individuals and consequently the occurrence of specific human parasites, transmitted by direct contact with environments and/or contaminated foods. In addition, the agricultural surplus was stored in deposits, increasing the potential risk of infection by contamination of the grain or other foodstuffs and by attracting animals like rodents^7,31,87, the natural hosts of various zoonoses affecting humans⁹².

With domestication, humans kept animals close to them for consumption, like cattle, goats, and pigs, as well as companion animals like dogs and cats. ROCHA et al.¹¹² and FERNANDES et al.³⁷, studying material from Medieval European latrines, showed that specific human parasites like Ascaris lumbricoides and Trichuris trichiura, and animal parasites like Ascaris suum and Trichuris suis, that infect swine, appeared in association with each other, thus proving the close relationship between man and these animals, already demonstrated by archaeological records. This constant contact with animals facilitated the transmission of parasites, including zoonotic ones, that were previously acquired sporadically, like Taenia sp., Capillaria sp., and Fasciola sp., causing an increase in the number of animal parasite infections in human populations^{8,15,16,18,19,34,35,36,37,61,62,67,68,71,86,110}.

Still, little or nothing is known about the parasites that affected Old World populations before the domestication of plants and animals, since most parasite findings in archaeological material date to after the introduction of agriculture as a means of subsistence. The oldest records of animal parasites in human archaeological remains are from the African continent and Middle East, already in agricultural societies, where eggs from the genera Diphyllobothrium, Dicrocoelium, Taenia, and Fasciola were found in material dating close to 10,000 BP in Israel, South Africa, and Egypt^33,61,81.

In Europe, the oldest records date to 4,500 year old Fasciola hepatica eggs found in human and cattle coprolites in Germany³⁴, and 3,900 - 2,900 BP, with Dicrocoelium sp., Fasciola hepatica, Opistorchiformes, Diphyllobothrium sp., Taenia sp., and Dioctophyma renale eggs found in archaeological material belonging to lacustrine communities in the Swiss and French Alps^35,36,71. Although these findings are from communities that dominated farming techniques, they belong to the period in which the Pfn-Horgen transition occurred in the Neolithic (3,900 - 2,500 BC), when climate changes affected the production of cultivated grains, leading to subsistence crises. The population was thus forced to turn to the consumption of wild vegetables, and also hunting and fishing, often consuming raw items^35,36,71.

East and Southeast Asia

In Asia, especially in Japan, findings are related mainly to parasites acquired through the consumption of raw fish, a cultural tradition that dates to prehistoric times, popularized with the emergence of sushi in the 4^th century AD⁶⁵ (Table 2). Clonorchis sinensis, Paragonimus sp., Metagonimus yokogawai, and Diphyllobothrium sp. eggs have been found in fecal material from Japanese archaeological sites dated from 2,300 BP to the 12^th century 12 AD⁷⁸. Unlike Japan, in China, where foods are traditionally cooked before eating, C. sinensis, Schistosoma japonicum, and T. solium eggs have been found in archaeological remains dated from 2,300 BP to 2,100 BP^{27,72,129,136}. In Korea, C. sinensis eggs have been found in human remains dated to 668 - 935 AD and 1,411 ± 42 AD^58,117. A mummy from 1,650 - 1750 AD was also found with Metagonimus yokogawai and Gymnophalloides seoi eggs¹¹⁸.

Currently, the main zoonotic helminths in the Asian population are still related to the consumption of raw fish and other seafood²⁵.

New World

Agriculture was not adopted at the same in the New World as in the Old World. Various prehistoric populations either continued their hunting-gathering habits - despite knowledge of farming techniques adopted by other groups in the same region - or used them jointly^32,103.

PICKERSGILL⁹⁷ reports four independent areas in which vestiges of agricultural development in the Americas by pre-Colombian groups can be observed: Southeast North America, Mesoamerica, the Andes region, and tropical lowlands in South America, with the cultivation of corn (Zea mays), beans (Phaseolus vulgaris), potatoes (Solanum tuberosum), manioc (Manihot esculenta), squash (Cucurbita spp.), and peanuts (Arachis hypogaea), among others, by pre-Colombian groups^{74,97,101,102,122}.

However, the domestication of animals shows major differences in comparison to the process that occurred in the Old World²². DIAMOND³¹ explains this difference by local geography and climate, since the majority of large herbivores were located in Eurasia, while the Americas had few large species with chances of domestication, especially after the great extinctions of mammals in the Late Pleistocene.

Importantly, however, is that the great herds of Old World herbivores are migratory or occupy large areas, requiring continuous shifting of human populations to follow this resource, through areas that are sometimes inhospitable or used by other human groups, a phenomenon known as transhumance¹³⁹. From this perspective, the investment in domestication brings advantageous results⁷⁰. However, in the Americas, despite the existence of medium and large social herbivores like the Rocky Mountain Bighorn sheep (Ovis canadensis), American bison (Bison bison), moose (Alces alces), and others in North America⁵¹, there is no evidence that these species were domesticated, although they were hunted for food.

The domestication of animals in the New World occurred mainly in the Andean region and Mexico, where native groups domesticated ducks (Cairina moschata), turkeys (Meleagris gallopavo), guinea pigs (Cavia porcellus), and llamas (Lama glama), from which they obtained milk and meat, and alpaca (L. pacos), used mainly for wool^22,123. Dogs were also raised for food in Mexico¹³³, but domestication of the dog did not occur on this continent. Dogs (already domesticated) came in the company of prehistoric humans when they arrived on the American continent some 14,000 years ago¹¹⁵.

For most native groups in the South American lowlands, animals were not domesticated for food. In Brazil, for example, various indigenous groups kept wild animals either as pets or for plucking feathers in the case of birds¹⁰¹. Although there is no abundance of large herbivores in groups, like those that exist in Eurasia, North America, and Africa, some, like peccaries (Tayassu pecari and Pecari tajacu) and tapirs (Tapirus anta) could have been domesticated. However, since the browsing and grazing areas for these species are relatively small, they are not migratory. Other species such as wild pigs and capybaras live in large herds^80,127 and thus provide permanently available food, in addition to the abundant supply of fish in many South American lowland regions⁸¹.

Unlike the Old World, in the New World there are samples of coprolites available from both hunting-and-gathering and farming populations, thus allowing to expand the knowledge on the possible consequences of the domestication of animals and especially of plants as alternative food sources in prehistoric populations, although in different scenarios and situations.

North and Central America

In North America, animal parasite findings in human coprolites are concentrated in the USA^{42,43,44,55,56,57,58,59,84}. REINHARD¹⁰² reviews the occurrence of parasites in the United States according to the geographic areas where they were found. The author showed that most of the findings are situated in the southern part of North America and Mexico, with Acanthocephala and Hymenolepididae eggs, among others. A peculiar case is the finding of eggs from Moniliformis clarki, an acanthocephalan transmitted by consuming insects, a common eating habit among North American indigenous peoples. For a long time Acanthocephala findings were attributed to false parasitism. However, the frequency of these findings in prehistoric material from the Americas in association with cultural customs favoring infection suggests that these parasites really infected these populations. However, this frequency may only reflect the preference or abundance of the available supply of insects for eating.

Data obtained by REINHARD¹⁰², principally among the ancestral Pueblo of the United States (the ancient Anasazi), show that as occurred with Old World populations, the incidence of specific human parasites increased with the introduction of agriculture. Another episode that increased the occurrence of parasites in these populations occurred during an apparent ecological collapse which, similar to one that occurred in Europe⁷¹, led the inhabitants of the last occupation of the Antelope House in Arizona to consume wild plants like cacti to replace the lack of cultivated crops. This strategy was also apparently adopted during dry seasons, when wild plants and also dogs, rabbits, whole rodents, lizards, and other animals were consumed¹⁰³.

In addition to the findings cited above, BOUCHET et al^17,20 found eggs from genus Diphyllobothrium in samples from Alaska.

South America

In South America, a zoonosis that is known to have occurred in a prehistoric population and that still exists in current-day populations in Peru and Chile is the presence of Diphyllobothrium pacificum. Swiss parasitologist Jean BAER¹⁰, called to Peru to study parasites found in persons with an intestinal clinical condition, identified the species D. pacificum in the patients, a parasite of sea lions whose larvae contaminate saltwater fish and shellfish. The presence of this parasite in the population is explained by the consumption of a traditional dish by the Pacific coastal populations, cebiche, made with raw sea fish. BAER raised the hypothesis that the prehistoric populations also had this parasitosis, a fact confirmed years later when D. pacificum eggs were found in Chilean coprolites 4,000 years old by FERREIRA et al.³⁹, who commented on the coincidence in the findings. Other researchers also confirmed the presence of this parasite in prehistoric populations on the Pacific coast^{23,93,106,108}.

In Brazil there are only three records of animal helminths in human coprolites. The first was by ARAÚJO et al.¹, who found Trichostrongylus sp. eggs associated with T. trichiura eggs in a mummified body from the colonial period. GONÇALVES et al.⁵² found Acanthocephala eggs in material dated 4,905 - 1,325 BP in Minas Gerais. But perhaps the most significant finding of a zoonosis in archaeological material in Brazil came from a paleoparasitological review of coprolite samples from a naturally mummified body in the State of Minas Gerais, Southeast Brazil, dated 600 - 1,200 BP, which allowed the correct identification of Echinostoma sp. eggs and the certainty of this parasite's occurrence in humans¹¹⁹Echinostomiasis is an endemic zoonosis in Asia, that can produce debilitating symptoms in infected individuals^41,53. Humans become infected by the ingestion of Echinostoma spp. larvae present in raw mollusks, fish, or amphibians, the parasite's intermediate hosts¹¹¹. This is the first record of Echinostoma sp. in humans in Brazil, and the finding enriched the data on the circulation of other zoonotic parasites in ancient populations.

Echinostoma sp., Paragonimus sp., Diphyllobothrium sp., Diphyllobothrium pacificum, Capillaria spp., Trichostrongylus sp., and Acanthocephala are the zoonotic helminths that have already been found in South American populations (Table 3). We only considered findings that dated up to close to contact with Europeans, since they are what we can positively classify as pre-Colombian. Thus, the current study excluded the findings by HORNE & TUCK⁶⁶ and FUGASSA⁴⁵, of Taenia sp. eggs in 17^th-century material from Canada and 19^th-century material from Argentina, since they are related respectively to the introduction of swine and beef cattle on the American continent after discovery.

Present Day

Currently, zoonoses caused by helminths have important impacts on human development around the world^49,77,92. Recent publications have classified the majority of emerging or reemerging pathogens as zoonotic^88,126,135.

Nevertheless, records are rare on the occurrence of zoonoses among current native populations in Brazil. This is curious, since many Brazilian indigenous groups have maintained their traditional eating habits and continue to hunt and consume wild animals as their principal source of protein^81,85. Many game animals are natural hosts of parasites, including helminths^46,64,109.

The explanation for this gap may lay in the fact that after contact with Brazilian national society, many indigenous communities have undergone social, economic, and environmental changes. Such changes have influenced the epidemiological profile of these groups, which have obtained easy access to antihelminthic drugs through indigenous health agents¹²⁰, often administered without any control. In addition, geographical restrictions imposed by territorial demarcation and transformation of semi-nomadic into sedentary behavior in the majority of the South American indigenous groups have contributed to fixing large groups, resulting in villages with high population densities and precarious sanitation, facilitating the transmission of specific human parasites that compete with those of animal origin^28,29,134.

Such data are provided by the publications by VIEIRA¹²⁸ and SILVA¹²⁰, both on intestinal parasitosis in Brazilian indigenous populations. In the literature review by VIEIRA¹²⁸ covering indigenous groups from throughout Brazil, Hymenolepis sp., Taenia sp., and Capillaria sp. were the only zoonotic helminths cited.

SILVA¹²⁰ conducted an extensive coprological analysis of the Suruí population, an indigenous tribe in the State of Rondônia in the Brazilian Amazon. Stool specimens were analyzed in two laboratories and were positive for the tapeworm Hymenolepis diminuta in 21/541 (3.9%) samples, and for Capillaria sp. in 28/541 samples (5.2%) of the specimens in this same set. A middle-aged woman's stool test showed eggs from Dipylidium caninum, a tapeworm rarely found in humans. D. caninum is a parasite of domestic and wild canids and felines that infects humans through the ingestion of an infected arthropod⁹². D. caninum and Hymenolepis diminuta have still not been found in paleoparasitological analyses. Hymenolepis spp. eggs were found in samples from the USA and Sudan^61,107, although the species were not identified and may be H. nana, specific to humans.

Many Brazilian indigenous groups consider viscera from animal, especially liver, a delicacy. The liver is consumed raw, and thus the presence of Capillaria sp. eggs in the feces of native Brazilian populations is not uncommon^{24,29,50,113,114}. Capillaria sp. eggs have also been found in paleoparasitological analyses in Europe^7,37, but not in Brazil.

DISCUSSION AND CONCLUSION

Although in this review we adopted the World Health Organization's definition of zoonosis, we did not consider A. lumbricoides a zoonotic helminth as the WHO does. The A. lumbricoides cycle is direct and independent of another animal, and its origin is by the phylogenetic route, that is, descending from a common ancestor of humans and primates^3,4. Parasites originating from the ecological route can be classified in two categories: (1) those that originated from other species and underwent modification over the course of the evolutionary process and became species-specific to humans (meaning that they differ from the original species) and (2) zoonoses. An example of the first category is the human immunodeficiency virus (HIV). MARX et al.⁷⁶ argue that AIDS is not a zoonosis, since the virus underwent modifications from the original version to infect humans, which goes against the concept of zoonosis as a disease naturally shared by animals and humans. Among the helminths, a good example is H. nana. According to the Pan-American Health Organization, some parasitologists classify the species that infects humans as H. nana var. nana and the species that infects rodents as H. nana var. fraterna, on grounds that there is a parasite host-specificity, justified by the lack of evidence of H. nana transmission from rodents to humans⁹².

The parasitism phenomenon consists of dynamic relations within a natural evolutionary process as old as life itself³⁸. An animal parasite that does not infect humans may begin to do so if pressure, genetic potentiality and plasticity allow it. The pressures for such an alteration can come from the environment itself, especially if the original hosts become scarce and thus its survival comes to depend on the incorporation of new hosts into its cycle^12,95. A zoonosis occurs when these conditions appear. But if the alteration is so great that the parasite becomes totally specific to the new host^9,90, the outcome could be similar to HIV infection⁷⁶. This may be taken as a general rule, as probably different responses occur from virus to other parasite organisms.

During human history, populations have faced different environmental conditions with biological and cultural adaptations. Scarcity of food and other resources necessary for survival, and also climatic and environmental changes have facilitated contact between humans and parasites, from animal origin or even not known to science, as evidenced by the work of LE BAILLY⁷¹, FUGASSA⁴⁵, and REINHARD¹⁰³ in prehistoric populations of Europe, Argentina, and North America, respectively.

McMICHAEL⁸⁰ argues that the historical transitions experienced by our prehistoric ancestors when they climbed down out of the trees onto the savannahs, incorporated meat into their diet, and more recently since the emergence of Homo sapiens, the development of agriculture, and the conquest of new territories and civilizations favored the emergence of (and exposure to) infectious agents of animal origin. ARMELAGOS et al.⁷ analyzed the epidemiological transitions experienced by humankind and concluded that we are undergoing a new transition, in which parasitic infections that were common 10,000 years ago, at the time of the first transition (with the development of techniques for cultivation of plants and domestication of animals), are now reemerging with the possibility of causing major economic impacts. The agricultural frontier's encroachment on natural areas and parasites' resistance to conventional treatments can explain this reemergence.

Paleoparasitological findings are important clues for knowledge on human adaptive progress since prehistory, in addition to revealing eating habits of extinct populations and the domestication of animals. The current study shows that various zoonoses known today have occurred since prehistoric times. The knowledge of which parasites circulated in the past and their geographic distribution helps understand whether a zoonosis is emerging or reemerging⁷⁷.

Thus, the fact that D. caninum, Capillaria sp., and other parasites have not been found in human archaeological material in South America does not mean that they did not exist or that these infections did not occur.

We recently identified genus Spirometra (Cestoda) in feline coprolites from the Serra da Capivara National Park in Piauí State, Brazil (unpublished data). This parasite is the causative agent of sparganosis in humans, and one cannot ignore the possibility of this and other parasites circulating in the local human population. Few authors conduct studies with archaeological material of animal origin. This may represent a loss of information, since the parasite's presence in the local fauna, associated with environmental and socio-cultural factors like diet and type of dwellings, may indicate transmission routes for the parasites to human populations.

To the extent that more sensitive diagnostic techniques become available, more parasitic infections from the past are detected, and new paleoparasitological findings are recorded around the world. Additional studies on zoonotic infections from the past will expand the knowledge on biological and sociological aspects of the health-disease process and the co-evolution between parasites and animal and human hosts.

In addition, the identification of zoonoses that affected ancestral peoples, understanding their mechanisms of transmission and the factors affecting this dynamic (whether biogeographic, ecological, cultural, historical, or social), can help development of forecasting models to control parasitic diseases soon after their emergence or even to prevent them before they become public health problems.

Geographic, biotic, and abiotic factors from the environment in which prehistoric populations lived (biocenosis) and their cultural characteristics can trace models for the predictability and transmission of the parasite fauna in these groups, as done by MARTINSON et al.⁷⁵ and REINHARD¹⁰⁴, and are based on models grounded in the theory of natural foci^94,96,121. These studies are especially applicable to zoonoses, since biocenosis in natural ecosystems is well defined¹²¹, but they can also be applied to human-specific parasites.

Recent advances correlating the processes of fragmentation and isolation of natural areas to genetic loss, the interruption of gene flow between species, and the introduction of invasive exotic species in the wild fauna^26,69 can help compose prehistoric scenarios that favored the occurrence of animal parasites in humans, as well as drawing scenarios for the future.

ACKNOWLEDGEMENTS

Funding: CNPq, FAPERJ, CAPES

Received: 17 November 2008

Accepted: 7 April 2009

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