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Parasites: signs on our way

The mysteries of human evolution, their development and their movementsthroughout history continue to create great interest and expectation. There are stillmany things to discover and understand about ancient societies, but thanks to thehelp of the science we are increasingly closer. Can parasites of the past shed light on those communities? We will discover it in thehands of the paleoparasitology.

WHAT IS PALEOPARASITOLOGY?

This is a branch of paleontology that study parasitological evidences in archaeological records, i.e.,studying parasites or remains of these found in ancient archaeological sites. The objective of these studies is to shed light on the origin and evolution of parasitic diseases that exist, as well as determine their phylogenetic relationships.  The study of ancient parasites allows us to know socio-cultural aspects of ancient societies as for example their diets, their level of hygiene, if human  were nomadic or sedentary, their migrations etc.

The materials studied by the paleoparasitology are generally fossilized tissueremains, mummies, fossils, coprolites (feces mummified) or sediments that have been able to be in contact with those who were the hosts of these parasites.

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Mummified human coprolites. (Image: M. Beltrame)

Find remains of a parasite in some of the samples is difficult, since the passage oftime destroys all evidence. Even so, usually eggs or Oocyst parasites found (since theyare forms of resistance that have managed to stay over the millennia).

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A egg of a louse (Pediculus humanus) found in a mummy of Brazil (12,000 years old). B. egg of Trichuris sp. found in Cape virgins, Argentina (6000 years old). (Image: Araujo).

In certain cases, manuscripts and drawings of ancient societies have providedinformation on the presence of certain parasites, such as for example ceramics thatwe observe below, where lesions that presents a person who suffers from cutaneous leishmaniasis is faithfully represented. In the next image we see a fossilized skull which presents very similar lesions.

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A. Modified image of a ceramic moche representing (red circle) lesions caused by leishmaniasis. (Image: Oscar Anton, Pinterest) B. mummified skull that shows very similar injuries. (Image: Karl J. Reinhard).

THE ARRIVAL TO AMERICA: HUMAN MIGRATIONS AND PARASITES

About 150,000 years ago appeared a new species of hominid in Africa: Homo sapiens. It began to expand in several waves to the rest of the continent, Europe, and Asia,carrying with them some parasites that had inherited from his ancestors (known as heirloom parasites). At the same time, they were acquiring along their journey a range of parasites due to interactions with other humans and animals (souvenir parasites).

Following the archaeological remains and parasitological  clues what ancient humans have left during their migrations, is possible to determine the routes followed by them. One of these routes was the arrival in the new world (America). We have always believed that the first inhabitants of the Americas came across the Beringia Strait (which joined at some point by ice Siberia with Alaska) about 13,000 years ago.

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Representation of the path followed by the first American settlers by the Beringia Strait Bridge. (Image: The siberian Times).
A few very interesting parasites that can be found in the American archaeological remains are Trichuris trichiura (nematode known as whipworm  and Ancylostoma duodenale (hookworm). These parasites need tropical or subtropical climatic conditions since the eggs are expelled with faeces and mature in the ground.
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A. At the top adult A. duodenale (Christopher Noble). At bottom we can view an A.duodenale egg (Image: Universidad Antioquia) B. Adult Trichuris trichiura (Invertebrate zoology Virtual collection) and at bottom its egg. (Microbiolgia blogspot).

How do they then survived the cold conditions of the regions of Siberia and Alaska in the last ice age? They could not. These parasites would have not survived those harsh climatic conditions, since to their maturation and transformation infective they need warm and moist environments. In addition, signs of infections not found by these parasites in Arctic populations, such as the Inuit.

So, researchers believe that migration across the Bering Strait was not the only one. Paleoparasitologic experts  Adauto Aráujo and Karl J. Reinhard proposed that there were two alternative routes. On the one hand proposed a costal route (along the coast, route b in the image) and a trans-pacific route (crossing the Pacific Ocean, route c). By these routes parasites had been able to survive and continue infecting humans.

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The arrival of man in America routes proposed by Aráujo and Reinhard based on paleoparasitologic remains. (Image: Aráujo, et al.)

Could they have been already there? This question has an easy answer. These intestinal parasites are specific from man, therefore, they need human hosts to complete their life cycles. If there were no humans in America, surely there would be this kind of parasites.

Another  parasitological fact that confirm this theory is the presence of Enterobius vermicularis, popularly known as pinworm. This parasite was linked for the first time to the ancestors of Homo sapiens and throughout history, has coevolved with them to give rise to several different subspecies. On the American continent have been found remains of two lineages of E.vermicularis, that could be because arrived hominids from different places with different parasites. In this case, the parasite if he could get through the Beringia Strait, since its life cycle does not depend so strongly on the environmental conditions.

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“Parasites suffer the same phenomena for evolution that humans and other organisms, as selection, extinction and colonization. For this reason, these specific parasites of man are excellent evidence that shed light on the movements of our ancestors”Adauto Aráujo, 2008.

REFERENCES

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