Sunday, October 5, 2014

A Journey into the World of Paleoparasitology: Learning New Things from Old Stuff

Given my research interests, this type of post is LONG overdue. I've decided that I need to do a series of posts about the field of paleoparasitology. Today, I'm going to start with some basic introductory stuff to prepare you for the next few weeks. So, pull up a chair, pour yourself a nice cup of hot tea, and prepare to be amazed by the work of researchers exploring a lost world of parasites.

First things first. Let's talk terminology...after all, without understanding the proper technobabble one can't hold a conversation about a given subject. We'll start with an easy one:

Paleoparasitology--This word refers to a subfield of Paleontology that focuses on parasitic organisms of the past and on the relationships of parasites, vectors, and hosts in the past. Goncalves et al. (2003) stated, "Paleoparasitology is the study of parasites in archaeological material." Indeed, the majority of paleoparasitological studies have derived from the use of ancient materials most often obtained via excavation. The word is sometimes used in reference to any such materials, but in 1992 Dr. Karl J. Reinhard (my major professor) called for this term to refer solely to studies of "non-human, paleontological materials". In the same paper, he suggested that the term "archaeoparasitology" be used to describe the analysis of materials from human contexts for evidence of parasitism. 

Ascaris lumbricoides egg
from a Lithuanian mummy.
This brings us to Archaeoparasitology, which you now know refers to the
study of parasites from ancient materials of strictly human origin (e.g. coprolites, latrine sediments, and mummy intestines). This field is specific,
but highly interdisciplinary at the same time. The researchers within this field come from diverse backgrounds as organismal biologists, epidemiologists, ecologists, archaeologists, anthropologists, and paleopathologists, just to name a few. Many of the methods utilized in this field are borrowed from techniques used in other fields, such as veterinary parasitology or palynology.

While we are on the subject: Coprolites, if you don't already know, are desiccated feces.

Also, palynology refers to the study of "palynomorphs", which are tiny things found in air, water, or sediments including things like dinocysts, spores, or the little guys I like known as pollen. This field grew out of geology and is important for lots of reasons, but we will focus on the use of pollen as it relates to diet and environment so that we can tie it in with our understanding of parasitism in antiquity.

A Brief History of Paleoparasitology
The history of this field could fill a week's worth of lectures in a formal class setting (possibly more depending on the professor). I won't go through all of the details, but here's a few of the highlights in a timeline format:

Sir Marc Armand Ruffer, the first person to
describe parasite eggs from archaeological contexts.
~1910--Sir Marc Armand Ruffer publishes his findings of Schistosoma haematobium eggs (that's one of the three species of blood flukes that infect humans) in mummified kidneys from Egyptians dating to the 20th Dynasty (1250-1100 BC). This is the first time anyone had reported parasites from mummies, or any type of archaeological material for that matter.

~1921--Samuel T. Darling published a paper discussing the origins of South American hookworm infections among indigenous peoples based on assumptions regarding prehistoric human migrations.

~1925--Ernest T. Seton publishes On the Study of Scatology in the Journal of Mammology, which was important for demonstrating how fecal shape and content could be used to identify what order of mammal had deposited the material.

~1944--Lothar Szidat reported finding eggs from two geohelminth species (Trichuris trichiura a.k.a. the human whipworm and Ascaris lumbricoides a.k.a. "mawworms") in bog bodies from Prussia.

~1947--Van Cleave and Ross published an important methological paper describing the use of trisodium phospate for the rehydration of coprolites. The use of trisodium phosphate has now been applied to the rehydration of mummified tissues as well.

~1955--E.L. Taylor publishes his discovery of parasitic helminths recovered from a medieval cesspit. He was the first person to examine cesspits from this time period. Many others have followed in his footsteps to give us an exciting look into medieval parasitism.

~1955 & 1960--In two separate publications, Eric Callen and Thomas Cameron improved rehydration techniques. The 1960 article is one of the most frequently cited paleoparasitological papers.

The 1960s and 1970s saw an explosion of highly influential articles published in the field. The time period from 1910 up to the 1970s is often referred to as the "Exploratory Phase" of archaeoparasitology. This phase was followed by the "Population Phase" of the late 1970s through the late 1980s and by the "Synthesis Phase" in during which archaeology fused with parasitological theories. We will talk more about the predominant theoretical constructs of the field in a later post.

An example of an ELISA
(enzyme-linked immunosorbent assay)
used to detect parasite antigens.
The Synthesis Phase of archaeoparasitology was characterized by the integration of methodologies from other disciplines into the field. These borrowed techniques were adapted, reviewed, and refined throughout the 1980s and 1990s to establish methodological standards for studying parasitism via archaeological materials. Sadly, many of these standards have been lost in the influx of poorly-trained new-comers to the field and the well-established and painstakingly tested techniques can be found perverted in contemporary journal articles. Evolution of methods will be the subject of a future post.

With new technological advances in other fields came the application of new techniques in the field of paleoparasitology. The use of molecular techniques stretching from the 1990s onward has opened the door to paleoserology and the study of ancient DNA for looking at parasitism in the past. These topics will also be covered by a future post within this series.

The Big Questions of the Field
Every field has "big questions" associated with it, and paleoparasitology is no different. However, these questions are far broader and vary in their importance based on which researcher you are talking to.

The co-evolution of hosts and parasites is one region with lots of big questions. How long have humans been associated with parasite x? Did dinosaurs have parasites that evolved to parasitize modern archosaurians? Have modern advancements in helminth removal led to over-active immune systems leading to autoimmune diseases?

Tying into co-evolution questions are ecological questions, such as how host associations led to zoonotic infections in the past. ("Zoonosis" refers to a disease passed from animals to humans, e.g. rabies.) How long ago did Toxoplasma gondii establish itself in human populations?

Ecological questions involving humans, in turn, lead to behavioral and cultural questions. How did living in rockshelters and eating woodrats pull humans into the transmission cycle of Trypanosoma cruzi? How did domestication lead to human acquisition of new parasites? How did the diets of early people affect parasitism among populations? How did the lifestyles of hunter-gatherers as compared to agriculturalist predispose these groups to different types of parasites (and vice versa)?

Further branching off of these kinds of questions are questions of what parasitism can tell us about past societies. Was population x dealing with a sanitation crisis? How could a culture living far inland be infected with a parasite associated with marine fish? If parasite x requires conditions a, b, and c, how could population y have ever traveled using route z?

Questions regarding how parasitic infections were recognized, diagnosed, treated, spread, and otherwise dealt with during a variety of time periods at numerous geographic locations are the heart of paleoparasitology. Additional questions about human cultures, societal structures, subsistence patterns, migrational patterns, and trading routes can also be raised when dealing with parasite data.

The Moral of the Story
The field of paleoparasitology has a long and colorful past painted by the adroit work of observant naturalists and archaeologists. As we will learn over the course of the next several weeks, this field is interesting for both what has been discovered and for what is yet to be discovered. I suppose this could be said for any area of science, but it is especially exciting, for me at least, to add a time component to the research of parasitism. The big questions that come up within this field are as diverse as the researchers attempting to address them. The window of the past brings forth a better understanding of things as they were so that we can more efficiently address the nature of things as they are. I hope that over the next several weeks you will join me on this journey into the world of paleoparasitology.

Further Readings
If you are interested in the field of paleoparasitology or any subdiscipline thereof, I would encourage you to purchase this book. It is the best compilation of work in this area. In fact, it won one of Brazil's most natural sciences book awards, the Prêmio Jabuti, or "Tortoise Award." (Which you can learn more about here if you are interested. Also, here is a link to a news release about the book and about the Science Without Borders grant related to the collaborative work of the editors.) I'll be using my copy of this book as a reference for the series of posts relating to this field. (Also, the timeline stemmed from a much more detailed and informative timeline found in the first chapter of this book.)

Additionally, here's a great article published in the special edition 100th volume of the Journal of Parasitology that relates to paleoparasitology. It's a must-read for anyone interested!

Also, here are the citations mentioned in the post above:

Gonçalves, M.L.C., A. Araújo, and L.F. Ferreira (2003) Human intestinal parasites in the past: New findings and a review. Memórias do Instituto Oswaldo Cruz 98(Suppl 1):103-118.

Reinhard, K.J. (1992) Parasitology as an interpretive tool in archaeology. American Antiquity 57(2):231-245.