In her introduction to Parasites: Tales of Humanity's Most Unwelcome Guests, author Rosemary Drisdelle, a clinical parasitologist living in Nova Scotia, begins by saying what we all know: that parasites and their influences are often unknown, hidden, ignored, and otherwise unrecognized. Indeed, join two parasitologists for coffee or beer, and you are likely to hear a similar tale of fascinating animals that have somehow escaped recognition. But the author is clearly not content with this state of ignorance, and she uses it as a springboard to launch her mission in this book: “In the pages that follow, I seize the parasites one by one, drag them into the light, and ask, ‘What are you and what are you up to?’” Right there, on page 3, is the last time she says much of anything that we all know. This is a book of surprises.
Drisdelle introduces many, if not most, parasites of humans in this book, but she does much more than commandeer a march through medical parasitology. Instead, she is an expert tour guide, sharing her excitement at finding the next unexpected view, the next little-known connection, the next worm, flea, tick, or protist set to make its living on humans—all the while regaling her readers with the stories that swirl around parasites but that are often left out of textbooks. Therefore, we not only learn about Trichinella spiralis, we learn about the prolonged effect of T. spiralis on one person who consumed uncooked pork, and we learn about the broader effect of T. spiralis on food-safety regulations. We not only learn about the deadly tapeworm Echinococcus multilocularis, we learn about how parasites travel, sometimes as stowaways in animals that are themselves smuggled into a country. We learn about the role of parasites in crime—or in preventing crime—and about their role in world affairs. And we are introduced to that most far-flung group of parasites, sometimes the most devastating of all: those that inhabit the imagination.
Committed to this layered approach, Drisdelle resists the temptation to organize the book along taxonomic or even diagnostic lines. Instead, the themes of her nine central chapters, bookended by an introduction and an epilogue, reflect the stories she tells. One chapter is devoted to the effects of parasites on history, another to parasite immigrants, yet others to parasite emergence and extinction. Not surprisingly, there is one chapter focusing on food and another on water. Within each of these chapters, Drisdelle weaves stories together with remarkable skill. For instance, she begins the chapter on immigrant parasites with hookworms arriving in Jamestown, Virginia, in 1694, carried by slaves. She detours into the pathology associated with Necator americanus, which leads to a discussion of its role in the American Civil War. From there, we are introduced to a broader swath of immigrants and their parasites, ranging from honeybees with mites to reindeer with worms. The flow of her writing reminds us that these parasite-host associations do not exist in a vacuum but are part of a much larger network, and Drisdelle takes care to demonstrate that not all of the connections and outcomes are bad.
From St. Thomas à Becket's lice (impressive even to his “lousy” medieval contemporaries) to modern terrorists who are stopped in their tracks by parasites, Drisdelle's subject matter is interesting enough, but her writing style makes the book even more engaging. She writes humorously, sharing advice that one is not likely to pick up on any street corner (e.g., “If you don't want your intestinal contents analyzed thousands of years after your death, do not defecate in caves.” p. 6). In addition, her use of imagery is creative and instructional. For instance, in chapter 3, she asks us to imagine that we are touring a watershed (and a water treatment facility) while perched on an oocyst of Cryptosporidium, which evades centrifugation and rises “like a shimmery hot air balloon.” She informs us that because of our very small size, we can clear the filtration system—we are “veteran whitewater rafter [s] on a giant [oocyst] beachball” moving through “boulders” of anthracite and sand. If we peer inside the oocyst, we see the sporozoites, which look “like fat sleeping maggots.”
In the chapter on food-borne parasites, Drisdelle asks us to examine a fly that has been stopped in midair and magnified 500 times. Amid spines and eyes “like the surface of a ripe raspberry,” there are “glittering balls,” “slightly flattened grains of cooked tapioca”—Toxoplasma gondii oocysts. We find all manner of hitchhikers inhabiting the surface of a fly; Drisdelle's narrative is at once disconcerting and skillful, flowing between tapeworm eggs that resemble golden-brown marbles and the biological backstory that reminds us of fecal contamination, which is the ultimate source of those marbles, that tapioca, and the serpentine nematode hatched from yet another egg.
Drisdelle has written one of those rare books that is fun to read but does not skimp on scholarly rigor. Both the chapter notes and the selected bibliography are detailed; together, they make up almost 30 pages of the book. It is a treasure trove of anecdotes, not to mention novel perspectives, that professors of organismal animal biology will find invaluable in their teaching. It is also a fabulous auxiliary text for courses about parasitology or public health.
The word parasite originated as a Greek term for someone who eats at someone else's table, often without payment. We have all had unwelcome guests in that sense. Some of those folks whose visits we have endured might have been more welcome were they half as interesting as the guests we meet in Parasites: Tales of Humanity's Most Unwelcome Guests.