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Parasites and Other Creeps that Violate Your Body

David Bruce Conn, M.S., Ph.D.

While many important human infections are caused by bacteria, viruses, fungi, and other infectious agents, the next several chapters will deal with the extremely complex pathogens known by scientific convention as parasites.  If we are to understand parasitic diseases, we must start by understanding a bit about parasites and parasitism in general.  Beyond that, we must develop a basic understanding about the nature of disease, and how a diseased person differs from a healthy person.

Let’s start by saying that we humans are not in any way separate from any other part of the vast, dynamic, and astonishingly varied natural world.  Humans may appear, both as individuals and as a global gene pool, to be discrete entities. But the truth is that all of life on earth is in a constant state of flux, with energy and matter constantly changing form at a rapid rate.  The substance of carbon atoms that made up some part of a cell membrane of a lettuce leaf yesterday, along with the energy stored in the covalent bonds that link those carbon atoms, are today the substance and energy that are part of your body.  The same matter, the same energy, yesterday a lettuce leaf, today a human, tomorrow a bacterium that lives in an infected cut on the human’s hand. Your digestive enzymes dismantled the material in the lettuce so that the anabolic synthetic processes inside your cells could re-organize that material into the stuff of humanity. The next day, the bacterium’s digestive secretions dismantled the material in your skin cell so that the synthetic processes inside its single-celled body could reorganize that same material into the stuff of bacterial life. Soon, the bacterium will be eaten by something else. And on, and on, and on, and on. Even photosynthetic plants rely on carbon dioxide and other materials recycled from other living things to build their own bodies. Matter and energy, never created anew, never destroyed; just constantly, tirelessly, endlessly changing form.

As soon as we grasp this basic tenet of thermodynamics, we can begin to understand parasitism. Put simply, every living thing is constantly busy consuming and rearranging other living things. Each species uses its own unique body form and physiological processes to accomplish this consumption and rearrangement. Many, in fact most, of these millions of species on our planet, accomplish this by establishing intimate long-term living relationships with other species on which they feed, actually residing on or within the species that serves as their food source. This is the nature of infection. This is a biological phenomenon known as symbiosis, which literally means “living together”.  Both the food and the feeder may be referred to as symbionts, but in many cases the food species is typically called the host, while the smaller feeder is called the symbiont.  If it lives inside its food species it is an endosymbiont; if on the outside it is an ectosymbiont.

But not all symbiotic associations are the same in terms of their impact on the two species involved, or in terms of the relative benefit or harm to symbiont and host.  If all symbionts were reasonably harmless to us when we play the role of host, we probably would not spend a lot of time thinking about it. A harmless ameba living in your intestine and feasting on bits of the pizza you just digested probably would go unnoticed, or would be regarded as a simple curiosity, banished to the mostly unread pages of biology textbooks.  But if that ameba has the ability and propensity to switch from pizza to human flesh, digesting ulcers as it eats its way into your intestinal lining, we would all sit up and take notice.

As it turns out, both types of ameba live in humans.  The harmless kind is referred to as a commensal or commensalist; the flesh-eating, ulcer-producing, harmful kind is referred to as a parasite. In both cases, the human is the host. The two relationships are referred to, respectively, as commensalism and parasitism.

Less commonly, there may be situations in which both species derive benefit from the relationship.  In other words, the relationship is mutually beneficial; thus, we refer to it as mutualism.  Among other species, however, mutualism is critical to the survival of both partners. An example of this is hypermastigid flagellate protists that live in the intestine of termites, and provide the only means by which the termite can digest the wood that it eats.  Without the flagellates, the termite would starve to death on a full stomach. Similarly, the coral animals that build the great reefs in tropical oceans could not survive without zooxanthellae, symbiotic algae that live within the coral’s tissues and manufacture carbohydrates that provide energy nutrients for the coral. Mutualism is not commonly recognized in humans, though it is often argued that some bacteria living in our intestine (i.e., enteric) actually benefit us by aiding in the processing of certain nutrients. Because such cases typically do not involve disease, I will not say much more about them in this treatise.

Before we close this matter, however, we must recognize that the nature of symbiotic relationships is not static.  A symbiont may be basically commensalistic, simply living inside the host without causing harm, but becoming harmful when certain conditions change. Thus, the enigmatic organism, Pneumocystis jirovecii, may live in the respiratory tract of healthy humans, going undetected because it causes no damage. But when that human becomes infected with Human Immunodeficiency Virus (HIV), and develops AIDS, Aquired Immune Deficiency Syndrome, the symbiont becomes a deadly pathogen, often killing the human whose immune system is no longer able to keep the symbiont under control. Thus, the commensal becomes a parasite because the host’s immune status changes.  Similarly, there are many parasites that are harmless or only mildly irritating as long as the host is well nourished, but can become seriously pathogenic to malnourished hosts.  This is an important point since the same regions of the world where malnutrition is rampant are often the very parts of the world where parasites species are most common.

So, now we can construct a concise definition for a parasite: an organism that lives on or in another organism of a different species, maintaining a long-term intimate relationship with that host species, and ultimately causing harm to the host. This sounds pretty good, but unfortunately, scientists have a propensity for filling seemingly simple definitions with words that must be qualified.

The first qualification that is demanded here is the one about a parasite and host being different species. If anyone ever tells you that a human fetus living inside the womb of her mother is a parasite, that person is misinforming you. The special placental bond between the human mother and child (or other placental mammals), is a fundamental part of the reproductive strategy for that species.

The second qualification is what we mean by “long-term” relationships. Some parasites are known to reside inside their host for many years – even decades. Others may live in the host for only a few days.  The longevity of the relationship has nothing to do with time per se since, as we all know, there is tremendous variation in the longevity of different species, from hours to hundreds of years.  By “long-term”, we mean that the parasite must fulfill and complete a critical part of its life cycle in intimate association with the host.  Thus, a louse that lives on your head, feeds on your tissue fluids, mates and lays eggs on your hair shafts, ultimately staying for generations on your scalp, is a true parasite. Because it lives externally, it is an ectoparasite.  Similarly, a tapeworm that resides in your intestine, grows from juvenile to sexually reproducing adult, draws nourishment from what you have eaten, and produces young that disperse to the outside only to colonize a new host, is a true parasite. Because it lives internally, it is an endoparasite.

On the other hand, a mosquito does feed on your blood, but it doesn’t live on you. You are not her host, but just a convenient source of fresh blood.  The neighbor’s dog, or even the mouse in your garden might have sufficed for the blood meal that the mosquito seeks.  You are nothing more than prey for a predatory mosquito.  But because this predator takes only a small bit of its prey rather than wolfing down the whole thing, it is often referred to as a micropredator.  But sometimes the distinction between ectoparasite and micropredator is difficult to discern, such as in the case of ticks, which spend long times on their host, or prey, while feeding.

Unfortuately, even after adding these qualifications, nothing in the natural world is quite that simple and clear cut.  We’ll stick with the basic definition above, but it will be necessary to add further modifying language when we discuss any of the myriad versions of parasites, hosts, or host-parasite relationships.

Most organisms that meet all the criteria for a parasite have no choice but to live a parasitic existence.  These are known as obligate parasites, and they cannot fulfill all their necessities for survival and reproduction unless they can live at least part of their lives in association with the host.  For obligate parasites, some stages in the life cycle may be free living, but this free-living phase is typically only a period of dispersal or transmission to another host.  However, if an organism can live its entire life, possibly even generation after generation, without a host, but can also survive within a host given the opportunity, we refer to it as a facultative parasite.

Facultative parasites may also be referred to as opportunistic, since they are essentially free-living organisms that only become parasitic when the opportunity arises.  However, the concept of opportunism may also be applied to obligate parasites that require a host, but typically occur in small numbers, reaching much higher infection levels when opportunities arise.  Such an opportunity might be the suppression of the host’s immunity, as occurs in a person with AIDS, or who is under immunosuppressive therapy for cancer.

Before going further, however, there is one more point that must be made regarding the nature of parasites, or at least the scientific history and traditions related to the study of parasites. Scientific disciplines do not always follow nature’s pattern, but rather the whims of human culture and scholarly traditions. This writing is actually about the field of parasitology – which literally means the scientific study of parasites.  But parasitology as a defined field is not really about all parasitic organisms, but only the more advanced or sophisticated organisms that use humans and other animals as hosts.  Thus, the field of parasitology eliminates a vast number of parasitic relationships simply by ignoring those organisms that use plants as hosts.  Some scientists who study the roundworm parasites of plants also study related roundworm parasites of animals, but only the latter would be publishable in the scientific journals that are devoted to the field of parasitology. Research on the roundworms that use plants as hosts are more likely to be the subject of journals in plant pathology (the study of plant diseases), or nematology (the study of roundworms or nematodes).  Likewise, parasitologists do not concern themselves with the many organisms that are parasites of algae and fungi.  They just focus on parasites of animals.

If that weren’t restrictive enough, parasitology as a discipline also ignores many types of parasites of animals.  For example, there are many parasitic bacteria that use animals as hosts; but parasitology does not concern itself with bacteria.  Bacterial parasites are more typically studied by bacteriologists, or microbiologists.  Why this distinction?  It relates, again, to the history and traditions of scientific fields, which ultimately are the reflection of those human communities or societies that have found common cause in the study of like organisms.  Bacteria are very simple organisms.  As prokaryotes (meaning early or before nucleus), they have very simple naked DNA, quite unlike the eukaryotes (meaning true nucleus), which are organisms with exceedingly complex DNA packaged into sophisticated nucleosomes, which are then packaged further as chromosomes and further organized into complex nuclei. In other words, prokaryotes like bacteria are genetically simple, while eukaryotes are genetically advanced. Humans and other animals are eukaryotic, and the field of parasitology concerns itself only with parasites that are also eukaryotic.  In a way this makes sense, because parasites that are eukaryotic are genetically as sophisticated as their eukaryotic hosts, and thus must be understood and controlled by much more sophisticated approaches than prokaryotes.  It is little surprise, then, that bacterial (prokaryotic) infectious diseases generally have been controlled more easily that parasitic (eukaryotic) infectious diseases.  Nevertheless, parasitic bacteria, fungi (which are also eukaryotic), and even tiny viruses and prions can cause serious diseases that have proven difficult to control.  We will cover more about all of these, but with emphasis on the parasitic eukaryotes, including single-celled protists, helminths (or worms), and arthropods such as lice.

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Further Reading (click on reference to link to full text):

Chomicz, L., D.B. Conn, J.P. Szaflik, and B. Szostakowska. 2016.  Newly Emerging Parasitic Threats for Human Health: National and International Trends. BioMed Research International – Parasitology, Special Issue. Hindawi Publishing Corporation, London, United Kingdom. 73 pp.

Conn, D.B. 2002. Parasite collections at the Museum of Comparative Zoology, Harvard University. In: Proceedings of the 10th International Congress of Parasitology. Monduzzi Editore, Bologna, Italy. pp. 585-589.

Conn, D.B. 2006. The John H. Sandground Helminthological Collection at Harvard University’s Museum of Comparative  Zoology. In: Proceedings of the 11th International Congress of Parasitology. Medimond/Monduzzi Editore, Bologna, Italy. pp. 299-305.

Garin, Y.J.F., M.-T. Galán-Puchades, A. Moulignier, G. Robert, F. Héran, M. Polivka, P.D. Olson, F. Lorenzo, F. Derouin, and D.B. Conn. 2005. Case report: human brain abscess due to a tetra-acetabulate plerocercoid metacestode (Cyclophyllidea). American Journal of Tropical Medicine and Hygiene 72: 513-517.

Prof. Dr. David Bruce Conn is a biomedical scientist who has conducted research, taught university students, and advised governments and industries about parasitic and other infectious diseases, invasive species, and environmental health for 40 years.  He is Associate of Invertebrate Zoology responsible for the parasite research collections at Harvard University’s Museum of Comparative Zoology, and Gund Professor of Biology in the Berry College One Health Center. (Disclaimer: Dr. Conn is a senior advisor to the U.S. Department of State on issues of health and foreign policy, but the contents of this post are his own views and do not officially represent any unit of the U.S. federal government).

Copyright © 2017 by David Bruce Conn.  Free use and distribution permitted with attribution.

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Neglected Infectious Diseases on a Rapidly Shrinking Planet

David Bruce Conn, M.S., Ph.D.

Planet Earth is shrinking.  It has been shrinking for centuries, but the rate of its shrinkage has accelerated at a staggering rate during the last century, and within the past two decades has left our heads spinning.  To a geologist, such reduction in the earth’s size may not be an empirical reality.  But it is a reality to a biologist who studies the dispersal of species, a political scientist or economist concerned about increasing demands for multinational cooperation, or a climatologist who questions how human activity on one continent might influence weather patterns halfway around the globe.

           The effects of living in a smaller world pervade virtually every aspect of our lives. Even my work in writing is radically different than it was in the larger planet of a decade ago.  I type the words into my computer, which is equipped with a transmitter that links to a wireless hub in the other room, which then sends my work along instantaneously to my readers all around the world to read my article only minutes after I have written it.  By logging onto the internet, my computer can send the same article to any one of my colleagues or readers on any continent within minutes.  The ease and speed of communication such as this open myriad opportunities for global commerce, technology transfer, and political dialog.  These opportunities are enhanced by the speed at which modern airplanes allow us to travel physically around the globe, and the volume of cargo that we can transport on superfreighter ships and jumbo cargo jets.

           As we take advantage of these opportunities, it becomes increasingly important that we understand the far-flung localities with which we are now associating and doing business. We may profit from the breakdown of barriers to our isolation, but we also inherit the problems that were once too distant to concern us.  The things that affect the economy and politics of our new neighbors now affect the economy and politics of our own homeland.  Diseases play a major role in shaping the economic, political, and cultural features of any society; so it follows that we can survive and flourish on a shrinking planet only if we understand human diseases that affect other parts of the world.

           Many years ago, I decided to devote myself to the study of parasitic diseases.  By a time-honored convention, biomedical scientists use the term parasitic diseases in reference to diseases caused by worms, arthropods (such as mites, ticks, and insects), and complex single-celled protists.  Diseases caused by protists and fungi, as well as by the much simpler bacteria and viruses are generally referred to as microbial diseases due to the microscopic size of the pathogenic organisms. However, pathogens (literally, makers of disease) of all these groups have a parasitic lifestyle.  Both parasitic and microbial diseases are types of infectious diseases, since they involve one organism infecting another. Many infectious diseases are also communicable diseases, since they can be passed, or communicated, directly from one person to another.  However, not all infectious diseases are directly transmissible; many require time to develop in the external environment, or inside another host such as a mosquito.  The breakdown into parasitic and microbial is artificial in many ways, but reflects the historical development of parasitology and microbiology as separate fields of biological science.

           When I began studying parasitology several years ago, I came to realize that, like me, most Americans, Europeans, and people from other highly developed parts of the world are rather sophisticated in their general medical knowledge, but relatively uninformed about the plight of their neighbors in less affluent circumstances. In tropical and subtropical areas around the globe, the climate has allowed parasitic diseases to flourish over the millennia, while such diseases have been suppressed by the temperate climates to the north.  Because we live in areas where most parasitic diseases are not major problems, it is natural for us to assume that these diseases either do not exist or are of only minor medical concern.  Two events early in my career as a university professor made this point clear to me.

           The first occurred shortly after U.S. troops began returning from the First Gulf War in the early 1990s, and the media began to report that some U.S. military personnel had contracted a “rare disease.”  Despite its great “rarity,” medical authorities had been able to identify the disease as leishmaniasis.  The newspapers and media did not report that each year, what they incorrectly referred to as a “rare disease” is contracted by more than twelve million people, severely debilitating and disfiguring several million of them, and killing thousands more.  The reports also failed to note that the World Health Organization (WHO) and other health organizations had for many years considered leishmaniasis to be one of the major tropical diseases – one of the most significant human health problems in the world.

           The second event involved a brief encounter with one of my students at St. Lawrence University, who had just returned to our campus in New York State from participating in the university’s Kenya Semester.  She had picked up a benign infection of some sort, so we had a short chat about human health problems in tropical Africa.  She informed me confidently that there were indeed a few tropical infections one might encounter in Africa, but that they were “no big deal.”  What she did not know was that African trypanosomiasis (African sleeping sickness), regarded as an oddity by many westerners, infects one million people each year and is on the top tropical diseases list of several organizations. She was not yet aware that onchocerciasis, or river blindness, completely blinds tens of thousands of people each year in parts of tropical Africa (see information box below).  She was not aware that tropical Africa is the world’s primary center of schistosomiasis, a disease that kills as many as one million people each year and infects up to 300 million—nearly equivalent to the entire population of the United States. She did not realize that every year in Africa, one million children die of malaria alone, and that 100 million people around the world are infected with malaria—nearly a third the number of the  entire population of the United States! 

           The first anecdote is not a testimony to any ignorance unique to the American press, nor is the second a reflection of unusually poor education on the part of American universities. Rather, both reflect a lack of information available to educated citizens of prosperous temperate-zone countries regarding the nature of global human health problems.  Few westerners realize that the major diseases of affluent developed countries in temperate climates are comparatively minor problems to the majority of the world’s populations, who live primarily in tropical and subtropical Third-World countries.  On a global scale, cancer and heart disease rank below such diseases as malaria, schistosomiasis, and soil-transmitted helminths (parasitic roundworms) as significant human health problems.  One reason is simply that cancer and heart disease are often, though not exclusively, maladies that affect a disproportionate number of older people.  Another reason is seen in the sheer numbers; cancer and heart disease affect only a fraction of the number of people who are affected by the major parasitic diseases.  For example, it is estimated that more than one billion people – nearly one of every six people on the planet – are infected by soil-transmitted helminths.

           Why do these major diseases occur primarily or exclusively in tropical Third-World countries? There are many contributing factors, including the relative shortage of healthcare and sanitation technology in economically underdeveloped countries.  But the most important factor is simply that most of the parasites and/or the organisms that transmit them are restricted to tropical climates. That such geographic variations in disease should occur as a normal part of biotic distribution patterns should come as no surprise.  This is basically the same reason that polar bear attacks on humans are more likely to occur in the Arctic than in deserts or tropical rain forests, but crocodile attacks don’t occur in the Arctic.  Whether we are dealing with polar bears and crocodiles or tapeworms and blood flukes, most animals are restricted in their geographic distribution, and it is a basic biological principle that life is vastly more diverse in the tropics.  This higher biodiversity is not restricted to pretty tropical birds and butterflies; many more species of human parasites also live in the tropics, as do their insect vectors.

           Historically, people in one part of the world have paid scant attention to the health concerns peculiar to people living in other regions.  Exceptions can be found among medical workers who deal with international tourists, military personnel who often encounter exotic diseases in foreign countries, and public health professionals who deal with the ever increasing tide of immigrants from developing countries.  With expanding global travel and commerce causing our planet to shrink at a rapidly accelerating pace, the time has come for this to change.  For this and other humanitarian reasons, an initiative known as “The Great Neglected Diseases” campaign was begun in the 1980’s by the Rockefeller Foundation and other groups around the world that were seeking to increase an awareness among westerners of the plight of tropical developing countries in dealing with health problems unique to or vastly more devastating in the tropics.  A major focus of this program was to generate funding for and increase research activity related to tropical parasitic diseases.  This program and more recent initiatives like it, including the Neglected Tropical Disease program of the U.S. Global Health Initiative, have enjoyed varying degrees of success, but much remains to be done.  The original Great Neglected Diseases program inspired my undergraduate college course of that same name, which I have now taught at several universities to growing and increasingly enthusiastic groups of bright young people.  We can only hope that as we continue to learn about parasites, we can help to make the diseases they cause become less “neglected”, and in turn ultimately to come to be problems that are not as “great” as they now are.  Otherwise, as our planet continues to shrink, our problem with parasitic diseases will loom larger than ever with each passing year.

Further Reading:

Chomicz, L., D.B. Conn, J.P. Szaflik, and B. Szostakowska. 2016.  Newly Emerging Parasitic Threats for Human Health: National and International Trends. BioMed Research International – Parasitology, Special Issue. Hindawi Publishing Corporation, London, United Kingdom. 73 pp.

Conn, D.B. 2009. Presidential address: Parasites on a shrinking planet. Journal of Parasitology 95: 1253-1263.

Conn, D.B.  2011. Neglected Diseases, Emerging Infections, and America's Global Health Century.  Jefferson Science Distinguished Lecture Series, U.S. Department of State, Washington, D.C.  Transcript and streaming video:  https://2009-2017.state.gov/e/stas/series/180126.htm

Conn, D.B. 2014. Aquatic invasive species and emerging infectious disease threats: A One Health perspective.  Aquatic Invasions 9: 383-390.  http://dx.doi.org/10.3391/ai.2014.9.3.12h

*** Prof. Dr. David Bruce Conn is a biomedical scientist who has conducted research and taught at universities around the world, and advised governments and industries about parasitic and other infectious diseases, invasive species, and environmental health for 40 years.  (Disclaimer: Dr. Conn is a senior advisor to the U.S. Department of State on issues of health and foreign policy, but the contents of this post are his own views and do not officially represent any unit of the U.S. federal government).

Copyright © 2017 by David Bruce Conn.  Free use and distribution permitted with attribution.

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(via David Bruce Conn on Twitter: "Warning: The Plague Still Exists! New in advocacy poster series by students of the @BerryCollege #OneHealth Center https://t.co/VE0O0hGyqH")

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With the serious migrant situation continuing to unfold across Europe, and the continuing movement of migrant populations across borders in North

International Refugees, Migrants, and Infectious Diseases: Helping People on the Move is a Good Way to Help Ourselves | David Bruce Conn, M.S., Ph.D. | Pulse | LinkedIn

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Dr. Marc LaForce speaking at Berry College: The world's children everywhere have a right to survival, nutrition, health service, education, and protection against abuse and exploitation.

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The year 2017 has barely begun and we already have a new and potentially major infectious disease situation flaring up. During the first three weeks

New 2017 Brazilian Outbreak of Deadly Yellow Fever is Cause for Immediate and Sustained International Action! | David Bruce Conn, M.S., Ph.D. | Pulse | LinkedIn

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Discovering the World of Parasites and Parasitic Diseases

David Bruce Conn, M.S., Ph.D.

My determination to become an ornithologist dissolved during the spring of 1973.  My passion for birds had begun five years earlier, at the age of twelve.  Now in 1973, as a high-school senior, I was making the rounds to prospective colleges where I might continue my education.  During one of my college visits, I found myself sitting in on a biology laboratory at Lee College, a liberal arts school in my home town in Tennessee.  An undergraduate student had brought in a road-killed opossum to show the class.  The professor, Dr. Myrtle Fleming, stood over the carcass, her gloved hand deftly wielding a scalpel.  As the sharp steel blade slid smoothly through the opossum’s stomach wall, a writhing mass of worms poured from the incision.

            Disgusting?  Hardly!  Quite to the contrary, I was mesmerized.  You see, over the past few years of studying birds I had become fascinated not so much by their colorful plumage and mellifluous songs, but by the marvelous and varied ways that each species had adapted to its particular habitat and available food resources.  I had come to see each sparrow, chickadee, or heron as an integral part of an exceedingly complex environment.  It was this intricate relationship between an animal and its environment that had come to captivate me–to dominate my times of contemplation on nature.  And there, in this college laboratory, I came face to face with what I could see was the most intricate of all such relationships.  The opossum’s digestive tract was to these worms what the river’s edge was to the heron; what the oak/hickory woodland was to the chickadee; what the broomsedge field was to the sparrow.  Standing there, knowing nothing really about the worms, I guessed (correctly as it turns out) that the parasitic worms must have adaptations to this enteric environment that are just as elaborate and well designed as the heron’s long wading legs, and the chickadee’s slender bill suited for probing insects from tree bark.

            At the time of this revelation, the fact that these worms caused disease in the opossum was the farthest thing from my mind.  I simply marveled at the worms’ adaptive ingenuity.  However, a seed had been planted that began to grow into a much different and more ferocious beast in my mind.  As a college student a couple of years later, my curiosity about the worms prompted me to take a course in parasitology.  There, I became aware that similar parasites exact a dreadful toll on human health, particularly in underdeveloped tropical countries.  No, that is an understatement.  I discovered a horrifying reality of which I had been ignorant all of my life.  I learned that the human suffering associated with such parasites is far greater in its severity and ubiquity than anything most Americans and Western Europeans have ever encountered in their comparatively sheltered and sanitized lives.  I learned that such parasites kill millions of children each year, and that mothers in many parts of the world must live with the grim expectation that their children have little chance of surviving through their first birthday.  I learned that millions of people in tropical Third-World countries spend their entire lives in incessant and indescribable pain, their vitality draining slowly away as their bodies struggle to feed the parasites that demand a share of their food and their flesh.

            As my interest in parasitology continued to grow and evolve, I enrolled in a Ph.D. program at the University of Cincinnati.  There, I worked under the skillful hand and practiced eye of Professor Frank J. Etges, whose insights into the relationship between parasites and human health helped me to understand the many ways that I might satisfy my intellectual curiosity about the natural world while simultaneously contributing to our understanding of this global health concern.

           More than 40 years later, I still am fascinated by the lives of parasites and their ingenuity at making their way successfully through an unforgiving world – unforgiving for them even as they are unforgiving toward us and their other hosts.  But while I still conduct research and teach about parasites as amazing animals and parasitism as a remarkable strategy for life, my passions over the years have grown increasingly toward understanding parasites as agents of horrible human diseases that need to be understood so that we can prevent or treat them, thus reducing human suffering.  My intellectual evolution has taken me to teach and conduct research at universities around the world, and to collaborate with many of the brightest and most productive parasitologists the world has to offer. I am presenting my personal journey here to set the stage for the following series of blogs, each a lesson on parasites and parasitic diseases.

I start with the parasites themselves, because we must understand them if we are to stop them from hurting us.  One of the greatest failures of biomedical science is the all-too-frequent failure to understand that infectious diseases center around other non-human organisms, each unique and highly, constantly adaptable, each striving to make its way in the world for itself and the progeny it will spawn.  If we think of parasites as static “things” for which we can find a simple permanent solution, we will continue to fail.  Just as we will never put an end to earthquakes, hurricanes, and other physical forces on our planet, we will never put an end to the equally unstoppable natural force of continued adaptation of parasites to us and our medicines, vaccines, and control strategies.  On the other hand, if we recognize the dynamic and never-ending interplay between parasites and us as their hosts, and with our shared environment, we might hope for success in eliminating the most severe state of human misery parasites cause.  Follow my blogs to learn more.

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Prof. Dr. David Bruce Conn is a biomedical scientist who has conducted research and taught at universities around the world, and advised governments and industries about parasitic and other infectious diseases, invasive species, and environmental health for 40 years.  (Disclaimer: Dr. Conn is a senior advisor to the U.S. Department of State on issues of health and foreign policy, but the contents of this post are his own views and do not officially represent any unit of the U.S. federal government).

Copyright © 2017 by David Bruce Conn.  Free use and distribution permitted with attribution.