Guess who got full marks on today’s geohelminth MCQ? That’s right, I just know my parasitic nematodes that well. Honestly, Nematoda (the roundworms) isn’t nearly the most disturbing phylum of parasitic worms. A few of its members are global health problems, such as Ascaris (an intestinal worm which has over a billion infections worldwide) and Wuchereria or Brugia, which both cause lymphatic filariasis (the most globally damaging infection by the W.H.O.’s Disability Adjusted Life Years measure for impact – you may be familiar with pictures of elephantiasis). However, as glad as I was that I skipped breakfast today, the phylum Platyhelminthes is more frightening. That’s the one that has digeneans (flukes) and cestodes (tapeworms), which are responsible for schistosomiasis, cysticercosis, and hydatid disease. Trust me, if you like your supper on the inside, you won’t wiki those.

After being a good student and doing my reading, I spent most of last night dreaming that I’d gotten ascariasis and hydatid disease. Perhaps fortunately this gave me insomnia, because the only other sleep I remember was dreaming that I had a Taenia solium larval cyst in my CNS and was experiencing epileptic progression. Fortunately the course lecturer is excellent, and I think that, after this term, very, very little will turn my stomach.

The thing that gets me about parasitic diseases is how little is being done to counter them, especially given the global prevalence of the problem. Above I mentioned Ascaris, which has about 1.4 billion infections worldwide. That falls into the broader category of  geohelminths, which has an estimated 3 billion infections, with 4.5 billion people at risk. There are only 6.76 billion people in the world. Now consider a few other major helminth diseases: schistosomiasis at 200+ million infections, onchocerciasis at 18 million infections, and lymphatic filariasis at 120 million infections, and the picture gets ugly. At risk, respectively, are 600 million, 120 million, and 1 billion people.* There aren’t even any cestodes on that list. Of course, a lot of these infections overlap, and that just makes them worse. Moreover, most (and by far the worst) infections are in children.

Drug-wise, between 1975 and 1995, although 1,223 new types of drugs were introduced worldwide, only 14 were for tropical diseases. In truth, most of those were developed for veterinary medicine, and came to people second.** There is no vaccine nor acquired immunity to infection, so chemotherapy would have to be administered to each infected individual every 6 months. Even with inexpensive drugs like benzamidazoles and ivermectin, that’s terrifically expensive, and a logistic nightmare. The only way we can effectively control or eliminate helminth diseases is with sanitation and piped water for washing and drinking. Give those two things to a community, and helminth infections pretty much spontaneously disappear. However, that’s a tall order for the developing world, which hasn’t the funding or the infrastructure to do much of anything. Currently, treatment relies solely on the charity of a few pharmaceutical companies and nonprofits. I keep asking myself why, and I never like my answers.

*taken from Watkins, B.M. (2004). Trends in Parasitology 19:477-8

world population count is from the US Census Bureau

**Dr. Phil Whitfield. “HB.0317 Parasitology of Tropical Disease.” Lecture series given in room 1.10 Franklin Wilkins Building, King’s College London. 15 January, 2009.