By: Alanna Shaikh

Animals and insects play a huge role in the transmission of neglected tropical diseases. From the snails that carry schistosomiasis to the wild animals infected with African sleeping sickness, the NTDs rarely travel alone. That means any effort to control and eliminate NTDs must take into account their many vectors and reservoirs of disease.

The NTDs are not zoonoses. That is, they are not diseases that animals can directly infect humans with. It’s more complicated than that. For example, in the case of human African trypanosomiasis, infected animals are bitten by the tsetse fly, which then carries the parasite to human victims. As long as animals remain infected, there is a risk of human infection.

In the case of schistosomiasis, the parasite that causes the disease has to spend part of its life living in certain kinds of snail. In this case, eradicating the snail would probably eliminate the disease, but doing it isn’t essential. They’re not a reservoir for the parasite, just a stopping point at one time in its revolting little life.[1] The animals reservoirs of schistosomiasis are dogs, cats, rodents, pigs, horses and goats[2], who just get infected with the disease the same way people do.

Be they roundworm, hookworm, nematode, or whipworm, the NTDs have got you totally covered for wormy horror.  In possibly the most yucky arrangement of all, many NTDs are causes by actual visible to the eye worms that LIVE INSIDE YOU. I hope my use of all caps conveyed my sheer horror to you. If it didn’t, go take a look at , then come back here and try to pretend you aren’t horrified.

So, worms that live inside you. Perhaps your intestines, perhaps just your tissues in general.

Trichuriasis is worms in your large intestine, transmitted when you consume food or water that’s contaminated by feces. It infects 604 million people around the world, and it stunts the growth of children and leads to cognitive defects. No vaccine, but it can be treated with albendazole or mebendazole.

Hookworm is worms anywhere in your intestine. They come in through your feet, go through your mouth and lungs to get to your bloodstream, and settle down in your guts. You get in by stepping in infected feces[3] – it can’t travel person to person, which is one small favor I guess. Almost ten percent of the world’s population has hookworm. It’s especially hard on children, babies, and pregnant women.It can be treated with albendazole or mebendazole.

Ascariasis – roundworm – is another that affects all through your intestines. You swallow the eggs, they grown in your gut into larvae. Then the larvae have a nice grand tour of your whole body and then come home to your intestine to lay tons of eggs. Ugh. Ascariasis affects even more people than hookworm. Over 807 million people are infected, and it can be treated with our trusty friends albendazole and mebendazole.

You’ll notice there that all three kinds of worms have a single effective treatment. That among other things, is why mass drug administration is so effective. Trypanosomiasis and schistosomiasis, with their animal reservoirs, are going to take more effort, and research, to eliminate.

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[1] I guess that’s kind of gratuitous. It’s probably no more revolting than any other parasite just trying to get by in the world.

[2] Actually the CDC website says “hourse” but I am going to assume that’s a typo. I did a google search for “hourse,” just to be sure, and came away amazed by the number of people in this world who can’t spell horse.

[3] Yes, the worms are all about the poop.

Alanna Shaikh is an expert in health consulting, writing about global health for UN Dispatch and about international relief and development at Blood & Milk. She also serves as a frequently contributing blogger to ‘End the Neglect.’ The views and opinions expressed by guest bloggers are not necessarily the views and opinions of the Global Network. All opinions expressed here are Alanna’s own and not those of any employer or the US government.