There were a couple of comments in an earlier entry, “Shoo! Donations”, that got into a discussion of hookworm. There was also a question about barefoot running in Southeast Asia on the Barefoot Runners Society forum that seemed to be hookworm related.
I’ve written about hookworm before, but I thought I’d take this opportunity to say a few more words about it.
One thing to keep in mind about human hookworm is that it really needs a warm, moist climate to thrive. That means that it is really only a problem in tropical or semitropical regions. In my hookworm entry, I included a map of where hookworm had been endemic in North America. For the sake of completeness, here are corresponding maps for the rest of the world. These are from the 1929 book, Hookworm Disease, by Asa Chandler. Obviously, hookworm has been defeated since then in many parts of the developed world, but the maps give an excellent view of the potential range of hookworm. And if you live in a lesser-developed part of the world that might still have hookworm, the maps can show whether your area is susceptible.
The darker the stippling, the higher the concentration of hookworm infestations.
Africa:
Asia:
Australia/Melanesia
Europe:
South America
The life cycle relies on adult hookworms attached to the intestines of their human host. Those hookworms lay eggs which are excreted in the feces. The eggs then take about 5 days to develop and hatch, producing the larvae. The larvae feed on the remains of the feces while they wait for a new host to come along, but if they don’t get picked up, they die in about another 5 days. During that time, they have limited movement, with most of it being restricted to moving up and down in an effort to stay moist (moving down in the heat of the day).
If a hookworm larva dries out, it’s toast. If a possible new host steps on the hookworm (or sits, or gets any sort of skin contact with it), then the larva twists and turns (using water tension to help) to get a purchase and burrow into the skin. From there it makes its way into a vein, and when near the lungs, burrows out of the vein into the lungs. From there it’s coughed up and swallowed, following which it makes its way to the intestine, becomes an adult, and the cycle begins anew.
Interestingly, people who are regular spitters tend to have a lower load of hookworm infestation, since the spitting interrupts that cycle for at least some of the hookworm larvae.
Shoes can also interrupt the cycle. But, as pointed out in that earlier entry, the larvae can penetrate cloth shoes. Flip-flops can have the same problem if contaminated mud gets on the side of the foot.
Generally, conditions have to be just right for the hookworm larvae to penetrate the skin, and it takes time for them to do so. Simply walking on contaminated soil won’t particularly do so, because that doesn’t give them time to get a purchase. However, walking on contaminated mud can be an issue, since the mud sticks (mostly on the side of the foot, which has thinner, and easier, skin to bore through).
On non-muddy soil and dirt, you have to actually stand there for them to have time to get started. I also suspect that the thicker skin on the heel and ball is just too hard for the larvae—most of the stuff I’ve read suggests that their preferred point of entry is between the toes.
This again emphasizes why proper sanitation is so important. When there isn’t proper sanitation, people will defecate “in the bush”, (almost) literally. They’re not going to do it in the middle of a field, where everybody can see them. Instead, they find a bush for a bit of privacy. That’s probably the same bush that some other person used not that long ago for similar privacy. The feces will have dissolved so they don’t look like feces any more, but the hookworm larvae are still there. And squatting there not moving gives the larvae the perfect opportunity to do their thing.
Obviously, in addition to sanitation and the general availability of properly built outhouses, education is also important. People need to know that “in the bush” is not a good place to defecate.
For barefooters like us, being educated with all of the above information is also important so that we can continue to go barefoot while minimizing our risk of infestation. If people are throwing night soil out into muddy streets, you need to know that and avoid them. Use latrines and outhouses. But out in the open, and using regularly used paths that are not dumped on, you are pretty safe from acquiring hookworm. Of course, if you have any suspicions you might have picked some up, it is fairly easy to inspect your own feces looking for eggs (that’s what vets do when you take your dog in). You just need a bit of magnification. And if you do get an infestation, there are various medicines available that are quite effective.
Even in the absence of latrines, locals need to be educated. If you are out in the bush, a backpacking trowel (or even a stick will do) is the way to go. Backpackers have known for a long time to dig a hole, defecate in that, and then fill the hole back in. There is no way the larvae can climb up through the dirt. Anything that interrupts the cycle is important to do.
If you look at the maps above, you will see that Israel is within the range of hookworm. But ancient Israelis figured that out. Thus, here is what should probably be barefooters’ second favorite bible verse, Deuteronomy 23:12-13.
Thou shalt have a place also outside thy camp, which thou shalt go forth to; And thou shalt have a paddle upon thy weapon; and it shall be, when thou wilt ease thyself there, thou shalt dig with it, and shalt turn back and cover that which cometh from thee.
For those of you wondering, a barefooter’s favorite bible verse is Exodus 3:5.
And God said: Do not draw near. Take thy shoes from off of thy feet, for thou standest upon holy ground.
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