From: Robert A. Neinast Subject: Hookworm Date: Sun, 27 Jul 2003 20:45:15 -0400 I recently got a copy of "Hookworm Disease - Its Distribution Biology, Epidemiology, Pathology, Diagnosis, Treatment and Control" by Asa C. Chandler (New York: The Macmillan Company, 1929). While the work is pretty darn old, it presents many scientific findings that ought to have held up over time (with the exception of, I suspect, treatment for hookworm). It also provides a historical perspective on a time when hookworm infestation was endemic. I present below a summary of many points from the book about hookworm. This is a question we often get from others, and it behooves us all to know enough about it to be able to discuss it intelligently. Hookworm is a parasitic nematode that attaches itself to the intestinal wall of its host, feeding from there, and weakening the resistance and vitality of the host. Before 1930, hookworm was so prevalent in the Southeastern United States that the so-called "laziness" of many blacks or white crackers was probably due to the negative effects (including severe anemia from iron deficiency) of hookworm infestations. The hookworm nematode requires warm, moist conditions. It was practically unheard of in areas that receive less than 40 inches per year of rain. In the United States, only the Southeastern US had problems. It went north only as far as Virginia and southern Kentucky. It only occurred as far west as Arkansas, and an eastern strip of Texas. Any other place in the United States is either too cold, or too dry for the hookworm to survive. [Note: I am discussing human hookworm here, /Necator/ /americanus/ and /Ancylostoma/ /duodenale/. Canine hookworm, /Anclyostoma/ /caninum/ is able to survive somewhat colder temperatures than human hookworm.] Hookworms lay their eggs while attached to the intestines of their hosts. These eggs pass out of the body with defecation. It takes about 5 days for the eggs to develop into larvae that start looking for a new host. During this time, the larvae feed on material in the feces. The larvae invade a new host by burrowing into the skin. [Note: the "Parents for Barefoot Children" site claims that they do not have this ability. See . This is simply wrong. They can enter either through breaks in the skin, or through pores.] The book references a bunch of studies that clearly have shown that their main mode of entry is through the skin. (In fact, before 1898, it was thought that their only way of entry was through the mouth--while still possible, it was shown in that year that it penetrates the skin, and it was later shown that skin penetration is the main mode of infection.) The hookworms penetrate by twisting about, and by using the surface tension of water to provide them with something to push against as they enter. Once in the body, they enter a vein, where they are taken through a ventrical of the heart and into the lung area, where they burrow through the arteries into the lungs. From there, they are coughed up to the mouth, swallowed (interestingly, people who regularly spit have lowers rates of infestation than those who do not), and then passed through the stomach to the intestines, where they attach to the intestine walls, allowing the cycle to begin again. Hookworms can live about a year or two, though 5-6 months seems to be more typical. Among those infested, it appears that they reach an equilibrium where they are re-infested at the rate they lost the hookworms. There are a number of spots where this cycle can be interrupted. One of them *is* by wearing shoes. The book had an interesting plot (Fig. 17, page 174) of number of hookworms harbored by age, taken in Alabama. As children get older, they got more exposure, and harbored more hookworms. However, around age 15, the number starts dropping, and pretty much disappeared by around age 20. Dr. Chandler attributes this to "the custom of beginning the constant use of shoes at about fourteen years of age." At that point, with no (or few) new re-infections, eventually the older hookworms die out, and the person is finally rid of the infestation. However, there are other habits that are much more important for controlling hookworm. Sanitation is primary, since the eggs are passed in the feces. During the period of the book, people in the south often didn't even use privies(!). They would end up standing where they had defecated before (this would not always be obvious, since dung beetles would have removed the feces, but *not* the larvae). Even a primitive outhouse prevents people from standing where the larvae might be. Other facts about the larvae prevent them from becoming an issue today. As already mentioned, the larvae must be kept moist. If they dry out, they die. Outdoors, they can dry out during the daytime. They are able to move a bit, and use their stores of energy for moving up when it is moist in the morning, and down to where it is wetter during late day. However, if they are not "picked up" soon enough, they soon exhaust their stores of energy, and die. Also, if it gets too cold, they die (winter pretty much takes care of them). Studies have also shown that the larvae do not move laterally much at all. That means that, to pick one up, you have to stand almost right on top of where an infested person defecated within the last 5 days. The larvae can be spread slightly by water runoff, but that dilutes them so much that the odds of getting one within the necessary 5 day period is miniscule. I already mentioned how they need moisture (water tension) to burrow into the skin. They also need some time to get started. That means that simply walking on a place with hookworm larvae is not sufficient to get one. You must stand there (or, step in some mud with larvae that stays on the foot). The primary mode of infection is to *stand* (or squat) on older infected feces. That gives them the purchase and time to start burrowing. By the way, people getting infected with hookworms can often feel it happening. It was given the name "ground itch", "dew itch", "water sore", and "mazamorra." It's fairly easy to see why modern sanitary conditions have eliminated human hookworm (and why barefooters need not worry about it). Even if an infected person used a modern toilet and missed, such that feces containing eggs got on the floor, it takes at least 5 days for the eggs to develop into larvae. The toilet (and floor) would have been cleaned before there was any chance for the eggs to develop. I just don't see how human hookworms can be considered any sort of a threat today in the United States. For those of you in other parts of the world, pay attention that you don't stand in places of regular defecation, or temporarily put something on your feet when you do. (Note: even flip-flops may not provide total protection if you get infected mud on top of your feet). An additional tidbit: there are a few quite northerly places that had hookworm infestations: mines. Even as far north as England mines would get infected (they were nice and damp, and never got too cold). And I guess the miners would just go into a side tunnel to relieve themselves. Finally, a few words on canine hookworm (which the book just barely touched upon). First, canine hookworm does seem to be able to tolerate colder conditions than human hookworm, so it can be a concern farther north. However, they just are not very good at penetrating human skin (it appears that hookworm target specific proteins to know which way to go). What can happen is that the hookworms get lost burrowing in and can give something called "creeping eruption." But even then they don't make it into the bloodstream. Again, just walking through a mine field doesn't give the larvae the opportunity to get started--you have to stand in the stuff (or step in it and not wipe it off). And, given today's sanitary conditions, you are not going to pass it to anybody else. I realize this has been rather long, but I thought it contained information we should all be at least a bit familiar with. Regards, Bob -- " . . . and shun the Frumious Bandersnatch." Robert A. Neinast Pickerington, OH