Faceless. Fanged. Ravenous. Blood-sucking. This is the stuff of horror films. It's also the stuff of reality, albeit substantially smaller in stature than the monsters of Hollywood. In Hollywood, this monster would be large, appear suddenly and dramatically, attacking and devouring people by the dozens, and be virtually unstoppable. In reality, they are small and have been around for millennia. What isn’t different though, is the massive number of people affected and the struggle to quell their impact.
So who or what is this real monster?
Hookworms are a small, parasitic worm (of the phylum Nematoda, so it's related to whipworms and roundworms). Adult hookworms are found only within their host (humans, cats, dogs, etc. depending on the species of worm). It is within the host that they mate and reproduce, and the eggs are released in the host’s feces. The larvae hatch out and develop in the soil, and then migrate away from the site of deposition. When an unsuspecting host passes by, the larvae infect (either through direct skin contact or inhalation) and burrow through the host’s tissues and organs before finally reaching the intestine, clamping on, feeding, and maturing to adulthood.
Today over 700 million people worldwide suffer from hookworm infections. Cases of hookworm infection are concentrated in poverty stricken areas of sub-Saharan Africa and the Indo-Pacific. The most common impact of hookworm infection is tiredness and anemia, but intense infections can lead to malnutrition, blood loss, and among children, interruption of proper growth and cognitive development. Infection is particularly dangerous for pregnant women who can experience more extreme complications and also pass large numbers of the parasite to the baby.
Treatment is a challenge in many of the regions where hookworms are more common because re-infection rates are high. A patient can be treated with anti-hookworm medications to kill a current infection and then shortly thereafter encounter another hookworm. The medical response to this problem is to develop vaccines which could be administered immediately following an anti-worm treatment; significant progress towards this end is being made. But medication is expensive and those communities suffering most from hookworm infections are poverty stricken, with poor sanitation. Thus prevention , rather than treatment , remain the best solution to the problem; and luckily, in the case of hookworm, prevention is possible.
The same attributes of the hookworm's life cycle that contribute to the problem of frequent exposure and re-infection, also provides a realistic solution. It is the same solution that has contributed to the near eradication of human-borne hookworm in all but the most remote pockets of the world’s wealthier nations.
As early as the 1830s, scientists recognized the connection between illness and human excrement. A group of Italian scientists observed an outbreak of diarrhea and anemia among miners and connected the illness to shabby footwear and the frequent defecation, which occurred out of necessity, in the tunnels. A few decades later, hookworms were identified as the infective agent and the life cycle and mode of transmission were established. These scientific discoveries would contribute to a social change in the American South with the help of mogul, John D. Rockefeller.
Rockefeller, in his pursuit of wealth, expanded his business into the rural South. However, his profits did not roll in as expected. Instead he found his rural southern employees to be of low productivity, contributing to northerners’ perception of “lazy” southerners. After sending teams of professionals and eventually doctors to investigate this “epidemic” of laziness, an epidemic of hookworm was discovered, and a search for a method to decrease infection commenced. Scientists already knew that hookworm was found in feces and transmitted through contact, so the natural solution was to minimize proximity. They also soon discovered that larval hookworms migrate.
The question: how far from the initial deposit location can the larvae travel?
Every time scientists tested them, it was four feet, nothing more, nothing less. With this discovery, we have the development of the modern outhouse, with a 6 foot pit.
Here's the complete story on NPR's Radiolab
Because of the unique life cycle of hookworms, many infections can be reduced with education and improved sanitation. There will continue to be problems with hookworm transmission from other species (such as cats and dogs), but there is at least promise for decreasing human -borne hookworms.
Ailments of Wealthy Nations
As with any story, however, there is another side.
While many doctors, researchers, and world health organizations are working to eradicate hookworms, others are seeking out and intentionally infecting themselves. As it turns out, these “monsters” may not be all bad…
I remember, as a child, hearing a news report that extreme cleanliness may be contributing to increasing frequency of illnesses. They went on to report a study, if childhood memory serves me, showing that children who aren’t exposed to “dirt” (and the potentially infectious agents therein) were more likely to get sick. Of course as a child, this meant that cleaning your room could make you sick! The perfect excuse for not cleaning my room!
Now of course that isn’t exactly what the
science was reporting. The basic idea,
termed the “hygiene hypothesis”, is that our immune system learns what to react
to and what not to react to during
early developmental exposure to environmental agents (from pollen to bacteria). So in modern society, where we often severely limit exposure to potential pathogen agents, the immune system doesn't learn what not to react to entirely.
What does this have to do with hookworms?
Since its original inception in 1989, the "hygiene hypothesis" has been expanded to explain increasingly common allergies and autoimmune diseases in wealthier nations. Parasites, such as hookworms, have been implicated as agents, which previously, when encountered in low doses, would elicit an immune system response and allow our bodies to learn. It is also suggested that the immune response induced by parasitic infection may help the body to regulate other immune responses (such as those related to allergies).
While this hypothesis is still highly debated, evidence supporting it is increasing. There are many correlative studies showing that with decreasing presence of parasite (hookworms, bacteria, etc.), there is an increase in autoimmune diseases (at a population level). At an individual level, correlations have been shown between hygiene and allergies. But correlation, is not causation. Controlled laboratory experiments with mice are showing evidence that certain species, such as the hookworm Necator americanus (the same species responsible for the “laziness epidemic” in the South), at controlled doses, can alter the response of the immune system to other agents. These studies are beginning to elucidate a potential mechanism for this process. Of course there is still plenty of research to be done to determine the balance of benefit and harm associated with hookworm infections.
Although there is not yet a consensus within the medical community as to the validity of this hypothesis and it’s practical application, helminth therapy (the term used to describe any treatment plan involving dosing with live parasites) is being utilized as a self-prescribed treatment for a variety of autoimmune related ailments from asthma to Crohn’s disease.
This avenue of research is still very young, but it poses an interesting opportunity for medical advances in treatment of disease. It also reminds me of the important role that the pathogens we often seek to eradicate may play in our health and in nature.
Hotez, Peter J., et
al. "Hookworm:“the great infection of mankind”." PLoS Medicine
2.3 (2005): e67. http://www.plosmedicine.org/article/info%3Adoi%2F10.1371%2Fjournal.pmed.0020067
Erb, Klaus J. "Can helminths or helminth-derived products be used in humans to prevent or treat allergic diseases?." Trends in immunology 30.2 (2009): 75-82.
Strachan, David P. "Hay fever, hygiene, and household size." BMJ: British Medical Journal 299.6710 (1989): 1259.
et al. "Effect of sanitation on soil-transmitted helminth infection:
systematic review and meta-analysis." PLoS medicine 9.1 (2012):
Resources:Global Health initiative for the treatment and prevention of the leading 7 negelected tropical diseases: http://www.globalnetwork.org/hookworm
Health and epidemiology information: http://www.cdc.gov/parasites/hookworm/
Rockefeller Educational Film from 1920s aimed at educating and improving sanitation standards: http://www.rockarch.org/feature/hookworm.php
Radiolab episode about hookworms and the invention of the outhouse: http://www.radiolab.org/story/91691-sculptors-of-monumental-narrative/