A paper in PLOS Medicine (January 24, 2012) reports that “sanitation is associated with a reduced risk of transmission of helminthiases to humans.” The authors looked at 36 previously published studies that measured prevalence of intestinal helminths (A. lumbricoides, large intestinal roundworm; T. trichiura, whipworm; and hookworm) compared to availability and use of sanitary facilities. They found that “people who either had or used a latrine were half as likely to be infected with a soil-transmitted helminth as people who neither had or used a latrine.”

Pit Latrine, Rémi Kaupp, CC-BY-SA, Wikimedia Commons

I submit that there are no surprises here. One acquires hookworm by coming in contact with hookworm larvae from feces contaminating the soil. They penetrate skin. Trichuris trichiura and A. lumbricoides eggs, infective a week or so after being deposited in warm moist soil in feces, must be swallowed. Obviously if feces were deposited in a pit latrine, septic system or other sanitary arrangement, instead of on the ground, those eggs and larvae would not be available to infect new hosts.

The fact that intestinal helminthes are much less common, even rare, in developed countries is no mere accident of climate, especially for the tough A. lumbricoides. It is because the majority of people in developed countries don’t defecate outside on the ground.

The best point in this paper, though understated, is that periodically treating people for intestinal worms is perhaps not the best long term approach to getting rid of these parasites. Without good sanitation, people will quickly be reinfected due to contamination of their environment. Lets build toilets.

Read the paper:

Ziegelbauer K, Speich B, Mäusezahl D, Bos R, Keiser J, et al. (2012) “Effect of Sanitation on Soil-Transmitted Helminth Infection: Systematic Review and Meta-Analysis.” PLoS Med 9(1): e1001162. doi:10.1371/journal.pmed.1001162