The Hidden Threat Beneath Bare Feet in Tropical Soil

In many rural areas of tropical and subtropical regions, walking barefoot on moist soil is an entirely ordinary part of daily life. Yet in certain environments this simple habit may expose people to a concealed health risk: hookworm infection. Hookworms are parasitic nematodes that inhabit the human small intestine. The most common species infecting humans are Necator americanus and Ancylostoma duodenale. These tiny parasites are capable of penetrating human skin directly, meaning that when people walk barefoot on contaminated soil, they may unintentionally provide the larvae with an entry route into the body.

（圖片來源：Datiharry，採用 CC BY-SA 4.0 授權）

The life cycle of hookworms begins when adult worms living in the small intestine lay thousands of eggs each day. These eggs are expelled from the host through feces. In warm and humid soil, the eggs hatch into rhabditiform larvae, which subsequently develop into infective filariform larvae. At this stage the larvae are highly resilient and can survive for weeks or even longer under favorable environmental conditions. When bare skin comes into contact with contaminated soil, these larvae can quickly penetrate the skin of the feet, enter the bloodstream, and travel through the circulation until they reach the lungs. From there they migrate up the trachea to the throat, are swallowed, and ultimately arrive in the intestine, where they mature into adult parasites and complete their life cycle.

圖片來源：CDC，CC0 1.0 公共領域

Once established in the intestine, hookworms sustain themselves by feeding on blood from the intestinal wall. The blood loss caused by a single worm is usually minimal. However, when infections are heavy or prolonged, the cumulative blood loss can lead to chronic intestinal bleeding. This may result in iron-deficiency anemia and hypoalbuminemia, and in children it can interfere with normal growth as well as cognitive development. Pregnant women are particularly vulnerable, as hookworm infection may increase the risk of anemia during pregnancy and contribute to impaired fetal development. Studies have long recognized these complications as characteristic outcomes of chronic hookworm infection.

In a rural community in Chachoengsao Province in central Thailand, a survey once found that approximately 12% of the population carried hookworm eggs in their stool samples. A subsequent cohort study followed local residents over time and observed that, on average, about seven to eight new infections occurred per 100 individuals each year. Two major risk factors emerged from this research: walking barefoot and raising water buffalo near the household. Individuals who did not wear shoes were about 4.2 times more likely to become infected, while those living in close proximity to buffalo had a 4.8-fold increased risk.

Water buffalo frequently wallow in muddy areas surrounding rural homes, keeping the soil moist—conditions that are ideal for the survival of hookworm larvae. When people walk barefoot in agricultural fields or around livestock areas, infective larvae can easily penetrate their skin. The same investigation also detected hookworm species originating from dogs and cats, including Ancylostoma ceylanicum, a parasite capable of infecting both humans and animals. These findings highlight the fact that domestic animals may also serve as potential sources of infection.

A similar pattern has been observed in studies conducted elsewhere. In northwestern Ethiopia, for example, researchers examined stool samples from 333 school-aged children and found that 14.7% were infected with hookworms. The principal factors associated with infection included walking barefoot, poor hand-washing habits, improper use of latrines, and the absence of deworming treatment. Children who did not wear shoes were found to have approximately twenty-one times the risk of infection compared with those who regularly wore footwear.

Such findings illustrate how strongly hookworm transmission is linked to environmental sanitation and daily habits. Moist soil, open defecation, limited access to footwear, and inadequate sanitation facilities all create ideal conditions for the parasite to persist across generations. Globally, soil-transmitted helminth infections—including hookworm disease—remain a major public health concern. In tropical and subtropical regions where sanitation and healthcare infrastructure are limited, large populations remain at risk.

In places such as Taiwan, however, hookworm infection has become extremely rare. Improved sanitation, access to medical treatment, and the widespread habit of wearing shoes have greatly reduced opportunities for transmission. Without a steady supply of human hosts shedding eggs into the environment, the likelihood of hookworm larvae persisting in soil decreases dramatically. Nevertheless, it is still advisable to avoid walking barefoot on soil in natural environments, particularly in areas where sanitation conditions are uncertain.

The clinical symptoms of hookworm infection depend on both the number of worms present and the overall health of the host. Mild infections may produce no noticeable symptoms. Moderate to heavy infections, however, can lead to chronic abdominal pain, gastrointestinal discomfort, fatigue, dizziness, and shortness of breath. The skin at the site where larvae penetrate may sometimes develop itching or a rash. Fortunately, hookworm infection is generally easy to treat. Anthelmintic medications such as albendazole or mebendazole are commonly used and can effectively eliminate adult worms with a single dose or short treatment course.

Yet medication alone cannot fully solve the problem in heavily affected regions. Even after treatment, individuals may quickly become reinfected if infective larvae remain present in the surrounding soil. Effective long-term control therefore requires broader public health measures, including hygiene education, improved sanitation facilities, regular deworming programs, wider access to footwear, and better food and water hygiene. Only by addressing these environmental and behavioral factors can the cycle of infection truly be broken.

Author: Shui-Ye You

Reference:

1. Chen J et al. (2024). Global burden of soil‑transmitted helminth infections, 1990–2021. Infectious Diseases of Poverty.

2. Hailu T et al. (2019). Prevalence and determinant factors of hookworm infection among school age children in Jawe district, NorthWest Ethiopia. African H 2439 ealth Sciences.

3. Jiraanankul V et al. (2011). Incidence and Risk Factors of Hookworm Infection in a Rural Community of Central Thailand. Am. J. Trop. Med. Hyg.