Trichuriasis is caused by the intestinal nematode, Trichuris trichiura, commonly known as the whipworm. Humans are the principal hosts for this parasite. T trichiura is found in coexistence with other soil-transmitted helminths, most commonly Ascaris lumbricoides and hookworms (Ancylostoma duodenale and Necator americanus).
PATHOGENESIS AND EPIDEMIOLOGY
The life cycle of trichuriasis begins with the passage of eggs in the stool (Fig. 328-1). In optimal soil and temperature conditions, the eggs embryonate in 2 to 4 weeks. After ingestion of eggs via contaminated hands or food, larvae are released into the small intestine and travel to the cecum and colon. In 2 to 3 months, the larvae mature into adult worms that measure approximately 3 to 5 cm in length (Fig. 328-2). The distinctive whiplike anterior portion burrows into the mucosa, while the broader posterior end remains free in the intestinal lumen. Although adult whipworms live preferentially in the cecum and ascending colon, in heavy infections, they can be found throughout the colon and rectum. In those with large worm burdens, the colonic mucosa becomes inflamed, edematous, and friable. One to 2 months after infection, adult females begin to produce 5000 to 20,000 eggs per day. The total life span of the adult is 1 to 3 years.
Life cycle of Trichuris trichiura, the human whipworm.
Adult female and male Trichuris trichiura. (Courtesy Parasites Without Borders [Parasitic Diseases 6th ed].)
T trichiura is one of the most prevalent human helminthiases, with an estimated 1 billion people infected worldwide. Trichuriasis is found in humid tropical environments and in temperate zones during warm and humid months, with the highest prevalence in Southeast Asia and Africa. It is especially common in poor rural communities with inadequate sanitary conditions and soil contamination with human feces. Transmission of infection occurs by ingestion of the eggs, which contaminate hands, food (raw fruit and vegetables fertilized by human feces), or drink. Children are especially vulnerable to this helminth infection, with the highest rate of infection occurring among those 5 to 15 years of age, presumably because of their high exposure risk and incomplete protective immunity. In endemic communities, people with heavy worm burdens typically represent less than 10% of the population and are the ones who develop overt disease.
Although trichuriasis is not highly pathogenic, the amount of disease caused by T trichiura is proportional to the intensity of infection. Most infected people harbor fewer than 20 worms, but a small proportion, usually children, may harbor more than 200 worms. Those with low worm burdens are asymptomatic or may only have a peripheral eosinophilia. Inflammation at the site ...