A family with one child (a three-year-old boy) has been working with an international relief agency in Central America for a little over a year. They are stationed in a very remote and very impoverished village. The local people grow most of their own food and, as is common in the area, they often use human feces as a fertilizer on the local soil. The family's son has been accepted by the local children, so he often plays outdoors with them and can speak the local dialect quite well. The family was in good health when they arrived in Central America and, until recently, they had not experienced any major medical problems. A few weeks ago, the son started to experience abdominal pain and diarrhea. The pain has slowly worsened over time and the diarrhea, which is often bloody, has not abated. Moreover, the boy has become anorexic, is very weak, and is losing weight. The family then takes their son to the nearest substantial medical facility, in a small city about 200 miles from the village in which they have been working. The physicians take a history, do a physical examination, and collect stool and blood specimens for analysis. They find that the boy has no history of unexplained skin lesions or other cutaneous symptoms. The tests show that the patient has mild eosinophilia. The stool sample is examined microscopically and found to contain bile-stained, lemon-shaped eggs that are approximately 20 x 50 (m in size and have distinctive-looking polar plugs.

Question 12.1: What is the most likely causative agent?

The presence of eggs in the feces implies some type of helminthic infection. The lack of a history of skin lesions argues against an agent that invades through the skin (e.g., Strongyloides or hookworm). However, such infections sometimes fail to produce noticeable skin symptoms. A number of helminthic causative agents are possible based on the symptoms. In this case, the lab identified the eggs in the feces as being those of Trichuria trichuris, a type of nematode that is commonly known as the whipworm.

Question 12.2: What is the life cycle of this causative agent?

T. trichuria has a comparatively simple life cycle. Infection is via the oral route. Ingested eggs hatch into a larval worm in the small intestine and then migrate to the cecum, where they penetrate the mucosa and mature into adults. This organism does not migrate to the lungs, so there is no pulmonary stage of infection. About three months after migrating to the cecum, the fertilized female worms start laying eggs, possibly producing 3,000 to 10,000 eggs per day. The female worms can live up to 8 years. Eggs are passed in feces and when the fecal material is deposited on a soil, the eggs mature in the soil and become infectious within three weeks. The eggs have a distinctive appearance, with dark bile staining, a lemon-shaped body, and prominent polar plugs at each end of the cell.

Question 12.3: What are the usual consequences and possible complications of this disease?

Tissue reactions to whipworms are usually mild. Most infected individuals are asymptomatic or have mild eosinophilia. Heavy infections can result in the abdominal symptoms (pain, anorexia, bloody diarrhea, etc.) as described in this case. The symptoms often mimic inflammatory bowel disease (IBD). As is the case with many other helminthic parasites, heavy infections require repeated exposure to the infectious eggs and repeated re-infection of the GI tract. Rectal prolapse can result from massive infections in children, as a result of irritation and straining during defecation. Moderately heavy whipworm infections also contribute to growth retardation.

Question 12.4: How is this disease transmitted?

Disease is initiated when an individual swallows the infectious eggs that are most often found in soils fertilized with human fecal material. Prevalence is directly associated with poor sanitation and poor hygienic practices of young children. The parasite is globally distributed in the tropics and subtropics but is most often seen among children living in poverty-stricken areas. There is no known animal host for T. trichuria, so infections are not zoonotic.

Question 12.5: How is this pathogen identified by the lab?

The characteristic lemon-shaped whipworm eggs are readily detected on examination of a stool specimen when cases are symptomatic. Adult worms, which are 3-5 cm long can sometimes be seen on proctoscopy.

Question 12.6: How is this disease treated and prevented?

Mebendazole or albendazole are both safe and effective. Prevention of whipworm infections depends on education, good personal hygiene, adequate sanitation, and avoidance of the use of human feces as fertilizer.