Intestinal parasites infect more than a third of the global population. The highest infection rates occur amongst school aged children. The transmission typically occurs through soil, vegetation, food and water contaminated by parasite eggs. The most common soil transmitted helminthes in Haiti are Ascaris lumbricoides, Trichuris trichiura (whipworm) and Necator americanus (hookworm). Infection with these organisms results in malnutrition and impaired growth.
After ingestion, ova hatch in the small intestine. They penetrate the intestinal wall and travel through the blood and lymphatic system to the lungs. The larva mature in the lungs. They then ascend the bronchial tree and are swallowed. Once in the small intestine, they mature into adult worms. The adult worms produce eggs which are shed in the feces.
Most infections produce no symptoms. Heavy infection can lead to nutritional deficiency or intestinal obstruction. Occasionally the adult worms may migrate into the biliary system.
Necator americanus larva penetrate human skin. They then travel through the bloodstream to the lungs. After a period of maturation, they ascend the bronchial tree and are swallowed. In the small intestine, the worms mature and attach to the intestinal wall resulting in chronic blood loss. Each worm consumes approximately 0.3 cc of blood daily resulting in host anemia. Eggs are shed into the stool.
After ingestion, Trichuris trichiura eggs hatch in the small intestine. The adult worms typically reside in the cecum and ascending colon. Adults measure about 4 cm in length. Shaped like a whip, the thin end is embedded in the mucosa while the thin end extends into the bowel lumen. Colitis, dysentery and rectal prolapsed may occur in those with heavy infection. Eggs are shed into the stool.
The diagnosis is made in all cases by identifying characteristic egg in the stool by stool microscopy. Blood eosinophilia is often a clue to worm infection. The treatment is albendazole 400 mg PO x 1 or mebendazole 500 mg PO x 1 for patients >2 yrs. For infants 1 to 2 years of age, the dosage is albendazole 200 mg PO x 1 or mebendazole 500 mg PO x 1.
The WHO recommends prophylactic therapy via mass drug administration in areas of high disease burden. This avoids the long-term morbidity associated with these diseases. Deworming has been shown to be a low-cost but highly effective public health intervention. The WHO defines high-risk communities as those with a prevalence of STHs >50% in school age children. The recommended action is biannual mass drug administration. Excluded individuals are children <1 year and pregnant women in their first trimester. A low-risk community is defined as one in which the prevalence of STHs is >20% and < 50%. These communities should receive annual therapy. References: 1. Prevalence and intensity of soil-transmitted helminthes in Latin America and the Caribbean countries (PAHO 2011). 2. Preventative chemotherapy in human helminthiasis (WHO 2006). 3. CDC website.