Nematodes, or roundworms, are abundant animals, and while many are free-living, some parasitic species cause human infections. An infection occurs when a person hosts a parasitic worm, which often lives in the intestinal tract. These infections are widespread globally, affecting billions of people, particularly in regions with warm climates and developing sanitation systems.
Pathways to Nematode Infection
Humans acquire nematode infections primarily through contact with or ingestion of the parasite’s infective stages. A common pathway is consuming food or water contaminated with nematode eggs or larvae, such as unwashed produce from contaminated soil. Once ingested, the eggs hatch in the digestive system, where the worms mature and establish an infection.
Another transmission route is direct skin penetration by larval worms, which occurs when walking barefoot on contaminated soil. Larvae from species like hookworms can burrow through the skin and enter the bloodstream. They then travel to the lungs and intestines to develop into adults.
Ingesting undercooked meat from an infected animal is another transmission method. Nematode larvae can encyst in an animal’s muscle tissue. If the meat is not cooked to a temperature that kills the larvae, the cysts release worms into the host’s intestine to mature.
Some nematode infections are transmitted by the bites of infected insects acting as vectors. Mosquitoes and certain flies carry nematode larvae, injecting them into a person’s bloodstream during a blood meal. These larvae circulate through the body and develop into adult worms, causing conditions like filariasis.
Recognizing Different Nematode Infections
Ascariasis, caused by Ascaris lumbricoides, is the most common human worm infection. Once ingested, the eggs hatch, and larvae penetrate the intestinal wall, traveling to the lungs before being coughed up and swallowed. Returning to the intestine, they mature into large adult worms that can exceed 30 cm. While light infections may be asymptomatic, heavy loads can cause abdominal pain, malnutrition, and intestinal blockage.
Hookworm infection is caused by Necator americanus and Ancylostoma duodenale. After penetrating the skin, larvae migrate to the lungs and are swallowed, eventually attaching to the small intestine’s wall. These worms feed on blood, which can lead to iron-deficiency anemia, protein energy malnutrition, and developmental issues in children. Symptoms include a local “ground itch” at the entry site, abdominal pain, diarrhea, and weight loss.
Pinworm infection (enterobiasis), caused by Enterobius vermicularis, is common in children. The adult worms reside in the colon, and female worms migrate to the perianal region at night to lay eggs, causing intense itching. This itching facilitates the spread of eggs to fingers, bedding, and other surfaces, promoting reinfection and transmission.
Trichinosis, caused by Trichinella spiralis, is acquired from undercooked meat. Once ingested, the larvae mature and reproduce in the intestine. Newborn larvae then migrate from the intestines into the bloodstream and burrow into muscle tissue, causing inflammation. Initial symptoms include nausea and diarrhea, followed by fever, muscle pain, and swelling around the eyes (periorbital edema) as larvae invade muscles.
Medical Approaches to Nematode Infections
Diagnosing a nematode infection involves evaluating a patient’s symptoms and potential exposures. The most common method is a stool analysis, where a sample is examined under a microscope for nematode eggs or larvae. The specific shape and size of the eggs help determine the species of worm causing the infection.
Blood tests can also support a diagnosis. These tests may detect elevated levels of eosinophils, a type of white blood cell produced in response to parasites. Other blood tests may look for specific antibodies that the immune system has created to fight the nematode infection, indicating a past or present infection.
For infections where worms migrate outside the intestines, imaging studies may be used. In cases of trichinosis, a muscle biopsy can be performed to find encysted larvae. X-rays, ultrasounds, or other imaging can sometimes reveal adult worms or organ damage.
Once confirmed, treatment involves anthelmintic medications like mebendazole and albendazole. These drugs are effective against a broad range of intestinal worms by preventing them from absorbing nutrients, leading to their death. The specific drug and treatment duration depend on the nematode species and infection severity.
Strategies for Preventing Nematode Infections
Preventing nematode infections involves several key strategies:
- Maintain personal hygiene by washing hands thoroughly with soap and water, especially after using the toilet, changing diapers, and before preparing or eating food. This practice helps remove any nematode eggs from contaminated surfaces.
- Ensure food and water safety. Carefully wash all fruits and vegetables, particularly those eaten raw. Cook meats, especially pork and wild game, to temperatures high enough to kill any potential larval cysts. Drink purified or boiled water to avoid ingesting eggs.
- Support proper sanitation and waste management. The sanitary disposal of human and animal feces prevents soil and water contamination. In areas with limited sanitation, wear shoes when walking outdoors to prevent larvae from penetrating the skin.
- Control insect vectors in regions where they transmit infections. Use insect repellent, sleep under mosquito nets, and support community efforts to reduce insect breeding grounds to minimize bites from infected vectors.