More than 1.2 billion people are infected with at least one species.
Most helminth infections are contracted by ingesting the eggs, except strongyloides and hookworm whose larvae penetrate bare skin when it is contact with the soil.
The roundworm (Ascaris lumbricoides) life cycle involves migration through the lung tissue which can cause pneumonitis. Patients can present with interstitial infiltrates, wheeze, and blood tinged sputum. Ascaris than migrates to the intestines where it can cause partial small bowel obstruction. In pediatric patients, the appendix may be invaded causing gangrene with symptoms indistinguishable from appendicitis. In adults, the worms can invade the biliary tract and cause biliary disease or pancreatitis. Fever causes this helminth to migrate and it can emerge from the nasopharynx or the anus.
Whipworms (Trichuris trichiura) present as colitis or symptoms similar to inflammatory bowel disease. Chronic illness can involve anemia and clubbing. In severe cases, trichuris can cause dysentery and rectal prolapse.
Hookworms (Necator americanus or Ancylostoma duodenale) also have a pulmonary phase, but with milder symptoms than Ascaris. Eventually hookworms cause iron deficiency anemia and malnutrition. They can be a primary cause of anemia in pregnancy in endemic areas.
Threadworm (Strongyloides stercoralis) can cause a wide spectrum of disease presentations. The infection can start with a rash, larva currens. The infection may be subclinical or may invade the lung, intestinal wall, or the nervous system. Eventually hyperinfection may develop which is a very large increase in worm burden and then the infection becomes disseminated.
Toxocara canis or toxocara cati have affected approximately 14% of the US population. These helminthes reproduce in dogs or cats, and human infection is not part of the normal life cycle. Most infections are subclinical but it can produce a mild pneumonitis that is very similar to asthma. There can be pain and inflammation as the helminthes travel through organs such as the liver or lung and is called visceral larva migrans. The helminth may also move through the eye and optic never causing an ocular form of the disease, ocular larva migrans.
Pinworms (Enterobius vermicularis) are the cause of most common helminth infection in US and can present with anal pruritus leading to trouble sleeping. When an infection is identified, everyone in the household should be treated, regardless of symptoms.
University of Maryland Section of Global Emergency Health
Author: Jenny Reifel Saltzberg, MD, MPH
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