Humans as Accidental and Natural Hosts for Worms.

Abstract

Worms and creepy crawly creatures are often associated with an “ick factor.” In this time of novel coronavirus 2019 (COVID-19), increased sanitation, handwashing, and social distancing can prepare us for other natural causes of infestations, secondary infections, and sometimes serious sequelae. North Americans enjoy beaches, lakes, and outdoor activities in the summer. As we have recently learned, being aware and prepared can be life saving. After social distancing and many weeks of sheltering at home from COVID-19, being outdoors again will necessarily need to be balanced with caution around other potential (although unusual) infestations and infections. This month’s CE/CME article, Exploring Tropical Infections: A Focus on Cutaneous Larva Migrans (CLM), documents two cases of travelers (to Chile and Jamaica, respectively) who were infected with CLM after walking barefoot on warm, moist surfaces contaminated by dog or cat feces. The egg hatching (first stage) and survival of the developing rhabdiform larvae (second stage) require an additional intermediate host (molluscs) to form filiform larvae (third stage) that can accidently infect human skin.1,2 Feet or lower legs can become infected with the parasite, which leaves the characteristic, migrating, serpiginous trails for several weeks before the larvae die or are destroyed with physical (liquid nitrogen) or chemical (topical or systemic) agents. Infection with CLM may be complicated by secondary bacterial infections, eczematization, local or general allergic reactions, or (in more severe cases) Loeffler syndrome (eosinophilia and transient pulmonary infiltrates). Systemic treatment (as in this month’s CE/CME cases) is not always necessary but ivermectin or albendazole are most effective.3 Although CLM is mostly diagnosed in travelers returning home to North America, we have our own endemic parasitic diseases. These diagnoses are often delayed or initially missed, resulting in severe pruritus, secondary infections, or other complications. For example, pinworms (thin, white roundworms that cause enterobiasis) lay eggs in the perianal areas of humans–most commonly in young children. Look for them 3 hours after the victim falls asleep, take tape samples on three consecutive mornings for eggs, or examine the skin under the nails for eggs with a dermatoscope. Over-the-counter or prescription medication can successfully treat this infestation.4 That said, hemorrhoids, contact dermatitis, and other causes of perianal itch also exist. Another infection that can affect individuals of any age, often after swimming in freshwater lakes or saltwater oceans, is cercarial dermatitis. Called swimmer’s itch, parasites released by infected snails burrow into the skin, causing an allergic reaction. Austrobilharzia variglandis require a primary host (often birds–especially geese) or other mammal species to complete their life cycle. Related lesions under bathing garments can be numerous, especially around the buttocks, and are self-limiting but may require topical steroids and oral antihistamines.5 Keep the cream in the refrigerator for a greater cooling effect! One of the authors (Dr Sibbald) encountered a life-changing case as a final year medical student. A previously healthy young patient went on a camping and canoeing trip with a friend. After his return, he was admitted to a tertiary hospital ICU and placed on a ventilator for respiratory failure. His skin developed hemorrhagic lesions and he had diffuse pulmonary infiltrates. A lung biopsy revealed mesocercariae of the trematode Alaria americana. It was later determined that this parasite was contracted from inadequately cooked frogs’ legs the patient ate less than 2 weeks before he succumbed to his illness. Many thousands of organisms were found within most of his internal organs.6 Although we may not like to think about it, parasites and their associated clinical syndromes are ubiquitous. Just like the precautions for COVID-19, we need to consider good hygiene and public health precautions around time spent in natural settings, swimming, or in contact with wildlife and domestic animals. This July, as always, please be smart, be safe, and enjoy the environment by giving it the respect it deserves! R. Gary Sibbald, MD, DSc (Hons), MEd, BSc, FRCPC (Med Derm), FAAD, MAPWCA, JM Elizabeth A. Ayello, PhD, MS, BSN, RN, CWON, ETN, MAPWCA, FAAN