Saturday, June 15, 2024

Pediatric Ascariasis

Background

Ascaris lumbricoides, which causes ascariasis, is the largest of the round worms (nematodes), with females measuring 30 cm x 0.5 cm. It is present in the GI tract (small intestine) of 1.2–1.5 billion individuals in tropical and subtropical areas, making it the most common nematode infection in the world. The number of cases in the United States is estimated to be 4 million, with transmission occurring in the Gulf States and southern New Mexico and southern Arizona. See the image below.

The roundworm Ascaris lumbricoides causes ascarias

The roundworm Ascaris lumbricoides causes ascariasis. Worms can reach 10-30 cm in length. Clinical disease results from effects of pulmonary larval migration, intestinal obstruction, or migration through the biliary tree.

The parasite is acquired through ingestion of embryonated eggs. Ascariasis is usually asymptomatic but can be complicated by several conditions, including appendicitis, bowel perforation, cholecystitis, intestinal obstruction (large numbers), malabsorption (eg, lactose, nitrogen, vitamin A), and pancreatitis. The mortality rate is 5% if complications occur. When the parasite migrates through the lung early in its parasitic cycle, it can also cause pneumonitis. The mainstays of chemotherapy include albendazole, mebendazole, and pyrantel pantoate (for alternatives, see Medication).

A lumbricoides is one of the soil-transmitted helminths (STH), a group that includes 16 worms. Many individuals are infected with 2-3 of the 3 major parasites (ie, A lumbricoides, Trichuris trichiura, and hookworm).

Table 1. Major Soil-Transmitted Helminths
(Open Table in a new window)

Parasite*

Disease

Prevalence

A lumbricoides

Common roundworm infection, ascariasis

800 million to 1.4 billion

T trichiura

Whipworm infection, trichuriasis

600 million to 1 billion

Necator americanus and

Ancylostoma duodenale

Hookworm infection

580 million to 1.2 billion

Strongyloides stercoralis

Threadworm infection, strongyloidiasis

30-300 million

Enterobius vermicularis

Pinworm infection

4-28% of children

Toxocara canis and

Toxocara cati

Visceral larva migrans and ocular larva migrans

2-80% of children

*All major parasites are found in tropical, subtropical, and temperate climates.

Table 2. Minor Soil-Transmitted Helminths
(Open Table in a new window)

Minor Parasite

Disease

Distribution

Ancylostoma braziliense

Cutaneous larva migrans

Costal regions worldwide

Uncinaria stenocephala

Cutaneous larva migrans

Costal regions worldwide

Ancyclostoma canium

Eosinophilic enteritis

Australia

Ancylostoma ceylanicum

Hookworm infection

Asia

Oesophagostomum bifurcum

Nodular worm infection

North America

Strongyloides fuelleborni

Swollen belly syndrome

West Africa

Ternidens diminutus

False hookworm infection

Southern Africa

By chronically infecting school-aged children, usually in developing countries, these parasites significantly contribute to cognitive deficits, growth stunting, mental retardation, and malnutrition. The 3 most important infections are ascariasis (A lumbricoides) , trichuriasis (T trichiura), and hookworm (N americanus and A duodenale); often, all 3 parasites can be found in a single individual. The combined disease burden of the STHs is estimated to be equivalent to malaria or tuberculosis.

Although A lumbricoides has been present in humans for many thousands of years, science only began to elucidate its biology in the 17th century, and effective chemotherapy was only developed in the late 20th century. The earliest recovered eggs are from the 30,000-year-old Upper-Paleolithic site of Arcy-sur-Cure in Yonne, France. Infertile eggs have been reported in coprolites dating to 2277 BCE from an archeological site at Los Gavilanes, Peru. Desiccated human feces from Big Bone Cave, Tennessee dating to approximately 2177 BCE contained A lumbricoides. In the Nubian aspect of the Nile River, eggs have been recovered inside a mummy dating to 2050-1750 BCE.

In 1683, Tyson discussed ” Lumbricus teres …observations on the Round Worm bred in human bodies….that common Round Worm which children u[s]ually are troubled with.” In 1758, Linnaeus proposed the name Ascaris lumbricoides. In 1856, Ransom reported that finding eggs in fecal samples was a reliable means of diagnosis. In 1862, Davaine concluded that ingested embryonated eggs produced ascariasis and that the infected host would produce eggs in feces that could pass the infection to another host. In the 1980s, several reviews noted the public health impact of STH infection and suggested control strategies using antihelminthic drugs, some of which were introduced in the 1960s (eg, pyrantel pantoate) and 1970s (eg, mebendazole).

The genus Ascaris is composed of 17 species. A lumbricoides has a high host specificity for humans and, rarely, for pigs. It has been reported in other hosts, including cats, chimpanzees, domestic dogs, gibbons, gorillas, guinea-pigs, lambs, macaques, monkeys, rabbits, rats, and squirrels; however, it has not been demonstrated to achieve sexual maturity or to produce fertile eggs in these hosts.

Ascaris suum has a high host specificity for domestic pigs and, rarely, humans. It has been reported in other hosts, including domestic cattle, gorillas, goats, lambs, monkeys, mice, rabbits, and rats. As with A lumbricoides, A suum has not been demonstrated to achieve sexual maturity or to produce fertile eggs in these hosts. The other 15 species of Ascaris are not reported in humans. Therefore, A lumbricoides does not have an animal reservoir.

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