Ascaris lumbricoides is an intestinal roundworm that in the adult form is 15-40 cm long, 0.3-0.6 cm in diameter and cream-coloured.
Ascariasis is worldwide in distribution and is very common in developing countries (estimated 1.2 milliard cases). Fatal cases are encountered mainly in developing countries only, yearly about 75 000.
The inoculation occurs by ingestion of eggs that have ended up in the soil or e.g. in irrigation water through faeces. The eggs only become infectious in a couple of weeks after they have ended up in the soil so direct contact infection is very unlikely. The eggs remain infective in the soil for more than a year.
The larvae hatch in the gastrointestinal tract and invade the bloodstream. They migrate through lungs to the pharynx from where they are again swallowed into the gut where the adult worms live for about two years.
Roundworms that have animals as their definitive hosts may also infect humans. Roundworm of pigs (Ascaris suum) may cause a similar disease as Ascaris lumbricoides. The respective worms found in dogs and cats (Toxocara canis and T. cati) cause toxocariasis (visceral larva migrans disease) that manifests itself as abdominal pains and eosinophilia.
Clinical picture
Most infestations are asymptomatic or the symptoms are very mild.
The most usual intestinal symptoms include nausea and abdominal pains varying from mild to colicky.
During the migratory stage of the larvae cough and fever may occur; urticaria may also develop.
Large amounts of worms cause deficiency of vitamin A, malnutrition due to loss of proteins and energy-containing nutrients and in rare cases intestinal obstruction.
Since the adults are actively motile nematodes, they may enter the biliary tract causing symptoms of biliary obstruction. They may even penetrate the intestinal wall and cause peritonitis as a rare complication. Deaths are mainly caused by biliary tract complications and intestinal obstructions.
Diagnosis
Eggs in a faecal sample are identified through microscopy.
A worm found in the faecal sample is identified as Ascaris lumbricoides by the appearance or by microscopic inspection.
During the migratory stage of the larvae, eosinophilia and an increase in the serum IgE concentration may be detected. Occasionally the larvae are detected in sputum.
Treatment
Ascariasis should always be treated. If the patient has several different worms, treatment for ascariasis should precede treatment of other worms in order to prevent the Ascaris worm to migrate into the biliary tract as a consequence of the administration of other antihelmintic drugs.
The drug of choice is mebendazole, 100 mg b.i.d for 3 days (or 500 mg as a single dose) for adults and children >1 years. Albendazole is an alternative, 400 mg as a single dose (for children < 2 years 200 mg).
Special regulations concerning the prescription of these drugs in different countries may apply.
Mebendazole should not be used during pregnancy, but, according to WHO recommendations, albendazole may be used during the 2nd and 3rd trimesters. Either of the drugs may be used during breast-feeding.
Also ivermectin (0.15-0.2 mg/kg in a single dose) is effective against Ascaris.
During pregnancy pyrantelpamoate (10 mg/kg as a single dose) is usually given, maximal dose 1 g.
Treatment success is controlled after 3 weeks by a stool specimen.
References
Acs N, Bánhidy F, Puhó E, Czeizel AE. Population-based case-control study of mebendazole in pregnant women for birth outcomes. Congenit Anom (Kyoto) 2005 Sep;45(3):85-8. [PubMed]
World Health Organization (anonymous). Breastfeeding and maternal medication - Recommendations for Drugs in the Eleventh WHO Model List of Essential Drugs, 2003. WHO and UNICEFhttp://whqlibdoc.who.int/hq/2002/55732.pdf
Dold C, Holland CV. Ascaris and ascariasis. Microbes Infect 2011;13(7):632-7. [PubMed]