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U.S.
Food & Drug Administration Center for Food Safety & Applied Nutrition Foodborne Pathogenic Microorganisms and Natural Toxins Handbook |
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Ascaris lumbricoides and Trichuris trichiura
| 1. Name of the Organism:
Ascaris lumbricoides and Trichuris trichiura |
Humans worldwide are infected with Ascaris lumbricoides and Trichuris trichiura; the eggs of these roundworms (nematode) are "sticky" and may be carried to the mouth by hands, other body parts, fomites (inanimate objects), or foods. |
| 2. Nature of Acute Disease: | Ascariasis and trichuriasis are the scientific names of these infections. Ascariasis is also known commonly as the "large roundworm" infection and trichuriasis as "whip worm" infection. |
| 3. Nature of Disease: | Infection with one or a few Ascaris
sp. may be inapparent unless noticed when passed in the
feces, or, on occasion, crawling up into the throat and
trying to exit through the mouth or nose. Infection with
numerous worms may result in a pneumonitis during the
migratory phase when larvae that have hatched from the
ingested eggs in the lumen of the small intestine
penetrate into the tissues and by way of the lymph and
blood systems reach the lungs. In the lungs, the larvae
break out of the pulmonary capillaries into the air sacs,
ascend into the throat and descend to the small intestine
again where they grow, becoming as large as 31 X 4 cm.
Molting (ecdysis) occurs at various points along this
path and, typically for roundworms, the male and female
adults in the intestine are 5th-stage nematodes. Vague
digestive tract discomfort sometimes accompanies the
intestinal infection, but in small children with more
than a few worms there may be intestinal blockage because
of the worms' large size. Not all larval or adult worms
stay on the path that is optimal for their development;
those that wander may locate in diverse sites throughout
the body and cause complications. Chemotherapy with
anthelmintics is particularly likely to cause the adult
worms in the intestinal lumen to wander; a not unusual
escape route for them is into the bile duct which they
may occlude. The larvae of ascarid species that mature in
hosts other than humans may hatch in the human intestine
and are especially prone to wander; they may penetrate
into tissues and locate in various organ systems of the
human body, perhaps eliciting a fever and diverse
complications. Trichuris sp. larvae do not migrate after hatching but molt and mature in the intestine. Adults are not as large as A. lumbricoides. Symptoms range from inapparent through vague digestive tract distress to emaciation with dry skin and diarrhea (usually mucoid). Toxic or allergic symptoms may also occur. |
| 4. Diagnosis of Human Illness: | Both infections are diagnosed by finding the typical eggs in the patient's feces; on occasion the larval or adult worms are found in the feces or, especially for Ascaris sp., in the throat, mouth, or nose. |
| 5. Associated Foods: | The eggs of these worms are found in insufficiently treated sewage-fertilizer and in soils where they embryonate (i.e., larvae develop in fertilized eggs). The eggs may contaminate crops grown in soil or fertilized with sewage that has received nonlethal treatment; humans are infected when such produce is consumed raw. Infected foodhandlers may contaminate a wide variety of foods. |
| 6. Relative Frequency of Disease: | These infections are cosmopolitan, but ascariasis is more common in North America and trichuriasis in Europe. Relative infection rates on other continents are not available. |
| 7. Course of Disease and Complications: | Both infections may self-cure after the larvae have matured into adults or may require anthelmintic treatment. In severe cases, surgical removal may be necessary. Allergic symptoms (especially but not exclusively of the asthmatic sort) are common in long-lasting infections or upon reinfection in ascariasis. |
| 8. Target Populations: | Particularly consumers of uncooked vegetables and fruits grown in or near soil fertilized with sewage. |
| 9. Food Analysis: | Eggs of Ascaris spp. have been detected on fresh vegetables (cabbage) sampled by FDA. Methods for the detection of Ascaris spp. and Trichuris spp. eggs are detailed in the FDA's Bacteriological Analytical Manual. |
| 10. Selected Outbreaks: | Literature references can be found at the links below. |
| Although no major outbreaks have occurred, there are many individual cases. The occurrence of large numbers of eggs in domestic municipal sewage implies that the infection rate, especially with A. lumbricoides, is high in the U.S. | |
| Morbidity and Mortality Weekly Reports | For more information on recent outbreaks see the CDC. |
| 11. Education and Background Resources: | Literature references can be found at the links below. |
| Loci index
for genome Ascaris
lumbricoides Trichuris trichiura |
Available from the GenBank Taxonomy database, which contains the names of all organisms that are represented in the genetic databases with at least one nucleotide or protein sequence. |
| 12. Molecular Structural Data: | None currently available. |
| 13. FDA Regulations or Activity: | Ascarids and trichurids are considered pathogens and foods eaten without further cooking should not be contaminated with viable embryonated eggs of either genus. |
mow@cfsan.fda.gov
April 1991 with periodic updates
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