Ascaris lumbricoidesis the largest and, globally, the most widespread of all human intestinal roundworms (Nematode).
Human is the definitive host. There is no intermediate host
Tramission is human - feces - human
Adult ascarids live in the small intestines.
Females produce 200 000 eggs per day. Eggs are deposited in the lumen, passed in feces, and must embryonate for 3 weeks in the soil before becoming infectious.
Ingestion of infective eggs by another human from contaminated soil results in infection.
After ingestion, the hatched larvae penetrate intestinal mucosa and invade portal venules.
They are carried to the liver, and travel via the hepatic vein to the right heart and into the lungs.
Larvae enlarge and rupture into alveoli, are coughed up and subsequently swallowed.
Upon reaching the small bowel, they mature, mate and deposit eggs.
If the infection is untreated, adult worms can live for 12 to 18 months, resulting in daily excretion of large numbers of ova.
The incubation period is prolonged. The interval between ingestion of the egg and the development of egg-laying adults is approximately 8 weeks.
The diagnosis is established by finding characteristic eggs in the feces.
Eggs are elliptical in shape, measure 30 by 50 pm, and have a rough, wavy, albuminous coat over their shell.
They are highly resistant and may remain viable up to 6 years.
The pulmonary phase may be diagnosed by finding larvae and eosinophils in sputum.
Occasionally, patients pass adult worms from
the nose following migration through the nares in febrile patients
the mouth in vomitus.
Can be recognized with barium studies
The differential when the worm is visible to the naked eye
Ascaris lumbricoides is the largest and most common of the intestinal helminths, and measure 1.5-3 cm in length.
The adult female of Enterobius vermicularis (pinworm) is 10 mm long and may occasionally be visible.
The adult whipworm (Trichuris trichuria) is 30-50 mm long, and is seen only on a prolapsed rectum.
Ancylostoma duodenale and necator americanus measure 10 mm in length; the adult worm is not seen in stool.
Strongyloides stercoralis is
only 2 mm long, and the worm is not seen in stool.
Medically important nematodes.
Nematodes (or round worms) can be divided into intestinal and tissue dwellers.
Intestinal nematodes that are human parasites include Enterobius, Trichuris, Ascaris, Ancylostoma, Necator and Strongy1oides.
Tissue nematodes include members of the family Filarioidea (Wuchereria bancrofti, Brugia malayi, Loa loa, Onchocerca volvulus).
parasites that can cause human disease are Capillaria, Anisakis, Toxocara,
and Ancylostoma brazilienses, but cannot complete their life cycle in the human host.
and Pyrantel pamoate are highly effective. Mebendazole is preferred if
Trichuris trichiura is also present.
Reexamination of stool specimens 3 weeks after therapy to determine whether the
worms have been eliminated is helpful for assessing therapy but is not essential.
In cases of partial or complete intestinal obstruction due to a heavy worm load: