Ascariasis is infection with Ascaris lumbricoides, the large roundworm of man. The adults mature in the small intestine and can produce disease by intestinal obstruction or migration. The passage of larvae through the lungs may result in pneumonitis.
Etiology of Ascariasis.
Ascariasis is a large whitish nematode; the female (20 to 35 cm.) is larger than the male (15 to 30 cm.), which often has a curly tail. The vulva of the female is situated ventrally at the junction of the anterior and middle thirds of the worm. Frequent copulation is necessary to ensure the continuous production of fertile eggs. A female worm has a reproductive capacity of 26 to 27 million eggs and a daily output of 200,000. The life span of the adult worms is relatively short (12 to 24 months). They are not attached to the wall of the jejunum, but bridge themselves across the lumen and by their muscle tone maintain themselves against the fecal stream. In a largely anaerobic environment they obtain nourishment from the semi digested food of the host and possibly from epithelial cells of the intestinal mucosa. The high protein and vitamin content of the parasite suggests that they deprive the host of nutrients.
The brownish eggs with a thick shell and albuminous coat become infective ten days after being passed in the stool. Fertile and infertile eggs have a different morphology. On ingestion of infective eggs by man, the larvae hatch in the small intestine, and, penetrating its wall, are carried by the blood and lymphatic system to the .lungs. It has been suggested that this migration is necessitated by the need for oxygen, which is not available in the intestine, at this stage of the life cycle. Here, like hookworm and Strongyloides, the larvae migrate up the respiratory passages to the epiglottis and down to the esophagus. A new generation of eggs appears in the feces approximately two months after the ingestion of embryonated eggs.
Epidemiology of Ascariasis.
Although cosmopolitan, this worm is most abundant in the tropics, where sanitation is poor. One in every four people in the world is infected with Ascaris lumbricoides. The eggs are killed by direct sunlight and temperatures above 45° C.; nevertheless, under optimal conditions they may remain viable for one year. The eggs pass unchanged through the intestine of animals with the possible exception of the pig. The pig Ascaris, Ascaris suum, is morphologically identical to the human Ascaris, and there is some evidence that cross infections can occur. The susceptibility to infection is greatest in childhood, reaching a peak at puberty, and transmission is by fecal contamination of food and drink. Circulating antibodies appear to play some role in host immunity.
Pathology and Clinical Manifestations of Ascariasis
Light infections of a dozen or so worms often pass unnoticed, especially in adults. During the phase of larval migration, especially if many eggs have been ingested, respiratory symptoms may appear 4 to 16 days after infection. The pulmonary migration of larvae is associated with fever, cough, occasionally hemoptysis, and either crepitations or more rarely the signs of consolidation on auscultation of the chest. The sputum contains larvae and eosinophils, and there is a high blood eosinophilia. Sections of the lungs at this stage would show larvae in the bronchioles with patchy infiltration of alveoli with polymorphs and eosinophil leukocytes. Aberrant larvae may lodge in the liver, producing granulomatous lesions and hepatomegaly. More rarely such larvae which fail to re-enter the circulation, are found in other abdominal organs.
When adult worms are present in the intestine, the established infection is often associated with occasional colicky abdominal pain and some abdominal distention. These adults may produce complications by mechanical effects within the gastrointestinal tract, or by wandering outside it, or more rarely by producing allergic manifestations in a sensitized host.
Heavy loads of worms may particularly be associated with intestinal obstruction, intussusception, volvulus, appendicitis, and hernia strangulation. A bolus of Ascaris may. be a common cause of intestinal obstruction in childhood in an endemic area. Before undertaking bowel surgery, an Ascaris infection should always be excluded,, because these worms are difficult to. control once the bowel is opened, and considerable peritoneal soiling may result. Migration of adult worms may occur spontaneously or as a result of some stimulus such as fever or tetrachloroethylene. The Ascaris adults may perforate a suture line or cause a bile or paz create duct obstruction. Occasionally they are into the stomach and are vomited up, or pass down into the large bowel and out with the stool. Adult worms have been described issuing from umbilical fistulas, and even from the nose or ear.
Obstruction of the bile duct is associated with cholangitis, and eggs may be deposited in the liver. .4. lumbricoides has been said by some to be second only to E. histolytica in producing liver abscesses. Blockage of the pancreatic duct results in acute pancreatitis. Once the adult worm has left the bowel, it often dies, releasing foreign protein that may produce a reaction in a sensitized host. These reactions range from facial edema and giant urticaria to acute local necrosis and anaphylaxis. Laboratory personnel who work with .Ascaris invariably become sensitized to the worms. Young pigs infected with Ascaris do not gain weight normally, and it is possible that heavy loads of human Ascaris may affect children similarly, as the worms will consume much food in the actively growing phase.
Diagnosis of Ascariasis.
Examination of the feces reveals the characteristic ova. Usually in view of the number of ova produced, they can be found in ordinary direct smear. Although fertilized eggs are easy to recognize, unfertilized eggs assume bizarre shapes and may be mistaken for debris. Rarely one encounters infections of immature worms or only male worms. Sometimes an infection is diagnosed in barium meal examination, as the barium can be seen in the Ascaris gut. Although many serologic tests have been developed for Ascaris, including complement-fixation, hemagglutination, and gel diffusion, they are seldom used for diagnostic purposes.
Treatment of Ascariasis
Piperazine citrate is the drug of choice in the treatment of Ascaris infestations. The piperazine salts are simple, safe, and efficient. They act by blocking the neuromuscular junctions of the worm. The paralyzed worm can no longer bridge itself across the intestinal lumen and is carried along in the fecal stream and passed in the stool. Piperazine citrate is given in a dose of 75 mg. per kilogram to a maximal single dose of 4 grams. This will clear 75 per cent of patients of their worms, but the dose can be repeated the following day with safety. No special preparation or purgation is necessary. Neurotoxic effects from piperazine have been reported in patients with renal failure who cannot excrete the drug.
Thiabendazole in the same dose as for strongyloidiasis and Alcopar in the same dose as for hookworms are both effective in ascariasis as well. In the presence of Ascaris plus one or another of these intestinal parasites, single drug therapy may be preferred. However, neither of these drugs is as effective in ascariasis as piperazine. In multiple intestinal helminth infections, Ascaris should always be treated first.When examining stools for ova after therapy, it must be remembered that eggs may be passed in the stool for up to a week after the worms have been eradicated owing to the delay in the colonic circulation of feces.
The following regimen is suggested to deal with intestinal obstruction owing to Ascaris. Initially conservative treatment with nasogastric suction, intravenous fluids, and piperazine therapy should be tried for 48 hours. If no improvement follows, at laparotomy it is often possible to manipulate the bolus of worms into the large bowel through the terminal ileum. Only -if this is not possible should enterotomy and worm extraction be performed.
Prevention of Ascariasis.
This consists of disposal of human excreta in sanitary privies and toilets. Children must be taught to use these facilities and avoid contamination of food with’ ova