PREDOMINANT SEX: Both sexes probably equally affected, with a possible slight female preponderance
PREDOMINANT AGE: Most common in children, with estimated mean age of approximately 5 yr based on surveys in highly endemic areas
PEAK INCIDENCE: Unknown
NEONATAL INFECTION: Probable transmission, though not specifically studied
PHYSICAL FINDINGS & CLINICAL PRESENTATION
• Occurs approximately 9 to 12 days after ingestion of eggs (corresponding to the larva migration through the lungs)
• Nonproductive cough
• Substernal chest discomfort
• In patients with large worm burdens, especially children, intestinal obstruction associated with perforation, volvulus, and intussusception
• Migration of worms into the biliary tree giving clinical appearance of biliary colic and pancreatitis as well as acute appendicitis with movement into that appendage
• Rarely, infection with A. lumbricoides producing interstitial nephritis and acute renal failure
• In endemic areas in Asia and Africa, malabsorption of dietary proteins and vitamins as a consequence of chronic worm intestinal carriage
• Transmission is usually hand to mouth, but eggs may be ingested via transported vegetables grown in contaminated soil.
• Eggs are hatched in the small intestine, with larvae penetrating intestinal mucosa and migrating via the circulation to the lungs.
• Larval forms proceed through the alveoli, ascend the bronchial tree, and return to the intestines after swallowing, where they mature into adult worms.
• Estimated time until the female adult worm to begin producing eggs is 2 to 3 mo.
• Eggs are passed out of the intestines with feces.
• Within human host, adult worm lifespan is 1 to 2 yr.
The diagnosis is made by finding eggs on faecal microscopy. In infections heavy enough to cause anaemia these will be present in large numbers. The aim of treatment in endemic areas is reduction of worm burden rather than complete eradication: albendazole or mebendazole, which can both be given as a single dose, are the best drugs (Box 4.5). The WHO is promoting mass treatment programmes for schoolchildren in many parts of the world, together with treatment for schistosomiasis where appropriate.
• Radiologic manifestations and eosinophilia to be distinguished from drug hypersensitivity and Loffler’s syndrome
• Examination of the stool for Ascaris ova
• Expectoration or fecal passage of adult worm
• Eosinophilia: most prominent early in the infection and subsides as the adult worm infestation established in the intestines
• Anti-ascaris IgG4 blood levels by ELISA is a sensitive and specific marker of infection and may be useful in the evaluation of treatment
• Chest x-ray examination to reveal bilateral oval or round infiltrates of varying size (Loffler’s syndrome); note: infiltrates are transient and eventually resolve.
• Plain films of the abdomen and contrast studies to reveal worm masses in loops of bowel
• Ultrasonography and endoscopic retrograde cholangiopancreatography (ERCP) to identify worms in the pancreaticobiliary tract
Aggressive IV hydration, especially in children with fever, severe vomiting, and resultant dehydration
ACUTE GENERAL Rx
• Mebendazole (Vermox)
1. Drug of choice for intestinal infection with A. lumbricoides
2. 100 mg PO tid given for 3 days
• Albendazole, given as a single 400-mg dose PO
• Both mebendazole and albendazole are contraindicated in pregnancy.
• Pyrantel pamoate (Antiminth)
1. Given at a dose of 11 mg/kg PO (maximum dose of 1 g/day)
2. Considered safe for use in pregnant women
• Piperazine citrate
1. Recommended in cases of intestinal or biliary obstruction
2. Administered as a syrup, given via nasogastric tube, a 150 mg/kg loading dose, followed by six doses of 65 mg/kg q12h
3. Considered safe in pregnancy, but cannot be given concurrently with chlorpromazine
• Complete obstruction should be managed surgically.
Ascariasis is a parasitic infection caused by the nematode Ascaris lumbricoides. The majority of those infected are asymptomatic; however, clinical disease may arise from pulmonary hypersensitivity, intestinal obstruction, and secondary complications.
Ascaris lumbricoides is a pale yellow worm, 20-35 cm in length (Fig. 4.3). It is found world-wide but is particularly common in poor rural communities, where there is heavy faecal contamination of the immediate environment. Larvae migrate through the tissues to the lungs before being expectorated and swallowed; adult worms are found in the small intestine. Ova are deposited in faeces, and require a 2- to 4-month maturation in the soil before they are infective.
Infection is usually asymptomatic, although heavy infections are associated with nausea, vomiting, abdominal discomfort and anorexia. Worms can sometimes obstruct the small intestine, the most common site being at the ileocaecal valve. They may also occasionally invade the appendix, causing acute appendicitis, or the bile duct, resulting in biliary obstruction and suppurative cholangitis. Larvae in the lung may produce pulmonary eosinophilia. Heavy infection in children, especially those who are already malnourished, may have significant effects on nutrition and development. Serious morbidity and mortality are rare in ascariasis, but the huge number of people infected means that on a global basis roundworm infection causes a significant burden of disease, especially in children.
Ascaris eggs can be identified in the stool, and occasionally adult worms emerge from the mouth or the anus. They may also be seen on barium enema studies. Appropriate drug treatments are shown in Box 4.5. Very rarely, surgical or endoscopic intervention may be required for intestinal or biliary obstruction.
EPIDEMIOLOGY & DEMOGRAPHICS
INCIDENCE (IN U.S.):
• Three times the infection rates found in blacks as in whites
PREVALENCE (IN U.S.): Estimated at 4,000,000, the majority of which live in the rural southeastern part of the country
Fig. 4.3 Ascaris lumbricoides, approximately 20 cm long.
Box 4.5 Drugs used for treating human intestinal nematodes (single dose unless otherwise stated)