Ascariasis

Etiology

Ascaris lumbricoides, a soil-transmitted large nematode, causes Ascariasis. The female adult can reach up to 20 cm to 30 cm in length, and adult males up to 15 cm to 20 cm. The nematodes are pink/yellow/white roundworms. The female worms are thicker and have a straight rear end. The male worm is more slender with a ventrally incurvated rear end with two retractile copulating spicules. The average life of the adult parasite is one year, after which it dies, and it is spontaneously eliminated as it evacuates through the digestive tract. This is the reason why a spontaneous cure of disease can happen if there is no reinfection. Adult worms do not multiply in the human host.[4][5]

Epidemiology

Ascariasis is one of the most common human parasitic infections. It is found worldwide. Ascariasis has been a disease that has affected the world population for centuries. It was described in ancient Egyptian papyruses and has been identified in Egyptian mummies from around 800 B.C. Even Hippocrates and Aristotle described the helminth. This disease has been described in children and adults in tropical and subtropical areas with poor sanitation and poor personal hygiene and in places where human feces are used as fertilizer. There is a higher risk of infection in nonendemic areas due to the increased rate of migration and travel.[6][7]

Pathophysiology

Infection occurs when the host ingests eggs found in stool-contaminated soil. Once in the duodenum, larvae are released and enter the circulation via the enteric mucosa. Once in the capillaries (venous, arterial or lymphatic), it reaches the liver via the portal vein and then the lungs within the first week. In the lung, they damage the alveolar membrane and mature in the alveolus. Eventually, the larvae are expectorated and swallowed, reentering the gastrointestinal tract. Once in the small intestine lumen, the larvae mature into adult worms in about 20 days. When the adult female and male worms are present, they copulate, and the female can produce approximately 200,000 eggs per day. They are later eliminated in the feces of the soil. In the appropriate conditions of a moist, shady, and warm environment, the eggs mature to infective form in two to eight weeks and remain viable for up to 17 months. They can be ingested and restart the infective cycle.[5][8][9]

History and Physical

Patients infected with ascariasis can be asymptomatic, only showing long-term manifestations of growth retardation and malnutrition. If symptoms are present, abdominal pain, bloating, nausea, vomiting, anorexia, intermittent diarrhea are the most common manifestations. If the number of larvae passing through the lung is significant, pneumonitis and eosinophilia can be seen (also known as Loeffler syndrome). Symptoms include wheezing, dyspnea, cough, hemoptysis, and fever. In superinfection, adult worms can migrate to tubular structures like the biliary and pancreatic system causing cholecystitis, cholangitis, pancreatitis, small bowel obstruction, volvulus, appendicitis, and intussusception. Children are more susceptible to complications than adults.

Evaluation

A female worm can produce up to 200,000 eggs a day. This makes retrieval from a stool exam easier. The best diagnostic test is still the stool exam for ova and parasites, searching for large oval brown trilayered eggs with a mamillated coat. It is important to note that stool can be negative while the worm migrates and matures (approximately one month). Only when worms are mature do they start secreting eggs. Sometimes an adult worm can be seen in the stool or coming out of the rectum but can also be coughed up or passed in the urine. A complete blood count can show eosinophilia during the active migration phase from the intestine to the lungs, and larvae can be found in the sputum. Abdominal x-rays can be sensitive but not specific when a whirlpool sign is present. Ultrasound and CT scans can be used to identify worms in the biliary duct and gallbladder. Endoscopic retrograde cholangiopancreatography (ERCP) can be used for diagnosis and treatment.[10]

Treatment / Management

Even mild cases of Ascaris infection should be treated to prevent complications from parasite migration, and however, during active migration through the lungs, medical therapy is not indicated, secondary to the increased risk of pneumonitis. Medical therapy with albendazole 400 mg as a single dose is the drug of choice. The second choice of treatment is mebendazole 100 mg twice a day for three days or 500 mg as a single dose or ivermectin 100 microgram/kg to 200 microgram/kg once. In pregnancy, piperazine 50 mg/kg/day for five days or 75 mg/kg one dose or pyrantel pamoate (11 mg/kg up to a maximum of 1 g) is administered as a single dose; the latter is the drug of choice. Medical therapy will target adult worms, which is the reason why treatment should be repeated after one to three months, to give time to larvae that can be present to mature to adulthood and be susceptible to therapy. Alternative agents include nitazoxanide and levamisole.[11][12][13](A1)

If partial bowel obstruction is present, a nasogastric tube should be placed, give nothing per mouth, give intravenous fluids and piperazine. If total bowel obstruction is present, the patient may need laparotomy for enterotomy for the extraction of worms, but if necrosis is found, they may need resection and reanastomosis. Once the surgery is performed and intestinal transit is restored, medical anti-parasitic treatment should be given to kill any residual eggs.

Differential Diagnosis

• Acute cholangitis
• Acute pancreatitis
• Appendicitis
• Ascending cholangitis
• Asthma
• Cholecystitis and biliary colic
• Hookworm
• Intussusception
• Large bowel obstruction
• Small bowel obstruction

Prognosis

Studies from Asia and Africa reveal that single-dose treatment with albendazole results in cure rates of over 95% with a gradual reduction in eggs over the next few weeks in 995 of cases.

However, patient relocation is vital to prevent a recurrence. There is also a great need to improve basic sanitation and provide clean drinking water in these areas.

Many communities are now being targeted for improvement in socioeconomics to help reduce the burden of ascariasis.

Avoiding contact with manure, wearing proper shoes, and education are vital in preventing ascariasis.

Complications

• Bleeding per rectum
• Bowel obstruction
• Appendicitis
• Hepatobiliary disease
• Pancreatic pseudocyst