NAME: Ascaris spp.
SYNONYM OR CROSS REFERENCE: Ascaris lumbricoides, Ascaris suum, large roundworm, ascariasis, pulmonary ascariasis Footnote 1.
CHARACTERISTICS: A. lumbricoides and A. suum belong to the family Ascarididae. A. lumbricoides is the largest and most common intestinal roundworm of man. Adult males measure 15 to 31 cm long by 2 to 4 mm wide, while females are 20 to 40 cm long by 3 to 6 mm wide. A. suum is the common roundworm of pigs Footnote 2Footnote 3. Adult males and females are yellow-white or pinkish-grey color. Both species differ slightly morphologically, such as in the labial denticles in both sexes and the spicules in males Footnote 1. Female worms produce up to 200,000 fertilized or unfertilized eggs per day. Fertilized eggs tend to be shorter and wider than unfertilized eggs. Fertilized eggs are oval to round in shape, 45 to 75 µm long by 35 to 50 µm wide and have a rough, mammillated, albuminous coat over their chitinous shells. Unfertilized eggs are usually more elongated in shape, 85 to 95 µm long by 43 to 47 µm wide and may have distorted mammillations. Adult worms usually inhabit the jejunum, but may be found higher and lower in the gut Footnote 3-5.
PATHOGENICITY/TOXICITY: The severity of the disease is determined by the worm load Footnote 1. Most infections with A. lumbricoides are mild and asymptomatic, but nonspecific abdominal symptoms may occur. The clinical manifestations of ascariasis are broad, ranging from abdominal to pulmonary symptoms. There is increasing risk of intestinal obstruction with increasing worm burden. The large adult worms can elicit abdominal distension and pain, nausea, dyspepsia, appetite changes, and diarrhea. Occasionally, an adult worm migrates to the appendix, bile duct, or pancreatic duct, causing obstruction and inflammation of the organ. This may result in biliary colic, cholecystitis, acute cholangitis, acute pancreatitis, appendicitis, or a hepatic abscess. The migration of developing larvae through the lungs may result in eosinophilic pneumonitis with fever, dyspnea, and bronchospasm. This pulmonary ascariasis may occur up to 2 weeks after infection and last approximately 3 weeks Footnote 4Footnote 5. Very rarely, fatal cases can occur due to organ obstruction or gangrene Footnote 6. A. suum infection in pigs is often associated with liver lesions Footnote 7.
EPIDEMIOLOGY: Ascaris spp. has a worldwide distribution and is most common in tropical and subtropical areas of the developed and undeveloped world. It is particularly associated with crowding and poor sanitation and young children tend to maintain the cycle. A. lumbricoides infection is one of the most common human infections, with an estimated 1.2 billion people infected worldwide Footnote 1Footnote 5Footnote 8.
INFECTIOUS DOSE: Unknown.
MODE OF TRANSMISSION: The primary mode of transmission is via the fecal-oral (hand-to-mouth) route: ingestion of mature eggs from soil contaminated with human or pigs feces, and ingestion of fecally contaminated water, food, agriculture products, fomites, fingers, and other sources Footnote 2Footnote 5Footnote 7Footnote 11. Eggs may become airborne and be inhaled or swallowed in areas of dry, windy climate Footnote 4. Fresh feces do not contain infective eggs – it takes up to two weeks before they may infect humans Footnote 5.
INCUBATION PERIOD: The incubation period (interval between ingestion of eggs and development of egg-laying adults) is approximately 6 to 8 weeks Footnote 3Footnote 5Footnote 12. Even if A. lumbricoides can live for as long as 2 years and is then expelled from the gut when it dies, new worms are continually acquired so that people remain persistently infected with slowly changing numbers of worms Footnote 11.
COMMUNICABILITY: Ascaris spp. cannot be transmitted directly from host to host, however, infected humans can pass eggs in feces Footnote 4Footnote 11Footnote 13. However, the eggs are not immediately infective because they must incubate in soil under certain conditions before they become infectious.
RESERVOIR: Humans (A. lumbricoides and A. suum), dogs (A. lumbricoides) play an important role in environmental contamination in some areas Footnote 9Footnote 14, pigs (A. suum) Footnote 10, eggs can survive in soil Footnote 8.
DRUG SUSCEPTIBILITY/RESISTANCE: Susceptible to albendazole (drug of choice) Footnote 1Footnote 4Footnote 16, mebendazole Footnote 1Footnote 4Footnote 16, pyrantel pamoate Footnote 1Footnote 4Footnote 16, levamisole Footnote 8, ivermectin Footnote 1Footnote 8Footnote 12, and nitrazoxanide Footnote 12Footnote 17.
SUSCEPTIBILITY/RESISTANCE TO DISINFECTANTS: While specific disinfectant susceptibility has not been demonstrated for Ascaris spp., Ascaris spp.eggs appear to be resistant to some strong acids, strong base oxidants, and synthetic detergents Footnote 18. The eggs can embryonate successfully in 50% solutions of hydrochloric, sulfuric, nitric, and acetic acids, 2% formalin and potassium dichromate, but have not been noted to develop in, and survive prolonged exposure to 10% formalin Footnote 19.
PHYSICAL INACTIVATION: Sensitive to microwave irradiation (700 W, 2450 MHz, 60s) Footnote 18. UV irradiations and ozone treatments are often not effective at inactivating Ascaris spp. eggs Footnote 18. Ascaris suum has shown sensitivity to moist heat (121°C for at least 15min) and dry heat (160°C for 1 to 2 hours) Footnote 20Footnote 21.
SURVIVAL OUTSIDE HOST: Eggs are highly resistant to environmental conditions and may remain viable up to 6 years in mild climate Footnote 4Footnote 7Footnote 8Footnote 22. Ascaris suum eggs remained viable for as long as 40 days when exposed to temperatures ranging from -18°C to -27°C Footnote 19.
SURVEILLANCE: Monitor for symptoms. Diagnosis is generally made by finding eggs in the feces. The pulmonary phase of ascariasis is diagnosed by the finding of larvae and eosinophils in the sputum. Examination of the chest radiographs usually reveals fleeting pulmonary infiltrates and examination of the sputum may reveal Charcot-Leyden crystals Footnote 23. Occasionally, an A. lumbricoides adult worm may be passed in feces or may spontaneously migrate out of the anus, mouth, or nares, particularly in children Footnote 4Footnote 5. Adult worms sometimes are detected by computed tomographic scan of the abdomen or by ultrasonographic examination of the biliary tree Footnote 12Footnote 22.
Note: All diagnostic methods are not necessarily available in all countries.
FIRST AID/TREATMENT: Albendazole is the primary agent used for treatment Footnote 1Footnote 4Footnote 16. Mebendazole and pyrantel pamoate are highly effective Footnote 1Footnote 4Footnote 16. Ivermectin and nitrazoxanide are also effective Footnote 12Footnote 17.
LABORATORY-ACQUIRED INFECTIONS: 8 reported cases of laboratory-acquired infections with Ascaris spp. Footnote 24.
PRIMARY HAZARDS: Ingestion of infective eggs, accidental parenteral injection, direct contact of eggs with mucous membranes, and skin penetration of the larvae are the primary hazards associated with this agent Footnote 26.
SPECIAL HAZARDS: Avoid exposure to aerosolized sensitizing antigens of Ascaris spp. as it can lead to hypersensitivity reactions to Ascaris antigens, which can include respiratory, dermatologic, and gastrointestinal symptoms Footnote 13Footnote 26.
RISK GROUP CLASSIFICATION: Risk Group 2. This risk group applies to the genus as a whole, and may not apply to every species within the genus.
CONTAINMENT REQUIREMENTS: Containment Level 2 facilities, equipment, and operational practices for work involving infectious or potentially infectious material Footnote 28. These containment requirements apply to the genus as a whole, and may not apply to each species within the genus.
PROTECTIVE CLOTHING: Lab coat. Gloves when direct skin contact with infected materials or animals is unavoidable Footnote 28. Eye protection must be used where there is a known or potential risk of exposure to splashes.
OTHER PRECAUTIONS: All procedures that may produce aerosols, or involve high concentrations or large volumes should be conducted in a biological safety cabinet (BSC) Footnote 28. Even if the eggs of Ascaris spp. require an extrinsic maturation period to become infective, preserved specimens should be handled with care. Ascaris spp. eggs are sticky, and contaminated laboratory surfaces and equipment must be thoroughly cleaned Footnote 13.
SPILLS: Allow aerosols to settle and, wearing protective clothing, gently cover the spill with paper towels and apply an appropriate disinfectant, starting at the perimeter and working towards the centre. Allow sufficient contact time before clean up Footnote 28.
DISPOSAL: Decontaminate all wastes that contain or have come in contact with the infectious organism before disposing by autoclave, chemical disinfection, gamma irradiation, or incineration Footnote 28Footnote 29.
STORAGE: The infectious agent should be stored in leak-proof containers that are appropriately labelled Footnote 28.
REGULATORY INFORMATION: The import, transport, and use of pathogens in Canada is regulated under many regulatory bodies, including the Public Health Agency of Canada, Health Canada, Canadian Food Inspection Agency, Environment Canada, and Transport Canada. Users are responsible for ensuring they are compliant with all relevant acts, regulations, guidelines, and standards.
UPDATED: December 2011
PREPARED BY: Pathogen Regulation Directorate, Public Health Agency of Canada.
Although the information, opinions and recommendations contained in this Pathogen Safety Data Sheet are compiled from sources believed to be reliable, we accept no responsibility for the accuracy, sufficiency, or reliability or for any loss or injury resulting from the use of the information. Newly discovered hazards are frequent and this information may not be completely up to date.
Copyright © Public Health Agency of Canada, 2011 Canada