Ascaris lumbricoides

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    Ascaris species are not suitable for use in helminthic therapy.

    While Ascaris lumbricoides (the "giant roundworm" of humans) was estimated to infect approximately 1.2 billion people (20% of the worlds population) in 2005, according to the World Health Organisation, [1] it is not risk-free.

    • A. lumbricoides grows up to 35 cm (14 in) in length and up to 6 mm (0.2 in) wide, making it the largest parasitic worm in humans. Its large surface area might make it a very effective immune modulator, but it’s size is also a potential threat since tangles of Ascaris can cause a blockage of the bowel that may require surgery. [2] [3] This is of particular concern for anyone with Crohn’s disease who might have intestinal strictures that could become blocked by even a single ascaris.
    • A. lumbricoides can cause bowel necrosis, bowel perforation, appendicitis, [4] intestinal obstruction, [5] gallbladder perforation [6] and obstruction of the bile duct.
    • A. lumbricoides colonisation might be associated with a disturbed microbiota with reduced overall diversity. [7]
    • Ascaris species in general are associated with an increase in allergy, and this has been linked to cross-reactivity between worm proteins (e.g., tropomyosins) and highly similar molecules in dust-mites and insects. [8]
    • Ascaris roundworms are also known to significantly increase the risk of asthma. [9] [10] [11] [12]
    • There is a risk of mis-migration with some ascaris species.
    Occasionally an adult will migrate to the stomach and cause nausea, and sometimes vomiting. In these cases, the human host can expel the worm in the vomit. (Expelled worms as big as 1 ft long have been reported.) Worms that reach the esophagus while a person is asleep can exit the body through the nose or mouth. Instances have been reported in which Ascaris have migrated into and blocked the bile or pancreatic duct or in which the worms have penetrated the small intestine resulting in acute (and fatal) peritonitis. [13]

    Mis-migration in humans is a particular risk with Ascaris species that are adapted to living in other animals. For example, the roundworms of dogs and raccoons are well known for migration through the brain and eyes of the wrong species. [14]

    • Ascaris species have an aversion to some general anaesthetics and may exit the body, sometimes through the mouth, when an infected individual is put under general anaesthesia. [15]
    … numerous cases have been documented where patients in surgical recovery rooms have had worms migrate from the small intestine, through the stomach, and out the patient's nose or mouth. [16]

    In view of these issues, ascaris species are unsuitable for use in helminthic therapy and, if one is acquired accidentally, it would arguably be sensible to terminate it.