Giant Roundworm, Ascaris lumbricoides

The giant roundworm (Ascaris lumbricoides) is a parasitic worm within the Nematoda phylum. This species can be found throughout the world, but occurs in higher numbers in tropical and subtropical areas. It causes the disease known as ascariasis in its human hosts and infects about one quarter of the entire world’s human population. It displays a sexual dimorphism, with females growing larger than males. Females reach an average body length between 7.8 and 19.2 inches, while males reach a length between 5.9 and 12.2 inches. Males have a curved back end and females hold a vulva on the front end, which takes up about one third of their entire body.

Female giant round worms can hold up to 27 million eggs in their uteri, although only two hundred thousand eggs can be laid each day. The lifecycle of this species begins when a human host ingests one of these eggs, usually by eating food that was not washed properly before being eaten. When the egg hatches in the first section of the small intestine, or duodenum, the resulting larvae will break through the tissue and travel through the blood stream to the heart or liver. From these areas, the larvae travel to the pulmonary circulation, where they can enter the lungs break off the alveoli, and molt. After about three weeks, the larvae are coughed up and swallowed and will travel back to the small intestine where they can mature. After the eggs are fertilized and released from the host’s body into soil, they can infect another human host after two weeks. These eggs are highly persistent and can remain active in soil for over ten years.

Giant roundworm infections occur more often in areas that have poor sanitation or in places where human excrement is used as fertilizer. Hosts do not typically show signs of infection, but if the infection is bad, hosts may have fever, coughing, abdominal pain, worms in their stool, and bloody sputum. Infections can easily be diagnosed, due to the size of the worms and prevalence of the eggs within the feces. Infections are treated by using medicines known as ascaricides. These drugs include Ivermectin and Nitazoxanide, but Mebendazole is most often used.

Prevention of giant roundworm infection can be difficult, due to the pervading nature of the eggs. Education and enhanced hygiene practices are the best way to prevent an infection. However, this is not always possible in countries where the species is native. The eggs appear on vegetables that were fertilized with human feces, but can also be found on clothes, containers, and even food that is not cooked properly. Bleach can be used to remove the sticky coating that covers the eggs, but it will not kill them, so vegetables and other foods should still be washed. The number of eggs within human feces can be reduced by raising the temperature of the compost to at least 120 degrees Fahrenheit for at least one day, in a process known as “unusually” hot composting. Using specialized chemicals, iodine, rubbing alcohol, or a high cooking heat may kill the eggs found on food.

Image Caption: An adult Ascaris lumbricoides worm. Diagnostic characteristics: tapered ends; length 15 to 35 cm (the females tend to be the larger ones). This worm is a female, as evidenced by the size and genital girdle (the dark circular groove at bottom area of image). Credit: CDC Division of Parasitic Diseases / Wikipedia