Worms are parasitic, soft-bodied organisms that can infect humans and animals. Parasitic worms fall into several different classes and include flukes, roundworm, and tapeworm.
Worms are parasites that live within a host organism (human or animal) for the purpose of obtaining food. This relationship causes harm to the host, and, with severe cases of infection, can be fatal. The term worms commonly refers to intestinal worms, although worms can infect other organs and the bloodstream. Intestinal worms are helminths and fall into three classes: cestodes (tapeworms), nematodes (roundworms), and trematodes (flukes).
Tapeworms have a ribbon-like body composed of a scolex, which attaches the worm to the intestinal wall, and a long chain of progressively developing proglottids. Proglottids at the tail end of the worm contain eggs. Tapeworms can have 3–4,000 proglottids and be several meters long. Tapeworms that infect humans include Taenia saginata, Taenia solium, Hymenolepsis nana, and Diphyllobothrium latum. Tapeworms live in the small intestine and absorb food from the intestinal contents.
The complex life cycles of cestodes differ with each genus and involve two or three different hosts. In general, one host (the intermediate host) ingests eggs that develop into a larval stage. A second host (the definitive host) ingests the larva, which develop into adult worms in the intestine. Humans can become infected with tapeworm by eating raw or inadequately cooked, contaminated fish, pork, or beef. Humans can serve as both intermediate and definitive hosts for certain cestodes. Although humans can experience severe disease when serving as an intermediate host, they may show few signs of disease when harboring adult tapeworms.
Intestinal nematodes, or roundworms, are the most worm-like of all the helminths and resemble the earthworm. Nematodes have a mouth with either three lips or teeth (hookworms), a complete digestive tract, and separate sexes. Nematodes can range from a few millimeters to over one meter long. Roundworms that can infect humans include Trichuris trichiura (whipworm), Enterobius vermicularis (pinworm), Capillaria philippinensis, Trichostrongylus species, Ascaris lumbricoides, Ancylostoma duodenale (hookworm), Necator americanus (hookworm), and Strongyloides stercoralis. Infection occurs following contact (ingestion or skin) with contaminated soil. Pinworms are not uncommon in children and are easily spread to other family members.
There are five stages (four larval and one adult) in the life cycle of the roundworm. Each genus has a unique life cycle that can be classified into one of three patterns. A person becomes infected by ingesting eggs or larva or through skin penetration by larva. Once ingested, depending upon the genus, eggs may either develop into adult worms in the intestines, or a larval stage may gain access to the bloodstream, enter the lungs, be swallowed, and then develop into adult worms in the intestines. For certain genera, larva penetrate the skin, arrive at the lungs via the bloodstream, are swallowed, and become mature worms in the intestines. Eggs are passed out in the stool, or with pinworms, the female lays eggs on the skin surrounding the anal opening.
Trematodes, or flukes, are flat, leaf-shaped, and range in length from a few millimeters to 75 millimeters. Intestinal flukes are primarily found in the Asian continent. Intestinal flukes that can infect humans are Fasciolopsis buski, Heterophyes heterophyes, Metagonimus yokogawai, Echinostoma species, and Nanophyetus salmincola.
The life cycles of all flukes involve freshwater snails as an intermediate host. Flukes are contracted by ingestion of eggs or encysted (encased) larva from contaminated water, raw water plants (water chestnuts, water bamboo shoots, etc.), or raw or inadequately cooked fish or snails. The eggs or larva mature into adult worms in the intestines.
Infection by worms is caused by the ingestion of or skin contact with helminth eggs or larva, as described above.
Symptoms of helminth infections vary depending upon the genera and number of worms involved. Infection with adult tapeworms often causes no symptoms, however, some patients may experience diarrhea, abdominal pain, anemia, and/or vitamin B12 deficiency. Roundworm infection often causes no symptoms but some patients may experience abdominal pain, diarrhea, growth retardation, anemia, and bloody, mucusy stools. Pinworms cause irritated, itchy skin surrounding the anal opening. Itching may be more severe at night and interfere with sleep. Mild infection with flukes may cause no symptoms, but heavy infections can cause diarrhea, abdominal pain, and profuse stools containing undigested food.
One side effect of worm infestation that is presently being studied for potential applications in treating atopy (a type of inherited allergic response) is the release of certain anti-inflammatory chemicals in the body. These chemicals, called cytokines, may prove to be useful in preventing atopy.
The patient will be questioned about travel and ingestion of high-risk foods. Worms are diagnosed by microscopic examination of stool samples to identify eggs and adult worms. Three samples may be taken: two from normal bowel movements and one following the use of a laxative. Pinworms are diagnosed using the "Scotch tape" method in which a piece of tape is applied to the skin surrounding the anal opening. Pinworm eggs, and occasionally an adult worm, adhere to the tape and are identified by microscopic examination.
Although alternative remedies may help treat worms, the patient should consult a physician to obtain an accurate diagnosis and appropriate antihelmintic medication.
Dietary modifications help to rid a person of worm infection. Processed foods and foods that contain sugar, white flour, and milk products should be avoided. The diet should be comprised of 25% fat, 25% protein, and 50% complex carbohydrates. At least two tablespoons of unprocessed sesame, safflower, canola, or flax oil should be taken daily.
Herbals that may kill and expel worms include:
Roundworms are treated with the herbs Chuan Lian Gen Pi (Cortex meliae radicis) and Bing Lang (Semen arecae) and the patent medicines Wu Mei Wan (Mume Pill) and Qu Hui Wan (Dispel Roundworms Pill). Pinworms are treated with the herbs Ku Lian Gen Pi (Cortex meliae radicis) and Shi Jun Zi (Fructus quisqualis). Flukes are treated with the herbs Bing Lang (Semen arecae) and a mixture of Bing Lang (Semen arecae), Da Huang (Radix et rhizoma rhei), and Qian Niu Zi (Semen pharbitidis). Hookworm is treated with the herbs Lei Wan (Sclerotium omphaliae) and a combination of Guan Zhong (Rhizoma dryopteris crassirhizomae), Ku Lian Gen Pi (Cortex meliae radicis), Tu Jing Jie (Herba chenopodii ambrosioidis), and Zi Su Ye (Folium perillae).
Other remedies for intestinal worms include:
Intestinal worm infection is treated with medications, many of which are effective with one oral dose. Helminth infections are treated with albendazole (Albenza), levamisole (Ergamisol), mebendazole (Vermox), praziquantel (Biltricide), pyrantel (Antiminth, Ascarel, Pin-X), or thiabendazole (Mintezol).
In treating tapeworm infestations, it is important to completely eliminate the head and neck regions of the tapeworm, as the entire worm can regenerate from these parts.
Medications are very effective in eliminating helminth infections; however, reinfection is always a possibility. Some types of worms appear to trigger changes in the human immune system that make reinfection easier. Patients should be retested following treatment to ensure that the infection has been eliminated. Complications of severe untreated infections include anemia, growth retardation, malnourishment, intestinal blockage, rectal prolapse (when the rectum extrudes out of the anal opening), and death.
Most intestinal worm infections may be prevented by properly washing the hands after using the bathroom, washing skin after contact with soil, wearing shoes outside, and eating thoroughly cooked fish, meats (including meat from wild game), and freshwater plants. A number of cases of worm infections caused by eating raw salmon and crayfish were reported in North America in 2003; in addition, there was an outbreak of trichinellosis in Saskatchewan in 2000 that was traced to infected bear meat.
Skin penetration by larva may be reduced by eating foods rich in vitamin A including squash, carrots, sweet potatoes, yams, and greens.
People who live on farms, or have dogs or cats as house pets, should have their animals checked by a veterinarian on a regular basis and have them dewormed if necessary.
The Centers for Disease Control and Prevention (CDC) recommends that people traveling abroad should wash their hands with soap and water before handling food; should wash and peel all raw vegetables and fruits before eating; and should drink only bottled or boiled water, or carbonated drinks in cans or bottles.
As of late 2003, researchers in developing countries are working on a vaccine for pigs to help control worms transmitted by pigs to humans; however, the vaccine is not likely to be available for several years.
"Cestodes (Tapeworms)." Section 13, Chapter 161 in The Merck Manual of Diagnosis and Therapy, edited by Mark H. Beers, MD, and Robert Berkow, MD. Whitehouse Station, NJ: Merck Research Laboratories, 2002.
Garcia, Lynne S. and David A. Bruckner. Diagnostic Medical Parasitology. Washington, DC: American Society for Microbiology, 1997.
Markell, Edward K., David T. John, and Wojciech A. Krotoski. Markell and Voge's Medical Parasitology. 8th edition. Philadelphia: W.B. Saunders Company, 1999.
"Nematode (Roundworm) Infections." Section 13, Chapter 161 in The Merck Manual of Diagnosis and Therapy, edited by Mark H. Beers, MD, and Robert Berkow, MD. White-house Station, NJ: Merck Research Laboratories, 2002.
Pearson, Richard D. Parasitic Diseases: Helminths. Textbook of Gastroenterology, 3rd edition. Edited by Tadataka Yamada et al. Philadelphia: Lippincott Williams & Wilkins, 1999.
Ying, Zhou Zhong and Jin Hui De. "Common Parasitoses." In Clinical Manual of Chinese Herbal Medicine and Acupuncture. New York: Churchill Livingston, 1997.
Albonico, Marco, D.W.T. Crompton, and L. Savioli. "Control Strategies for Human Intestinal Nematode Infections." Advances in Parasitology (1999): 277-341.
Castilla, E. A., R. Jessen, D. N. Sheck, and G. W. Procop. "Cavitary Mass Lesion and Recurrent Pneumothoraces Due to Paragonimus kellicotti Infection: North American Paragonimiasis." American Journal of Surgical Pathology 27 (August 2003): 1157–1160.
Couture, C., L. Measures, J. Gagnon, and C. Desbiens. "Human Intestinal Anisakiosis Due to Consumption of Raw Salmon." American Journal of Surgical Pathology 27 (August 2003): 1167–1172.
Ferreira, M. B., S. L. da Silva, and A. G. Carlos. "Atopy and Helminths." Allergy and Immunology (Paris) 34 (January 2002): 10-12.
Gittleman, Ann Louise. "Parasites." Total Health (May/June 1997): 47+.
Guarrera, Paolo Maria. "Traditional Antihelmintic, Antiparasitic and Repellent Uses of Plants in Central Italy." Journal of Ethnopharmacology (1999): 183-192.
Jenson, J. S., R. O'Connor, J. Osborne, and E. Devaney. "Infection with Brugia Microfilariae Induces Apoptosis of CD4(+) T Lymphocytes: A Mechanism of Immune Unresponsiveness in Filariasis." European Journal of Immunology 32 (March 2002): 858-867.
Kumaran, A. M., P. D'Souza, A. Agarwal, et al. "Geraniol, the Putative Anthelmintic Principle of Cymbopogon martinii." Phytotherapy Research 17 (September 2003): 957.
Roy, S. L., A. S. Lopez, and P. M. Schantz. "Trichinellosis Surveillance—United States, 1997–2001." Morbidity and Mortality Weekly Report Surveillance Summaries 52 (July 25, 2003): 1–8.
Schellenberg, R. S., B. J. Tan, J. D. Irvine, et al. "An Outbreak of Trichinellosis Due to Consumption of Bear Meat Infected with Trichinella nativa, in 2 Northern Saskatchewan Communities." Journal of Infectious Diseases 188 (September 15, 2003): 835–843.
American Veterinary Medical Association (AVMA). 1931 North Meacham Road, Suite 100, Schaumburg, IL 60173-4360. <http://www.avma.org>.
Centers for Disease Control and Prevention. 1600 Clifton Rd., NE, Atlanta, GA 30333. (800) 311-3435, (404) 639-3311. <http://www.cdc.gov>.
Rebecca J. Frey, PhD