Helminths that parasitize humans are diverse, ranging from barely visible roundworms (0.3 mm) to huge tapeworms (25 m long). Worm infection usually provokes an increase in granular leukocytes called eosinophils, which have a specialized capacity to destroy multicellular parasites. This increased, termed eosinophilia, is a hallmark of helminthic infection and is detectable in blood counts. Helminthic infections may be acquired through the fecal-oral route or through penetration of the skin. Helminths have numermous adaptations that allow them to survive in their host such as specialized mouthparts for attaching to tissue and for feeding as well as enzymes with which they liquefy and penetrate tissues. The damage they cause in the host is very often the result of the host’s response to the presence of the invader. Diagnosis includes the “O&P test” which is microscopic examination of a stool sample to look for ova or parasites. A differential blood count showing increased eosinophile and serological tests indicating sensitivity to helminthic antigens all provide indirect evidence of worm infection. A history of travel to the tropics or immigation from those regions is also helpful, even if it occurred years ago, because some flukes and nematodes persist for decades. There are no vaccines but prophylactic treatment twice a year with antihelminthic drugs has been shown to keep people healthy. Some anihlminthic drugs suppress a metabolic process that is more important to the worm than to the human.

Nematodes (Roundworms)

Intestinal roundworms acquired by ingestion

–Enterobius vermicularis (pinworm) The Pinword (Enterobius vermicularis) is is the most common worm disease of children in temperate zones. It is transmitted by the fecal-oral route (ingestion of ova) and treatment is mebendazole. Pinworms are white, parasitic worms that can live in the large intestine of humans. They are about one-half inch long. While the infected person sleeps, female pinworms leave the intestinal tract and lay their eggs on the skin around the anus. The eggs are laid in a sticky, jelly-like substance that, along with the wriggling of the female pinworm, causes severe itching. Fresly deposited eggs have a sticky coating that causes them to lodge beneath the fingernails and to adhere to fomites. Upon drying, the eggs become airbone and settle in house dust. Eggs are ingested from contaminated food or drink and from self inoculation from one’s own fingers. Eggs hatch in the small intestine and release larvae that migrate to the large intestine. When one member of the famaily is diagnosed, the entire family should be tested and/or treated because it is likely that multiple members are infected. Pinworms are thin and white, measuring about 1/4 to 1/2 inch (about 6 to 13 millimeters) in length.  The medications used for the treatment of pinworm are either mebendazole, pyrantel pamoate, or albendazole. Any of these drugs are given in one dose initially, and then another single dose of the same drug two weeks later. Pyrantel pamoate is available without prescription. The medication does not reliably kill pinworm eggs. Therefore, the second dose is to prevent re-infection by adult worms that hatch from any eggs not killed by the first treatment. Health practitioners and parents should weigh the health risks and benefits of these drugs for patients under 2 years of age.Mayo Clinic. See CDC  See NY Health Dept

–Ascaris lumbricoides can be a particular problem with persons who have AIDS. Infection is again by ingestion of ova and the worm may cause intestinal obstruction. Infective stages are found where human feces are used as a fertilizer. Ascaris lumbricoides is a nematode, or roundworm, that parasitizes the human gastrointestinal tract. Worldwide, ascariasis is among the most common helminthic human infections with an estimated 800 million to 1.2 billion people infected, and it causes more than 60,000 deaths annually,  In fact, ascariasis is considered one of the “neglected tropical diseases,” or NTDs – a diverse group of infectious diseases that exist in tropical and subtropical environments in 149 countries across the world, and which affect more than 1 billion individuals, costing developing economies billions of dollars each year.  In the life cycle of A. lumbricoides, the definitive host for infection is human and the mode of transmission is the fecal-oral transfer of embryonated eggs. After oral ingestion, via contaminated food or water, the eggs hatch in the small intestine within 4 days and release larvae. See Shaw

–Dracunculiasis (Guinea worm disease), caused by the parasite Dracunculus medinensis, is acquired by drinking water containing small crustacean copepods (water fleas) infected with D. medinensis larvae. Recent evidence suggests that the parasite also appears to be transmitted by eating fish or other aquatic animals. About 1 year after infection, the worm typically emerges through the skin on a lower limb of the host, causing pain and disability. No vaccine or medicine is available to prevent or treat dracunculiasis. Eradication relies on case containment* to prevent water contamination and other interventions to prevent infection, including health education, water filtration, treatment of unsafe water with temephos (an organophosphate larvicide), and provision of safe drinking water.  Cama, CDC

–Trichuris trichiura (whipworm) The whipworm (Trichuris trichiura): has its highest incidence in the areas of the tropics and subtropics that have poor sanitation. It is again transmitted by ingestion of the ova. Symptoms are asymptomatic unless the worm burden reaches a certain point at which time there is anemia, eosinophilia and bloody diarrhea. Transmission occurs where sanitation is poor and human feces are used for fertilizer.  Symptoms include localized hemorrhage of the bowel caused by worms burrowing and piercing intestinal mucosa. Thsi can also provide a portal of entry for secondary bacterial infection. Heavier infections can cause dysentery, loss of muscle tone and rectal prolapse, which can prove fatal in children.  An estimated 604-795 million people in the world are infected with whipworm. Whipworms live in the large intestine and whipworm eggs are passed in the feces of infected persons. If the infected person defecates outside (near bushes, in a garden, or field) or if human feces as used as fertilizer, eggs are deposited on soil. They can then mature into a form that is infective. Whipworm infection is caused by ingesting eggs. This can happen when hands or fingers that have contaminated dirt on them are put in the mouth or by consuming vegetables or fruits that have not been carefully cooked, washed or peeled. See CDC  Trichiura has a worldwide distribution, principally within the tropical and subtropical zones, although it may have been more widely distributed in the past. However, with improvements in sanitation and public health in the richer countries, it has been largely eliminated from areas such as Southern USA, Japan, and much of the Mediterranean basin. See Horton.  Trichuris trichiurareceived the common name of whipworm from their distinctive body shape. Whipworms have an elongated anterior end that contains the mouth and esophogus that stretches into a thread-like point.Trichuris trichiurareceived the common name of whipworm from their distinctive body shape. Whipworms have an elongated anterior end that contains the mouth and esophogus that stretches into a thread-like point.Trichuris trichiurareceived the common name of whipworm from their distinctive body shape. Whipworms have an elongated anterior end that contains the mouth and esophogus that stretches into a thread-like point.

Intestinal roundworms usually acquired by passage through skin

–Necator americanus and Ancylostoma duodenale usually penetrate the skin of the legs and feet (“ground itch”) and are usually found where the soil is shaded, but warm and the air is humid. Wearing shoes helps prevent exposure. Treatment is mebendazole or iron therapy to treat anemia. Ancylostoma brziliense is a dog and cat hookworm that penetrates human (inadvertant host) skin but cannot develop further. People often get infected after dogs have been brought to the beach.

–Strongyloides stercoralis (strongyloidiasis) is a particular problem for AIDS patients. Treatment is with thiabendazole. 

Tissue  Nemathelminths (Roundworms)

–Trichinella spiralis cause trichinosis after eating poorly cooked meat which contains encysted larval forms. No eggs are involved (just larvae)  in their life cycle. Freezing meat for longer than 20 days in a home freezer will kill larvae. 

–Toxocara canis and T. cati have a similar life cycle to A. lumbilcoides in humans. Corticosteroids may be helpful in treatment.

–wucheretia bancrofti and Brugia malayi are transmitted by mosquitoes and are not endemic to the US.

–onchocera volvulus are transmitted by blackflies and cause Onchocerciasis (river blindness) and are not endemic to the U.S.  see WHO.  Onchocerca volvulus,is spread by the bite of an infected Simulium blackfly. It is also called river blindness because the fly that transmits infection breeds in rapidly flowing streams, mostly near remote rural villages, and the disease that is caused by O. volvulus following repeated bites from infected blackflies can lead to blindness.

Cestodes (Tapeworms)

Tapeworms are long (mm to meters) and have an extensive reproductive system (proglottids). If man is the definitive host, disease is minor but if man is the intermediate host serious disease may develop. All tapeworms are hermophrodditic, with male and female reproductive organs present on each mature proglottid. Taeniasis is the infection of humans with the adult tapeworm of Taenia saginata or Taenia solium. Humans are the only definitive hosts for T. saginata and T. solium. Eggs or gravid proglottids are passed with feces,  The eggs can survive for days to months in the environment. Cattle (T. saginata) and pigs (T. solium) become infected by ingesting vegetation contaminated with eggs or gravid proglottids,  See CDC

–Taenia saginata (beef) contain sucking discs but no hooklets like the pork tapeworm. Niclosamide is the drug of choice for treatment.

–Taenia solium (pork):  Taenia solium (pig tapeworm) is a tapeworm and is usually 5 meters long and have a scolex swith hooklets and suckers to attach to the itnestine. T. solium is distributed worldwide but is concentrated in areas where human live in close proximity with pigs or eat undercooked pork. The cycle starts in the pigs, when the eggs hatch in the small intestine and the released larvae migrate throughout the organs. Ultimately, they encyste in the pig’s muscles, becoming cysticerci, young tapeworms that are the infective stage for humans. When humans ingest a live cysticercus in pork, the coat is digested and the organism is flushed into the intestine, where it firmly attaches by the scolex and develops into an adult tapeworm. Infection with T. solium can take another form when humans ingest the tape-worm eggs rather than infected meat. Then the human, instead of the tapeworm in the gut, becomes the host of the encysted alrvae, or cysticerci, leading to cysticercosis, one of the five neglected parasitic infections in the U.S. It is estimated that thens of thousands of Latinos living in the U.S. are affected by cysticercosis. Niclosamide can be used to treat it. Adult worms may cause mild gastrointestinal symptoms or passage of a motile segment in the stool. The tapeworm Taenia (T.) solium can be responsible for two different conditions: taeniasis and cysticercosis. Taeniasis is infection with an adult tapeworm, while cysticercosis is infection with larval stages (of T. solium) in body tissues. Taeniasis occurs only in the human host, after ingestion of undercooked pork infected with cysticerci. In taeniasis an adult worm is present in the intestine, and the infestation is usually asymptomatic and generally recognized when segments of proglottids are found in stool specimens. Cysticercosis is caused by ingestion of food contaminated with feces, or by autoinfection. In the latter case, a human infected with adult T. solium can ingest eggs produced by that tapeworm, either through fecal contamination or, possibly, from proglottids carried into the stomach by reverse peristalsis. Once eggs are ingested, oncospheres hatch in the intestine invade the intestinal wall, and migrate to striated muscles, as well as the brain, liver, and other tissues, where they develop into cysticerci. Cysticercosis is usually asymptomatic unless larvae invade the central nervous system, resulting in neurocysticercosis, which can cause seizures and various other neurologic signs.  Intestinal infection is treated with prazincuantel 5 to 10 mg/kg orally as a single dose to eliminate adult worms. See Merk Manual.  See Gangemi

–Diphyllobothrium latum (fish) results from eating improperly cooked fresh water fish (can occur in Florida). Diphyllobohrium latam has an intermediate host in fish. It is common in the Great Lakes, Alaska and Canada. It develops in the intestine and can cause long-term symtpoms. It can be transmitted in raw food such as sushi and sashimi made form salmon. It is the largest human tapeworm known, growing up to 30 feet. Diphyllobothrium latum and related species (the fish or broad tapeworm), the largest tapeworms that can infect people, can grow up to 30 feet long. Several other Diphyllobothrium species infect humans, but less frequently.  Most infections are asymptomatic. However symptoms can include abdominal discomfort, diarrhea, vomiting, and weight loss. Vitamin B12 deficiency leading to pernicious anemia may occur. Complications include intestinal obstruction and gall bladder disease caused by migration of proglottids. Diagnosis is made by identification of eggs or segments of the tapeworm in a stool sample with a microscope. Eggs are usually numerous, but more than one stool sample may be needed to find them. You got infected by eating raw or undercooked fish. Examples of fish include salmon, trout, perch, walleyed pike, and other species — usually freshwater fish. Some fish such as salmon live in both fresh and salt water and can harbor Diphyllobothrium larvae. Lightly salted, smoked, or pickled fish also may contain infectious organisms.  Effective medications are available to treat Diphyllobothrium infection (praziquantel or niclosamide are used most often). See CDC

–Echinococcus ganulosis (dog tapeworm): Man is an accidental/inadvertant host. Echinococcosis is a parasitic disease caused by infection with tiny tapeworms of the genus Echinocococcus. Echinococcosis is classified as either cystic echinococcosis or alveolar echinococcosis. Cystic echinocccosis (CE), also known as hydatid disease, is caused by infection with the larval stage of Echinococcus granulosus, a ~2–7 millimeter long tapeworm found in dogs (definitive host) and sheep, cattle, goats, and pigs (intermediate hosts). Although most infections in humans are asymptomatic, CE causes harmful, slowly enlarging cysts in the liver, lungs, and other organs that often grow unnoticed and neglected for years. Alveolar echinococcosis (AE) disease is caused by infection with the larval stage of Echinococcus multilocularis, a ~1–4 millimeter long tapeworm found in foxes, coyotes, and dogs (definitive hosts). Small rodents are intermediate hosts for E. multilocularis. Although cases of AE in animals in endemic areas are relatively common, human cases are rare. AE poses a much greater health threat to people than CE, causing parasitic tumors that can form in the liver, lungs, brain, and other organs. If left untreated, AE can be fatal.  See CDC.

–Hymenolpsis: species are small tapeworms and are the most common human tapeworm infections in the word (however in U.S. is only 0.4%). They follow a life cycle where the adult matures in the human intestine, eggs are released into the environment, eggs are then eaten by grazing animals, larval forms and incyst in tissue and then humans eating animal flesh are infected. People can also ingest the eggs, which become larval cysts in their tissues. Hymenolepiasis is caused by two cestodes (tapeworm) species, Hymenolepis nana (the dwarf tapeworm, adults measuring 15 to 40 mm in length) and Hymenolepis diminuta (rat tapeworm, adults measuring 20 to 60 cm in length). Hymenolepis diminuta is a cestode of rodents infrequently seen in humans and frequently found in rodents. Hymenolepsis nana, known as the “draft tapeworm” because it is only 1-540 mm in lenght, and H. diminuta (rat tapeworm) which is usually 20-60 cm in lenght as an adult. Hymenolepis nana is the most common cause of all cestode infections, and is encountered worldwide. In temperate areas its incidence is higher in children and institutionalized groups. Hymenolepis diminuta, while less frequent, has been reported from various areas of the world. Hymenolepis nana and H. diminuta infections are most often asymptomatic. Heavy infections with H. nana can cause weakness, headaches, anorexia, abdominal pain, and diarrhea.  See CDC

Trematodes (Flukes and Schistosomes)

Trematodes are hermaphroditic with both male and female reproductive organs in a single body, with the exception of schistosomes. They are broad, leaf-like flat worms. 2 intermediate hosts are required; snail and then man.

Three  schistosomes most frequently associated with human disease are mansoni, haematobium and japonicum. They collectively produce the disease schistosomiasis.  The female lives in the ventral groove of the male for life. The avian species is acquired by wading in fresh water where aquatic birds frequent.

Blood flukes (Schistosomiasis): When liver swelling or malfunction is accompanied by easinophilia, schistosomiasis should be suspected. Shistosomes are trematodies or flukes but they are more cylindrical than flat. The life cycle is complex and begins when infected humans release eggs into irrigation fields or ponds, either by deliberate fertilization with excreta or by defecating or urinating direclty into the water. The disease is endemic to 74 countries located in Afica, South America, the Middle East and the Far East. Schistosomiasis (including the urinary tract form) is the second most prominent parasitic disease after malaria, probably affecting 200 millin people at any one time worldwide.

–-Schistosomiasis mansoni: is a severe public health problemin many tropic countries, affecting more than 200 million worldwide. Two Schistosoma mansoni adult worm proteins, Sm31 and Sm32 have been found to be highly immunogenic in mice and humans and have also been proposed as potential serodiagnostic antigens for detection of infection by S. mansoni, Schistosoma japnicum and Schistosoma haematobium. Noya (Parasite Immunology, 2001, 23, 567-573) disclose the synthesise of 17 polymericable 20 amino acid long peptides comprising the entire Sm31 sequence, and the immunization of rabbits with a pool of 4-5 different synthetic peptides. Using a multiple antigen blot assay (MABA), Noya simultaneously identified that 10 out of the 17 synthetic Sm31 peptides were highly immunoglenic. The use of chemically synthesized peptides may imporve the performance of serological assays based on the detection of antibodies, by enhancing the sensitivity and specificity of the immunoassay.

—Schistosoma japonicum: is an important cause of intestinal schistosomiasis. It has been a particular problem in China and the Philippines. One problem is that the snail hosts are amphibious and can proliferate in a diverse array of microhabitats and that infection is a zoonosis transmitted from a diverse array of mammalin hosts, expercially water buffaloes in the marshland reigon of China.

Patients infected with Schistosoma japnicum in the CNS may present with an acute meningoencephalitis. CNS symptoms (headache, fever, stiff neck, vomiting, or seizures) may be noted within days after the apeparance of mucosanguienous stools in patients in the Philippines and within months in Japan and China. Partial seizures resutls form brain invasion by eggs or adult worms.

Diagnosis is by stool microscope. Praziquantel, an anticonvulsant and occasionally corticosteroids are used for treatment. The dosage of prziquantel may vary with the worm burden.

Leeches:

Most leeches live in freshwater, although a few are murine and some tropical leeches occupy terrestrail habitats. About half the known species of leeches eat detritus or devour small animals. The others suck blood or other fluids form their hosts. Blood sucking leeches secrete an anticoagulant into the wound to prevetn the blood from clotting, and vasodilators to keep the blood flowing. The leech’s powerful pharynx pumps the blood out quickly once a hole has been opened.

Leeches are used to remove excess blood after surgery or to keep blood from coagulating in severed appendages that have been reattached. Accumulations of blood can cause the tissue to die; when leeches remove such blood, new capillaries form in about a week, adn the tissues remain healthy.

–Hookworms: are gastrointestinal nematodies that infect about 600 million people in developing countries. Adult hookworms bury their ehads beneath the mucosa of the human intestine and feed on blood. Moderate to heavy infections result in iron deficiency anaemia,. The resulting hookworm disease and anemia has a serious deleterious impact on many aspects of the health of infected individuals, including child hood growth retardation and cognitive development,  and impaired fetal development during pregnancy. While anthelminthic drugs of the benzimidazole class are highly effective at eliminating existing hookworm infections, they do not protect against rapid re-infection. In areas of high transmission, hookworm re-infection will occur within 4-12 months. In addition, the efficacy of benzimidazole drugs decreases with frequent use.