Global Forest watch (monitors forests –habitat is very important for disease transmission)
Introduction/Classification/Characteristics:
Helminths that parasitize humans are diverse, ranging from barely visible roundworms (0.3 mm) to huge tapeworms (25 m long). There are about 50 species of helminths which cause disease in humans.
On the basis of body type, two major groups of pathogenic helminths are flatworms which have a very thin, often segmented body plan and roundworms (also called nematodes), which have an elongated, cylindrical, unsegmented body.
Flatworms are subdivided into the cestodes (tapeworms) named for their long, ribbonlike arrangement and trematodes (flukes) characterized by flat, ovoid bodies.
Pinworms are subdivided into pinworms which cause a very common infestation of the large intestine.
All helminths are multicellular animals, with organs to some degree. In disease cuasing helminths, the most developed organs are those of the reproductive tract, with less sophistication in the digestive, excretory, nervous and muscular systems.
Life cycle & reproduction:
The complete life cycle of helminths includes the fertilized egg (embryo), larval and adult stages. In the majority of helminths, adults derive nutrients and reproduce sexually in a host’s body. Fertizlied eggs are usually released to the environment and packaged in a protective shell with some extra food to aid their development into alrvae.
In nematodes, the sexes are separate and are usually different in appearance. In trematodes, the sexes can be either separate or hermaphroditic (both male and female sex organs are in the same individual worm). Cestodes are generally hermaphroditic.
Helminths must complete their life cycle by transmitting an infective form, usually an egg or larva, to the body of another host, of either the same or a different species. The host in which larval development occurs is the intermediate (secondary host) and the host in which adulthood and mating occur is the definitive (final) host.
Pinworm/enterobiasis Example: a person swallows microscopic eggs picked up form another infected eprson by direct contact or by touching artciles that person has touched. The eggs hatch in the intestine and then release alrvae that mature into adult worms within about 1 month. Male and female worms mate, and the female migrates out to the anus to deposit eggs, which casues intesnse itchiness that the infected human usually releives by scratching. Sratching contaiminates the fingers which in turn transfers egggs to bed sheets and other objects. This person is thus a host and a source of eggs that can spread to others. Enterobiasis occurs most often among families and in other close living situations.
Transmission & etiology:
Helminthic infections may be acquired through the fecal-oral route or through penetration of the skin. Helminths have numerous 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.
Not all flatworms and roundworms are parasites by nature; many live free in soil and water.
Diagnosis:
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.
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.
Prevention/Treatment:
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. However, treating helminthic infections has been one of the most difficult and challenging of all chemotherapeutic tasks. Flukes, tapeworms and round worms are much larger parasites than other microorgianisms and being animals, have greater similarities to humans. Also, the usual strategy of using drugs to clock their reproduction is not usually successful in eradicating the adult worms.
The most effective drugs immobilize, disinterate or inhibit the metabolism in all stages of the life cycle.
Albendazole: is a broad spectrum antiparasitic drug used for several types of round worm intestinal infestations. It works in the intestine to inhibit the function of the microtubules of worms, eggs and larvae. This means the parasites can not longer utilize glucose, which leads to death.
Ivermectin is a prescription anti-parasitic medication used to treat certain infections caused by parasitic worms and external parasites like lice and rosacea. While known for treating tropical diseases, it became controversial due to its unproven use as a COVID-19 treatment.
Pyramtel: paralyzes the muscles of itnestinal foundworms. Consequently, the worms are unable to maintian thier grip on the itnestinal wall and are expelled along with the feces by the normal peristaltic action of the bowel.
Praziquantel: is a newer antihelminthic drug used for vairous tapeworm and fluke infetions.
Nematodes (Roundworms)
Intestinal roundworms acquired by ingestion
–-Baylisascaris procyonis, (raccoon roundworm): enters the human body primarily through the ingestion of infective eggs present in raccoon feces or contaminated materials. These eggs can be found in soil, water, or on objects that have come into contact with raccoon waste. Children, due to their tendency to put things in their mouths, are particularly susceptible to infection.
Baylisascaris procyonis (raccoon roundworm) is an intestinal parasite that causes widespread, typically asymptomatic infection in raccoons (Procyon lotor) in the United States. Raccoons, the primary definitive host of B. procyonis, can shed millions of roundworm eggs in their feces every day. Eggs become infective after 2–4 weeks in the environment and can survive for years. When consumed by nondefinitive hosts, the eggs develop into larvae and migrate through body tissues. Human cases are rare: only 35 cases have been reported in the United States. Most patients have been young and male with developmental disabilities and pica, conditions associated with compulsive consumption of nonfood items such as soil. Serious complications include prolonged migration and persistence of helminth larvae in the viscera (visceral larva migrans), the brain (neural larva migrans), and the eye (ocular larva migrans); some cases have been fatal. No vaccine to prevent baylisascariasis exists. In cases in which suspicion of exposure is high (e.g., known oral exposure to raccoon feces), treatment with oral albendazole (25–50 mg/kg per day for 10–20 days) might be appropriate, and should be initiated as soon as possible after ingestion of infectious material, ideally within three days. See CDC
–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. Human ascariasis is indeed caused by the roundworm Ascaris lumbricoides. It is the most common human roundworm infection, prevalent worldwide but most common in areas with poor sanitation and contaminated food or water. The infection involves the small intestine and is spread by ingesting the parasite’s eggs.
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
Transmission occurs as a consequence of the accidental ingestion of embryonated eggs from contaminated soil, food and/or water. Ascaris eggs are resistant and have the potential to survive for long periods of time, particularly under warm and moist conditions. The commonest method used for the diagnosis for Ascaris infection is the microscopic detection of eggs in faecal samples. Counting adult worms upon expulsion following treatment is regarded as a “gold standard” for estimating the intensity of infection. Pigs infected with Ascaris can represent a reservoir for human infection.
Despite variations in treatment efficacy among STHs, albendazole and mebendazole appear to remain efficacious anthelmintics against human ascariasis. However, anthelmintic treatment alone will not lead to a marked reduction or elimination of ascariasis without accompanying improvements in socioeconomic conditions and the provision of clean water, improved sanitation and hygiene. See Rostami
–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
-Trichinella is a parasitic roundworm. The infection caused by this worm is called trichinellosis, which occurs when a person eats meat containing Trichinella larvae. These worms can burrow into the intestines and later migrate to muscle tissue, causing symptoms like fever, muscle pain, and swelling.
Neurotrichinellosis represents one of the most important complications of severe trichinellosis in humans and is sometimes fatal, especially when Trichinella spiralis is involved.
Trichinellosis is a food-borne parasitic zoonosis acquired by the consumption of raw or inadequately cooked meat and meat-derived products of pigs, horses, and game animals (e.g., wild boars, bears, walruses, jackals, badgers) in which nematode larvae of the genus Trichinella are present (Gottstein et al., 2009). In the period 1986–2009, trichinellosis has been documented in 65 818 people with 42 deaths, in 41 countries of the world (Murrell and Pozio, 2011). Today, 12 species/genotypes have been identified and they are characterized by different geographical distributions and host range. All species are potentially infectious for human beings, however, only Trichinella spiralis is identified as the main etiological agent (Pozio et al., 2009).
After the ingestion of infected meat, the parasites reach the adult stage in the gut causing diarrhoea in approximately 26% of patients (Murrell and Pozio, 2011). Six days after infection, females begin to produce the new larval generation (new born larvae, NBL), which continues for 2–3 weeks. NBL then reach the lymphatic and blood vessels and disseminate into the general circulation (Pozio, 2007a). NBL reach all the body sites, however only those which reach the striated skeletal muscles actively penetrate into the muscle cells and develop into the infective stage (Pozio, 2007a). NBL that do not reach the striated muscles are destroyed by the host immune reaction but they can still cause lesions in the organs such as heart, lung, kidney, liver, central nervous system (CNS), and eye (Kociecka, 2000).
–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. This 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):
Strongyloidiasis is a helminth infection most commonly caused by the intestinal nematode Strongyloides stercoralis (S. stercoralis) and less commonly by S. fuelleborni. Previous reports estimate S. stercoralis, which is endemic to tropical and subtropical areas, to be responsible for 30-100 million infections annually. Strongyloidiasis caused by the soil-transmitted helminth Strongyloides stercoralis is an infection recently included by WHO in the group of neglected tropical diseases (NTD)
Strongyloidiasis is a helminth infection affecting 613.9 million people annually, mainly in the tropics and subtropics. The reported seroprevalence in the United States is 4% with most of the cases reported in immigrants. Human T-lympho-tropic virus 1 (HTLV-1) infections, hypogammaglobulinemia, immunosuppressant use – particularly steroid use, alcoholism, and malnutrition have been associated with an increased risk of strongyloidiasis. Recently, cases of strongyloidiasis hyperinfection syndrome have been described in coronavirus disease 2019 (COVID-19) patients treated with steroids as well. Strongyloidiasis is a particular problem for AIDS patients. Treatment is with thiabendazole.
Strongyloidiasis can be asymptomatic or present with mild symptoms. Strongyloides stercoralis is known to cause autoinfection. In immunocompromised individuals, it can present with severe symptoms, hyperinfection, or disseminated disease. Reported mortality in cases of disseminated Strongyloidiasis is 87.1%. ctivities that increase exposure to soil, such as walking barefoot, contact with human waste or sewage, and occupations that involve working with contaminated soil, like farming and coal mining, increase the risk of infection
Serology and detection of larvae in stool by direct microscopy are the most commonly used methods to diagnose strongyloidiasis. Although confirmation diagnosis relies on the visualisation of S. stercoralis larvae through different techniques, serological tests are increasingly being used worldwide given the high sensitivity
The drug of choice for the treatment is ivermectin. However, the use of ivermectin in human pregnancy is not well studied, and its teratogenic risks are unknown. Proactive screening of strongyloidiasis is necessary in immunocompromised individuals to prevent severe disease.
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.
–River Blindness: (onchocerciasis)
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.
Human onchocerciasis—commonly known as river blindness—is one of the most devastating
yet neglected tropical diseases, leaving many millions in Sub–Saharan Africa blind and/or with
chronic disabilities. Almost everyone severely affected with OSD and river blindness lives in Sub-Saharan Africa or Yemen in the Middle East.
Attempts to eliminate onchocerciasis, primarily through the mass drug administration of ivermectin remains challenging and has been heightened by the recent news that drug–resistant parasites are developing in some populations after years of drug treatment.
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. Most taeniid species develop into adult tapeworms in carnivorous mammals. Most taeniid species develop into adult tapeworms in carnivorous mammals. The pork tapeworm, Taenia solium, and the beef tapeworm, Taenia saginata, are exceptional in that they require humans as definitive hosts.
The genus Taenia consists of nearly 50 species. 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 larvae, 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
Almost all cases of human cysticercosis (CC) are caused by the larval (metacestode) stage of T. solium. However, there are reports of at least eight additional Taenia species, including Taenia crassiceps, occasionally resulting in CC in humans. Neurocysticercosis (NCC), caused by cysticerci of the pork tapeworm, Taenia solium, is one of the most lethal helminthic zoonoses. Cysticercosis, including NCC, is not only found in traditional remote/rural areas with known T. solium transmission, but cases can also be diagnosed in non-endemic areas, including big cities in developed countries. Cases in non-endemic regions are often related to T. solium tapeworm carriers who have immigrated for work or are found in individuals who have a history of travel to an endemic region for work or leisure. See Budke
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):
According to World Health Organization (WHO) data, schistosomiasis is endemic in 78 countries, 51 of which require preventive drug administration for moderate to severe transmission. The infection is caused by a trematode belonging to the genus Schistosoma.
Human schistosomiasis is caused by species of schistosome trematode worms: Schistosoma mansoni, S. haematobium, S. japonicum, S. intercalatum, and S. mekongi. These infections manifest in two main forms: intestinal schistosomiasis, attributed to S. haematobium, and urogenital schistosomiasis, associated with other species such as S. mansoni.
The life cycle of Schistosoma initiates when parasitic eggs from infected human feces or urine enter freshwater sources. Under favorable environmental conditions, these eggs hatch into miracidia, which actively seek out and penetrate suitable IH snails. Asexual reproduction occurs within the snails, leading to the development of cercariae. At this advanced stage, the cercariae are released into the water as free-living parasites and can penetrate human skin, thereby completing the cycle and causing the disease.
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.
Lung Flukes:
–Paragnimus: Foodborne trematodes target their hosts, including humans, by residing in tasty food items. Lung flukes of the genus Paragonimus are no exception. Humans like to eat crabs and crayfish, often raw or incompletely cooked. If these crustaceans harbour metacercariae of a Paragonimus species, then human infection (paragonimiasis) can ensue. Paragonimiasis is unusual among foodborne zoonotic trematodes in having a very broad geographical distribution (tropical and some subtropical regions of Asia, Africa and the Americas), a large number of actual or potential causative Paragonimus species and a considerable range of clinical signs and symptoms, many of which mimic those of other diseases, especially tuberculosis and cancer.
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.