| Hymenolepiasis | |
|---|---|
| Specialty | Infectious diseases, helminthologist  |
Hymenolepiasis is infestation by one of two species of tapeworm: Hymenolepis nana or H. diminuta . Alternative names are dwarf tapeworm infection and rat tapeworm infection. The disease is a type of helminthiasis which is classified as a neglected tropical disease.
Hymenolepiasis does not always have symptoms, but they usually are described as abdominal pain, loss of appetite, itching around the anus, irritability, and diarrhea. However, in one study of 25 patients conducted in Peru, successful treatment of the infection made no significant difference to symptoms. [1] Some authorities report that heavily infected cases are more likely to be symptomatic. [2] [3]
Symptoms in humans are due to allergic responses or systematic toxaemia caused by waste products of the tapeworm. Light infections are usually symptomless, whereas infection with more than 2000 worms can cause enteritis, abdominal pain, diarrhea, loss of appetite, restlessness, irritability, restless sleep, and anal and nasal pruritus. Rare symptoms include increased appetite, vomiting, nausea, bloody diarrhea, hives, extremity pain, headache, dizziness, and behavioral disturbances. Occasionally, epileptic seizures occur in infected children.[ citation needed ]
Examination of the stool for eggs and parasites confirms the diagnosis. The eggs and proglottids of H. nana are smaller than H. diminuta. Proglottids of both are relatively wide and have three testes. Identifying the parasites to the species level is often unnecessary from a medical perspective, as the treatment is the same for both.[ citation needed ]
Abdominal discomfort and, in case of prolonged diarrhea, dehydration are possible complications.[ citation needed ]
In 2015 an unusual complication was noted in a man whose immune system had been compromised by HIV. He developed multiple tumors of malignant cell nests within his body that had originated from a tapeworm in his intestines. [4]
Hymenolepis worms live in the intestines of rats and are common in warm climates, and are generally found in the feces of rats, which are consumed by their secondary hosts—beetles. The worms mature into a life form referred to as a "cysticercoid" in the insect; in H. nana, the insect is always a beetle. Humans and other animals become infected when they intentionally or unintentionally eat material contaminated by insects. In an infected person, it is possible for the worm's entire lifecycle to be completed in the bowel, so infection can persist for years if left untreated. H. nana infections are much more common than H. diminuta infections in humans because, in addition to being spread by insects, the disease can be spread directly from person to person by eggs in feces. When this happens, H. nana oncosphere larvae encyst in the intestinal wall and develop into cysticercoids and then adults. These infections were previously common in the southeastern USA, and have been described in crowded environments and individuals confined to institutions. However, the disease occurs throughout the world. H. nana infections can grow worse over time because, unlike in most tapeworms, H. nana eggs can hatch and develop without ever leaving the definitive host.[ citation needed ]
The risk of human infection from H. diminuta is very low, since its main host is the rat. Also known as the rat tapeworm, H. diminuta adults live and mate in the bowels of rats. Eggs of H. diminuta are excreted by the rats in droppings, which are frequently consumed by beetles. Once inside the beetle, the eggs mature into a cysticercoid. The juvenile tapeworms claw their way out of the beetle gut into the circulatory system by means of their three pairs of hooks. There, they wait for a rat to ingest the host beetle, where they mature to adult form, lay eggs, and restart the entire cycle. [5]
H. diminuta has an effective mechanism for interspecies transfection. Beetles prefer to ingest rat droppings infected with tapeworm eggs, because of their odor. It is not known if the odor is produced specifically by the eggs or the droppings. H. diminuta also sterilizes its beetle host, if female. This is so the beetle does not waste energy in its reproductive system, allowing H. diminuta to further exploit the beetle's metabolic resources. [5]
H. nana is a tapeworm, belonging to the class Cestoidea, phylum Platyhelminthes. It consists of a linear series of sets of reproductive organs of both sexes; each set is referred to as a genitaluim and the area around it is a proglottid. New proglottids are continuously differentiated near the anterior end in a process called strobilation. Each segment moves toward the posterior end as a new one takes its place and, during the process, becomes sexually mature. The proglottid can copulate with itself, with others in the strobilla, or with those in other worms. When the segment reaches the end of its strobila, it disintegrates en route, releasing eggs in a process called apolysis.[ citation needed ]
H. nana is the only cestode capable of completing its lifecycle without an intermediate host. [6] It can, however, pass through an intermediate host, as well. The most common intermediate hosts for H. nana are arthropods (e.g. flour beetles). When an egg is ingested by the definitive host, it hatches and releases a six-hook larva called the oncosphere (hexacanth) which penetrates the villi of the small intestine and develops into a cysticercoid. [2]
Transmission of H.nana occurs by the fecal-oral route. It also occurs by accidental ingestion of an insect containing the cysticercoid.[ citation needed ] [7]
H. nana in mice is used because:[ citation needed ]
Method:[ citation needed ]
H. nana lodges itself in the intestines and absorbs nutrients from the intestinal lumen. In human adults, the tapeworm is more of a nuisance than a health problem, but in small children, many H. nana worms can be dangerous. Usually, the larvae of this tapeworm cause the most problem in children; they burrow into the walls of the intestine, and if enough tapeworms are present in the child, severe damage can be inflicted. This is done by absorbing all the nutrients from the food the child eats. Usually, a single tapeworm will not cause health issues. H. nana usually will not cause deaths unless in extreme circumstances and usually in young children or in people who have weakened immune systems. In some parts of the world, individuals who are heavily infected are a result of internal autoinfection.[ citation needed ]
Good hygiene, public health and sanitation programs, and elimination of infected rats help to prevent the spread of hymenolepiasis. Preventing fecal contamination of food and water in institutions and crowded areas is of primary importance. General sanitation and rodent and insect control (especially control of fleas and grain insects) are also essential for prevention of H. nana infection.[ citation needed ]
The two drugs that have been well-described for the treatment of hymenolepiasis are praziquantel and niclosamide. Praziquantel, which is parasiticidal in a single dose for all the stages of the parasite, is the drug of choice because it acts very rapidly against H. nana. Although structurally unrelated to other anthelminthics, it kills both adult worms and larvae. In vitro, the drug produces vacuolization and disruption of the tegument in the neck of the worms, but not in more posterior portions of the strobila. Praziquantel is well absorbed when taken orally, and it undergoes first-pass metabolism and 80% of the dose is excreted as metabolites in urine within 24 hours. Repeated treatment is required for H. nana at an interval of 7–10 days.[ citation needed ]
Praziquantel as a single dose (25 mg/kg) is the current treatment of choice for hymenolepiasis and has an efficacy of 96%. Single-dose albendazole (400 mg) is also very efficacious (>95%).[ citation needed ]
A three-day course of nitazoxanide is 75–93% efficacious. The dose is 1 g daily for adults and children over 12; 400 mg daily for children aged 4 to 11 years; and 200 mg daily for children aged 3 years or younger. [1] [8] [9]
Cure rates are extremely good with modern treatments, but successful cure results may be of no symptomatic benefit to patients. [1]
A cysticercoid is the larval stage of certain tapeworms, similar in appearance to a cysticercus, but having the scolex filling completely the enclosing cyst. In tapeworm infections, cysticercoids can be seen in free form as well as enclosed by cysts in biological tissues such as the intestinal mucosa. Also referred to as metacestodes, they produce proteins enabling them to invade and to survive in the host.
Taenia solium, the pork tapeworm, belongs to the cyclophyllid cestode family Taeniidae. It is found throughout the world and is most common in countries where pork is eaten. It is a tapeworm that uses humans as its definitive host and pigs as the intermediate or secondary hosts. It is transmitted to pigs through human feces that contain the parasite eggs and contaminate their fodder. Pigs ingest the eggs, which develop into larvae, then into oncospheres, and ultimately into infective tapeworm cysts, called cysticercus. Humans acquire the cysts through consumption of uncooked or under-cooked pork and the cysts grow into an adult worms in the small intestine.
Taenia saginata, commonly known as the beef tapeworm, is a zoonotic tapeworm belonging to the order Cyclophyllidea and genus Taenia. It is an intestinal parasite in humans causing taeniasis and cysticercosis in cattle. Cattle are the intermediate hosts, where larval development occurs, while humans are definitive hosts harbouring the adult worms. It is found globally and most prevalently where cattle are raised and beef is consumed. It is relatively common in Africa, Europe, Southeast Asia, South Asia, and Latin America. Humans are generally infected as a result of eating raw or undercooked beef which contains the infective larvae, called cysticerci. As hermaphrodites, each body segment called proglottid has complete sets of both male and female reproductive systems. Thus, reproduction is by self-fertilisation. From humans, embryonated eggs, called oncospheres, are released with faeces and are transmitted to cattle through contaminated fodder. Oncospheres develop inside muscle, liver, and lungs of cattle into infective cysticerci.
Echinococcus granulosus, also called the hydatid worm, hyper tape-worm or dog tapeworm, is a cyclophyllid cestode that dwells in the small intestine of canids as an adult, but which has important intermediate hosts such as livestock and humans, where it causes cystic echinococcosis, also known as hydatid disease. The adult tapeworm ranges in length from 3 mm to 6 mm and has three proglottids ("segments") when intact—an immature proglottid, mature proglottid and a gravid proglottid. The average number of eggs per gravid proglottid is 823. Like all cyclophyllideans, E. granulosus has four suckers on its scolex ("head"), and E. granulosus also has a rostellum with hooks. Several strains of E. granulosus have been identified, and all but two are noted to be infective in humans.
Dipylidium caninum, also called the flea tapeworm, double-pored tapeworm, or cucumber tapeworm is a cyclophyllid cestode that infects organisms afflicted with fleas and canine chewing lice, including dogs, cats, and sometimes human pet-owners, especially children.
The Hymenolepididae are family of cyclophyllid tapeworms. Their characteristic feature is the small number of testes. The unilateral genital pores and large external seminal vesicle allow for easy recognition. Most species are small, transparent, and easy to study. The family contains over 90 genera with over 900 species, having as their definitive host birds or mammals. Most reside in the intestines of their definitive hosts. The majority of species with known lifecycles have arthropods as intermediate hosts.
Dwarf tapeworm is a cosmopolitan species though most common in temperate zones, and is one of the most common cestodes infecting humans, especially children.
Hymenolepis diminuta, also known as rat tapeworm, is a species of Hymenolepis tapeworm that causes hymenolepiasis. It has slightly bigger eggs and proglottids than H. nana and infects mammals using insects as intermediate hosts. The adult structure is 20 to 60 cm long and the mature proglottid is similar to that of H. nana, except it is larger.
Taenia pisiformis, commonly called the rabbit tapeworm, is an endoparasitic tapeworm which causes infection in lagomorphs, rodents, and carnivores. Adult T. pisiformis typically occur within the small intestines of the definitive hosts, the carnivores. Lagomorphs, the intermediate hosts, are infected by fecal contamination of grasses and other food sources by the definitive hosts. The larval stage is often referred to as Cysticercus pisiformis and is found on the livers and peritoneal cavities of the intermediate hosts. T. pisiformis can be found worldwide.
Eucestoda, commonly referred to as tapeworms, is the larger of the two subclasses of flatworms in the class Cestoda. Larvae have six posterior hooks on the scolex (head), in contrast to the ten-hooked Cestodaria. All tapeworms are endoparasites of vertebrates, living in the digestive tract or related ducts. Examples are the pork tapeworm with a human definitive host, and pigs as the secondary host, and Moniezia expansa, the definitive hosts of which are ruminants.
Diphyllobothriasis is the infection caused by tapeworms of the genus Diphyllobothrium.
Hymenolepis is a genus of cyclophyllid tapeworms responsible for hymenolepiasis. They are parasites of humans and other mammals. The focus in this article is in Hymenolepis commonly parasitizing humans.
Cestoda is a class of parasitic worms in the flatworm phylum (Platyhelminthes). Most of the species—and the best-known—are those in the subclass Eucestoda; they are ribbon-like worms as adults, known as tapeworms. Their bodies consist of many similar units known as proglottids—essentially packages of eggs which are regularly shed into the environment to infect other organisms. Species of the other subclass, Cestodaria, are mainly fish infecting parasites.
Bertielliasis is the infection of Bertiella, a cestode tapeworm parasite that primarily infects nonhuman primates, rodents and Australian marsupials. Occasionally, human infections have been documented by one of two species: Bertiella studeri, or Bertiella mucronata. Of 29 different Bertiella species, only these two can infect humans.
Raillietina is a genus of tapeworms that includes helminth parasites of vertebrates, mostly of birds. The genus was named in 1920 in honour of a French veterinarian and helminthologist, Louis-Joseph Alcide Railliet. Of the 37 species recorded under the genus, Raillietina demerariensis, R. asiatica, and R. formsana are the only species reported from humans, while the rest are found in birds. R. echinobothrida, R. tetragona, and R. cesticillus are the most important species in terms of prevalence and pathogenicity among wild and domestic birds.
Moniezia expansa is commonly known as sheep tapeworm or double-pored ruminant tapeworm. It is a large tapeworm inhabiting the small intestines of ruminants such as sheep, goats and cattle. It has been reported from Peru that pigs are also infected. There is an unusual report of human infection in an Egyptian. It is characterized by unarmed scolex, presence of two sets of reproductive systems in each proglottid, and each proglottid being very short but very broad.
Hymenolepis microstoma, also known as the rodent tapeworm, is an intestinal dwelling parasite. Adult worms live in the bile duct and small intestines of mice and rats, and larvae metamorphose in the haemocoel of beetles. It belongs to the genus Hymenolepis; tapeworms that cause hymenolepiasis. H. microstoma is prevalent in rodents worldwide, but rarely infects humans.
Anoplocephala perfoliata is the most common intestinal tapeworm of horses, and an agent responsible for some cases of equine colic.
Raillietina tetragona is a parasitic tapeworm belonging to the class Cestoda. It is a cosmopolitan helminth of the small intestine of pigeon, chicken and guinea fowl, and is found throughout the world.
Raillietina cesticillus is a parasitic tapeworm of the family Davaineidae. Sometimes called 'broad-headed tapeworm', it infects the small intestine of chicken and occasionally other birds, such as guinea fowl and turkey, which are generally in close proximity to backyard poultry. It is a relatively harmless species among intestinal cestodes in spite of a high prevalence. In fact it probably is the most common parasitic platyhelminth in modern poultry facilities throughout the world.