Strongyloides stercoralis

Last updated

Threadworm
Strongyloides stercoralis larva.jpg
First stage larva (L1) of S. stercoralis
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Nematoda
Class: Chromadorea
Order: Rhabditida
Family: Strongylidae
Genus: Strongyloides
Species:
S. stercoralis
Binomial name
Strongyloides stercoralis
Bavay, 1876

Strongyloides stercoralis is a human pathogenic parasitic roundworm causing the disease strongyloidiasis. Its common name in the US is threadworm. In the UK and Australia, however, the term threadworm can also refer to nematodes of the genus Enterobius , otherwise known as pinworms. [1]

Contents

The Strongyloides stercoralis nematode can parasitize humans. The adult parasitic stage lives in tunnels in the mucosa of the small intestine. The genus Strongyloides contains 53 species, [2] [3] and S. stercoralis is the type species. S. stercoralis has been reported in other mammals, including cats and dogs. However, it seems that the species in dogs is typically not S. stercoralis, but the related species S. canis. Non-human primates are more commonly infected with S. fuelleborni and S. cebus, although S. stercoralis has been reported in captive primates. Other species of Strongyloides that are naturally parasitic in humans, but with restricted distributions, are S. fuelleborni fuelleborni in central Africa and S. fuelleborni kellyi in Papua New Guinea. [4]

Geographic distribution

S. stercoralis infection is associated with fecal contamination of soil or water. Hence, it is a very rare infection in developed economies. In developing countries, it is less prevalent in urban areas than in rural areas (where sanitation standards are poor). S. stercoralis can be found in areas with tropical and subtropical climates. [5]

Strongyloidiasis was first described in the 19th century in French soldiers returning home from expeditions in Indochina. Today, the countries of the old Indochina (Vietnam, Cambodia, and Laos) still have endemic strongyloidiasis, with the typical prevalences being 10% or less. Regions of Japan used to have endemic strongyloidiasis, but control programs have eliminated the disease. Strongyloidiasis appears to have a high prevalence in some areas of Brazil and Central America. It is endemic in Africa, but the prevalence is typically low (1% or less). Pockets have been reported from rural Italy, but the current status is unknown. In the Pacific islands, strongyloidiasis is rare, although some cases have been reported from Fiji. In tropical Australia, some rural and remote Australian Aboriginal communities have very high prevalences of strongyloidiasis. [6]

In some African countries (e.g., Congo), S. fuelleborni was more common than S. stercoralis in parasite surveys from the 1970s, but the current status is unknown. In Papua New Guinea, S. stercoralis is endemic, but prevalence is low. However, in some areas, another species, S. kellyi, [7] is a very common parasite of children in the New Guinea Highlands and Western Province. [7]

Knowledge of the geographic distribution of strongyloidiasis is of significance to travelers who may acquire the parasite during their stays in endemic areas.

Because strongyloidiasis could theoretically be transmittable through unsanitary bedclothes care must be taken never to use unclean hotel bed sheets in endemic areas. Using plastic slippers when showering may be very important when travelling in tropical regions.

Estimates of the number of people infected vary with one estimate putting the figure at 370 million worldwide. [8] [9] Local prevalence can exceed 40% in some tropical and subtropical countries. [10]

Life cycle

The life cycle of this parasite is more complex than that of most nematodes, with its alternation between free-living and parasitic cycles, and its potential for autoinfection (the parasite has the ability to complete its life cycle without the involvement of another host) and multiplication within the host. The parasitic cycle is homogonic, while the free-living cycle is heterogonic. The heterogonic life cycle is advantageous to the parasite because it allows reproduction in the absence of a host.

In the free-living cycle, the rhabditiform larvae passed in the stool can either molt twice and become infective filariform larvae (direct development) or molt four times and become free-living adult males and females that mate and produce eggs from which rhabditiform larvae hatch. In the direct development, first-stage larvae (L1) transform into infective larvae (IL) via three molts. The indirect route results first in the development of free-living adults that mate; the female lays eggs, which hatch and then develop into IL. The direct route gives IL faster (three days) versus the indirect route (seven to 10 days). However, the indirect route results in an increase in the number of IL produced. Speed of development of IL is traded for increased numbers. The free-living males and females of S. stercoralis die after one generation; they do not persist in the soil. The latter, in turn, can either develop into a new generation of free-living adults or develop into infective filariform larvae. The filariform larvae penetrate the human host skin to initiate the parasitic cycle. Upon contact with contaminated soil, infectious larvae contained in the soil can penetrate the skin.

Some of the larvae enter the superficial veins and are carried in the blood to the lungs, where they enter the alveoli. They are then coughed up and swallowed into the gut, where they parasitise the intestinal mucosa of the duodenum and jejunum. In the small intestine, they molt twice and become adult female worms. The females live threaded in the epithelium of the small intestine and, by parthenogenesis, produce eggs, which yield rhabditiform larvae. Only females will reach reproductive adulthood in the intestine. Female strongyloids reproduce through parthenogenesis. The eggs hatch in the intestine and young larvae are then excreted in the feces. It takes about two weeks to reach egg development from the initial skin penetration. By this process, S. stercoralis can cause both respiratory and gastrointestinal symptoms. The worms also participate in autoinfection, in which the rhabditiform larvae become infective filariform larvae, which can penetrate either the intestinal mucosa (internal autoinfection) or the skin of the perianal area (external autoinfection); in either case, the filariform larvae may follow the previously described route, being carried successively to the lungs, the bronchial tree, the pharynx, and the small intestine, where they mature into adults; or they may disseminate widely in the body. To date, occurrence of autoinfection in humans with helminthic infections is recognized only in Strongyloides stercoralis and Capillaria philippinensis infections.[ citation needed ] In the case of Strongyloides, autoinfection may explain the possibility of persistent infections for many years in persons not having been in an endemic area and of hyperinfections in immunodepressed individuals.

Strongyloides is thought to be attracted to humans via paired thermosensory neurons. [11] While S. stercoralis is attracted to chemicals such as carbon dioxide or sodium chloride, these chemicals are not specific. Larvae have been thought to locate their hosts via chemicals in the skin, the predominant one being urocanic acid, a histidine metabolite on the uppermost layer of skin that is removed by sweat or the daily skin-shedding cycle. [12] Urocanic acid concentrations can achieve at least fivefold greater levels on the foot sole than any other part of the human body. [12] [13] [ verification needed ]

Zoonotic transmission

Dogs can act as a host for this parasite both in the wild and in the laboratory, but transmission from dog to human has been difficult to prove. Molecular genetic analyses have shown that there are two populations of this parasite in dogs, one of which (type B) is exclusive to dogs and a second (type A) that is common to dogs and humans. [14] [15] These two genotypes may be separate species. The identity of the genes suggests that dog to human transmission may occur.

Morphology

Whereas males grow to only about 0.9  mm (0.04  in ) in length, females can grow from 2.0 to 2.5 mm (0.08 to 0.10 in). Both sexes also possess a tiny buccal capsule and cylindrical esophagus without a posterior bulb. [16] In the free-living stage, the esophagi of both sexes are rhabditiform. Males can be distinguished from females by two structures: the spicules and gubernaculum.

Autoinfection

An unusual feature of S. stercoralis is autoinfection. Only one other species in the genus Strongyloides, S. felis, has this trait. Autoinfection is the development of L1 into small infective larvae in the gut of the host. These autoinfective larvae penetrate the wall of the lower ileum or colon or the skin of the perianal region, enter the circulation again, travel to the lungs, and then to the small intestine, thus repeating the cycle. Autoinfection makes strongyloidiasis due to S. stercoralis an infection with several unusual features.

Persistence of infection is the first of these important features. Because of autoinfection, humans have been known to still be infected up to 65 years after they were first exposed to the parasite (e.g., World War II or Vietnam War veterans). Once a host is infected with S. stercoralis, infection is lifelong unless effective treatment eliminates all adult parasites and migrating autoinfective larvae.

Symptoms

Many people infected are asymptomatic at first. Symptoms include dermatitis: swelling, itching, larva currens, and mild hemorrhage at the site where the skin has been penetrated. Spontaneous scratch-like lesions may be seen on the face or elsewhere. If the parasite reaches the lungs, the chest may feel as if it is burning, and wheezing and coughing may result, along with pneumonia-like symptoms (Löffler's syndrome). The intestines could eventually be invaded, leading to burning pain, tissue damage, sepsis, and ulcers. Stools may have yellow mucus with a recognizable smell. Chronic diarrhea can be a symptom. [17] In severe cases, edema may result in obstruction of the intestinal tract, as well as loss of peristaltic contractions. [18]

Strongyloidiasis in immunocompetent individuals is usually an indolent disease. However, in immunocompromised individuals, it can cause a hyperinfective syndrome (also called disseminated strongyloidiasis) due to the reproductive capacity of the parasite inside the host. This hyperinfective syndrome can have a mortality rate close to 90% if disseminated. [19] [20] [21]

Immunosuppressive drugs, especially corticosteroids and agents used for tissue transplantation, can increase the rate of autoinfection to the point where an overwhelming number of larvae migrate through the lungs, which in many cases can prove fatal. In addition, diseases such as human T-lymphotropic virus 1, which enhance the Th1 arm of the immune system and lessen the Th2 arm, increase the disease state. [20] Another consequence of autoinfection is the autoinfective larvae can carry gut bacteria back into the body. About 50% of people with hyperinfection present with bacterial disease due to enteric bacteria. Also, a unique effect of autoinfective larvae is larva currens due to the rapid migration of the larvae through the skin. Larva currens appears as a red line that moves rapidly (more than 5 cm or 2 in per day), and then quickly disappears. It is pathognomonic for autoinfective larvae and can be used as a diagnostic criterion for strongyloidiasis due to S. stercoralis.

Diagnosis

Locating juvenile larvae, either rhabditiform or filariform, in recent stool samples will confirm the presence of this parasite. [22] Other techniques used include direct fecal smears, culturing fecal samples on agar plates, serodiagnosis through ELISA, and duodenal fumigation. Still, diagnosis can be difficult because of the day-to-day variation in juvenile parasite load.

Prevention

Ideally, prevention, by improved sanitation (proper disposal of feces), practicing good hygiene (washing of hands), etc., is used before any drug regimen is administered.

Treatment

Ivermectin is the drug of choice for treatment, due to its low side effect profile. [23] Albendazole is also effective in treating strongyloidiasis. Mebendazole has a much higher failure rate in clinical practice than albendazole or ivermectin. [24] However, these drugs have little effect on the autoinfective larvae. Hence, repeat treatments with ivermectin or albendazole must be administered to kill newly matured parasites that have developed from the autoinfective larvae. This means a full treatment dose every two weeks until all larvae capable of maturing into adults have been extirpated. Follow-up stool samples, potential additional treatment, and blood tests are necessary to ensure a cure. [25]

Chemoattractant

This parasite depends on chemical cues to find a potential host. It uses sensor neurons of class AFD to identify cues excreted by the host. [26] S. stercoralis is attracted to nonspecific attractants of warmth, carbon dioxide, and sodium chloride. Urocanic acid, a component of skin secretions in mammals, is a major chemoattractant. Larvae of S. stercoralis are strongly attracted to this compound. [12] This compound can be suppressed by metal ions, suggesting a possible strategy for preventing infection.

See also

Related Research Articles

<span class="mw-page-title-main">Parasitology</span> Study of parasites, their hosts, and the relationship between them

Parasitology is the study of parasites, their hosts, and the relationship between them. As a biological discipline, the scope of parasitology is not determined by the organism or environment in question but by their way of life. This means it forms a synthesis of other disciplines, and draws on techniques from fields such as cell biology, bioinformatics, biochemistry, molecular biology, immunology, genetics, evolution and ecology.

<span class="mw-page-title-main">Hookworm infection</span> Disease caused by intestinal parasites

Hookworm infection is an infection by a type of intestinal parasite known as a hookworm. Initially, itching and a rash may occur at the site of infection. Those only affected by a few worms may show no symptoms. Those infected by many worms may experience abdominal pain, diarrhea, weight loss, and tiredness. The mental and physical development of children may be affected. Anemia may result.

<i>Baylisascaris</i> Genus of worms

Baylisascaris is a genus of roundworms that infect more than fifty animal species.

<i>Necator americanus</i> Species of hookworm

Necator americanus is a species of hookworm commonly known as the New World hookworm. Like other hookworms, it is a member of the phylum Nematoda. It is an obligatory parasitic nematode that lives in the small intestine of human hosts. Necatoriasis—a type of helminthiasis—is the term for the condition of being host to an infestation of a species of Necator. Since N. americanus and Ancylostoma duodenale are the two species of hookworms that most commonly infest humans, they are usually dealt with under the collective heading of "hookworm infection". They differ most obviously in geographical distribution, structure of mouthparts, and relative size.

<span class="mw-page-title-main">Strongyloidiasis</span> Medical condition

Strongyloidiasis is a human parasitic disease caused by the nematode called Strongyloides stercoralis, or sometimes the closely related S. fülleborni. These helminths belong to a group of nematodes called roundworms. These intestinal worms can cause a number of symptoms in people, principally skin symptoms, abdominal pain, diarrhea and weight loss, but also many other specific and vague symptoms in disseminated disease, and severe life-threatening conditions through hyperinfection. In some people, particularly those who require corticosteroids or other immunosuppressive medication, Strongyloides can cause a hyperinfection syndrome that can lead to death if untreated. The diagnosis is made by blood and stool tests. The medication ivermectin is widely used to treat strongyloidiasis.

<span class="mw-page-title-main">Cutaneous larva migrans</span> Medical condition

Cutaneous larva migrans is a skin disease in humans, caused by the larvae of various nematode parasites of the hookworm family (Ancylostomatidae). The parasites live in the intestines of dogs, cats, and wild animals; they should not be confused with other members of the hookworm family for which humans are definitive hosts, namely Ancylostoma duodenale and Necator americanus.

Spirometra erinaceieuropaei is a parasitic tapeworm that infects domestic animals and humans. The medical term for this infection in humans and other animals is sparganosis. Morphologically, these worms are similar to other worms in the genus Spirometra. They have a long body consisting of three sections: the scolex, the neck, and the strobilia. They have a complex life cycle that consists of three hosts, and can live in varying environments and bodily tissues. Humans can contract this parasite in three main ways. Historically, humans are considered a paratenic host; however, the first case of an adult S. erinaceieuropaei infection in humans was reported in 2017. Spirometra tapeworms exist worldwide and infection is common in animals, but S. erinaceieuropaei infections are rare in humans. Treatment for infection typically includes surgical removal and anti-worm medication.

<i>Ancylostoma duodenale</i> Species of the roundworm genus Ancylostoma

Ancylostoma duodenale is a species of the roundworm genus Ancylostoma. It is a parasitic nematode worm and commonly known as the Old World hookworm. It lives in the small intestine of hosts such as humans, cats and dogs, where it is able to mate and mature. Ancylostoma duodenale and Necator americanus are the two human hookworm species that are normally discussed together as the cause of hookworm infection. They are dioecious. Ancylostoma duodenale is abundant throughout the world, including Southern Europe, North Africa, India, China, Southeast Asia, some areas in the United States, the Caribbean, and South America.

The soil-transmitted helminths are a group of intestinal parasites belonging to the phylum Nematoda that are transmitted primarily through contaminated soil. They are so called because they have a direct life cycle which requires no intermediate hosts or vectors, and the parasitic infection occurs through faecal contamination of soil, foodstuffs and water supplies. The adult forms are essentially parasites of humans, causing soil-transmitted helminthiasis (STH), but also infect domesticated mammals. The juveniles are the infective forms and they undergo tissue-migratory stages during which they invade vital organs such as lungs and liver. Thus the disease manifestations can be both local and systemic. The geohelminths together present an enormous infection burden on humanity, amounting to 135,000 deaths every year, and persistent infection of more than two billion people.

<i>Strongyloides</i> Genus of roundworms

Strongyloides, anguillula, or threadworm is a genus of small nematode parasites, belonging to the family Strongylidae, commonly found in the small intestine of mammals, that are characterized by an unusual lifecycle that involves one or several generations of free-living adult worms.

Capillaria philippinensis is a parasitic nematode which causes intestinal capillariasis. This sometimes fatal disease was first discovered in Northern Luzon, Philippines, in 1964. Cases have also been reported from China, Egypt, Indonesia, Iran, Japan, Korea, Lao PDR, Taiwan and Thailand. Cases diagnosed in Italy and Spain were believed to be acquired abroad, with one case possibly contracted in Colombia. The natural life cycle of C. philippinensis is believed to involve fish as intermediate hosts, and fish-eating birds as definitive hosts. Humans acquire C. philippinensis by eating small species of infested fish whole and raw.

Friedrich Fülleborn was a physician who specialized in tropical medicine and parasitology. He was a native of Kulm, West Prussia, which today is known as Chełmno, Poland.

<i>Oesophagostomum</i> Genus of roundworms

Oesophagostomum is a genus of parasitic nematodes (roundworms) of the family Strongylidae. These worms occur in Africa, Brazil, China, Indonesia and the Philippines. The majority of human infection with Oesophagostomum is localized to northern Togo and Ghana. Because the eggs may be indistinguishable from those of the hookworms, the species causing human helminthomas are rarely identified with accuracy. Oesophagostomum, especially O. bifurcum, are common parasites of livestock and animals like goats, pigs and non-human primates, although it seems that humans are increasingly becoming favorable hosts as well. The disease they cause, oesophagostomiasis, is known for the nodule formation it causes in the intestines of its infected hosts, which can lead to more serious problems such as dysentery. Although the routes of human infection have yet to be elucidated sufficiently, it is believed that transmission occurs through oral-fecal means, with infected humans unknowingly ingesting soil containing the infectious filariform larvae.

<i>Toxascaris leonina</i> Species of roundworm

Toxascaris leonina is a common parasitic roundworm found in dogs, cats, foxes, and related host species. T. leonina is an ascarid nematode, a worldwide distributed helminth parasite which is in a division of eukaryotic parasites that, unlike external parasites such as lice and fleas, live inside their host. The definitive hosts of T. leonina include canids and felines (cats), while the intermediate hosts are usually rodents, such as mice or rats. Infection occurs in the definitive host when the animal eats an infected rodent. While T. leonina can occur in either dogs or cats, it is far more frequent in cats.

Strongyloides procyonis is a parasitic roundworm infecting the small intestine of the raccoon, Procyon lotor, hence its name. It was first described from Louisiana. It is morphologically similar to S. stercoralis, and as such infections of S. procyonis in humans, dogs, and other animals might be mistaken for the former.

Pterygodermatites peromysci is an intestinal parasitic nematode in the genus Pterygodermatites of the family Rictulariidae.

Carcinogenic parasites are parasitic organisms that depend on other organisms for their survival, and cause cancer in such hosts. Three species of flukes (trematodes) are medically-proven carcinogenic parasites, namely the urinary blood fluke, the Southeast Asian liver fluke and the Chinese liver fluke. S. haematobium is prevalent in Africa and the Middle East, and is the leading cause of bladder cancer. O. viverrini and C. sinensis are both found in eastern and southeastern Asia, and are responsible for cholangiocarcinoma. The International Agency for Research on Cancer declared them in 2009 as a Group 1 biological carcinogens in humans.

Strongyloides westeri, commonly referred to as intestinal threadworm, is a species of small nematode parasite in the family Strongylidae. Strongyloides are commonly found in the small intestine of mammals, that are characterized by an unusual lifecycle that involves one generations of free-living adult worms.

<span class="mw-page-title-main">Gastropod-borne parasitic disease</span> Medical condition

Gastropod-borne parasitic diseases (GPDs) are a group of infectious diseases that require a gastropod species to serve as an intermediate host for a parasitic organism that can infect humans upon ingesting the parasite or coming into contact with contaminated water sources. These diseases can cause a range of symptoms, from mild discomfort to severe, life-threatening conditions, with them being prevalent in many parts of the world, particularly in developing regions. Preventive measures such as proper sanitation and hygiene practices, avoiding contact with infected gastropods and cooking or boiling food properly can help to reduce the risk of these diseases.

<span class="mw-page-title-main">Nematode infection in dogs</span> Threadworm infections of dogs are frequent

Nematode infection in dogs - the infection of dogs with parasitic nemamotodes - are, along with tapeworm infections and infections with protozoa, frequent parasitoses in veterinary practice. Nematodes, as so-called endoparasites, colonize various internal organs - most of them the digestive tract - and the skin. To date, about 30 different species of nematode have been identified in domestic dogs; they are essentially also found in wild dog species. However, the majority of them often cause no or only minor symptoms of disease in adult animals. The infection therefore does not necessarily have to manifest itself in a worm disease (helminthosis). For most nematodes, an infection can be detected by examining the feces for eggs or larvae. Roundworm infection in dogs and the hookworm in dogs is of particular health significance in Central Europe, as they can also be transmitted to humans (zoonosis). Regular deworming can significantly reduce the frequency of infection and thus the risk of infection for humans and dogs.

References

  1. Vanderkooi, M. (2000). Village Medical Manual (5th ed.). Pasadena: William Carey Library. ISBN   0878087788.
  2. Speare, R. (1989). "Identification of species of Strongyloides". In Grove, D. I. (ed.). Strongyloidiasis: a major roundworm infection of man. London: Taylor & Francis. pp. 11–83. ISBN   0850667321.
  3. Skerratt, L. F. (1995). "Strongyloides spearei n. sp. (Nematoda: Strongyloididae) from the common wombat Vombatus ursinus (Marsupialia: Vombatidae)". Systematic Parasitology. 32 (2): 81–89. doi:10.1007/BF00009506. S2CID   45308882.
  4. Bradbury, Richard S. (2021). "In New Guinea: Neglected, ignored and unexplored". Microbiology Australia. 42 (4): 169–172. doi: 10.1071/MA21048 . S2CID   243462184.
  5. Segarra-Newnham, M. (2007). "Manifestations, diagnosis, and treatment of Strongyloides stercoralis infection". Ann Pharmacother . 41 (12): 1992–2001. doi:10.1345/aph.1K302. PMID   17940124. S2CID   38184274.
  6. Johnston, F. H.; Morris, P. S.; Speare, R.; McCarthy, J.; Currie, B.; Ewald, D.; Page, W.; Dempsey, K. (2005). "Strongyloidiasis: A review of the evidence for Australian practitioners". The Australian Journal of Rural Health. 13 (4): 247–54. doi:10.1111/j.1440-1584.2005.00710.x. PMID   16048468.
  7. 1 2 Dorris, M.; Viney, M. E.; Blaxter, M. L. (2002). "Molecular phylogenetic analysis of the genus Strongyloides and related nematodes". International Journal for Parasitology. 32 (12): 1507–17. doi:10.1016/s0020-7519(02)00156-x. PMID   12392916.
  8. Olsen, A; Van Lieshout, L; Marti, H; Polderman, T; Polman, K; Steinmann, P; Stothard, R; Thybo, S; Verweij, J. J.; Magnussen, P (2009). "Strongyloidiasis—the most neglected of the neglected tropical diseases?" (PDF). Transactions of the Royal Society of Tropical Medicine and Hygiene. 103 (10): 967–72. doi:10.1016/j.trstmh.2009.02.013. PMID   19328508.
  9. Schär, F; Trostdorf, U; Giardina, F; Khieu, V; Muth, S; Marti, H; Vounatsou, P; Odermatt, P (2013). "Strongyloides stercoralis: Global Distribution and Risk Factors". PLOS Neglected Tropical Diseases. 7 (7): e2288. doi: 10.1371/journal.pntd.0002288 . PMC   3708837 . PMID   23875033.
  10. Laymanivong, S; Hangvanthong, B; Insisiengmay, B; Vanisaveth, V; Laxachack, P; Jongthawin, J; Sanpool, O; Thanchomnang, T; Sadaow, L; Phosuk, I; Rodpai, R; Maleewong, W; Intapan, P. M. (2016). "First molecular identification and report of genetic diversity of Strongyloides stercoralis, a current major soil-transmitted helminth in humans from Lao People's Democratic Republic". Parasitology Research. 115 (8): 2973–80. doi:10.1007/s00436-016-5052-z. PMID   27083185. S2CID   18567198.
  11. Bryant, Astra S.; Ruiz, Felicitas; Lee, Joon Ha; Hallem, Elissa A. (2022). "The neural basis of heat seeking in a human-infective parasitic worm". Current Biology. 32 (10): 2206–2221.e6. Bibcode:2022CBio...32E2206B. doi:10.1016/j.cub.2022.04.010. PMC   9158753 . PMID   35483361. S2CID   9158753.
  12. 1 2 3 Safer, D.; Brenes, M.; Dunipace, S.; Schad, G. (2007). "Urocanic acid is a major chemoattractant for the skin-penetrating parasitic nematode Strongyloides stercoralis". Proceedings of the National Academy of Sciences. 104 (5): 1627–30. Bibcode:2007PNAS..104.1627S. doi: 10.1073/pnas.0610193104 . PMC   1785286 . PMID   17234810.
  13. Kavanagh G, Crosby J, Norval M (1995). "Urocanic acid isomers in human skin: analysis of site variation". British Journal of Dermatology. 133 (5): 728–731. doi:10.1111/j.1365-2133.1995.tb02746.x. PMID   8555024.
  14. Nagayasu, Eiji; Thet Hnin Htwe Aung, Myo Pa Pa; Hortiwakul, Thanaporn; Hino, Akina; Tanaka, Teruhisa; Higashiarakawa, Miwa; Olia, Alex; Tomoyo, Taniguchi; Thu Win, Soe Moe; Ohashi, Isao; Odongo-Aginya, Emmanuel I.; Aye, Khin Myo; Mon, Mon; Win, Kyu Kyu; Ota, Kei; Torisu, Yukari; Panthuwong, Siripen; Kimura, Eisaku; Palacpac, Nirianne M.Q.; Kikuchi, Taisei; Hirata, Tetsuo; Torisu, Shidow; Hisaeda, Hajime; Horii, Toshihiro; Fujita, Jiro; Htike, Wah Win; Maruyama, Haruhiko (2017). "A possible origin population of pathogenic intestinal nematodes, Strongyloides stercoralis, unveiled by molecular phylogeny". Scientific Reports. 7 (1): 4844. Bibcode:2017NatSR...7.4844N. doi:10.1038/s41598-017-05049-x. PMC   5501853 . PMID   28687738.
  15. Jaleta, Tegegn G.; Zhou, Siyu; Bemm, Felix M.; Schär, Fabian; Khieu, Virak; Muth, Sinuon; Odermatt, Peter; Lok, James B.; Streit, Adrian (2017). "Different but overlapping populations of Strongyloides stercoralis in dogs and humans—Dogs as a possible source for zoonotic strongyloidiasis". PLOS Neglected Tropical Diseases. 11 (8): e0005752. doi: 10.1371/journal.pntd.0005752 . PMC   5565190 . PMID   28793306.
  16. Roberts, L.; Janovy, J. Jr. (2005). Foundations of Parasitology (7th ed.). Boston: McGraw Hill. p. 412. ISBN   0071112715.
  17. Thamwiwat, Alisa; Mejia, Rojelio; Nutman, Thomas B.; Bates, Jeffrey T. (6 July 2014). "Strongyloidiasis as a Cause of Chronic Diarrhea, Identified Using Next-Generation Strongyloides stercoralis-Specific Immunoassays". Current Tropical Medicine Reports. 1 (3): 145–147. doi: 10.1007/s40475-014-0026-7 .
  18. Roberts, L.; Janovy, J. Jr. (2005). Foundations of Parasitology (7th ed.). Boston: McGraw Hill. pp. 414–415. ISBN   0071112715.
  19. Igra-Siegman, Y; Kapila, R; Sen, P; Kaminski, ZC; Louria, DB (1981). "Syndrome of hyperinfection with Strongyloides stercoralis". Reviews of Infectious Diseases. 3 (3): 397–407. doi:10.1093/clinids/3.3.397. PMID   7025145.
  20. 1 2 Marcos, L. A.; Terashima, A.; Dupont, H. L.; Gotuzzo, E. (2008). "Strongyloides hyperinfection syndrome: An emerging global infectious disease". Transactions of the Royal Society of Tropical Medicine and Hygiene. 102 (4): 314–318. doi:10.1016/j.trstmh.2008.01.020. PMID   18321548.
  21. Newberry, AM; Williams, DN; Stauffer, WM; Boulware, DR; Hendel-Paterson, BR; Walker, PF (Nov 2005). "Strongyloides hyperinfection presenting as acute respiratory failure and gram-negative sepsis". Chest. 128 (5): 3681–4. doi:10.1378/chest.128.5.3681. PMC   1941746 . PMID   16304332.
  22. Roberts, L.; Janovy, J. Jr. (2005). Foundations of Parasitology (7th ed.). Boston: McGraw Hill. p. 415. ISBN   0071112715.
  23. Luvira, Viravarn; Watthanakulpanich, Dorn; Pittisuttithum, Punnee (2014-08-30). "Management of Strongyloides stercoralis: a puzzling parasite". International Health. 6 (4). Oxford University Press (OUP): 273–281. doi:10.1093/inthealth/ihu058. ISSN   1876-3413. PMID   25173343.
  24. Boulware, DR; Stauffer, WM; Hendel-Paterson, BR; Rocha, JL; Seet, RC; Summer, AP; Nield, LS; Supparatpinyo, K; Chaiwarith, R; Walker, PF (June 2007). "Maltreatment of Strongyloides infection: case series and worldwide physicians-in-training survey". The American Journal of Medicine. 120 (6): 545.e1–8. doi:10.1016/j.amjmed.2006.05.072. PMC   1950578 . PMID   17524758.
  25. PEARSON.RICHARD (2018-08-31). "Strongyloidiasis – Infectious Diseases". Merck Manuals Professional Edition. Retrieved 2018-09-03.
  26. Forbes, WM; Ashton, FT; Boston, R; Zhu, X; Schad, GA (2004). "Chemoattraction and chemorepulsion of Strongyloides stercoralis infective larvae on a sodium chloride gradient is mediated by amphidial neuron pairs ASE and ASH, respectively". Veterinary Parasitology. 120 (3): 189–98. doi:10.1016/j.vetpar.2004.01.005. PMID   15041094.