Helminthiasis, also known asworm infection, is anymacroparasitic disease of humans and other animals in which a part of the body is infected withparasiticworms, known ashelminths. There are numerous species of theseparasites, which are broadly classified intotapeworms,flukes, androundworms. They often live in thegastrointestinal tract of theirhosts, but they may also burrow into otherorgans, where they induce physiological damage.
Helminthiasis has been found to result in poor birth outcome, poor cognitive development, poor school and work performance, poor socioeconomic development, and poverty.[3][4] Chronic illness,malnutrition, andanemia are further examples of secondary effects.[5]
Soil-transmitted helminthiases are responsible for parasitic infections in as much as a quarter of the human population worldwide.[6] One well-known example of soil-transmitted helminthiases isascariasis.
Ascaris life cycle: Adult worms in the lumen of the small intestine (1). The female produces eggs (approximately 200,000 per day) that are excreted with the feces (2). Unfertilized eggs are harmless, but fertilized ones are infective after 18 days to several weeks (3). Infective eggs are ingested (4), enter the gut (5), develop into larvae in the intestine, and penetrate the blood vessel to enter lungs, where they develop further (6), after 10 to 14 days, penetrate the alveolar walls, ascend the bronchial tree to the throat, and are re-swallowed (7). Upon reaching the small intestine, they develop into adult worms (8). It takes 2 to 3 months for one complete cycle. Adult worms can live 1 to 2 years.Collage of various helminth eggs, from left to right:Trichosomoides egg,Ascaris lumbricoides with larva hatching, sample of adult roundworms,Hymenolepis nana,Schistosoma mansoni andToxocara canis with larva hatching
Of all the known helminth species, the most important helminths with respect to understanding their transmission pathways, their control, inactivation and enumeration in samples of human excreta from dried feces,faecal sludge,wastewater, andsewage sludge are:[7]
Example clinical photo: Guinea worm infection (dracunculiasis), worm coming out of the foot of an infected person.Ascaris infection: Antimesenteric splitting of the outer layers of the bowel wall due to a large amount of ascaris (South Africa)
The signs and symptoms of helminthiasis depend on a number of factors including: the site of the infestation within the body; the type of worm involved; the number of worms and their volume; the type ofdamage the infesting worms cause; and, the immunological response of the body. Where the burden of parasites in the body is light, there may be no symptoms.[citation needed]
In extreme cases ofintestinal infestation, the mass and volume of the worms may cause the outer layers of the intestinal wall, such as the muscular layer, to tear. This may lead toperitonitis,volvulus, andgangrene of the intestine.[9]
Micrograph of cut section of humanappendix showing a pin worm.
In humans,T helper cells andeosinophils respond to helminth infestation. It is well established that T helper 2 cells are the central players of protective immunity to helminths,[12] while the roles for B cells and antibodies are context-dependent.[13] Inflammation leads to encapsulation of egg deposits throughout the body. Helminths excrete into the intestine toxic substances after they feed. These substances then enter the circulatory and lymphatic systems of the host body.[citation needed]
Chronic immune responses to helminthiasis may lead to increased susceptibility toother infections such astuberculosis,HIV, andmalaria.[14][15][16] There is conflicting information about whether deworming reduces HIV progression and viral load and increasesCD4 counts inantiretroviral naive and experienced individuals, although the most recent Cochrane review found some evidence that this approach might have favorable effects.[17][18] Helminth infection also lowers the immune responses to vaccination for other diseases such asBCG,measles, andHepatitis B.[19]
Chronic helminthiasis may cause severemorbidity.[20] Helminthiasis has been found to result in poor birth outcome, poor cognitive development, poor school and work performance, decreased productivity, poor socioeconomic development, and poverty.[3][4][5]
Helminthiasis may cause chronic illness through malnutrition includingvitamin deficiencies,stunted growth,anemia, andprotein-energy malnutrition. Worms compete directly with their hosts for nutrients, but the magnitude of this effect is likely minimal as the nutritional requirements of worms is relatively small.[21][22][23] In pigs and humans,Ascaris has been linked tolactose intolerance andvitamin A,amino acid, and fatmalabsorption.[3] Impaired nutrient uptake may result from direct damage to the intestinal mucosal wall or from more subtle changes such as chemical imbalances and changes in gut flora.[24] Alternatively, the worms' release ofprotease inhibitors to defend against the body's digestive processes may impair the breakdown of other nutrients.[21][23] In addition, worm induced diarrhoea may shorten gut transit time, thus reducing absorption of nutrients.[3]
Malnutrition due to worms can give rise toanorexia.[22] A study of 459 children inZanzibar revealed spontaneous increases in appetite afterdeworming.[25] Anorexia might be a result of the body's immune response and the stress of combating infection.[23] Specifically, some of thecytokines released in the immune response to worm infestation have been linked to anorexia in animals.[21]
Helminths may causeiron-deficiency anemia. This is most severe in heavyhookworm infections, asNecator americanus andAncylostoma duodenale feed directly on the blood of their hosts. Although the daily consumption of an individual worm (0.02–0.07 ml and 0.14–0.26 ml respectively) is small, the collective consumption under heavy infection can be clinically significant.[3][23] Intestinalwhipworm may also cause anemia. Anemia has also been associated with reduced stamina for physical labor, a decline in the ability to learn new information, and apathy, irritability, and fatigue.[3] A study of the effect of deworming and iron supplementation in 47 students from theDemocratic Republic of the Congo found that the intervention improved cognitive function.[26] Another study found that in 159Jamaican schoolchildren, deworming led to better auditoryshort-term memory and scanning and retrieval oflong-term memory over a period of nine-weeks.[27]
Malnutrition due to helminths may affect cognitive function leading to low educational performance, decreased concentration and difficulty with abstract cognitive tasks. Iron deficiency in infants and preschoolers is associated with "lower scores ... on tests of mental and motor development ... [as well as] increased fearfulness, inattentiveness, and decreased social responsiveness".[21] Studies in the Philippines and Indonesia found a significant correlation between helminthiasis and decreased memory and fluency.[28][29] Large parasite burdens, particularly severe hookworm infections, are also associated withabsenteeism, under-enrollment, and attrition in school children.[21]
Helminths are transmitted to thefinal host in several ways. The most common infection is throughingestion of contaminated vegetables, drinking water, and raw or undercooked meat. Contaminated food may contain eggs of nematodes such asAscaris,Enterobius, andTrichuris; cestodes such asTaenia,Hymenolepis, andEchinococcus; and trematodes such asFasciola. Raw or undercooked meats are the major sources ofTaenia (pork, beef and venison),Trichinella (pork and bear),Diphyllobothrium (fish),Clonorchis (fish), andParagonimus (crustaceans). Schistosomes and nematodes such as hookworms (Ancylostoma andNecator) andStrongyloides can penetrate the skin directly.[20]
The roundworm,Dracunculus has a complex mode of transmission: it is acquired from drinking infested water or eating frogs and fish that contain (had eaten) infected crustaceans (copepods); and can also be transmitted from infected pets (cats and dogs).[30] Roundworms such asBrugia,Wuchereria andOnchocerca are directlytransmitted by mosquitoes.[31][32] In the developing world, the use of contaminated water is a major risk factor for infection.[33] Infection can also take place through the practice ofgeophagy, which is not uncommon in parts ofsub-Saharan Africa. Soil is eaten, for example, by children or pregnant women to counteract a real or perceived deficiency of minerals in their diet.[34]
Identification and quantification of helminth eggs at UNAM university in Mexico City, Mexico
Specific helminths can be identified throughmicroscopic examination of their eggs (ova) found in faecal samples. The number of eggs is measured in units ofeggs per gram.[35] However, it does not quantifymixed infections, and in practice, is inaccurate for quantifying the eggs of schistosomes and soil-transmitted helminths.[36] Sophisticated tests such asserological assays,antigen tests, andmolecular diagnosis are also available;[35][37] however, they are time-consuming, expensive and not always reliable.[38]
Disrupting the cycle of the worm will prevent infestation and re-infestation. Prevention of infection can largely be achieved by addressing the issues ofWASH—water,sanitation andhygiene.[39][40][41] The reduction ofopen defecation is particularly called for,[42][43] as is stopping the use ofhuman waste asfertilizer.[6]
Further preventive measures include adherence to appropriatefood hygiene, wearing of shoes, regulardeworming of pets, and the proper disposal of their feces.[3]
Scientists are also searching for a vaccine against helminths, such as ahookworm vaccine.[44]
Broad-spectrumbenzimidazoles (such asalbendazole andmebendazole) are the first line treatment of intestinalroundworm andtapeworm infections. Macrocyclic lactones (such asivermectin) are effective against adult and migrating larval stages of nematodes.Praziquantel is the drug of choice for schistosomiasis, taeniasis, and most types of food-borne trematodiases.Oxamniquine is also widely used in mass deworming programmes.Pyrantel is commonly used for veterinary nematodiasis.[45][46]Artemisinins and derivatives are proving to be candidates as drugs of choice for trematodiasis.[47]
Inregions where helminthiasis is common, mass deworming treatments may be performed, particularly among school-age children, who are a high-risk group.[48][49] Most of these initiatives are undertaken by theWorld Health Organization (WHO) with positive outcomes in many regions.[50][51] Deworming programs can improve school attendance by 25 percent.[52] Although deworming improves the health of an individual, outcomes frommass deworming campaigns, such as reduced deaths or increases in cognitive ability, nutritional benefits, physical growth, and performance, are uncertain or not apparent.[53][54][55][56]
Example ofascariasis (ascaris infection) - Difficult surgical procedure in South Africa on a gangrenous piece of bowel that had to be cut out; live ascaris worms are emerging.Piece of intestine, blocked by worms, surgically removed from a 3-year-old boy in South Africa.[57]
If complications of helminthiasis, such asintestinal obstruction occur, emergency surgery may be required.[9][57] Patients who require non-emergency surgery, for instance for removal of worms from thebiliary tree, can be pre-treated with the anthelmintic drug albendazole.[9]
Areas with the highest prevalence of helminthiasis aretropical andsubtropical areas including sub-Saharan Africa, central and east Asia, and the Americas.[citation needed]
Roundworm infections such aslymphatic filariasis, dracunculiasis, and onchocerciasis
Trematode infections, such as schistosomiasis, and food-borne trematodiases, including fascioliasis, clonorchiasis, opisthorchiasis, and paragonimiasis
Tapeworm infections such as cysticercosis, taeniasis, and echinococcosis
The soil-transmitted helminths (A. lumbricoides,T. trichiura,N. americanus,A. duodenale),schistosomes, andfilarial worms collectively infect more than a quarter of the human population worldwide at any one time, far surpassing HIV and malaria together.[35][37]Schistosomiasis is the second most prevalent parasitic disease of humans after malaria.[59]
In 2014–15, the WHO estimated that approximately 2 billion people were infected with soil-transmitted helminthiases,[6] 249 million with schistosomiasis,[60] 56 million people with food-borne trematodiasis,[61] 120 million with lymphatic filariasis,[62] 37 million people with onchocerciasis,[63] and 1 million people with echinococcosis.[64] Another source estimated a much higher figure of 3.5 billion infected with one or more soil-transmitted helminths.[65][66]
In 2014, only 148 people were reported to havedracunculiasis because of a successful eradication campaign for that particular helminth, which is easier to eradicate than other helminths as it is transmitted only by drinking contaminated water.[67]
Because of their high mobility and lower standards of hygiene, school-age children are particularly vulnerable to helminthiasis.[68] Most children from developing nations will have at least one infestation. Multi-species infections are very common.[69]
In a developing country like Bangladesh, the most common species are round worm (Ascaris lumbricoides), whipworm (Tricurias tricuras) and hookworm(Ancylostoma duodenalis).[71]
Even in areas of high prevalence, the frequency and severity of infection is not uniform within communities or families.[72] A small proportion of community members harbour the majority of worms, and this depends on age. The maximum worm burden is at five to ten years of age, declining rapidly thereafter.[73] Individual predisposition to helminthiasis for people with the same sanitation infrastructure and hygiene behavior is thought to result from differingimmunocompetence,nutritional status, andgenetic factors.[72] Because individuals are predisposed to a high or a low worm burden, the burden reacquired after successful treatment is proportional to that before treatment.[72]
It is estimated that intestinal nematode infections cause 5 milliondisability-adjusted life years (DALYS) to be lost, of which hookworm infections account for more than 3 million DALYS and ascaris infections more than 1 million.[74] There are also signs of progress: TheGlobal Burden of Disease Study published in 2015 estimates a 46 percent (59 percent when age standardised) reduction inyears lived with disability (YLD) for the 13-year time period from 1990 to 2013 for all intestinal/nematode infections, and even a 74 percent (80 percent when age standardised) reduction in YLD from ascariasis.[75]
As many as 135,000 die annually from soil transmitted helminthiasis.[3][37][76]
The 1990–2013Global Burden of Disease Study estimated 5,500 direct deaths from schistosomiasis,[77] while more than 200,000 people were estimated in 2013 to die annually from causes related to schistosomiasis.[78] Another 20 million have severe consequences from the disease.[79] It is the most deadly of the neglected tropical diseases.[80]
^abWHO (2012). "Research priorities for helminth infections".World Health Organization Technical Report Series.972 (972):xv–xvii,1–174, back cover.PMID23420950.
^Maya C, Torner-Morales FJ, Lucario ES, Hernández E, Jiménez B (October 2012). "Viability of six species of larval and non-larval helminth eggs for different conditions of temperature, pH and dryness".Water Research.46 (15):4770–82.Bibcode:2012WatRe..46.4770M.doi:10.1016/j.watres.2012.06.014.PMID22794801.
^abcMadiba TE, Hadley GP (February 1996). "Surgical management of worm volvulus".South African Journal of Surgery. Suid-Afrikaanse Tydskrif vir Chirurgie.34 (1):33–5, discussion 35–6.PMID8629187.
^Minciullo PL, Cascio A, David A, Pernice LM, Calapai G, Gangemi S (October 2012). "Anaphylaxis caused by helminths: review of the literature".European Review for Medical and Pharmacological Sciences.16 (11):1513–8.PMID23111963.
^John DT, William Jr AP (2006).Markell and Vogue's Medical Parasitology, 9th Edition. Saunders Elsevier Press.ISBN0-7216-4793-6.
^Cortés A, Muñoz-Antoli C, Esteban JG, Toledo R (September 2017). "Th2 and Th1 Responses: Clear and Hidden Sides of Immunity Against Intestinal Helminths".Trends in Parasitology.33 (9):678–693.doi:10.1016/j.pt.2017.05.004.PMID28566191.
^van Riet E, Hartgers FC, Yazdanbakhsh M (2007). "Chronic helminth infections induce immunomodulation: consequences and mechanisms".Immunobiology.212 (6):475–90.doi:10.1016/j.imbio.2007.03.009.PMID17544832.
^Mkhize-Kwitshana ZL, Mabaso MH (June 2012). "Status of medical parasitology in South Africa: new challenges and missed opportunities".Trends in Parasitology.28 (6):217–9.doi:10.1016/j.pt.2012.03.005.PMID22525798.
^abcdeLevinger B (1992).Nutrition, Health, and Learning: Current Issues and Trends(PDF). School Nutrition and Health Network Monograph Series, #1. Archived fromthe original(PDF) on July 18, 2011.Please note that this estimate is less current than the Watkins and Pollitt estimate, leading Levinger to underestimate the number infected.
^Pilotte N, Unnasch TR, Williams SA (October 2017). "The Current Status of Molecular Xenomonitoring for Lymphatic Filariasis and Onchocerciasis".Trends in Parasitology.33 (10):788–798.doi:10.1016/j.pt.2017.06.008.PMID28756911.
^Hunt PW, Lello J (May 2012). "How to make DNA count: DNA-based diagnostic tools in veterinary parasitology".Veterinary Parasitology.186 (1–2):101–8.doi:10.1016/j.vetpar.2011.11.055.PMID22169224.
^Bundy DA, Walson JL, Watkins KL (March 2013). "Worms, wisdom, and wealth: why deworming can make economic sense".Trends in Parasitology.29 (3):142–8.doi:10.1016/j.pt.2012.12.003.PMID23332661.
^abFincham, J., Dhansay, A. (2006).Worms in SA's children - MRC Policy Brief. Nutritional Intervention Research Unit of the South African Medical Research Council, South Africa
^WHO (2013).Schistosomiasis: progress report 2001 - 2011, strategic plan 2012 - 2020. WHO Press, World Health Organization, Geneva, Switzerland. pp. 1–270.hdl:10665/78074?mode=full.ISBN978-92-4-150317-4.
^"Malaria".Fact sheet N°94. WHO Media Centre. May 2015. Archived fromthe original on June 14, 2004. Retrieved7 February 2016.
^abcMagill AJ, Hill DR, Solomon T, Ryan ET (2013).Hunter's tropical medicine and emerging infectious diseases (9th ed.). New York: Saunders. p. 804.ISBN978-1-4160-4390-4.
^Magill A (2013).Hunter's tropical medicine and emerging infectious diseases (9th ed.). New York: Saunders. p. 804.ISBN978-1-4160-4390-4.
^abThétiot-Laurent SA, Boissier J, Robert A, Meunier B (July 2013). "Schistosomiasis chemotherapy".Angewandte Chemie.52 (31):7936–56.doi:10.1002/anie.201208390.PMID23813602.
^abcdefghijConnor R (March 2015)."Water for People Water for Life"(PDF).The United Nations world water development report 2015: water for a sustainable world. Barcelona, Spain: UNESCO publishing.
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