|Classification and external resources|
Helminthiasis // (alternatively spelled helminthosis; plural helminthiases) is any macroparasitic disease of humans and animals in which a part of the body is infected with parasitic worms, called helminths. These parasites are broadly classified into tapeworms, flukes, and roundworms. They often live in the gastrointestinal tract of their hosts, but may also burrow into other organs, where they induce physiological damages. They remain the major cause of wildlife diseases and economic crisis in livestock industry, and human socio-economic problems in developing countries.
Major helminthiases are among the neglected tropical diseases targeted under the joint action of the world's leading pharmaceutical companies and non-government organisations through an ambitious project called London Declaration on Neglected Tropical Diseases which was launched on 30 January 2012. It aims to control/eradicate the diseases by 2020, by ensuring necessary supply of drugs and other intervention, and promoting sanitation and health education.
The most serious helminth infections are prevalent in poor tropical and subtropical areas, where helminthiases are classified as neglected tropical diseases. They remain the most common parasitic infection of human in developing countries. Ascaris lumbricoides, Trichuris trichiura, Necator americanus, Ancylostoma duodenale, schistosomes and filarial worms collectively infect more than a billion people, rivalling HIV/AIDS and malaria. Schistosomiasis alone is the second most prevalent parasitic disease of all times in humans, next only to malaria.
According to current estimate, over a billion people in Subsaharan Africa, Asia and the Americas are infected at any moment with at least one helminth species; most of them leading to severe morbidity, accompanied by persistent poverty, decreased productivity, and poor socioeconomic development. Helminthiasis can have immunomodulatory effects on the host, with implications for any coinfecting pathogens. In fact, in endemic areas, malaria, HIV and tuberculosis are established to be exacerbated by helminthiases. In many cases, they can induce severe hypersensitivity reaction leading to chronic allergy called anaphylaxis.
Tapeworm infection (cestodiasis) 
- Echinococcosis (Echinococcus infection)
- Hymenolepiasis (Hymenolepis infection)
- Taeniasis/cysticercosis (Taenia infection)
Roundworm infection (nematodiasis) 
- Ancylostomiasis (Ancylostoma duodenale infection)
- Ascariasis (Ascaris infection)
- Filariasis (Wuchereria bancrofti, Brugia malayi infection)
- Onchocerciasis (Onchocerca volvulus infection)
- Soil-transmitted helminthiasis (infection of Ascaris lumbricoides, Trichuris trichiura, Necator americanus, Ancylostoma duodenale)
- Trichuriasis (whipworm infection)
- Trichostrongyliasis (Trichostrongylus spp. infection)
Trematode infection (trematodiasis) 
- Amphistomiasis (amphistomes infection)
- Clonorchiasis (Clonorchis sinensis infection)
- Fascioliasis (Fasciola infection)
- Fasciolopsiasis (Fasciolopsis buski infection)
- Opisthorchiasis (Opisthorchis infection)
- Schistosomiasis/bilharziasis (blood fluke infection)
Mode of Infection 
Helminths are transmitted to the final host in several ways. The most common infection is through ingestion of contaminated vegetables, drinking water and raw/undercooked meat. The infective form can be eggs (for most nematodes] or the immature larvae. Many species of helminths require invertebrate vectors, such as insects and snails, for effective transmission, hence, for their complete life cycle. Some larvae of trematodes (specifically the cercaria of schistosomes) can directly penetrate the skin when an individual is in direct contact with an infested water body.
Pathogenesis and Symptoms 
The most obvious pathogenic effects are direct damages on tissues resulting from the blockage of internal organs or from the immense pressure exerted by the growing parasites. As the most common target organs of infections are those of alimentary tract and sometimes, circulatory system, effects of infection are predominantly found in those organs and associated tissues. General symptoms are stomachache, fever, vomiting, diarrhoea, loss of appetite, haemorrhage, fatigue and listlessness. In human population, under chronic infections, such as those in schistosomiasis, extreme mobidity is the common symptom. A severe case of taeniasis can occur when the brain is infected by accidental ingestion of cysts, a clinical condition called neurocysticercosis, which is the leading cause of acquired epilepsy.
Indirect effects also associate with the disease. As pathogens, helminths induce immune reactions. Immune-mediated inflammatory changes occur in the skin, lung, liver, intestine, CNS, and eyes as they invade these tissues. Systemic changes such as eosinophilia, oedema, and joint pain reflect local allergic responses to parasites.
One of the major drawbacks in the control of helminthiases is the technical limitations of currently available diagnostic methods. Lack of standard clinical tests is encouraging widespread infestation and poses a hindrance to health managements. For basic diagnosis, specific helminths can be generally identified from the faeces, and their eggs microscopically examined and enumerated using fecal egg count method. This is generally useful for most species as each has unique feature, especially in veterinary investigations. However, there are certain limitations such as the inability to identify mixed infections, and on clinical practice, the technique is highly inaccurate and unreliable, such as those for schistosomes and soil-transmitted helmiths. Although the application of modern biotechnological tools to improve diagnostics for helminth infection has considerably advanced, the genuine uptake has not been practised. A range of diagnostic tools currently available is: 1) parasitological tests, where the parasite microscopically identified; 2) serological assays, where parasite-specific antibodies are detected in serum samples; 3) antigen tests, where a parasite biomarker is detected; 4) molecular diagnosis, where the parasite nucleic acid is detected; and 5) other specific tools for detection in the intermediate hosts. However, there are certain limitations such as the inability to identify mixed infections, and on clinical practice, the technique is highly inaccurate and unreliable, such as those for schistosomes and soil-transmitted helminths.
Prevention and Chemotherapy 
A large variety of chemotherapeutic drugs have been developed and commercialised. Yet all major helminthiases are classified under neglected diseases, with infestations rampant as ever. Large scale prevention and treatment remain a global crisis due to constraints on the application of theses otherwise effective drugs; one of which is drug resistance and the other is poverty, which facilitates progression of the parasite population. Of the most commercially available drugs, broad-spectrum benzimidazoles (such as albendazole and mebendazole) are recommended for treatment of roundworm and tapeworm infections; while macrocyclic lactones (such as levamisole) and ivermectin are prescribed for taeniasis; and praziquantel is the drug of choice for schistosomiasis, taeniasis and all types of food-borne trematodiases. In endemic regions, mass treatment is practiced, particularly among school-age children, who are the high risk group.
See also 
- London Declaration (30 January 2012). "London Declaration on Neglected Tropical Diseases". Retrieved 2013-03-26.
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- WHO (2013). Schistosomiasis: progress report 2001 - 2011, strategic plan 2012 - 2020. WHO Press, World Health Organization, Geneva, Switzerland. pp. 1–270. ISBN 9241503174 Check
- WHO (2012). "Research priorities for helminth infections". World Health Organization Technical Report Series 972: 1–174. PMID 23420950.
- van Riet E, Hartgers FC, Yazdanbakhsh M (2007). "Chronic helminth infections induce immunomodulation: consequences and mechanisms". Immunobiology 212 (6): 475–9. PMID 17544832.
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- Del Brutto OH (2012). "Neurocysticercosis: a review". The ScientificWorldJournal 2012: 159821. doi:10.1100/2012/159821. PMC PMC3261519. PMID 22312322.
- Krauth SJ, Coulibaly JT, Knopp S, Traoré M, N'Goran EK, Utzinger J (2012). "An in-depth analysis of a piece of shit: distribution of Schistosoma mansoni and hookworm eggs in human stool". PLoS Negl Trop Dis 6 (12): e1969. doi:10.1371/journal.pntd.0001969. PMC PMC3527364. PMID 23285307.
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- Humphries D, Nguyen S, Boakye D, Wilson M, Cappello M (2012). "The promise and pitfalls of mass drug administration to control intestinal helminth infections". Curr Opin Infect Dis 25 (5): 584–589. doi:10.1097/QCO.0b013e328357e4cf. PMID 22903231.
- WHO (2006). Preventive chemotherapy in human helminthiasis : coordinated use of anthelminthic drugs in control interventions : a manual for health professionals and programme managers. WHO Press, World Health Organization, Geneva, Switzerland. pp. 1–61. ISBN 9241547103.
- Prichard RK, Basáñez MG, Boatin BA, McCarthy JS, García HH, Yang GJ, Sripa B, Lustigman S (2012). "A research agenda for helminth diseases of humans: intervention for control and elimination". PLoS Negl Trop Dis 6 (4): e1549. doi:10.1371/journal.pntd.0001549. PMC PMC3335868. PMID 22545163.
- Information at WHO
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