|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 known as 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 damage. They remain the major cause of wildlife diseases, economic crises in the 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-governmental organizations through an ambitious project called London Declaration on Neglected Tropical Diseases which was launched on 30 January 2012. It aims to control or eradicate the diseases by 2020, by ensuring necessary supply of drugs and other intervention, and promoting sanitation and health education.
- 1 Epidemiology
- 2 Diseases
- 3 Mode of infection
- 4 Pathogenesis and symptoms
- 5 Diagnosis
- 6 Prevention and chemotherapy
- 7 See also
- 8 References
- 9 External links
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 hypersensitivity leading to an acute allergy reaction called anaphylaxis.
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)
Tapeworm infection (cestodiasis)
- Echinococcosis (Echinococcus infection)
- Hymenolepiasis (Hymenolepis infection)
- Taeniasis/cysticercosis (Taenia 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)
- Moniliformis 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 or 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 morbidity 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, edema, 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 the fecal egg count method. This is generally useful for most species as each has unique features, 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 these 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 intestinal roundworm and tapeworm infections; while macrocyclic lactones (such as ivermectin) are effective against adult and migrating larval stages of nematode; and praziquantel is the drug of choice for schistosomiasis, taeniasis, and most types of food-borne trematodiases. In endemic regions, mass treatment is practiced, particularly among school-age children, who are the high-risk group.
- London Declaration (30 January 2012). "London Declaration on Neglected Tropical Diseases". Retrieved 2013-03-26.
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- Information at WHO
- London Declaration Uniting to Combat NTDs
- WHO Western Pacific Region
- Information at Right Diagnosis
- USAID's Neglected Tropical Diseases Program
- Deworm the World
- Global Network Neglected Tropical Diseases
- Travel health information
- Health Society of South Africa