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Bilharzia ^NEW^



Schistosomiasis, also known as bilharzia, is a disease caused by parasitic worms. Although the worms that cause schistosomiasis are not found in the United States, people are infected worldwide. In terms of impact this disease is second only to malaria as the most devastating parasitic disease. Schistosomiasis is considered one of the neglected tropical diseases (NTDs).The parasites that cause schistosomiasis live in certain types of freshwater snails. The infectious form of the parasite, known as cercariae, emerge from the snail into the water. You can become infected when your skin comes in contact with contaminated freshwater. Most human infections are caused by Schistosoma mansoni, S. haematobium, or S. japonicum.




bilharzia



Schistosomiasis, also known as bilharzia or snail fever, is an acute and chronic disease caused by parasitic flatworms called schistosomes or blood flukes. Most human infections are caused by Schistosoma mansoni, S. haematobium, or S. japonicum. The parasites spend part of their lifecycle in freshwater snails. The infectious, larval form emerges from the snail and contaminates water.


Sometimes referred to as bilharzias, bilharziasis, or snail fever, schistosomiasis was discovered by Theodore Bilharz, a German surgeon working in Cairo, who first identified the etiological agent Schistosoma hematobium in 1851. [6] A Schistosoma egg is seen below.


Most human schistosomiasis is caused by S haematobium, S mansoni, and S japonicum. Less prevalent species, such as S mekongi and S intercalatum, may also cause systemic human disease. Less importantly, other schistosomes with avian or mammalian primary hosts can cause severe dermatitis in humans (eg, swimmer's itch secondary to Trichobilharzia ocellata). (See Etiology.)


Schistosomiasis, or bilharzia, is a disease that is caused by parasitic worms. Infestation occurs when parasites that are released by certain types of freshwater snails come in contact with the skin or are ingested.


One of 10 so-called neglected tropical diseases, schistosomiasis (also known as bilharzia) is an illness that develops when people come into contact with water contaminated with disease-causing worms. These microscopic worms penetrate the skin without detection and move throughout the body causing severe sickness. Its root cause is poor sanitation, including the widespread practice of using lakes and rivers instead of toilets or latrines. Those same bodies of water are used for washing clothes and dishes, bathing and fishing, playing and more. This creates a harmful cycle of disease.


The paper considers a model for the transmission of bilharzia based on Macdonald's assumptions, in the light of data observed in the field. It is shown, in particular, that the threshold parameter governing whether or not an endemic cycle can be established is closely related to the proportion of infected snails in a community, and that this proportion is normally observed to be rather smaller than is compatible with the model. By considering more sophisticated models, allowing for the latent period of infection in the snails, and also for spatial and seasonal heterogeneity, the effective proportion of infected snails, from the point of view of Macdonald's model, is shown to be rather larger, and expressions are given whereby it can be evaluated from observable quantities. However, for the data from Malirong which are taken as illustration, it is also demonstrated that an even more plausible threshold value is obtained from a simple model incorporating human immunity in addition to the assumptions of Macdonald's model, and that, if this model were reasonable, human immunity would appear to be the most important factor in controlling the level of the disease in Malirong.


Schistosomiasis (bilharziasis) is an endemic parasitic disease of a major source of morbidity and mortality for developing countries. It is caused by different species of blood flukes (trematode worms) of the genus Schistosoma, the most important of which are S. haematobium which infests the genitourinary tract and S. mansoni and S. japonicum which infest the gastrointestinal tract. The incidence of schistosome-induced male infertility is not known and probably underestimated being overshadowed by the more severe and often fatal urinary and gastrointestinal complications. Several causes may contribute to schistosomiasis-induced male infertility, such as hormonal imbalance, testicular tissue damage and genital ductal system obstruction, in addition to decreased libido and erectile dysfunction due to associated hormonal imbalance and prostatic infestation. Demonstration of the schistosome ova in seminal plasma or testicular tissue confirms the diagnosis. Treatment of schistosomiasis-induced male infertility depends on clinical evaluation and includes, besides anthelmintic treatment, hormonal replacement and assisted reproduction (IVF/ICSI) in cases of severe oligozoospermia and or obstructive and nonobstructive azoospermia.


The fight against bilharzia, mainly through distribution of medicine (praziquantel) among affected communities, had largely ignored pregnant and breast-feeding women until 2002 when a World Health Organization team of experts recommended that treatment for bilharzia during pregnancy should be carried out. This recommendation has allowed women of childbearing age to be included in bilharzia control programmes. However, there is still limited information on the effects of bilharzia or its treatment during pregnancy on pregnant women and their offspring.


Maternal bilharzia or its treatment during pregnancy may have an influence on regulation of the body's immune responses to bilharzia worms. "This may have some effect on the progress of disease manifestations," says Dr. Robert Tweyongyere.


"Provision of clean water, which may indirectly reduce mothers accessing the lake, would have a direct impact in reducing bilharzia infection in the children," says Prof. Alison Elliott of LSHTM working with UVRI. The researchers further recommend inclusion of sanitation and hygiene to help break the cycle by preventing eggs in faeces from getting to the lake by encouraging the affected communities to use latrines properly.


(English pronunciations of bilharzia from the Cambridge Advanced Learner's Dictionary & Thesaurus and from the Cambridge Academic Content Dictionary, both sources Cambridge University Press)


As an African, Jim prefers a more informed approach to minimising the risk of bilharzia, based on an understanding of the ecology and supported by the evidence and the experience of South African bilharzia experts. He is also aware of the offence that may be inadvertently caused by foreigners behaving in an over-precious way, when local people have no choice but to draw water, wash and fish for food from a particular body of water, and may have to live with the consequences of infection, without access to serology tests.


Jim has grown up in Africa and explored many waterways in his native continent by canoe. He has swum in Lake Malawi/Lago Niassa on at least 200 occasions, in communities where he knows there is bilharzia, because his team has been treating it. He is, however, selective when and where he goes in the water, and he tests himself every time he comes home: he has never tested positive for schistosomiasis. He must be doing something right!


Schistosomiasis, also known as bilharzia or snail fever, is a parasitic disease caused by tiny blood-dwelling worms. Infection occurs when individuals, particularly children, come into contact with contaminated water.


NAIROBI, 23 January (IRIN) - Healthofficials have expressed concern over the high rates of bilharzia - a waterborneparasite that attacks the liver, lungs and eyes of humans - among childrenliving around the vital regional water resource of Lake Victoria.Scientifically known as schistosomiasis,after the schistosome parasites which cause the disease, bilharzia is contractedwhen blood flukes enter the body by way of contact with infested surfacewater, mainly among people engaged in agriculture and fishing.


Bilharzia is of concern throughout EastAfrica, especially among people living around bodies of water such as lakes,rivers, irrigation schemes and swamps, where the snails which spread thebilharzia-causing parasites [schistosomes] thrive, according to Joyce Onsongoof Kenya's communicable and vector disease control department.


"Children are especially vulnerableto bilharzia, because most of them walk barefooted and play in swampy waters,"she added. In many areas where it is prevalent, bilharzia infects a largeproportion of children, according to the WHO.


In countries where urinary bilharziais endemic, it causes a specific type of bladder cancer. In some areasof Africa, the incidence of bladder cancer linked with the disease is 32times higher than that of simple bladder cancer in the USA, according tothe WHO fact sheet on the disease.


The economic and health effects of bilharziashould not be underestimated, it says, citing retardation of the schoolperformance and growth patterns of infected children, although the effectsare (on average) 90 percent reversible with treatment. In Egypt and Sudan,the work capacity of rural inhabitants is severely reduced due to weaknessand lethargy caused by the disease, it adds.


The vector control division of the Ugandanhealth ministry in November 2001 indicated that between 31 and 67 percentof all school-going children along the waters of the River Nile and LakeVictoria were infected with bilharzia, the government-owned The New Visionnewspaper reported on 27 November. Another 43 to 79 percent suffered fromother worm infections, a major cause of school absenteeism, it added.


Some 3.5 million people in Uganda arereported to be at risk from bilharzia infection. The districts most affectedinclude Bundibugyo, Busia, Mpigi, Mukono, Hoima, Kibale, Iganga and Bugiri,according to health workers.


The WHO Kenya country head of diseaseprevention and control, Dr Dominic Mutie, told IRIN on Tuesday that tacklingbilharzia in Kenya would be costly, and needed interventions to be "designedvery well" in order to succeed. 041b061a72


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