Schistosoma haematobium
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| Schistosoma haematobium | ||||||||||||||
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| Schistosoma haematobium (Bilharz, 1852) |
Schistosoma haematobium is an important digenetic trematode, and found in the Middle East, India, Portugal and Africa.
It is a major agent of schistosomiasis; more specifically, it is associated with urinary schistosomiasis.
Adults are found in the Venous plexuses around the urinary bladder and the released eggs traverse the wall of the bladder causing haematuria and fibrosis of the bladder. The bladder becomes calcified, and there is increased pressure on ureters and kidneys otherwise known as hydronephrosis. Inflammation of the genitals due to S. haematobium may contribute to the propagation of HIV.[1] There are also studies being done into the relationship of S. haematobium infection to the development of bladder cancer.[2]
LIFE CYCLE
The free swimming infective larval cercariae burrow into human skin when it comes into contact with contaminated water. The cercariae enter the blood stream of the host where they travel to the liver to mature in to adult flukes. In order to avoid detection by the immune system inside the host, the adults have the ability to coast themselves with host antigens. [3] After a period of about three weeks the young flukes migrate to the bladder to copulate. The female fluke lays as many as 3,000 eggs per day eggs which migrate to the lumen of the urinary bladder and ureters. The eggs are eliminated from the host into the water supply with micturition. In fresh water, the eggs hatch forming free swimming miracardiae which penetrate into the intermediate snail host.[3] Inside the snail, the miracardium sheds it epithelium and develops into a mother sporocyst. After two weeks the mother begins forming daughter sporocysts. Four weeks after the initial penetration of the miracardium into the snail furcocercous cercariae begin to be released. The cercariae cycle from the top of the water to the bottom for three days in the search for a human host. Within half an hour the cercariae enter the host epithelium.[4]
DIAGNOSIS
The majority of diagnosis’ are done by examination of the urine for eggs. In chronic infections, or if eggs are difficult to find, an intradermal injection of schistosome antigen to form a wheal is effective in determining infection. Alternate diagnosis’ can be done by complement fixation tests.[3]
PREVENTION
The main cause of schistomiasis is the dumping of human waste into water supplies. Hygienic disposal of waste would be sufficient to eliminate the disease.[3]
IMMUNOPATHOLOGY
The immune system responds to eggs in liver causing hypersensitivity; an immune response is necessary to prevent damage to hepatocytes. The hosts' antibodies which bind to the tegument of the Schistosome don't bind for long since the tegument is shed every few hours. The schistosome can also take on host proteins. Schistomiasis can be devided into three phases: the migratory phase lasting from penetration to maturity, the acute phase which occurs when the schistosomes begin producing eggs, and the chronic phase which occrs mainly in endemic areas.[3]
TREATMENT
The drug of choice is praziquantel, a quinolone derivative.
[edit] References
- ^ Leutscher PD, Pedersen M, Raharisolo C, et al. (2005). "Increased prevalence of leukocytes and elevated cytokine levels in semen from Schistosoma haematobium-infected individuals". J Infect Dis 191 (10): 1639–47. doi:. PMID 15838790.
- ^ S.A. Sheweita, M. R. Abu El-Maat, F. G. El-Shahat, M. A. Bazeed (April 2001). "Changes in the expression of cytochrome P450 2E1 and the activity of carcinogen-metabolizing enzymes in Schistosoma haematobium-infected human bladder tissues". Toxicology 162 (1): 43–52. doi:.
- ^ Black, J. (2005). Microbiology: Principles and Explorations. Wiley, New York.
- ^ Roberts, L., Janovy, J. (1996). Foundations of Parasitology, 5th edition. Wm. C. Brown Publishers, Dubuque, Iowa.
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