Schistosoma haematobium
Encyclopedia
Schistosoma haematobium is an important digenetic
trematode, and is 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 plexus
es 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. Studies have shown the relationship between S. haematobium infection and the development of squamous cell carcinoma of the bladder.
. In order to avoid detection by the immune system inside the host, the adults have the ability to coat themselves with host antigen
s. 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 miracidiae which penetrate into the intermediate snail host (Bulinus
spp., e.g. B. globosus
, B. forskalii
, B. nyassanus
and B. truncatus
). Inside the snail, the miracidium sheds it epithelium
and develops into a mother sporocyst
. After two weeks the mother begins forming daughter sporocyst
s. 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 of a human host. Within half an hour the cercariae enter the host epithelium.
is effective in determining infection. Alternate diagnosis can be made by complement fixation tests.
; an immune response is necessary to prevent damage to hepatocyte
s. 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 divided into three phases: (1) the migratory phase lasting from penetration to maturity,(2) the acute phase which occurs when the schistosomes begin producing eggs, and (3) the chronic phase which occurs mainly in endemic areas.
s and multinucleated giant cells may be seen.
Digenea
Digenea is a subclass within the Platyhelminthes consisting of parasitic flatworms with a syncytial tegument and, usually, two suckers, one ventral and one oral. Adults are particularly common in the digestive tract, but occur throughout the organ systems of all classes of vertebrates...
trematode, and is found in the Middle East, India, Portugal and Africa. It is a major agent of schistosomiasis
Schistosomiasis
Schistosomiasis is a parasitic disease caused by several species of trematodes , a parasitic worm of the genus Schistosoma. Snails often act as an intermediary agent for the infectious diseases until a new human host is found...
; more specifically, it is associated with urinary schistosomiasis.
Adults are found in the Venous plexus
Venous plexus
A venous plexus is a congregation of multiple veins.Examples of venous plexuses are:* Vesical venous plexus* Vaginal venous plexus* Uterine venous plexus*Pterygoid plexus...
es around the urinary bladder
Urinary bladder
The urinary bladder is the organ that collects urine excreted by the kidneys before disposal by urination. A hollow muscular, and distensible organ, the bladder sits on the pelvic floor...
and the released eggs traverse the wall of the bladder causing haematuria and fibrosis of the bladder. The bladder becomes calcified
Calcification
Calcification is the process in which calcium salts build up in soft tissue, causing it to harden. Calcifications may be classified on whether there is mineral balance or not, and the location of the calcification.-Causes:...
, and there is increased pressure on ureters and kidneys otherwise known as hydronephrosis
Hydronephrosis
Hydronephrosis is distension and dilation of the renal pelvis calyces, usually caused by obstruction of the free flow of urine from the kidney, leading to progressive atrophy of the kidney...
. Inflammation of the genitals due to S. haematobium may contribute to the propagation of HIV. Studies have shown the relationship between S. haematobium infection and the development of squamous cell carcinoma of the bladder.
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 into adult flukesTrematoda
Trematoda is a class within the phylum Platyhelminthes that contains two groups of parasitic flatworms, commonly referred to as "flukes".-Taxonomy and biodiversity:...
. In order to avoid detection by the immune system inside the host, the adults have the ability to coat themselves with host antigen
Antigen
An antigen is a foreign molecule that, when introduced into the body, triggers the production of an antibody by the immune system. The immune system will then kill or neutralize the antigen that is recognized as a foreign and potentially harmful invader. These invaders can be molecules such as...
s. 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
Lumen (anatomy)
A lumen in biology is the inside space of a tubular structure, such as an artery or intestine...
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 miracidiae which penetrate into the intermediate snail host (Bulinus
Bulinus
Bulinus is a genus of small tropical freshwater snails, aquatic gastropod mollusks in the family Planorbidae, the ramshorn snails and their allies....
spp., e.g. B. globosus
Bulinus globosus
Bulinus globosus is a species of a tropical freshwater snail with a sinistral shell, an aquatic gastropod mollusk in the family Planorbidae, the ramshorn snails and their allies.- Further reading :* Cridland C. C....
, B. forskalii
Bulinus forskalii
Bulinus forskalii is a species of a tropical freshwater snail with a sinistral shell, an aquatic gastropod mollusk in the family Planorbidae, the ramshorn snails and their allies.- Distribution :...
, B. nyassanus
Bulinus nyassanus
Bulinus nyassanus is a species of small air-breathing freshwater snail with a sinistral shell, an aquatic pulmonate gastropod mollusk in the family Planorbidae, the ramshorn snails and their allies.This species is endemic to Malawi....
and B. truncatus
Bulinus truncatus
Bulinus truncatus is a species of air-breathing freshwater snail with a sinistral shell, an aquatic pulmonate gastropod mollusk in the family Planorbidae, the ram's horn snails.-Distribution:Distribution of Bulinus truncatus include:...
). Inside the snail, the miracidium sheds it epithelium
Epithelium
Epithelium is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. Epithelial tissues line the cavities and surfaces of structures throughout the body, and also form many glands. Functions of epithelial cells include secretion, selective...
and develops into a mother sporocyst
Sporocyst
Sporocyst is a common name of a lifecycle stage in two unrelated groups of species:*Apicomplexa parasites: see Apicomplexa lifecycle stages*Trematode flatworms: see Trematode lifecycle stages...
. After two weeks the mother begins forming daughter sporocyst
Sporocyst
Sporocyst is a common name of a lifecycle stage in two unrelated groups of species:*Apicomplexa parasites: see Apicomplexa lifecycle stages*Trematode flatworms: see Trematode lifecycle stages...
s. 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 of a human host. Within half an hour the cercariae enter the host epithelium.
Diagnosis
The majority of diagnoses are made 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 whealWheal
Wheal may refer to:*Wheal response, a cutaneous condition left by a blow or as part of an allergic reaction*Wheal, a Cornish mine...
is effective in determining infection. Alternate diagnosis can be made by complement fixation tests.
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.Immunopathology
The immune system responds to eggs in liver causing hypersensitivityHypersensitivity
Hypersensitivity refers to undesirable reactions produced by the normal immune system, including allergies and autoimmunity. These reactions may be damaging, uncomfortable, or occasionally fatal. Hypersensitivity reactions require a pre-sensitized state of the host. The four-group classification...
; an immune response is necessary to prevent damage to hepatocyte
Hepatocyte
A hepatocyte is a cell of the main tissue of the liver. Hepatocytes make up 70-80% of the liver's cytoplasmic mass.These cells are involved in:* Protein synthesis* Protein storage* Transformation of carbohydrates...
s. The hosts' antibodies which bind to the tegument
Tegument
Tegument may refer to:* Integumentary system* Tegument * Viral 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 divided into three phases: (1) the migratory phase lasting from penetration to maturity,(2) the acute phase which occurs when the schistosomes begin producing eggs, and (3) the chronic phase which occurs mainly in endemic areas.
Pathology
The ova are initially deposited in the muscularis propria which leads to ulceration of the overlaying tissue. Infections are characterized by pronounced acute inflammation, squamous metaplasia, blood and reactive epithelial changes. GranulomaGranuloma
Granuloma is a medical term for a tiny collection of immune cells known as macrophages. Granulomas form when the immune system attempts to wall off substances that it perceives as foreign but is unable to eliminate. Such substances include infectious organisms such as bacteria and fungi as well as...
s and multinucleated giant cells may be seen.