山东大学 医学院 病原生物学研究所 寄生虫学教研室 郭淑玲 . Schistosoma( 裂体吸虫 ). They belong to Genus Schistosoma, live in blood vessel and cause schistosomiasis. People call them blood flukes. There are four species infecting human body. They are:
病原生物学研究所 寄生虫学教研室 郭淑玲
They belong to Genus Schistosoma, live in blood vessel and cause schistosomiasis. People call them blood flukes. There are four species infecting human body. They are:
1. Schistosoma japonicum（日本血吸虫）is prevalent in Far East. In china, it is prevalent in Yangtze valley and south of Yangtze except Guizhou Province. The adults live in the portal vein system, causing liver cirrhosis（肝硬化）and portal vein hypertension syndrome（门脉高压征候群）.
2. Schistosoma mekongi (湄公血吸虫) is merely distributed in Mekong River Valley（澜沧江：青海，西藏，云南――湄公河：老挝，泰国，柬埔寨), resembles Schitosoma japonicum except intermediate host.
3. Schistosoma haematobium（埃及血吸虫）widely spreads in Africa, chiefly in Nile River valley. The adults live in the vesical and pelvic plexus causing painless terminal haemuresis, renal failure complicated by the ureter obstruction. In the endemic area infection is so common that haemuresis is accepted as a sign of manhood in young boy.
4. Schistosoma mansoni（曼氏血吸虫）is distributed in Africa and focal area in Latin America. Lives in the portal and hemorrhoidal vein plexus, causing stool with fresh blood, liver cirrhosis and portal vein hypertension.
Only Schistosoma japonicum is found in China. Schistosomiasis is one of the “five major parasitic diseases”. It is prevalent in 13 provinces, city and autonomic regions (except Guizhou ) along Yangtze River Valley and south of Yangtze where are main areas for producing rice.
1. Adult worms are elongated cylindrical in shape, unlike other flukes. Two sexes are separate, gray white in color, but the female is much dark and slender, the male is shorter and thicker, sickle-like. In human body the male usually embraces the female into its gynecophoral canal (抱雌沟), appears “ K ”like (or the female usually resides in male’s gynecophoral canal).
Male: 10-20 x 0.5-0.55mm in size, oral sucker at top near by ventral sucker. Just behind the ventral sucker there is a longitudinal groove-gyncophoral canal in which the female normally resides. The esophagus is divided into two branches in front of the ventral sucker, and then unite to form a cecum at the posterior third part of the body. Seven testes are situated one by one, each has a delicate efferens which combine to form the vas deferens and dilate to become a seminal vesical opening in the genital pore just behind ventral sucker.
Female: Longer and slender than the male, much dark colored thread-like, 12-26x 0.1-0.3mm in size. The digestive system is similar to that of male. The vitellaria are located in the posterior part of the body surrounding the cecum. The unbranched, oval ovary lies in the mid-portion of the body. The uterus lies in the anterior portion of the body filled with 50-300 eggs arranged in a single row, arising from ootype to genital pore behind the ventral sucker.
2. Mature egg is oval in shape, slight yellow in color, 89 x 67µ, shell is thin without an operculum but with a lateral spine. The content is a miracidium. Under the electron microscope there are many micro-tubules on the shell, through which the soluble egg antigen (SEA) secreted by a miracidium.
3. Cercaria is infective stage. It is composed of the body and forked tail (including tail stem and fork) and has 5 pairs of penetrating glands in the body.
oval in shape, slight yellow in color, 89 x 67 µ shell is thin without an operculum but with a lateral spine.
1. Site of inhabitation: the portal vein system, mainly in the inferior mesenteric vein.
2. Infective stage: cercaria
3. Infective route: by skin
4. Intermediate hosts: Oncomelania snail (钉螺)
5. Reservoir hosts: mammals such as buffalo, cattle, wild rodents, goat, monkey, pig, fox.
6. Eggs are main pathogenic factor: (They are inlaid in the liver and intestinal wall. Some of them are discharged in feces to complete its life cycle).
7. The development in human body requires 25-30 days. Cercaria can live 1-3 days. Life span of the adults is about 20-30 years.
*8. Blood fluke is a special kind of flukes because of following characters:
(1) The adult worms look like nematodes, elongated cylindrical in shape.
(2) Two sexes are separate.
(3) egg without operculum, but with a lateral spine.
(4) only one intermediate host required.
(5) The infective stage is cercaria.
(6) The infective route is by skin.
(7) The eggs are main pathogenic stage.
Liver Mesenteric vein Adults, ♂embosoms♀
3 weeks migrate to in the portal vein system
Lungs Liver cirrhosis Liver Eggs
Right heart IN HUMAN BODY intestinal
( adolescent ) in feces
cast off tail
Man and reservoir host Eggs get into water
contact with contaminated In WATER 20-30℃
water, cercariae 6 hours
penetrate the skin Miracidia hatch
escape from the snail Oncomelania snail
Carcariae Daughter sporocysts Mother sporocysts
1.pathogenic mechanism of blood fluke
SEA type IV allergy
Local tissues necrosis, proliferation and fibrosis
Liver cirrhosis stool with blood,
Pus and eggs
Spleen Portal vein hypertension syndrome
Immunity Anemia Collateral circulation
between portal vein and ascites, albumin,
secondary infection vena cava are established emaciation
Esophageal Umbilicus Hemorrhoid
varicosity varicosity varicosity
Hemorrhage of superior digestive tract
Die of hepatic coma, superior digestive
tract bleeding and infective complication
When human schistosome cercaria repeatedly penetrate the human skin, typeI allergy takes place. The cercarial dermatitis appears , petechiae(瘀点) and rashes ensue. The migration of the adolescents may induce localized pneumonitis and urticaria(荨麻疹).
(2) Due to adults:
The mechanical effect and toxic effect of adults and their metabolites cause mesenteric phlebitis, hepatitis, and abdominal pain; the immune complex may cause the damage to the kidney, schistosome nephritis results from typeIII allergy, the esinophile increase in peripheral blood.
The most serious damage is done by eggs. Colon and liver are most seriously involved.
1) In liver: Soluble egg antigen Eosinophils infiltration
Granuloma Eosinophilic abscess formation
Fibrosis Liver cirrhosis (pipestem fibrosis)
Portal vein hypertension ascites esophageal varicosity
varicosity varicosity surrounding
Soluble egg antigen Eosinophils infiltration
Granuloma Eosinophilic abscess
Ulceration Fibrosis or polyp
(1) Initial phase: It is characterized by fever, dry cough (pneumonitis), urticaria. These phenomena are due to adolescents migration.
*(2) Acute stage: The characteristics symptoms is dysentery. The patient may pass stool with blood, pus and mucus5-10 times per day, in which a large number of eggs can be found. Chill, fever, and malaise occur.
*(3) Chronic stage:Chief manifestation of the patients are interval diarrhea or dysentery.The patients experience fatigue, general condition and strength deteriorate, loss of weight and interest, retardation of both physical and mental growth in children. Spleen and liver enlargement, anemia, in women menopause, sterility and abortion may occur. This stage may last from several years to 20 years.
*(5) Terminal stage is characterized by portal vein hypertension syndrome, common saying, abdomen distention looks like a big drum, emaciation looks like a fire wood (腹大如鼓，骨瘦如柴). Ascites, emaciation, varicosity, splenomegaly and anemia are commonly found. The patients die of secondary infection, upper digestive tract bleeding, hepatic coma.
(6) Ectopic lesion: The damage to the central nervous system ( brain, spinal ) may cause paralysis (monoplegia, hemiplegia ).
abdomen distention looks like a big drum, emaciation looks like a fire wood. Ascites, emaciation, varicosity, and splenomegaly
abdomen distention looks like a big drum, emaciation looks like a fire wood.
The symptoms, signs and history of living in endemic areas only give a presumptive diagnosis. The definitive diagnosis depends on the pathogen examination.
1. Stool examination
(1) Direct fecal smear for acute stage
(2) Concentration method: Water sedimentation method and miracidia hatching test can be done at same time; nylon net method may be used.
2. Biopsy can be done by proctoscope for terminal stage.
3. Immunological tests are subsidiary for reference only.
**1. Epidemiological investigation: Investigate whether Oncomelania snail can exist in local natural environment; local residents are used to defecate, work and play in the same water; and examine the pathogen: Examine the feces from local residents and domestic animals; also can dissect the suspicious reservoir hosts, such as buffalo, goat, wild rodents and etc. If the source of infection, intermediate hosts, transmitting route and susceptible crowd exist at same time and local, an endemic area of schistosomiasis can be confirmed.
(1) Treat the patients, carriers and domestic animals. Drug of choice for man: Praziqantel is pretty effective, side effects is very light. The other effective drugs , such as hexachloroparaxylol, bithionol may be used.
(2) Kill the wild animals which may be infected.
(1) Health education is in progress, give up habits.
(2) Control and deal with night soil.
(3) Avoid directly contacting with the water contaminated by cercariae, lay up water in a container for 3 days, exposed to sun shine; put on protective clothes; apply some chemical repellent on the skin (dibutyl phthalate 邻苯二甲酸二丁酯 或灭蚴宁）
(4) Kill the intermediate hosts and wild reservoir hosts.
(5) Change the bad environment, realize modernization of agriculture.
1. Geographical distribution: The disease is prevalent in China, Japan, Philippines, Indonesia. In China, this disease is found in 13 province, city and autonomic region along the Yangtze River Valley and south of the Yangtze ( north from Jiangsu, Baoying county to south end Guangxi, Heng County ). In Taiwan, only animals, no humans are infected by S. japonicum.
2. Natural factors:
(1) Endemic areas along river, stream, canal, irrigation canal with grass and vegetation growth.
(2) The geographil distribution of schistosmiasis is limited by the existence of Oncomelania snails. They live in warm ( temperature always over 0℃ ) and rainy ( average rainfall over 750mm per year ) regions where grass and vegetation grow along canals, streams and rivers with slowly flowing water or pools and lakes.
(3) Source of infection include the patients, carriers and reservoir hosts. Rodents and buffaloes are especially dangerous sources of infection.
(2) Local economy and culture fall behind.
卫生部制定血吸虫病疫情应急处理预 案(全文) 卫生部办公厅14日发出通知，印发《血吸虫病重大疫情应急处理预案(试行)》，规定凡发生血吸虫病暴发流行和重大突发疫情，即启动该应急处理预案。 据2002年全国血吸虫病调查统计，中国现有血吸虫病病人81万，钉螺面积35.2亿平方米。目前血吸虫病在湖北、湖南、江西、安徽、江苏五省湖区及四川、云南两省部分山区流行较为严重。中新网2003年5月18日
血吸虫病回升 卫生部下发应急预案2003.08.23 09:59:43针对中国局部地区血吸虫病疫情明显回升的情况，卫生部日前要求，采取切实有效措施，尽快遏制血吸虫病快速上升的势头。 近年来，全国血吸虫病疫情出现反复，主要表现在：钉螺扩散明显，阳性螺分布范围扩大，人畜感染危险增加；病人数居高不下，局部传播严重，急性感染呈上升趋势；新疫区不断增加，部分已达标地区疫情严重回升，并逐步向城市蔓延。目前，湖南、湖北、江西、安徽、江苏、四川、云南7个省的110个县(市、区)尚未控制血吸虫病流行，现有血吸虫病病人81万，晚期血吸虫病人2.6万，病牛约6万头，钉螺面积35.2亿平方米，受血吸虫病威胁人口约6500万人。 人民日报报道说，为此，卫生部加强了对血吸虫病防治工作的检查督导，并于近期下发了《血吸虫病重大疫情应急处理预案(试行)》，对重疫区血吸虫病急性感染的疫情实行周报告和零报告。卫生部还将开展以下工作：一、在各级政府的领导下，卫生、农业、水利、林业等多部门密切配合，逐步完善“政府领导，部门配合、社会参与”的工作机制。二、加大血防工作经费投入。三、加大血吸虫病综合治理力度，压缩疫区范围。结合农村爱国卫生运动，加强改水改厕和粪水管理，改变钉螺孳生环境，切断传播途径。四、加强立法进程，实施依法管理。五、优化整合血防专业机构。六、加强血吸虫病科学研究，提高科学防治水平。 来源：新华网
1. Adult worm is flattened ribbon-like, without body cavity.
2. The body is composed of a head, neck and segmented strobilus(链体). The head has suckers, rostellum(顶突) and hooklets or sucking grooves. The neck is the budding zone from which segments are formed. The strobilus consists of immature, mature and pregnant proglottides.
3. They are hermaphroditic. There is a set of female and male reproductive organs in every mature proglottid.
4. Digestive tract is absent. Nutrition is absorbed by villi of body surface.
5.They are biohelminths. Intermediate hosts are indispensable.
7.The developing stages in intermediate hosts are called metacestode (中绦期), such as cysticercus(囊尾蚴), hydatid cyst(棘球蚴), cysticercoid(似囊尾蚴), procercoid(原尾蚴）, plerocercoid（裂头蚴）.
8. Tapeworms are classified into two orders:
Cyclophyllidea(圆叶目）: The head is spherical with suckers, hooklets. The uterus has no opening. One intermediate host is required. The eggs contain an oncosphere(六钩蚴). They are medically important, such as Taenia solium(链状带绦虫), Taenia saginata(肥胖) and Echinococcus granulosus(细粒棘球绦虫).
Pseudophyllidea（假叶目）: The head is with sucking grooves. The uterus has an opening. Two or more intermediate hosts are required. The eggs contain a coracidium（钩球蚴） and have to get into water to develop. Human being occasionally get infection. This worms include Spirometra mansoni（曼氏迭宫绦虫） and Diphyllobothrium latum（阔节裂头绦虫）.
See You Next Time