1. Parasites" harms on man
(1)Depriving the host of nourishment: example, hookworms suck blood.
(2)Mechanical effects of parasites on host tissues and organs: example, biliary ascariasis and larva migrans.
(3)Toxic effect: Arthropods introduce toxin into the host skin, inducing the host local and systemic reactions. Example, mosquitoes, spiders and ticks introduce venom when they insert their mouth parts into the skin.
(4)Immuno-pathological lesion: example, schistosoma liver cirrhosis; when hydatid fluid is released from the rupture of a hydatid cyst anaphylaxis often results. 2. Characteristics of Class Nematode
(1)Body is non-segmented, elongate, and circular in cross-section.
(2)Two sexes are separated. ♀is larger with a straight tail and a double set of reproductive organs. ♂is smaller with a curled tail and a single set of reproductive organs.
(3)Digestive tract (system) is complete.
(4)The body cavity is a protocoele(原体腔).
(5)Life cycle: infective stage is embryonated egg or larva3.
Egg→larva (several stages)→adolescent→adult
3. Factors favoring the ascarid spread
(1)Simple life cycle.
(2)Enormous egg production ( 240,000 eggs/ day/ female ).
(3)These eggs are highly resistant to ordinary disinfectants( due to the ascroside). The eggs may remain viable for several years.
(4)Social customs and living habits.
(5)Disposal of feces is unsuitable. 4. Enterobius vermicularis(pinworm)[An clinical case]
The major symptom is anal itch, which is associated with the noctural migration of the gravid females from the anus and deposition of eggs in the perianal folds of the skin.
Diagnosis: Cellophane tape technique is first choice.
The examination should be made in the morning, before the patient has washed the anus or defecated. Drugs: Albendazole or mebendazole are very effective.
Since life span of pinworm is about one mouth, the major problem is re-infection.
Repeated treatment may be necessary for a radical cure.
5. Life cycle of ascarid and whipworm
Ascaris lumbricoides
Trichuris trichiura Site of inhabitation Upper part of small intestine Ileocecum
Infective stage Embryonate eggs Embryonate eggs Route of infection By mouth By mouth Intermediate host No
No
Egg output 240000/♀/day 5000/♀/day Life span About 1 year About 3~5 years Feeding habits Intestinal contents Blood , Tissue fluid Migration
Yes
No
Others
Boring habits: going deep into the openings of other organs on the intestinal wall Parasitizing mode: the slender head goes deep into the intestinal mucosa 6. How do hookworms cause anemia
It results from hookworms sucking blood and excessive blood loss.
The excessive blood loss is due to the large worm burden; worms secreting several antiagglutinating materials (antiagglutinin, etc.), often changing the place to suck blood and discharging undigested blood; the old injured sites of the intestinal wall continuing to bleed.
The other reason for the anemia is that the patient can not get enough noutrition.
7. Factors favoring the hookworm spread
(1)simple life cycle.
(2)pollution of the soil by feces containing enormous hookworm eggs.
(3)warm and moisture climate is favorable for the development of hookworm eggs and larvae.
(4)human gets infection by skin contacting with the infective larvae in fertilized soil or on plants.
The hookworm incidence of farmers is the highest. 8. Life cycle of ascarid and hookworm
Ascaris lumbricoides
Hookworm
Site of inhabitation Upper part of small intestine Upper part of small intestine
Infective stage Embryonate eggs L3/ filariform larva Route of infection By mouth By skin Intermediate host No ( geohelminth ) No ( geohelminth )
Final host Human
Human
Egg output 240000/♀/day 10000~30000/Ad/day 5000~10000/Na/day Life span About 1 year Average 3 years Feeding habits Intestinal contents Blood Blood-lung Migration
Pass through the liver
In lungs of host, larvae
molt twice and stay in the lung for 10days
Don"t pass through the liver
the larvae don"t molt and stay in the lungs
9. Nocturnal periodicity and its clinical significance
The microfilariae present in the peripheral blood during daytime is very low in density. The number of microfilariae gradually increase from evening to midnight.
The phenomenon is called nocturnal periodicity.
In diagnosis of filariae, first choice method is thick blood smear, taking blood during the night from 10 pm to 2 am.
The confirmative diagnosis depends on the demonstration of the microfilariae in peripheral blood during the night from 10 pm to 2 am. 10. Common Features about Trematoda
(1)Most adult trematodes are dorso-ventral flattened, bilaterally symmetric, leaf-like or tongue-like covered with spines or tubercles.
(2)Armed with an oral sucker and a ventral sucker.
(3)The digestive tract is degenerate. The end of intestine is a cecum without anus.
(4)The reproductive system is developed and hermaphroditic.
(5)Eggs of most species have an operculum (lid) and /or a small spine (knob). The developed egg contains a miracidium.
(6)They are biohelminths. Eggs continue to develop in fresh water. Their intermediate hosts are in water. 1st intermediate hosts are all snails; 2nd intermediate hosts varies from species.
(7)Typical life cycle of the digenetic trematodes include sexual generation and asexual generation(Digenesis /Alternation of generations)
(8) Life cycle model:
sexual reproduction
get into fresh water
in the 1 st
int. host Adult
eggs
miracidiae
sporocysts
asexual reproduction
radiae
cercariae
metacercariae(the 2 nd
int. host)
(9)Infective stage is usually a metacercaria
(10)They have their reservoir hosts. The fluke diseases are zoonoses. 11. Epidemiological survey of Clonorchis sinensis
(1) int. hosts (snail, fish, shrimp)
(2) reservoir hosts
(3) discovery of patients and carriers
(4) habits of eating raw fish
(5) mode of raising fish
(6) mode of stool disposal 12. Why Schistosoma japonicum is a special fluke
(1)The adult worms look like nematodes, elongated cylindrical in shape.
(2)Two sexes are separate (dioecism).
(3)Egg without operculum, 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.
(8)Adults live in the blood vessels. 13. What"s the clinical manifestations of Schistosomiasis in acute stage and terminal stage
(1) Acute stage: The characteristics symptoms is dysentery. The patient may pass stool with blood, pus and mucus 5-10 times per day, in which a large number of eggs can be found. Chill, fever, and malaise occur.
(2)Terminal stage is characterized by portal vein hypertension
syndrome. (common saying, abdomen distention looks like a big drum, emaciation looks like a fire wood). Ascites, emaciation, varicosity, splenomegaly and anemia are commonly found. The patients die of secondary infection, upper digestive tract bleeding, hepatic coma. 14. Common features of Class Cestoda
(1)Adult worm is flattened ribbon-like, without body cavity.
(2)The body is composed of a head, neck and segmented strobile (链体). The head consists of attachment organs including suckers, rostellum (顶突) and hooklets or sucking grooves. The neck is the budding zone from which segments are formed. The strobile (a chain of segments) consists of immature, mature and pregnant proglottides.
(3)They are hermaphroditic. There is a set of female and male reproductive organs in every mature proglottides.
(4)Digestive tract is absent. Nutrition is absorbed by villi of body surface.
(5)They are biohelminths. Intermediate hosts are indispensable.
(6)All adult worms parasitize digestive tracts of mammals.
(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. 15. Transmission, diagnosis and treatment of Taenia solium
Transmission: by eating raw bean-pork
Diagnosis:(1)Taeniasis: Confirmative diagnosis of taeniasis is made by finding gravid proglottides or egg in stool. Looking for gravid proglottids in stool Looking for eggs in stool(direct fecal smear; brine floatation method)]
(2)Cysticercosis: Biopsy of subcutaneous nodules X-ray , Computerized tomography (CT) and magnetic resonance (MR) are used for the diagnosis of brain type.
○3 Ophthalmoscope examination is used for ocular form. Treatment:(1)Chinese herb medicine:pumpkin seed, areca nut and MgSO4.
(2)Praziquantel may be used. 16. Person who has taeniasis and the people around him are easier to have cysticercosis, why?
The principle of taeniasis treatment.
(1)The eggs of T. Solium can infect human and develop to cysticercus, causing cysticercosis.
But it can"t develop to adult.
People are infected by eggs through three pathways:endo-auto-infection
exo-auto-infection ○3 foreign infection
(2)Principles: Pork taeniasis should be diagnosed and treated as early as possible and treated thoroughly.
The recognition of a scolex in the patient"s stool after the application of taenifuge is important. 17. Which is more harmful to man between pork tapeworm and beef tapeworm? Why?
The lesion of T. Solium is more severe.
(1)T. Saginata only causes taeniasis; T. Solium causes taeniasis and three type of cysticercosis.(subcutaneous type, ocular type, brain type)
(2)Both of them parasite in the intestine, causing injure to mucosa of intestine.
But because of the rostellum and hooklets, T. Solium cause more severe injure to the mucosa. 18. Pathogenic mechanism of protozoa
(1)Damage by proliferation of protozoa.e.g.Plasmidium vivax
(2)Damage by of diffusion of protozoa.e.g.Entamoeba histolytica
(3)Damage by toxin.e.g.Entamoeba histolytica.
(4)Damage by opportunistic protozoa: The protozoan living in the human body in commensalisms make the host attack when his immunity is lower or restrained, such as Pneumocystis and Toxoplasma gondii. 19. What"s oppo...