MEKANISME INFEKSI

PARASITE

DEWI M. DARLAN

PARASITOLOGY DEPARTMENT

• Gastrointestinal route

• Introduced percutaneously• Introduced percutaneously

• Others

e.g.

• Nematodes: A. lumbricoides, T. trichiura, E. vermicularis

e.g.e.g.

• Cestodes: T. saginata, T. solium

• Intestinal protozoans: E. histolytica, G. lamblia, B. coli

• Toxoplasma gondii thru cat’s infected feces

: e.g.

• Trematodes: Fasciolidae, C. sinensis, O. viverrini

• Hookworms • Hookworms

(Ancylostomatidae) thru

filariform larvae

• Strongyloides stercoralis thru

filariform larva

• Schistosoma sp. thru cercaria

• Enterobius vermicularis

• Toxoplasma gondii

• Plasmodium sp.

• Trichomonas vaginalis

Transmission of the parasites

� Parasite can be transmitted thru vector or

intermediate host

� An intermediate host is one that is required for

parasite development but one in which the parasite development but one in which the

parasite does not reach sexual maturity,

though it remains alive and infective to

another host

� A vector is a host that transmits parasite to

human in active way

Transmission of the parasites

� Classification of vector:

• Mechanical vectors: the pathogens are

carried thru the surface appendages of body,

e.g.: legs, wings, scales, furls, etce.g.: legs, wings, scales, furls, etc

• Biological vectors: the pathogens undergo

developments and/ multiplication within the

vector

Transmission of the parasites

� Cockroaches

� Houseflies

�Propagative:• No developmental changes of pathogens

• Multiplication of pathogens

• E.g.: dengue virus in Aedes mosquitoes

�Cyclo-propagative:�Cyclo-propagative:• Pathogens undergo development & multiplication

• E.g.: malaria parasites in Anopheles mosquitoes

�Cyclo-developmental:oPathogens undergo developmental changes without multiplicatioN

oE.g.: filaria worm in mosquitoes

� Transovarian:• Pathogens transmitted to off-springs of the vector

• E.g.: scrub typhus, dengue virus in mosquitoes

� Exposure may not necessarily lead to disease state

� Parasite that is exposed to human may be

established. Though the person doesn’t develop

signs and symptoms, he is still infected, but in carrier

statestate

� Parasite exposed established infection

develop pathological changes, with or without signs

and symptoms disease state

� Parasite that is exposed may also be destroyed (not

established). Thus the person is not infected, and

will not develop disease

SOIL TRANSMITTED HELMINTHS

� STH is helminths (nematodes) that are

exposed to human thru their infective forms

in soil

� These nematodes include:

• A. lumbricoides• A. lumbricoides

• Ancylostomatidae (hookworms)

• T. trichiura

• S. stercoralis

• Toxocara sp. (zoonotic)

� Transmissions of A. lumbricoides, T.trichiura,

and Toxocara sp. are acquired by ingestion of

infective (embryonated) eggs from

contaminated soilcontaminated soil

� Ancylostomatidae and S. stercoralis require

skin penetration by filariform larvae

� Infection occurs when embryonated eggs of A. lumbricoides are swallowed with contaminated food and water

� Hatch in duodenum (L1) penetrate mucosa and submucosa enter lymphatics or venulessubmucosa enter lymphatics or venules

� Passing thru the right heart pulmonary circulation molt twice (10 days) become L3

� Move up the respiratory tree molt to L4 swallowed

� L4 juveniles are resistant to the acidity of gastric juice pass thru to intestine adults

� If Toxocara sp. gain entry to improper host

do not complete the migration

developmental arrest random wanderingdevelopmental arrest random wandering

thru various body organs and tissues

� T. trichiura after swallowed, infective juveniles

hatch and enter the large intestine mucosa.

After penetration, worms begin to grow and

the tunnel back toward the lumenthe tunnel back toward the lumen

� As the worm approach maturity, the

enlarging posterior portions breaks out the

epithelium and protrudes into the intestinal

lumen.

TAENIA SP.

� Gravid segment detach and either pass out with feces or migrate out of the anus

� As the segment begins to dry up, it becomes rupture allowing eggs to escaperupture allowing eggs to escape

� When eaten by suitable host, eggs hatch in the duodenum

� Hexacanths penetrate the mucosa intestinal venule carried out throughout the body enter muscle fiber cysticerci(2 months)

� When the infected beef meat eaten by a

person, the invaginated scolex of cysticerci

evaginate in response to bile salt

� The bladder is digested by the host, and � The bladder is digested by the host, and

budding of proglottid begins, and shedding

gravid proglottid within 2-12 weeks

� When the infected pork meat eaten by a

person, the invaginated scolex of cysticerci

evaginate in response to bile salt

� The bladder is digested by the host, and � The bladder is digested by the host, and

budding of proglottid begins, and shedding

gravid proglottid within 2-12 weeks

� Since human serve as intermediate host as

well, infection with eggs results in

development of cysticerci in man’s tissue