Pathogenesis of Parasites Flashcards
What type of parasite lives on the host and causes infestations?
Ectoparasite
What kind of parasite lives in the host and causes infections?
Endoparasite
Types of hosts
Definitive
Intermediate
Incidental
What type of host harbors adult helminths or sexual stage protozoa?
Definitive host (human with pork tapeworm in intestine)
What type of host harbors larval helminths or asexual stage protozoa?
Intermediate host (mosquitoes, pig with tapeworm larva, human with pork tapeworm larva in brain)
What’s the deal with incidental hosts?
Unusual. Unnecessary for the maintenance of the parasite in nature.
Parasite-host specificity: how picky are they?
Specificity for particular definitive and intermediate hosts.
Often parasite life cycles can only be completed in a particular host.
Can we use animal models to study human parasites?
Nah. Parasite won’t thrive.
Common routes of parasite entry (6)
Ingestion Skin/mucosal penetration Transplacental (prenatal) Transmammary (milk) Arthropod bite (vector) Sexual contact
Virulence and pathogenesis depend on what factors?
Infective dose and exposure Penetration of anatomic barriers Attachment Cell/tissue damage Loss of nutrients Disruption, evasion, inactivation of host defenses
Infective dose and exposure factors of protozoa
Multiply in hosts. Severity of disease may increase as parasites reproduce.
Infective dose and exposure factors of helminths
Do not multiply in the definitive host! Worms will die over time unless host is re-exposed.
Severity of the disease is proportional to the initial amount of worms introduced into the host.
Penetration of anatomical barriers
Penetrating unbroken skin (Cercaria - causes schistosomiasis)
Methods of parasite attachment
Mechanical or biting mouthparts
Molecular interaction
Types of mechanical attachment (5)
Oral cavity (capsule) Attachment organs Suction disk Biting mouthparts Direct penetration (giggity)
Hookworm attachment
Ancylostoma tubaeform and caninum have 3 pairs of teeth in the buccal cavity. Attach to intestinal villi.
*0.2ml blood loss per worm per day
Tapeworm (Taenia) attachment
Scolex
Giardia intestinalis attachment
Attach to villi of small intestine
Molecular attachment targets and receptors (4 targets)
Fibroblast: fibronectin and its receptor (Trypanosoma cruzi)
Macrophage: MSP or GP63, and CR2. (Leishmania mexicana)
Erythrocytes: C3b receptor (Babesia)
Duodenal and jejunal epithelium: Lectin and mannose-6-phosphate adherence molecule1 on disk. (Giardia duodenalis)
3 methods of cell and tissue damage
Mechanical
Toxic products
Immunopathologic reactions
Blockage of internal organs, pressure atrophy, and migration through tissues are what type of tissue damage?
Mechanical
What parasite causes cysts in the liver (pressure atrophy)?
Echinococcus granulosus
What type of mechanical damage is caused by ascarids, tapeworms, schistosomes, and filrial worms?
Blockage of internal organs
What parasite migrates through tissues, causing pathology like Toxocariasis (zoonotic)?
Helminth larva
3 types of toxic products produced by parasites
Destructive enzymes - hookworms, schistosomes
Endotoxins - African trypanosomes, malaria
Toxic secretions - tick paralysis
Ways a parasite can cause loss of nutrients (3)
Competition with host - fish tapeworm
Interference with host absorption - giardia
Nutrient loss - hookworm (iron)
