PARA Lecture 15 10/23/26

Pathogenesis

capacity to cause disease

Disease

alteration in normal cells, organs, or organismal activity

Subclinical infection

infection with no accompanying signs or symptoms

What three factors does likelihood of disease depend on

• Status of host defenses

• Number of parasites present

• Virulence of parasites

Threshold of disease

number of parasites required to cause detectable signs and symptoms in an infected individual

Does a more or less virulent parasite lead to disease

more

Does a more or less rapidly reproducing parasite lead to disease

more

What are three mechanisms pathogenicity can be caused by parasitic infections

• Vitamin deficiencies

• Tissue damage

• Host cell destruction

What can be a byproduct of parasite infection

parasite-induced pathology with no obvious adaptive value to parasite

Example of parasite-induced pathology with no obvious adaptive value to parasite

Southeast Asian liver fluke-

• adults inhabit bile ducts of mammalian definitive host

• chronic infections lead to cancer of bile duct

What causes the bile duct cancer caused by southeast asian liver flukes

• mechanical damage caused by parasite

• products released by co-infecting bacteria

• persistent production of cytokines and growth factors associated with inflammation and wound healing

Example of pathology being adaptive strategy for parasite

Yersinia pestis blocks digestive system of host oriental rat flea leading to repetitive bites as flea tries to feed increasing transmission of Y. pestis

Three examples things that cause pathology associated with parasitic infections

• Changes in cellular growth patterns

• Parasite-induced trauma to cells, tissues, and organs

• Toxins released by parasites

What can occur as parasites migrate, develop, feed, and/or reproduce

damage

Pork example of damage caused by reproduction

Taenia solium (pork tapeworm)-

• forms tissue cysts where damage and severity depends on location, number, and size of cysts

• CNS infection can lead to dizziness, seizures, headaches, vision problems, dementia, death

Human example of damage caused by reproduction

Echinococcus species-

• Location, size, and number of cysts impact disease

• Can be huge impacting surrounding tissues and breaking bones

What types of parasites can cause tissue trauma through larval migration

tapeworms and helminths

What is the tissue damage from larval migration caused by

parasite itself and host immune inflammatory responses

Tissue damage by plasmodium falciparum

• expression of PfEMP-1 by P. falciparum on surface of RBCs forming sticky knobs

• adhesion to endothelium of capillaries

• accumulation leads to severe tissue damage

What other host molecules can P. falciparum proteins expressed on surface of RBCs bind to

Other P. falciparum proteins expressed on surface of RBCs can bind to chondroitin sulfate A on placental tissue leading to increased inflammatory response, oxidative stress, and apoptosis as well as decreased heat shock protein expression

Example parasite where pathogenesis can be placed in multiple categories

Ascaris lumbricoides

What do ascaris lumbricoides larvae do to cause damage

migrating larvae lead to damage to intestinal epithelial cells

What do ascaris lumbricoides larvae do to lungs

respiratory distress when larvae penetrate capillaries in alveoli

What does ascaris lumbricoides do to block stuff

Heavy infection can block intestines, bile ducts, or pancreatic ducts

What does ascaris lumbricoides do with nutrients

Nutrient deficits caused by chronic infection

What does ascaris lumbricoides do to host immune response

Damage host immune response