Parasitology Exam 4

What des pathogenesis mean?

The capacity to cause disease

What does disease mean

alteration in normal cells, organs, or organismal activity

What does subclinical infection mean?

an infection with no accompanying signs or symptoms

What’re the three factors that effect likelihood of disease

• The status of host defenses

• The number of parasites present

• The virulence of those parasites

What is a threshold of disease?

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

• The threshold of disease varies depending on the virulence of the parasite

What’re the examples listed in class for how pathogenicity is caused by parasitic infections caused my variety mechanisms?

• Vitamin deficiencies

• Tissue damage

• Host cell destruction

Parasite induced pathology can be a [ ] of the Infection

Parasite induced pathology can be an unfortunate byproduct of the infection that is of no obvious adaptive value to the parasite

What is an example of a parasite that causes pathology as a byproduct?

Southeast Asian liver fluke

• Adults inhabit bule ducts of mammalian defensive host

• Chronic infections lead to cancer

What is an example of a parasite that causes pathology as an adaptive strategy?

Yersinia Pestis

• When it affects the rat flea, it blocks its digestive system, so that it’ll be super hungry and bite as many times as possible to try and feed

What’re the difference types of pathology causes by parasitic infections? (6)

1. Parasite-induced trauma to cells, tissues, and organs

2. Changes in cellular growth patterns

3. Interference with host nutrient acquisition

4. Toxins released by the parasite

5. The host immune response to infection

6. Disruption of the microbiome

Pathogenesis caused by a particular parasite can be placed in multiple categories

What is an example f a parasite that causes multiple types of pathology through infection ?

Intestinal Nematode

• Migrating larvae can damage intestinal epithelial cells

• Causes respiratory distress

• Lead to blockage of intestines

• Lead to inflammation

• Lead to nutrient deficits

What’re examples of parasites that cause direct trauma to host cells, tissues, and organs?

Damage occurs as the parasite moves, develops, and feeds. They can cause tissue trauma as larvae migrate through the host.

Tissue cysts by tapeworms

Taenia Solium (pork tapeworm)

• Causes formation of cysts; can create some within the CNS, which causes major problems

Echinococcus species

• Can cause HUGE impact on surrounding tissues and break bones

What is an example of tissue damage caused by Plasmodium falciparum

P. Falciparum express PfEMP- 1 on surface RBCs.

• These form sticky knobs which adhere to the endothelium of capillaries, where accumulation then leads to severe tissue damage.

How does entamoeba histolytica cause tissue damage?

Many people infected with the parasite remain asymptomatic.

• Some individuals develop amoebic dysentery

• Some may create ulcers, and continue to spread across membranes and other muscle/tissue.

• Invasive E. Histolytica enter the circulatory system.

What is a virulence factor?

Molecules produced by parasites, such as toxins and enzymes, that allow them to colonize a host, evade immune defenses, and cause disease

What virulence factors contribute to pathogenicity of virulent strains?

• overexpression of various digestive enzymes

• Over abundance of surface proteins (lectins) for binding host cells

• Activate of host cell apoptotic pathway

• Phagocytosis and trogocytosis of host cells

• Secretion of immunomodulatory proteins

What’re the different ways parasitic infections can alter host cell growth patterns

1. Hypertrophy

2. Hyperplasia

3. Metaplasia

What does hypertrophy mean?

An increase in the size of of an organ or tissue resulting from an enlargement of its component cells

What does hyperplasia mean?

An increase in cell number

• can be a normal response to a stimulus

• can be response to abnormal stimuli

What does metaplasia mean?

Cells of one type are replaced by cells of another type (usually reversible)

What’re well known examples of parasite induced hypertrophy

1. Leishmania donovani:

2. Trypanasoma Cruzi:

3. Merocystis kathae:

What are examples of parasite induced hyperplasia?

Liver fluke (Fasciola hepatica)

• Beneficial to the parasite

• Adults mature in bile duct, which lead to proliferation of duct epithelial cells, which flukes can feed on

Glochidia

• larval stages of certain freshwater bivalves. They can attach to gill filaments of host fish, which can provide benefits

What are examples of parasite induced metaplasia?

Trichinella spiralis

• Muscle fiber cells become nurse cells

• Adults inhabit cytoplasm of several adjacent mucosal epithelial cells. And the larvae proceed to travel through the circulatory system

• The penetration of muscle fiber cells can then change gene expression

What is parasite induced neoplasia

Cell growth patterns usually return to normal if the stimulus causing hyperplasia or metaplasia is removed; neuroplasia results if it does not happen

Abnormal proliferation of cells in response to an external stimulus that continues even after cessation of the stimulus.

What are examples of parasite induced neoplasia?

Opisthorichis viverrini

• can cause cancer of bile duct

• Release bacterial toxins

• Harbors H.Pylori in its gut

Spirocerca lupi

• Esophogeal worm

• larvae can penetrate dog stomach then get to esophagus

• can lead to esophogeal sarcoma

What are examples of parasites having adverse effect on host nutrition?

Parasites divert nutrients to themselves; intestinal helminths can lead to nutrient depletion and/or internal bleeding

Broad fish tapeworm

• Most humans are either asymptomatic or have mild symptoms

• Can cause a severe Vitamin B12 deficiency, needed for cell metabolism

What are the main takeaways from discussion paper 6?

1. Mature hairworms induce activity in infected crickets

2. Hairworm-induced activity is reversible

3. Infected crickets display positive phototactic behavior

4. Positive phototactic behavior may be distinct from water seeking behavior

How does Giardia Lamblia effect host nutrition?

• They adhere to host intestinal microvili, cause nutrient absorption issues

• Fat absorption compromised

• Appetite loss due to GI discomfort

• Induces intestinal cells to secrete chloride ions into intestinal lumen

• Increased lactose intolerance

How does plasmodium infection infect host?

Plasmodium infections can result in host iron deficiency, common in malaria infections

• Causes red blood cells lysis

• May also be result of competition between parasite strains

  • once parasitemia hit, replicating merozoites have strategy to prevent newly inoculated sporozoites from replicating in the liver. releases iron regulatory hormone hepcidin

    • iron conc in hepatocytes declines, inhibiting growth inside hepatocytes

What is a toxin

A poisonous or venomous substance produced naturally by a living organism.

• targets and adversely affect specific molecules, leading to direct interference with host processes

What’re the two types of fungal toxins and disease presented in class?

Oral and vaginal candidiasis

• Produces candidalysin as a byproduct of hyphae formation. Calcium ion influx into host cells, osmotic balance, and host cell lysis.

Parasite of rye grass

• Produces ergot toxin, if infected grains used to make bread, consumption of this toxin. Leads to vasoconstriction and mental disturbances.

What is hemozoin?

Hemozoin is produced as an insoluble waste of hemoglobin digestion by Plasmodium.

What’re the effects of hemozoin?

• When released by lysed RBCs, can be ingested by phagocytes. Inhibits respiratory bursts

• Forms complexes with other Plasmodium molecules and can bind toll like receptors leading to an inflammatory response due to upregulation of Il2 and TNF alpha

• Recent studies have demonstrated toxicity to cells of central nervous system

  • Uptake by neurons and astrocytes lead to apoptosis

What is an example of pathology from immune mediated damage to host cells and tissues?

A significant amount of pathology results from indirect effects of the host immune response- immunopathology

Onchocerca vulvulus

• Nematode that causes river blindness

• Live worms cause little inflammation, but when worms die, their endosymbiont bacteria are released

• As bacteria die, they release Wolbachia surface protein (WSP)

  • Acts as PAMP for TLR

  • Proinflammatory cytokine response

Why hasn’t natural selection eliminated harmful immune mediated responses?

Immunopathology and a successful immune defense demonstration that evolution results in compromise

• Hosts must have powerful array of defensive immunological weapons to combat array of parasite

• parasites must exploit their host to survive

What is a granuloma?

A tiny cluster of white blood cells and other tissue. It can be found in the lungs, skin or other parts of the body

• They form in response to infections, inflammation, irritants, or foreign objects.

Results from a delayed-type hypersensitivity response (DTH)

• A type of cell-mediated response initiated by an antigen. Delayed because the reaction occurs hours or days after exposure to the antigen.