Viral, Fungal, and Parasite Pathogenesis

Question 1

Infection does not always result in disease–subclinical infection is the rule for some viruses.

Where does the virus have to replicate in order to produce clinical symptoms?

Answer 1

In the host cells of the target organ

Question 2

What is the difference between localized infection and systemic/disseminated infection?

Which one has the longer incubation time?

Answer 2

Localized infections result from virus replication at the site of entry.

Systemic infection results from the virus traveling from the site of entry to the target organ.

Systemic infections have longer incubation periods because it takes time for the virus to travel tot he tarvel organ.

Question 3

What is the difference between acute viral disease and persistant/chronic viral disease?

Answer 3

Acute viral disease is characterized by the appearance of symptoms relatively shortly following viral infections (a couple days to a week). Like influenza or rabies (even though rabies has to travel)

Persistent or chornic viral disease has symptoms which appear months to years following infection (this is often when the virus hides in a non-target tissue and doesn’t move to the target tissue until much later) Like hepatitis B.

Question 4

What are some general aspects of viral pathogenicity?

How do they cause disease?

What aspects of the body’s defense contributes to disease?

Answer 4

They have no LPS or exotoxins.

Disease results form direct or indirect effects of virus replication in host cells. Viruses do not need to kill cells, but may merely alter cellular physiology (like viroporins).

Inflammation, tissue damage and delayed hypersensitivity reactions attribute to the disease

latency is common in some viruses.

Question 5

What are 5 examples of viral mode of dissemination? Gives virus examples.

Answer 5

1. Dissemination free in the plasma (poliovirus, HBV, and togaviruses)
2. Inside WBCs (measles, EBV, CMV, HSV, and HIV–these cause transient immunosuppression)
3. Inside RBCs (colorado tick fever)
4. Inside nerve fibers (rabies, HSV, VZV–this shields the virus from the immune system)
5. Direct spread (influenza within the respiratory tract or adenovirus from the respiratory tract to the GI tract)

Question 6

What does a virus require in a host cell?

Answer 6

The necessary receptors and host replication factors

Question 7

Where do the most prominent viral symptoms occur?

Answer 7

in the target organ

Question 8

What inclusion bodies are associated with the following:

rabies

CMV

HSV

Answer 8

rabis - negri bodies (intracytoplasmic)

CMV - owl’s eyes (intranuclear)

HSV - Cowdry’s type A (intranuclear)

They’re aggreagations of viral protein material

Question 9

What two viruses have toxins?

Answer 9

Adenovirus and rotavirus

Question 10

GI infections are always naked or enveloped viruses?

Answer 10

naked viruses–enveloped viruses can’t survive the pH

Question 11

What are some circumstances that affect whether or not a virus will cause a subclinical or clinical disease?

Answer 11

1. inoculum size
2. competence of immune system
3. health of host
4. genetic constitution of host
5. age and nutritional condition of host

Question 12

WHat is the only sure way to determine if someone has been infected with a virus?

Answer 12

check for antibodies.

disease is an insensitive indicator because many viruses like EBV and HPV cause subclinical infections

Question 13

What are the three categories of transmission?

Answer 13

Horizontal Transmission

(respiratory, intestinal, urogeital (STD), oropharynx (saliva), skin and skin glands (physical contact), blood (needles and arthropod bites)

Vertical transmission

(transplacental, perinatal (infected birth canal), postnatal (mild or direct contact), germline (many retroviruses)

Animals

(arthropod borne, vertebrates)

Question 14

What would give you viremia? A localized infection like influenza or a dissemiated infection like mumps or measles?

Answer 14

the disseminated infection. You would not be able to find influenza virus in the blood because it causes disease at its point of entry and does not spread beyond.

Question 15

Persistent infections can be persistent for 4 different reasons. WHat are they and give examples.

Answer 15

Persistent/Persistent: viruses persist in infectious form with continuous or intermittent shedding, such as HBV and EBV

Persistent/slow: long incubation time with no symptoms for months or years following infection, which may follow acute disease (like HIV and HTLV-1) or it may not follow acute disease (creutsfeld jakob)

Persistent/latent: virus persists in latent, non-infectious form (such as HXV, and VZV)

Persistant/Reactivation of persistent infections: in old age, pregnancy, leukemias, lymphomas, post transplant immunosuppression and HIV you can get reactivation of any persistent infection that remains in the body

Question 16

What are important examples of disseminated infections?

Answer 16

HepA (implant in alimantary, spreads in blood, targets liver, sheds in alimentary)

AIDS

Measles

Chickenpox

Herpes Simplex 1

Rabies

Hep B

Herpes SImplex 2

Question 17

What are the three branches of nonspecific resistance to viral infections?

Answer 17

1. innate immunity: anatomical and chemical barriers like skin and lactic acid
2. Cellular resistance (a lack of the virus’ receptor sites, non-permissive cells like small lymphs
3. Inflammation (creates an unfavorable viral replication condition for any virus)

Question 18

What do interferons do?

What prompts their release?

Answer 18

An interferon is the first host defense mechanism at the site of infection (unless the body already has IgG to the virus)

It’s a polyppetide cytokines produced by immune cells in response to viral infection and other stimuli like endotoxin or unusual RNA

WHen an infected cells releases these interferons, other nearby cells that are not infected cell will be induced to make it a harder environment for any virus to reproduce.

They do this by increases the synthesis of endonucleases to degrade viral mRNA.

THey also synthesize protein kinases to phosphorylate and inactivate EIF-2 to inhibit protein synthesis.

Question 19

What are three examples of specific resistance to viruses?

Answer 19

1. Human immunity–antiviral antibodies

(neutralization, cytolysis of viruse infected cells, opsonins to enhance phagocytosis)

2. Cell-mediated immunity - antiviral cells

(sensitized T cells to kill virus infected cells, NK cells to attack cells with viral glycoprotein on their surface, release perforin and toxins), and activated macrophages)

Question 20

Which are more important for cytolytic infections accompanied by viremia? Antibodies or interferons?

How about for non-cytolytic infections?

Answer 20

Antibodies and interferons are more important for cytolytic infections accompanied by viremia and infections of epithelial surfaces because the cells lyse and you need to have the antibodies neutralize the virions and the interferons to warn other cells.

For non-cytolytic infection, the virus doesn’t lyse the cell, it just makes it keep pumping out more virions. So in that case it’s better to destroy the viral infected cell. This is why cellular immune response is more important for these infections.

Question 21

What are two roles for antibody-antigen complexes in disease?

Answer 21

1. they play a role in maculopapular rashes like those seen in measles and rubella
2. They also play a role in tissue deposition, such as HBV deposits in the kidney. THis may initiate intravascular coagulation

Question 22

What are some viruses that cause immune suppression?

Answer 22

HIV

EBV

measles

CMV

VZV

Question 23

What are the 5 types of fungal infections (mycoses)?

Answer 23

1, Superficial–involve keratinized outer layers of nails, hair, and skin

2. Cutaneou - involve keratin containing epidermis and depper layers of nail, hair, and skin
3. Subcutaneous–involve dermis, subcutaneous tissue, muscle and fasci
4. Systemic - usually begin in the lungs but disseminate to other organs, particularly in immunocompromised individuals
5. opportunistic–occur in immune compromised patients

Question 24

Where do fungi usually live?

WHat do they require for growth?

How do they obtain nutrients?

Answer 24

They usually live in the soil or decaying organic matter.

They require preformed organic compounds for growth, which they obtain through the secretion of degrading enzymes like cullulase and protease.

Once the nutrients are soluble they transport them across their cell membranes.

Question 25

What do superficial and cutaneous mycoses use for nutrition?

Do they generate an immune response?

What are some examples?

What are the symptoms?

How are they transmitted (2)?

Answer 25

They use keratin as a source of nutrition.

THey don’t generate an immune reposnse

They cause cosmetic probems like athlete’s foot, ringworm, jock itch, etc.

They are characterized by itching and scaling skin problems which can become inflamed

Transmission usually from soil or infected skin scales from humans or animals

Question 26

What about subcutaneous mycoses?

How do they enter the body?

Can they be transmitted from human to human?

WHat are the 3 things they can typically cause?

Answer 26

Causative agent found in soil and decaying vegetation like thorns

THey enter the body through cuts or punctures

not really transmissible form human to human

They cause: granulomatous ulcers, warty nodules, or localized abscesses

Question 27

What are some characteristics of systemic mycoses?

What fungal form are most agents?

Why is a history very important in diagnosing these?

How do they enter the body usually?

What does the infection present as in healthy individuals?

Answer 27

Most agents are dimorphic fungi.

Taking a history is important because infections occur in defined geological areas where the organisms live in the soil

THey usually enter the body as airborne spores which germinate in the lung.

In healthy individuals infection is usually asymptomatic or mild pulmonary infection

Question 28

What are the two main mechanisms of antifungal agents?

Answer 28

1. target ergosterol (inhibit synthesis–Imidazoles) (bind to it to disrpt membrane-amphotericin B and nystatin)
2. Inhibit fungal glycan synthesis (echinocandins)

Question 29

What are the two different kinds of pathogenic parasites?

Answer 29

pathogenic protozoa

(ameba, flagellates, ciliates, and sporozoa)

pathogenic helminths

(hematodes, cestodes, and trematode)

Question 30

What can protoxoa form in unfaborable conditions?

Answer 30

cysts to ensure survival.

cysts also facilitate transmission from host to host

Question 31

FOr helminth infections, what form migrates to various tissues?

Do they multiply in the host?

Answer 31

larval forms migrate to various tissues.

They do not multiply in hosts typically.

Question 32

What type of immune response is directed to the parasite, egg or larval antigens?

Answer 32

Cell mediated immune responses including allergic reactions

the immune response definitely contributes to the disease

Question 33

How does one usually get nematodes?

cestodes?

Trematodes?

Answer 33

Nematodes are acquired by ingestion of eggs or through larva in the soil that penetrate the skin

Cestodes are from ingesting larval forms in raw or poorly cooked meat or fresh water fish

Trematodes are usually from ingesting freshwater fish, mollusks, or plants, but schistosomal certicaria penetrate the skin, srpread to circulation and move through the body to target tissues

Question 34

What are 6 examples of parasitic mechanisms for evading the host immune response?

Answer 34

1. antigenic variation
2. intracellular infection (hide in cells)
3. Encystation (
4. Camouflage
5. CLeavage of antibodies or compoement components
6. Suppression or redirection of the cellular immune repsonse