Virus Pathogenesis

Process by which a virus infects a host resulting in the development of disease

Pathogenesis

The ability of a pathogen to infect a host and cause disease

Pathogenicity

The ability of a pathogen to invade and establish replication within a host

Infectivity (fitness)

The severity of disease exhibited by the infected host

Virulence

What is the pathogenecity equation?

Pathogenecity = infectivity x virulence

What are some factors of viral virulence?

Host and viral determinants of disease

Dose and route of exposure

Host species

Age of host

Immune status

Immune response

Environmental factors

How can the immune response exacerbate disease?

1) Cytokine storm

Sudden acute increase in circulating levels of pro-inflammatory cytokines and immune cell hyperactivation

2) Antibody-dependent enhancement

Local vs systemic infections

Local = remains in one part of body

Systemic = travels to rest of body

What is a popular way of achieving a systemic infection?

Viremia

Acute vs persistent infections

Acute = short clinical course, rapid elimination, increased production, highly contagious (canine parvo)

Persistent = Prolonged course, constant or intermittent shedding, immunosuppression

What are the 3 types of persistent infections?

1. Latent - persistence of virus in non-productive form → periodic re-emergence (herpesvirus)

2. Chronic - continued presence of virus following primary infection (Feline CoVs into FIP)

3. Slow - long incubation period, progressive clinical course, often fatal (lentiviruses)

What are 4 mechanisms of viral spread?

1. Local (epithelium) → neighboring cells

2. Lymphatic → via leukocytes

3. Viremia → free virus or cell-associated

4. Neural → to and from CNS

Mechanisms of viral injury → respiratory tract:

• What do they affect?

• What does it cause?

Affects: ciliary activity, mucous layer

Causes: cell destruction and inflammation; airway obstruction; respiratory distress; secondary infections

Mechanisms of viral injury → GI tract:

• Affects?

• Results?

Enterocyte destruction

Malabsorption

Osmotic effects = diarrhea

Mechanisms of viral injury → Skin:

• Affects?

• Causes?

Local infection = epithelium

Systemic infections = edema; hemorrhage; blisters; papillomas' hairless and nonpigmented areas

Mechanisms of viral injury → CNS:

• Causes?

Nerve and/or brain damage

Mechanisms of viral injury → Hematopoietic system:

• Causes?

Leukopenia (infect bone marrow)

Inflamation

Immunosuppression

Mechanisms of viral injury → repro system:

• Causes?

Viremia (placental infection)

Can transmit virus to fetus via placenta and cause it to replicate in fetus

Inflammation and fetal death (abortion)

• depends on stage of gestation

What causes viruses to become carcinogenic?

Oncogenes

Viruses can cause tumor production in what two ways? What kind of virus can use both ways?

1. v-onc genes are integrated in proviruses (rous sarcoma virus)

2. Causing overexpression or inappropriate expression of c-onc genes due to random integration of strong viral promoters (HPV)

Retroviruses uses both

What are the 7 ways viruses cause diease?

Viral injury to:

1. Resp. tract

2. Skin

3. GI tract

4. CNS

5. Hematopoeitic system

6. Repro. system

7. Cause cancer