Module 8 Flashcards

Common routes of virus entry into human host

• Respiratory

• GI
  genitourinary

• conjunctiva

• skin

Types of Viral Infections

1. Localized infection

2. Disseminated infection

3. Systemic infection

Localized infection

Replication at primary site of infection that spreads to adjacent cells

Disseminated infection

Virus breaches physical and immunological barriers and extends beyond primary site of infection → migrates through blood and capillaries

Systemic infection

Virus that affects many organs/systems

Virus Transmission: Aerosols

Droplets (ie. sneeze/cough, saliva) - Flu, Covid, Rhinovirus

Virus Transmission: Fecal-Oral

Diarrhea/Vomiting associated with gastroenteritis - often transmitted from contaminated food or water (ie. shellfish)

• rotavirus, norovirus, hepatitis A and E

Virus Transmission: Skin Lesions

virus replicates and releases within skin lesion

• Herpes

Virus Transmission: Blood

Viral exposure from contaminated blood, infected fluid, sexual activity, childbirth

• HIV, Hep B/C

Virus Transmission: Body Fluids

Semen

• HIV, CMV, Hep B

Breast Milk

• CMV

Urine

• Hantaviruses

Immunopathology

The study of the immune response's role in the pathogenesis of diseases

• often occurs when cytokine stimulate T cells that cause lesions of host tissue

Two major types of parasites that affect humans

1. Plasmodium

   • Causes Malaria - Th1

2. Leishmania

   • Causes Leishmaniasis - Th2

Mechanism of killing parasites

Normally:

• Parasite can be killed by macrophages or neutrophils

If parasite persists:

1. monocytes are recruited to the Leishmania lesion via CC-chemokine receptor 2

   • monocytes are great at killing Leishmania parasites

2. monocytes differentiate into dendritic cells, migrate to lymph nodes, and synth IL-12 to promote differentiation of TH1 cells

3. TH1 cells migrate to skin and eliminate parasites by inducing nitric oxide

Th1 Cells

• cell mediated T cells

• develop following infections by intracellular bacteria and some viruses

• stimulate cellular immune response (T cells) and activate macrophages

• Stimulate B cells to produce IgM and IgG

Th2 Cells

• humoral mediated (B cell)

• predominate in response to infestations by GI parasites, nematodes, and helminths

• stimulates humoral immune reponse = B cell proliferation

• induces antibody production (IL-4)

Mechanism of if a lesion will occur

1. Parasite enters the skin

   • complement system, innate immune sys, macrophages, leukocytes

2. If above fails to kill parasites:

   • monocytes differentiate into;

     • dendritic cells → stimulate production of Th1 and Th2

     • macrophages - M1 or M2

3. Th1 can stimulate production of M1 = killing of parasite

4. Th2 stimulates M2 production = immunopathology and lesion formation

5. Treg is a regulatory T cell that amplifies this response in lesion formation

Anergic Diffuse Cutaneous Leishmaniasis (ADCL)

A form of leishmaniasis characterized by widespread skin lesions

• occurs when Th2 cells are predominant over Th1 cells

Mucocutaneous Leishmaniasis (MCL)

Lesions characterized by a chronic and hyperactive inflammatory immune response

• predominant Th1 over Th2

• IFN-gamma and TNF stimulate Th1 and cytotoxic CD8+ for tissue destruction

Polarization of Th1 and Th2

Extreme levels of either Th1 or 2 causes severe disease

Types of Vaccines

1. Live attenuated or inactivated virus vaccine

2. Subunit vaccine

3. Recombinant virus vaccine

4. mRNA/DNA vaccine

Live attenuated or inactivated virus vaccine

• highly immunogenic

• reversion to virulence

• can be dangerous for immunosuppressed people

  • ex,, MMR, polio, yellow fever, chicken pox

Subunit vaccine

• safe

• poorly immunogenic → requires adjuvant

• can self assemble into virus-like particles

  • ex,, HepB, HPV, pertussis, meningicoccal, shingles, covid (novavax)

Recombinant virus vaccine

• strong cellular immune response

• pre-existing immunity to vector reduces vaccine efficacy

  • ex,, covid (astra zeneca), ebola, flu

mRNA /DNA vaccine

• easily produced

• high efficacy

• poor durability of immunity

  • ex,, covid (moderna, pfizer)

Three sites of vaccine activation

1. Muscle/skin

   • infiltration of pro-inflammatory cells

   • takes up antigen and adjuvant

   • migrates to lymph nodes for immune response

2. Lymph nodes

   • vaccine delivered directly to where immunity is generated

   • activates T and B cells

3. Blood

   • antibodies administered (humoral immunity) or effector T cells delivered (cell-mediated immunity)

Action of antibodies

Neutralizing: block pathogen binding/entry into host cells

Opsonization: mark pathogens for destruction by immune cells (phagocytosis, complement system)

Action of memory B cells

• rapidly produce antibodies

Effector and Memory T cells

• produce antiviral cytokines

• can directly kill infected cells

• can be circulating or tissue resident

Challenges in vaccine development

• Potency, quality, durability

• vulnerable populations

• vaccine stability

Reason for adjuvants

increase peak immune response and durability

Types of carrier adjuvants

• aluminum salts

• emulsions

• liposomes

Types of immunostimulatory adjuvants

• Natural organic extracts

• pathogen products

Steps of Vaccine testing

1. preclinical trials - animals and human tissue models

2. clinical trials

   • Phase I - Safety, dose range, side effects

   • Phase II - Immunogenicity, number of doses, side effects

   • Phase III - Random clinical trial, effectiveness, protection against disease, side effects

   • Phase IV - monitoring long-term effects and safety after approval

Cytomegalovirus (CMV)

is a dsDNA virus and member of herpesvirus family

• Symptoms: fever, sweats, tiredness, uneasiness, sore threat, joint/muscle pain, low appetite, weight loss, mouth ulcers

  • generally does not cause severe issue in healthy people

• At Risk: pregnant and immunocompromised

• Prevention: protected sex, not sharing personal items (toothbrush)

• Diagnosis: blood test

• Complications: vision loss, encephalitis, seizures, pneumonia,

• Treatment:

  • prophylaxis with (val)ganciclovir for 3-12 months after organ transplant

  • pre-emptive approach - viral load monitoring, treat with valganciclovir if viral load is detecable

  • treat with (val)ganciclovir if affected with CMV

(val)ganciclovir

Drug class: nucleoside analogue

Mechanism of action: stops viral DNA elongation

Use: against CMV, HSV, EBV, VZV, HBV

Prodrug: valganciclovir → becomes ganciclovir

Treatment: 900mg or 5 mg/kg 2x daily for 14-21 days

• prophylaxis 900mg or 5 mg/kg once daily

• drug should be adjusted based on renal clearance

DDIs: nephrotoxic

Adverse reactions: diarrhea, leukopenia, nausea, anemia, headache, cough, dyspnea, abdominal pain, lower appetite, kidney problem

Herpes Simplex Virus (HSV)

dsDNA virus and member of herpesvirus family

• Symptoms - ulcers around mouth and genitals

• Prevention - avoid contact with infected regions, no sharing personal items

• Diagnosis - PCR

• Complications - encephalitis (neonates), meningitis (adults)

• Treatments - acyclovir, valacyclovir, famciclovir

• DDIs - nephrotoxic and immunosuppressive drugs

• Adverse reactions - diarrhea, leukopenia, nausea, anemia, headache, cough, dyspnea, abdominal pain, lower appetite, kidney problem

(Val)aciclovir

Drug class: nucleoside analogue

Mechanism of action: stops DNA viral replication

Use: HSV, VZV

Prodrug: valaciclovir → aciclovir

Treatment: 400-800 mg oral or 5-10 mg/kg IV every 8 hr for 5-14 days

• Prophylaxis: 400-800mg oral 2x daily

Monitor clearance and adjust dose

Hepatitis B

circular partial-dsDNA virus - part of Hepdnavirus family

• 8 known genotype of HepB: A-H

• present in blood, tissue fluids, saliva, semen

• considered a non-curable disease

Label the parts of HBV

What part of HBV is tested for

HBsAG - serum testing from blood

• core antigen cannot be directly tested

Epidemiology of HBV

~1% of australian pop

>290 million ppl worldwide - migrants/refugees = 95% of cases

Concentration of HBV in body fluids

HIGH: blood, serum, exudate

MODERATE: semen, vaginal, saliva

LOW: urine, feces, sweat, tears, breast milk

Transmission HBV

• birth or childhood (most common)

• needles

• sexual contact

Chronic HepB can lead to

• Liver cirrhosis (30%), liver failure, hepatocellular carcinoma (53%), death

Treatment of HepB

1. Supportive care - provide fluids, diet, remove alcohol

2. Medicine - 3 dose vaccine series

3. Liver transplantation - last resort

4. Oral treatment - entecavir or tenofovir → well-tolerated but lasts for only one year

5. Subcutaneous injection - Peginterferon alpha-2a → lasts forever but has many adverse side effects

Phases of HBV infection

1. Immune tolerance

   • ALT (alanine aminotransferase - keep inflammatory enzyme in liver) = low

   • HBV DNA = high

   • HBeAg = positive

2. Immune Clearance

   • ALT fluctuates

   • HBV DNA fluctuates opposite to ALT

3. Immune Control

   • Low ALT

   • Low HBV DNA

   • HBeAg = positive

   • Low viraemia

4. Immune escape

   • can become viraemic at times

Possible Outcomes in HBV infection

Clinical Illness: <5yrs = <10%, >5yrs = 30-50%

Acute case fatality rate: 0.5-1%

Chronic infection rate: <5yrs = 30-90%, >5yrs 2-10%

Premature mortality from liver disease: 15-25%

Interpretations of HBV serology

Hep B surface antigen (HBsAg)

Presence: HBsAg is present during acute and chronic HepB

• is a protein on the surface of HepB

• can be detected in blood during active infection

• is earliest marker of infection

Hepatitis B core Antigen (HBcAg)

Present during acute phase of HepB infection - not typically detectable during chronic infection

• is an internal antigen of HepB virus

• not directly detectable during acute phase

  • detected by measuring HepB core antibodies

Hepatitis B surface Antibody (HBsAb)

present after recovery from acute HepB infection or after vaccination

• antibody produced by immune system in respone to HepB surface antigen

Hepatitis B e Antigen (HBeAg)

typically present during acute and early chronic phases of HepB infection

• indicates active viral replication and high likelihood of transmission

• cannot be detected bc antigen is not on surface

Hepatitis B core Antibody (HBcAB)

appears during acute phase of HepB infection and persists during chronic infection

• detectable in blood and is a marker of prior HepB exposure

Hepatitis C virus (HCV)

enveloped positive-strand RNA virus - part of hepacivirus genus of flaviviridae family

• curable disease but no vaccine exists

• 7 major genotypes (1-7)

• rapid replication bc RNA polymerase does not require proof-reading

• weakens T cell response

Pathogenesis of HCV

Liver injury is caused by the virus suppressing the immune response (NOT the virus attacking hepatocytes itself) - via release of cytokines and chemokines that lead to inflammation and fibrosis of liver

Symptoms of HCV

loss of appetite, fatigue, nausea, rash, pain, fever, jaundice, mood swings, liver damage

Transmission of HCV

• oral exposure

• needles

• blood transfusions

• mother-child

Diagnosis of HCV

Serology and PCR testing for viral RNA

• PCR ensures no false positive bc antibodies exists even when infection resolves

Clinical features of HCV

• incubation period: 6-7 wks

• Acute infection illness = <20%

• Acute infection fatality = very low

• Chronic infection = 60-90%

• Cirrhosis = 5-20%

• Mortality from chronic infection = 3%

Acute HepC infection

• Serum HCV RNA detectable around 3 months post infection

  • 50-70% antibodies detectable right at symptoms

  • 90% detectable after 3 months

• can be severe, but rarely liver failure

• symptoms uncommon

Chronic HepC infection

Leads to:

• liver cirrhosis

• liver failure

• hepatocellular carcinoma death

~30% of HCV resolves on its own (better chances: younger, female, genetics [IL-28B polymorphism])

~70% of HCV becomes chronic

Treatment of HCV

goal =

• achieve sustained virological response (no virus detected)

• prevent/delay cirrhosis and hepatocellular carcinoma

• improve outcomes of liver transplant

Treatment:

• antivirals

• protease inhibitors

• polymerase inhibitors

=works in 95% of patients

Testing for Cirrhosis

1. Blood test, APRI score, and hepascore

2. Liver biopsy

3. Transient elastography

   • mechanical pulse that assesses fibrosis

Liver Biopsy F scores

F1: portal fibrosis

F2: portal fibrosis with few septa

F3: Septal Fibrosis

F4: Cirrhosis

Pattern of acute HCV

Pattern of Acute → Chronic HCV

Hepatitis D virus

defective single-stranded RNA virus

• requires HBV infection to form envelope made of HBsAg

• only ppl with HBV can get HDV

• no vaccine

Modes of HDV Transmission

• injections

• sexual contact

Prevention of HDV (and associated HBV)

Coinfection (getting HBV and HDV at the same time): treat HBV with vaccine to prevent onset of HDV

Superinfection (getting HDV after chronic HBV): no specific vaccine exists - educate patient on risk prevention

Human Immunodeficiency Virus (HIV)

retrovirus (in lentivirus group) containing single stranded RNA

• integrates in host cell genome = permanent

• infects CD4+ T cells (mainly), macrophages, monocytes

Quiescent T cells

Form reservoirs for HIV but not actually producing HIV - can be activated to produce lots of HIV

Features of HIV

• RNA (for replication)

• Reverse transcriptase (RNA → DNA)

• Integrase (viral integration into host genome)

• Protease (new virus formation)

Types of HIV

HIV1 and HIV2

• HIV1 is responsible for most global infections - most common cause of AIDS

• HIV2 is mostly confined to west africa

High risk groups for HIV

• female sex workers

• men who have sex with men

• injections

• truckers

• migrant labourers

Transmission of HIV

1. sexual contact

2. mother-child

3. contact with infected blood

Preventing HIV

If HIV-negative: use HIV pre-exposure prophylaxis (PrEP) prior to exposure

If HIV-positive: HIV treatment to achieve undetectable viral load

• involves combo of 3-4 antiretroviral (ARV) drugs

Label the HIV virus

Important structures of HIV virus

Reverse transcriptase (p64): converts RNA to DNA

Integrase (p32): integration of virus into host genome

Protease (p10): cleaves viral proteins to make viruses viable

GP120,41 (glycoprotein): helps the virus attach to host cells

HP41 (glycoprotein): for entry in host cell

Lipid Bilayer: increases vulnerability of human cell to HIV - bc lipid bilayer matches that of human cells

P24 (protein): capsule protein — is first to show up in antigen testing

HIV Life cycle

1. HIV fuses into the phospholipid bilayer of a normal cell

   • GP120 and GP41 attach to CR5 receptors on the human cell

     • people w/o this receptor are resistant to HIV this way

2. Inside cell, reverse transcriptase converts HIV RNA into dsDNA

3. Virus integrates with cell, DNA is duplicated and becomes prominent DNA of host cell

4. Once new DNA is established, HIV buds from cell to find new host cell to infect

When does HIV integration occur after infection?

72 hours - HIV is preventable if treated before this

Pathogenesis of HIV Infection

1. Dendritic cells at HIV entry site capture virus

2. migrates virus to lymph nodes and delivers them to CD4+ T cells

3. Virus replicates in lymph node and enters blood = viremia

4. Triggers adaptive immune system

5. Antibodies try to control replication - HIV replicates slowly but this leads to progressive loss of T cells

6. Virus destroys lymphoid tissue and deplete CD4+ T cells = host susceptible to other pathogens

Course of untreated HIV infection

CD4+ T cell Count

Viral Load

Phases of HIV

1. Acute Phase (rise in HIV viral load, decrease in CD4+ T cells)

2. Chronic Phase (clinical latency)

3. Final Phase (AIDS)

4. Death

First 2 weeks of HIV

Decline in CD4 and rapid rise in viral load

• Symptoms

  • rash, fever, chills headache, sore throat

  • fatigue

  • swollen lymph nodes

  • sweats

  • loss of appetite

  • muscle aches

  • diarrhea

  • ulcers

6-9 Months into HIV infection

Stable viral load (patient is usually asymptomatic)

Gradual decline in CD4 count, gradual increase in Viral Load

Opportunistic infections occur due to weakened immune sys. (CD4 <200 cells/ul)

• Candida, CMV, etc.

10-12 Years into HIV infection

Untreated patients die from opportunistic infections

Virus vs. Retrovirus

Difference in replication pattern

• most viruses replicate using their own DNA/RNA

• retroviruses convert their RNA into DNA before entering host and then integrate into host cell genome

• Retroviruses are usually permanent — viruses can eventually be cleared by host immune sys after acute infection

Potential Opportunistic Infections: CD4 <200 cells/ul

• Candidiasis

• Oral Hairy Leukoplakia

• Pneumocystis jirovecii pneumonia (PJP)

• Toxoplasmosis

Potential Opportunistic Infections: CD4 <100 cells/ul

• Cryptococcosis

• Cryptosporidiosis

Potential Opportunistic Infections: CD4 <50 cells/ul

• Mycobacterium avium complex (MAC)

• Cytomegalovirus

• Microsporidiosis

• Cerebral Lymphoma

Potential Opportunistic Infections: Any CD4 count

• Kaposi’s sarcoma

• Progressive Multifocal Leukoencephalopathy (PML)

Potential Opportunistic Infections: Exotic and Rare

• Multicentric Castleman’s Disease

• Penicilliosis

• Histoplasmosis

• Bartonellosis

• Rhodococcus

Skin and Oral Conditions by CD4 count: >500 cells/ul

• seroconversion rash

• seborrheic dermatitis

• psoriasis

• tinea

• anychomycosis

Skin and Oral Conditions by CD4 count: 200-500 cells/ul

• oral candidiasis

• OHL

• herpes zoster

• herpes simplex

• psoriasis

• warts

• aychomycosis

• xerosis

Skin and Oral Conditions by CD4 count: <200 cells/ul

• Disseminated HSV

• folliculitis

• molluscum contagiosum

• kaposi sarcoma

• penicilliosis

• bacillary angiomatosis

• CMV

• ulcers

• scabies

Kaposi Sarcoma (KS)

AIDS defining virus

• caused by herpesvirus-8 (HHV8) when HIV destroys immune sys

formation of tumors in endothelium characterized by abnormal angiogenesis, inflammation and proliferation

• causes skin lesions (macules, papules, nodules, plaque) — pink, purple, or brown

HIV diagnostic test

Screening test

• ELISA

• detects all infected individuals and true negatives (no infection)

Confirmation test

• higher specificity

• Western Blot

• identify true positives and false positives from ELISA

Goals of Antiretroviral Therapy

1. Virology control

2. Immunological recovery

3. Maintain future options for ARV therapy

4. Minimize side effects

5. Prevent onward transmission

Antiretroviral regime

Consists of two nucleoside reverse transcriptase inhibitors (NRTIs) and one active drug that is either:

• integrase strand transfer inhibitor (INSTI)

• non-nucleoside reverse transcriptase inhibitor (NNRTI)

• protease inhibitor (PI) with pharmacokinetic enhancer

Example of NRTI drugs

• abacavir

• lamivudine

• emtricitabine

• stavudine

• zidovudine

• didanosine

• tenofovir