Virology Exam 3

What animal reservoirs does rabies have?

What animal reservoirs does rabies have?

dogs, raccoons, skunks, cattle, mongoose, vampire bat, foxes

Why is rabies a difficult disease to eradicate?

Too many animal reservoirs

Why does rabies have such a large animal reservoir

Incredibly conserved Ach receptor across species

What are pre-exposure treatments to rabies

Immunization, Serologic Tests, Booster Vaccinations

What vaccines are used in the US for rabies

HDCV (human cultured fibroblasts), RVA (fetus rhesus lung culture), PCECV (chick embryo cell culture)

What are rabies vaccines inactivated with?

B-Propiolactone

What is the post-exposure prophylaxis treatment for rabies?

Vaccination and passive immunity by human rabies immune globulin (HRIG)

What does HRIG - Human Rabies Immune Globulin do?

Provides passive immunity until active antibodies are induced by the vaccine

Prodromal Symptoms of Rabies

headache, malaise, fever, anorexia, nausea, vomiting

major symptoms of rabies

hydrophobia, aggression, hypersalivation, psychological changes, brain neurons infected

secondary furious rabies symptoms

difficulty swallowing, agitation, anxiety, hallucination, hypersalivation, bizarre behavior, biting, jerky and violent contractions of the diaphragm

secondary paralytic rabies symptoms

weakness, ascending paralysis

Hydrophobia

a symptom of rabies in humans consisting of an aversion to swallowing liquids. individual can only breath when attempting to swallow. caused by destruction of brain stem neurons that inhibit respiratory motor neurons

Pathogenesis of Rabies

virus enters from animal bite and multiplies in myocytes for weeks to months. virus binds to nAch receptors at neuromuscular junction and then travels along axons in peripheral nerves (using retrograde transport) to the CNS. The viruses then replicate in motor neurons of the spinal cord and dorsal root ganglia and ascend to the brain. Rabies then spreads along nerves to salivary glands, skin, cornea and other organs. Saliva is infectious for two weeks before symptoms show

Where does replication of rabies occur?

myocytes and neuronal cell body (in the cytoplasm)

Rabies appearance

helical bullet shaped, 400 glycoprotein spikes that are recognized by Ab and RBP . NP and L are part of the RNP core

Rabies DNA type

non-segmented, -ssRNA, linear

Rabies Baltimore Classification

Baltimore Category V

Composition of viral genome of rabies

coat protein nucleocapsid (n), polymerase-associated phosphoprotein (p), matrix protein (m), glycoprotein (g), polyprotein (l)

When does rabies switch from production to replication

After N is synthesized in sufficient quantity

What are N, M, P, and L mRNAs translated by? (rabies)

Free ribosomes

What are glycoprotein mRNAs translated by (rabies)?

membrane bound ribosomes of the ER

When and by what is G glycosylated?

Post-translationally glycosylated by the golgi

Function of N in Rabies

Coat protein, part of the RNP core

Function of P in Rabies

Polymerase-associated phosphoprotein; part of the RNP core

Function of M in Rabies

Matrix protein, part of RNP core

Function of G in Rabies

Glycoprotein, receptor binding proteins, major surface antigen

Function of L in Rabies

Polyprotein with RNA replicase: 5' capping, methylation, 3' polyadenylation activity

Rabies receptors

nAchR, NCAM (Neuronal Cell Adhesion Molecule) and p75NR (p75 Neurotrophin Receptor)

Rabies replication cycle

How does rabies evade the immune system?

RVP phosphoprotein antagonizes interferon IFN response by blocking IFN I and II signaling. Kills migrating T Cells and sneaks into NS without triggering apoptosis of infected neurons and preserving integrity of neurites.

Poxvirus DNA type

dsDNA, non-segmented, linear, terminal repeat (ITR) on the ends of genomes

Poxvirus Baltimore Class

Baltimore I

Poxvirus Characteristics

brick shaped, enveloped, dumbbell shaped core and lateral bodies containing enzymes essential for replication while core contains proteins involved in morphogenesis of virus particles or transcription

Description of the Poxvirus genome

200 Genes, 90 essential genes in the center of the viral genome while inessential genes are on the ends

What is coded for in the poxvirus genome

RNA pol, early TF's, topoisomerase, DNA helicase, structural proteins, Virokines, viroreceptors

Virokines

resemble cytokines, bind to cellular receptors but don't simulate a response. they are antagonistic ligands for host cellular receptors

Viroreceptors

Altered cellular receptors that lost their transmembrane anchor sequences. These sequester cytokine response and produce virokines.

Vaccinia gene expression is _________ and _____________ ____________

sequential; temporally regulated

Early Poxvirus mRNA's

encode enzymes and factors needed for transcription of the intermediate class of mRNAs, also DNA replication and immunosuppression

Intermediate Poxvirus mRNAs

Encode enzymes and factors required for late gene expression after DNA replication

Late mRNAs

expression occurs after DNA replication, encodes factors and enzymes packed into the virion (structural proteins, early TF factors, viral transcriptional machinery)

Poxvirus Replication Cycle

Where in the cell does poxvirus replication occur?

the cytoplasm

Mature Virion

2 membranes from golgi and endosomes, released upon lysis

Extracellular virion

only contains inner membrane, outer membrane is lost by exocytosis

How are poxvirus genes regulated

Gene sequences are regulated by promotors and are both temporal and sequential

Poxvirus pathogenesis

Specificities are unknown - Only grows in human tissue.

Variola enters respiratory tract, seeds in mucous membranes and passes into lymph nodes. Viremia followed by 4-14 day latent period. Virus invades capillary epithelium of dermal layer leading to development of lesions. Migration of macrophages to lymph nodes elicits production of cytotoxic T and B cells. Death is a result of toxemia

Clinical Presentation of Poxvirus

Pustules, crusts, eruptions and desquamation on the skin

Poxvirus progression

Poxvirus inhaled, prodromal period in which you feel sick, continuum of rashes

Poxvirus distribution

Centrifugal, clusters on extremities

Horsepox/Variola Vaccine

Early American smallpox vaccine was based on horsepox, smallpox's closest relative. Caused a localized reaction and may cause severe and systemic disease in an immunocompromised individual or those with pre-existing skin conditions

Dryvax

Live attenuated, cultured on the skin of calves and freeze dried. Mixed population of vaccinia virus strains. Delivered by bifurcated needle. Can spread. Has complications (1000/1,000,000, eczema, dermatitis, weakened immune systems, high blood pressure, diabetes, high cholesterol

ACAM

6 clones from dryvax pool, passaged 5x in human embryonic lung fibroblast cell, safe and effective, live attenuated, replication competent, cell culture based, one dose

JYNNEOS

live attenuated, replication incompetent, two doses,

Why was smallpox able to be eliminated

Effective Vaccine, Virus has not changed much, Obvious clinical hallmark, narrow host range, no animal reservoirs, disease is acute and self limiting (die or survive), WHO eradication program

Monkeypox

typically rare, before 1970 was a disease of animals in Africa. First human (1996-1997) reported from western Africa. Fatality rate 1-14%. Signs and symptoms similar to smallpox but milder. Smallpox vaccines protect against monkeypox. lymphadenopathy in early stages

molluscum contagiosum

Transmitted through direct contact. More common spread through fomites, rapid transmission in daycares and kindergartens. MCV caused significant opportunistic infection in patients with HIV. Incubation period: 2-8 weeks. Pin, pearl like lesions on face arm and legs. Lesions have dimples in the center. Infection is self-limiting in individuals with a good immune system. Secondary bacterial infections are a complication of molluscum contagiosum in AIDS.

Poxvirus Vaccines

ACAM, JYNNEOS, Horsepox-Vaccinia Vaccine, Dryvax Vaccine

Poxvirus Novel Treatments

Brinviofovir and Tecovirimat (ST-246 and TPOXX), Vaccine Immune Globulin Intravenous (VIGIV)

Brinviofovir

DNA polymerase inhibitor

Tecovirimat/ST-246/TPOXX

Inhibition of extracellular virus formation through an interaction with f13L protein

HSV1/HHV1

Human Herpesvirus 1/ Herpes simplex virus 1

Causes cold sores, eye infection, mat herpes, eczema herpeticum and herpes regbeiorum

HHV-2/HSV-2

Human herpesvirus 2 or human simplex virus 2

genital herpes, aseptic meningitis, neonatal herpes

HHV-3/VZV

Human herpesvirus 3, Varicella zoster virus

chicken-pox, shingles

HHV-4 or EBV

Human herpesvirus 4 or Epstein-Barr Virus

Mononucleosis, hepatitis, encephalitis

HHV-5 or CMV

Human herpesvirus 5/ Cytomegalovirus

Mononucleosis, congenital infection

HHV-6A and HHV-6B

Human herpesvirus 6A and 6B

Sixth disease in young children, Roseola

HHV-7

Human herpesvirus 7

Exanthem subitum or fever illness and seizures in children and babies

HHV 8 or KSVH

Human herpesvirus 8 Kaposi's sarcoma associated herpes virus

Fever associated with a rash and mononucleosis

Herpes Virus B or CeHV-1

Monkey B virus

Mucocutaneous lesions, encephalitis

Type of HSV genome

non-segmented linear dsdna

HSV Baltimore Category

Category 1

Ends of HSV DNA sequences are...

repetitive sequences that serve in replication and packaging

U-sequences (HSV)

Unique - serve in unique protein products (over 50)

DNA replication enzymes, glycoproteins, host defense and capsid

Enzymes required to increase nucleotide pool and replicate viral genome (Herpesvirus)

thymidine kinase, ribonucleotide reductase, uracil dna glycosylase, deoxyuridine triphosphatase

50% of genome encodes what in hsv-1 and hsv-2?

regulatory proteins involved in latency and evading the host immune system (like creating virokines)

Where does HSV replicate?

HSV undergoes a productive infection in epithelial cells of the genital or oral mucosal surface. During latency, the herpesvirus travels up the axon to the neuronal cell body, where it remains dormant. Once reactivated, the virus travels down the axon and establishes productive, lytic infection in epithelial cells at the end of the axon

replicates in the nucleus

HSV Lifecycle

receptors TNF and Nectin 1/2

Where does HSV replicate in the cell?

in the nucleus

Membrane glycoproteins that participate in entry for HSV

gB, gC, gD, gH, gL

gC and gB function

Bind to cell surface proteoglycans (binding receptor)

gD function

binds to entry receptor (TNF, Nectin 1/2) to trigger fusion

gB, gH and gL function

along with other glycoproteins these release nucleocapsid with tegument proteins into the cytoplasm of the cell.

Circular replication

Bidirectional DNA replication. RNA primers (blue arrows) are synthesized by a herpesvirus. Viral proteins bind to origins of replication on the DNA and open it. Proteins serving as primases, helicases and primers help to synthesize DNA. Replicated DNA rolls of the template forming a concatemer (a long continuous DNA molecule that contains multiple copies of the same DNA sequence linked in series)

What polymerase does HSV use for transcription?

Hosts RNA pol II

Classes of genes for HSV?

immediate early (a), early (b), late (y)

Immediate early (a) hsv genes

Activated by VP16, play a role in transcription of B genes

Early (B) genes HSV

Encode DNA replication and additional viral transcription factors

Late (y) HSV genes

Encode late structural proteins that are produced after viral genome replication has begun. Y proteins transported to the nucleus

What are LATs

Latency Associated Transcript

A non-protein coding RNA. Appears to limit HSV immediate-early gene expression. Suppresses apoptosis, reduces frequency of reactivation to full lytic replication. No viral particles are detected during latency. Virus hides for months or years until reactivated and travels the nerve pathway to the surface of the skin

During latency only one region of the viral genome is actively transcribed. LAT region has pathogenic functions (neuron survival, anti-apoptosis, virulence, suppression of latent transcription and establishment of latency.

What causes reactivation of HSV

Immune suppression by cytotoxic drugs Sexual contact Physical and emotional stress Temperature changes (hot or cold) Excessive UV light exposure Menstruation Pregnancy Lactation Malnutrition Excessive fatigue

Mechanism of reactivation of HSV

Virus travels down the axon and establishes productive lytic function

Vaccines for Varicella Zoster

Varivax, 2 doses, passed through embryonic/guniea and human lung fibroblasts

Vaccines for Shingles

Zostavax and Shingrix

Treatments for HSV1 and HSV2

Nucleotide analogs (chain terminators), inhibited herpesvirus encoded dna pol

acyclovir

mostly prescribed for hsv1, hsv2 and vzv guanosine analog chain terminator, prevents dna elongation relatively nontoxic can be used for long-term prophylaxis topically, intravenously or orally taken

Clinical Hallmarks of Hepatitis

Decreased liver function, jaundice, decreased alt/ast, dark urine

What genome does hepatitis A resemble and why

Polio, hairpin IRES, Baltimore category 4, +ssRNA

same virus family picornaviradae

is hep a enveloped or nonenveloped

nonenveloped