CLS SJSU LECTURE 10: VIROLOGY

Viruses are obligate intracellular parasites that require what to replicate?

host

what is a virion

infectious virus particle

how are viruses classified?

nucleic acid, DNA or RNA \> ss/ds, segment/nonsegment

Viral capsids that protect the protein coat are made from subunits called

capsomeres

Compare the two different viral structures and stability

- Naked virus: NO ENVELOPE, NUCLEOCAPSID (genome + protein coat), structural proteins, nucleic acid binding proteins, more stable
- Enveloped virus: NUCLEOCAPSID + ENVELOPE (has viral glycoproteins from host that aid w/mutation), more susceptible to heat, pH, disinfectants

Steps for viral replication

1. attachment (receptor/membrane interaction)
2. entry (direct, fusion, endocytosis)
3. uncoating (DNA/RNA released)
4. biosynthesis & replication (transcription, translation, genome replication)
5. assembly
6. release

Viral attachment

virus attach to host cellular receptor (soluble receptors \= float away, no binding)

What are the host cell receptors for COVID-19, Influenza, Rabies, and HIV?

ACE-2, Sialic acid, Acetylcholine, CD4

How do naked viruses enter the host?

direct penetration, capsid attach to cell \> viral genome released

How do enveloped viruses enter the cell?

endocytosis (engulfed by host) or membrane fusion (viral glycoproteins remain on membrane)

where do DNA viruses replicate?
- exception?

nucleus
- exception: poxvirus replicates in the cytoplasm

Where do RNA viruses replicate?

cytoplasm

Upon viral replication, the host cell makes viral proteins that?

stops cell metabolism (polio) or restricts cell metabolism (influenza)

What is tropism factors in a virus?

host cell range
- susceptible cells can be infected by the virus due to receptors/factors that the virus needs to enter and replicate inside the cell
- permissive cells not only can be infected but also allow the virus to replicate and produce new infectious particles

how do viruses exit the cell?

budding, lysis, exocytosis

What is the most common method of viral detection?

nucleic acid base detection (PCR)
can also use cell culture, serology

Enzyme immunoassay for viral detection

used to RSV, influenza, Hep-B, HIV, negative reactions confirmed with IF, cell culture, PCR

what are the 3 techniques used to viral isolation?

CELL CULTURE, animal inoculation, embryonated eggs

Why aren't serologic assay the best tool for viral detection?

CROSS REACTIVITY, does not detect acute infections, no seroconversion
BUT, good diagnostic info for HIV

what cell lines are used in viral cell cultures?

RMK (rhesus monkey kidney) cell - 1X
Diploid (semi-continuous) cell lines - 20-50X
Tumor lineage (continuous) cecll line - Hep2

What are shell vial cultures?

uses centrifugation to enhance viral absorption \> monolayer of cells \> incubate \> IF to detect CPE

What are cytopathic effects?

virus-induced damage to cells

Cytopathic effects of West Nile virus in RMK cells?

swelling of nuclei

Cytopathic effects of Rabies?

negri bodies (inclusion bodies) in nucleus

Cytopathic effects of HSV/RSV?

syncytia (giant multinucleated cells)/classical syncytia

What are other cytopathic effects seen in viruses?

vacuoles in cytoplasm, apoptosis

how are viral specimens prepared/transported?

Collect during HEAVY VIRAL SHEDDING \> aseptically collect Dacron/Rayon swabs/tissues in Viral transport media \> culture ASAP or store at 4C for best recovery

which viral specimens do not require VTM?

body fluids: urine, blood, bone marrow, CSF

tropism for adenoviruses

respiratory tract, GI tract, eye

what diseases are associated with adenoviruses?

respiratory, conjunctivitis (acute infection)
gastroenteritis (stool/urine during convalescence), obesity

tropism for hepatitis B virus (hepadnaviridae)?

hepatocytes (liver cells)

what diseases are associated with HBV?

Hepatitis B

presence of surface antigen HBsAg?

active infection (

presence of Anti-HBs?

convalescence (recovery) or immune status

presence of core antigen HBcAg

active infection (found in liver cells, not blood)

presence of anti-HBcAg

persist for life

presence of anti-HBcAg IgM

acute infection

presence of Hepatitis B antigen HBeAg

high infectivity of virus

long term HBV carriers serology

HBsAg in serum, absence of HBeAg, presence of Anti-HBe, normal ALT level, undetected/low HBV DNA

How to diagnose HIV?

Positive ELISA test, Alanine Amino Transferase levels (ALT)

State of patient with HBsAg -ve, Anti-HBs -ve, Anti-HBc -ve

Susceptible to Hepatitis B

State of patient with HBsAg -ve, Anti-HBs +ve, Anti-HBc -ve

Vaccinated against Hepatitis B

State of patient with HBsAg -ve, Anti-HBs +ve, Anti-HBc +ve

past infection with Hepatitis B

State of patient with HBsAg +ve, Anti-HBs -ve, Anti-HBc IgM +ve

acute infection with Hepatitis B

State of patient with HbsAg +ve, Anti-HBs -ve, Anti-HBc IgG +ve

chronic infection with Hepatitis B

how is hepatitis B spread?

blood, sexual

Hepatitis B symptoms

fatigue, nausea, vomiting, ab pain, CLAY-COLORED STOOL, dark urine, loss of appetite, low grade fever, joint pain

complications of HBV

cirrhosis and hepatocellular carcinoma,
Hepatitis delta virus coinfection/superinfection with active HBV

which virus can manifest as latent infection re-activation?

Herpesviridae virus

HSV I vs II

Type 1 oral
Type 2 genital

which virus is the most common cause of corneal infection and fetal encephalitis in USA?

HSV (Encephalitis: II in neonates, I in adults)

how is HSV detected?

IF of lesion specimen

How is varicella zoster transmitted?

contact with lesions or droplet inhalation

what are the two clinical forms of varicella zoster virus?

varicella \= chickenpox, zoster \= shingles (latent in IMC/elderly)

how is varicella zoster virus detected?

scrapping of lesion, Tzank smear (large multinucleated cells)

what disease is caused by epstein barr virus?

infectious mononucleosis (15-24 y/o)

how is epistein barr virus transmitted?

saliva, infects resting mature B cells (latent)

indication of epstein barr virus infection?

aptypical lymphocytosis, \>4000/mm3

What cancers are associated with epstein barr virus?

Burkitt lymphoma, Hodgkins disease (reed-sternberg cells), naospharyngeal carcinoma, multiple sclerosis

diagnosis of epstein barr virus/IM?

SEROLOGY: heterophile antibody test

Patient did heterophile antibody test for EBV, found anti-VCA (viral capsid antigen), this indicates?

IgM present for up to 4 weeks

Patient did heterophile antibody test for EBV, found anti-EA IgG (early antigen), this indicates?

present/recurrent infection of IM (acute IM)

Patient did heterophile antibody test for EBV, found anti-EBNA (EB nuclear antigen), this indicates?

past infection, recent infection

How is Cytomegalovirus (CMV) transmitted?

close contact in saliva, tears, urine, stool, breast milk, sexually, blood

What is the pathogen of interest in transfusion medicine/most common congenital infection in US?

Cytomegalovirus

what is the most commonly submitted specimen for detection of CMV?

urine

how to diagnose CMV?

PCR

What disease is associated with Human papillomavirus?

skin warts, cervial cancer, oropharyngeal cancer, penile cancer

what specimen is used for HPV testing?

cervical swab/cervical scrapping (pap smear)

diagnosis of HPV

look for koilocytes, confirm with PCR

what is the smallest DNA virus?

Parvovirus B19

What disease is associated with parvovirus?

immune competent 5th disease (erythema infectiosum) - SLAPPED CHEEK rash, self limiting

immune compromised patients with parvovirus?

erythroid precursors \> transient aplastic anemia

what is the largest virus?

Poxvirus

what disease is associated with variola virus?

smallpox, eradicated in 1980

what is an arbovirus?

arthropod borne virus: transmitted to humans through bites of anthropods like mosquitos, ticks, etc.

what is the vector for flavivirus?

Mosquito

Vector: aedes aegypti
Reservoir: humans
4 serotypes, causes dengue fever (1st infection w/ 1 serotype) that leads to dengue hemorrhagic fever (2nd infection w/ diff serotype)

Dengue virus

Vector: Aedes aegypti
Reservoir: Monkeys \> humans \> humans
Africa/South America

Yellow-fever virus

Vector: Culex mosquito
Reservoir: birds, human \= dead end host
Midwestern/southern states, mild in children, atypical in adults

St. Louis Encephalitis

Vector: Culex mosquito
Reservoir: birds \> humans (mother to baby or blood transfusion/transplant)
Leading cause of vector borne virus, IgG/IgM ELISA diagnosis

West Nile virus

Vector: Aedes aegypti
Transmission: sexual, vertical, transfusion
Manifest as mild febrile disease \> Guillain-Barre syndrome (damaged myelin sheath \> difficulty walking)
IMC children - microcephaly, neuro deformities in fetus, congenital

Zika

Vector: Rodent
infects peritoneal cavity, kidney, thoracic cavity, lungs
has 3 loops of RNA, dominant in dry areas, rodent feces as soil \> inhalation

Bunyaviridae, Hantavirus

What diseases are associated with Hantavirus?

Pulmonary edema, hemorrhagic fever w/ renal syndrome (UK/Asia), hantavirus pulmonary syndrome (USA)

hepatitis A

inflammation of the liver caused by the hepatitis A virus (HAV), usually transmitted orally through fecal contamination of food or water, asymptomatic in children

How is HAV diagnosed?

presence of anti-HAV IgM, vaccine avail

hepatitis C

inflammation of the liver caused by the hepatitis C virus (HCV), which is transmitted by exposure to infected blood; this strain is rarely contracted sexually

what is unique about hepatitis C?

only flaviviridae that is not vector borne, highest mortality rate

How is hepatitis C diagnosed?

Acute HCV - serum ALT levels 7X higher, HCV viral RNA
Chronic HCV - anti- HCV + viral RNA

Hepatitis C epidemiology

most people are chronic carriers \> cirrhosis OR hepatocellular carcinoma

how is influenza categorized?

matrix protein + nucleoprotien A/B/C/D

Influenza Group A classification

surface glycoproteins: hemagglutinin (attach to siliac acid) and neuraminidase (release virus from mucus)
ex. H1N1, H3N2 (swine flu \= pigs) + H7N9, H5N1 (avian flu \= birds)

antigenic drift vs antigenic shift in influenza

- Antigenic drift (A, B): RNA replication errors \> mutations
- Antigenic shift (A): viral H or N (or both) antigen change suddenly
- Group C \= neither/stable, Group D \= only infects cows

how does the CDC make flu vaccine?

CDC monitors strains of flu virus to include in vaccine

types of flu vaccine

Quadrivalent flu vaccine (H1N1, H3N2 + 2 B virus), egg-based, cell-based, recombinant

how does influenza present in tracheobronchial tree + nasopharynx?

respiratory cilia \= destroyed \> cleaning mechanism doesn't work \> more mucus in airway \> clog \> cough, could lead to secondary bacterial infection

Symptoms: abrupt fever, chills, headachce, myalgia, arthralgia, dry cough, rhinitis, sore throat, ocular symptoms

Influenza

What are some complications of influenza

primary viral pneumonia, secondary bacterial pneumonia, sinusitis, otitis, REYE'S SYNDROME, GUILLAIN BARRE SYNDROME

What is Reye's syndrome?

complication of influenza B \> acute encephalopathy, fatty liver, elevated transaminase
* DONT GIVE ASPIRIN TO KIDS!

What is Guillain-Barre syndrome?

autoimmune disease that involves demyelination of motor nerves \> paralysis