CLS SJSU LECTURE 10: VIROLOGY

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Viruses are obligate intracellular parasites that require what to replicate?

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1

Viruses are obligate intracellular parasites that require what to replicate?

host

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what is a virion

infectious virus particle

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how are viruses classified?

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

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

capsomeres

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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

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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

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Viral attachment

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

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

ACE-2, Sialic acid, Acetylcholine, CD4

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How do naked viruses enter the host?

direct penetration, capsid attach to cell > viral genome released

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How do enveloped viruses enter the cell?

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

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where do DNA viruses replicate?

  • exception?

nucleus

  • exception: poxvirus replicates in the cytoplasm

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Where do RNA viruses replicate?

cytoplasm

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

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

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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

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how do viruses exit the cell?

budding, lysis, exocytosis

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What is the most common method of viral detection?

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

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Enzyme immunoassay for viral detection

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

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what are the 3 techniques used to viral isolation?

CELL CULTURE, animal inoculation, embryonated eggs

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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

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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

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What are shell vial cultures?

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

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What are cytopathic effects?

virus-induced damage to cells

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Cytopathic effects of West Nile virus in RMK cells?

swelling of nuclei

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Cytopathic effects of Rabies?

negri bodies (inclusion bodies) in nucleus

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Cytopathic effects of HSV/RSV?

syncytia (giant multinucleated cells)/classical syncytia

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What are other cytopathic effects seen in viruses?

vacuoles in cytoplasm, apoptosis

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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

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which viral specimens do not require VTM?

body fluids: urine, blood, bone marrow, CSF

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tropism for adenoviruses

respiratory tract, GI tract, eye

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what diseases are associated with adenoviruses?

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

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tropism for hepatitis B virus (hepadnaviridae)?

hepatocytes (liver cells)

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what diseases are associated with HBV?

Hepatitis B

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presence of surface antigen HBsAg?

active infection (
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presence of Anti-HBs?

convalescence (recovery) or immune status

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presence of core antigen HBcAg

active infection (found in liver cells, not blood)

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presence of anti-HBcAg

persist for life

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presence of anti-HBcAg IgM

acute infection <6 months

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presence of Hepatitis B antigen HBeAg

high infectivity of virus

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long term HBV carriers serology

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

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How to diagnose HIV?

Positive ELISA test, Alanine Amino Transferase levels (ALT)

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

Susceptible to Hepatitis B

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

Vaccinated against Hepatitis B

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

past infection with Hepatitis B

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

acute infection with Hepatitis B

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

chronic infection with Hepatitis B

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how is hepatitis B spread?

blood, sexual

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Hepatitis B symptoms

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

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complications of HBV

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

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which virus can manifest as latent infection re-activation?

Herpesviridae virus

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HSV I vs II

Type 1 oral Type 2 genital

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

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

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how is HSV detected?

IF of lesion specimen

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How is varicella zoster transmitted?

contact with lesions or droplet inhalation

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what are the two clinical forms of varicella zoster virus?

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

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how is varicella zoster virus detected?

scrapping of lesion, Tzank smear (large multinucleated cells)

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what disease is caused by epstein barr virus?

infectious mononucleosis (15-24 y/o)

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how is epistein barr virus transmitted?

saliva, infects resting mature B cells (latent)

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indication of epstein barr virus infection?

aptypical lymphocytosis, >4000/mm3

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What cancers are associated with epstein barr virus?

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

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diagnosis of epstein barr virus/IM?

SEROLOGY: heterophile antibody test

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

IgM present for up to 4 weeks

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

present/recurrent infection of IM (acute IM)

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

past infection, recent infection

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How is Cytomegalovirus (CMV) transmitted?

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

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

Cytomegalovirus

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

urine

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how to diagnose CMV?

PCR

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What disease is associated with Human papillomavirus?

skin warts, cervial cancer, oropharyngeal cancer, penile cancer

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what specimen is used for HPV testing?

cervical swab/cervical scrapping (pap smear)

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diagnosis of HPV

look for koilocytes, confirm with PCR

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what is the smallest DNA virus?

Parvovirus B19

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What disease is associated with parvovirus?

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

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immune compromised patients with parvovirus?

erythroid precursors > transient aplastic anemia

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what is the largest virus?

Poxvirus

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what disease is associated with variola virus?

smallpox, eradicated in 1980

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what is an arbovirus?

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

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what is the vector for flavivirus?

Mosquito

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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

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

Yellow-fever virus

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

St. Louis Encephalitis

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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

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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

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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

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What diseases are associated with Hantavirus?

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

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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

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How is HAV diagnosed?

presence of anti-HAV IgM, vaccine avail

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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

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what is unique about hepatitis C?

only flaviviridae that is not vector borne, highest mortality rate

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How is hepatitis C diagnosed?

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

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Hepatitis C epidemiology

most people are chronic carriers > cirrhosis OR hepatocellular carcinoma

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how is influenza categorized?

matrix protein + nucleoprotien A/B/C/D

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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)

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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

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how does the CDC make flu vaccine?

CDC monitors strains of flu virus to include in vaccine

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types of flu vaccine

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

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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

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

Influenza

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What are some complications of influenza

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

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What is Reye's syndrome?

complication of influenza B > acute encephalopathy, fatty liver, elevated transaminase

  • DONT GIVE ASPIRIN TO KIDS!

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What is Guillain-Barre syndrome?

autoimmune disease that involves demyelination of motor nerves > paralysis

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