Module 15 - Virology

virology

the study of viruses

genome

inner nucleic acid core; DNA (ss or ds) or RNA

capsomere

repeating structural units of a capsid; form capsid and characteristic virus structure

capsid

structural protein that surrounds and protects the nucleic acid; composed of capsomeres

nucleocapsid

nucleic acid genome surrounded by a protein coat (capsid); nucleic acid +capsid

envelope

a membrane-like layer that covers the capsids of some viruses; lipid rich and responsible for virus entry into host cell; many contain glycoprotein spikes, hemagglutinin, neuraminidase, and other structures that stabilize virus attachment to host cell

virion

complete virus particle

reverse transcriptase

an enzyme encoded by some certain viruses (retroviruses) that uses RNA as a template for DNA synthesis

tissue tropism

the range of tissue types that a virus can infect; predilection for certain organs/cell types

jaundice

yellowing of the skin

antigenic drift

minor change in influenza virus antigens due to gene mutation; many do share the same antigen

antigenic shift

major change in influenza virus antigen due to gene reassortment; people will have little immunity to new strain

hemagglutinin

one of the enzymes found on the surface of the influenza virus; responsible for binding the virus to the cell that is being infected

neuraminidase

helps release visions from the host cell after replication and assembly; surface antigen on influenza A and B

virus

incapable of growth or replication outside of a living cell

RNA viruses

Reoviridae, astroviridae, picornaviridae, caliciviridae, togaviridae, flaviviridae, coronaviridae, filoviridae, bunyaviridae, orthomyxoviridae, paramyxoviridae, rhabdoviridae, arenaviridae, retroviridae, hepeviridae

Astroviridae

RNA virus, non-enveloped; gastroenteritis

Reoviridae

rotavirus, infantile gastroenteritis

picornaviridae

Rhinovirus (cold and hepatitis A) and Enterovirus (polio, meningitis, encephalitis)

Rhinovirus

A picornavirus. Cause of common cold and hepatitis A.

Enterovirus

a picornavirus; polio, meningitis, encephalitis

caliciviridae

norovirus, gastroenteritis

togaviridae

Rubella (German measles) and encephalitis

flaviviridae

Arbo: yellow fever, dengue, zika, encephalitis, West nile fever
Non-Arbo: hepatitis C (liver cancer)

coronaviridae

SARS, COVID-19

filoviridae

Ebola/Marburg hemorrhagic fever

bunyaviridae

Arbo: california encephalitis
Non-Arbo: Hantavirus pulmonary syndrome (Hanta fever)

Orthomyxoviridae

Influenza A, B, C

Paramyxoviridae

mumps, measles, respiratory syncytial virus (RSV)

Rhabdoviridae

rabies

Arenaviridae

Lassa fever, aseptic meningitis

Retroviridae

HIV-AIDS, human adult T-cell leukemia/lymphoma (HTLV)

hepeviridae

hepatitis E

DNA viruses

Adenoviridae, hepadnaviridae, herpesviridae, papillomaviridae, polyomaviridae, papovaviridae, parvoviridae, poxviridae

Adenoviridae

common cold, viral meningitis, respiratory diseases, GI diseases, conjunctivitis

hepadnaviridae

hepatitis B, liver cancer

herpesviridae

cold sores, genital herpes, chickenpox, shingles, infectious mononucleosis, cancer, birth defects, 6th disease, Kaposi sarcoma

papillomaviridae

cancer (HPV), warts

polyomaviridae

possibly prostate cancer; no definitive diseases

papovaviridae

warts, genital warts, cervical cancer

parvoviridae

5th disease, gastroenteritis

poxviridae

smallpox, monkeypox

attachment, penetration, biosynthesis, assembly, release

5 steps of the lytic cycle of a viral infection

attachment

lytic cycle: recognition of suitable host cell; specific binding of virus to host cell

penetration

lytic cycle: viral entry into host cell; internalization of virus into host cell; fusion of neighboring host cells to form multinucleate cells (syncytia)

uncoating

lytic cycle: removal of outer viral capsid layer; exposing nucleic acid

biosynthesis

lytic cycle: production of nucleic acids and proteins; making viral components

assembly

lytic cycle: viral components (nucleic acids, proteins, capsids) come together into virus particles/virions

release

lytic cycle: host cell lysis or budding from cytoplasm with minimal damage to host or integration into host genome

lytic infection

virus production and eruption of the cell; release of viral particles from lysed host cell

lysogenic infection

integration of viral nucleic acid into host genome

reverse transcriptase

in retroviruses; allows transcription of RNA into DNA and subsequent integration of viral DNA into host genome

viremia

viruses in the blood

3 steps of viral disease

Acute, Latent, Chronic

acute viral infection

step of viral infection: has evident signs and symptoms

latent viral infection

step of viral infection: has no visible signs or symptoms, but virus is present in host cells in lysogenic state (inserted into host genome) and is inactive until manifestation later

chronic viral infection

step of viral infection: low levels of virus are detectable; degree of visible signs and symptoms varies; transmission generally through fecal-oral route or sexual contact

innate immunity

production of anti-viral proteins; interferons activate natural killer cells; complement cascade activation (damage outermost layer of enveloped viruses OR coats receptors of non enveloped viruses)

adaptive immunity

production of antibodies (humor immunity)
IgA (mucosal immunity)
IgM (early antibody response)
IgG (later and continued antibody response: antigen memory)

less common techniques used to diagnose viral diseases

use of embryonic eggs; use of animal inoculation

immunodiagnostics/viral serologies

direct and indirect immunofluorescent; enzyme immunoassays (EIA or ELISA); latex agglutination; immunoperoxidase stain methods; radioimmunoassays

plaque assays

require cell culture; virus-specific cell lines are needed; living cells are maintained in vitro for virus isolation; once patient specimen is inoculated, viral growth takes 1-4 weeks; virus causes distinctive changes in the cells (cell rounding/detachment from plate, multinucleate cells, lysis detectable by plaque assays)

molecular methods

PCR, RT-PCR for diagnosis of viral diseases

Herpes, influenza, hepatitis, HIV

4 predominant viruses isolated and identified commonly during a one-year period in a community hospital

Herpes and influenza

culture, PCR, assay

Hepatitis and HIV

serology

3 methods of virus prevention

immunizations, hand washing, avoiding contact

2 methods of virus treatment

antiviral agents and immune prophylaxis

immune prophylaxis

administration of exogenously produced Ab to prevent infections in exposed individuals

antibody-rich plasma

one method of prophylaxis discussed

adenoviruses

respiratory infections (croup, colds, tonsillitis, pharyngitis), GI disease, conjunctivitis, keratitis

HSV-1

oropharyngeal mucosa; cold sores/oral herpes; reoccurrence of skin lesions following primary infection; latency in the sensory ganglia; most common reported viral CNS infection

HSV-2

infection of genitals; reoccurrence of skin lesions following primary infection; latency in the sensory ganglia

VZV

varicella zoster virus

HSV

herpes simplex virus

VZV

chickenpox; hides in the CNS; establishes latency in the CNS sensory ganglia; reactivation of dormant virus causes shingles which occurs mostly in people >45 y/o, painful neuralgia

EBV

Epstein-Barr virus

EBV

infection mononucleosis; Burkett's lymphoma; nasopharyngeal cancer

CMV

cytomegalovirus

CMV

common cause of congenital birth defects; lab diagnostics is TORCH panel in infants; causes IM-like illness in immunocompromised patients

Burkitt's lymphoma

cancer of lymphatic system, specifically B lymphocytes; chronic EBV infection seen in Africa; confection or superinfection of EBV with malaria

nasopharyngeal cancer

caused by combination of factors -- EBV, environment, hereditary

HHV-6

become latent following primary infection and are reactivated from time to time, especially during period of immunosuppression; firmly associated with roseola infantum (6th disease); t-lymphocytic but can infect other cell types

HHV-7

become latent following primary infection and are reactivated from time to time, especially during periods of immunosuppression; t-lymphocytic but can infect other cell types; not conclusively associated with human disease

HHV-8

Kaposi sarcoma-associated herpes virus

cutaneous or mucosal tissue

identify tissue tropism of the papillomaviruses (2)

HPV

state the most prevalent sexually transmitted viral disease in the USA

HPV 1

plantar warts

HPV 2 and 4

common warts of the hands

HPV 6, 11, 16, 18

genital warts

HPV 16

responsible for some cases of oropharynx and penile cancer in men

Parvovirus B19

single human pathogen in the parvovirus group

Parvovirus B19

5th disease; aplastic crisis in patients with underlying hemoglobinopathies; hydros fettles results from transplacental inoculation

Edward Jenner

Developed a vaccine for smallpox in 1798

localized and systemic

2 courses of infection with smallpox

localized infection

smallpox infection stays at site of inoculation

systemic infection

smallpox infection with fulminant virus spread throughout body

Lassa fever

etiologic agent: arenavirus
transmission: inhalation of aerosols of rodent excrement
disease progression: viral hemorrhagic fever leading to capillary leak, hemorrhage, organ failure, and respiratory distress
2-21 day duration

Hanta fever

etiologic agent: non-arbovirus bunyravirus
transmission: rodent-borne viruses transmitted via aerosolized rodent excrement
disease description: acute respiratory failure syndrome; Sin Nombre virus is the prototype; mortality up to 55%

Norovirus

disease: viral gastroenteritis
Outbreaks: cruise ships, nursing homes, schools
RT-PCR to identify