Microbiology- Virology Flashcards
Viral structure—general features
Naked virus with icosahedral capsid
Enveloped virus with icosahedral capsid
Enveloped virus with helical capsid
Bacteriophage
Recombination
Exchange of genes between 2 chromosomes by crossing over within regions of significant base sequence homology.
Reassortment
When viruses with segmented genomes (eg, influenza virus) exchange genetic material.
Complementation
When 1 of 2 viruses that infect the cell has a mutation that results in a nonfunctional protein, the nonmutated virus “complements” the mutated one by making a functional protein that serves both viruses.
Phenotypic mixing
Occurs with simultaneous infection of a cell with 2 viruses.
Genome of virus A can be partially or completely coated (forming pseudovirion) with the surface proteins of virus B. Type B protein coat determines the tropism (infectivity) of the hybrid virus. However, the progeny from this infection have a type A coat that is encoded by its type A genetic material.
DNA viral genomes
All DNA viruses have dsDNA genomes except
Parvoviridae (ssDNA).
All are linear except papilloma-, polyoma-, and
hepadnaviruses (circular).
RNA viral genomes
All RNA viruses have ssRNA genomes except Reoviridae (dsRNA).
⊕ stranded RNA viruses: I went to a retro (retrovirus) toga (togavirus) party, where I drank flavored (flavivirus) Corona (coronavirus) and ate hippie (hepevirus) California (calicivirus) pickles (picornavirus).
Naked viral genome infectivity
Purified nucleic acids of most dsDNA (except poxviruses and HBV) and ⊕ strand ssRNA (≈ mRNA) viruses are infectious.
Naked nucleic acids of ⊝ strand ssRNA and dsRNA viruses are not infectious. They require polymerases contained in the complete virion.
Viral envelopes
Naked (nonenveloped) viruses include:
DNA = PAPP; Papillomavirus, Adenovirus, Parvovirus, Polyomavirus
RNA = CPR: Calicivirus, Picornavirus, Reovirus, and Hepevirus.
“Give PAPP smears and CPR to a naked hippie
(hepevirus)”.
DNA viruses
Are HHAPPPPy viruses:
Hepadna, Herpes, Adeno, Pox, Parvo, Papilloma, Polyoma.
DNA virus characteristics
Are double stranded; Except parvo (single stranded).
Have linear genomes; Except papilloma and polyoma (circular, supercoiled) and hepadna (circular, incomplete).
Are icosahedral; Except pox (complex)
Replicate in the nucleus; Except pox (carries own DNA-dependent RNA polymerase). “Pox is out of the box (nucleus).”
Poxvirus
- Envelope
- Medical importance
yes
Smallpox eradicated world wide by use of the liveattenuated vaccine.
Cowpox (“milkmaid blisters”)
Molluscum contagiosum—flesh-colored papule with
central umbilication
Hepadnavirus
- Envelope
- Medical importance
Yes
HBV:
- Acute or chronic hepatitis
- Not a retrovirus but has reverse transcriptase
Adenovirus
- Envelope
- Medical importance
No
Febrile pharyngitis — sore throat Acute hemorrhagic cystitis Pneumonia Conjunctivitis—“pink eye” Gastroenteritis Myocarditis
Papillomavirus
- Envelope
- Medical importance
No
HPV–warts (serotypes 1, 2, 6, 11), CIN, cervical
cancer (most commonly 16, 18)
Polyomavirus
- Envelope
- Medical importance
No
JC virus—progressive multifocal leukoencephalopathy (PML) in HIV.
BK virus—transplant patients, commonly targets kidney
JC: Junky Cerebrum; BK: Bad Kidney
Parvovirus
- Envelope
- Medical importance
No
B19 virus—aplastic crises in sickle cell disease, “slapped cheek” rash in children (erythema infectiosum, or fifth disease).
RBC destruction in fetus leads to hydrops fetalis and death, in adults leads to pure RBC aplasia and rheumatoid arthritis–like symptoms.
Herpes simplex virus-1
- Transmission
- Clinical significance
Respiratory secretions, saliva
Gingivostomatitis, keratoconjunctivitis, herpes labialis, herpetic whitlow on finger, temporal lobe encephalitis, esophagitis, erythema multiforme.
*Most commonly latent in trigeminal ganglia. Most common cause of sporadic encephalitis
Herpes simplex virus-2
- Transmission
- Clinical significance
Sexual contact, perinatal
Herpes genitalis, neonatal herpes.
*Most commonly latent in sacral ganglia. Viral meningitis more common with HSV-2.
Varicella Zoster virus (HHV-3)
- Transmission
- Clinical significance
Respiratory secretions
Varicella-zoster (chickenpox, shingles), encephalitis, pneumonia.
Most common complication of shingles is postherpetic
neuralgia.
*Latent in dorsal root or trigeminal ganglia; CN V1 branch involvement can cause herpes zoster ophthalmicus.
Epstein-Barr virus (HHV-4)
- Transmission
- Clinical significance
Respiratory secretions, saliva; aka “kissing disease,”
Mononucleosis—fever, hepatosplenomegaly, pharyngitis, and lymphadenopathy (especially posterior cervical nodes). Avoid contact sports until resolution due to risk of splenic rupture.
Associated with lymphomas (eg, endemic Burkitt lymphoma), nasopharyngeal carcinoma (especially Asian adults), lymphoproliferative disease in transplant patients.
Epstein-Barr virus (HHV-4)
- Diagnosis
- Highlights
Infects B cells through CD21.
Atypical lymphocytes on peripheral blood smear —not infected B cells but reactive cytotoxic T cells.
⊕ Monospot test—heterophile antibodies detected by agglutination of sheep or horse RBCs.
Use of amoxicillin in mononucleosis can cause characteristic maculopapular rash.
Cytomegalovirus (HHV-5)
- Transmission
- Clinical significance
Congenital transfusion, sexual contact, saliva, urine, transplant.
Mononucleosis (⊝ Monospot) in immunocompetent patients; infection in immunocompromised, especially pneumonia in transplant patients; esophagitis; AIDS retinitis (“sightomegalovirus”): hemorrhage, cotton-wool exudates, vision loss.
*Infected cells have characteristic “owl eye” intranuclear
inclusions.
Human herpesviruses 6 and 7
- Transmission
- Clinical significance
Saliva
Roseola infantum (exanthem subitum): high fevers for several days that can cause seizures, followed by diffuse macular rash.
“Roseola: fever first, Rosy (rash) later”.
Human herpesvirus 8
- Transmission
- Clinical significance
Sexual contact
Kaposi sarcoma (neoplasm of endothelial cells). Seen in HIV/AIDS and transplant patients. Dark/violaceous plaques or nodules representing vascular proliferations
*Can also affect GI tract and lungs.
HSV identification
Viral culture for skin/genitalia.
CSF PCR for herpes encephalitis.
Tzanck test—a smear of an opened skin vesicle to detect multinucleated giant cells commonly seen in HSV-1, HSV-2, and VZV infection.
PCR of skin lesions is test of choice.
Intranuclear eosinophilic Cowdry inclusions also seen with HSV-1, HSV-2, VZV
Receptors used by viruses
- CMV
- EBV
- HIV
- Parvovirus B19
- Rabies
- Rhinovirus
- Integrins (heparan sulfate)
- CD21
- CD4, CXCR4, CCR5
- P antigen on RBCs
- Nicotinic AChR
- ICAM-1
RNA viruses
All replicate in the cytoplasm (except retrovirus and influenza virus).
Reoviruses (RNA)
- Caspid symmetry
- Medical importance
Icosahedral (double)
Coltivirusa— Colorado tick fever
Rotavirus—c ause of fatal diarrhea in children
Picornaviruses (RNA)
- Caspid symmetry
- Medical importance
Icosahedral
“PERCH”
Poliovirus—polio-Salk/Sabin vaccines—IPV/OPV
Echovirus—aseptic meningitis
Rhinovirus—“common cold”
Coxsackievirus—aseptic meningitis; herpangina (mouth blisters, fever); hand, foot, and mouth disease; myocarditis; pericarditis
HAV—acute viral hepatitis
All are enteroviruses except rhinovirus and HAV.
Hepevirus (RNA)
- Caspid symmetry
- Medical importance
Icosahedral
HEV
Caliciviruses (RNA)
- Caspid symmetry
- Medical importance
Icosahedral
Norovirus—viral gastroenteritis
Flaviviruses (RNA)
- Caspid symmetry
- Medical importance
Icosahedral
HCV Yellow fever Denguea St. Louis encephalitis West Nile virus- meningoencephalitis Zika virusa
Togaviruses (RNA)
- Caspid symmetry
- Medical importance
Icosahedral
Rubella
Western and Eastern equine encephalitis
Chikungunya virus
Retroviruses (RNA)
- Caspid symmetry
- Medical importance
Icosahedral (HTLV), complex and conical (HIV)
Have reverse transcriptase
HTLV—T-cell leukemia
HIV—AIDS
Coronaviruses (RNA)
- Caspid symmetry
- Medical importance
Helical
“Common cold,” SARS, MERS
Orthomyxoviruses (RNA)
- Caspid symmetry
- Medical importance
Helical
Influenza virus
Paramyxoviruses (RNA)
- Caspid symmetry
- Medical importance
Helical
PaRaMyxovirus:
Parainfluenza—croup
RSV—bronchiolitis in babies
Measles, Mumps
Rhabdoviruses (RNA)
- Caspid symmetry
- Medical importance
Helical
Rabies
Filoviruses (RNA)
- Caspid symmetry
- Medical importance
Helical
Ebola/Marburg hemorrhagic fever—often fatal.
Arenaviruses (RNA)
- Caspid symmetry
- Medical importance
Helical
LCMV—lymphocytic choriomeningitis virus
Lassa fever encephalitis—spread by rodents
Bunyaviruses (RNA)
- Caspid symmetry
- Medical importance
Helical
California encephalitisa
Sandfly/Rift Valley feversa
Crimean-Congo hemorrhagic fevera
Hantavirus—hemorrhagic fever, pneumonia
Delta virus (RNA)
- Caspid symmetry
- Medical importance
Uncertain
HDV is a “defective” virus that requires the
presence of HBV to replicate
Negative-stranded viruses
“Always Bring Polymerase Or Fail Replication”
Arenaviruses, Bunyaviruses, Paramyxoviruses, Orthomyxoviruses, Filoviruses, and Rhabdoviruses.
Segmented viruses
All are RNA viruses.
“BOAR”
Bunyaviruses, Orthomyxoviruses (influenza viruses), Arenaviruses, and Reoviruses.
Rhinovirus
Acid labile—destroyed by stomach acid; therefore, does not infect the GI tract (unlike the other picornaviruses).
Yellow fever virus
A flavivirus (also an arbovirus) transmitted by Aedes mosquitoes. Virus has a monkey or human reservoir.
Symptoms: high fever, black vomitus, and jaundice. May see Councilman bodies (eosinophilic apoptotic globules) on liver biopsy.
Rotavirus
Most important global cause of infantile gastroenteritis. Major cause of acute diarrhea in the United States during winter.
Villous destruction with atrophy leads to absorption of Na+ and loss of K+.
routine vaccination of all infants except those with a history of intussusception or SCID.
Influenza viruses
Contain hemagglutinin (binds sialic acid and promotes viral entry) and neuraminidase (promotes progeny virion release) antigens.
Patients at risk for fatal bacterial superinfection, most commonly Saureus, S pneumoniae, and Hinfluenzae
Genetic/antigenic shift
Causes pandemics. Reassortment of viral genome segments, such as when segments of human flu A virus reassort with swine flu A virus.
Genetic/antigenic drift
Causes epidemics. Minor (antigenic drift) changes based on random mutation in hemagglutinin or neuraminidase genes.
“Sudden shift is more deadly than gradual drift.”
Rubella virus
once known as German (3-day) measles. Fever, postauricular and other lymphadenopathy, arthralgias, and fine, maculopapular rash that starts on face and spreads centrifugally to involve trunk and extremities .
Congenital rubella findings include “blueberry muffin” appearance due to dermal extramedullary hematopoiesis.
Paramyxoviruses
include those that cause parainfluenza (croup), mumps, measles, RSV, and human metapneumovirus, which causes respiratory tract infection (bronchiolitis, pneumonia) in infants.
All contain surface F (fusion) protein, which causes respiratory epithelial cells to fuse and form multinucleated cells.
Palivizumab (monoclonal antibody against F protein) prevents pneumonia caused by RSV infection in premature infants.
“Palivizumab for Paramyxovirus (RSV) Prophylaxis in Preemies”.
Croup (acute laryngotracheobronchitis)
Virus membrane contains hemagglutinin and neuraminidase antigens.
Results in a “seal-like” barking cough and inspiratory stridor. Narrowing of upper trachea and subglottis leads to characteristic steeple sign on x-ray. Severe croup can result in pulsus paradoxus 2° to upper airway obstruction.
Measles (rubeola) virus Disease
prodromal fever with cough, coryza, and conjunctivitis, then eventually Koplik spots. followed 1–2 days later by a maculopapular rash that starts at the head/neck and spreads downward.
3 C’s of measles:
Cough
Coryza
Conjunctivitis
*Vitamin A supplementation can reduce morbidity and mortality
Measles (rubeola) virus Sequelae
Lymphadenitis with Warthin-Finkeldey giant cells (fused lymphocytes) in a background of paracortical hyperplasia.
Possible sequelae: - SSPE (subacute sclerosing panencephalitis, occurring years later) - Encephalitis (1:2000) - Giant cell pneumonia (rare except in immunosuppressed)
Mumps virus Disease
POM-Poms.
Parotitis, Orchitis (inflammation of testes), aseptic Meningitis, and Pancreatitis.
Can cause sterility (especially after puberty)
Rabies virus Characteristics, incubation, prophylaxis
Bullet-shaped virus. Negri bodies (cytoplasmic inclusions) commonly found in Purkinje cells of cerebellum and in hippocampal neurons.
has long incubation period (weeks to months).
Postexposure prophylaxis is wound cleaning plus immunization with killed vaccine and rabies immunoglobulin.
Rabies virus Transmission, Physiophatology and Disease
Infection more commonly from bat, raccoon, and skunk bites than from dog bites in the United States; aerosol transmission (eg, bat caves) also possible.
Travels to the CNS by migrating in a retrograde fashion (via dynein motors) up nerve axons after binding to ACh receptors.
Progression of disease: fever, malaise agitation, photophobia, hydrophobia, hypersalivation paralysis, coma death.
Ebola virus Disease and Diagnosis
targets endothelial cells, phagocytes, hepatocytes.
Following an incubation period of up to 21 days, presents with abrupt onset of flu-like symptoms, diarrhea/vomiting, high fever, myalgia. Can progress to DIC, diffuse hemorrhage, shock.
Diagnosed with RT-PCR within 48 hr of symptom onset. High mortality rate.
Ebola virus Transmission and Treatment
Transmission requires direct contact with bodily fluids, fomites (including dead bodies), infected bats or primates (apes/monkeys); high incidence of nosocomial infection.
Supportive care, no definitive treatment.
Zika virus Transmission, Disease, Diagnosis
transmitted by Aedes mosquito bites. Sexual and vertical transmission possible.
Causes conjunctivitis, low-grade pyrexia, and itchy rash in 20% of cases. Can lead to congenital microcephaly or
miscarriage if transmitted in utero.
Diagnose with RT-PCR or serology.
Hepatitis viruses
Pag 172
Extrahepatic manifestations of hepatitis B
Aplastic anemia
Membranous GN >membranoproliferative GN
Polyarteritis nodosa
Extrahepatic manifestations of hepatitis C
Essential mixed cryoglobulinemia, risk B-cell NHL, ITP, autoimmune hemolytic anemia.
Membranoproliferative GN >membranous GN
Leukocytoclastic vasculitis
Sporadic porphyria cutanea tarda, lichen planus
risk of diabetes mellitus, autoimmune hypothyroidism
