10 - DNA Viruses Flashcards
Herpes viruses
- Large dsDNA genomes encoding 100-200 genes
- All herpesviruses are enveloped icosahedral viruses
- Induce latent infections in humans
Subfamilies of herpesviruses
- Alpha subfamily (neurons and epithelia)
- Beta and gamma subfamilies (leukocytes and epithelia)
Alpha subfamily of herpesviruses
- Herpes simplex virus type 1
- Herpes simplex virus type 2
- Varicella zoster
Beta and gamma subfamilies of herpesviruses
- Human cytomegalovirus
- Epstein Barr virus
- Human herpes virus 6-8
- B virus
Where does HSV-1 persist in a latent state
Trigeminal ganglia and is reactivated by trauma, fatigue, sunlight, emotional stress
Herpes simplex virus type 1 (HSV-1)
- cold sore, is a recurrence of the first or primary infection
- Herpetic whitlow is HSV infection of fingers and thumbs (often caused by autoinoculation secondary to genital herpes and health care workers)
Herpes simplex virus type 2 (HSV-2)
- Associated with genital herpes
- Infects epithelial cells of external genitalia, rectum and adjacent skin
Neonatal herpes
- HSV-2 can be transmitted to newborns during delivery
- Results in blindness and neurological disease in babies.
- Caesarian delivery recommended
Varicella Zoster Virus (VZV)
- Receptor is mannose-6-phosphate
- Acquired by respiratory route (airborne)
- Vesicles similar to those produced in HSV are formed, and form lesions, but unlike the HSV lesions are not infectious
- Shingles is reactivation of chickenpox
2 main syndromes caused by VZV
- Varicella (chickenpox)
- Zoster (shingles)
Shingles
- the virus becomes dormant in the dorsal root ganglion but can also affect any sensory nerve
- Can be reactivated to cause shingles
- Usually only one such event in a lifetime (elderly or immunocompromised)
Example of drug to treat HSV and VZV
Acyclovir
Human cytomegalovirus (HCMV)
- 80% prevalence
- Infection is initiated through a nonspecific interaction with heparan sulfate proteoglycans
- Life long
- Interferes with host immune functions including antigen presentation, cytokine production, and natural killer cell activity
Cytomegalo
Enlarged cell
Risk groups for HCMV
- Organ transplant recipients
- Immunocompromised (especially AIDS patients)
- Newborns
Epstein Barr virus (EBV)
- Causes infectious mononucleosis (glandular fever/kissing disease)
- Infects epithelial cells lining the throat.
- New virus particles infect memory B cells, which rapidly proliferate and take on an atypical appearance that is useful in diagnosis
How does EBV spread
Present in oropharyngeal secretions and therefore is spread by mouth-to-mouth contact or shared drinking glasses
Manifestations of EBV
Enlargement of lymph nodes and spleen, sore throat, fever, headache, and general tiredness and weakness
Severe diseases caused by EBV
- Burkitt’s lymphoma
- nasopharyngeal carcinoma
Burkitt’s lymphoma
- Tropical africa
- Coinfection with malaria, or immunodeficiency
- Those infected with HIV
Human papilloma virus (HPV)
- Nonenveloped icosahedral, small dsDNA viruses
- Infect epithelial cells through micro-abrasions causing genital warts and/or cancerous lesions
- Spread by direct contact and by autoinoculation via scratching
How many strains of HPV are there and how many are transmitted sexually
> 170 strains with >40 transmitted sexually
HPV16 and 18
Responsible for most cervical cancers in women
HPV 6 and 11
Responsible for genital warts and laryngeal papillomatosis
how are early pre cancerous changes of HPV detected
Via pap smears
Nona-valent human papillomavirus vaccine
- 9 HPV strains, including 6, 11, 16 and 18
- School-based National HPV Vaccination Programs (Targets young adolescent)
Hepatitis B virus (HBV)
- dsDNA virus
- Infect liver cells (hepatocytes) and causes hepatitis (inflammation of the liver)
- Most infections are acute and the virus is cleared by immune response
Transmission of HBV
- Parenteral transmission
- Highest concentration of virus found in blood (lower conc. in semen, vaginal fluid)
- 50% of acute HBV is acquired sexually
- Needlestick injury, needle sharing, tattooing, acupuncture
Clinical features of HBV
- symptomatic acute
hepatitis: fatigue, malaise, fever, abdominal
pain, icterus (jaundice), pruritus (itching) - Usually asymptomatic in neonates and young
children
Hepatitis B replication
- Virus enters the cell
- Capsid disassembly
- Viral relaxed circular DNA
enters nucleus of cell - CCC-DNA created
- Transcription to RNA occurs
- RNA is packaged up into a
new capsid - New virus is created
- Virus leaves cell.
What happens if HBV is not cleared
- Virus continues to replicate and patient becomes chronic carrier (continued HBV infection 6 months after infection)
- Associated with development of cirrhosis (liver damage and scarring) and liver cancer (hepatocellular carcinoma)
Prevention of perinantal HBV transmission
providing hepatitis B immune globulin and hepatitis B vaccine to infants within 12 hours of birth
Blood tests for HBV
- Hepatitis B surface antigen (HBsAg) is detectable in blood soon after infection
- Clearance of HBsAg from blood, and appearance of anti-HBs, indicates recovery
- Persistence of HBsAg (> 6 months after infection), lack of anti-HBs, indicates chronic infection (carrier state)
Polyoma virus JC
Fatal demyelinating disease of the CNS: progressive multifocal leukoencephalopathy (PML) in which oligodendrocytes are destroyed
