فايروسات

• Herpes viruses that commonly infect humans


  • Herpes simplex viruses type 1&2
  • Varicella-Zoster virus
  • Cytomegalovirus(CMV)
  • Epstein-Barr viruses
  • Human herpes viruses 6,7
  • Kaposi's sarcoma virus or human herpesvirus 8
  • Herpes B virus of monkey
• Virion


  • Spherical
• Genome


  • dsDNA, Linear
• Protein


  • More than 35 proteins in virion
• Envelope


  • Contains viral glycoprotein and Fc receptor
• Replication

  • In the nucleus and bud from the nuclear membrane
• Structural components of all Herpes viruses

  • Genome
  • Capsid
  • Envelope
  • Tegument
• Herpes virus subfamilies

  • Alpha Herpes
  • Beta Herpes
  • Gamma Herpes
• Alpha Herpes

  Rapid replication cycle (12-18 hrs), variable host range, tendency to form latency in sensory ganglia, produce rapid CPE & release virus from infected cells
• Beta Herpes


  Narrow host range, slow replication cycle (more than 24 hrs)
• Gamma Herpes


  Infect lymphoid tissue & cause latency in lymphocyte
• Herpes simplex viruses (HSV)


  Wide spread in human, wide host range, two types (1&2) with similar genome organization and 50-70% homology
• HSV-1 transmission

  Direct contact with infected saliva, skin lesions or respiratory secretions
• HSV-2 transmission

  Sexually (Venereal disease) and from maternal genital to newborn (Perinatal)
• HSV pathology

  Cytolytic, leads to ballooning of infected cells and formation of intracellular inclusion bodies
• HSV pathogenesis - primary infection

  Virus enters through defects/broken skin or mucous membranes, multiplies locally with cell-to-cell spread, enters cutaneous nerve fibres and transported intra-axonally to dorsal root ganglia where it replicates, migrates from ganglia to skin/mucosa to cause lesions
• HSV latent infection

  Virus stays latent in infected cells for lifetime, can be reactivated by stimuli like axonal injury, fever, stress, UV/sunlight exposure, infection
• HSV-1 clinical features

  Herpes Labialis - Painful ulcerating vesicles on lips that spontaneously resolve in <2 weeks
• HSV-2 clinical features

  Genital herpes - Painful vesicular lesions in genital area, Neonatal herpes from contact with maternal genital to newborn
• HSV laboratory diagnosis

  • Direct detection (Giemsa stain, EM, Immunofluorescence)
  • PCR
  • Virus isolation
  • Serology (IgM & IgG ELISA)
• Varicella-Zoster Virus (VZV)

  Causes two diseases: Varicella (Chickenpox) and Zoster (Shingles)
• VZV pathogenesis - Varicella

  Infection occurs through mucosa of conjunctiva and upper respiratory tract, initial replication in regional lymph nodes, then primary and secondary viremia transports virus to skin causing vesicles
• VZV pathogenesis - Zoster


  Reactivation of latent VZV in neurons of sensory ganglia, virus travels down nerve to skin inducing vesicle formation
• VZV laboratory diagnosis

  • Direct detection (multinucleate giant cells)
  • Virus isolation
  • Serology (IgG, IgM)
• Epstein-Barr Virus (EBV)

  Latency in B lymphocytes, associated with Infectious Mononucleosis, Nasopharyngeal Carcinoma, Burkitt Lymphoma, Oral hairy leukoplakia
• EBV pathogenesis - primary infection

  Transmitted by saliva, infects B lymphocytes by binding to CD21 receptor, integrates viral DNA into cell genome, establishes latent infection
• EBV viral antigens

  • Viral capsid antigen (VCA)
  • Early antigen (EA)
  • Epstein-Barr nuclear antigen (EBNA)
  • Viral membrane antigen (VMA)
• EBV laboratory diagnosis

  • Monospot test for heterophil antibody
  • Serology for VCA IgM, VCA IgG, EBNA IgG
  • Histology for Burkitt's lymphoma and Nasopharyngeal Carcinoma
• No vaccine available for EBV, Acyclovir reduces EBV shedding but has no effect on symptoms
• Cytomegalovirus (CMV)

  Ubiquitous herpes virus, causes characteristic cytopathic effect and nuclear inclusion bodies
• CMV transmission

  Direct contact with infected saliva, blood, urine, semen, cervical/vaginal secretions or breast milk, Perinatal
• CMV pathogenesis - normal host

  Transmitted by close contact, causes systemic infection after 4-8 weeks, primary infection usually asymptomatic but can cause Infectious Mononucleosis
• CMV pathogenesis - immunocompromised host

  Primary infection more severe, can cause pneumonia, leukopenia, transplant rejection
• CMV pathogenesis - congenital/perinatal infection

  Can cause severe fetal/newborn disease, developmental defects, mental retardation, deafness, high mortality
• CMV laboratory diagnosis

  • Direct detection (histology, pp65 antigenemia, PCR)
  • Virus isolation
  • Serology (IgG, IgM)
• Human Herpes virus 6

  Two forms (A and B), associated with exanthema subitum (roseola infantum), rejection of transplanted kidneys, fulminant hepatitis, CNS infections
• Human Herpes virus 7

  Associated with some cases of exanthema subitum, found in saliva of majority of adults
• Human Herpes virus 8


  Associated with Kaposi's sarcoma in AIDS patients and intra-abdominal solid tumors
• Shingles is caused by Varicella-Zoster Virus (VZV)
• pp65 antigenemia is found in Cytomegalovirus (CMV) infection