Viral Infections of Humans

• Viruses multiply within host cells
• It is during their escape from those cells—either by cell lysis or budding—that the host cells are destroyed
• Cell destruction leads to most of the symptoms of a viral infection, which vary depending on the location of the infection
• Viral infections of the skin

  • Chickenpox and shingles
  • German measles (rubella)
  • Measles (hard measles, rubeola)
  • Monkeypox
  • Smallpox
  • Warts
• Varicella-zoster virus


  A DNA virus which is also known as human herpesvirus 3
• Rubella virus


  An RNA virus
• Measles (rubeola) virus


  An RNA virus
• Monkeypox virus


  A DNA virus
• Variola virus


  Two strains: variola minor and variola major, a DNA virus
• Human papillomaviruses (HPV)


  At least 70 different types, DNA viruses
• Viral infections of the eyes

  • Adenoviral conjunctivitis and keratoconjunctivitis
  • Herpes simplex and varicella-zoster viruses can also cause keratoconjunctivitis
  • Hemorrhagic conjunctivitis
  • Retinitis
• Adenoviruses and enteroviruses


  Cause hemorrhagic conjunctivitis
• Cytomegalovirus (CMV)


  Mostly causes retinitis
• People with viral infections (e.g., cold sores) should wash their hands thoroughly before inserting or removing contact lenses or otherwise touching their eyes
• Viruses that cause the common cold

  • Rhinoviruses (more than 100 serotypes)
  • Coronaviruses
  • Parainfluenza viruses
  • Respiratory syncytial virus (RSV)
  • Human metapneumovirus
  • Influenza viruses
  • Adenoviruses
  • Enteroviruses
• Transmission of the common cold occurs via respiratory secretions by way of hands and fomites or direct contact with or inhalation of airborne droplets
• Viruses that cause acute, febrile, viral respiratory disease

  • Parainfluenza viruses
  • Respiratory syncytial virus (RSV)
  • Adenovirus
  • Rhinoviruses
  • Certain coronaviruses
  • Coxsackieviruses
  • Echoviruses
• Transmission of acute, febrile, viral respiratory disease occurs via direct oral contact or by droplets
• Avian influenza virus type A


  Three prominent subtypes—H5, H7, and H9
• Avian influenza (bird flu) transmission occurs via contact with infected poultry or contaminated surfaces
• Hantaviruses


  At least five different types (Sin Nombre, Bayou, Black Creek Canal, New York-1, Monongahela) cause hantavirus pulmonary syndrome (HPS)
• Hantavirus pulmonary syndrome (HPS) transmission occurs via inhalation of aerosolized rodent feces, urine, and saliva
• Influenza viruses


  Types A, B, and C; RNA viruses
• Influenza transmission is via infected humans; pigs and birds also serve as reservoirs
• MERS transmission occurs via contact with animals (camels, bats?), infected individuals by respiratory droplets, or by touching the mouth, nose, or eye after touching a contaminated surface or object
• Herpes simplex virus type 1 (HSV-1) and herpes simplex type 2 (HSV-2)


  DNA viruses in the family Herpesviridae that cause cold sores (fever blisters, herpes labialis)
• Either HSV-1 or HSV-2 can also infect the genital tract, although genital herpes infections are most often caused by HSV-2
• Viruses that cause viral gastroenteritis (viral enteritis, viral diarrhea)

  • Enteric adenoviruses
  • Astroviruses
  • Sapoviruses
  • Caliciviruses
  • Rotaviruses
  • Norovirus-like viruses
• Transmission of viral gastroenteritis occurs via infected humans, most often by way of the fecal–oral route; possibly from contaminated water and shellfish
• Hepatitis A virus (HAV)


  A linear ssRNA virus that causes type A hepatitis (HAV infection, infectious hepatitis, epidemic Hepatitis)
• Hepatitis A transmission is via the fecal–oral route
• Hepatitis B virus (HBV)


  An enveloped, circular dsDNA virus that causes type B hepatitis (HBV infection, serum hepatitis)
• Hepatitis B transmission is via sexual transmission or household contact with an infected person; injected drug use; tattooing; needlesticks
• Hepatitis C virus (HCV)


  An enveloped, linear ssRNA virus that causes type C hepatitis (HCV infection, non-A non-B hepatitis)
• Hepatitis C transmission is primarily parenterally transmitted; rarely sexually
• Hepatitis D virus (HDV, delta virus)


  An enveloped, circular ssRNA viral satellite that causes type D hepatitis (HDV infection, delta hepatitis); coinfection with HBV is necessary
• Hepatitis D transmission is via exposure to infected blood and body fluids
• Hepatitis E virus (HEV)


  A nonenveloped, ssRNA virus that causes type E hepatitis
• Hepatitis E transmission is via fecally contaminated drinking water; also person-to-person
• Viral STDs


  • Anogenital herpes viral infections (genital herpes)
  • Genital warts (genital papillomatosis, condyloma acuminatum)