Viral Infections in Humans

• Viral Pathogenesis


  1. Implantation of virus at the portal of entry

  2. Local replication

  3. Spread to target organs

  4. Spread to sites of shedding of virus into the environment
• Factors affecting pathogenic mechanisms


  • Accessibility of virus to tissue
  • Cell susceptibility to virus multiplication
  • Virus susceptibility to host defenses
• Chickenpox


  A highly contagious disease caused by the varicella-zoster virus (VZV)

  
• Chickenpox can be serious, especially in babies, adolescents, adults, pregnant women, and people with bodies that have a lowered ability to fight germs and sickness (weakened immune system)

  
• Chickenpox transmission

  1. The virus spreads easily from people with chickenpox to others who have never had the disease or never been vaccinated

  2. If one person has it, up to 90% of the people close to that person who are not immune will also become infected

  3. The virus spreads mainly through close contact with someone who has chickenpox

  4. A person with chickenpox is considered contagious beginning 1 to 2 days before rash onset until all the chickenpox lesions have crusted (scabbed)

  5. Vaccinated people who get chickenpox may develop lesions that do not crust

  6. It takes about 2 weeks (from 10 to 21 days) after exposure to a person with chickenpox or shingles for someone to develop chickenpox

  
• The varicella-zoster virus also causes shingles. After chickenpox, the virus remains in the body (dormant). People get shingles when VZV reactivates in their bodies after they have already had chickenpox.

  
• The best way to prevent chickenpox is to get the chickenpox vaccine.

  
• Measles


  A virus in the paramyxovirus family (Rubeola Virus) that is normally passed through direct contact and through the air

  
• Measles is a human disease and is not known to occur in animals.

  
• Measles signs and symptoms

  1. High fever beginning about 10 to 12 days after exposure

  2. Runny nose, cough, red and watery eyes, and small white spots inside the cheeks in the initial stage

  3. Rash erupts, usually on the face and upper neck, and spreads to the hands and feet over about 3 days

  4. Rash lasts for 5 to 6 days, then fades
• Measles transmission


  1. Spread by coughing and sneezing, close personal contact or direct contact with infected nasal or throat secretions

  2. The virus remains active and contagious in the air or on infected surfaces for up to 2 hours

  3. Can be transmitted by an infected person from 4 days prior to the onset of the rash to 4 days after the rash erupts

  
• No current treatment available for measles

  
• Routine measles vaccination for children, combined with mass immunization campaigns in countries with high case and death rates, are key public health strategies to reduce global measles deaths.

  
• Conjunctivitis


  May accompany the common cold and other systemic viral infections (especially measles, but also chickenpox, rubella, and mumps)

  
• Epidemic keratoconjunctivitis


  Usually results from adenovirus serotypes Ad 5, 8, 11, 13, 19, and 37 and tends to cause severe conjunctivitis

  
• Genotype HAdV-D is associated with conjunctivitis and HAdV-D53 and HAdV-D54 have been associated with epidemic keratoconjunctivitis.
• Conjunctivitis signs and symptoms

  1. After an incubation period of about 5 to 12 days, conjunctival hyperemia, watery discharge, and ocular irritation usually begin in one eye and spread rapidly to the other

  2. Follicles may be present on the palpebral conjunctiva

  3. A preauricular lymph node is often enlarged and painful
• Uveitis


  Inflammation of the uvea, the middle layer of the eye, which contains the iris, ciliary body and the choroid

  
• Retinitis

  Inflammation of the retina, the innermost layer of the eye

  
• Types of uveitis

  • Anterior uveitis (affects the inside of the front of the eye)
  • Intermediate uveitis (affects the retina and blood vessels just behind the lens as well as the vitreous)
  • Posterior uveitis (affects the retina or the choroid)
  • Panuveitis (all layers of the uvea are inflamed)

  
• Symptoms of uveitis include blurry vision, floaters, eye pain, redness, and sensitivity to light.
• Common cold

  Sore throat and runny nose are usually the first signs, followed by coughing and sneezing. Most people recover in about 7-10 days.
• Although many types of viruses can cause a common cold, rhinoviruses are the most common cause.
• How the common cold spreads

  1. A cold virus enters your body through your mouth, eyes or nose

  2. The virus can spread through droplets in the air when someone who is sick coughs, sneezes or talks

  3. It also spreads by hand-to-hand contact with someone who has a cold or by sharing contaminated objects

  
• Common cold symptoms


  • sore throat
  • runny nose
  • coughing
  • sneezing
  • headaches
  • body aches
• You can help reduce your risk of getting a cold by washing your hands often, avoiding close contact with sick people, and not touching your face with unwashed hands.
• How to prevent spreading a cold

  1. Stay at home while you are sick and keep children out of school or daycare while they are sick

  2. Avoid close contact with others, such as hugging, kissing, or shaking hands

  3. Move away from people before coughing or sneezing

  4. Cough and sneeze into a tissue then throw it away, or cough and sneeze into your upper shirt sleeve

  5. Wash your hands after coughing, sneezing, or blowing your nose

  6. Disinfect frequently touched surfaces and objects
• Influenza

  A contagious respiratory illness caused by influenza viruses that infect the nose, throat, and sometimes the lungs

  
• Influenza symptoms

  • fever or feeling feverish/chills
  • cough
  • sore throat
  • runny or stuffy nose
  • muscle or body aches
  • headaches
  • fatigue (tiredness)
  • some people may have vomiting and diarrhea

  
• There are four types of influenza viruses: A, B, C and D. Human influenza A and B viruses cause seasonal epidemics of disease (known as flu season) almost every winter in the United States. Influenza A viruses are the only influenza viruses known to cause flu pandemics.

  
• Avian influenza

  Disease in birds caused by infection with avian (bird) influenza (flu) Type A viruses
• Infected birds can shed avian influenza A viruses in their saliva, nasal secretions, and feces. Susceptible birds become infected when they have contact with the virus as it is shed by infected birds.

  
• Influenza A viruses have infected many different animals, including ducks, chickens, pigs, whales, horses, and seals. However, certain subtypes of influenza A virus are specific to certain species, except for birds, which are hosts to all known subtypes of influenza A viruses.

  
• Currently circulating Influenza A subtypes in humans are H3N2 and H1N1 viruses.

  
• Middle East Respiratory Syndrome (MERS)

  A viral respiratory illness that is new to humans, first reported in Saudi Arabia in 2012 and has since spread to several other countries

  
• Most people infected with MERS-CoV developed severe respiratory illness, including fever, cough, and shortness of breath.

  
• MERS-CoV has spread from ill people to others through close contact, such as caring for or living with an infected person.

  
• Different animals

  • Ducks
  • Chickens
  • Pigs
  • Whales
  • Horses
  • Seals
• Certain subtypes of influenza A virus are specific to certain species, except for birds, which are hosts to all known subtypes of influenza A viruses

  
• Currently circulating Influenza A subtypes in humans are H3N2 and H1N1 viruses