Virology Public Health

VIROLOGY

  • Virology is the study of viruses and viral diseases, including their distribution, biochemistry, physiology, molecular biology, ecology, evolution, and clinical aspects.

VIRUS

  • Viruses are smaller than any known bacteria.
  • Viruses cause diseases in organisms and consist of a core of nucleic acid surrounded by a protein coat (CAPSID).
  • Viruses are obligate intracellular parasites.

VIROIDS

  • Small circular RNA molecules infecting plants.
  • Do not have protein capsids.
  • No cure for plants that are infected.

PRIONS

  • Particles of proteins that cause some diseases in animals.
  • Do not contain nucleic acids.
  • First disease-causing agent that multiplies but does not contain nucleic acid.

Notable diseases caused by Prions:

  • Mad Cow Disease
  • Scrapie
  • Kuru
  • Creutzfeldt-Jacob Disease

DNA VIRUSES

PARVOVIRIDAE

PAPOVAVIRIDAE

  • Human Papilloma

HEPADNAVIRIDAE

  • Hepatitis B

POXVIRIDAE

  • Variola
    • Habitat: Infected humans
    • Transmission:
      • Respiratory tract (droplet spread)
      • Skin inoculation
      • Patients most contagious before appearance of rashes
    • Disease: Smallpox
      • Rash similar to chicken pox
      • Can become severe with bleeding into the skin and mucous membranes followed by death
  • Vaccinia
    • Large complex enveloped virus. Also called Cowpox.
    • Constituent of smallpox vaccine.

HERPESVIRIDAE

  • Herpes Simplex
    • Characterized by vesicles.
      • HSV-1: Transmitted by saliva or by direct contact.
      • HSV-2: Transmitted by sexual/transvaginal.
  • Varicella Zoster
  • Epstein-Barr
    • Causative agent: Epstein Barr Virus (Human Herpes Virus)
    • Transmission:
      • Kissing
      • Sharing food
      • Coughing
      • Genital secretions
    • Disease:
      • "Kissing Disease"
      • Acute infections, Chronic Active Infections
      • Nasopharyngeal infection
      • Lymphoma (Burkitt's most common)
      • Some conditions associated with HIV
  • Human Herpes Virus

ADENOVIRUS

  • Affects Upper respiratory tract, Lower Respiratory Tract, Gastro Intestinal Tract, Genitourinary tract.

RNA VIRUSES

REOVIRIDAE

  • Double-stranded RNA virus
  • Rotavirus causes gastroenteritis
  • Colorado Tick Fever

FLAVIVIRIDAE

  • West Nile
  • Dengue
    • Causative agent: Dengue Virus
    • Has 5 serotypes (DENV1 to 5)
    • Habitat: Domestic water container
    • Transmission: Mosquito bite (Aedes aegypti or Aedes albopictus)
    • Disease: Dengue Fever, Dengue Hemorrhagic Fever
      • High fever, headache, nausea, vomiting
      • Joint & muscle pain ("Breakbone fever")
      • Rash (after 24 hours)
      • Potentially deadly complication
      • High fever
      • Enlargement of liver
      • Circulatory failure (severe cases)
  • Yellow Fever
  • Hepatitis C
  • Zika Virus
    • Causative agent: Zika Virus
    • Transmission: Mosquito bite (Aedes aegypti or Aedes albopictus), Placental
    • Disease:
      • Birth defects in infants of mothers infected during pregnancy
      • Fever, rash, headache, joint & muscle pain
      • Conjunctivitis

TOGAVIRIDAE

  • Rubella
  • Alphavirus
    • Causative agent: Alphavirus
    • Transmission: Mosquito bite (Aedes aegypti or Aedes albopictus)
    • Disease: Chikungunya
      • Fever, headache, joint (severe for a few days or weeks) & muscle pain
      • Nausea, fatigue, rash
  • Eastern Equine Encephalitis
  • Western Equine Encephalitis

RETROVIRIDAE

  • HIV
    • Causative agent: Human Immunodeficiency Virus
    • Transmission: Transfer of body fluids, transplacental, needlestick
    • Disease:
      • Phase 0: Infection
      • Phase 1: Window Period: rapid viral replication
      • Phase 2: Seroconversion
      • Phase 3: Latent Period
      • Phase 4: Early Symptomatic
      • Phase 5: AIDS

CORONAVIRIDAE

  • Causative agent:
    • Severe acute respiratory syndrome-related virus or SARS-CoV
    • Middle East respiratory syndrome-related coronavirus or MERS-CoV or EMC/2012
    • Severe acute respiratory syndrome coronavirus 2 or or SARS-CoV-2
      • is a strain of coronavirus that causes COVID-19 (coronavirus disease 2019), the respiratory illness responsible for the ongoing COVID-19 pandemic.
      • The virus previously had a provisional name, 2019 novel coronavirus (2019-nCoV).
  • Transmission: Spread by aerosols and in large droplets
  • Disease:
    • High fever (>38°C), chills, rigors
    • Headache, dizziness
    • Malaise, myalgia
    • Cough, difficulty of breathing that could lead to acute respiratory distress syndrome
    • Patients may also develop diarrhea (20%)
    • Fever, cough shortness of breath
    • Diarrhea
    • Progresses to respiratory failure more rapidly than SARS
    • SARS produces flu-like symptoms and may include fever, muscle pain, lethargy, cough, sore throat, and other nonspecific symptoms. The only symptom common to all patients appears to be a fever above 38°C38 °C (100°F100 °F). SARS may eventually lead to shortness of breath and pneumonia; either direct viral pneumonia or secondary bacterial pneumonia.

CALICIVIRUS

  • Hepatitis E
  • Norwalk Virus - most common cause of non-bacterial diarrhea in adults

PICORNAVIRIDAE

  • Poliovirus
    • Causative Agent: Polio Virus
    • Habitat: Infected human
    • Transmission: Fecal-oral route
    • Disease: Poliomyelitis
      • Throat infection
      • Infantile paralysis w/or w/o flaccid paralysis
      • Stiffness of the neck and back
  • Echovirus
  • Rhinovirus
  • Coxsackie Virus
  • Hepatitis A

PARAMYXOVIRIDAE

  • Parainfluenza
  • Measles (Rubeolla)
  • Mumps

FILOVIRIDAE

  • Marburg
  • Ebola
    • Causative agent: Ebola Virus
    • Habitat: Wild animals (Fruit bats, Chimpanzees)
    • Transmission:
      • Introduced to humans through close contact to secretions of wild animals
      • Human-to-human spread
    • Disease:
      • Fever, fatigue, headache sore throat
      • Diarrhea, vomiting, rash, symptoms of impaired liver and kidneys
      • Internal and/or external bleeding (gums and stools)

ORTHOMYXOVIRIDAE

  • Causative Agent: Influenza Virus
    • Influenza A
      • Habitat:
        • Infected humans
        • Birds
        • Pigs
      • Transmission:
        • Airborne spread
        • Direct contact
      • Disease
        • Severe symptoms
        • Pandemics
        • 1. AH1N1
          • "Flu Pandemic" "Swine Flu Pandemic"
          • Killed healthy young adults
          • From frozen tissue samples
          • Causing overreaction of immune system
    • Influenza B
      • Major outbreaks
    • Influenza C
      • Mild respiratory symptoms
      • Transmission:
        • Respiratory droplet
      • Disease
        • Fever and chills
        • Headache
        • Viral respiratory infection
        • Pain throughout the body
    • 2. AH5N1
      • Habitat: Infected wild & domesticated animals
      • Transmission:
        • Infected poultry or surfaces
        • Contaminated by excretions
      • P2P transmission is rare
      • "Bird Flu" "Avian Influenza"

RHABDOVIRIDAE

  • Rabies Virus
    • Causative Agent: Rabies Virus
    • Habitat:
      • Animals
      • Dogs
      • Foxes
      • Coyotes
      • Wolves
      • Raccoons
      • Bats
    • Transmission:
      • Bite, saliva
      • Airborne
    • Disease
      • Acute encephalomyelitis of mammals
  • Stomatitis

ARENAVIRIDAE

  • Lassa Fever
    • Reservoir: Rodents
    • Transmission: Inhalation or ingestion (from urine and droppings)
    • Disease:
      • Neurological
      • Encephalitis
      • Multiple-organ failure
      • Most common complication is deafness

BUNYAVIRIDAE

  • Causative agent: Bunyavirus
  • Transmission:
    • Mosquito, tick, or flea bite
  • Habitat:
    • Rodents
    • Phlebotomus flies
    • Birds
  • Hantavirus (under the Bunyaviridae family of viruses)
    • Transmission: Inhalation of aerosols contaminated with infected urine
    • Habitat & Vector: Rodents
    • Disease:
      • Rift-Valley Fever
        • Hepatic necrosis
      • Crimean-Congo Hemorrhagic Fever
        • Varying degrees of skin bleeding
        • Nosebleed
      • Hantaan Hemorrhagic Disease
        • Sign of upper GI bleeding
        • Bleeding of the gums
        • Leakage of plasma and erythrocytes through the vascular endothelium
        • Leakage of plasma and erythrocytes through the vascular endothelium
      • La Crosse Virus "California Encephalitis"
        • Vector: Day-biting Aedes triseriatus
        • Sudden onset
        • Fever, headache, vomiting
        • Seizures
        • Signs of meningitis
      • Hantavirus Pulmonary Syndrome
        • Changes most prominent in the kidney and is usually accompanied by hemorrhagic necrosis of the kidney
        • Interstitial pulmonary edema, respiratory failure, and death within days
          Mental depression
          Restlessness
          Salivation
          Spasms of throat muscles (death by respiratory failure
          Convulsions
          Photosensitivity
          Hydrophobia

RELATIVE SIZES

The size of a virus is very small relative to the size of cells and organelles.

Virions, single virus particles, are very small, about 20-250 nanometers (1 nanometer=11,000,000 mm1 \text{ nanometer} = \frac{1}{1,000,000} \text{ mm}).

These individual virus particles are the infectious form of a virus outside the host cell. Unlike bacteria (which are about 100 times larger), we cannot see viruses with a light microscope, with the exception of some large virions of the poxvirus family.

VIRUSES AND DISEASE

Viruses cause a variety of diseases in animals, including humans, ranging from the common cold to potentially fatal illnesses like meningitis. These diseases can be treated by antiviral drugs or by vaccines, but some viruses, such as HIV, are capable of avoiding the immune response and mutating so as to become resistant to antiviral drugs.

OVERVIEW OF VIRAL INFECTIONS

  • Encephalitis/meningitis
    • JC virus
    • Measles
    • LCM virus
    • Arbovirus
    • Rabies
  • Pharyngitis
    • Adenovirus
  • Common cold
    • Rhinoviruses
    • Parainfluenza virus
    • Respiratory syncytial virus
  • Gingivostomatitis
    • Herpes simplex type 1
    • Epstein-Barr virus
    • Cytomegalovirus
  • Cardiovascular
    • Coxsackie B virus
  • Hepatitis
    • Hepatitis virus types A, B, C, D, and E
  • Skin infections
    • Varicella-zoster virus
    • Human herpesvirus 6
    • Smallpox
    • Molluscum contagiosum
    • Human papillomavirus
    • Parvovirus B19
  • Sexually transmitted diseases
    • Herpes simplex type 2
    • Human papillomavirus
    • Rubella
    • Measles
    • Coxsackie A virus
    • HIV
  • Eye infections
    • Herpes simplex virus
    • Adenovirus
    • Cytomegalovirus
  • Parotitis
    • Mumps virus
  • Pneumonia
    • Influenza virus types A and B
    • Parainfluenza virus
    • Respiratory syncytial virus
    • Adenovirus
    • SARS coronavirus
  • Myelitis
    • Poliovirus
    • HTLV-I
  • Gastroenteritis
    • Adenovirus
    • Rotavirus
    • Norovirus
    • Astrovirus
    • Coronavirus
  • Pancreatitis
    • Coxsackie B virus

IMMUNOBIOLOGIC

Contains preparations from human or animal donors including globulins. These are used for immunization.

  1. Vaccine - suspension of live attenuated or killed microorganisms or fractions thereof administered to induce immunity and prevent infectious disease.
  2. Toxoid - modified bacterial toxin that has been rendered, nontoxic but retains the ability to stimulate the formation of antitoxin
  3. Immunoglobulin - sterile solution containing antibody from human blood. It is a percentage protein fraction obtained by fractionation of large pools of blood plasma. It is primarily indicated for routine maintenance of certain immunodeficient persons and for passive immunization against measles and hepatitis A.
  4. Antitoxin - solution of antibodies derived from the serum of animals immunized with specific antigens (diphtheria, tetanus) used to achieve passive immunity or effect a treatment.