Unit 5 Viral Diseases

Part I: Characteristics of a Virus

Definition of a Virus

  • A virus is composed of a DNA or RNA core housed within a protective capsid.

  • It is classified as a pathogenic intracellular parasite.

  • Viruses rely exclusively on the host cell for metabolism and reproduction, highlighting their parasitic nature.

  • Viruses are neither classified as living nor non-living entities.

Structure of a Virus

  • Components:

    • Virus Spikes: Assist in attachment to host cells.

    • Head: Contains the protein capsid and the viral genome (DNA/RNA).

    • Neck, Tail Sheath, Tail Fibers: Involved in penetration and transfer of genetic material into the host.

    • Endplate & Pins: Aid in anchoring and infection process.

    • Lipid Envelope: Present in enveloped viruses such as the influenza virus.

    • Bacteriophages: A specific type of virus that infects bacteria, illustrating the diversity of viral structures.

Part II: Viral Diseases

1. Hepatitis A

  • Hepatitis A Virus (HAV): Causes acute liver infection but doesn’t progress to a chronic stage.

  • Characteristics: The disease typically resolves without medical intervention, and individuals who recover gain lifelong immunity.

Transmission of Hepatitis A

  • Routes:

    • Water and food contaminated by feces

    • Fecal-oral route

    • Mechanical vectors such as flies and contaminated fomite surfaces.

Susceptible Hosts

  • Children in daycare centers

  • Adult daycare workers

  • International travelers

  • Men who have sex with men

Signs and Symptoms

  • Prodromal Phase:

    • Nausea

    • Vomiting

    • Loss of appetite

    • Muscle pain

    • Fatigue

    • Malaise

    • Fever

  • Icteric Phase:

    • Jaundice (yellowing of the skin)

    • Dark urine and pale stool

    • Skin rash and itching

    • Hepatomegaly (enlarged liver)

    • Inflammation of liver tissue

Diagnostic Tests

  • Serology Tests:

    • Detection of Anti-HAV IgM (recent infection) and Anti-HAV IgG (previous infection).

    • Nucleic Acid Amplification Tests, including RT-PCR.

Treatment

  • Supportive Care: Managing symptoms.

  • Post-Exposure Immunoglobulin: Use of immunoglobulin for temp immunity and Hepatitis A vaccine to prevent infection.

2. Hepatitis B

  • Hepatitis B Virus (HBV): Causes liver infection that can develop into a chronic stage.

  • Characterized by a potential lifelong infection if untreated.

Transmission of Hepatitis B

  • Routes:

    • Body fluids including blood, semen, and vaginal discharge.

At-Risk Populations

  • Sexually active individuals

  • Injection drug users

  • Healthcare workers

Signs and Symptoms

  • Prodromal Phase: Same as Hepatitis A, including nausea, vomiting, and malaise.

  • Icteric Phase: Similar to Hepatitis A.

  • Chronic Phase: Can lead to liver cirrhosis and liver cancer.

Diagnostic Tests

  • Serology Tests: Detects HBsAg (antigen), HBcAg (antigen), Anti-HBsAb (antibody indicating immunity), and different forms of Ab-anti-HBc.

Treatment

  • Supportive care and management of symptoms.

  • Hepatitis B vaccine for prevention.

  • Antiviral medications for chronic infection, liver transplant may be necessary in severe cases.

3. Dengue

  • Dengue Virus: Transmitted by the bite of infected Aedes aegypti mosquitoes.

  • Serotypes: There are four serotypes of dengue virus (DENV-1 to DENV-4).

Transmission Details

  • The virus is spread through infected mosquitoes' saliva.

Signs and Symptoms

  • Nonspecific Symptoms: Fever, nausea, vomiting, muscle and joint pain.

  • Specific Symptoms: Retro-orbital pain, maculopapular rash.

  • Severe Symptoms: Thrombocytopenia, circulatory collapse, dangerously low blood pressure.

Diagnostic Tests

  • Blood Tests: Detect IgM antibodies and identify the serotype.

Disease Management

  • No specific antiviral treatment; supportive care is recommended.

  • Avoid ibuprofen and aspirin due to bleeding risk.

Vaccine

  • Dengvaxia: A tetravalent vaccine, indicated for children aged 9-16 who have had previous dengue infection.

4. Mumps

  • Mumps Virus: Infects the parotid salivary glands, usually results in immunity post-infection or vaccination.

Transmission

  • Spread through saliva droplets, fomites contaminated with saliva.

Signs and Symptoms

  • Nonspecific Symptoms: Fever, headache, fatigue.

  • Specific Symptoms: Pain in ear or jaw, swollen cheeks, and difficulty swallowing.

Diagnostic Tests

  • Nucleic Acid Amplification Tests, including RT-PCR.

Disease Management

  • Supportive care and isolation during the infectious period.

Vaccine

  • MMR Vaccine: Combination vaccine that provides immunity against measles, mumps, and rubella.

5. Chickenpox

  • Varicella Zoster Virus: Causes chickenpox; immunity develops post-infection or through vaccination.

Transmission

  • Inhalation of aerosolized fluid from blisters, direct contact with blisters.

Signs and Symptoms

  • Nonspecific Symptoms: Fever, headache, fatigue.

  • Specific Symptoms: Itchy blisters developing on the chest, face, and back.

Diagnostic Tests

  • Visual inspection of a characteristic rash and confirmation via nucleic acid amplification tests.

Disease Management

  • Supportive care and isolation; avoid aspirin.

Vaccine

  • Varicella vaccine for those aged 12 months and older.

6. Shingles

  • Varicella Zoster Virus: Results from the reactivation of latent chickenpox virus.

Transmission

  • Similar to chickenpox; aerosolized particles or direct contact with shingles sores.

Signs and Symptoms

  • Nonspecific Symptoms: Fever, headache, malaise.

  • Specific Symptoms: Painful, itchy rash on one side of the body.

Diagnostic Tests

  • Visual inspection and RT-PCR for confirmation.

Disease Management

  • Antiviral medications prescribed for quicker recovery.

Vaccine

  • Shingrix Vaccine: Recommended for healthy adults aged 50 and older.

7. Measles

  • Rubeola Virus: Distinct from rubella; immunity acquired postinfection or via vaccination.

Transmission

  • Respiratory droplets, inhalation of airborne pathogens, and fomites.

Signs and Symptoms

  • Nonspecific Symptoms: Fever, cough, conjunctivitis.

  • Specific Symptoms: Koplik spots in the mouth, a rash starting from the face and spreading throughout the body.

Diagnostic Tests

  • Visual inspection for Koplik spots; serology tests for IgM detection.

Disease Management

  • No specific treatment; supportive care and vitamin A supplements.

Vaccine

  • MMR Vaccine: Effective in preventing measles, mumps, and rubella.

8. German Measles

  • Rubella Virus: Distinguished from rubeola; immunity upon recovery or vaccination.

Transmission

  • Similar to measles: respiratory droplets, inhalation of pathogens in air, and fomites.

Signs and Symptoms

  • Nonspecific Symptoms: Low-grade fever, cough, malaise.

  • Specific Symptoms: Characteristic rash starting from the face, with no Koplik spots.

Diagnostic Tests

  • Serology testing for IgG and IgM. Nucleic acid amplification tests are not generally recommended due to the testing window.

Disease Management

  • No specific treatment; supportive care.