8 - Viral Diseases

Pathogenic DNA Viruses

• Types of DNA Viruses

  • Enveloped and Nonenveloped

  • Strands: Double-stranded and Single-stranded

• Notable DNA Viruses

  • Poxviruses

  • Adenoviruses

  • Polyomaviruses

  • Herpesviruses

  • Parvoviruses

  • Papillomaviruses

Poxviruses

• Characteristics

  • Produce eruptive skin pustules known as pocks or pox

  • Are the largest and most complex animal viruses with the largest genome of all viruses

  • Composed of dsDNA

• Notable examples

  • Variola: causes smallpox

  • Vaccinia: closely related to variola, used in vaccines

  • Monkeypox

  • Cowpox

Smallpox

• Historical significance: First disease eliminated by vaccination

• Transmission: Exposure through inhalation or skin contact

• Symptoms

  • Fever, malaise, prostration, followed by a rash

• Types of Smallpox

  • Variola major: Highly virulent; causes toxemia, shock, intravascular coagulation

  • Variola minor: Less virulent

• Vaccination history: Routine vaccination ended in the US in 1972; reintroduced in 2002

Molluscum Contagiosum

• Primarily affects children

• Transmission: Direct contact and fomites

• Atypical forms in AIDS patients

• Characteristics

  • Attacks skin of the face, forms tumor-like growths

• Treatment options include freezing, electric cautery, and chemical agents

Monkeypox

• Rash Characteristics

  • May occur near genitals or anus and other areas (hands, feet, chest, face, mouth)

  • Rash can develop into painful or itchy blisters

  • Progresses through stages, including scabbing

• Other symptoms:

  • Fever, chills, swollen lymph nodes, headache, respiratory symptoms

  • Symptoms can vary in presentation

Herpesviruses

• General Characteristics

  • All members show latency and cause recurrent infections

  • Severity increases with age and immune compromise

Herpesviridae Family

• Consists of 8 types affecting humans

  • HSV-1 (Herpes Simplex Virus Type 1)

  • HSV-2 (Herpes Simplex Virus Type 2)

  • VZV (Varicella-Zoster Virus)

  • EBV (Epstein-Barr Virus)

  • CMV (Cytomegalovirus)

  • HHV-6, HHV-7, HHV-8 (KSHV)

Epidemiology of Herpes Simplex Viruses: HSV-1 & HSV-2

• Transmission

  • Direct exposure to secretions containing the virus; active lesions are significant sources

• Latency

  • HSV-1 enters the 5th cranial nerve; HSV-2 enters lumbosacral spinal nerve ganglia

Recurring Infections

• Triggers

  • Fever, UV radiation, stress, mechanical injury

  • New virus forms migrate to surface, leading to lesions

HSV-1 & HSV-2 Differences

• HSV-1

  • Most commonly associated with oral infections (Herpes labialis, ocular herpes)

  • Generally transmitted via close contact, primarily affects trigeminal ganglion

• HSV-2

  • Primarily associated with genital herpes

  • Transmitted through sexual contact, associated with sacral ganglia

Clinical Manifestations of Herpes

• HSV-1 Conditions

  • Herpes labialis, gingivostomatitis, herpetic keratitis

• HSV-2 Conditions

  • Genital herpes characterized by malaise, fever, clusters of vesicles

Herpes in Newborns

• HSV-1 and HSV-2 infections can be fatal; preventive screening is important

• C-section recommended during outbreaks to prevent infection

Herpetic Whitlow

• Localized infection caused by HSV-1/HSV-2, mainly in healthcare workers

Varicella-Zoster Virus (VZV)

• Causes chickenpox and shingles; transmitted via respiratory droplets

• Virus remains latent in neurons; reactivation leads to shingles

• Treatment includes antivirals and vaccination

Epstein-Barr Virus (EBV)

• Transmission: Direct oral contact, particularly with saliva

• Symptoms: Mononucleosis, sore throat, lymphadenopathy

• Associated complications include heart defects and spleen rupture

Cytomegalovirus (CMV)

• Generally asymptomatic but can cause severe complications

• Transmission through bodily fluids; high-risk groups include fetuses and immunodeficient individuals

HHV-6 and HHV-7

• Found commonly in childhood diseases (roseola) but can cause severe complications in adults

Papillomavirus

• Causes benign growths (warts); transmitted mainly through skin contact

• Genital warts linked to HPV types associated with cervical and penile cancers

Hepatitis Viruses

• Hepatitis Types: A, B, C

  • A: Transmitted through contaminated food, self-limiting

  • B: Bloodborne, leads to chronic infections and liver disease

  • C: Also bloodborne, primary cause for liver transplants

Key Features of Hepatitis Types

• Different incubation periods, reservoir types, modes of transmission, and vaccine availability

Pathogenesis of Hepatitis B

• Entry through skin breaks; multiplication in liver, leading to potential liver cancer

Adenoviruses

• Cause a variety of illnesses, notably conjunctivitis and respiratory infections, treated with interferon

Zika Virus

• Transmitted by Aedes mosquitoes; mild symptoms but severe implications during pregnancy

Rabies

• A progressive zoonotic disease with high mortality characterized by varied clinical phases

Prions

• Misfolded proteins causing spongiform encephalopathies; difficult to diagnose and prevent.