Makindo Medical Notes

Related Subjects: |Bacteria and their Infections |Viruses and their Infections |Herpes Varicella-Zoster (Shingles) Infection |Chickenpox Varicella Infection |Varicella Cerebral Vasculopathy |Herpes Viruses |Herpes Zoster Ophthalmicus (HZO) Shingles |MonkeyPox |Mumps |Measles |Rubella (German Measles) |Epstein-Barr Virus infection

Viruses are microscopic infectious agents that require a host cell to replicate. They consist of genetic material (DNA or RNA) enclosed in a protein coat called a capsid, and sometimes an outer lipid envelope. Viruses infect all types of life forms, including animals, plants, and microorganisms, and are responsible for a wide range of diseases in humans.

Viral Structure

• Nucleic Acid :
  • Contains either DNA or RNA, which can be single-stranded or double-stranded.
  • Encodes the genetic information necessary for viral replication and protein synthesis.
• Capsid :
  • A protective protein coat surrounding the nucleic acid.
  • Composed of protein subunits called capsomeres, arranged in shapes like helical, icosahedral, or complex structures.
• Envelope (in some viruses):
  • A lipid bilayer derived from the host cell membrane.
  • Contains viral glycoproteins essential for host cell recognition and entry.

Viral Life Cycle

• Attachment :
  • Viruses attach to specific receptors on the host cell surface.
  • This determines host specificity and which tissues the virus can infect (tissue tropism).
• Entry :
  • Viral particles or their genomes enter the host cell via fusion, endocytosis, or direct penetration.
• Replication and Transcription :
  • The viral genome is replicated using the host cell's machinery.
  • Viral genes are transcribed into mRNA, directing the synthesis of viral proteins.
• Translation and Protein Synthesis :
  • Host ribosomes translate viral mRNA to produce viral proteins.
• Assembly :
  • New viral particles are assembled from the replicated genome and synthesized proteins.
• Release :
  • New viruses are released to infect new cells, either by cell lysis, budding, or exocytosis.

Viral Pathogenesis

• Entry and Initial Replication :
  • Viruses enter through mucosal surfaces, skin breaches, or direct inoculation.
  • They begin replicating at the site of entry, potentially leading to local symptoms.
• Spread and Dissemination :
  • Viruses spread locally or systemically via the bloodstream (viremia) or lymphatic system.
• Cellular Damage and Immune Response :
  • Direct damage includes cell lysis, apoptosis, or fusion of cells into syncytia.
  • Indirect damage is mediated by immune responses, causing inflammation and cytokine release.
• Clinical Manifestations :
  • Acute infections : Rapid onset, such as influenza or common cold.
  • Chronic infections : Persistent infections, such as HIV or hepatitis B.
  • Latent infections : Dormant virus with potential reactivation, such as herpes simplex.

Influenza

Host Immune Response

• Innate Immunity :
  • First line of defense with physical barriers, phagocytes, natural killer cells, and interferons.
  • Interferons inhibit viral replication and activate immune cells.
• Adaptive Immunity :
  • Humoral immunity : B cells produce antibodies to neutralize viruses and promote their clearance.
  • Cell-mediated immunity : Cytotoxic T cells kill infected cells; helper T cells coordinate the response.
• Immune Evasion Strategies :
  • Viruses evade immunity by antigenic variation, inhibiting antigen presentation, and latency.

Examples of Viral Diseases

• Influenza :
  • Caused by influenza viruses (types A, B, and C).
  • Characterized by fever, cough, sore throat, body aches, and fatigue.
  • Prevention includes vaccination and antiviral medications.
• HIV/AIDS :
  • Caused by human immunodeficiency virus (HIV).
  • Targets CD4+ T cells, leading to immune system failure and susceptibility to infections and cancers.
  • Managed with antiretroviral therapy (ART).
• Hepatitis :
  • Caused by hepatitis viruses (A, B, C, D, and E).
  • Results in liver inflammation, fibrosis, and potential cirrhosis or cancer.
  • Prevention includes vaccination (for hepatitis A and B) and antiviral treatments (for hepatitis B and C).
• Herpes Simplex Virus (HSV) Infections :
  • Caused by HSV-1 and HSV-2, resulting in recurrent painful vesicular eruptions.
  • Treatment includes antivirals to reduce outbreak severity and frequency.
• COVID-19 :
  • Caused by SARS-CoV-2, leading to symptoms from mild respiratory illness to severe ARDS.
  • Prevention includes vaccination, social distancing, and masks.

Clinical and Diagnostic Approaches

• Laboratory Diagnosis :
  • Virus isolation, PCR (polymerase chain reaction), and serology for detecting antibodies/antigens.
• Imaging Techniques :
  • Radiography, CT, and MRI to assess organ involvement.
• Therapeutic Interventions :
  • Antiviral medications, immunomodulatory agents, and supportive care.
• Preventive Measures :
  • Vaccination and public health measures, including sanitation and vector control.

Summary

Viruses are small infectious agents reliant on host cells for replication. They have diverse structures and life cycles, causing a wide array of diseases in humans. Understanding viral structure, pathogenesis, and the immune response is essential for diagnosing, treating, and preventing infections. Advances in antiviral therapies and vaccines continue to enhance our ability to manage viral diseases effectively.

Viral Diseases

Viral Infection	Clinical Diagnosis	Treatment
Influenza (Flu)	Diagnosis: Sudden onset of fever, chills, muscle aches, cough, and fatigue. Common during flu season (winter). Diagnosis can be clinical or confirmed with rapid antigen tests or PCR.	Antivirals: Oseltamivir or zanamivir for high-risk patients or severe cases. Supportive care: Rest, fluids, and antipyretics for most patients. Vaccination: Annual flu vaccination recommended for prevention.
Herpes Simplex Virus (HSV-1, HSV-2)	Diagnosis: Painful vesicles on the skin, lips, or genital areas. HSV-1 commonly causes cold sores, while HSV-2 affects the genitals. Diagnosed with PCR, viral culture, or Tzanck smear.	Antivirals: Acyclovir, valacyclovir, or famciclovir can reduce symptom duration and frequency of outbreaks. Chronic suppression: For recurrent genital herpes, daily antiviral therapy may be used.
Varicella-Zoster Virus (VZV)	Diagnosis: Chickenpox (primary infection) presents with itchy, vesicular rash; shingles (reactivation) presents with painful dermatomal rash. Confirmed with PCR or direct fluorescent antibody (DFA) test of lesion samples.	Antivirals: Acyclovir or valacyclovir for chickenpox in adults and all cases of shingles. Pain management: Gabapentin or pregabalin for postherpetic neuralgia (chronic pain following shingles). Vaccination: Varicella and zoster vaccines prevent primary infection and reactivation.
Hepatitis B Virus (HBV)	Diagnosis: Acute infection presents with jaundice, fatigue, and elevated liver enzymes. Chronic infection may lead to cirrhosis or liver cancer. Diagnosed via serology (HBsAg, HBeAg, anti-HBc) and PCR for viral load.	Antivirals: Tenofovir or entecavir for chronic hepatitis B. Prevention: Hepatitis B vaccine. Post-exposure prophylaxis (PEP) with hepatitis B immunoglobulin (HBIG) and vaccine in non-immunized individuals.
Hepatitis C Virus (HCV)	Diagnosis: Often asymptomatic until liver damage occurs. Diagnosed via serology (anti-HCV antibodies) and PCR for viral RNA.	Antivirals: Direct-acting antivirals (DAAs) such as sofosbuvir, ledipasvir, or glecaprevir, which have cure rates >95% for chronic hepatitis C.
HIV (Human Immunodeficiency Virus)	Diagnosis: Acute infection may present with flu-like symptoms. Chronic infection progresses to AIDS if untreated, with opportunistic infections. Diagnosed by HIV antibody/antigen testing (4th generation test) and PCR for viral load.	Antiretroviral therapy (ART): Combination of medications such as tenofovir, emtricitabine, and efavirenz. Lifelong treatment required. Prevention: Pre-exposure prophylaxis (PrEP) with tenofovir/emtricitabine for high-risk individuals.
Measles (Rubeola)	Diagnosis: Fever, cough, conjunctivitis, and Koplik spots (white spots in the mouth) followed by a widespread red rash. Confirmed by serology (measles IgM antibodies) or PCR.	Supportive care: Hydration and antipyretics. Prevention: Measles, mumps, rubella (MMR) vaccine.
Human Papillomavirus (HPV)	Diagnosis: Causes warts, genital warts, and is associated with cervical and oropharyngeal cancers. Diagnosed via clinical examination, PCR, or biopsy.	Treatment: Cryotherapy or topical agents (e.g., imiquimod) for warts. Surgical removal for severe cases. Prevention: HPV vaccine (e.g., Gardasil) to protect against high-risk cancer-causing strains.
Epstein-Barr Virus (EBV)	Diagnosis: Causes infectious mononucleosis (glandular fever), presenting with fever, sore throat, swollen lymph nodes, and fatigue. Associated with Burkitt's lymphoma and nasopharyngeal carcinoma. Diagnosed with serology (heterophile antibodies/monospot test) and EBV-specific antibodies.	Supportive care: Hydration, rest, and analgesics.