virus

Study Notes on Viral Taxonomy and Pathogenesis

Page 1: Influenza Virus

1. Taxonomy

  • Family: Orthomyxoviridae

  • Genres:

    • Influenza A: Animal & human strains

    • Influenza B: Human virus

    • Influenza C: Human & swine virus

    • Influenza D:

2. Morphology

  • Type: RNA Virus

  • Nature: Spherical; pleomorphic

  • Genetic Material: Segmented RNA genome (8 pieces)

  • Components:

    • Enveloped

    • Inner membrane

    • Outer protein layer

    • Lipid layer

    • Matrix protein (M)

    • M2 protein

3. Complications

  • Envelope Components: Contains spikes of

    • Hemagglutinin (HA): Responsible for virus uptake into host

    • Neuraminidase (NA): Facilitates release from host cells

    • M protein: Important for viral assembly

4. Antigenic Variation

  • Types:

    • Antigenic Drift:

    • Minor changes; frequent mutation

    • Involves minor antigenic variation leading to formation of new strains from existing subtypes

    • Occurs in Influenza A & B, leading to periodic epidemics

    • Antigenic Shift:

    • Major changes, abrupt; leads to significant antigenic variation

    • Occurs due to re-assortment of genes from two different strains

    • Can lead to novel viral strains causing pandemics

5. Transmission and Pathogenesis

  • Reservoirs: Humans; Animals

  • Transmission: Air droplet spread

  • Pathogenesis: Negative sense segmented ssRNA

6. Antigenic Structure

  • Internal Antigens:

    • Ribonucleoprotein antigen (RNP)

    • M protein antigen (subtype specific)

  • Surface Antigens:

    • Hemagglutinin (HA)

    • Neuraminidase (NA)

7. Lab Diagnosis

  • Specimens: Nasal swabs; throat gargles

  • Isolation Methods:

    • Cell culture (Human; Monkey; Guinea pig; Chick embryo)

  • Testing Methods:

    • Hemagglutination inhibition (HAI)

    • Complement fixation tests (CFT)

    • Enzyme-linked immunosorbent assay (ELISA)

    • Immunofluorescence microscopy (demonstrate viral antigens)

8. Classification

  • Influenza A Classification:

    • Based on HA and NA types (e.g. H1N1, H3N2)

    • Notable strains include:

    • H1N1: Spanish Flu

    • H2N2: Asian Flu

    • H3N2: Hong Kong Flu

9. Treatment & Prophylaxis

  • Medications:

    • Amantidine (Type A)

    • Rimantadine (rapid resistance)

    • Zanamivir (blocks NA, inhibits HA attachment)

  • Vaccines:

    • Inactivated quadrivalent influenza vaccine

    • Live attenuated monovalent and polyvalent vaccines

    • Recombinant quadrivalent influenza vaccine

    • Formalin-killed vaccine

    • Challenges in vaccine development due to antigenic variation

Page 2: Coronaviruses

1. Taxonomy

  • Family: Coronaviridae

  • Genus: Betacoronavirus

  • Species: SARS-CoV-2

2. Morphology

  • Characteristics:

    • Spherical structure

    • Enveloped with matrix protein (M)

    • Club-shaped peplomers (spike protein) for viral attachment/entry

  • Genetic Material: Positive sense ssRNA

3. Reservoirs and Transmission

  • Reservoirs: Humans; Animals (bats, possibly other intermediate hosts)

  • Pathogenesis: Virus spreads via air droplets, aerosols, or surface contamination

4. Lab Diagnosis

  • Specimens: Nasal & throat swabs; sputum

  • Testing Methods:

    • RT-PCR

    • ELISA or indirect immunofluorescence (to detect antibodies)

    • Electron microscopy for visualization

5. Treatment & Prophylaxis

  • Supportive Care:

    • Oxygen therapy and fluid management

  • Antiviral Treatment: Remdesivir, Dexamethasone

  • Vaccination:

    • mRNA-based vaccines (e.g., Pfizer, Moderna)

    • Adenovirus-based vaccines (e.g., Sputnik V, CoviShield)

  • Preventive Measures:

    • Social distancing and personal protective equipment (PPE)

Page 3: Poliovirus (Picornaviridae)

1. Taxonomy

  • Family: Picornaviridae

  • Genus: Enterovirus

  • Species: Poliovirus

2. Morphology

  • Characteristics:

    • Spherical shape

    • Non-enveloped; Icosahedral capsid with four proteins (VP1, VP2, VP3, VP4)

  • Genome: Positive sense ssRNA

3. Pathogenesis

  • Transmission: Fecal-oral route, person-person

  • Symptoms: Fever, fatigue, headache, vomiting

    • Enters through oral routes, colonizes the nasopharynx

    • Travels through lymph nodes to bloodstream, leading to possible paralysis

4. Clinical Forms

  • Diseases:

    • Mild illness, aseptic meningitis, paralytic poliomyelitis (spinal, bulbar, bulbospinal)

5. Lab Diagnosis

  • Specimens: Stool, throat, blood, CSF

  • Diagnosis Methods:

    • Tissue culture, serology, PCR

6. Treatment & Prophylaxis

  • Immunization:

    • Active: Oral polio vaccine (live attenuated)

    • Inactivated polio vaccine

    • Schedule: 1st dose (2 months), 2nd dose (4 months), 3rd dose (6-18 months)

    • Booster (4-6 years)

Page 4: Hepatitis A Virus (Hepatovirus)

1. Taxonomy

  • Family: Picornaviridae

  • Genus: Hepatovirus

  • Species: Hepatitis A virus

2. Morphology

  • Characteristics:

    • Icosahedral; non-enveloped; inactivated by heating, UV, chlorine

    • One serotype known, foodborne infection

3. Pathogenesis

  • Transmission: Fecal-oral (contaminated food/water)

    • Virus infects intestinal epithelial cells, spreads to liver

    • Activation of immune response leads to inflammation and hepatocyte necrosis

4. Lab Diagnosis

  • Specimens: Blood, serum, feces

  • Serology: Detection of antibodies (anti-HAV IgM for acute infection and IgG for past infection)

  • Liver function tests: Increase in bilirubin and aminotransferases

5. Treatment & Prophylaxis

  • Prevention: Safe drinking water, personal hygiene, vaccine availability

  • Immunization:

    • ELISA-based vaccine, 1st dose (12-23 months), 2nd dose (6 months after)

Page 5: Hepatitis B Virus (HBV)

1. Taxonomy

  • Family: Hepadnaviridae

  • Genus: Orthohepadnavirus

  • Species: Hepatitis B virus

2. Morphology

  • Characteristics:

    • Lipid envelope; spherical particle; filamentous/tubular particles

    • Genome: partially double-stranded circular DNA

3. Pathogenesis

  • Transmission: Vertical (mother to child), horizontal (blood, oral, sexual)

  • Clinical Symptoms:

    • Prodromal: Fever, malaise, anorexia, abdominal pain, jaundice

    • Chronic: Liver cirrhosis, hepatocellular carcinoma

4. Lab Diagnosis

  • Specimens: Blood, serum, plasma

  • Testing:

    • Serology (HBsAg, anti-HBc), DNA detection via PCR

5. Treatment & Prophylaxis

  • No specific treatment for acute HBV infections

  • Chronic Treatment:

    • Antivirals like Entecavir, Tenofovir

    • HBIG for passive immunization

  • Vaccination:

    • Recombinant vaccine at specific ages

Page 6: Herpes Simplex Virus (HSV)

1. Taxonomy

  • Family: Herpeviridae

  • Genus: Simplexvirus

  • Species: HSV-1 (oral), HSV-2 (genital)

2. Morphology

  • Characteristics:

    • Enveloped; icosahedral nucleocapsid; tegument

    • Contains glycoprotein spikes for host attachment

3. Pathogenesis

  • Transmission:

    • Oral-oral or oral-genital contact

    • Entry through skin or mucosal membrane, results in skin lesions

4. Clinical Features

  • Symptoms: Itching, burning sensation, painful blisters, fever, malaise

    • Mucosal ulcerations common

5. Lab Diagnosis

  • Specimens: Skin swab, vesicle fluid, brain biopsy

  • Testing Methods:

    • Tzanck smear, fluorescent antibody techniques, PCR

6. Treatment & Prophylaxis

  • Medications: Acyclovir, Valacyclovir

  • Preventive Measures: Safe sexual practices

Page 7: Varicella Zoster Virus (VZV)

1. Taxonomy

  • Family: Herpesviridae

  • Genus: Varicellovirus

  • Species: Varicella zoster virus

2. Morphology

  • Characteristics:

    • Same as HSV, distinguished by specific clinical features

3. Pathogenesis

  • Transmission: Air droplets, close contact

  • Symptoms:

    • Fluid-filled vesicular rash, fever

  • Latency: Virus can remain dormant in ganglia and reactivate as shingles

4. Lab Diagnosis

  • Testing Methods:

    • Direct viral detection via microscopy, PCR, culture, serology

5. Treatment & Prophylaxis

  • Vaccination: Live attenuated vaccine to improve immunity

  • Medications: Acyclovir for treatment, preventative measures against exposure

Page 8: Rabies Virus (Lyssavirus)

1. Taxonomy

  • Family: Rhabdoviridae

  • Genus: Lyssavirus

  • Species: Rabies lyssavirus

2. Morphology

  • Characteristics: Bullet-shaped, enveloped, with glycoprotein spikes

3. Pathogenesis

  • Transmission: Saliva from infected animals, typically through bites

  • Symptoms: Initial flu-like symptoms, progressing to neurological dysfunction

4. Lab Diagnosis

  • Diagnosis Methods:

    • Direct immunofluorescence, detection of Negri bodies in brain tissue, PCR

5. Treatment & Prophylaxis

  • Post Exposure Treatment: Clean wound, active immunization with human diploid cell vaccine, passive immunization with rabies immunoglobulin

  • Preventive Vaccination: Vaccination of domestic animals and wildlife

Page 9: Human Immunodeficiency Virus (HIV)

1. Taxonomy

  • Family: Retroviridae

  • Genus: Lentivirus

  • Species: HIV-1, HIV-2

2. Morphology

  • Characteristics: Spherical, enveloped with glycoprotein spikes, pleomorphic structure

  • Genome: Positive sense ssRNA

3. Pathogenesis

  • Transmission: Sexual contact, blood, breast milk

  • Symptoms: Acute HIV infection presents with flu-like symptoms, progressing to AIDS

4. Lab Diagnosis

  • Testing Methods: ELISA, Western blot for antibodies, RT-PCR for viral load detection

5. Treatment & Prophylaxis

  • Antiretroviral Therapy (ART): Reduces viral load and improves immune function

  • Post Exposure Prophylaxis (PEP): 28-day course of ART after potential exposure

Page 10: Human Papillomavirus (HPV)

1. Taxonomy

  • Family: Papillomaviridae

  • Genus: Papillomavirus

2. Morphology

  • Characteristics: Small, non-enveloped, icosahedral

3. Pathogenesis

  • Transmission: Sexual contact, direct skin contact

  • Inflammation: HPV infects epithelial tissues leading to warts and potentially cervical cancer

4. Lab Diagnosis

  • Testing Methods: PCR for viral DNA, ELISA for antibody detection

5. Treatment & Prophylaxis

  • Treatment: Cryotherapy, laser therapy, topical treatments

  • Vaccination: Cervarix protects against HPV types 16 and 18, reducing cancer risk.