Notes on Viral and Parasitic Infections (NUR1021 Lecture 7)

Viral Infection

• Definition: Tiny germs made of genetic material inside a protein coating.

  • Behavior: Viruses invade living cells, use them to multiply, which can kill or damage the cells and result in illness.

Types of Viral Infections

• Acute Viral Infection: Occurs suddenly, resolves quickly or results in death.

• Chronic Viral Infection: Virus remains in specific cells, leading to persistence.

Viral Life Cycle

1. Attachment: Virus attaches to a target epithelial cell.

2. Penetration: Cell engulfs the virus via endocytosis.

3. Uncoating: Viral contents are released into the cell.

4. Biosynthesis: Viral RNA enters the nucleus and replicates.

5. Assembly: New viral particles are assembled.

6. Release: New viruses are released into extracellular fluid.

Highlighted Viruses

• Acute Viral Infections:

  • Influenza virus

  • Ebola virus

  • Dengue virus

  • Zika virus

  • Rabies virus

  • Human coronaviruses (SARS-CoV, MERS-CoV, SARS-CoV-2)

• Chronic Viral Infections:

  • Human Immunodeficiency Virus (HIV)

  • Oncogenic viruses (EBV, HTLV-1, Hepatitis B and C, HPV, KSHV)

  • Herpes simplex virus

  • Varicella-zoster virus

Influenza Virus

• Characteristics: Segmented, negative-sense single-stranded RNA viruses.

• Symptoms: Fever, chills, dry cough, muscle aches, sore throat.

• Transmission: Inhalation of aerosols/droplets, fomites play a minor role.

• Prevention: Annual vaccination (trivalent/quadrivalent).

• Treatment: Neuraminidase inhibitors (Oseltamivir, Zanamivir).

  • Mechanism: Inhibits neuraminidase activity, blocking viral release.

Hemorrhagic Fever Diseases

• General Info: Severe fever, bleeding due to capillary fragility. Highly lethal.

• Examples: Ebola, Yellow Fever, Dengue, Marburg.

Ebola Virus

• Description: Causes Ebola virus disease (EVD); involves high mortality rate (around 50%).

• Symptoms: Fever, muscle pain, vomiting, diarrhea, rash, bleeding.

• Transmission: Contact with bodily fluids of infected animals (fruit bats) and humans.

Dengue Virus

• Overview: Acute mosquito-borne infection; four serotypes exist.

• Symptoms: Fever, severe headache, rash, joint/muscle pain.

• Severe Dengue: Can cause bleeding, shock, and requires hospitalization.

Zika Virus Disease

• Overview: Linked to microcephaly in infants. Symptoms include rash, joint pain, and conjunctivitis.

Rabies Virus

• Overview: Causes fatal encephalitis, notable for a long incubation period (1-2 months).

• Transmission: Via saliva of infected animals (especially canines).

• Prevention/Treatment: Inactivated vaccine, post-exposure immunization (Rabies immune globulin + vaccination).

Human Coronaviruses

• Varieties: SARS-CoV-2, MERS-CoV, etc.

• Symptoms: Range from mild (common cold) to severe respiratory diseases (ARDS).

• Transmission: Zoonotic; variable pathogenicity.

Enterovirus 71 and Maculopapular rash diseases

• Enterovirus 71: Causes hand, foot, mouth disease, especially in children.

• Maculopapular Diseases: Includes measles, rubella, fifth disease, roseola.

Measles

• Transmission: Extremely contagious, spread via respiratory droplets.

• Symptoms: Maculopapular rash, respiratory symptoms, fever.

Chronic Viral Infections

Oncogenic Viruses

• Definition: Viruses that can induce cancer.

• Examples:

  • EBV: Associated with Burkitt’s lymphoma, nasopharyngeal carcinoma.

  • Hepatitis B and C: Cause liver cancer.

  • HPV: Cervical cancer associated subtypes.

Herpes Simplex Virus (HSV)

• Types: HSV-1 (oral), HSV-2 (genital).

• Symptoms: Painful vesicular lesions. Can be severe in neonates.

• Treatment: Acyclovir.

Varicella-zoster Virus (VZV)

• Manifestations: Chickenpox and shingles.

• Treatment: Acyclovir, vaccines available.

Parasitic Infections

• Categories of Helminths:

  • Nematodes (roundworms)

  • Trematodes (flukes)

  • Cestodes (tapeworms).

Helminth Life Cycles

1. Cycle A: Host Ingestion

   • Example: Ascaris (roundworm), Trichuris (whipworm).

   • Description: Eggs are ingested by the host through contaminated food or water, hatch in the intestine, and develop into adult worms.

2. Cycle B: Skin Penetration

   • Example: Hookworms (Ancylostoma, Necator).

   • Description: Larvae penetrate the skin of the host, typically through bare feet, migrate through the bloodstream to the lungs, and then ascend to the throat where they are swallowed to reach the intestines.

3. Cycle C: Cyst Encystment in Animals

   • Example: Taenia (tapeworm).

   • Description: The larval stage encysts in the tissues of intermediate hosts like pigs or cattle, and humans become infected by ingesting undercooked meat containing cysts.

4. Cycle D: Direct Penetration into Hosts

   • Description: Some helminths can directly penetrate the host’s skin or mucous membranes without intermediaries. This includes transitions through larvae that develop directly into adults within the host without an intervening stage in another host.

Pathogenesis and Prevention

• Virulence Factors: Specialized mouthparts, enzymes for tissue penetration.

• Prevention/Treatment: Antihelminthic medications and hygiene measures are essential to prevent transmission and treat infections.