Viral Diseases Notes with PDF

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Viruses: Basic Characteristics

• Definition: An infectious agent that infects living cells, including bacteria.
  • A virus that infects bacteria is called a bacteriophage.
• Structure & Metabolism:
  • Lacks the enzymes necessary for generating energy.
  • Do not have their own enzymes for metabolic functions.
  • Cannot be cultured in synthetic media; they require a living host cell to replicate.
• Transmission: Can occur through various methods (e.g., polluted food, water, air), not just biological vectors.

Specific Viral Diseases

Respiratory & Systemic Viral Diseases

• Coronaviruses:
  • Causes diseases including MERS (Middle East Respiratory Syndrome), SARS (Severe Acute Respiratory Syndrome), and COVID-19.
  • ACE2 is a receptor used by the SARS-CoV-2 virus (cause of COVID-19) to enter human cells.
• Common Cold: Caused by the Rhinovirus.
• Hepatitis:
  • Hepatitis B:
    • Caused by a DNA virus.
    • Transmission is similar to HIV (sexual contact, blood transfusion, placental transfer).
    • A safe and effective vaccine is available.
    • Infected individuals may not show symptoms for many years.
  • Hepatitis C: Infected individuals may not show symptoms for many years.
  • Global Impact: The number of people infected with Hepatitis B and C viruses is several times greater than that of those infected with HIV.
• Measles: Caused by a virus; a disease that antibiotics cannot cure.
• Mumps: Caused by a virus.
• Chicken Pox: Caused by a virus.
• Smallpox:
  • Caused by a virus and has been eradicated in India.
  • Patients should be isolated to prevent transmission.
• Swine Flu: Caused by the H1N1 virus.
• Ebola Virus Disease:
  • Caused by a deadly virus named after the Ebola River.
  • It is not the cause of Smallpox (incorrectly matched pair).

Mosquito-Borne Viral Diseases

• Dengue:
  • Transmitted by the bite of an infected mosquito (Aedes aegypti or tiger mosquitoes).
  • It is a viral disease, not a protozoan one.
  • Causes a decrease in platelet count.
  • Symptoms include skin rash, bleeding from the nose and gums, and retro-orbital pain (pain behind the eyes).
• Yellow Fever: Spread by mosquitoes (tiger mosquitoes are a vector).
• Chikungunya: Transmitted by tiger mosquitoes.
• Japanese Encephalitis:
  • Caused by a virus that infects the brain.
  • Transmitted by mosquitoes (primarily Culex mosquitoes, not typically tiger mosquitoes).
  • Pigs are a host, so keeping pigs away from human settlements aids eradication.
• Zika Virus Disease:
  • Transmitted by the same mosquito that transmits dengue.
  • It can also be transmitted sexually.

Other Viral Diseases

• Rabies:
  • Caused by a virus.
  • Also known as Hydrophobia.
  • Transmitted through the saliva of an infected animal, often via a bite.
• Poliomyelitis (Polio):
  • Caused by the Poliovirus.
  • Enters the body through polluted food and water.
  • It is not transmitted by monkeys.
• AIDS (Acquired Immune Deficiency Syndrome):
  • Cause and Pathogen:
    • Caused by a virus known as HIV (Human Immunodeficiency Virus), which is a retrovirus.
    • The genetic material of the AIDS virus is RNA + Protein.
    • The discovery of the virus (HTLV-III) is credited to Robert Gallo.
  • Effect on the Body:
    • Primarily affects the immune system, severely damaging T-lymphocytes.
  • Symptoms: Include swollen lymph nodes, sweating at night, loss of memory, and loss of weight.
  • Transmission and Testing:
    • Modes of transmission: Sexual intercourse, blood transfusion, across the placenta (from mother to child).
    • It can be transmitted through procedures like tattooing (along with Hepatitis B).
    • It is not transmitted by mosquitoes or other blood-sucking insects.
    • A common diagnostic test is the ELISA Test.
  • Treatment and Strains:
    • The most frequently used medicine is Zidovudine (Azidothymidine).
    • The dominant strain of HIV found in India is HIV 1C.
• Herpes: Caused by a virus.
  • Herpes Simplex is noted as not being considered an infectious disease in one specific context.

Bacterial Diseases

• Human Diseases: Tuberculosis, Diphtheria, Cholera, Whooping Cough (Pertussis), Leprosy, Tetanus. Some diarrhoea is caused by bacteria like E. coli.
• Animal Diseases:
  • Infectious Diseases in Milking Animals: Anthrax and Black Quarter are infectious bacterial diseases.
• **AIDS is not a bacterial disease.

Other Disease-Causing Agents & Terminology

• Rotavirus: A major viral cause of severe diarrhoea, especially in infants.
• Meningitis: Caused by the swelling of the membrane over the spinal cord and brain (can be viral or bacterial).
• Tapeworm: A parasite transmitted by pigs.

Disease Transmission & Terminology

• Pandemic: When a disease breaks out across a large region of the world (e.g., multiple continents).
• Waterborne Diseases: Caused by water contamination (e.g., Typhoid, Jaundice/Hepatitis A or E, Cholera).
  • Hepatitis B is not typically waterborne; its main routes are blood and sexual contact.
• Zoonotic Diseases (Transmitted from Animals):
  • Plague: Transmitted by rats.
  • Rabies: Transmitted by dogs.
  • Tapeworm: Transmitted by pigs.
  • Incorrect Pairing: Polio is not transmitted by monkeys.

Vaccines and Eradication Programs

• Polio Vaccine:
  • Discoverer: Jonas Salk.
  • The Government of India replaced the Trivalent Oral Polio Vaccine (OPV) with the Bivalent OPV for its eradication program.
• Disease Eradication in India:
  • Eradicated Disease: Smallpox.
  • Diseases NOT Eradicated: Diphtheria and Chickenpox.

Animal Diseases (Zoonotic)

• Bird Flu (Avian Influenza): Caused by the H5N1 virus; also referred to as a global pandemic influenza.
• Foot and Mouth Disease:
  • Caused by a virus.
  • Mainly found in cattle, sheep, goats, and pigs (cloven-hoofed animals).
  • It is an infectious disease in milking animals.
• Ranikhet Disease: A viral disease that affects chickens.
• Cowpox: Caused by a virus; an infectious disease in milking animals.
• Historical Context: The livestock disease marked for global eradication in the year 2011 was Rinderpest.

Virology and Immunology: Key Figures

• The father of Immunology is Edward Jenner.

General Health Facts

• Diseases that antibiotics cannot cure include viral infections, such as measles. (Other diseases mentioned include bacterial ones like Tuberculosis, Dysentery, Cholera, Leprosy, and Tetanus, which are bacterial and can be treated with antibiotics, and non-communicable diseases like Cancer).

Know More About Viral Diseases:

• Viral Diseases – Old Year Questions
• Viral Diseases One Liner Questions & Answers