In-Depth Notes on Zoonotic Diseases

Zoonotic Diseases (Zoonoses)
  • Diseases transmitted from animals to humans.
  • Account for approximately 75% of all emerging diseases in humans.
  • Can be caused by four main types of pathogens:
    • Viruses: Biological agents that invade living cells; dependent on a host. Can kill or alter cell functions.
    • Bacteria: Single-celled organisms that can exist independently of a host.
    • Parasites: Organisms that live on or inside a host organism.
    • Fungi: Can be single or multicellular; reproduce via spores.
Types of Bacterial Zoonotic Diseases

  • Anthrax:

    • Caused by spore-forming bacteria found in soil.
    • Infection routes:
    • Inhalation: Exposure to contaminated animal products (e.g., wool).
    • Ingestion: Consuming undercooked meat.
    • Cutaneous: Spores enter through the skin via cuts.

  • Plague:

    • Infectious disease affecting rodents and humans.
    • Spreads through flea bites from infected hosts.
    • Forms of plague:
    • Pneumonic plague: Most severe; can spread between people through droplets.

  • Lyme Disease:

    • Caused by a tick bite.
    • Most common vector-borne disease in the U.S.
    • White-footed mice: Principal reservoir of the bacteria.

  • Psittacosis:

    • Caused by infected birds.
    • Transmission: Inhaling dried feces or respiratory secretions of birds.
    • Not associated with bats or soil.
Types of Parasitic Zoonotic Diseases

  • Cryptosporidium:

    • Waterborne disease caused by a parasite in intestines.
    • Infection: By ingesting contaminated food or water.
    • Resistant to chlorine.

  • Trichinella:

    • Caused by roundworms found in the intestines of infected animals.
    • Infection through consuming raw or undercooked meat (especially pork).

  • Toxoplasmosis:

    • Affects infants if mothers are infected during pregnancy.
    • Transmission via cat feces and contaminated food/water.
Types of Viral Zoonotic Diseases

  • Rabies:

    • Disease affecting the central nervous system.
    • Rare in the U.S. but usually fatal when contracted.
    • Route of infection: Bite or scratch from an infected animal.

  • Hantavirus:

    • Deadly disease spread primarily by rodent feces, urine, and saliva.
    • Commonly found in the white-footed mouse.
    • Infection: Inhaling dried excretions.

  • SARS-CoV-2:

    • Novel coronavirus responsible for COVID-19.
Types of Fungal Zoonotic Diseases

  • Found in various environments:

    • Outdoors: On plants, trees, and soil.
    • Indoors: On different surface types and human skin.

  • Aspergillus:

    • Common mold infection; harmful for those with weakened immune systems.
    • Infection through inhaling spores.

  • Histoplasma:

    • Present in soil contaminated with bird or bat droppings.
    • Infection through inhalation of fungal spores when disturbed.
Vector-Borne Diseases
  • Transmitted by insects such as mosquitos, ticks, and fleas.