Investigating the transmission of a disease during an epidemic

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Describe a variety of infectious diseases caused by pathogens, including microorganisms, macroorganisms and non-cellular pathogens, and collect primary and secondary-sourced data and information relating to disease transmission, including: (ACSBL097, ACSBL098, ACSBL116, ACSBL117)

  • investigating the transmission of a disease during an epidemic

Transmission of diseases during an epidemic:

  • Epidemic is an outbreak of a disease where the occurrence level of the disease increases drastically in a given population and can cause a huge a number of deaths as well.
  • Epidemics of infectious disease are generally caused by several factors including:
    • A change in the ecology of the host population (e.g. increased stress or increase in the density of a vector species)
    • Genetic change in the pathogen reservoir or the introduction of an emerging pathogen to a host population (by movement of pathogen or host)
    • Reduction of host immunity to either an established pathogen or newly emerging novel
  • Transmission methods include:
    • Airborne transmission: Airborne transmission is the spread of infection by droplet nuclei or dust in the air. Without the intervention of winds or drafts the distance over which airborne infection takes place is short, say 10 to 20 feet.
    • Arthropod transmission: Arthropod transmission takes place by an insect, either mechanically through a contaminated proboscis or feet, or biologically when there is growth or replication of an organism in the arthropod.
    • Biological transmission: Involving a biological process, e.g. passing a stage of development of the infecting agent in an intermediate host. Opposite to mechanical transmission.
    • Colostral transmission: A form of vertical transmission via successive generations.
    • Contact transmission: The disease agent is transferred directly by biting, sucking, chewing or indirectly by inhalation of droplets, drinking of contaminated water, traveling in contaminated vehicles.
    • Cyclopropagative transmission: The agent undergoes both development and multiplication in the transmitting vehicle.
    • Developmental transmission: The agent undergoes some development in the transmission vehicle.
    • Fecal-oral transmission: The infectious agent is shed by the infected host in feces and acquired by the susceptible host through ingestion of contaminated material.
    • Horizontal transmission: Lateral spread to others in the same group and at the same time; spread to contemporaries.
    • Mechanical transmission: The transmitter is not infected in that tissues are not invaded and the agent does not multiply.
    • Propagative transmission: The agent multiplies in the transmission vehicle.
    • Vertical transmission: From one generation to the next, perhaps transovarially or by intrauterine infection of the fetus. Some retroviruses are transmitted in the germ line, i.e. their genetic material is integrated into the DNA of either the ovum or sperm.

Extract from HSC Biology Stage 6 Syllabus. © 2017 Board of Studies NSW.