5.2 Mechanisms of Transmission

There are five main routes examined in BS0005 (nosome zoonoses may have at least one mode of transmission):

1. DIrect contact

   This is spread via bites or scratches, contact with an infected organism’s tissues, abrasions on the skin, or even contact with mucous membrane (e.g., Rabies, HFM disease, etc).

2. Oral or Ingestion

   Here, pathogens are spread by contaminated food or water or direct consumption (e.g., unwashed fruits and vegetables, unpasteurized dairy, etc).

   During Germany in 2011, there was a deadly E. coli outbreak that infected 3950 people and killed 53 people.

3. Fomites

   A fomite is an object that is commonly handled - for instance, clothing, shoes, brushes, bedding, and cages.

   Several pathogens like E. coli O157.H7 and MRSA are spread via fomites.

4. Aerosol

   This involves droplet particle formation, the transfer of which involves close contact.

   Such aerosol transmissions are spread by infected animals’ sneezing and coughing and may even be spread by contaminated dust or soil stirred up by wind (e.g., bubonic plague, hantaviruses, etc).

5. Vector-borne

   This involves the transfer of pathogens by arthropods - animals are typically reservoirs for the pathogen.

   Sometimes, pets even serve as means to carry the vector (e.g., plague, Lyme disease, West Nile virus, etc).

5.2.1 Courses of disease in humans

There are two possible courses:

1. Humans become ‘dead-end’ hosts

   Here, the disease spills over from an animal reservoir into the human population. There is no human-to-human transmission thereafter (e.g., Dengue fever).

2. The disease ‘spills over’ into the human population

   Here, the disease is able to spread to other humans before “burning out” from the human population. When it does, there is no residual infection except in its animal host (e.g., SARS, COVID-19[?]).

3. Persisting in humans

   These disease spilled out of primates decades ago and have stuck around in the human population since (e.g., AIDS).