factors involved in disease transmission

• • pathogen: biology, e.g. transmission, incubation period, virulence
• • host: overall health, e.g. functioning immune system, underlying conditions, use of pharmaceuticals
• •  societal: education, anti-vaccination campaigns. movement of human populations, e.g. international travel
• environmental & geographical

  • natural disasters, e.g. earthquakes, hurricanes, cyclones, flooding 
  • human impacts, e.g. deforestation may expose reservoirs with pathogens
  • environmental conditions may favour the preservation of the pathogen