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• Factors attributed to emergence of infectious disease


  • Deforestation
  • Agricultural development
  • Urbanisation
  • Habitat fragmentation
  • Road construction
  • Air and water pollution
  • Climate change
  • Hydrological changes, dam building
  • Population movement
  • Drug resistance
  • Better detection/diagnosis
• Biodiversity Intactness Index (BII)


  Estimates how much originally present biodiversity remains on average across the terrestrial ecological communities within a region
• Among threatened wildlife species, those with population reductions owing to exploitation and loss of habitat

  Share more viruses with humans
• Encroachment into the habitats of wild species brings them into contact with: Humans, Pets, Farmed animals
• Zoonosis


  Any disease or infection that is naturally transmissible from vertebrate animals to humans (WHO)
• Spillover event


  When a zoonotic disease is transmitted from animals to humans
• Reservoirs of human disease


  • Single species reservoir
  • Multiple species
  • Complex
• Reservoir species


  • Wildlife (75%)
  • Domestic animals (42%) - Livestock (24%), Companion animals (22%)
  • Rodents (36%)
  • Carnivores (25%)
  • Even toed-ungulates (21%)
  • Birds (10%)
  • Primates (3.8%)
  • Odd toed-ungulates (3%)
  • Bats (3%)
• Reservoir species had faster life history characteristics than mammals overall, exhibiting traits associated with greater reproductive output rather than long-term survival
• Birds, primates, and bats were over-represented in the scientific literature
• Viruses that bats are a host of


  • Ebola
  • Rabies
  • Chikungunya
• A study found an average of 2.67 Coronaviruses per bat species (sampled), extrapolated to an estimate of 3204 Coronaviruses across the 1,200 bat species
• More viruses will be found in regions where bat diversity is higher
• Human Immunodeficiency Virus (HIV)


  • Caused by two lentiviruses, human immunodeficiency viruses types 1 and 2 (HIV-1 and HIV-2)
  • Both HIVs are the result of multiple cross-species transmissions of simian immunodeficiency viruses (SIVs) naturally infecting African primates
  • One transmission event, involving SIVcpz from chimpanzees in southeastern Cameroon, gave rise to HIV-1 group M—the principal cause of the AIDS pandemic
  • The contacts were likely caused by hunting/eating chimpanzees
• Continual Ebola incidence


  • 40% death rate
  • R0 estimates vary between 1.5 – 2.5
• Frequent 'spillover' events from wild species populations
• Bats are the natural reservoir of Ebola infection
• Middle East Respiratory Syndrome (MERS)


  • MERS-CoV originated in bats, crossed to dromedary camels
  • Camels are now a reservoir species, and required for persistence, as human to human transmission is low
  • 2,500 cases since 2012
  • 35% death rate
• COVID-19 is a symptom of ecological disruption and encroachment
• Natural reservoirs of infectious disease are not the enemy – not covered in the lecture, but homes host microbial agents that could be pathogenic to wild animal species
• Encroachment and interference with wild species provide a route of zoonotic EIDs
• An infection with the R0 of SARS-CoV-2 and mortality rate of Ebola could be devastating
• Or even a Coronavirus with the death rate of MERS and the R0 of COVID-19
• All only an introduction to EIDs