Zoonoses

• Zoonoses


  Diseases or infections "naturally transmitted between vertebrate animals and humans"

  
• Zoonoses are not just restricted to diseases whose agents are consistently and readily transmitted between vertebrates and people

  
• Zoonoses includes diseases where the causative agent has skipped once (e.g. HIV), or every now and again (e.g. influenza) from their animal to animal cycle to people with then an almost person to person cycle

  
• Zoonoses is the study of diseases that cause infections in vertebrate animals and are also transmissible naturally to humans

  
• Everyone involved with animals must know zoonoses risk
• Majority of human pathogens are zoonotic (868 species or 61%). Approximately 75% of human emerging infectious diseases are caused by zoonotic pathogens (Taylor et al., 2001)

  
• Zoonoses


  Diseases or infections "naturally transmitted between vertebrate animals and humans"

  
• Agents responsible for global mortality

  • HIV-1 and -2
  • Influenza virus
• Zoonoses are not just restricted to diseases whose agents are consistently and readily transmitted between vertebrates and people

  
• Agents that cause limited deaths but result in high case fatality rates and for which no effective therapies or vaccines exist

  • Ebola virus
  • Hantaviruses
  • Nipah virus
  • Severe acute respiratory syndrome (SARS)-associated coronavirus
• Zoonoses includes diseases where the causative agent has skipped once (e.g. HIV), or every now and again (e.g. influenza) from their animal to animal cycle to people with then an almost person to person cycle

  
• For zoonotic diseases to occur from animals to humans

  1. Animal must be infected (not necessarily diseased)

  2. Must be transmitted to people

  3. People must be ill (not just infected)

  
• Zoonoses is the study of diseases that cause infections in vertebrate animals and are also transmissible naturally to humans

  
• All animal species should be considered as potential sources of infections that can be transmitted to other animals or man
• Everyone involved with animals must know zoonoses risk
• In general, the closer the phylogenetic relationship, the greater the risk for zoonoses. This is one reason for often avoiding the use of apes as laboratory animals

  
• Majority of human pathogens are zoonotic (868 species or 61%). Approximately 75% of human emerging infectious diseases are caused by zoonotic pathogens (Taylor et al., 2001)

  
• Transmission of zoonotic agents

  • Through the air – respiratory, includes dust, fomites
  • Through the physical environment – includes food, water, soil and pasture
  • Through biological vectors – mosquitoes, sand flies, tsetse flies, ticks
  • Through direct contact – Bites, Iatrogenic: corneal & dura mater transplants; blood transfusions and via wounds
• Agents responsible for global mortality

  • HIV-1 and -2
  • Influenza virus
• Transmission of many pathogens falls into more than one of these categories, for example, Yersinia pestis or the flaviviruses
• Agents that cause limited deaths but result in high case fatality rates and for which no effective therapies or vaccines exist

  • Ebola virus
  • Hantaviruses
  • Nipah virus
  • Severe acute respiratory syndrome (SARS)-associated coronavirus
• Those transmitted by vectors of indirect contact are most likely to be zoonotic (few fungi are transmitted by vectors and helminths are very rarely transmitted by direct contact), suggesting that these transmission routes may be associated with lower host specificity
• For zoonotic diseases to occur from animals to humans

  1. Animal must be infected (not necessarily diseased)

  2. Must be transmitted to people

  3. People must be ill (not just infected)

  
• Classification of zoonoses


  • Mechanism of transmission
  • Natural cycle
  • Etiology
  • Occupation or risk group
  • Animal reservoirs
• All animal species should be considered as potential sources of infections that can be transmitted to other animals or man
• Anthropozoonoses


  Animals → man
• In general, the closer the phylogenetic relationship, the greater the risk for zoonoses. This is one reason for often avoiding the use of apes as laboratory animals

  
• Zooanthroponoses


  Man → animals
• Transmission of zoonotic agents

  • Through the air – respiratory, includes dust, fomites
  • Through the physical environment – includes food, water, soil and pasture
  • Through biological vectors – mosquitoes, sand flies, tsetse flies, ticks
  • Through direct contact – Bites, Iatrogenic: corneal & dura mater transplants; blood transfusions and via wounds

  
• Amphixenoses


  Animals <-> man
• Transmission of many pathogens falls into more than one of these categories, for example, Yersinia pestis or the flaviviruses
• Examples


  • Anthropozoonoses: Rabies, Bovine TB, Brucellosis
  • Zooanthroponoses: Diptheria, Amoebiasis
  • Amphixenoses: Staphylococcal, Influenza – lesser transfer or swine than avian flu
• Direct Zoonoses


  Involves a single vertebrate species
• Those transmitted by vectors of indirect contact are most likely to be zoonotic (few fungi are transmitted by vectors and helminths are very rarely transmitted by direct contact), suggesting that these transmission routes may be associated with lower host specificity
• Classification of zoonoses


  • Mechanism of transmission
  • Natural cycle
  • Etiology
  • Occupation or risk group
  • Animal reservoirs
• Examples of Direct Zoonoses

  • Rabies, Trichinella, Brucellosis
• Cyclozoonoses


  Require >1 vertebrate and no invertebrates required
• Anthropozoonoses


  Animals → man
• Examples of Cyclozoonoses


  • Echinococcosis, Taeniasis
• Zooanthroponoses


  Man → animals