L21 - Emerging viral pathogens

• Emerging viruses


  Viruses that have recently started to infect humans or have increased in prevalence
• Over the > 30 years, a number of emerging and re-emerging viruses have dominated the scientific literature
• Examples of emerging viruses by decade

  • 1970s: enteric (rotavirus, Norwalk), Ebola viruses
  • 1980s: retroviruses including HIV AIDS and hepatitis C
  • 1990s: HEV, HGV, Nipah & Hendra, West Nile viruses
  • 2000s: Foot and mouth disease virus, avian influenza, SARS-HCoV
  • More recently: Zika virus, Ebola, SARS-CoV-2

  
• Generally there are no new viruses. Viruses have co-evolved with us for millennia and no doubt will continue to do so
• In most cases it is simply that we can now detect the viruses present
• Increased exposure to a "new or different" virus promotes research and diagnosis
• Generally we are to blame for these emerging viruses
• Zoonosis


  Diseases that can be passed from animals, whether wild or domesticated, to humans

  
• Animals and the diseases they may carry

  • Bats and dogs - rabies
  • Camels, cats and bats - SARS
  • Horses - influenza and West Nile Virus
  • Cattle - European tick-borne encephalitis
  • Pigs - influenza, Japanese encephalitis virus
  • Sheep and goats - Foot and Mouth Disease virus
• Factors leading to emerging viral diseases

  • Increases in the human population
  • Urbanization - more people concentrated in cities often without adequate infrastructure
  • Increases in the elderly populations
  • Increases in children in daycare
  • Fast paced lifestyles - increase in convenience items and more stress
  • High-risk behavior - Drug use and unprotected sex
• International travel and commerce facilitate the spread of emerging viruses
• Humans have encroached on wildlife habitats, increasing exposure to new viruses
• Zika virus (ZIKV)


  First identified in Uganda in 1947, recent outbreaks in French Polynesia (2013) and Brazil/Americas (2015) linked to severe outcomes
• The current trend of climate change is expected to put 1.5-2.5 billion more people at risk of contracting Dengue Virus
• Hendra virus


  Transmitted from bats to horses, then from horses to humans, with a 75% death rate in horses and 57% in humans
• Nipah virus


  Paramyxovirus with a case fatality rate of 40-75%, spread due to deforestation and climate change
• Coronaviruses


  SARS-CoV-2 (1-3.5% mortality), MERS (35% mortality), SARS (10% mortality)

  
• Viral evolution plays a key role in the emergence of new viruses
• Public health measures like testing, isolation and quarantine helped control the SARS-CoV-1 outbreak
• SARS-CoV-2 is the third coronavirus pandemic of the 21st century, with over 216 million infections and 4.5 million deaths as of August 2021

  
• The rapid identification of SARS-CoV-1 in 2003 shows we can be better prepared for future pandemics