Disease evolution Brian O’Meara EEB464 Fall 2015

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Presentation transcript:

Disease evolution Brian O’Meara EEB464 Fall

Learning objectives Connect ideas about symbiosis and game theory to disease evolution Understand natural history of disease

Susceptible InfectiousRecovered

Virus AVirus BVirus C Kills host in a day Kills host in a month Kills host in a year 2 pt each row: which disease will increase at the fastest rate?

Virus AVirus BVirus C Kills host in a day Kills host in a month Kills host in a year Each host infects 1 person on average Each host infects 40 people on average Each host infects 100 people on average 2 pt each row: which disease will increase at the fastest rate?

Virus AVirus BVirus C Kills host in a day Kills host in a month Kills host in a year Each host infects 1 person on average Each host infects 40 people on average Each host infects 100 people on average 1/1=1.040/30 = /365 = pt each row: which disease will increase at the fastest rate?

Virulence: ability of an organism to cause disease Virus AVirus BVirus C Kills host in a day Kills host in a month Kills host in a year Each host infects 1 person on average Each host infects 40 people on average Each host infects 100 people on average 1/1=1.040/30 = /365 = 0.3 Why not just evolve to be less virulent?

Effect on virulence of: Change from horizontal to vertical transmission Unprotected sexSharing needlesFrom parent (typically mother) HIV horizontalHIV vertical

Effect on virulence of: Increased number of sexual partners Bearman et al 2004

Effect on virulence of: Spatial structure UnstructuredStructured

Effect on virulence of: Vaccination

Effect on virulence of: Vaccination Gandon et al Nature

Effect on virulence of: Vaccination Gandon et al Nature Blue = anti-infection vaccine Green = transmission-blocking vaccine Red solid = anti-growth rate vaccine (slow parasite growth) Red dashed = anti-toxin immunity (make parasite less harmful w/o affecting transmission and growth rates)

Effect on virulence of: Number of innocula

How do we then get pandemics?

Origins of virus Origins of a particular virus (SARS, HIV, flu) Origins o f viruses as a biological entity

Gao et al. 1999

Origins o f viruses as a biological entity Three hypotheses Virus-first Reduction Escape Forterre 2006

Virus-first: Viruses evolve, use the prebiotic soup for replication, later parasitize cells Not favored: requires ribosomes (protein synthesis for coats), other complex structures, need Darwinian evolution for that

Forterre 2006

Transposons

Cows (Bovine spongiform encephalopathy, aka “mad cow”) Sheep (Scrapie) Mink Cats Deer (chronic wasting disease) Humans (kuru; variant Creutzfeldt-Jakob Disease (vCJD))