Biodiversity and Disease Transmission Stavros Calos

Agriculture Agriculture Lyme Disease and West Nile Virus Lyme Disease and West Nile Virus ↑ Mammalian and bird diversity leads to ↓ Lyme Disease and WNV in humans. ↑ Mammalian and bird diversity leads to ↓ Lyme Disease and WNV in humans. Higher biodiversity can reduce disease transmission

Case 1: A disease specializes on a single host species, and transmission is by direct contact. dS/dt = (b – m)S – βSI + (αδ + b’)I dS/dt = (b – m)S – βSI + (αδ + b’)I dI/dt = βSI – (αδ + m’)I dI/dt = βSI – (αδ + m’)I Densities of susceptible (S) and infected (I) hosts b, b’, m, and m’ are birth and deaths for susceptible and infected host αδ – the rate of encounter of between infected hosts and susceptible ones (α) times the probability of transmission (δ). γ - Recovery rate

dS/dt = (b – m)S – αδSI + (γ + b’)I dS/dt = (b – m)S – αδSI + (γ + b’)I dI/dt = αδSI – (γ + m’)I dI/dt = αδSI – (γ + m’)I Case 1 Assumptions: Host is regulated solely by pathogen. All recovered individuals can be reinfected. Disease only transmissible within one species. Abundances of susceptible (S) and infected (I) hosts b, b’, m, and m’ are birth and deaths for susceptible and infected host Recovery rate (γ) αδ – the rate of encounter of between infected hosts and susceptible ones (α) times the probability of transmission (δ).

Biodiversity and Case 1: dI/dt = αδSI – (γ + m’)I Reduce rate of encounter (α) by adding species Reduce rate of encounter (α) by adding species Reduce probability of encounter leading to transmission (δ) by adding species Reduce probability of encounter leading to transmission (δ) by adding species Increase death rate of infected individuals (m’) by adding species Increase death rate of infected individuals (m’) by adding species

Case 2: A disease specializes on a single host species, and vectors transmit the disease. dI/dt = αδ’SZ – (μ+m’) I dI/dt = αδ’SZ – (μ+m’) I Densities of uninfected (W) and infected (Z) vectors λ = Vector recruitment rate μ = vector death rate αδ – the rate of encounter (α) times by the probability of transmission (δ). dW/dt = λ –μW-αδIW dW/dt = λ –μW-αδIW dZ / dt = αδIW –μZ dZ / dt = αδIW –μZ

Biodiversity with a Vector Species: dW/dt = λ –μW-αδIW dW/dt = λ –μW-αδIW dZ / dt = αδIW –μZ dZ / dt = αδIW –μZ dI/dt = αδ’SZ – (μ+m’) I dI/dt = αδ’SZ – (μ+m’) I Encounter Reduction Encounter Reduction Reduce dI/dt by increasing m’ Reduce dI/dt by increasing m’ Reducing rate of encounter between infected vectors (α) and susceptible hosts. Reducing rate of encounter between infected vectors (α) and susceptible hosts. The Dilution Effect! The Dilution Effect! Added species are still preyed upon by vector, but they are not as capable of carrying the disease and transmitting it to the vector. Added species are still preyed upon by vector, but they are not as capable of carrying the disease and transmitting it to the vector.

Reservoir Hosts Vector Species Incidental Host

Reservoir Hosts Vector Species Incidental Host

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