Simulation of the seasonal cycles of bird, equine and human West Nile virus cases.

This study presents a model for simulating the dynamics of West Nile virus (WNV) transmission among birds, horses, and humans in the Minneapolis region of the United States. The model, which takes environmental temperature into account, was used to analyze data from 2002 to 2009.

Study Objective

• The primary objective of this research is to build a model capable of simulating the transmission dynamics of the West Nile Virus (WNV). Notably, this model considers the effects of environmental temperature on the transmission cycle of the virus. This is vital as environmental temperature influences the population dynamics of mosquitoes (the vector responsible for virus transmission) and the virus’s extrinsic incubation period (the time it takes for the virus to reproduce in the mosquito before it can be transmitted).

Research Methodology

• A total of 19 compartments, divided into categories of mosquitoes, birds, horses, and humans, are included in the epidemic model of the WNV, which operates on an SEIR (Susceptible-Exposed-Infectious-Recovered) model basis.
• The model was then used to run simulations for the period between 2002 and 2009, with environmental temperature as the controlling parameter.
• The model parameters were adjusted to fit the monthly reported cases of bird, horse, and human WNV cases in the Minneapolis metropolitan area.

Key Findings

• This model is the first one to integrate the effects of seasonal temperature variation into WNV transmission simulations.
• The researchers deduced that, out of all WNV-induced bird deaths, approximately 0.8% were reported. The figures were slightly higher for horses and humans, with 7.3% and 10.7% of cases respectively reported. These findings are consistent with previous studies that suggest around 90% of WNV cases in horses and humans are asymptomatic and usually go unreported.
• Despite the limitations with data completeness, the simulated results closely matched the actual data with correlation coefficients ranging from 0.75 to 0.96 for different host species.