Changes in West Nile virus seroprevalence and antibody titers among Wisconsin mesopredators 2003-2006.

The research paper investigates how the prevalence and resistance to West Nile virus (WNV) in mesopredators (medium-sized, middle trophic level predators) from Wisconsin changed from 2003 to 2006, providing indications on the animals’ role in the virus’ life cycle and its potential spillover into human and equine populations.

Research Context and Methodology

• The study was prompted by the first recorded occurrence of West Nile virus (WNV) in Wisconsin in 2001. In response, the researchers collected serological data (blood samples to assess immunity levels) from mesopredators in the south-central region of the state, during the period from 2003 to 2006.
• The collected samples were tested to determine the prevalence of WNV antibodies (signaling past infection and possible immunity) and the geometric mean antibody titer (GMAT – a method to quantify the concentration of antibodies, pointing at the strength of the immune response).

Findings and Implications

• Higher antibody prevalence and GMAT in 2003-2004 suggested a higher exposure to WNV among mesopredators during this period, which was likely the ‘epizootic’ phase wherein the virus rapidly spreads among animal populations.
• The drastic fall in WNV antibody prevalence during 2005-2006 was associated with the ‘enzootic’ phase of the virus life cycle, which implies stable, endemic existence of the virus in the host population.
• The study indicated that vector-borne transmission is the primary route of WNV infection in mesopredators, meaning they typically contract the virus from mosquito bites rather than from other animals.
• The research also suggested that WNV antibodies in these animals persist for less than one year, which indicates their potential susceptibility to annual WNV outbreaks.
• Given their role in the life cycle of WNV, mesopredators could serve as sensitive indicators of the virus spill-over into populations of concern such as humans and horses. Their susceptibility and reaction to WNV could provide useful data for predicting outbreaks and timing public health interventions.
• Reflecting these findings, the authors argued that serological surveys of mesopredators could be an effective way to supplement existing surveillance efforts, which mainly rely on monitoring dead crows (since birds are the primary hosts of WNV).
• The authors concluded by calling for further research to clarify the role of mesopredators as potential amplifiers of WNV. This could help shape more effective strategies for preventing and controlling virus transmission.