Equine West Nile virus disease occurrence and the Normalized Difference Vegetation Index

Area of Science:

• Environmental Science
• Veterinary Epidemiology
• Remote Sensing

Background:

• Equine West Nile virus encephalomyelitis (WNV) poses a significant threat to animal health.
• Environmental factors, such as vegetation health, are suspected to influence WNV transmission dynamics.

Purpose of the Study:

• To investigate the association between Normalized Difference Vegetation Index (NDVI) and reported cases of equine WNV in Texas.
• To determine if NDVI can be used as an indicator for predicting WNV outbreaks.

Main Methods:

• A time-series analysis was conducted on biweekly equine WNV case reports in Texas from 2002-2004.
• Standardized case ratios were calculated and correlated with mean NDVI values.
• The influence of NDVI on case ratios was assessed with different temporal lags, considering regional variations.

Main Results:

• Mean NDVI was significantly higher during periods with reported WNV cases compared to periods without cases (P<0.001).
• The strongest association between standardized case ratios and NDVI was observed when NDVI data preceded case reports by 4 weeks.
• Regional differences were noted: the Prairies and Lakes ecoregion showed a 19-20 week lag, while the Panhandle Plains showed a 1-4 week lag.

Conclusions:

• NDVI is a potential predictor of equine WNV risk.
• The temporal relationship between vegetation indices and WNV transmission varies geographically.
• These findings support the development of NDVI-based early-warning systems for WNV.