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Eastern Equine Encephalitis and West Nile

Thursday, March 25, 2021

New York (NY): Equine arbovirus cases are reported by the Cornell AHDC to regulatory agencies so that they may be captured in annual USDA-APHIS census data for the United States. This information is available on their website. During the year 2020, the AHDC received 93 serological test requests on equids for Eastern Equine Encephalitis (EEE), which were sent to the National Veterinary Services Laboratories (NVSL) in Ames, Iowa. The presence of an EEE IgM ELISA titer is consistent with recent infection. Of 39 AHDC requests from NY clinicians, 6 cases were confirmed positive based upon serum EEE IgM ELISA results. Two additional NY EEE cases were reported to the USDA-APHIS, making a total of eight identified cases in NY state during the 2020 arbovirus season. Additional EEE diagnostics currently undergoing validation at the AHDC include EEE PCR on EDTA whole blood for use in equine clinical cases, and EEE PRNT to detect equine vaccine antibody titers.

The AHDC in 2020 performed 370 total serological tests on equids residing in the United States for the detection of West Nile Virus (WNV) infection or response to vaccination. While 8 equids from other states tested positive at the AHDC on the WNV IgM Capture ELISA, there were no WNV cases in NY. Similarly, in 2019 no NY state WNV cases were reported, which contrasts with the 20 cases reported during the 2018 arbovirus season. Due to the endemic presence and cyclical nature of West Nile in NY state, we do anticipate additional cases of WNV in the coming years. 

Vaccination of equids for EEE and WNV remains the mainstay of prevention for these arbovirus infections. It is recommended that these vaccines be given annually despite the waxing and waning of arbovirus infections in our equid populations. For infectious disease surveillance reports in a variety of species in the United States, please visit the USDA-APHIS Animal Health website.

Equine Arbovirus Cases Diagnosed in NY

  1. Ribeiro, G. S. et al. Influence of herd immunity in the cyclical nature of arboviruses. Current Opinion in Virology 40, 1–10 (2020).