West Nile Virus/Eastern Equine Encephalitis Letter to Veterinarians

State of New York Department Of Agriculture And Markets
10B Airline Drive
Albany, New York 12235

Date: 6/25/2008

Dear Veterinarian:

The veterinary community has been invaluable in tracking the occurrence of West Nile virus (WNV) as it has spread throughout New York State since its introduction in 1999. However, we want to make sure you are aware of the reappearance of another more serious type of encephalomyelitis, eastern equine encephalitis (EEE).

We are asking the veterinary community to consider EEE in horses with neurologic signs and are seeking your help in identifying EEE cases. Signs of EEE can mimic a variety of encephalitic diseases including rabies, WNV, botulism, hepatic encephalopathy, equine protozoal myeloencephalitis (EPM), tetanus, equine herpes virus 1 (EHV1), lead poisoning, and others. Most equine cases of EEE have dates of onset between mid-August and mid-September, although the onset date for the earliest New York case was July 14th and the latest October 21st. EEE outbreaks have also resulted in fatal infections in pheasants, quail, captive whooping cranes, and most recently in emus.

The first equine EEE cases in New York were reported from Suffolk County in 1970. The following year, the first human case and three equine cases were reported from Oswego County. From 1971-1977, there were equine cases each year in one or more of the four Oneida Lake Basin counties (Madison, Oneida, Onondaga and Oswego). Equine cases were also documented in Basin counties in 1983, 1990 and 1991. Basin counties reported 89 of the 93 total equine cases from 1970-1991. The other equine cases were in 1990 from Suffolk (3 cases) and Orange (1 case) counties. After a 12 year absence, equine cases reappeared in 2003 and were documented each year from 2003-2006. Basin counties again reported most (16/24) of the equine cases in this period, with additional cases in Suffolk and Orange counties, and for the first time in Chemung, Lewis, Sullivan and Ulster counties. There were no equine or human cases in 2007. Fortunately no human cases have occurred in New York in recent years, but human and equine cases have been reported from New Jersey, Massachusetts and New Hampshire, with equine cases in Connecticut and Rhode Island.

The reporting system for EEE is laboratory-based. Isolation of virus from brain tissue is the best method of confirming cases of EEE. For deceased horses which had neurologic signs, or ones that will be euthanized due to neurologic signs, please contact the New York State Department of Health Wadsworth Center Rabies Laboratory to submit appropriate brain tissue for testing along with the Rabies Specimen History form (518-869-4527; see http://www.wadsworth.org/rabies/ for instructions). Rabies is the neurologic disease of highest risk to humans and other mammals. Rabies must be ruled out quickly by the Wadsworth Center to determine the need for human postexposure treatment and management of other mammal contacts. After rabies is ruled-out, brain specimens will be tested for EEE and other viruses at the Wadsworth Center's Arbovirus Laboratory, and for other diseases at Cornell University's Animal Health Diagnostic Center (AHDC).

To obtain the most rapid testing for other potential causes of neurologic disease, it is recommended that veterinarians also send specimens to AHDC at the same time as the Wadsworth Center. Please contact AHDC at 607-253-3900; see http://diaglab.vet.cornell.edu/ for additional information. It is essential that collection of neurologic tissue for testing at AHDC does not interfere with the collection of a full cross-section specimen of fresh brainstem and adequate samples of cerebellum required for the rabies diagnosis at the Wadsworth Center (see http://www.wadsworth.org/rabies/prof/livestk.htm ). When it is not feasible to take a brain specimen (i.e., in ill horses with neurologic signs), please report the case and discuss submission of serum and/or cerebrospinal fluid for viral testing with AHDC.

Reporting and testing of neurologic horses will assist us in insuring that rabies is diagnosed in time to provide post-exposure treatment to appropriate individuals, determining the distribution and spread of EEE, and obtaining as soon as possible for the horse owner and veterinarian a diagnosis of any other infectious disease, toxic exposure, or other cause of illness and death.


John Huntley, DVM, MPH
Director, Division of Animal Industry
NYS Department of Agriculture and Markets

Millicent Eidson, MA, DVM, DACVPM
State Public Health Veterinarian and
Zoonoses Program Director
NYS Department of Health

cc: Local health departments and NYSDOH regional offices