Tag: west nile virus

By Alice Collins / Jump Media

The warm late summer of 2024 has paved the way for more mosquitos and heralded the start of West Nile Virus (WNV) and Eastern Equine Encephalitis (EEE) season for both horses and humans. WNV and EEE are both equine encephalitis viruses spread by infected mosquitos. They can cause severe brain inflammation and neurological issues in humans and horses and can be fatal in unvaccinated or under-vaccinated equine populations. 

With almost daily cases of WNV in horses being reported in several U.S. states throughout August 2024, plus news of humans contracting the rare but extremely serious EEE virus, people are rightfully concerned about how to protect their animals and themselves from both WNV and EEE. The Wellington, Florida-based Palm Beach Equine Center (PBEC)advises on what you can do to minimize the risk of exposure and infection.

WNV and EEE by the Numbers

Both WNV and EEE circulate in the environment between mosquitoes and birds and are spread to horses and humans by the bite of an infected mosquito. However, even though they get sick, humans and horses are dead-end hosts that do not, in turn, spread these viruses back to mosquitoes that bite them.

Since 1999, more than 27,600 U.S. horses have been confirmed to have WNV, with an estimated fatality rate of 30-40%. With yearly activity of around 300 equine cases in the U.S., WNV is now considered endemic, persisting at a consistent level with fairly predictable rates of infection and spread.

EEE, also known as sleeping sickness, causes inflammation of the brain and spinal cord. Mortality can exceed 90% in unvaccinated horses and is lower in horses with partial protection or previous vaccination. Death usually occurs within two to three days of the onset of signs. Horses that survive may have permanent neurologic deficits.

While the diseases sound alarming, the good news is that vaccination is a very effective barrier for your horse. EEE and WNV inoculations are considered core vaccines by the American Association of Equine Practitioners. Annual injections for all horses, preferably in the spring before mosquito season, are strongly recommended. Initial vaccination is followed in four to six weeks with a booster, with yearly revaccination thereafter. Horses living in areas with mosquitos year-round may need EEE vaccinations two or three times a year for full protection.

Clinical Signs

The clinical signs of the two illnesses are almost identical, and can include:

• Depression and anorexia without fever when initially infected 
• Mild low-grade fever in about 25% of affected horses with WVN
• Moderate to high fever in horses with EEE
• Lack of appetite 
• Lethargy/drowsiness 
• Neurologic signs, the onset of which are frequently sudden and progressive
  • Periods of hyperexcitability, apprehension and/or drowsiness  
  • Fine tremors of the face and neck muscles 
  • Cranial nerve paralysis — facial paralysis and weakness of the tongue are very common 
  • Head tilt, droopy lip, muzzle deviation
  • Weakness, ataxia, and lack of coordination in one or more limbs 
  • Complete paralysis of one or more limbs 
  • Colic 
  • Inability to stand

Diagnosis and Treatment

A veterinarian will diagnose both WNV and EEE by testing the horse’s serum, a component of whole blood. There is no cure for either virus, but horses showing clinical signs are given supportive care.

Prevention

Aside from vigilant vaccination suitable for the horse’s environment, there are other measures owners can take to prevent infection from both WNV and EEE. They include frequent use of insect repellent, which should be reapplied after rain, keeping horses stabled at night, minimizing standing water, and eliminating areas in which water can collect, such as leaf piles or old tires. 

PBEC President Dr. Scott Swerdlin advises, “We can vaccinate against all these diseases, and it’s really important to remember that it’s not just the first set; it takes at least two injections for the horse to develop immunity.”

Swerdlin also points out that horses traveling into an affected region can be put at far greater risk, adding, “People who bring horses to the U.S. from South America or Europe are exposing them to different diseases than they are accustomed to in their native country. They should vaccinate the horses immediately on arrival and then, after the first vaccine, every 12 months. In Florida, where there is a huge mosquito population, we recommend vaccinating against EEE and WNV, as well as rhinovirus, every six months for maximum protection.”  

There are no approved human vaccines for WNV or EEE. Personal protective measures include using mosquito repellents, wearing long-sleeved shirts tucked into long pants, and limiting time outdoors from dusk to dawn. Using air conditioning and installing screens further decreases the risk of exposure. 

For additional questions, veterinary assistance, or to book your horse’s vaccinations, call Palm Beach Equine Clinic at 561-793-1599.