Surviving Mosquito Season

Most people aren't a fan of the pesky mosquito.  Their high pitched buzzing and annoying persistence are enough to ruin even the most pleasant trail ride.  However, horse owners have another reason to dislike mosquitoes.  There are 3 major diseases that can be transmitted by mosquitoes: Western Equine Encephalomyelitis (WEE), Eastern Equine Encephalomyelitis (EEE), and the West Nile Virus (WNV).  While these diseases are becoming less and less common in the United States, knowing the cause, clinical signs, treatment, and, most importantly, how to prevent these diseases can be the difference between saving your horse and losing your horse.

West Nile Virus (WNV)

Source: http://www.ahsequilink.co.za/west-nile-virus/

WNV is a type of virus that causes encephalitis, the inflammation of the brain.  The virus is usually transmitted from wild birds to horses via mosquitoes.  Symptoms of WNV typically occur between 3-14 days after being bitten by an affected mosquito.  Clinical signs include: loss of appetite, depression, fever (101 degree Fahrenheit or higher for 2 or more days), weakness or paralysis of hind legs, impaired vision, and paralysis.  Some horses, however, may be infected with WNV without ever showing clinical signs.  If you think your horse is infected with WNV, call your Veterinarian immediately.  Treatment of WNV includes supportive therapy, anti-inflammatory medications (sometimes including corticosteroids), and intravenous fluids.

Western Equine Encephalomyelitis (WEE) and Easter Equine Encephalomyelitis (EEE)

Source: https://easternequineencephalitis.wordpress.com/

WEE and EEE are transmitted to horses from wild birds via mosquitoes, just like WNV.  In addition, WEE and EEE are caused by viruses from the same family (Togaviradae), so the early stages of these diseases are also similar.  After being bitten by an affected mosquito, it may take anywhere from 3-10 days for horses to start showing signs of the virus.  Early clinical signs are nonspecific for both WEE and EEE and include: severe fever (103-106 degree Fahrenheit) that lasts for 24-28 hours, poor appetite, and stiffness.  Many cases of WEE do not progress beyond this point; however, with EEE, progression is certain.  EEE is a fast acting virus, so horses will develop chronic symptoms - propulsive walking (or "staggering"), blindness, circling, uncontrollable muscle trembling in their face and legs, paralysis of the pharynx, larynx, and tongue, and inability to stand - only 2 to 4 days after the first clinical signs appear.  If left untreated, EEE will result in complete paralysis and death.  Call your Veterinarian immediately if you suspect that your horse has EEE or WEE.  There is no cure for either EEE or WEE.  The mortality rate for these diseases ranges from 75-100% (EEE) and 20-50% (WEE).  Catching these diseases in their early stages are key.  Around the clock intensive nursing and Veterinarian care can save an infected horse's life; however, since the viruses attack the nervous system horses that survive WEE or EEE are likely to suffer brain damage.

Prevention is the best protection against WNV, WEE, and EEE.  Vaccinating horses in the early spring with either a "3-way" (protects against EEE, WEE, and tetanus) or a "4-way" (protects against EEE, WEE, tetanus, and influenza) is highly recommended.  Notice that neither a "3-way" nor a "4-way" protect against WNV.  There are several licensed vaccines available, so be sure to ask your Veterinarian what would work best for you and your horse.  These vaccines only last for 6-8 months, though.  So remember to vaccinate your horses annually (or even twice a year if you live in an area heavily infested with mosquitoes).

You can also protect your horses by limiting the amount of contact they have with mosquitoes by:

• Using insect repellents to prevent bites,
• Having fans in barns and stables to blow mosquitoes off horses,
• Covering horses with fly sheets,
• Avoiding outdoor activities at dawn or dusk when mosquitoes are most active (especially around stagnant water), or
• Removing standing water - such as water found in old tires, pet bowls, kiddie pools, buckets, ect.

For more information: http://animalscience.uconn.edu/extension/publications/mosquito.htm