West Nile Virus can be fatal for your horse.
Harmony/Cresco veterinarian Dr. Lynn Aggen reported that the first case of West Nile Virus in the area this year was officially confirmed in McIntire, Iowa, near Riceville. The Amish-owned horse died and another horse, also Amish owned, died from what was expected to be WNV, although not officially confirmed. A third case of WNV was confirmed south of Granger; this horse survived. The fourth case near Highland which was confirmed to have WNV, also died.
The Board of Animal Health reports there have been eight confirmed cases in Minnesota this year so far. The first confirmed case in Minnesota in 2018 was near Pine City. The last case of WNV reported in Minnesota in 2017 occurred in November. Positive results for WNV must be reported to the Board of Animal Health.
Aggen explained WNV first came to eastern United States about 18 years ago. The first cases to be confirmed in this part of the United States occurred about 15 years ago.
Prior to 1999 WNV was found only in Africa, Eastern Europe, and West Asia.
WNV can be fatal for about 30 to 40% of horses that develop the disease. Horses are susceptible to infection. The pathogen is introduced to the horse through a mosquito bite. Wild birds host the WNV and mosquitos that have previously fed on an infected bird can transmit the virus when they bite a horse. Dead wild birds, especially crows or jays, can be a sign of WNV.
We have had a wet spring and early summer, conditions that produce a large mosquito population. Infection is most likely to occur in late summer or through the fall. The pathogen can cause encephalitis and meningitis.
A horse that develops the disease can display a variety of serious symptoms which may include depression, weakened muscles, fever, seizures, blindness, a lack of coordination, and an inability to stand/paralysis. Aggen noted he has seen infected horses sit like a dog.
Not all horses with some of the above symptoms have the virus. Other diseases may cause similar symptoms.
While there is no specific treatment or cure for WNV, Aggen explained supportive care administered to an infected animal can help and may include IV DMSO (dimethylsulfoxide), banamine, and fluids.
Some horses that survive may have longer lasting impairments to their mobility or their behavior.
This disease is not contagious; an infected horse is not a carrier of the disease. The infected horse can not transmit the virus to other horses, people, or mosquitos. It takes the wild bird-mosquito cycle to transmit the virus.
Your veterinarian can confirm a diagnosis, ruling out other ailments, through serological testing. An effective test is the IgM capture ELISA, which will confirm an exposure to the virus in the last three months. Aggen said the incubation period could be under a week.
Aggen said there was a suspected case of WNV near Rushford that was officially diagnosed as lyme disease. There is a vaccine for lyme disease.
The best way to protect your horse against WNV is vaccination followed by an annual booster. Dr. Aggen encourages horse owners to vaccinate their horses. He admits the vaccine is expensive (about $28 for a single dose for just WNV). There is also a six-way vaccine that would normally be given in the spring that includes the WNV. Either way, a booster should be given annually.
The vaccine is relatively cheap if compared to the cost of supportive care given to save an infected horse or the loss of your horse. Vaccines for horses are available and proven to be effective in preventing infection.
A horse that has survived the disease should also be given an annual booster. It has not been confirmed that a horse that has survived the disease can not be reinfected.
Prevention starts with vaccination. Dr. Aggen recommends an initial vaccination for a previously non-vaccinated horse should be administered in two doses of vaccine about two to three weeks apart, followed by an annual booster. During an outbreak of WNV Dr. Aggen would recommend a booster during the outbreak.
Good management is important. Minimize mosquito populations (especially by removing stagnant water) and discourage the roosting of wild birds like crows.