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One horse's battle with West Nile

Jean Morris

(This story first appeared in Horse Sport magazine February 2003)

"Riley and I are pretty close," says Julia Ruhl of the six-year old Thoroughbred gelding ambling across the paddock to greet us. "I’ve had him since he was 18 months old. He was butt-ugly, but we clicked".

On a chilly October morning, it is hard to imagine the robustly healthy horse in that bleak landscape fighting a virus exotically named "West Nile".

Riley lives with a Clydesdale called Montserrat, on the property of Julia and Jeff Ruhl, near Tottenham, Ontario. The house and barn sit on a hill overlooking fields that sweep down to a creek. On a chilly October morning, it is hard to imagine the robustly healthy horse in that bleak landscape fighting a virus exotically named "West Nile".

It began on the evening of Thursday, 29 August, when Julia called the horses in for their feed. Riley seemed disinterested; pacing in the field and neighing. Maybe he was simply attracted to the neighbours’ filly, but Julia and Jeff hung over the fence for a while, just in case. Riley eventually came up to say "Hi" and started eating his hay.

Friday morning: Jeff hurried in from the morning feed to tell Julia, "You’d better call the vet".

Riley looked drunk. He was stumbling so badly he could hardly walk up the hill to the barn. He was trembling over his head, neck, withers and shoulders and was extremely sensitive to touch. Julia put him into his stall. He seemed alert and ate his hay in spite of the "bizarre" shaking, but he called if Julia left his sight. Julia telephoned the vet.

When Dr. Mallu Postons, of Beeton, examined Riley, she found no sign of physical trauma, but his temperature was up 1°F and he was uncoordinated when jogged.

Dr. Postons listed the possibilities: Rabies, equine protozoal myeloencephalitis (EPM), Eastern and Western encephalomyelitis and West Nile virus (WNV).

Although veterinarians were vaccinating against WNV in April and May 2002, most owners chose not to, as the disease was not evident in the area at that time. Neither Dr. Postons nor Julia knew of any confirmed cases in Simcoe County. The wind and the August-dry creek discourage mosquitoes from infesting the Ruhl property, and it is mosquitoes that transmit the virus from birds to horses and humans.

Dr. Postons left with a sample of Riley’s blood. If a bacterial infection was the root of the problem, a complete blood count would show an elevated level of white blood cells, while a viral infection would tend to show a reduced level. An equine profile, by measuring levels of enzymes and electrolytes, would help determine if a liver malfunction was causing the central nervous system symptoms.

"He kept calling me, neighing to me. I knew something was going on and Riley knew, too. He didn’t want me to leave."

There was nothing to be done, except keep Riley safe and comfortable, until the results of the blood tests came back that evening. The Ruhls set up a baby monitor in the barn.

Within two hours, Riley’s shaking had intensified and his front legs were starting to buckle.

When he tried to turn, he fell onto his knees. Although he struggled to rise, he eventually gave up and stayed down. He ate the hay Julia put under his nose, "but," she said, "he kept calling me, neighing to me. Now I was worried. Before, I had been just concerned, but I knew something was going on and Riley knew, too. He didn’t want me to leave."

Friday evening: Dr. Postons returned with the results of the complete blood count - normal. The ataxia (lack of coordination) had spread to Riley’s hind legs, which were starting to buckle. He was becoming very anxious, so Dr. Postons administered 10 ml of flunixin meglumine (commonly known as Banamine). Riley’s anxiety decreased, but the tremors and leg buckling continued.

Saturday: Riley’s muscles were still trembling, but he was steadier on his feet.

Meanwhile, Dr. Postons had consulted with the Ontario Veterinary College. Diseases that attack the central nervous system, such as Eastern and Western encephalomyelitis, WNV, rabies, EPM and tetanus, have many symptoms in common, including: loss of appetite, fever, weakness, depression, impaired vision, ataxia, head pressing, convulsions, inability to swallow, circling, paralysis and coma.

Riley’s muscle twitching and hind leg ataxia pointed most strongly to WNV, but both EPM and rabies were still possibilities. Riley’s caregivers protected themselves from exposure to his saliva, in case rabies was the culprit, even though his vaccinations were up-to-date.

Riley’s caregivers protected themselves from exposure to his saliva, in case rabies was the culprit.

Dr. Postons administered another 10 ml of flunixin meglumine to reduce inflammation around the spinal cord and brain. The dose would be repeated twice daily for two more days. The consultant at OVC had also recommended the use of an antibiotic to fight secondary bacterial infection. Accordingly, Riley received 15 tablets of Apo-Sulfatrim-DS dissolved in water and squirted down his throat. This dose of 30 mg/kg was to be repeated twice daily for seven days. Riley was turned out covered in fly spray and wearing a fly mask.

Should Montserrat be vaccinated, since he was exposed to the virus? Dr. Postons explained that there was no point. Effective initial immunization requires two doses three to six weeks apart and immunity only commences about three weeks after the second dose. A horse must have his first dose of WNV vaccine at least six weeks prior to the start of mosquito season. August is too late. Annual boosters, preferably in spring to push the immunity level to its highest during the peak exposure period, are required.

Sunday: Julia, who was seven months pregnant and correspondingly large, held Riley while Jeff squirted the dissolved Apo-Sulfatrim down his throat. Riley, obviously feeling better, "kicked out with a front leg and grazed [her] tummy", so she was banned from the barn.

Because of the impending baby, Julia called the West Nile hotline. There were no data regarding pregnant women, nor was it known if the virus can cross the placenta into the foetus.

There was no danger of catching WNV from Riley, as horses and humans are "dead end hosts" – they cannot transmit the virus. However, if Riley had WNV, then infected mosquitoes were in the area. Every evening from dusk, Julia and her two-year-old son, Noah, stayed indoors. Julia’s "wonderful husband, who is not a horse person" and a "great friend, Cathy" took over Riley’s care.

"... throughout the entire episode, he was alert, eating and drinking and was never depressed."

By Sunday evening, the tremors had decreased and the leg-buckling had almost gone. "We didn’t know if this was symptomatic relief from the drugs or if he was really recovering, but Riley was obviously feeling better and had stopped neighing."

By Tuesday, Riley was galloping, turning and bucking. Only a little shaking in the muzzle remained and this had disappeared by Wednesday.

"The weird thing was," said Julia, "that throughout the entire episode, he was alert, eating and drinking and was never depressed."

About two weeks later, Riley was completely back to normal with neither paralysis nor stiffness.

Riley was never confirmed positive for WNV. Testing requires comparing the antibody titre in a blood sample taken at the start of the disease with a sample taken two to three weeks later. An increase in the antibody titre confirms exposure to the virus. The cost of the test is $130.00. Julia had to make one of those cost/benefit decisions so familiar to most horse owners. She decided to "put the money towards the vet bill. As Riley had recovered, it was not worth verifying the diagnosis."

Both OVC and Dr. Postons believe the disease was WNV: the hind leg ataxia and muscle tremors are particularly symptomatic, and the rapid onset and quick recovery is also a suggestive characteristic. Rabies is always progressive and fatal and EPM generally takes longer to resolve.

The Ruhls notified their horse-owning neighbours and parents of young children. One of the neighbours questioned her insurance company and was told that if her horse died of WNV without having been vaccinated, the insurance policy would be void.

Exposure to WNV might give anywhere from one year to lifelong immunity, but both the Ruhl horses will be vaccinated this spring.

Note: I would like to thank Dr. Mallu Postons for reviewing this article and for explaining the details of the diseases mentioned.

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