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By Tim O'Meilia
Palm Beach Post Staff Writer
Saturday, December 23, 2006
The equine herpes virus once was a lot like the common cold: nasty but almost never deadly.
But the highly contagious strain of rhinopneumonitis, or equine herpes virus 1, that has infected nine horses in the Wellington equestrian world, is responsible for the deaths of four and is suspected in a handful of other cases, is not your run-of-the-paddock herpes of a few years ago.
It has morphed from a runny nose, mild fever kind of infection into a lethal neurological disease.
Only a few years ago, typical agricultural extension pamphlets mentioned "very infrequent" fatal infections. But the herpes virus has been going to horses' heads far more often in recent years, veterinarians say, settling in the brain and spinal fluid and causing more frequent paralysis and death among racing thoroughbreds and show horses.
Besides those in Wellington, six other horses have died or been euthanized this year because of EHV-1. At least 27 died or were euthanized in the United States and Canada in 2005.
"It's a hotter and meaner strain of virus," said research scientist George Allen of the Gluck Equine Research Center at the University of Kentucky.
Allen, his colleagues and researchers in Newmarket, England, have developed a test to identify the neurological strain.
Samples sent to the university's livestock diagnostic center have confirmed that the Wellington strain is the more lethal neurological strain, Allen said this week.
In fact, 30 of the last 32 outbreaks of equine herpes in the U.S. were the mutant strain. The Wellington outbreak is the first in the state, according to veterinarian Bill Jeter of the Florida Department of Agriculture.
"The horses have been infected with a mutant strain that grows more rapidly, is more aggressive, affects more tissue and does more damage than the respiratory strain," he said.
The mortality rate is higher and neurological symptoms seem to develop earlier in the illness cycle. Allen compared it to the bird flu in humans - more deadly and more easily spread than more common strains of flu.
Equine herpes is transmitted through the air as far as 35 feet, usually by sneezes, by direct contact and on boots, clothing and equipment, Jeter said.
The virus usually incubates for one to three days, and sometimes as long as 10 days, before causing symptoms such as a mild fever, up to 102.5 degrees (normal temperature is 99 to 100.5). Often a second fever spike, higher and more noticeable, occurs.
Next, or simultaneously, is a runny nose or a cough. Horses "shed" the virus, or are contagious, before showing any symptoms.
The virus, a particle of nucleic acid encased in a layer of protein, settles in the cells of the lining of the horse's upper throat, where it reproduces. In the respiratory strain, the infection ends there. Herpes also can cause abortion in pregnant mares.
The more virulent strain replicates more rapidly, causing more damage, and moves into nearby lymph nodes, where it can migrate to white blood cells and into the vascular system. Sometimes horses with the neurological strain never develop respiratory symptoms.
Then the virus can travel to the brain and seep into spinal fluid. Depending on the severity of the infection, the horse can become uncoordinated, lose control of its hindquarters and bladder, or become paralyzed and unable to stand.
Those that cannot stand rarely recover and are usually destroyed. But death can come quickly, within one to three days of the onset of neurological symptoms. Horses that remain on their feet usually recover.
The virus remains latent for the remainder of the horse's life. In fact, a horse can carry the disease and never display symptoms, a sort of equine Typhoid Mary. The disease can manifest itself again if the horse is under stress, such as during travel.
"It seems to be occurring more often because of the high traffic of racehorses and show horses coming in and out of the state," Jeter said.
Equine herpes poses two problems for horse owners: diagnosis and treatment. The initial symptoms of fever and nasal discharge are the same as several other diseases, such as equine flu or other equine viral diseases. Only a lab test can tell.
That's one of the reasons EHV-1 wasn't suspected when the first ill horses arrived in Wellington. Horses often develop a fever during shipping.
A veterinarian at Pimlico Race Course in Maryland became suspicious in January when five horses became ill at once. He quarantined the barn before a diagnosis was definite and probably averted the spread of the disease further. Nevertheless, three horses died.
There is no treatment for the virus. It must run its course. Horses can be given drugs to reduce the fever and antibiotics for bacterial infections that sometimes develop as well.
The virus is killed with a bleach solution. Quarantine and the cleansing of equipment and clothing in contact with the horses is the standard practice to prevent EHV-1 from spreading.
"It appears the horse owners and the public have been very cooperative in following the procedures," Jeter said. "We're hopeful that by the first of the year, we'll have things under control."
There is a vaccine for equine herpes which can prevent or lessen the effects of the disease, but it doesn't affect the newer strain.
Researchers remain puzzled about what caused the deadly mutation.
"That's the $64,000 question," Allen said. "We're scratching our heads over that with not even a good guess."
~ tim_omeilia@pbpost.com
By Tim O'Meilia
Palm Beach Post Staff Writer
Saturday, December 23, 2006
The equine herpes virus once was a lot like the common cold: nasty but almost never deadly.
But the highly contagious strain of rhinopneumonitis, or equine herpes virus 1, that has infected nine horses in the Wellington equestrian world, is responsible for the deaths of four and is suspected in a handful of other cases, is not your run-of-the-paddock herpes of a few years ago.
It has morphed from a runny nose, mild fever kind of infection into a lethal neurological disease.
Only a few years ago, typical agricultural extension pamphlets mentioned "very infrequent" fatal infections. But the herpes virus has been going to horses' heads far more often in recent years, veterinarians say, settling in the brain and spinal fluid and causing more frequent paralysis and death among racing thoroughbreds and show horses.
Besides those in Wellington, six other horses have died or been euthanized this year because of EHV-1. At least 27 died or were euthanized in the United States and Canada in 2005.
"It's a hotter and meaner strain of virus," said research scientist George Allen of the Gluck Equine Research Center at the University of Kentucky.
Allen, his colleagues and researchers in Newmarket, England, have developed a test to identify the neurological strain.
Samples sent to the university's livestock diagnostic center have confirmed that the Wellington strain is the more lethal neurological strain, Allen said this week.
In fact, 30 of the last 32 outbreaks of equine herpes in the U.S. were the mutant strain. The Wellington outbreak is the first in the state, according to veterinarian Bill Jeter of the Florida Department of Agriculture.
"The horses have been infected with a mutant strain that grows more rapidly, is more aggressive, affects more tissue and does more damage than the respiratory strain," he said.
The mortality rate is higher and neurological symptoms seem to develop earlier in the illness cycle. Allen compared it to the bird flu in humans - more deadly and more easily spread than more common strains of flu.
Equine herpes is transmitted through the air as far as 35 feet, usually by sneezes, by direct contact and on boots, clothing and equipment, Jeter said.
The virus usually incubates for one to three days, and sometimes as long as 10 days, before causing symptoms such as a mild fever, up to 102.5 degrees (normal temperature is 99 to 100.5). Often a second fever spike, higher and more noticeable, occurs.
Next, or simultaneously, is a runny nose or a cough. Horses "shed" the virus, or are contagious, before showing any symptoms.
The virus, a particle of nucleic acid encased in a layer of protein, settles in the cells of the lining of the horse's upper throat, where it reproduces. In the respiratory strain, the infection ends there. Herpes also can cause abortion in pregnant mares.
The more virulent strain replicates more rapidly, causing more damage, and moves into nearby lymph nodes, where it can migrate to white blood cells and into the vascular system. Sometimes horses with the neurological strain never develop respiratory symptoms.
Then the virus can travel to the brain and seep into spinal fluid. Depending on the severity of the infection, the horse can become uncoordinated, lose control of its hindquarters and bladder, or become paralyzed and unable to stand.
Those that cannot stand rarely recover and are usually destroyed. But death can come quickly, within one to three days of the onset of neurological symptoms. Horses that remain on their feet usually recover.
The virus remains latent for the remainder of the horse's life. In fact, a horse can carry the disease and never display symptoms, a sort of equine Typhoid Mary. The disease can manifest itself again if the horse is under stress, such as during travel.
"It seems to be occurring more often because of the high traffic of racehorses and show horses coming in and out of the state," Jeter said.
Equine herpes poses two problems for horse owners: diagnosis and treatment. The initial symptoms of fever and nasal discharge are the same as several other diseases, such as equine flu or other equine viral diseases. Only a lab test can tell.
That's one of the reasons EHV-1 wasn't suspected when the first ill horses arrived in Wellington. Horses often develop a fever during shipping.
A veterinarian at Pimlico Race Course in Maryland became suspicious in January when five horses became ill at once. He quarantined the barn before a diagnosis was definite and probably averted the spread of the disease further. Nevertheless, three horses died.
There is no treatment for the virus. It must run its course. Horses can be given drugs to reduce the fever and antibiotics for bacterial infections that sometimes develop as well.
The virus is killed with a bleach solution. Quarantine and the cleansing of equipment and clothing in contact with the horses is the standard practice to prevent EHV-1 from spreading.
"It appears the horse owners and the public have been very cooperative in following the procedures," Jeter said. "We're hopeful that by the first of the year, we'll have things under control."
There is a vaccine for equine herpes which can prevent or lessen the effects of the disease, but it doesn't affect the newer strain.
Researchers remain puzzled about what caused the deadly mutation.
"That's the $64,000 question," Allen said. "We're scratching our heads over that with not even a good guess."
~ tim_omeilia@pbpost.com
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