Page 71 - Speedhorse November, 2018

There are several influenza vaccines available, that are updated periodically as influenza virus strains mutate and change over time.
The virus doesn’t last a long time in the environment. “It is spread most readily with nose-to-nose contact, but can be transmitted on objects. The virus generally doesn’t live more than a few hours outside the horse in conditions of heat, cold, dryness or exposure to disinfec- tants,” she says. If a horse coughed on hay or bedding and another horse came along within
a short time and nosed around in that hay or bedding, it might pick up the virus, but after a while the virus would no longer be viable.
There are outbreaks now and then in various regions. “Parts of the world have been influenza- free, but they don’t always stay free of this dis- ease,” says Wilson. “Australia was free of equine influenza up until 2007 when a huge outbreak occurred. The assumption is that the imported horses were not quarantined appropriately, caus- ing the disease to spread rapidly through the equine population in Australia, but was success- fully eliminated from the population again.
“The equine influenza strains have been responsible for sporadic outbreaks of influenza in dogs. This is a recent discovery after an outbreak in racing greyhounds. Looking back at other outbreaks in dogs, researchers recognized that the equine strains have the potential to affect dogs. But as far as I know, I don’t think any healthy human has been infected with equine influenza.
“We do need to think about the potential with other species and other influenza viruses that can mutate and be transmitted from one species to another. There are some that can jump from pigs to people, or from birds to people. All it takes is the right mutation. These viruses are mutating on a regular basis.”
Biosecurity is the best defense and any new horses should be kept in quarantine for at least two weeks to make sure they are not showing clinical signs of influenza.
trick the immune system into thinking that the whole live virus is there. “It does have parts of the virus in it, so it’s supposed to induce better immunity than just the fragments of virus that are in a killed vaccine,” she says. “This third type is an intramuscular injection.”
“Most brands of influenza vaccines come
in a combination with rhino (herpes), and can also be included in a 4 or 5-way vaccine with tetanus, eastern and western encephalomyeli- tis, or West Nile. There are some advantages and disadvantages to combination vaccines. In general, the more vaccines that a horse gets at one time, the less likely the immune system will be able to respond appropriately to each one
of those diseases. We try not to over-vaccinate horses with too many diseases at one time. For flu and rhino, it doesn’t really matter whether they are in combination or not, but neither the MLV intranasal vaccine nor the canary pox vec- tor vaccine have any combinations with them.”
There has been discussion regarding the best age to vaccinate foals for influenza. “Young foals tend to keep the maternal antibodies acquired from their dam’s colostrum for influenza for a longer time than the antibodies against other diseases,” Wilson explains. “If a foal still has cir- culating antibodies from the dam and you vac- cinate that foal with any vaccine that contains parts of the virus, the circulating antibodies will neutralize those virus parts and they won’t work to stimulate the immune system.
“Therefore, the recommendation is to not vaccinate foals for influenza until they are at least six months old. It won’t hurt them if you vaccinate them too young, but it just won’t stimulate immunity and won’t give them the protection you are hoping for.”
If the dam has never been vaccinated or has not been exposed to the disease and had no antibodies in her colostrum, the foal will not have maternal antibodies that would interfere with vaccination immunity. In this situation,
a person could vaccinate the foal at an earlier age. It is important to know the vaccination history of the mare. “The recommendation is to vaccinate broodmares with influenza, herpes, etc, to protect the fetus during the last 30 days of pregnancy and to produce antibodies for the colostrum.” Those antibodies give the foal a lot of protection during the first months of life.
PREVENTION
Vaccination is never 100% effective in protect- ing horses from influenza, so it’s important to practice biosecurity. “It is difficult to prevent influenza completely, except by keeping horses from becoming exposed. Any new horses coming into the farm should be kept in quarantine for at least two weeks to make sure they are not showing clinical signs,” says Wilson. Biosecurity is the best defense. Don’t share grooming tools/cloths/water buckets or other equipment among horses and wash hands between horses when handling them.
“Vaccination is never 100% effective in protecting horses from influenza, so it’s important to practice biosecurity.”
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EQUINE HEALTH