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EQUINE HEALTH
rattlesnakes is similar, this vaccine may also provide protection against venoms of the Prairie Rattlesnake, Great Basin Rattlesnake, North- ern and Southern Pacific varieties, Sidewinder, Timber Rattlesnake, Massasauga and Cop- perhead. This vaccine does not provide much protection against venom from Water Moccasin (Cottonmouth), Mojave Rattlesnake or Coral Snake, however, since their venom is different.
Dr. Jennifer Taylor was one of the researchers who helped develop the equine vaccine and get it licensed. “The first thing we tried was to test the dog vaccine on horses, but we had to change it a bit,” she says. As part of the licensing process, this vaccine was shown to generate significant levels of protective antibodies in horses, to neutralize the venom. Horses with enough antibodies expe- rience less pain and swelling from a bite. Several factors may influence antibody effectiveness against venomous snakebite, and these include the snake species, age of the snake and amount
of venom injected. Horse-related factors include location of the bite, how well the horse responded to the vaccine and the length of time since the last dose of vaccine was administered.
“I worked on most of the efficacy studies, where we vaccinated horses at different times, with differing doses, looking at immune re- sponses. We followed the animals over time to see how long they were protected,” says Taylor.
One of the first tests of the vaccine was on horses at an equine sanctuary, Home at Last, in Oroville, California. “This sanctuary was willing to let us vaccinate their horses several times. We were looking at immune response, longevity of immunity, protection in older horses, etc.,” says Taylor.
“One of the last things we did prior to putting it on the market was to vaccinate 600 horses for the first safety study—in addition to the 200 horses we’d vaccinated experimentally over the previous four years,” she explains.
The safety study utilized horses in different regions, including south- ern California, north-
ern California, Texas, Oklahoma and other states, and the horses
were observed daily for
a week after vaccination. “Throughout that study we only had a few minor local reactions—small,
temporary lumps,” says Taylor. The Crotalus Atrox Toxoid met USDA safety standards and is considered safe for use in horses, including pregnant and lactating mares, foals as young as six months and healthy older horses.
“Our research indicates that maximum pro- tection generated by vaccination with this product typically peaks about four to six weeks after the most recent vaccine booster dose. That protection then declines slowly over time. On average, vac- cinated horses receive good protection for about six months after vaccination,” says Taylor.
“When I first started working on this project, I was talking to an older veterinarian in his 70’s. He said the first thing he did whenever he went on a call to see a horse that had been bitten on the nose was to try to open the airways—with whatever
he had. One time he had to send the wife back in the house to get her hair curlers, the pink foamy kind. He shoved the curlers up into the nostrils to keep them open! I’ve heard of people using hoses and other things to stuff up the nose to enable the horse to keep breathing. But to this day I always picture a horse with pink fuzzy curlers in the nos- trils! It worked. The horse survived,” Taylor says.
“For our horse vaccine, we wanted to make sure the immune response is strong. Antibodies from vaccinated animals bind to the venom. If the animal is bitten on the nose, we want to be sure the venom can be neutralized as quickly
as possible to reduce the swelling. Most of our data on the vaccine comes from the dog vaccine because it’s been on the market longer and there are also more dogs that we’ve heard of being bitten after they were vaccinated. What we typically see is that vaccination signifi- cantly decreases the amount of swelling. This
is a huge factor for a horse bitten on the nose. We’ve also found that the swelling goes down very rapidly in the vaccinated horses,” she says.
“When an unvaccinated animal gets bitten, the swelling comes on quickly and continues for several days before it starts to go down at all. Veterinarians who have dealt with animals that were vaccinated and then bitten tell us that the swelling is almost gone within 12 to 24 hours. There is much less swelling and pain involved, and less tissue damage at the site of the bite and less necrosis.” Thus, there is less risk for systemic infection (septicemia from the infection that often follows snakebite, because it’s a dirty wound with lots of tissue damage which makes ideal environment for bacteria) and potential injury.
“We always recommend that horse owners still treat snakebite as an emergency, even if their horses were vaccinated. You never know how much venom they received from the bite, and it could have been enough to overwhelm the immunity obtained from the vaccine. They should have their veterinarian still treat it as
a snakebite, and administer appropriate treat- ment as required. Even bites by non-venomous snakes can lead to serious infections and anti- biotic treatment may be needed. A veterinarian is the best person to consult regarding medical decisions for your horse,” says Taylor.
EMERGENCY USE OF BENADRYL
Last year a rancher in Montana was bitten
by a rattlesnake when he was getting ready to bale hay and turned over a windrow to check the moisture. The snake was in the hay and wrapped around his arm and bit him on the wrist. He went straight to the house and put ice on it and got the hospital within an hour. By the time he got there his arm was starting to swell to the shoulder and his throat was getting tight. The first thing the emergency room nurse did was give him Benadryl. Antivenin must be received within 4 hours of the snakebite, but the immedi- ate threat is swelling and death of tissue, which can be treated with Benadryl. The swelling in his arm and throat started going down quickly. The antivenin had to be prepared and was not ready for a couple of hours, so he ended up getting two doses of antivenin and spent the night in the hospital, but came home healthy the next day.
A person can keep Benadryl on hand in their first aid kit. Children’s chewable Benadryl can be given according to body weight and used for adults also--just a larger dose. If you chew it and hold it in your mouth it will absorb just as fast or faster through the membranes of the mouth as from the stomach.
This will also work for a dog or a horse.
Rule of thumb would be one 25mg tablet for
a 25-pound dog. A 1000-pound horse would take 45 tablets if they were 30 mg, or 27 tablets if they were 50mg tablets. This dose can be repeated twice a day if needed. If all you had were the 25mg human-sized tablets, then it would take 54 tablets. To administer, you would have to crush them to a powder and mix with water to give by dose syringe into the mouth (or use a well-washed deworming syringe). To make it more palatable for the horse you could add a little molasses or applesauce.
The snakebite vaccine was created specifically against venom from Western Diamondback rattlesnakes and is most effective against this snake’s venom, but since venom from many other rattlesnakes is similar, it may also provide protection against venoms of the Prairie Rattlesnake, Great Basin Rattlesnake, Northern and Southern Pacific varieties, Sidewinder, Timber Rattlesnake, Massasauga and Copperhead.
66 SPEEDHORSE August 2020