We'll break this down into several sections, and dedicate a blog entry to each of them:
2. Physical examination, including ophthalmic examination
4. Coggins testing and other routine bloodwork
5. Fecal egg counts and deworming - already covered (click to read part 1, and part 2)
This week, we'll cover vaccinations, including core vs. elective vaccines. We'll discuss why we vaccinate with certain vaccines at certain times of year, and basically how vaccines work. Don't worry, you don't need a degree in immunology to understand it!
So, we take a small amount of killed or modified disease-causing bacteria or virus, and we inject it into the horse. Now what? In most vaccines, a chemical called an "adjuvant" is added to the vaccine to "alert" the immune system that something is happening. White blood cells will come to the site of injection, pick up the vaccine particles (including the killed or modified disease agent), and take them to the lymph nodes. An acute immune response is initiated, where some of the white blood cells become "trained" to fight this particular disease agent. This response isn't immediate, however; it takes a few weeks. And if it's the first time the immune system has seen this particular bacteria or virus, the response won't last very long (perhaps 3-12 months, but it depends on the vaccine). To make immunity more permanent, a "booster" vaccine must be given. Think of it as a trial run for the immune system. The second exposure cements the immunity, creating "memory" white blood cells that will persist in the blood stream for a longer time (again, it depends on the vaccine).
We divide vaccines into "core" and "elective" groups. Core vaccines are ones that every horse should receive, at least yearly, regardless of location or job description. Elective vaccines are given to some horses based on risk factors such as location, travel history, farm dynamics, age, or other criteria.
The core vaccines are:
2. Eastern Equine Encephalitis (EEE)
3. Western Equine Encephalitis (WEE)
5. West Nile Virus (WNV)
Rabies is a virus which is transmitted by the bite (or just the saliva) of an infected animal. All mammals can be potential carriers, but in this area bats, raccoons and skunks are the most likely culprits. Recently, several domestic cats in the New England area have tested positive for this virus (most recently in North Smithfield). In animals, rabies is 100% fatal without vaccination. In humans, the survival rate isn't much better. Sadly, a man in Massachusetts has recently been hospitalized with the virus (he contracted it from a bat bite). So, what we're trying to tell you is that it's out there. The vaccine is (nearly) 100% effective when given properly. (No vaccine is 100%, but this one comes really close.) For your horse's health, and for the health and safety of every human that comes in contact with him, do not skip this vaccine. It should be given once yearly to all horses. And while you're at it, make sure to vaccinate ALL the other domestic animals on your property, especially the dogs and cats.
EEE, WEE and WNV are all viruses that are carried by mosquitoes and can infect horses, birds and people. You can't contract these viruses from your horse or even a bird - you (or your horse) must be bitten by a mosquito carrying the virus. These are all "encephalitis" viruses, meaning they cause inflammation in the brain. Encephalitis isn't a good thing when you're a human, but it's really not a good thing if you're a horse. Dullness/depression can quickly lead to head pressing, inability to stand, seizures, and death. The good thing is, the vaccines are very effective. For horses that have never been vaccinated before, we recommend a booster vaccine 4 weeks after the first vaccine. Thereafter, horses in this area should be vaccinated once yearly in the spring, at least 2 weeks before the mosquitos emerge. The vaccines offer the best protection for about 6 months, and then starts to taper off. Therefore, if you travel south with your horses in the winter, they should be vaccinated twice yearly (once in spring, and once in fall before travelling). Horses that live south of Virginia routinely receive these vaccines twice yearly.
Tetanus is an important core vaccine as well. Tetanus is caused by toxins released by bacteria, which gain access to the body through a wound. The spores of the bacteria are normally present in soil, and are very common in a horse's environment. In an oxygen-deficient environment ("anaerobic"), these spores grow into bacteria, which begin producing their toxin. The toxin travels through the body, causing muscle spasms and rigidity. In a full sized horse, treatment is expensive and often not sufficient to prevent death; horses become unable to breathe due to spasms in their diaphragm. Once again, this highly deadly disease is very easy to prevent by vaccination. All horses should be vaccinated at least once yearly, and a booster vaccination is recommended if a wound occurs more than 6 months after vaccination. Since this vaccine is commonly bundled with EEE and WEE (in the E/W/T vaccine), it is usually given in the spring.
Risk-based "elective" vaccines include (not an exhaustive list):
1. Rhinopneumonitis (Equine Herpes/EHV)
3. Potomac Horse Fever
Whew! Again, this is not an exhaustive list; other elective vaccines exist, including Botulism and EVA, but we've outlined the most common ones for you here. Stay tuned for our next installment of this "Wellness" series, to learn about the importance of a routine physical examination.