CUSTOMIZE YOUR HORSE S VACCINATION

Transcription

1 CUSTOMIZE YOUR HORSE S VACCINATION 3 2 E Q U U S 3 9 5

2 PLAN By David Trachtenberg, DVM Which vaccines a horse requires depends on his age, lifestyle and other circumstances. Here s one veterinarian s approach to vaccinating seven very different horses. As a veterinarian I have observed firsthand the power of vaccination. Diseases that were once a very real threat to horses now rarely appear because of the regular use of vaccines. I have personally seen five equine rabies cases in my career, all in unvaccinated horses. I can assure you, you do not want your horse to contract this disease---it is a terrible way to die. If we get lax with vaccinations such scourges will surely return. That said, more is not necessarily better when it comes to vaccines. It s recommended that all horses receive the so-called core vaccinations--- against tetanus, rabies, eastern and western encephalitis (EEE, WEE) and West Nile virus (WNV)---unless we have a good reason, such as a history of severe adverse reactions, not to give them. But there is another category, called risk-based vaccines, that are administered when they are necessary based on the horse s lifestyle, management and other factors. These vaccines include rhinopneumonitis [equine herpesvirus (EHV) -1 and -4], influ - enza, Potomac horse fever (PHF), strangles, botulism, rotavirus, anthrax and equine viral arteritis. Life would be simpler if you could plug your horse s age, location and occupation into a database and receive a list of the vaccines he needs, but it s more complicated than that. To illustrate the factors that influence individual vaccination needs, I ve described seven hypothetical horses. Then, based on the details of their lives, I ve outlined how I would devise a vaccination protocol for each one. Although you may see reflections of your own horse in one or more of these scenarios, remember that he deserves his own vaccination plan, so use this information as a starting point for developing one with your veterinarian. P H O T O S B Y D U S T Y P E R I N E Q U U S

3 STAY-AT-HOME SCHOOL HORSE Leo is a 20-year-old gelding who lives on the outskerts of St Louis, Missouri. He s a school horse at a large boarding stable with a changing population. Leo, however, hasn t been off the property in years. He spends his time split between the field and the barn. Leo spends part of his time turned out as well as confined to a stall, so he will be exposed to plenty of mosquitoes. I would strongly recommend he receive vaccinations against viral encephalitis (EEE and WEE) and West Nile virus in the early spring before mosquito season. He also needs annual tetanus and rabies shots, the other core vaccinations. Because of the transient population at the barn, Leo is regularly mingling with new horses. Vaccinating him against EHV and influenza will be important because these viruses are easily transmitted among horses. His owner may also want to consider vaccination against strangles, which is also highly contagious and can be more difficult to control in a herd. Finally, given that there was an outbreak of Potomac horse fever in 2008 in the St Louis area, I would recommend the PHF vaccination. A client may not want, or be able, to give every vaccine that s recommended. If Leo s owner, for instance, told me to give only what is really important, I would go back to the core vaccines (West Nile virus, EEE, tetanus and rabies) and put the others in the optional category. If she mentioned she has been worried about strangles but can t afford that vaccination with all the others, I would evaluate her horse s overall risk of contracting all the other diseases. Then, depending on Leo s actual risk profile, I might suggest leaving out the West Nile virus vaccination and adding the strangles vaccine. It would be great if cost were never a consideration in caring for horses, but, in the real world, finances are always a factor. BUSY BROODMARE Chloe is a 10-year-old broodmare in Kentucky. She lives in a large pasture with a stable herd of a dozen broodmares, coming in to a stall only to foal. She travels to be bred each year. Broodmares have very different vaccination requirements than do pleasure horses. For one thing, I would strongly advise this client to vaccinate against EHV-1, which can cause abortions. The EHV-1 vaccine doesn t eliminate the risk of abortions, but it lowers it and greatly reduces the chances of an abortion storm running through a herd. Before the development of the EHV-1 vaccine, it was not uncommon for up to 60 percent of broodmares housed together to lose their foals in one of these storms. Now, even though a vaccinated individual may abort, storms are much more rare. I would administer the EHV-1 vaccine to Chloe in her fifth, seventh and ninth months of pregnancy. When Chloe is 10 months into gestation, we also need to vaccinate her against West Nile virus, EEE, tetanus, influenza and Potomac horse fever to ensure that high levels of antibodies can be passed on to her foal through the colostrum 0. This will give her foal good protection against these diseases for the first months of life. I usually give the rabies vaccine shortly after the mare delivers because that is one less vaccine we have to give at 10 months of gestation. In addition, if rotavirus---which can cause severe diarrhea in foals---has been a problem on the farm, I would recommend a vaccination against it. We administer this vaccine at eight, nine and 10 months of pregnancy. Finally, given that Kentucky is in a region where botulism is a threat, I d vaccinate Chloe against it to prevent shaker 0 foal syndrome. Because the 3 4 E Q U U S 3 9 5

4 mare has not had this vaccine before, we will administer it on the same schedule as the rotavirus vaccine, at eight, nine and 10 months. Chloe will pass antibodies from both of these vaccines to her foal through her colostrum. WEEKEND WARRIOR Sparks, a 6-year-old gelding in southern Texas, travels to local shows---no more than an hour away---most weekends during the summer. Only one other horse lives at his home farm, and they both live in a pipe corral with a run-in shed. Sparks had a minor reaction to EHV vaccine the last time he was inoculated, developing a stiff neck afterward. South Texas has its share of mosquitoes, so in the springtime, before the onset of buggy season, we will need to vaccinate Sparks against mosquitoborne viruses like West Nile, WEE and EEE. Tetanus vaccination can be given any time of year but is typically combined with the EEE vaccination. The rabies vaccination, the last core vaccine, is usually given in the spring out of convenience. It s easy to see how spring vaccines add up. Since Sparks travels to shows frequently, I would also recommend that he be vaccinated against influenza twice yearly and strangles annually. Last fall, Sparks developed a stiff neck after receiving an EHV vaccine, so I would discuss whether repeating that vaccination is advisable--- because this horse s risk of developing rhinopneumonitis is low I d be inclined to skip it. I would also discuss with his owner the risk of purpura hemorrhagica---a serious and potentially life-threatening disease of the blood vessels---when the strangles vaccine is given to a horse who already has high immunity to the disease. I recommend titers be drawn on all horses who have an unknown strangles history or have received strangles vaccination in the past few years. Together, we decide to take a titer for strangles and find Sparks has a high antibody count, so we opt not to give him that vaccination this time around. PROMISING FILLY Rose is a recently purchased warmblood yearling in northern California whose career path isn t determined yet. She ll be shipped out to a trainer when she s almost 2, but for now she lives on her owner s property with two other horses. The other horses travel occasionally, but Rose stays put. Rose will, of course, need the core vaccines: West Nile virus, EEE and WEE, tetanus and rabies. The EHV and influenza vaccines are also important for horses in this age group---they likely haven t acquired immunity through natural exposure---and will need to be boosted in the fall. I discuss strangles vaccination with Rose s owner and she decides she d like to give that as well. Because Rose was only recently purchased, I asked her owner about the filly s vaccine history. She told me that the previous owner mentioned Rose was up-to-date on all her shots. E Q U U S

5 I recommend that she find out specifically which vaccines were given. As it turns out, Rose was never given an EHV vaccine. I point out that if we had just assumed that Rose had received this vaccine already, we may not have given the follow-up booster needed to achieve full immunity. The same applies to the ELITE ATHLETE Wilton is an 8-year-old elite show jumper who travels on the circuit between Florida and New York each year. He s in a changing environment with other horses or on the road. He spends most of his time in stalls, except for one month in the early fall, when he s turned out in a pasture with a creek in New York. Wilton s vaccination schedule would be similar to Sparks, except that we would administer one for Potomac horse fever in the spring and late summer because he will be spending time at his home pasture in New York in the early fall, which is when insects that carry the causative bacteria are active. This horse also winters in Florida, so strangles vaccine, which it turns out Rose had never had, either. It s very important to get specific vaccination records and not accept upto-date or the standard vaccines because there is no one standard. It s also helpful to know if a new horse has ever had an adverse reaction to any vaccine. twice-yearly vaccination for EEE is also in order. Vaccination against rhinopneumonitis (EHV-1, -4) is more of a dilemma in Wilton s case. Adult horses rarely get the respiratory form of EHV, and this horse is not around broodmares, so we don t need to worry about him bringing EHV-1 infection back and causing abortions. However, his owner and I discuss the outbreak of neurological EHV-1 that occurred on the winter show circuit a few years ago. The current EHV vaccines are not labeled to prevent the neurological form of EHV-1, but a preliminary study found that a modifiedlive EHV vaccine showed promise in protecting against that potentially deadly complication. Based on what information we had, we decide to vaccinate for EHV-1 with the modified live product twice a year. A DOZEN DISEASES KEPT AT BAY Ever since Louis Pasteur developed the first livestock-specific vaccine in 1881 against anthrax, the science of immunology has advanced at a rapid pace. Today, vaccines are available for 12 equine diseases: Anthrax: systemic infection caused by the spore-forming bacterium Bacillus anthracis, which is found in the soil in some regions. Spores are typically picked up by horses as they graze or through bites from flies carrying the bacteria. Once inside the body, the spores multiply and produce a toxin. Signs include fever and colic, with swelling around a bite site if that was the mode of transmission. Even with prompt antibiotic treatment, infection can be fatal. Botulism: neuropoisoning caused by the toxin secreted by Clostridium botulinum bacteria, which can contaminate feed, water or wounds. Botulism is characterized by progressive paralysis, beginning with the muscles of swallowing. Horses may die from respiratory failure or complications of recumbency. Shaker foal syndrome is another form of the disease. Equine influenza: a common, acute viral infection involving the respiratory tract. Influenza is marked by inflammation of the nasal mucous membrane, the pharynx, the conjunctiva, the lungs and sometimes the heart muscle. The virus mutates easily and immunity is short-lived, making horses susceptible to influenza even after they ve had the disease. Equine viral arteritis (EVA): a highly contagious disease that causes mild respiratory signs in most horses. EVA can trigger abortion in broodmares. In fact, abortion storms may race through 3 6 E Q U U S 3 9 5

6 ALTERNATIVES: Methods of vaccine delivery in horses have expanded beyond intramuscular injection to include intranasal administration (below) for some products. an entire herd. Breeding stallions can be silent carriers, passing the disease along to mares without showing any signs of illness themselves. Equine viral encephalomyelitis (EEE/WEE): brain and spinal-cord inflammation caused by several species of alphaviruses that are usually transmitted by mosquitoes. Two forms that most commonly affect horses are eastern equine encephalomyelitis (EEE) and western equine encephalomyelitis (WEE). Both are characterized by fever, erratic behavior and lethargy as the brain begins to swell. WEE has a mortality rate of about 50 percent, while EEE is fatal in about 90 percent of cases. Potomac horse fever (PHF): a disease caused by the organism Neorickettsia risticii, contracted when the horse eats infected insects. Cases typically begin to appear with the arrival of warm weather and persist through the summer months. The disease is characterized by severe fever, diarrhea and laminitis. Rabies: a fatal viral disease of the central nervous system. There is a long incubation period as the virus migrates to the brain, so signs of rabies may not develop until days after exposure. Signs include lowgrade fever, convulsions, erratic behavior and recumbency. Because rabies can be transmitted to humans, it is considered a public health threat, and veterinarians are required to report all cases. Rhinopneumonitis (equine herpesvirus): a contagious disease caused by two forms of the same virus, EHV-1 or EHV-4. In most cases the virus causes coughing, nasal discharge and lethargy, with cases anywhere from mild to severe. EHV- 1 can cause respiratory issues, abortions in broodmares or neurological problems. EHV-4, known as the respiratory EHV, can also cause neurological signs, including progressive weakness and incoordination. The respiratory forms of EHV most commonly occur in young horses. Rotavirus A: primary cause of excessive diarrhea in foals younger than 3 months old. Mortality is less than 1 percent, but the disease is highly contagious and can spread through a breeding farm quickly. In addition to diarrhea, signs of the virus include depression, failure to nurse and diffi culty standing. Strangles (distemper): a highly contagious infection of the lymph nodes, usually of the throat, caused by Streptococcus equi bacteria. Abscesses that form may become so large they obstruct the airway. When they break internally, a thick, yellow pus drains through the nose. The abscesses may also rupture externally, draining through a spontaneous or surgical opening in the skin. The pus contains the organism, becoming a source of infection for the rest of the herd. Horses can become carriers of this disease and may shed the bacteria even if they look healthy. Tetanus: a paralytic disease caused by the neurotoxin of Clostridium tetani, a spore-forming anaerobic bacterium. C. tetani is ubiquitous in the soil, putting all horses at ongoing risk of exposure. Horses typically contract tetanus when the bacteria enter through a puncture wound or deep laceration, but foals can be infected through their umbilical stump and mares via their reproductive tracts following a difficult foaling. Signs include extreme sensitivity to light, sound and touch, followed by rigid paralysis that causes the horse to adopt a classic sawhorse stance, and protrusion of the third eyelid. West Nile virus (WNV): a flavivirus transmitted by mosquitoes. In horses, infection usually causes little or no illness. However, for some reasons not determined, West Nile infection sometimes triggers swelling of the brain (encephalitis) that produces limb weakness, muscle twitching, incoordination, behavioral changes and paralysis. E Q U U S

7 HAPPY RETIREE Chuckles is a 26-year-old retired pony in Maine. He isn t ridden, doesn t travel and lives alone outside 24/7 in a very rural area. Generally he s in good health, but does have Cushing s syndrome and had a slight bout of laminitis last spring. give the EWT vaccine---for EEE, WEE and tetanus---in the spring. One month later, we ll administer the West Nile virus vaccine. In the fall, he ll receive his rabies vaccination. If Chuckles has any further bouts of laminitis in association with any of these vaccinations, we may discontinue that one altogether. I ll cross my fingers hoping he doesn t have a reaction to the rabies vaccine. Rabies titers do not provide any assurance of protection for the horse, nor are they a great way to determine whether to vaccinate, especially given the human health implications if the horse contracts rabies. Chuckles may need that vaccine even if he has a reaction to it. GROWING BOY Coal is a 5-month-old foal ready to be weaned on a small private farm in Delaware. His dam will leave the property, while Coal hangs out with an older gelding who lives there. His dam will return several weeks later. There are no plans for Coal to travel anywhere soon. we administer boosters for these vaccinations and do a final round at 10 to 12 months of age. At 6 months of age, Coal will also receive an influenza vaccination followed by a booster at 7 months and another at 10 to 12 months. We decide to skip the strangles vaccine for now because he is not going to be exposed to strange horses for another year. We ll save that shot until he needs it. Vaccinations are a marvel of modern medicine. It s amazing to think that a simple shot can spare a horse from a deadly disease. But vaccines aren t fail-safe and we can t be cavalier with their use. Each horse deserves an inoculation protocol designed specifically for him that takes into consideration his lifestyle and overall health. Since Chuckles is not exposed to other horses, all he should need are the core vaccines of West Nile, EEE, tetanus and rabies. It s not that simple, however. I have seen laminitic episodes occur after vaccination, so I want to be cautious, considering Chuckles history. On the other hand, this pony---like many older horses---may have a weak immune system, and vaccination is even more important to protect against disease. After discussion with Chuckles owner, we decide that we will spread the vaccines out over the year. We will The vaccine requirements for foals have changed over the last few years. The current guidelines call for youngsters to receive several vaccinations. I tell Coal s owner that studies over the last decade have shown that the mother s colostrum can interfere with the effectiveness of vaccinations given at 3 to 4 months of age, even after multiple attempts are made at boostering them. Based on this, we decide to start vaccinating Coal at 5 months for West Nile virus, EEE, tetanus, rabies, Potomac horse fever and EHV-1. In another four weeks 3 8 E Q U U S 3 9 5