This is an update on the EHV1 situation in California provided by a polo playing veterinarian. It is followed by an essay on guidelines for prevention of the problem following possible exposure. I include in this my view regarding the rational use of vaccines in general and especially as used in the prevention of this particular disease. The essay is long but it is an important and timely topic.
There has been a well publicized outbreak of the neurological form of EHV1 that has occurred in Wellington, Fla. over the past two weeks. This outbreak has now spread to California. A cargo load of show horses shipped from New Jersey to CA on approximately 12/10/06. (Note: It is unclear if the horses were shipped in on a van or via air. Some reports indicate they flew into Ontario Airport other reports state they came in on a trailer. We are trying to get confirmation on this.) Included among the equine passengers was a horse already deeply into the contagious form of the disease that had vanned up from Wellington. After arriving in CA, this animal shipped to Del Mar. Within 48 hours of his arrival in Del Mar he began showing a high fever (over 105) and signs of depression. Despite appropriate treatment, he quickly showed the classic signs of weakness and ataxia (drunkenness) involving primarily the rear legs. He became recumbent, was unable to rise and was put down. This all happened within 72 hours of his arrival in CA (source, Dr. Paul McClellan, private correspondence, 12/18/06).
The other horses in the same load were unknowingly dispersed to various points in CA. As of this writing, several are showing fevers and the barns are under a voluntary quarantine. It remains to be seen whether these measures will be sufficient to prevent further spread of the disease. Most probably we will continue to see other small outbreaks. Please understand that these outbreaks do not feel small if they occur in or near your barn. The feelings that are generated among the unfortunate horse owning public in proximity to an outbreak must be akin to what people worldwide felt in the early part of the twentieth century as the Great Influenza Plague swept world wide. The outbreak is not small if you stand any chance of being involved. It is only through diligence that we will be able to control this outbreak. The earliest signs of infection are fatigue, depression and fever. Horses with this and many other diseases act like they have a deep, dull head ache (to me, if a horse acts like he has a headache, he has a headache). If you have a horse with these signs, especially if there has been horse traffic in your barn within the previous 10 days, please call your veterinarian. I will discuss the public’s and the veterinarian’s role in controlling this outbreak toward the end of this essay.
It is interesting to note that the disease is currently not a reportable disease in California. That means that health authorities are not required to track the disease, to keep statistics on it or to disseminate information to health workers. It also means that all quarantines in this state are strictly voluntary in nature. Horse owners tend to be a responsible, inquisitive sort and there would be intense peer pressure against any individual knowingly breaking even a voluntary quarantine. There may also be legal ramifications if a person willfully and knowingly breaks quarantine. This would be similar, I think, to AIDS carriers being sued for spreading the disease by continuing to engage in unprotected sex despite having knowledge that they are HIV positive.
EHV1 is a herpes viral infection. Like other herpes viruses, it can lie dormant within the body for weeks, months and even years. While dormant, it escapes notice of the bodies own immune system until it can begin to multiply rapidly enough to cause clinical signs. It is able to suddenly multiply not by undergoing some mutation that allows it to escape surveillance. Rather, it is via a breakdown in the body’s immune surveillance or response system. In essence, there is a “dip” in the ability to mount an appropriate immune response. The most common cause of a decreased immune response is that over worked word, stress. This can be in the form of poor nutrition, pain, the anti-inflammatory drugs used to decrease pain, travel, changed social structures (think: break up with a boyfriend and the cold sore that you sometimes get after that; of course, sometimes a break up is a joyous occasion!) or concurrent disease states. Vaccinations are a stress on the body sufficient to cause a transient but significant dip in immunity.
The majority of EHV infections in horses are EHV1 or 4. EHV1 is much more prevalent and more serious. There are three forms: respiratory, late term abortions in pregnant mares or, rarely, the neurological form. EHV4 is strictly respiratory infections. The neurological form is the most serious and often progresses to recumbancy and death. Treatment is limited to supportive help and some direct anti viral medication. Survivors are carriers and intermittent but chronic shedders.
The neurological form of the disease tends to occur in sporadic but deadly clusters. The first horses involved tend to be some population of horses subject to typical show or race stress. The typical stresses felt by this population include, but are not be limited to: intermittent travel, social isolation (stall confinement), exposure to a changing population of equine neighbors, exposure to other communicable diseases,continued performance in the face of low or moderate grade musculo-skeletal injuries, performance enhancing medications, a diet too rich in cereal grains but low in anti-oxidants, short or little breaks from the same training routine and little to no time spent outside, grazing green grass. There is often a history of a vaccination within the preceding 60 days, sometimes even for Rhinopneumonitis (EHV). Once started, infection can spread by direct contact, aerosolized particles or mechanical vectors. The virus is not especially long lived in the environment and is susceptible to almost all properly applied disinfectants.
In 2004 there was an outbreak of the neurological form of EHV1 at Finley University in Ohio. That outbreak claimed the lives of over 20 horses. This was despite heroic 24 hour care provided by the two veterinarians on staff. What was note worthy about that outbreak was that both the morbidity (attack rate) and mortality (death rate) were higher in horses vaccinated for the disease than among those never vaccinated (Dr. Stephen Reed, Ohio State University, January, 2004, personal communication). I am aware of how discouraging that statement reads to Vets and the public alike. If vaccinated horses are, at the very least, not more immune to the neurological form of EHV1, then what options do we have? We do have options available to us. These include the proper use of vaccines and a larger view of health. The answer to this puzzle lies in the way vaccines achieve their effectiveness.
Vaccines present to the body a modified form of the infectious agent that the body can quickly recognize as foreign and wage a brief and successful battle against. When exposed to the same infectious agent in the future (that is, exposed to the disease), the response will be quicker and more efficient. The body wins the battle without becoming sick at all or, perhaps, not as sick. Each and every vaccination causes a transient dip in the body’s level of immunity as the body fights the battle and processes the information for the future use. The more vaccines that are grouped together in one vaccine, the more profound are the transient negative effect upon the bodies’ immune status. Grouping vaccines together also negatively impacts the bodies’ ability to respond to each individual vaccine. For the sake of convenience and economy, most of our equine vaccines are grouped together in batches. For example, the commonly used 4-way vaccine contains Eastern and Western encephalomyelitis, Influenza (flu) and tetanus. We often add other vaccines at the same time such as Rabies or Rhino. There is now on the market a 6-way vaccine which adds Venezuelan encephalomyelitis and Rhino to the already over-loaded vaccine. I would advise you to try to limit your use of these vaccines. Do not use the 6-way vaccine; the downside is greater than the potential benefit. Try at the very least to avoid vaccination with more than one vaccine at a time. Do not go to vaccine clinics where horses are vaccinated for many diseases at the same time. If your veterinarian performs your vaccinations, see if you can influence him to not group vaccines. Perhaps if you offer to van the horse to his place of business or allow him to send a technician over to perform the mechanical act of giving one vaccine at a time. More effort will lead to better results and fewer complications.
The sense of urgency that we sometimes feel as regards vaccinations is generally due to external perceptions about the need to vaccinate. This is often due to the need to adhere to some new requirements such as travel to a foreign country,to a different state or to a new barn that has more stringent vaccination requirements. The most dangerous sense of urgency comes as an urge to vaccinate because of a fear of recent exposure to disease. The desire to vaccinate in the face of a potential recent exposure is an understandable one. After all, we are helping him to resist the disease, right?
The answer to that question, in the short term, is an emphatic no. It is the short term that we are concerned about after potential exposure. We have discussed how vaccination causes a short term dip in the immunity in general. This dip in immunity is, logically but unfortunately, especially pronounced for the disease we are vaccinating against! Thus, if your horse has had potential exposure to EHV1 (also known as Equine Herpes or Rhinopneumonitis) and is potentially incubating the virus, vaccinating him will actually increase the odds that he develops clinical signs. In the case of the neurological form of EHV1, this is a potentially fatal decision. For most other diseases, the ramifications are not so dire. Sickness is usually just an unfortunate event that horses and humans will generally recover from. Nature is, after all, on our side.
The experience of vaccinating and aiding the appearance of clinical disease was brought clear to me as when I worked as a farm veterinarian. I would inevitably see an increase in the number of runny noses, coughs and fevers following the herd administration of a round of flu/rhino vaccine given to young foals. Unfortunately, at that time I could not put the facts together correctly and, instead, reacted to the situation by stubbornly continuing to vaccinate horses at a younger and younger age.This did not solve the problem.
The correct response was probably to develop as hardy a group of foals as possible in a large farm situation. This would include allowing them opportunity for reasonable exercise (note: I did not say unlimited exercise unless Darwinian survival is what you are after. Most owners will have a very hard time with that explanation. I tried it once and will never go there again). Further potentially productive measures would include decreasing the relative and absolute over-crowding in all paddocks and pastures, decreasing dust and heat exposure and paying attention to correct nutrition. Correct nutrition includes both the creep feed for the suckling foals in addition to nutrition for the dam throughout her pregnancy. Also important is the benefit of quarantine of new arrivals, separating them from young stock for 21 days. This will cut down on preventable exposure. I know that vaccination is easier to institute than this list. Institution of all of these measures on a farm at the same time is seldom practical in my practice area. What remains true is that vaccination, in-of-itself is not sufficiently effective and can, in fact, be counter productive.
Does this mean we are not to vaccinate our livestock? Of course not, It does mean that you, as the horse owning public and ultimate consumer, can easily understand the more rational use of vaccines. Use the best quality vaccine possible, use them sparingly but at appropriate times, group vaccines as little as possible, separate their administration by 10 days, do not vaccinate 21 days before or after vanning horses. Perhaps most importantly, do not vaccinate in the face of possible exposure to a disease.
What then is the best response to possible exposure to a contagious disease? The response would be the same whether the disease is influenza, Strangles or, as in the current situation, EHV1. The rational approach is to bolster the immune response.
Decrease stress as much as possible, increase the quality and quantity of high quality nutritional support and begin immune stimulants as quickly as possible. The immune stimulants that we use are generally of two types, the oral supplements and the injectable medication designed for intra-venous administration. These two forms of administration can and should be combined. For oral support, we use Transfer Factor (Life Data Labs) and Platinum Performance (Platinum Products). We follow label administration directions. For IV use, Eq-stim and Zylexis (Pfizer) are the two choices. Zylexis has been tested specifically against viruses prior to its recent release on the open market. If there is a concern about exposure to EHV1, use the Zylexis and the oral supplements as discussed. . The administration schedule for both Eq-stim and Zylexis is similar. It is listed to give a total of 3 injections, day 1, day 4 and day 7. At the least, separate their administrations by 48 hours. A single shot helps, 2 shots are better than 1 and three better than 2. A situation may change dramatically in a short time period and not necessitate the expense, time and potential complications of IV shots. Stay informed and get the most current and accurate information from your veterinarian.
In Ohio in 2003, Finley University had a large scale outbreak of the neurological form of EHV1 in the show horse population. Despite heroic 24 hour care given by the 2 veterinarians on staff, over twenty animals died or were euthanized. What is of interest in this case was that animals vaccinated against EHV1/4 had both a higher morbidity (attack rate) and mortality (death rate) as compared to the horses that no vaccinations at all (Dr. Stephen Reed, The Ohio State University, private correspondence, January 24, 2003).
There is yet hope to be gleaned from this grim fact. The few horses that were vaccinated with a particular monovalent vaccine specific to EHV1, a modified life vaccine, suffered no deaths. The numbers, however, were small. Please understand, there are few miracles in life and there are no miracle drugs. However, there is a difference in the immunity conferred upon your horse depending on which vaccine you use. By far the preferred vaccine to use in the present situation is called Rhinomune (Pfizer). It is a modified life vaccine (easiest on the body), monovalent (no EHV4 or any other antigen to dilute the immune response) and it is safe. This is the same vaccine that was distributed by Norden in the 1970s and 1980s. It has been around for 35 years and has been proven to be safe. Do not use the Pneumobort K vaccine made by Fort Dodge. This is a poor quality vaccine with poor ability to stimulate immunity. Why else would brood mares have to be vaccinated with numbing regularity at months 5, 7 and 9 every year of pregnancy? How long would pregnant women remain quiescent if this were prescribed for them? Why do our horses continue to have to be subjected to this vaccine? If we were not so used to this situation we would raise our voices in disgust that this vaccine is still around. More effective than Pneumobort K are the flu/Rhino and EHV1/4 combination vaccines. These are better than nothing but horses vaccinated with these vaccines have been shown to succumb to the disease and still die.
In the simplest terms: Do not vaccinate your horse if your horse has potentially been exposed to EHV1. Treat him like royalty for 21 days and keep your ears and eyes open to what is happening in your local area. If he shows no signs of disease at 21 days, go back to your old routine. Feel free to vaccinate him at that point in time. The most effective vaccine to use prior to exposure is Rhinomune (Pfizer). Repeat the vaccination in three weeks.
We must all be vigilant to stop the spread of this disease in California. If you feel your horse is depressed, has a fever (especially if there is nasal discharge present), you can not assume, at this moment in time, that your horse has a cold and will self-heal. Please call your veterinarian, ask him to test the horse for Equine Herpes Virus exposure using blood (buffy coat PCR) or nasal swabs (virus isolation). He may not want to come out (give the guy a break, he deserves it). These are fairly simple diagnostic procedures that can be performed by a veterinary technician. Give him verbal permission to send a technician, and release him from liability concerns. The results should be available soon and chances are overwhelming that you can stop worrying. Your neighbors will appreciate your efforts.
Merry Christmas and good will to all, especially the hard working and talented polo ponies of this world
Noel S. Muller, DVM
Los Caballos Equine Practice, Inc
Galt CA 95632
209 334 1660
LosCaballos2@aol.com
12/22/06