Potomac Horse Fever can cause very serious diarrhea, and other symptoms may include fever, laminitis, and colic.  It is caused by Neorickettsia risticii, a bacteria found in freshwater snails that is believed to be transmitted to horses via inadvertent ingestion of infected aquatic insects.  It is usually seasonal, seen most commonly in the hot summer months or early fall. If Potomac Horse Fever has occurred in a particular geographic area, it is likely that additional cases will occur in future years. However, vaccination against this disease has been controversial.  Evidence of protection against clinical disease is lacking, possibly because the vaccine may not stimulate a protective immune response, or potentially because multiple strains of the bacteria may exist, whereas only one strain is present in the available vaccine.

                This is a difficult question to answer, and there is little scientific data to guide recommendations.  It is very convenient to have all vaccinations given all at once to save time and money, and it is very commonly done with little adverse effects.  There are no studies examining the safety or efficacy of the vaccines when multiple different ones are administered together.  This does not mean they are not safe or not effective if given in combination, just that this has not been proven.  It does appear that there is a higher rate of adverse reactions if multiple vaccinations are given at one time, however, the overall rate of adverse reactions is still very low.  If your horse has experienced an adverse reaction in the past, it may be wise to split up his or her future vaccinations, both to decrease the risk of an adverse event as well as to determine if a particular vaccination is the culprit causing the horse to react.  If multiple vaccinations are given on the same date, it must be considered that modified live vaccinations should not be given close to the site of a killed vaccination, as the adjuvant in the killed vaccine may interfere with the activity of the modified live vaccine.  Seek your veterinarian’s advice if this is a concern.

         We get this question quite often, and it would be convenient to combine the treatments to save on an additional call fee.  However, we generally recommend against this for a few reasons.  One of the drugs we typically use in joint injections is a steroid anti-inflammatory such as triamcinolone or methylprednisolone acetate.  These are very potent anti-inflammatory agents, and can cause immune suppression even in the small amounts used in joints.  This means that the immune response to a vaccine could be dampened by the steroids injected in the joint, and the horse may not be adequately protected by the vaccine if it is administered at the same time as intra-articular injections.  Also, in the case of the intranasal Strangles (Strep equi) vaccine, we are very careful not to have contamination of any injection sites with the snorting of the vaccine after the horse is given this vaccine.  If this modified live bacteria is inadvertently injected, it can set up a nasty abscess and this would be particularly devastating if this infection were to occur in a joint.

Most horse people have heard of Strangles, and many have had the unfortunate experience of dealing with an outbreak.  The disease, sometimes referred to as “distemper,” is not new—it was first reported in 1251.  The disease is highly contagious.  Young animals (weanlings, yearlings, and other young stock) are particularly susceptible, however any age of horse can be affected.

               This is a very interesting and common question, and there is a little bit of research available to help guide recommendations.  The first thing to consider is that sometimes, unpredictably, a horse will have a severe, immediate response to the vaccination such as anaphylaxis.  Obviously, being ridden when this occurs can worsen the situation, and would put the rider at risk if the horse were to become weak or wobbly, or even fall.  If you are going to ride the horse after a vaccination, wait at least 30 minutes to ensure these immediate adverse effects are not seen.  Some clinicians feel that if the horse is ridden lightly after a vaccination, they develop less stiffness at the injection site.  However, it has been shown that extreme exercise (for example, galloping sets or race training) in close proximity to a vaccination can reduce the horse’s ability to respond to the vaccine appropriately, therefore the vaccine may be less effective.  It seems the exercise essentially acts as a form of stress that reduces the horse’s immune response to the vaccine.  The bottom line—while it may be safe (or potentially beneficial) to exercise a horse lightly a little while after a vaccination is given, avoid strenuous exercise.

West Nile Virus was first reported in Canada in 2001, and first detected in a horses in Canada in 2002.  West Nile Virus in horses hit the peak of its prevalence in 2003 with 170 cases reported in Alberta alone.  Since then there have not been as many cases of the disease in Alberta, and so the question is often raised—do we still need to vaccinate our horses against West Nile Virus?

    If a human arrives for an influenza vaccination from a vaccine clinic or pharmacy, one of the first questions asked is, “Are you feeling well today?”  If the immune response is actively engaged fighting another virus or bacterial process, the response to a vaccination might not be optimal.  Therefore, if your horse demonstrates a nasal discharge, has a mild fever, or is recovering from another medical issue, we usually delay vaccination until their immune system is better able to respond to the vaccine reliably.

Eastern Equine Encephalitis (EEE) and Western Equine Encephalitis (WEE) are both neurological diseases spread to horses and humans from infected wild birds and rodents via blood sucking mosquitos. The disease typically culminates in a profound depression that characterizes these diseases in the late stages, and gives them the common name of “sleeping sickness.” The American Association of Equine Practitioners considers vaccines against EEE and WEE to be "core" vaccines, recommended for all adult horses.

Read Dr. Crystal Lee’s article from the Canadian Horse Journal on evaluating equine lameness.

  An upper respiratory tract infection or “cold” in a horse, like in a human, can be caused by many different viruses or bacterial infections—adenovirus, herpesvirus (Type 1, 2, 4, 5), influenza virus, rhinitis A or B virus, Strep equi (“Strangles”)—or even a combination of these agents.  Horses can be vaccinated against some respiratory pathogens, namely herpesvirus Type 1 and 4, Influenza, and Strangles, but many other viruses especially are not included in the routine vaccinations (much as humans can be vaccinated against influenza but not the common cold).  Additionally, each horse’s immune system will respond differently to a given vaccine, and a small percentage of horses will be “non-responders.” These horses do not mount an adequate immune response following even properly administered vaccinations.  If your horse develops an upper respiratory infection even when they have received their yearly vaccinations, they could be infected by one of these other viruses (adenovirus, other herpesvirus types, rhinitis virus), or their immune system simply did not respond to the vaccine as well as some other horses.

Of all the vaccines designated as “core” by the American Association of Equine Practitioners, vaccination against tetanus is considered the most basic for all horses, whether they are athletic competitors, companions, retired, young or old.  Why is this?

With the exception of Strangles, all our commonly used equine vaccines are given intramuscularly.  Rabies must be administered by a veterinarian, so it cannot be dispensed for owners to give, however the others can be dispensed.  A note of caution, however—any vaccine can produce immediate, unpredictable adverse effects such as hives or anaphylaxis, which can be fatal if not treated promptly.  If a veterinarian is administering a vaccination, they are required to have medications on hand that can address these concerns.  If administering a vaccine yourself, monitor very closely for signs of these adverse effects and have a plan in place for prompt treatment.