Tick-Borne Diseases by Dr. Scott Wilson

Tick-Borne Diseases by Dr. Scott Wilson

            Horses are afflicted by a variety of parasites that can carry diseases, including ticks.  These small spider-like blood-suckers can be found on horses almost any time of year, causing a variety of clinical signs.  A commonly observed behavior that might be seen is intense scratching (sometimes until the skin is raw).  Other signs often seen include a swollen area of skin where the tick has attached, and this area may drain yellow or white discharge.  Ticks usually inhabit areas of tall grass or brush piles, and wait for animals to walk nearby to crawl onto.  Once on the animal, ticks will crawl to an area where they are covered by hair or where it is very warm, and begin to feed.  Ticks will usually feed for several days before releasing and falling off of an animal. 

                During this feeding time on a horse, there is a potential for regurgitation of blood from the tick’s stomach into the horse.  This transfusion takes place approximately 1-2 days after the tick first attaches.  In certain ticks, namely Ixodes species, this regurgitation of blood can cause the horse to be inoculated with any bacteria that the tick may be carrying.  Commonly encountered bacteria within Ixodes ticks include Borrelia burgdorferi and Anaplasma phagocytophlium.  These are the agents that cause Lyme disease and equine anaplasmosis, respectively. 

                Lyme disease is a commonly misunderstood disease of horses.  It has been documented to be the causative agent in only a few cases, including horses with neurologic disease, skin lesions, or uveitis.  It has also been found in the lining of inflamed joints and has been suspected to have caused laminitis.  A diagnosis of Lyme disease has classically become associated with a horse that has lethargy, shifting-leg lameness, and hyperesthesia (overly dramatic response to being touched).  Numerous research projects involving B. burgdorferi have attempted to elicit clinical signs in horses that were experimentally infected, but these studies have not been able to produce consistent clinical disease in these test subjects.  That being said, we do know that ticks commonly carry B. burgdorferi and can transmit this bacteria to horses while the tick is feeding.   The most recently developed  diagnostic test comes from Cornell University and can differentiate vaccination from acute exposure and from chronic infection.  There is no licensed vaccine for horses, but numerous veterinarians elect to administer a vaccine that was developed for use in dogs.  There are numerous anecdotal reports of horses testing positive for Lyme disease and having a favorable response to antibiotic treatment; that makes this disease a difficult one to argue against.  Lyme disease has been shown to regularly affect people, dogs, cats, and other common species, but it still remains a bit of a mystery in horses.  Some more common differential diagnoses for horses suspected of Lyme disease include arthritis, muscle disorders, neurologic diseases (such as Equine Protozoal Myeloencephalitis), or gastric ulceration.

                Equine anaplasmosis, caused by Anaplasma phagocytophilum, is an emerging disease that has gained a lot of attention in the past half-decade.  This disease is also caused by a bacteria transmitted by ticks, and its prevalence is increasing rapidly.  The first case in Virginia was reported by the Virginia Tech Equine Field Services team in 2009, and the number of cases per year is on the rise.  Horses afflicted with anaplasmosis consistently have a high fever, lethargy, and have a very poor appetite.  They may have yellow-tinged mucous membranes, and also may have limb swelling or even mild neurologic signs.  Diagnosis can be confirmed by sampling the blood and observing a particular life-stage of the bacteria within some white blood cells under a microscope.  Other available tests include PCR (Polymerase chain reaction) that detects the bacteria’s DNA within the blood, and checking the horse’s antibody titer against the bacteria.    

            Treatment for both of these diseases is similar: daily administration of a tetracycline antibiotic.  A horse infected with B. burgdorferi needs to be treated for at least 3-4 weeks, as this bacteria can be difficult to clear from the horse’s system.  Clinically signs usually improve relatively quickly, but it is important to finish the antibiotic regimen so that persistent infection does not ensue.  A recheck  test can be performed a few weeks to months after initiation of treatment to assess the effectiveness of the antibiotic therapy.  A horse infected with A. phagocytophlium should be treated with a non-steroidal anti-inflammatory drug (NSAID), such as Banamine, in addition to a tetracycline, for a few days to help stimulate appetite and to decrease fevers.  Antibiotic therapy to treat anaplasmosis is much shorter than that for Lyme disease, with regimens lasting approximately 10 days.  Clinical signs associated with anaplasmosis typically abate within 1-2 days with appropriate treatment

There are three choices for a tetracycline antibiotic in the horse: Oxytetracycline, minocycline, and doxycycline.  Oxytetracycline is an injectable drug that has been shown to reach therapeutic levels in the blood when given once daily by intravenous injection.  Minocycline is an oral antibiotic that has recently been discovered to have excellent efficacy against B. burgdorferi, and is thus preferred over doxycyline, which is poorly absorbed as an oral tablet.  Minocycline and doxycycline must be given twice daily by mouth.  Oxytetracycline, if given too quickly intravascularly, can cause some horses to faint, as it binds the calcium in the horse’s blood.  Minocycline and doxycycline, as with any oral antibiotic, have the potential to cause a serious colitis.  The recommended treatment for a horse with Lyme disease is 2 weeks of intravenous oxytetracycline, followed by 2 weeks of oral administration of minocycline.

                There is evidence that some Ixodes ticks in this region of the nation carry both B. burgdorferi and A. phagocytophilum, and thus can infect horses with both of these bacteria in a single feeding.  Not all ticks carry one or both of these diseases, so simply finding a tick on your horse does not mean they will get sick.  Some simple management strategies for decreasing ticks on your farm include keeping grass length short, removing brush or leaf piles, and checking your horse daily for ticks.  There are some products available for killing ticks once they are attached to the horse, like Frontline (Fipronil) spray.  This product can be sprayed in the usual places that ticks like to attach, such as the mane, between the front legs, between the hind legs, and around and underneath the tail.  If your horse presents with any of the signs listed above, please contact Old Waterloo Equine Clinic and schedule a visit.

The Latest News on Lyme Disease and Vaccination

The Latest News on Lyme Disease and Vaccination by Dr. Alisha Oehling

In December 2013, Dr. Oehling attended a discussion on Lyme Disease at the national AAEP conference in Nashville.  While much of the talk created more questions than answers, what did come out was a clearer consensus on vaccination.  As most of you know there is not an equine vaccine.  At this time we use a canine vaccine that has proven to be efficacious in most of our equine population without confusing future test results.

The testing we perform looks at three different proteins OspA, OspC, and OspF.  In equine Lyme infections we rarely see elevation in OspA.  OspC indicates an early stage infection and OspF tends to show chronic infections.  So, in order to not confuse testing, most equine veterinarians are using vaccines that only raise OspA.  That way if your horse does acquire an infection even after vaccination, it's easy to recognize.  At this time we recommend testing before vaccination to determine the levels of all three proteins in your horse.  This allows us to see if the horse is actively infected and also gives us a baseline for OspA.  If the test results shows no active infection we recommend starting the vaccine series.

The first time the horse is vaccinated for Lyme Disease, the vaccine needs to be given in a three dose series.  Give dose #1, three weeks later we give dose #2, then dose #3 is given 3 months after dose #2.  Lastly, one month after the final dose we do a second test.  This second test evaluates how much your OspA protein has changed.  Ideally we would like it to climb quite a bit indicating your horse's body has responded to the vaccine.  If your horse responded well, we recommend vaccination every 6 months after completion of the series.  This will ensure your horse has the best protection possible against this dangerous disease.

If you have previously vaccinated your horse for Lyme disease, give us a call and we can help you figure out how to alter your program based on the new recommendation.  Our staff would be happy to discuss all of this with you to make it a little clearer.

Pastern Dermatitis and other Summer-time skin blues

Pastern Dermatitis by Dr. Tena Boyd

Pastern dermatitis is a condition that can occur year round but is often worse during summer months.  This is a very common and inconvenient problem in our area and many remedies are marketed. 

• · The mild form (scratches, mud fever, mud rash is the mildest and most prevalent. This form is characterized by hair loss, dry scales, and crusts; may be “itchy” and/or painful.

                                           

• · The exudative form (grease heel, dew poisoning) is more serious characterized by very inflamed skin, hair loss, and heavier crusting. More aggressive treatment is required

• · The hind-limbs are affected more commonly than forelimbs and white or non-pigmented skin  more than dark skin

• · The affected skin is often suffering from a mixed infection of bacteria, fungal organisms, and possibly even insect or mite infestation

• · Photosensitization may be a cause or contributing factor in more severe conditions

• · The most common  agent we see is exposure to clover pasture;  affects both the muzzle and lower limbs

• · Other agents implicated are St. John’s Wart, buckwheat, and perennial rye grass

• · A veterinary examination can lead to the most targeted treatment.  Bacterial and/or fungal cultures, skin scrapings or biopsy may assist in diagnosis. Treatment:

· Wash off the offensive agents from the skin after contact, such as when brought in from turnout or from exercise where the lower limbs are in contact with grass

· Medicated shampoos that have a broad spectrum of activity are most effective but even a sudsing non-medicated shampoo is helpful

· Keeping the legs dry for several hours per day following elimination of the offensive agents is key

· Topical treatments that decrease the scales and help heal the skin

· Systemic antibiotics for stubborn infections or those that lead to cellulitis, fever, or lameness

· Recently we have seen a few products that act as “socks” for horses and have been very effective in assisting treatment. 

Another Summertime Blue, Sunburned Skin

Sunshine is often considered therapeutic for the body and spirit!  Some of our favorite equine friends may have a different view.   For those white-faced breeds with no pigment or pink skin, prolonged exposure to sun can create several uncomfortable conditions.  As the skin becomes inflamed from this delicate skin “burning”, it is very susceptible to changes that can lead to a skin cancer, Squamous Cell Carcinoma (SCC). 

To protect these horses, fly masks can be worn by these horses year-round whenever it is sunny out.  Those with nose shields will also protect the muzzle of these sensitive horses.  As discussed previously, agents that can cause photo-sensitivity such as clover pasture, can exacerbate this condition.  Another helpful protection, is to apply children’s waterproof sunscreen to the faces and around the eyes of these horses.  If your horse shows any of the conditions seen in these photographs, please call for an appointment.

Compounded Drugs, What Does this Mean?

Drug compounding is a process to "produce a medication by combining or altering ingredients for the special needs of a patient". As stated in the AAEP Horse Health Article of June 2009, Your Horse's Life is Not Worth the Risk: What every horse owner should know about drug compounding; "Because there is a scarcity of approved medications for use in horses, there is a legitimate need for compounding in equine veterinary medicine. Some examples of legitimate compounding would include crushing a tablet and creating a paste or gel to aid in the administration to the patient or mixing two anesthetics in the same syringe for use in your horse."

Further this article states the American Association of Equine Practitioners (AAEP) position statement on this topic. "The AAEP acknowledges that reputable pharmacies produce legitimate compounded drugs to improve the health of horses when an FDA-approved option doesn't exist. However, when inappropriately compounded and used, these drugs may pose a serious threat to the health of your horse. Knowing the facts about legitimate and illegitimate compounded drugs will help you and your veterinarian decide on the best treatment option for your horse." For the full article refer to the reprint in the OWEC Newsletter, July 2009 issue or search for it on www.aaep.org.

The topic of compounded drugs often sparks much debate. From near conspiracy-theorists who feel that all drug companies are bad and are out to gouge consumers for profit only, to those who are trying to find cheaper or more palatable or easily administered drug options for their horse and everything in between. Bottom line, our horses depend on us to make the safest and best choices for their health and welfare. If a cheaper alternative does not work or is unsafe, have we saved any money? Have we done our best or even an "OK" job by our horse?

As many will remember, in April of 2009, 21 polo ponies were the tragic victims of inappropriately compounded medication given to them by their trainers or caretakers that resulted in sudden death. Several horses in Louisiana in 2006 suffered a similar fate. These are very dramatic examples of the worst consequence. The problem is, when do we know when a compounded product we have ordered (and sent payment) from a source we thought to be reputable is unsafe or ineffective?

Whenever possible, if an FDA-approved drug is available for medicating our horses, our horses depend on us to use them. The FDA-approval process assures the product is safe and effective for its intended use, but also the methods, facilities and controls used for the production of the drug meet FDA Standards to preserve it's identity, strength, quality, purity, and consistency from batch to batch. The FDA-approval process is a very expensive one and those manufacturers who have complied with this process and been granted approval have invested much time and expense to provide the product. As well, if problems are noted we have someone to go to seek solutions or recompense when adverse effects are noted. Compounders' products are unregulated by the government and not subject to the same standards for consumer protection or accountability.

What's All the Fuss About Polyglan? by Dr. Laura Fontana

Polyglcan is a commercially available patented formulation that is labeled for post-surgical joint lavage and joint fluid replacement. This solution is comprised of 3 fractions: hyaluronic acid, sodium chondroitin sulfate, and N-acetyl-D-glucosamine. These 3 fractions are all naturally occurring components of synovia and are instrumental in maintaining joint health. Before discussing the efficacy of this compound, let's review the specific function and independent use of these 3 constituents. Hyaluronan (hyaluronic acid or HA) is a normal joint fluid and cartilage constituent with anti-inflammatory effects as well as joint lubrication and protection properties (1). In equine practice, intra-articular and intravenous administration of HA (Legend) is commonly employed for the treatment of synovitis and osteoarthritis, and intravenous Legend is also used prophylactically. In fact, Legend is the only FDA-approved joint therapy labeled for both intravenous and intra-articular treatment of non-infectious synovitis. Chondroitin sulfate belongs to a class known as polysulfated glycosaminoglycans (PSGAGs), which are an important element of the extracellular matrix of articular (joint) cartilage. Included in this class is Adequan, which is made from cow lung and trachea extracts primarily containing chondroitin sulfate. Adequan and other drugs in this class have been referred to as chondroprotective, or more recently, as slow-acting disease modifying osteoarthritic drugs (SAMOAD) intended to preclude, slow, or revers the cartilaginous lesion of OA (2). Adequan is used intramuscularly, and like HA (Legend), it is also used intra-articularly in equine practice. Glucosamine is a precursor to the disaccharides (sugars) found in aggregan, a molecule that comprises a substantial portion of the extracellular cartilage matrix. Many equine oral joint supplements contain glucosamine as well as chondroitin. The objective of combining hyaluronic acid, chondroitin sulfate, and glucosamine (as Polyglycan), all of which have long been administered independently by a variety of methods, is to create a safe and efficacious product for intravenous and intra-articular use in horse to promote joint health. But, is this combination effective? Frisbie et al (2009) (3) conducted a study to assess intravenous and intra-articular Polyglycan for the treatment of osteoarthritis in horses. The authors concluded that intra-articular Polyglycan (when given once every 7 days for a total of 4 treatments) significantly improved lameness and disease progression in horses, as evidenced by improved lameness scores, decreased radiographic evidence of osteoarthritis, and improved cartilage. In contrast, the intravenous Polyglycan treated horses (which received a dose every 5th day for a total of 14 treatments) showed no improvement in lameness scores and increased radiographic evidence of osteoarthritis. These findings do not support intravenous use of Polyglycan, and suggest that intravenous use may in fact be counterproductive. At this time, and until more studies are performed, continued use of FDA-approved products labeled for intravenous and intra-articular treatment of osteoarthritis is indicated. (1) Frisbie DD, Kawcak CE, McIlwraith CW, et al. Evaluation of polysulfated glycosaminoglycan or sodium hualuronan administered intra-articularly for treatment of horses with experimentally induced osteoarthritis. Am J Vet Res 2009; 70:203 - 209. (2) Section XII, Musculoskeletal System in Equine Surgery 3rd edition. 2005. Jorg Auer and John Stick eds. WB Saunders. Pp 1055 - 73. (3) Frisbie DD, Kawcak CE, McIlwraith CW, Werpy MW. Assessment of intravenous or intra-articular hyaluronic acid, condroitin sulfate and N-acetyl-D-glucosamine in treatment of osteoarthritis using an equine experimental model. Presented at : 55th Annual AAEP Convention; Decemeber 5 - 9: Las Vegas, NV.

Why do we do Coggins' tests each year?

As of March 2, 2011, an updated regulation will take effect regarding the Coggins' test for Equine Infectious Anemia in Virginia. The Virginia Department of Agriculture and Consumer Services (VDACS) has updated the regulation and specifies that "all horses assembled at a show, fair, race meet or other such function or participating in any activity on properties where horses belonging to different owners may come into contact with each other in Virginia must be accompanied by a report of an official negative test for Equine Infectious Anemia". This update further defines what "when horses are assembled" means. Assembly of horses for a trail ride on public property such as a state park is an example of an activity requiring horse owners to have a valid Coggins report with them.

Starting March 2, rangers in state and national parks may check for Coggins' papers and owners without valid test reports could be charged with a Class I Misdemeanor and asked to leave the park. As is currently the case under existing regulations, owners presenting fraudulent paperwork can be charged with civil penalties as well.

The Coggins' test is laboratory test for the disease Equine Infectious Anemia(EIA). EIA is a very contagious (infectious) and possibly fatal disease that affects any species of equines (horses, donkey, mules, etc). It is caused by a virus, a type classified as a retrovirus. There is no vaccine or treatment for the disease. EIA is a blood-borne infection and can be transmitted from horse to horse by large biting insects (horse flies, deer flies) or from blood-contaminated materials.

There are three clinical forms of the disease: Acute, Chronic, and Inapparent. In the Acute form, if a horse is exposed the the EIA virus, they can develop severe signs (fever) of the disease and die within 2 - 3 weeks. In more mildly affected horses, there may an initial fever that resolves and the horse recovers without further symptoms but if this horse is then interacting with other horses, it may act as a potential source of infection for any horse living in its vicinity. There may be no indication at all of the disease until picked up by a routine annual Coggins' test.

In the Chronic form, the horse survives the acute bout of the disease and may develop recurring bouts of illness. Symptoms of this illness may include moderate to high fevers (105 F), petechial hemorrhages (pin point blood spots on mucous membranes or gums), depression/lethargy, weight loss, edema in limbs or underbody surfaces such as the chest or belly, and anemia.

In the Inapparent form, the horse carries the disease with no signs or symptoms of illness. However, they serve as "resevoirs" of infection. The majority of horses positive for EIA are in this category. These horses are carriers for life and the infection may become chronic or acute when under stress from hard work, transportation stress, or when dealing with another illness. Inapparent carriers have lower concentrations of the EIA virus in the bloodstream than horses with active clinical signs of EIA. It is said that only 1 horse fly out of 6 million is likely to pick up and transmit the virus from such horses.

Prevention of EIA is centered around identifying carriers and affected individuals and removing them from contact with other horses. When an equine has a positive result on an official test for EIA, the animal is placed under quarantine. Confirmation testing is initiated and the quarantine from other horses is in order to prevent further exposure and possible transmission of the disease. All exposed horses within 200 yards of the location of the "positive horse" must also be placed under quarantine. The quarantined area and horses are monitored by federal or state regulatory personnel. For more information on EIA Uniform Methods and Rules to implement and conduct a national control program for EIA formulated by APHIS-VS, go to http://ww.aphis.usda.gov/vs/nahps/equine/eia or contact an area APHIS - VS office.

"Equine Infectious Anemia is a serious disease," said Dr. Richard Wilkes, VDACS State Veterinarian. "It affects all members of the equine species and is found in nearly every country of the world. All infected horses, even those that are asympotmatic, become carriers and are infectious for life. Infected animals must either be destroyed or remain permanently isolated from other equines to prevent transmission. The change in regulation is not drastic, but it is important and horse owners need to take seriously the need for a valid Coggins test each year prior to anny assemblage with other equines."

EPM Update: New Treatment and Prevention

New EPM medication and proposed prevention regime

A medication similar to Marquis (the only approved medication to treat EPM), but in a top dress pellet form will be introduced in early December. Both Marquis and this new medication(generic name diclazuril), prevent the EPM protozoa from growing and replicating. Neither actually seem to kill the EPM organism. However, the body’s own immune system can kill the protozoa once it stops multiplying. Dr. Tom Divers, of Cornell Veterinary School, presented the information at a recent seminar. Dr. Divers explained that diclazuril more easily crosses the blood brain barrier than ponazuril, the active ingredient in Marquis. Both medications have a wide margin of safety. Diclazuril has been used to treat coccidial infections in other animals. The other class of medication used to treat EPM is pyrimethamine which actually kills the EPM organism. However, there are cases where the horse gets worse when treated with the pryimethamine as the protozoa die off and there is an inflammatory response.

One of the proposals to prevent EPM disease in the horse is to kill the EPM protozoa after it enters the horse’s body but before it makes it’s way into the nervous system. It takes about 4 days from ingestion of the infective stage of EPM organism to the transformation to the stage that enters of spinal cord and brain. If treatment is given every 4 days then the organism shouldn’t be able to cause damage to the nervous system. Since the horse is a dead end host for the EPM organism (i.e. the horse can’t pass the disease on to any other animal) this treatment should not lead to resistance.