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Lyme Disease and Anaplasmosis
If you have been walking in the woods or tall grass, you have probably noticed that the ticks are out in full force. With them comes the emergence of tick-borne diseases. In horses in the Northeast, we mainly see Anaplasmosis ( previously Ehrlichiosis) and Lyme Disease as causing problems.
Formerly known as Ehrlichia equi, Anaplasma phagocytophilum is a rickettsial bacteria in the same family as the organisms causing Typhus and Rocky Mountain Spotted Fever in humans. A. phagocytophilum is not contagious to humans, nor can horses transmit it to each other. The disease is transmitted to the horse by Ixodes sp. ticks, which in the Northeast is Ixodes scapularis, more commonly known as the Deer Tick or Blacklegged Tick. Immature ticks pick up the bacterium from rodents who serve as reservoirs, maintain it as they mature, and then transmit it to the horse they feed off of as adults. It is unknown how long the tick has to be attached before transmission occurs. It takes approximately 2-3 weeks after disease transmission for the horse to develop clinical signs of Anaplasmosis, meaning that by the time signs are noticed the tick is long gone. The most common signs seen by owners are depression/lethargy and a high fever, as high as 104-105° Fahrenheit. Other signs can include limb edema (swelling), petechial hemorrhages (small red/purple spots) on the mucous membranes, icterus (yellow mucous membranes), and poor appetite.
A. phagocytophilum organisms infect neutrophils and eosinophils in the blood, and this is one method of diagnosis. A direct evaluation of a blood smear from the horse can reveal the organisms within these cells, making the diagnosis very straightforward. Another method of diagnosis, usually used on farm and then confirmed with a blood smear, is the use of the canine 4Dx snap test. In dogs this simple test using only a few drops of blood tests for heartworm (Dirofilaria immitis), Lyme (Borrelia burgdorferi), Anaplasmosis (Anaplasma phagocytophilum and platys), and Ehrlichiosis (Ehrlichia canis). Conveniently, this test can be used in our horses for both Lyme and Anaplasma diagnosis. While it is not perfect, it is a good, quick, stall-side diagnostic tool that can be used to direct further testing or treatment. If laboratory bloodwork is submitted, thrombocytopenia (low platelet count) is very commonly seen, which can be low enough to cause spontaneous bleeding and hemorrhages of the mucous membranes. Low red blood cell and white blood cell levels can also be seen, which can be severe enough to cause weakness, and increase susceptibility to other infections, respectively. If questions exist about a diagnosis, an immunofluorescent antibody test (IFA) can be submitted to quantify an antibody response against A. phagocytophilum.
In the Northeast, a horse with an extremely high fever but no clinical signs of viral respiratory disease (another possible cause of such high fevers) is highly suspected of having Anaplasmosis. If confirmed by snap test or blood smear, the treatment is fortunately straightforward. Oxytetracycline intravenously for 3-5 days is the preferred treatment, although oral doxycycline may also be used with somewhat more variable results and timeline, as its absorption from the GI tract is not as predictable. The fevers usually subside very quickly and the horse feels much better within 2-3 days, with no lasting effects. Prolonged treatment is not necessary, and horses gain some protective immunity from the infection, although how long this protection lasts is not known. Anytime a horse has a very high fever, the concern for potential side effects such as laminitis and abortion cannot be ignored, however these are not generally seen with Anaplasmosis. Prevention is difficult; some horses have a natural immunity likely stemming from exposure and disease which was so mild it went unrecognized, but the key lies in tick control. Permethrin-containing tick repellant products are available but ticks may still be able to attach and transmit disease. Environmental management such as keeping grass trimmed short and horses out of the wooded and brushy areas preferred by ticks is helpful. Grooming your horse thoroughly after rides in tall grass or wooded areas may help dislodge ticks which haven’t attached, but it is difficult to comb through every hair of your horse to find all the areas ticks might be hiding. No vaccine is currently available.
Lyme disease is a commonly diagnosed problem in the Northeast, though many lameness or neurologic issues may be unfairly ascribed to it. A very large proportion of horses have been exposed to Borrelia burgdorferi and have antibodies to it, which are picked up in the canine snap test. A positive snap test may be associated with an active infection, but horses with a positive snap test plus clinical signs consistent with Lyme are commonly treated and in many cases, improvement is seen. The disease, like Anaplasmosis, is transmitted by Ixodes scapularis which pick up this spirochete bacterium from rodents as nymphs then transmit it to the horse as adults. Again, it is not known how long the tick must be attached for transmission (research has shown it may be 24-48 hours), and it may be several weeks before signs are noted, and infected horses do not transmit disease to humans or other horses. The signs of Lyme disease are varied and vague in horses, including shifting limb lameness (“Today the right front, yesterday the left hind, what’s going on?!?!”), mild fevers, stiffness, sensitivity to touch, muscle soreness, attitude changes, swelling in multiple joints, decreased appetite, and a host of things which fall into the ‘he’s just not quite right’ category.
If a snap test is positive, confirmation can be obtained by Western Blot and ELISA testing (usually performed concurrently). Likewise, if the snap test is negative but the disease is still highly suspected, these tests may be submitted to make sure the snap result was not a ‘false negative’. In horses with neurologic disease in which Lyme is suspected, cerebrospinal fluid may be submitted as well, to determine whether organisms have affected the central nervous system. Lyme frequently causes inflammation in the synovial lining of multiple joints, which accounts for many of the signs seen. A full lameness and neurologic evaluation may need to be performed along with testing to help rule in or rule out the disease. Laboratory bloodwork (CBC, Chemistry panel) does not tend to show anything specific.
If a horse is suspected or confirmed to have Lyme disease, like with Anaplasmosis, tetracyclines are the drugs of choice. Most horses are put on oral doxycycline as this is easy to do at home, but the course of treatment can be many weeks to months. Another way to treat is to give intravenous oxytetracycline in a hospital setting twice daily for 3 weeks. For these horses, kidney values must be monitored as the prolonged treatment can cause kidney damage in some cases. If elevations are seen, the treatment can be reduced to once a day; if elevations continue or are severe, the treatment must be stopped. The kidney damage, as long as it is caught quickly, is not permanent, but prolonged treatment with no knowledge of kidney function could result in permanent damage. Horses undergoing intravenous treatment may also continue treatment with oral doxycycline once they go home. Once treated, horses can be tested in 3-6 months as the antibodies take a long time to disappear from the blood stream, and a false positive result may be obtained. And again, a positive test in a horse who has been treated does not necessarily indicate another active infection, it could be exposure with an immune response that protects the horse from disease. There is no approved equine Lyme vaccine. However, in horses that test negative on ELISA and western blot, a canine Lyme vaccine may be used to attempt to prevent infection. This should be discussed with your veterinarian and the decision made based on an individual horse by horse basis.
If you have any questions about Anaplasmosis or Lyme disease please contact your veterinarian or the veterinarians at New England Equine Medical and Surgical Center.
Susan Barnett, DVM Jacqueline Bartol, DVM, DACVIM
Any horse that is not vaccinated properly is susceptible to Tetanus. With the poor prognosis for recovery and low cost for this vaccine, there is no reason that any equid should not be protected for this disease.
The classic picture of a horse with tetanus is a rigid stance with an inability to open the jaw muscles. Other clinical signs that accompany tetanus include elevated tail head, protrusion of the third eyelid over the eye and a spastic gait. These signs often become more pronounced following a sharp, loud noise, such as clapping of the hands.
The signs of tetanus are caused by a toxin released by the bacteria Clostridium tetani. The bacteria usually gains entry to the horse’s body through a hoof or other soft tissue wound and the toxin affects nerve function in the spinal cord and brain. Nerves in the body are influenced by signals (neurotransmitters) that stimulate and inhibit the nerve. The toxin secreted by Clostridium tetani blocks the signals that inhibit the nerves. This results in spastic muscle response, that can be exacerbated with sudden excitement.
A diagnosis of tetanus is based on the observed clinical signs in an unvaccinated horse. There are no blood tests, although culture of a concurrent wound for C. tetani can be attempted. Often, clinical signs are observed 7-10 days after a wound has occurred.
Although the prognosis for survival is poor, treatment can be attempted. Treatment focuses on five things:
1). Debriding and flushing the wound to reduce remaining number of Clostridium bacteria – The wound is left open for drainage and in some cases the antibiotic penicillin is flushed into the wound.
2). Neutralizing any unbound toxin that has not yet bound to the nerves – Toxin can be present circulating in the blood, as well as in the cerebrospinal fluid bathing the spinal cord.. Tetanus antitoxin is given intramuscularly to bind any circulating toxin in the blood. In some cases, it is also injected into the cerebrospinal fluid, as intramuscular administered antitoxin does not cross into the nervous system.
3). Providing muscle relaxation/tranquilization - Acepromazine, a tranquilizer, is given to relax the muscle spasticity and the patient’s excitement.
4). Supportive care – A quiet dark stall is best to minimize stimulation. The toxin also affects the muscles that are responsible for drinking and eating. Therefore, these horses are often placed on intravenous fluids to keep them hydrated. An indwelling stomach tube can also be placed to supply calories if the patient cannot swallow food.
5). Stimulating an immune response – An affected horse may not start producing antibodies against the toxin, since even a low level of toxin can cause disease. Therefore, the horse should also be vaccinated at some point with a tetanus toxoid. This is a killed version of the toxin that elicits an immune response.
In conclusion, every horse should be boostered yearly with a tetanus toxoid vaccine. If the horse has sustained a wound and has not received the vaccine within the past 6 months, it should also receive a booster at that time. Sometimes, a tetanus antitoxin is given to a horse with a current wound and unknown vaccination history. This only provides coverage for a few weeks. A potential side effect of the tetanus antitoxin in horses is serum hepatitis or liver failure. This is uncommon, but can occur and should be mentioned.
If you have any questions regarding tetanus or vaccination of your horse, then please don’t hesitate to call.
Andris J. Kaneps, DVM, PhD, DACVS
Karyn Labbe, DVM
Hyperkalemic Periodic Paralysis (HYPP)
Dominique Bouchard, DVM
New England Equine Medical and Surgical center
Dover, NH 03820
“Dream is a 4 year old Quarter Horse mare showing in Halter classes. She is well balanced and has a very well defined and developed musculature. She is sometimes reported to present with muscle tremors and her third eye lid flashing over her eyes after a stressful event. She also seems anxious during the “episode.”
In that case scenario, Dream presents with the classic clinical signs of HYPP or Hyperkalemic Periodic Paralysis. It is an inherited autosomal dominant condition seen in Quarter Horses, Appaloosas and Paints who are descendants from the sire Impressive. In other words, this is a genetic disease that causes a defect in muscle membrane transport. This defect results in increased amounts of potassium (hyperkalemia) in the blood causing an inability of the muscle cells to relax. The dominant character of the condition means that only one mutation of the gene is necessary to express clinical signs. Individuals having two mutations of the gene (homozygote-H/H) are more clinically affected than the horses with one mutation (heterozygote-N/H). When bred, an H/H horse will automatically pass the mutation to their offspring. These animals should not be bred to perpetuate the genetic disease. Since 2007, these H/H horses cannot be registered at AQHA.
Signalment, clinical signs, blood work, response to treatments and DNA genetic testing are used to diagnose the condition in suspected cases. Most commonly clinical signs are seen at the onset of training but are sometimes seen in foals or older horses. Often the first episodes develop after a stressful event such as colic, a dietary change, fasting, weather changes, anesthesia, etc. Each episode can last minutes to hours and can include one or more of the following clinical signs:
-Muscle tremors; usually starting at the head/neck and progressing to the whole body
-Weakness, dog sitting, recumbency
-Prolapse / flashing of the third eye lid
-Sudden death (reported with both N/H and H/H)
Treatments exist to manage the disease and control the clinical signs as well as resolve the signs during an episode depending on the severity. Often management can be performed to prevent episodes. Once it is known that a horse is affected, management of diet and exercise as well as medications can be used to control the disease. Included in management are special diets low in potassium (no alfalfa, brome grass hay or molasses), small frequent feedings, regular exercise, and minimal stress. More severe cases will often need medical treatment during episodes. Dextrose with or without insulin combined with calcium administered intravenously are used to shift the potassium back into the cells. Acetazolamide, a potassium wasting diuretic medication, is used either during an episode or as a daily medication to reduce the frequency and severity of the episodes in affected horses.
Although heterozygote (N/H) animals are still used routinely for breeding, riding, and showing, precautions should be taken when handling or riding those horses. The episodes are unlikely to develop when the horse is exercising, but any abnormal signs should be considered seriously. Eradication of the trait is still a very hot topic in the horse industry.
If you have any questions about HYPP or about matters relating to your horse’s health in general, please talk to your veterinarian about them, or feel free to contact the veterinarians at New England Equine Medical and Surgical Center.
Everyone who foals out a mare knows that colostrum is a good thing. Critical for immune defense in the first several months of life while the foal’s own immune system builds itself up, colostrum is produced by the mare only for a short time after foaling. The foal’s GI tract can only absorb the antibodies contained in colostrum for 12-24 hours after it first nurses, so ensuring that the events of foaling pass normally and the foal stands and nurses (and continues to do so) is extremely important. Foals who fail to do so require supplemental feeding or plasma transfusion to get them through the critical period and prevent problems such as infections and sepsis. However, there exists a situation where mare’s colostrum can be highly detrimental and even fatal to the foal: neonatal isoerythrolysis, or NI.
NI is a condition in which antibodies are produced by the mare against the foal’s red blood cells causing red blood cell destruction and anemia in the foal. This is very similar to Rh factor in human pregnancy when the father passes Rh positive status to the baby and the mother is Rh negative; her body makes antibodies against the ‘foreign’ Rh factor. Almost always, NI occurs with mares who have had multiple foals, and is more likely in the mare’s second foal by the same stallion. Horses have many blood groups, and it is not uncommon to cross a mare and stallion with different blood types and not have a problem. Certain of the blood types are more likely to cause NI than others; mares that do not have a Qa or Aa blood type, and are bred to stallions with Qa or Aa are the most likely to develop problems. If the mare is exposed to the ‘foreign’ blood type either from placental problems during pregnancy or from blood contamination at foaling, her body develops antibodies against the blood type. If the exposure occurs at foaling, the antibody response takes long enough to build that the current foal will not be affected. The next foal by that stallion (or another stallion with that blood type) would be affected because the antibodies are already in the colostrum and absorbed through the foal’s intestines in the first hours of life.
How will you know if you have an NI foal? Usually these foals are born normal, nurse well, and then begin to go downhill within the first few days of life. At their foal check, they usually have adequate passive transfer of antibodies (IgG levels). As the anemia progresses, they become weak, uninterested in nursing, have elevated heart and respiratory rates, and their mucous membranes (eyes and gums) will become yellow with bilirubin, a byproduct of red blood cell destruction. In milder cases, supportive care may be enough to get the foal through the event. Preventing nursing from the mare while providing supplemental feeding, avoiding dehydration, and keeping the foal as low-stress as possible is important. Antibiotics and steroids can be used to prevent infection and reduce the antibody response respectively. After 36-48 hours of life, the intestinal tract of the foal will no longer absorb antibodies from the mare’s milk, antibodies in the milk have declined dramatically, and nursing can be safely reintroduced. If the disease causes severe anemia, a blood transfusion will be required. The ideal donor is the foal’s dam, but the red blood cells must be ‘washed’ to remove all antibodies contained in her plasma. Other donors may be used but cross-matching is important to prevent making the problem worse.
Prevention of NI is possible with a bit of planning ahead. Blood typing the mare and stallion is easily performed with a small amount of blood. If the stallion is bred to many mares, he may already be typed. The mare’s first pregnancy is usually ‘safe’ unless she has had a blood transfusion in the past. In these cases, compatibility should also be checked. If the stallion is positive for Aa or Qa blood type, the mare is negative, and this is not her first foal (a foal by the same stallion is higher risk but remember, previous stallions may have had these blood types and resulted in exposure), she should be considered ‘high risk’ for an NI foal and steps taken in accordance. Muzzling the foal once it stands and before it nurses, and giving colostrum from another mare for 36-48 hours will protect the foal from the dam’s antibodies while ensuring it gets the colostral antibodies it needs. The foal may stay with the dam if the muzzle stays in place. She will need to be milked during this time, not only to keep her comfortable but to remove the colostrum from her udder. There are also tests that can be performed by your veterinarian with the foal’s blood and the mare’s blood or colostrum, to indicate whether there are antibodies present against the foal’s red blood cells.
NI is just one of the many things to think about when it comes time for foaling. As with many foal diseases, early recognition of a problem and quick intervention is key. Having your veterinarian out within the first 24 hours to do a foal check, and then alerting them quickly if anything seems to be abnormal goes a long way to control problems before they get out of hand. If you have any concerns about the possibility of NI in your breeding program, please contact your veterinarian or any of the veterinarians at New England Equine Medical and Surgical Center, to make a plan for prevention. If you have a foal on the ground that you are concerned about, for NI or any other reason, calling the veterinarian as soon as possible increases the chance for a happy outcome.
Susan Barnett, DVM
Jacqueline Bartol, DVM, DACVIM
Watch him drop – Penile cancer in horses
It’s a good idea to be observant when your older male horse urinates in his golden years. Penile cancer in horses typically affects geldings and stallions greater than 14 years of age. They can be located on the prepuce (sheath), although they are more commonly found on the penis. Some horses show no concurrent clinical signs with a penile mass. If the mass is extensive, then you may observe sheath swelling or difficulty urinating if the mass is compressing the urethra. Some cancers can also be ulcerated and may have an odor if they have become secondarily infected with bacteria.
The most common cancer that targets the penis is squamous cell carcinoma (SCC). Light colored horses tend to be predisposed to this type of cancer. They have less pigment in their skin, and sunlight affects the genetic material in the cells causing cancer. There are likely multiple factors, as horses can also get this type of cancer in their upper airway that is not exposed to sunlight.
When you observe a mass on the penis, you should call your veterinarian for an evaluation. The first thing that should be done is a biopsy. Other possibilities for penile masses include parasitic nodules, papillomas (warts) and other tumors (sarcoids, melanoma). It’s important to know what you’re treating, as no one wants to pay for surgery if they can treat a parasitic nodule with a $10 dewormer. If possible, 2-3 biopsies should be taken, especially if there are multiple masses. Although not common, additional diseases can be found on masses that also have SCC. A biopsy of the mass may also tell you how likely the tumor is to metastasize or spread to other organs in the body.
Once you know what you’ve got, then you need to discuss how to go about getting rid of it. There are basically six different treatment options depending on the size and location of the mass, the first two are the most common methods.
1. Surgical excision - This involves excising or cutting the mass away from the normal tissue. This is usually attempted for small tumors or tumors that do not extend into the deeper tissue of the penis.
2) Cryotherapy “cold therapy” - This procedure involves liquid nitrogen, a chemical that freezes the cancer tissue. It freezes the cells, then they die when they thaw after the chemical is removed. This treatment is usually used in conjunction with #1 or for very small masses to decrease the chances of recurrence.
3) Topical chemotherapy - The success depends on the size of the tumor and is variable. Basically it is a topical chemo treatment that is applied daily for a recommended period of time.
4) Surgical removal of mass and healthy tissue -If the tumor extends into the sheath tissue, then this requires cutting off part of the sheath to limit the chances of cancer recurrence.
5) Penile amputation, where a section of the penis containing the mass is removed.
6) Massive penis and prepuce resection and penile retroversion – This procedure is not done often, but is an option for extensive penile tumors that are high up on the penis and/or the horse is having difficulty urinating. Basically the major portion of the penis as well as the whole prepuce (sheath) are removed. The urethra that carries urine from the bladder is significantly shortened and needs a new outlet. This “reconstructive surgery” sutures the new opening below the anus; in effect the male horses start urinating like a female.
Although they have the capability to spread to other organs, squamous cell carcinoma tends to be locally invasive meaning that they just spread to the local lymph nodes. But metastasis to other organs is possible nonetheless. Recurrence rates depend on the extensiveness of the cancer, but in some cases have been as high as 50% and necessitate more than one round of treatment. In effect, it is important to be observant of the older male and to initiate treatment sooner than later with SCC of the penis and sheath. Routine and regular sheath cleaning by your veterinarian constitutes an excellent screening technique.
If you have any questions regarding penile masses, contact your veterinarian or any of the veterinarians at New England Equine.
Karyn Labbe, DVM
Omar Maher, DV, DACVS
Jacqueline Bartol, DVM, DACVIM
Urinary stones in horses
Dominique Bouchard, DVM
New England Equine Medical and Surgical center
Dover, NH 03820
Solo is an 11 year old Warmblood gelding that has been noticed by his owner passing red-colored urine for the past 2 weeks. He urinates more often than normal, passing small amounts at a time and stays in the urination posture longer than normal.
Major potential causes for red urine and difficulty to urinate:
-Urinary stone (urolith): can be in the bladder, urethra, kidneys or ureters
-Trauma: penile, vaginal, urethral or preputial
-Penile masses: usually tumors
-Urinary tract infection
-Acute muscle disorders: for example- tying-up
-Toxicity: for example- red maple toxicity
The most common cause for the clinical signs demonstrated by this horse would be a urinary stone. A urinary stone, or urolith, can be located anywhere within the urinary tract but they are most commonly found in the bladder. This condition is called cystic urolithiasis. Males are affected more commonly than females, although this is a relatively uncommon condition in horses compared to other species such as cats and dogs. Two steps are required to form a urinary stone: first a core of material, called a nidus, must form to set up an origin for accumulation of urinary minerals, called crystallization. Examples of factors that help predispose a horse for urolith formation are prolonged urine retention, incomplete bladder emptying, increased mineral content of the water as well as decreased water intake. Non-steroidal anti-inflammatory drugs such as phenylbutazone also may predispose to urolith formation because of possible kidney function impairment. In addition, once the process is activated, the alkaline (high pH) environment and high level of calcium carbonate mineral in normal equine urine favor crystallization.
Two types of uroliths are found in horses. They can be differentiated visually and by their composition, even though both are composed primarily of calcium carbonate. Type one uroliths are most common. They are a soft yellow-green stone with a very rough, crumbly surface. The rough surface irritates the urinary tract often resulting in bloody urine being passed. Type two uroliths are hard, grey and smooth. In addition to calcium carbonate type two uroliths also contain magnesium and phosphate.
Both urolith types can be detected by a meticulous rectal examination. Rectal ultrasound can confirm the primary diagnosis along with the history and the clinical signs. Urinary endoscopy is helpful when available because this allows visualization of the urinary tract and the stone if it is in either the urethra or bladder. This diagnostic tool helps the veterinarian to evaluate damage caused by the stone(s), determine the number of uroliths present and the upper urinary tract function. Other tests include renal ultrasound to determine if kidney anatomy appears normal, urinalysis and kidney function tests to determine kidney function and bacterial culture for evaluation of concurrent urinary tract infection. Even though urinary tract infections are usually rare in horses, they are often seen along with urinary stones.
Treatment of uroliths includes removal of the stone either surgically (most common in male horses) or manual removal via dilation of the urethra (which is only possible in mares). Optimal treatment will depend of the size, and number of calculi as well as the surgeon’s preference. Antibiotics will also be administered to treat concurrent urinary tract infection as well as post-surgically. Prevention of recurrence of a urinary stone includes attempting to acidify the urine, encouraging increased water consumption, and decreasing the amount of calcium in the diet.
If you have any questions about urolithiasis or about matters relating to your horse’s health in general, please talk to your veterinarian about them, or feel free to contact the veterinarians at New England Equine Medical and Surgical Center.