EquineSite.com

Winter is nearly upon us, bringing mosquito season to a close, and many horse owners are breathing a sigh of relief. Mosquitoes are not only a nuisance but can carry several diseases which can infect horses and humans alike. Of these, Eastern Equine Encephalitis (EEE, ‘Triple E’, or ‘Sleeping Sickness’) made the headlines this year with an unprecedented number of cases in equines throughout New England.
EEE, unlike the name suggests, occurs across the US and parts of Canada, as well as extending into Central and South America. The disease is caused by a virus that is maintained in wild birds, which usually show no signs of disease. The virus reaches high levels in the bloodstream of these birds, where it is picked up by the mosquito and may then be transmitted to a horse (or human) the mosquito later bites. Horses are considered a ‘dead end’ host for EEE, meaning that they do not produce enough virus in the blood to allow transmitting the disease to another animal or human. The peak incidence of this disease is during mosquito season (spring to fall), and tends to be highest late in the summer.

Once the virus is introduced into a susceptible horse, it enters and multiplies in white blood cells and cells lining the blood vessels. The virus then spreads through the blood to nerve tissue in the brain. It may take 1-3 weeks after the virus enters the body for clinical signs to develop. Horses with EEE usually show depression and fever at the outset, and neurologic signs follow. Early on, the horse may show anorexia, ataxia (unsteadiness) and proprioceptive deficits (lack of awareness of limb positioning). The horse may then develop signs such as severe depression or ‘sleepiness’, hyperexcitability to stimuli, compulsive walking in circles, blindness, and have cranial nerve deficits (drooping of the ear, eyelid, or lip, abnormal position of the head or eyes, trouble swallowing). As the disease continues to progress, affected horses will typically become recumbent, unable to rise, and enter a comatose state. Horses who reach this point have a very poor prognosis for survival, and humane euthanasia is typically recommended. Horses who survive severe infection usually have life-long neurologic deficits as a result of the disease. While infection with the disease confers long-lasting immunity against later infection, this is small comfort if the horse is no longer able to lead a normal life. Diagnosis of the disease is often made on clinical signs and an unvaccinated status. Analysis of cerebrospinal fluid (CSF) is the most common laboratory test, and can reveal elevation of white blood cells and protein. It is also possible to recover virus from CSF, or brain tissue post-mortem, though this process takes much longer.

While the disease is devastating to affected individuals, vaccination is highly effective. One of the core vaccines recommended by the American Association of Equine Practitioners, the EEE vaccine is given 1-3 times per year, depending on the level of risk for the disease. While the South is usually thought of as being the place of highest risk, and horses in the Northeast have long been vaccinated only on an annual basis, the recent outbreak would suggest that vaccination at least twice per year would be prudent. The vaccine is usually given in the spring, before the start of mosquito season, but incorporating it into the fall vaccine group is recommended for increased protection. While mosquitoes are not obviously present in the winter, the mild fall weather and earlier spring thaw can result in mosquito presence beyond what we would normally consider ‘mosquito season’. Vaccinated horses who are bitten by an infected mosquito stand an excellent chance of clearing the virus without ever developing clinical signs, and in the few cases in which signs develop, they tend to be far less severe and the horse is much more likely to survive. As they say, ‘an ounce of prevention is worth a pound of cure,’ especially in the case of EEE, where an inexpensive vaccine can save the life of your horse. Mosquito control is another important component to controlling mosquito-borne disease, so eliminate sources of standing water and use insect repellant on horses and humans alike, especially when mosquitoes are most active.

If you have any questions about EEE, other neurologic diseases, or vaccination protocols for horses, please contact your veterinarian or the veterinarians at New England Equine Medical and Surgical Center.

Susan Barnett, DVM
Jacqueline Bartol, DVM, DACVIM
www.newenglandequine.com

Everyone answers, “Yeah, my horse is regularly dewormed.” But these days it doesn’t mean that your horse isn’t still burdened with parasites. Wild horses had the right idea. They dewormed themselves by the low levels of toxins in certain weeds they grazed. Too bad it ain’t free these days. No horse is going to be free of parasites, but we should be educated to know how to control the numbers in our herds. What product to use, when to use it and what it is that we are killing are important questions. Also, what else can I do as a horse owner to limit parasite numbers on my farm?

1). Roundworms (Parascaris equorum), the long worms that you see coming out of your weanling or yearling. The earliest age that youngsters are affected is 3 months considering the worm cycle, so don’t deworm your 2 week old colt. We recommend first deworming for roundworms at 8 weeks old and thereafter treating every 6 weeks. The product? Well, that depends on what you suspect the worm burden is. If the weanling is skinny with a pendulous belly and lethargic, then he probably has more rounds in him that the active weanling of an appropriate weight. So treat the heavily parasitized youngster with Fenbendazole first, then six weeks later go to the more effective Ivermectin. Note that when you treat with Fenbendazole (panacur) specifically for roundworms, you treat with a double dose (10mg/kg) once daily for five days; Ivermectin is the regular dose given once. If you treat the heavily parasitized weanling with Ivermectin, then you could potentially cause a massive die off of the worms and possible impaction of the small intestine. Plus the worms are antigenic and can stimulate a pretty big inflammatory response. The lifecycle of the roundworm larvae involves migration through the lung tissue among other places. Some of these youngsters may also exhibit a cough and snotty nose. Older horses usually more than 1-2 years old tend to gain immunity to roundworms, their immune system may inhibit the migration of the larvae through different stages.

2. Large strongyles (Strongylus vulgaris), not so much a problem since the introduction of ivermection. Aka the bloodsuckers, these larvae migrate through the vessels that supply blood to the intestine causing blood clots and possible death of the intestine. But they could potentially be a problem in areas that don’t have any type of deworming protocol. Recommend Ivermectin to treat with.

3. Small strongyles (Cyathostomes), the larvae of this worm can cause serious diarrhea in horses. Diarrhea associated with these worms is typically seen in late winter or early spring as the encysted larvae in the large intestinal wall excyst. This results in quite an inflammatory response, altered water absorption and watery diarrhea. Moxidectin is pretty effective at killing cyathostomes, recommended to deworm prior to the winter months to decrease larvae numbers. Remember, don’t give moxidectin to weanlings under 5 months of age, as it can have toxic side effects. Can be troublesome to diagnose if infected with the larvae since they are encysted in the intestinal wall. With diarrheal cases will usually see the red worms in the manure.

4. Tapeworms (Anaplocephala perfoliata), high numbers can cause problems in the horse. They have a predilection for the junction between the small intestine and the cecum, attaching to the intestinal mucosa. They may cause enough mucosal ulceration to cause a mild anemia, it’s debated whether they are involved in intussusception (one part of the intestine telescoping into another part). The worm segments look like rice grains. They are eliminated periodicially, so a fecal float may not always show an infected animal. Praziquantel is the dewormer of choice for tapes, recommend deworming with Praziquantel once every six months (twice yearly), give at least one dose around fall time.

At least once yearly your veterinarian should take fecal samples of a percentage of the horses (doesn’t have to be all) on your farm to see whether your deworming protocol is effective. All horses on the farm should be on a similar deworming program and horses dewormed around similar time intervals. Programs are going to be different on each farm, the above are just recommendations. Fecals can also be used to see whether you can decrease the frequency of deworming in some situations, which may decrease the chance of resistance problems on your farm.

Manure control is also important. Manure collected and spread on the pasture just allows parasites to enter their cycle again. Composting is a great option to parasite control. The heat kills worm larvae, as well as also controlling fly larvae and eggs. 3ft by 4ft compost piles that are rotated periodically to mix the compost will usually be complete by 3 months so that the compost can then be spread on the pasture. For the horses already out to pasture, raking the field to break up the manure will allow the sun to dessicate or dry out some of the larvae. Roundworm eggs are difficult to eliminate once in the environment. They can potentially remain infective in the environment for up to 5 years.

If you have any any questions concerning deworming strategies, then please feel free to contact your veterinarian or any of the doctors at New England Equine Medical & Surgical Center.

Karyn Labbe, DVM
Jacqueline Bartol, DVM, DACVIM
www.newenglandequine.com

Dominique Bouchard, DVM
New England Equine Medical and Surgical center
Dover, NH 03820
www.newenglandequine.com

“Chester is a 10 year old Thoroughbred who was found extremely painful on his right hind this evening. He was ridden this morning without any lameness. Now his leg his swollen, firm, warm and he does not bare any weight on the limb.”

Major potential causes for an acutely painful swollen limb:
-Cellulitis: inflammation or infection of the subcutaneous tissues
-Thrombophlebitis: inflammation of a vein cause by a blood clot
-Vasculitis: inflammation of vessels caused mainly by infectious agents or hypersensivity
-Limb abscess
-Trauma: fracture, infected joint
-Insect/snake bite
-Topical irritant to the skin

Cellulitis is one of the most common causes of what veterinarians call painful peripheral edema. Because it involves an infectious agent (mainly bacteria) almost in all cases, this term is used and refers to the infection of the subcutaneous tissues.

Most of the time; the underlying cause is unknown as no lesion is observed by the owner or veterinarian. Some type of penetration through the skin is strongly suspected as a cause in most cases. Wounds, intra-articular injections, surgical procedures, abrasions and bruises are all examples of skin damage that has been associated with cellulitis. When the skin barrier is broken, the normal bacterial population of the skin may then infiltrate the underlying tissue and cause inflammation and possibly infection. This explains why bacteria common to the skin (mostly Staphyloccocus spp and Streptoccocus spp) are often isolated in this condition.

The swelling is caused when the bacteria release toxins in the tissues causing inflammation of blood vessels and lymphatic channels. This results in increasing fluid leakage from the vessels and decreasing fluid resorption from the lymphatic which leads to fluid accumulation under the skin, a process we call edema.

Cellulitis is a treatable condition, but has a high recurrence rate. Because it often involves an infectious cause, antibiotic therapy is usually necessary. Penicillin and gentamicin are the most frequent combination of antibiotics used to treat cellulitis. When a bacterial culture is performed, the antibiotic choice is adapted as needed. Anti-inflammatory and pain management are an essential part of the treatment as the condition is very painful. An epidural is necessary in cases of severe rear limb pain when other methods of pain management are ineffective. Hydrotherapy, hand walking and limb bandaging are also important treatment tools as they mechanically help the blood and lymph circulation allowing the edema to resorb.

The prognosis for this condition is guarded to good as some horses can return to their previous use if they response well to treatment. Cases where the limb swelling returns multiple times are more challenging as the chronic inflammation can lead to scar tissue formation. These horses may have a thicker leg permanently. Also, recurring cellulitis may damage the lymphatic channels with scar tissue. Chronic limb severe limbs welling may also damage the coronary band and may lead to laminitis. Laminitis may also occur in the opposite leg due to the extra weight carried on the healthy limb. Other principal complications are skin necrosis secondary to compromise vasculature associate with the severe swelling, vascular thrombosis associated with bacterial toxins and persistent lameness.

As cellulitis can be a life-treatening condition and has a guarded prognosis, early recognition can increase the survival outcome. Good hygiene, wound management and aseptic techniques are favorable preventive measures to take. If you have any questions about cellulitis 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.

Does your horse have a hairless patch of skin that looks like a wart and just won’t go away? Or maybe a lump on his body that seems to be slowly getting bigger. Sarcoids are the most common skin tumor of horses. While they tend to only be locally invasive, and do not metastasize to other areas or organs, they can be quite unsightly and irritating to the horse. Depending on their location, they may also affect the normal movement of the horse, and be very difficult to remove.
Equine sarcoids are tumors of connective tissue caused by a bovine papillomavirus, a virus which causes warts in cattle. The virus is believed to be transmitted by flies. Sarcoids are frequently found on the face, legs, or at old wound sites on horses, which are all favorite landing spots for flies. It is also believed that some horses are more susceptible to developing sarcoids than others. There are several different types of sarcoids, which differ in their appearance and level of invasion into the skin and deeper tissues. These are:

1. Occult: Circular and may be hairless or thinly-haired, and may look like ringworm or an abrasion that doesn’t heal. These are more commonly found on the head and neck.
2. Verrucous: Hairless, thickened, rough, and flaky. There may be raw, ulcerated areas within the sarcoid, and this type may also look like a wart, ringworm or a non-healing abrasion. There are more commonly found on the face, body, and groin.
3. Nodular: Nodules which are firm, raised, and round. These are more commonly found on the eyelids and groin.
4. Fibroblastic: Fleshy and ulcerated, may be covered with haired skin. These may look like proud flesh or squamous cell carcinoma, and are more commonly found on the lower legs, groin, and eyelids.
5. Mixed: One region having characteristics of 2 or more types of sarcoids.
6. Malignant (aggressive): Locally invasive, multiple nodules and cords which tend to be fast-growing.

A biopsy is the best way to diagnose any of these types of sarcoids. They may appear similar to a number of other skin diseases, but when submitted for histopathology to examine the tissue, the diagnosis is usually straightforward. Treatment, however, can prove more difficult. Some sarcoids, if small and in an area where they don’t interfere with movement, may be left alone. However, these must be monitored because they may grow to the point where other treatments become very difficult to perform. Surgical removal of sarcoids is possible, but can be difficult for those on the head or legs. Sarcoids also tend to recur when surgery is the only treatment, so injection of the chemotherapeutic drugs cisplatin or carboplatin is commonly performed with surgery. Medical treatment with cisplatin or carboplatin alone, either injected or implanted as beads in the tumor may be successful. Mycobacterial cell wall extracts may also be injected into sarcoids, though in some cases they may make the tumors worse. For tumors around the eye, radiation therapy is another option. 5-Fluorouracil is a topical chemotherapy agent that may cause some sarcoids to regress. Xxterra is a topical herbal product which may work on some sarcoids, but in some cases may make the sarcoids worse.
Treatment of sarcoids can be very difficult, and no one method is guaranteed to work on all sarcoids. Additionally, they tend to become more aggressive and harder to eradicate as more treatment methods are tried. If your horse has a mass or non-healing wound on its body that just won’t go away or gets bigger, it is probably worth finding out what it is so that it may be treated more successfully. Your veterinarian can examine the area and take a biopsy for examination to determine what you are dealing with, and make recommendations for treatment based on the examination and biopsy results.

If you have any questions about sarcoids or other skin tumors, 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.

Susan E. Barnett, DVM
Jacqueline Bartol, DVM, DACVIM

www.newenglandequine.com


Introduction: Your broodmare has just delivered a colt. You are relieved that the delivery went through without complication. But you should still be observant of your mare in the 48 hours that follow parturition. A number of mares exhibit colicky signs post-parturition. These may include lying down for longer periods than normal, looking at the flank area, pawing and decreased manure production. Often these signs are associated with discomfort as the uterus involutes or contracts down. Pelvic bruising during delivery can cause subsequent discomfort for the mare when passing manure post-partum as well. Owners should also be aware of the possibility of periparturient hemorrhage, or bleeding from the reproductive tract.

What is Periparturient Hemorrhage?
Periparturient hemorrhage has been estimated to occur in only a small percentage (2-3%) of the broodmare population. There are three arteries that provide the main blood supply to the uterus. The major artery is the middle uterine artery. When a tear occurs in any one of these arteries, it more commonly occurs post-partum, although a smaller percentage of mares may bleed in the last few months of gestation. Theories speculate that the arteries undergo age related degenerative changes, losing elasticity that may predispose to tearing. There are three main sites in the reproductive tract where the bleed may occur.
1). Into the broad ligament, a thin piece of tissue that suspends the uterus and through which course the blood vessels to the uterus.
2). Into the wall of the uterus.
3). Into the peritoneum (belly). These bleeds carry a worse prognosis because they cannot be contained as well as a bleed into the broad ligament or uterine wall.

Clinical Signs: Horses that bleed from the reproductive tract may show a variety of clinical signs. Horses with serious bleeds into the peritoneum (belly) are often found dead in the field. A number of mares may exhibit colicky behavior including sweating, muscle fasciculations, pawing and acting anxious. These colic signs may be due to a hematoma stretching the broad ligament or irritation of the peritoneal (belly) cavity that is filled with blood. Other broodmares may only show subtle signs including lethargy and decreased appetite.

Diagnostics: A rectal exam may be performed at the discretion of your veterinarian. There may be concern that rectal palpation may disrupt a forming hematoma. Transabdominal ultrasound is an easy way to diagnose a bleed that has occurred into the peritoneum (belly). Your veterinarian may also perform an abdominocentesis (belly tap) to sample the fluid bathing the intestines. This sample of fluid may indicate hemorrhage. Although bloodwork may not be indicative in the early stages of hemorrhage, later on it may show indices of blood loss.

Treatment: Treatment for mares with periparturient bleeding is aimed at restoring blood volume and stopping the bleeding. Some veterinarians don’t advocate transporting the mare for concern of destabilizing the clot. If the broodmare has lost a substantial volume of blood to the point of displaying “shocky” signs, then intravenous fluids, as well as blood products may be warranted. In some cases, “permissive hypotension,” or not restoring normal blood pressure may be the aim so that a fibrin clot can form at the tear. Although bleeds into the broad ligament probably contain themselves by the pressure, certain medications can be administered to stimulate coagulation. Since blood is a good culture medium for bacteria to grow in, these mares may be placed on antibiotics so that a hematoma does not become seeded with bacteria and form an abscess. Surgery is not recommended, as it is difficult to identify and ligate (tie off) the torn artery.

Prognosis: Periparturient hemorrhage has not been associated with age or parity. There has been no link between the number of previously delivered foals and the likelihood of a mare experiencing bleeding from the reproductive tract. The prognosis for broodmare survival is good for those mares that are found alive and are treated with veterinary care. Recent studies have shown that periparturient hemorrhage has not been found to decrease fertility in subsequent breedings.

If you have questions about this problem or any other equine health issues please discuss your concerns with your veterinarian or any of the veterinarians at New England Equine.

Karyn Labbe, DVM
Jacqueline Bartol, DVM, DACVIM