Health & Care

What Horse Owners Need to Know About Mosquito-Borne Diseases

22 August 2016
Mary
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Categories: Mosquito Borne Disease
 
No one can deny we live in a rapidly changing world. When you read the headlines and hear news reports, it’s only natural to wonder how close to home those stories will eventually come.
Take, for example, Zika Virus.
The first cases of this mosquito-borne disease that is related to West Nile Virus (WNV) and dengue fever, were diagnosed in the United States in 2015. The main concern for people exposed to Zika is the link to birth defects. While so far, the disease has only been found in humans and primates, it makes sense for horse owners to wonder if Zika could pose a problem in equines. After all, the disease is spread by mosquitoes.
Mosquito on skin
“We don’t yet have information to suggest that horses become infected with Zika or develop disease, and there are certainly horses present in many parts of the world where Zika Virus is present,” observes Martha Mallicote, DVM, a veterinarian in Large Animal Medicine at the University of Florida in Gainesville.
“Most of the human cases that have occurred in the U.S. have been related to travel or intimate contact with someone infected,” she explains. “Theoretically, the conditions are not right for Zika to be an endemic disease here in the U.S., but it would be dangerous to think that it could never happen. The risk for horses to become infected seems fairly minute at this point and the concern for human infections is much more important.”
Even if Zika never becomes an issue in the equine population, there are already enough mosquito-borne diseases that do infect horses.
“We are seeing more mosquito-borne diseases,” says Mallicote. “The range of many mosquito species is wider than previously, due to increased global temperatures, making environments more hospitable to these insects than previously. A great example of this is bluetongue virus in Europe, which attacks ruminants (cattle, sheep, etc.). The range of bluetongue has increased substantially because the mosquitoes are now present in places that they were not previously seen. When the vector is present, then the disease can flourish.”

Other Disease Concerns

There are three mosquito-borne diseases that every horse owner should recognize and vaccinate against: Eastern Equine Encephalitis (EEE), Western Equine Encephalitis (WEE) and West Nile Virus (WNV).
“Other than West Nile, which most horse owners are now aware of, we must also remain committed to continued vaccination against the ‘older’ mosquito-borne encephalitis viruses,” cautions Mallicote.
EEE was first diagnosed in New England in 1831 after the death of some six dozen horses. WEE was first identified in 1930 after a number of horses died in California.
EEE has a mortality rate of 75 to 95%, while the mortality rate for WEE is 20 to 50%. Both are referred to as “sleeping sickness” and are life-threatening viral diseases that attack the central nervous system. EEE and WEE are spread when infected mosquitoes bite horses after having picked up the virus, usually by feeding on an infected bird. There is no cure for either disease.
Compared to EEE and WEE, West Nile is relatively new to the U.S., but is a perfect example of how easily a disease can spread when carried by mosquitoes. WNV originated in Africa and the first U.S. cases were identified in 1999. Since that time, the prevalence and exposure area of WNV has spread significantly in our country.
“We now consider WNV to be a potential risk in almost the entire U.S.,” says Mallicote, adding that WNV has also been reported in most Canadian provinces.
While less likely to result in death to the horse than encephalitis, WNV can require extensive veterinary treatment and affected horses may suffer long-lasting neurologic deficits.

Vaccination is Crucial

“The vaccines that are available are effective and inexpensive. The frequency that those vaccines should be used varies, depending upon region and mosquito presence throughout the year,” says Mallicote.
“In Florida, for example, horses are vaccinated for these diseases two to three times annually. These vaccinations should not be skipped, particularly in areas like the Southeast, Gulf coast, and Southwest where mosquitoes are present much of the year.”
It’s important to discuss vaccination with your veterinarian to come up with a vaccination schedule that fits your particular horse and where you live. Strategic vaccination is very effective when it comes to protecting horses and ensuring immunity to these diseases is at its best during mosquito season.

Fight Back Against Mosquitoes

The war against mosquitoes involves more than vaccination. Take a good look at your property and stable management practices to see how you can markedly reduce exposure to mosquitoes.
“Just as important as vaccination is the use of mosquito control. This will ultimately protect the horses, humans and any other at-risk species that may be present on the farm,” says Mallicote.
Because female mosquitoes lay their eggs in or around water, any standing water is prime mosquito breeding ground, so take steps to eliminate it. Even a tin can or coffee cup that catches rain water can breed disease-vectoring mosquitoes.
Obviously, you need to have water tanks and troughs for horses to drink from, but during mosquito season, these should be dumped and cleaned out every three days. This dramatically helps prevent mosquito larvae in the water from developing into adults.
“Examine the farm for any areas where puddles develop and remain in wet weather conditions. Don’t over-water, as this creates puddles,” advises Mallicote.
Get rid of damp vegetation, brush, weeds and leaves around the barn where mosquitoes can hang out in the heat of the day. This includes cleaning out gutters regularly.
Make your horse less appealing to mosquitoes by taking practical steps:
  • Use equine insect repellent products designed to repel and kill mosquitoes
  • Reduce the amount of body exposure to mosquitoes by using fly sheets and fly masks
  • Whenever possible, avoid turning horses out at dawn and dusk, as these are peak mosquito activity times (One study showed that mosquito activity increased by 500% during a full moon!)
  • Use fans in stalls and throughout the barn to make it more difficult for mosquitoes to land and feed on horses
Horse owners shouldn’t be worried about mosquito-borne diseases, but they should be concerned, aware and proactive.
“We have not yet identified equine cases of some of the more novel mosquito-vectored diseases that are being seen in humans in Florida and the Caribbean,” notes Mallicote, “but that does not mean it won’t occur in the future. Stay tuned on that front.”
06 July 2016
By Cynthia McFarland
       

Prudent Use of Non-Steroidal Anti-inflammatories

22 August 2016
Mary
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Categories: Health & Care

Equine veterinarians commonly prescribe non-steroidal anti-inflammatory drugs (NSAIDS) for horses to treat a myriad of diseases, including colic, respiratory disease, and lameness. NSAIDs are also common in human medicine, and they include such drugs as aspirin and ibuprofen. Most horse owners have probably used NSAIDs too, such as phenylbutazone, or “bute” in one of their horses at some point in time.

“NSAIDs are an invaluable medication and have a multitude of uses in equine medicine. When used appropriately, they are very safe for horses”, said Bradley Nelson, DVM, a Washington State University equine medicine and surgery intern. “Like any medication, however, there can be side effects with NSAID use. It is important that horse owners only use these medications as directed by their veterinarian and when they are aware of the symptoms that horses with NSAID toxicity will demonstrate”.

The positive effects of NSAIDs include pain relief (analgesia) and the reduction of inflammation and fever. When a horse is injured, the body responds by producing inflammation. The horse will then likely have some associated swelling, pain, heat or redness in the affected area. This inflammatory process is a multiple-step pathway in the body and involves many enzymes. NSAIDs work by inhibiting an enzyme called cyclo-oxgenase (COX), which shuts down the pathway and reduces the inflammatory process. Depending upon the NSAID, other positive effects include blood thinning and the reduction of endotoxemia, or the presence of bacterial byproducts in the bloodstream.

The most commonly used NSAIDs are flunixin meglumine (Banamine) and phenylbutazone or “bute”.  Other NSAIDs equine veterinarians use include firocoxib (Equioxx), ketoprofen (Ketofen), etodolac (Etogesic), aspirin, naproxen, and diclofenac (Surpass). Flunixin meglumine is typically given to horses with pain originating from internal organs, such as colic. Phenylbutazone is given for conditions that involve lameness or other problems involved with the horse’s bones, ligaments, and tendons.

“While some NSAIDs have similar potency and activity, they are not interchangeable,”  Nelson said. “For example, although aspirin is the best medication for decreasing excessive blood clotting, it is not usually the best choice for musculoskeletal problems in horses.”

Some NSAIDs are reportedly safer to use than others, but no NSAID is free of risk. When used under recommended dosages, NSAIDs can be a valuable and economic choice for treating many equine diseases, but they can produce side effects when used inappropriately. Moreover, even at recommended doses, some horses can develop adverse effects.

The main side effects seen in horses occur in the gastrointestinal tract and kidneys. The pathways that regulate inflammation also help by producing substances called prostaglandins, which are needed to promote blood flow, increase mucus secretions, and decrease gastric acid secretions. Prolonged high doses of NSAIDs can decrease theses prostaglandins and make the horse susceptible to ulceration.

Clinical signs that can be seen with NSAID toxicity include diarrhea, colic, ulceration throughout the gastrointestinal tract (including the mouth), and weight loss. Kidney toxicity usually develops due to changes in the kidney’s blood flow.  If these medications are given to dehydrated horses or those with preexisting kidney disease, they are more susceptible to toxicity. Clinical signs seen with kidney disease may include increased or decreased urination or straining to urinate. While some of these side effects are mild, severe disease can develop.

“If a horse is on an NSAID medication and develops some of these symptoms, stop giving the NSAID and consult a veterinarian,” Nelson said.

NSAIDs are formulated for horses in several ways, including oral, injectable, or topical. Phenylbutazone and flunixin meglumine come in oral and injectable formulations. A veterinarian will prescribe the most appropriate medication for an individual horse and help owners with the proper way to administer it.

“The injectable formulation should only be injected into the vein, and not in the muscle because tissue damage can result. In addition, the injectable form of flunixin meglumine has been associated with causing serious secondary bacterial infections,” Nelson said. The flunixin meglumine injectable formula is readily absorbed when given orally to the horse and is an excellent alternative to giving it in the muscle if an oral formulation is not available.

“The topical NSAID, Surpass is marketed to be applied on an affected area without exposing the entire body”, he said. “However, this NSAID is typically not as effective as phenylbutazone for moderate to severe lameness.”

He also recommended that typical safe doses for phenylbutazone (for an average 1,000 lb horse) should not exceed 3 grams daily for three days unless on the advice of a veterinarian. After three days, the dose should be decreased to prevent any adverse side effects. In many horses, these lower doses can be safely maintained for longer periods of time, possibly for several months. But some horses are more sensitive to NSAID toxicity and may develop problems with lower doses.

For an average size horse, flunixin meglumine use should not exceed 500mg (10mLs) every 12 hours. These doses are also reserved for more painful conditions and should not be given for more than two days prior to decreasing the dose.

“When these doses of phenylbutazone or flunixin meglumine are exceeded, usually the horse does not benefit from increased pain relief and is much more likely to be harmed by the side effects,” Nelson said. “If a horse is given too much of an NSAID, a veterinarian should be consulted as they can help prevent sever side effects before they occur.”

Generally, horses should not be given NSAIDs if they have preexisting kidney or gastrointestinal disease. But, depending upon the disease, a veterinarian can determine if NSAIDs can safely be used in these cases.

Reprinted from the WSU College of Veterinary Medicine Equine News Winter 2010 issue.

Fighting White Line Disease in Horses

22 August 2016
Mary
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Categories: Hoof Care

fighting-white-line-disease

Your vet and farrier should work together to debride affected tissue and kill the fungi.

Photo: Erica Larson, News Editor

The late famed farrier Burney Chapman long ago stressed the importance of treating white line disease (WLD) aggressively and considering the overall picture rather than just the pathology (disease or damage). The fungi involved in white line disease attack the stratum corneum’s (the outermost layer of the epidermis) intermediate layer—called the stratum medium—and digest the membrane responsible for securing the hoof wall to the sensitive areas deeper in the center of the hoof. The end result is that air and debris, instead of cartilage, line and separate the living tissue layers. Tapping the hoof wall in these cases creates a hollow sound, which is why some call WLD hollow hoof syndrome.

This disease’s complex management and treatment aspects are probably best narrowed to three components: hoof care, diet, and environment. Ignoring any one of these can cause an otherwise good plan to fail.

Hoof care

A veterinarian and farrier team is best suited to address individual WLD cases, so we will cover only general principles here. First, the affected area must be opened and dried out with a topical product such as chlorine dioxide or Gentian violet. The degree of damage will dictate the amount of hoof wall debridement required, and care must be exercised not to damage healthy tissue or create more damage to the wall than is prudent—the horse still must bear weight comfortably. Treatment is aimed at killing fungi or fungal spores rather than trying to burn or harden sensitive tissue, as the latter actually slows the overall healing process. 

Second, the vet-farrier team should provide coffin bone support either by casting or shoeing and remove flares, seedy toe, and lamellar wedges (abnormal horn structure that develops within the lamellar region of the foot) to establish a proper weight-bearing structure for the horse. Finally—a step that’s often overlooked—your farrier should trim and shoe the horse to achieve a heel-first landing and proper weight bearing over the solar surface of the foot. 

Diet

We know many horses that suffer from WLD are insulin resistant or have equine metabolic syndrome, and we know forage type, quality, and quantity directly influence insulin levels. So we must consider feed types and sources for affected horses. Insulin resistance, for instance, can cause blood vessels at the extremities to contract, potentially compromising blood flow to the foot’s tissues, so we’d focus on a low-calorie/low-carb diet. 

Environment

Horses with poor blood circulation in their feet require adequate exercise to stimulate blood flow, so turnout and pasture time are critical to overall success. Stalling rather than turning out in a paddock environment may be the single biggest factor compounding pathogen growth and damage associated with white line disease. Horses moving even in small paddocks are much better equipped to battle opportunistic hoof pathogens than those living stationary in a stall environment. 

Hoof form and function has developed into an entire field of study and, as we gain knowledge pertaining to current practices, we have begun to rethink our current animal husbandry guidelines or practices. Researchers are examining how bedding types and footing (e.g., pea gravel vs. sand) affect foot growth and function. Results from one study showed that changes in confinement and footing materials were superior to current white line disease and laminitis treatment techniques. 

There is much more to white line disease than hoof wall separation or an ideal environment for fungi to become pathogenic. We need to realize that fungi are opportunistic and will continue to cause problems until we debride and treat the affected areas. While it’s still open for some debate, many researchers generally believe WLD is tied to the way we house and care for our horses. Volumes are being written on this subject, and the answers we seek will affect the future care and husbandry of our horses.

Preston Hickman, DVM