Merck Animal Health Equine Horse Owner Spotlight: Spring 2023

Spotlight HORSE HEALTH

5 (Surprising?!) Warm Weather Health Facts

Test your equine health knowledge and ensure your horse is ready to start the season well.

You probably know that some equine health risks ramp up along with show competition and rising temperatures. But the risks might not be what you think. Check out the facts below to shed some (sun)light on vaccination and deworming strategies to better protect your horse.

Strangles, equine flu and EHV-4 are the most common infectious diseases in the spring.

Strangles tops the list of springtime infections, with more and more horses being affected each year, according to a new study.1 (Get more strangles info on pages 8 and 9.) Equine flu and equine herpesvirus type 4 (EHV-4) round out the top three diseases for the season, with EHV-4 also coming in as the most common infectious upper respiratory disease overall.2 All three of these upper respiratory infections cause similar clinical signs in horses, including nasal discharge, fever and lethargy. Working with your veterinarian to get a proper diagnosis is essential so you can choose the most effective treatment and biosecurity measures.

Be prepared

When choosing an influenza vaccine, ensure it is updated to account for the Florida ’13 equine influenza strain, which is the most current.

Both traveling and non-traveling horses face similar risks for infectious diseases.

Heading to competitions increases a horse’s risk of

contracting infectious diseases because the stress of travel can weaken the immune system. Still, data from the Equine Respiratory Biosurveillance Program shows that a majority of horses infected with the three most common infectious diseases did not travel. See the table at right for more detail, including how other demographics impact a horse’s risk for infection.

Be prepared

The need for vaccination against strangles, equine flu and EHV-1&4 is determined in part by your horse’s age and lifestyle. Consult with your veterinarian about the vaccinations that make sense for your horse’s situation.

One shot may not be enough to protect against mosquito-borne diseases.

Many people assume that getting a so-called encephalitis shot protects horses against West Nile virus, Eastern equine encephalomyelitis (EEE) and Western equine encephalomyelitis (WEE). In fact, these are three distinct diseases, and some vaccines protect against only one or two. This misunderstanding could be why cases of West Nile and EEE/WEE are on the rise across the country, but especially in Northern and East Coast states. Some veterinarians believe horses are undervaccinated against the diseases, even though the American Association of Equine Practitioners recommends that every horse, regardless of location or travel status, be vaccinated because of the diseases’ high mortality rate.

Key Characteristics for Top Three Infectious Diseases (July – December 2022)2

Be prepared

Even though every horse should be vaccinated against West Nile and EEE/WEE, travel still impacts vaccination timing. Horses traveling to areas that experience year round mosquito activity, like the Southern United States, should consider a West Nile and EEE/WEE booster every 6 months. Unvaccinated Horses should receive an initial vaccination for West Nile and EEE/WEE that’s followed by a booster three to four weeks later.

4

Parasite control is not about completely eradicating parasites from your horse.

Horses are exposed to internal parasites by grazing on pasture that contains infective worm larvae. All horses that graze parasite-infested pastures develop parasites in their digestive systems. With this inevitability, the primary goal of a strategic parasite control program is to control parasite eggs that horses shed in fecal matter and limit parasite infections so your horse can avoid illness.

Be prepared

Work with your veterinarian to get a fecal egg count performed on your horse. This allows you to understand which intestinal parasites are present. Based on the results, your veterinarian can help you select which dewormer your horse needs and when. Avoiding unnecessary use of dewormers helps slow parasite resistance.

Natural approaches round out disease and parasite control.

Biosecurity measures and non-chemical strategies help protect your horse, as well as the horses that may come and go from your stable.

To reduce parasite egg and larvae buildup in the environment, implement the options that work for you:

• Feed hay and grain in raised containers.

• Clean water sources regularly to prevent fecal contamination.

• Remove manure from pastures and paddocks at least twice weekly.

• Compost manure.

• Don’t overstock pastures or allow pastures to become overgrazed.

• Cross-graze pastures with other ruminant species, preferably sheep.

• Keep pastures mowed.

• During hot, dry weather, harrow or rake pastures to disperse manure piles and expose larvae to sun. Rest the pasture a minimum of four weeks after harrowing.

• Harvest a hay crop off pastures.

• Plant an annual crop such as winter wheat.

Infectious diseases can spread quickly, so taking preventive measures helps keep them at bay:

• Quarantine new horses.

• Isolate sick horses.

• Regularly disinfect equipment.

• Maintain good hand hygiene.

• Monitor your horse’s temperature, especially when traveling.

• Avoid sharing tack.

• Limit nose-to-nose contact between horses.

Be prepared

Even if you’re not able to implement all the nonchemical parasite-control measures, practice the ones that make sense for your farm. When it comes to biosecurity measures, they make a great defense and an even better offense. After all, preventing the spread of infectious disease is better than trying to contain it.

With these (lesser known) facts, you and your horse can confidently get out to enjoy some sunshine-filled riding. A little preparation and proactive communication with your veterinarian helps ensure a season full of only good surprises.

1. Jaramillo-Morales, C.; James, K.; Barnum, S.; Vaala, W.; Chappell, D.E.; Schneider, C.; Craig, B.; Bain, F.; Barnett, D.C.; Gaughan, E.; et al. Voluntary Biosurveillance of Streptococcus equi Subsp. equi in Nasal Secretions of 9409 Equids with Upper Airway Infection in the USA. Vet. Sci. 2023, 10, 78. https://doi.org/10.3390/vetsci10020078

2. Merck Animal Health and University of California, Davis (Nicola Pusterla). Infectious Upper Respiratory Disease Surveillance Program. Ongoing research 2008–present.

UHVRC Awards 7,000 Vaccine Doses and Microchips for Horses in Need

This Old Horse, a Hastings, Minnesota-based provider of rescue, retirement and recovery support for older and special-needs horses through their farms and foster network, is among 223 nonprofit aftercare facilities to receive complimentary vaccines and microchips through the Unwanted Horse Veterinary Relief Campaign (UHVRC).

The longstanding partnership between Merck Animal Health and the American Association of Equine Practitioners provided 7,000 of the company’s HomeAgain® TempScan® Microchips and 7,000 doses of both Prestige® 5 + WNV and EquiRab® to help protect horses against Eastern and Western equine encephalomyelitis, equine rhinopneumonitis (EHV-1 and EHV4), West Nile virus, equine influenza, tetanus and rabies. Since inception of the UHVRC in 2008, Merck Animal Health has generously provided more than 53,000 doses of core vaccines valued at over $1 million.

“On any given day, we support more than 200 horses in our facilities, all of them requiring regular vaccination as part of their ongoing health maintenance,” said Nancy Turner, founder and president of This Old Horse. “Microchipping plays a big role in our safety net program to assure that any of ‘our’ horses placed in adoptive homes can always find their way back home if their circumstances change. The generous award of vaccines and microchips will reduce our health and safety expenses for each horse, enabling the savings to be reallocated to help horses in other ways.”

Dr. Dale Magnusson of Magnusson Veterinary Services in Hudson, Wisconsin, coordinated This Old Horse’s application for free vaccines and microchips.

Bunny, a 27-year-old American Paint Horse who was a successful show horse and broodmare until her retirement, is among the equine residents at This Old Horse to benefit from Merck Animal Health vaccines and microchips through the UHVRC.

The annual application deadline is Feb. 1.

Learn more at aaep.org/horse-owners/unwanted-horseveterinary-relief-campaign.

I’m hearing about more cases of equine flu. Why are more horses being infected?

By Duane E. Chappell, DVM, Merck Animal Health

Simply put, the equine influenza virus is evolving. Just like human flu, equine flu changes but at a much slower rate. Through the Merck Animal Health Equine Respiratory Biosurveillance Program, researchers found that horses involved in a 2013 influenza outbreak were infected with a new flu strain named Florida ’13.1

To reach this conclusion, researchers compared various equine influenza vaccine strains, revealing that the Florida ’13 strain differed significantly from older strains including Ohio ’03 and Kentucky ’97. Ongoing research through the Equine Respiratory Biosurveillance Program at the time of this article shows Florida ’13 is the vaccine strain closest to today’s equine influenza virus.2

In response to these findings, Merck Animal Health updated the PRESTIGE® influenza vaccines to account for the Florida ’13 strain. PRESTIGE® vaccines are the only vaccines available that contain the Florida ’13 vaccine strain.

Importance of updated vaccines

The equine influenza virus infects horses by binding to respiratory cells, and vaccines work by producing antibodies that bind to key sites on the virus, preventing cell infection. Mutations in an influenza virus decrease a vaccine’s ability to bind to these key sites, leading to reduction in or a total lack of protection.

Work with your veterinarian to determine the right time to protect your horses with an updated vaccine that includes Florida ’13. You can also implement a few straightforward biosecurity measures to help reduce horses’ risk of influenza.

Remember that even horses that don’t travel are still susceptible to equine flu, especially if they live at a barn with other horses coming and going.

To help protect time in the saddle—and most importantly, horses—remember these main points:

• The EIV virus is changing.

• Not all vaccines are created equally.

• Biosecurity measures help reduce horses’ risk (see examples on page 4).

Watch this video to see how a changing virus affects vaccination effectiveness.

1. Data on file, Merck Animal Health.

2. Merck Animal Health and University of California, Davis (Nicola Pusterla). Infectious Upper Respiratory Disease Surveillance Program. Ongoing research 2008–present.

COMBATTING AN UPTICK IN STRANGLES

Strangles, technically referred to as Streptococcus equi subspecies equi, is a common highly contagious bacterial infection. A recent study shows cases of strangles are increasing. Help protect your horse from this ubiquitous disease by learning the signs and strategies for decreasing the likelihood of infection.

How Horses Are Infected

• While no regional differences were observed, strangles is more common in the spring and winter (though positive cases were reported during all four seasons).1

• Strangles is spread through direct contact with infected horses, contaminated surfaces and food and water sources.

• Infected horses can spread disease without showing clinical signs.

• Horses can shed the disease for an undetermined period of time, infecting other horses even after clinical signs have resolved.

Signs of Infection

Signs of strangles are similar to those of other upper respiratory infections, so be sure to work with your veterinarian to get a diagnosis to determine appropriate treatment and isolation measures.1

• Fever (may precede other signs by 24 – 48 hours)

• Abscesses in throatlatch and below the jaw (the mandibular lymph nodes)

• Nasal discharge (often thick white/yellow mucus)

• Swelling of the throat

• Difficulty swallowing

• Wheezing

• Cough

1. Jaramillo-Morales, C.; James, K.; Barnum, S.; Vaala, W.; Chappell, D.E.; Schneider, C.; Craig, B.; Bain, F.; Barnett, D.C.; Gaughan, E.; et al. Voluntary Biosurveillance of Streptococcus equi Subsp. equi in Nasal Secretions of 9409 Equids with Upper Airway Infection in the USA. Vet. Sci. 2023, 10, 78. https://doi.org/10.3390/vetsci10020078

How Strangles Is Diagnosed

Diagnosis is performed with nasal swab/lavage or pus from abscess submitted to a laboratory for polymerase-chain reaction (PCR) testing and/or bacterial culture.

Recovery

• Strangles is rarely fatal, with most horses fully recovering in three to four weeks with few complications.

• Antibiotics may be used in severe cases, but most horses recover without them.

• Recovered horses can become carriers and shed the bacteria intermittently.

• Infected horses may develop long-term immunity.

Ways to Help Prevent an Outbreak

While isolation of horses with strangles remains the best method to prevent disease spread, there are biosecurity measures you can take to help prevent it before a case occurs.

• Isolate all new horses, as well as those horses returning from travel at least 7 to 14 days.

• Avoid nose-to-nose contact among horses.

• Check temperatures at least once daily, preferably twice (normal = 99o – 101o F).

• Isolate any horse with elevated temperature and/or unprovoked coughing.

• Do not share tack, water buckets or feed sources.

• Practice good hand hygiene (hand sanitizers in absence of soap and water).

• Clean and disinfect hauling equipment like trailers after each use.