October 2022 Equine Disease Quarterly

COMMENTARY - CELEBRATING 30 YEARS

This issue celebrates the 30-year anniversary of the Equine Disease Quarterly. The EDQ was first published in 1992 with a goal of providing accurate and current information on a variety of diseases affecting horses worldwide. The Quarterly has survived and thrived, thanks to the support of donors who helped keep the publication accessible as well as the many authors who have contributed their time and knowledge to the articles. Looking at the many topics covered over the last 30 years, one can see a snapshot of how our knowledge of equine health and disease has progressed. Of equal importance, articles emphasizing diseases of significance have been highlighted with regularity. In 1992, topics such as rabies, equine herpesvirus and leptospirosis were discussed. These diseases remain a continued concern today, and it is only through the appropriate vaccination, biosecurity and vigilance that losses due to these diseases are controlled.

In contrast, articles on equine rotavirus in the 1990s focused on neonatal diarrhea, morbidity and mortality associated with equine rotavirus A. Today we have added another equine rotavirus to our knowledge base, equine rotavirus B. Only recently identified as a cause of equine neonatal diarrhea, this new virus highlights the need for continued vigilance and communication to identify and publicize the emergence of infectious diseases.

Certain topics have recurred throughout the Quarterly, highlighting their continued importance to the equine community. These have often included communicable diseases such as equine infectious anemia, African horse sickness, equine viral arteritis and contagious equine metritis. These diseases must be continually recognized for their importance to the worldwide equine population, both from a health as well as

equine movement perspective. Similarly, topics in equine reproduction, biosecurity and toxicology have been common themes, highlighting the importance of these areas to the equine industry.

The progression of scientific knowledge has been of equal interest over the last 30 years. The EDQ has witnessed the introduction and spread of West Nile virus through North America, a disease that can now be well controlled with vaccination. Theiler’s disease, or equine serum hepatitis, a disease of acute liver failure in horses, progressed from a condition of unknown pathogenesis to being strongly linked to equine parvovirus-hepatitis virus. The search for the cause of this disease has additionally led to the discovery of multiple new equine viruses, as well as wide-reaching changes in the screening and management of equine plasma donors. Mare reproductive loss syndrome, which caused massive devastation to the equine industry, is now largely prevented with pasture management and monitoring. Equine metabolic syndrome and Cushing’s disease/pituitary pars intermedia dysfunction are two additional areas which have shown significant advances in our understanding, diagnosis and treatment of endocrine diseases. Veterinary researchers have shown a large percentage of laminitis in horses

Thank you for enrolling in our online Equine Disease Quarterly. Please feel free to share this publication in the equine community. Others may enroll visiting https://tinyurl.com/EDQemail. You may also email EDQ@uky.edu to be added to the listserv or for additional questions.

A

FUNDED

EQUINE DISEASE QUARTERLY

Celebrating 30 Years (Continued)

can be linked to these diseases and the testing options for both conditions are continuously evolving.

The emergence of genetics and modern drug testing have shown how advances in basic science have impacted equine research. We now have more articles dedicated to advances in testing for diseases, with PCR becoming readily available, affordable and accurate. Equine imaging has appeared to evolve daily with the use of computed tomography, magnetic resonance imaging and positron emission tomography. These modalities have allowed significant developments in the diagnosis and understanding of musculoskeletal and neurologic diseases.

We have watched carefully as the emergence of anthelmintic resistant equine intestinal parasites have been documented, resulting in shifts in the recommendations on how to both monitor and control parasites in equine herds. This has highlighted the importance and re-emergence of interest in Strongylus vulgaris associated arteritis and subsequent colic a disease that became a rarity in many locations following the development and widespread use of anti-parasitic drugs.

Despite enormous advances in the understanding, treatment and prevention of equine diseases, there are consistent threats to the health of the horse. The management of disease spread through monitoring, vaccination and controlled movement remains of the utmost importance. The Equine Disease Quarterly owes its success to the continued commitment of the equine community in understanding these diseases. We thank all our readers, authors and editors and look forward to the next several decades.

Rebecca Ruby, BVSc, DAVCP, DACVIM-LAIM (859)-257-8283

Rebecca.ruby@uky.edu

Veterinary Diagnostic Laboratory University of Kentucky, Lexington KY

EDITORS

Alan Loynachan Rebecca Ruby Lutz Goehring Allen Page

STAFF Holly Wiemers Anita Hatchet

INTERNATIONAL

International Report on Equine Infectious Diseases

The following data were primarily provided by the University of Kentucky Veterinary Diagnostic Laboratory and Equine Diagnostic Solutions, Inc., both located in Lexington, Kentucky, USA; International Thoroughbred Breeders Federation; International Collating Centre in Newmarket, United Kingdom; Equine Disease Communication Center of the American Association of Equine Practitioners; and other sources. This report is retrospective and does not claim to be complete. However, it provides an indication of heightened activity of contagious or environment-linked diseases among equids. Reports of equine infectious diseases were not received from Central or South America, most of Africa (with exception of the Republic of South Africa) and from most of Asia (with exceptions of Japan and Kazakhstan).

Strangles was reported from several regions across North America and Europe, including the British Isles. For this reporting period, the Lexingtonbased diagnostic laboratories (UKVDL and EDS) reported more than 200 positive nasal swabs for S. equi subsp equi; samples were received from the Atlantic coast, Midwest and Mountain West regions of the USA. EDCC reported increased frequencies of strangles from Florida and Michigan.

Few outbreaks of equine influenza virus were reported from regions of North America and various parts of Europe, primarily continental Europe and Scandinavia. Noteworthy for this quarter was an outbreak of EI among horses owned by the United States Bureau of Land Management (typically captive mustangs) in Canon City, Colorado. Between April 23 and May 10, more than 100 adult horses and nearly 20 foals died due to severe pneumonia associated with EI, often with S. equi subsp zooepidemicus co-infection.

Equine herpes virus associated respiratory disease, caused by either EHV-4 or 1, was infrequently reported in the USA and more frequently identified from operations in the UK, Ireland and continental Europe.

Despite pregnant mares in the Northern Hemisphere being in their vulnerable period for EHV abortion, few (mostly single) cases of abortions were reported from the Midwest region of the USA, British Isles, continental Europe and Japan. Incidentally, single EHV-4-associated abortions were also reported. Reports of equid herpesvirus-associated myeloencephalopathy continued throughout North America. The majority of outbreaks were reported in states

from the U.S. Pacific coast, and fewer outbreaks from the Midwest and Atlantic coast states; one outbreak was identified on a racetrack in New York state, USA. Six outbreaks of EHM were reported across the British Isles and central Europe, with one outbreak south of the Alps in Italy. A single confirmed case of EHM was reported from South Africa.

A little more than 30 equine infectious anemia virus positive animals (with rarely two or more animals testing positive on a farm) were identified in North America. One case was reported from Italy.

Four cases of Eastern equine encephalitis were reported from different premises in Florida, USA. Encephalitis caused by flaviviruses were reported from Australia, South Africa (one case) and Tennessee, USA (one case). South Africa also reported several outbreaks of equine encephalosis during the second quarter. African horse sickness virus is also endemic in this area. Both diseases have a seasonal occurrence coinciding with vector (Culicoides spp.) activity; hence, AHS outbreaks were reported (with exception from the controlled Western Cape province) during this quarter.

Miscellaneous: Contagious equine metritis: Fourteen premises, involving mostly single cases, tested positive for Taylorella equigenitalis in Germany and France. Rotavirus: Following the discovery of group B rotavirus during the 2021 foaling season, the Lexington, KY, USA area braced itself for recurring disease in the 2022 foaling season. As a result, EDS received more than 300 foal fecal samples (>95% from Kentucky) for equine rotavirus group A and B testing. About 100 samples tested positive (70 samples from Kentucky) with a noteworthy dichotomy of both viruses being detected through the reporting period. Out of 49 samples in April, 44 were positive for rotavirus group B and only five for rotavirus group A. The group incidence for June was reversed with 38 samples positive for group A and no samples positive for group B.

Lutz Goehring DVM, MS, Ph.D 1(859) 257-4757 l.goehring@uky.edu Gluck Equine Research Center University of Kentucky

Material published in the Quarterly is not subject to copyright. Permission is therefore granted to reproduce articles, although acknowledgment of the source and author is requested.

Maxwell H.

Gluck

Equine Research Center Lexington, Kentucky USA, 40546-0099

Telephone (859) 257-4757 Fax (859) 257-8542 gluck.ca.uky.edu

KENTUCKY

Equine Paranasal Sinus Disease

The equine paranasal sinuses are a complex network of paired air-filled structures located in the skull that include the frontal, maxillary (rostral and caudal), conchal (dorsal and ventral) and sphenopalatine sinuses. Horses with disease of the sinuses may present with abnormal airway noise, nasal discharge, facial swelling and, in some cases, increased tearing and bulging of an eye. Diseases within the sinuses can occur via two main routes, either through the nasal passages or by communication of the upper cheek teeth to the maxillary sinus. Diseases of the sinus are typically diagnosed via either endoscopy, radiography or computed tomography. Treatment of sinus disease is based on the primary diagnosis and may involve trephination (drilling) into the sinus to remove fluid and flush out the affected area, surgery to remove a cyst or mass or removal of teeth if dental disease is the primary cause of infection.

An eight-year retrospective at the University of Kentucky Veterinary Diagnostic Laboratory identified 79 cases with significant equine paranasal sinus pathology. Cases were submitted either as a biopsy from a live horse (60 cases), postmortem examination (17 cases) or cytology sample (two cases). Common reasons for case submission included nasal discharge, facial asymmetry or identification of a mass on radiography or computed tomography.

Where reported, the average age was 11 years old (range of 1 day to 25 years). There was a relatively equal gender distribution (36 males and 37 females) and the most common breeds included Thoroughbreds (n=42) and Warmbloods (n=9). Cases were localized to the left (n= 28), right (n=33) or both sides (n=2) of the skull. Forty-two cases involved one sinus and 21 cases involved multiple sinuses. Distribution of sinuses was as follows: frontal (n=33), maxillary (n=32), rostral maxillary (n=8), caudal maxillary (n=7), conchal (n=5), sphenopalatine (n=6) and ethmoid (n=1). Disease processes were categorized as sinusitis (n= 39), paranasal sinus cyst (n=18), ethmoid hematoma (n=9), lesions secondary to ongoing dental disease (n=6), neoplasia (n=4), aneurysmal bone cyst (n=2) or other (n=1).

Sinusitis comprised the majority of cases, and infectious agents were cultured or microscopically identified in 10 cases. Seven cases identified bacterial pathogens (Escherichia coli, Streptococcus zooepidemicus and Fusobacterium necrophorum) and three cases identified pathogenic fungus (Aspergillus sp.). Formalinfixed tissues were exclusively submitted in

most cases, which inhibited microbial culture. Case histories tended to indicate the presence of chronic infections that extended from months to years, and the horses often had a long history of antimicrobial treatment. Five cases reported tooth removal four months to one year prior with subsequent development of sinusitis. The frontal and maxillary sinuses were the most reported locations.

Paranasal sinus cysts occurred most in horses younger than 4. Sixteen cases were diagnosed from biopsy submissions and two on postmortem examination. Postmortem cases indicated a chronic history that failed to respond to treatment or invasion of surrounding bone and dental tissue. Frontal and maxillary paranasal sinuses were the most common locations.

Ethmoid hematomas, now referred to as equine progressive hemorrhagic nasal polyps, are a welldocumented entity composed of proliferative granulation tissue (proud flesh) with variable inflammation and chronic hemorrhage. Ethmoid hematomas typically arise from the ethmoidal submucosa but can arise from anywhere and may extend into the paranasal sinuses. These are non-cancerous masses that progress in size over time and are often associated with bloodtinged nasal discharge and reduced airflow. In this retrospective, all horses were over 6 years old except one yearling.

In six cases, oral pathology with extension to the paranasal sinuses was reported. These included odontoma (a benign dental tumor; n=3), odontogenic hamartoma (a benign dental proliferation; n=1) and orosinus diastema (communication between the tooth socket and sinus cavity; n=2). Finally, single cases of neoplasia (cancer) were comprised of a neurogenic carcinoma, osteoma, poorly differentiated sarcoma and adenocarcinoma. Aneurysmal bone cysts were identified in a yearling and perinate. One case was determined to be a chronic reactive process with the inciting cause no longer apparent.

In summary, diseases of the equine paranasal sinuses continue to be a common reason for biopsy and a relatively uncommon cause of euthanasia. Sinusitis is the most recognized condition with a combination of bacteria and/or fungal agents often associated with infection.

Jennifer Janes, DVM, PhD, DACVP (859)-257-8283

Jennifer.janes@uky.edu

Veterinary Diagnostic Laboratory University of Kentucky, Lexington KY

Computed tomography of the head showing loss of air filled spaces and bone within the sinuses.

NATIONAL

Standing Surgery in Horses: An Update

Waking up from general anesthesia is one of the most dangerous parts of equine surgery. Many drugs used for horse anesthesia produce weakness and disorientation, which makes standing after surgery challenging. In a worst-case scenario, a horse may catastrophically injure themselves after surgery and require humane euthanasia. While many methods have been developed to mitigate the risk of anesthesia in the horse, the risks of general anesthesia must always be considered when making surgical plans.

One method to avoid risks associated with recovery from general anesthesia is to perform the surgery utilizing standing sedation. With advances in sedative and local anesthetic techniques, many procedures that were once only performed under general anesthesia can now be performed safely while the patient is standing. This eliminates the need for horses to rise to a standing position at the conclusion of the procedure and may allow for the use of minimally invasive surgical approaches as well as improved visualization of the surgical site. This article highlights procedures that have recently been reported under standing sedation.

Several types of fracture repairs have been performed in the standing position. One of the most common types of fracture treated under standing sedation is a nondisplaced or incomplete fracture of the lower limb. This is ideal for standing repair because the fracture fragments are still very close together and do not require much manipulation for realignment. Recently, a pastern joint arthrodesis (joint fusion procedure) was also conducted. This technique may be especially important for larger draft horses, which have increased anesthetic risk.

Arthroscopy (using a small video camera to look inside a joint) under standing sedation is now more commonly performed and takes advantage of a small, single use camera. These camera systems have been used to explore several joints, including the stifle, fetlock and even cervical facet joints in the neck.

The upper airway is highly accessible in a standing horse, and sinus surgeries are routinely performed under standing sedation to improve visualization and hemostasis. Recently, small cameras have been used to improve visualization of the sinuses while working through a very small hole in the facial bones. Other upper airway surgeries, such as the laryngeal tie back and laser vocal cordectomies for roaring, are commonly performed under standing sedation. This is again especially advantageous in large draft horses often afflicted with this condition.

Ceratohyoidectomy, a less commonly performed upper airway surgery for the treatment of temporohyoid osteopathy, was recently performed under standing sedation. Ataxia (wobbliness) is one clinical presentation of THO, and the use of standing sedation may be valuable to avoid additional instability associated with general anesthesia.

While many types of abdominal surgery still require the horse to be under general anesthesia, several standing abdominal surgeries are considered relatively routine. These include laparoscopic ovariectomy (removal of an ovary) or cryptorchidectomy (removal of an undescended abdominal testicle). Recently, there have been more reports of colic surgeries performed under standing sedation; these range from laparoscopic exploratory surgery, biopsy collection, intestinal displacement correction and even intestinal resection and anastomosis. However, major difficulties with these surgeries can include keeping the patient stable and comfortable enough to remain standing throughout the procedure.

Standing surgery is not without drawbacks or additional complications. Because the patient is conscious for the procedure, they may continue to move despite sedation and analgesia. Additionally, the patient must remain standing, which may be difficult for horses with underlying orthopedic disease. Lastly, standing procedures often require extensive set up to ensure that a sterile surgical field is maintained, and they have a significant personnel requirement.

The number and types of standing surgical procedures that can be safely completed in the horse continues to grow on a regular basis. Standing surgery allows for expanded treatment options that may not have been previously possible due to risks associated with general anesthesia. While there are advantages of standing surgery, each case should be evaluated on an individual basis. If you have questions regarding the possibility of having a surgery performed under standing sedation, contact a large animal surgeon boarded by the American College of Veterinary Surgeons to discuss options.

Kayla Le, DVM, DACVS-LA

608 263 7600 kmle@wisc.edu

University of Wisconsin Madison Madison, WI

Equine Allergy Testing

Horses develop a number of conditions attributed to allergies, but two of the more common are pruritus (itching), which may manifest as rubbing or biting, and recurrent hives. Although biting insects account for many of these allergies, they can also be caused by sensitivities to environmental allergens such as grass, trees, weeds and mites. Environmental allergens should be considered when clinical signs are seasonal and persistent, despite elimination of common causes (e.g., biting flies).

If an environmental allergy is suspected, allergy testing can be a helpful tool to identify the cause. Allergy testing can be performed via two different methods. The first is known as serum or in vitro allergy testing. This test is performed by drawing a blood sample and sending it to a laboratory for interpretation. This route of testing offers several advantages in that a simple blood collection is all that is needed; sedation is not required and stoppage of ongoing treatments, such as antihistamines or steroids, is typically not necessary. The second method is performed via an intradermal skin test. An intradermal skin test requires the horse’s neck to be shaved and multiple injections of different known allergens to be administered under the skin and monitored for allergic reactions. This form of testing offers several advantages over blood testing. Specifically, it can test for more allergens, reactions are detected in the skin where the problem is manifesting and the results are immediately available, unlike blood results that may take a week to receive.

It is important to remember that there are several major limitations regardless of the test performed. First, neither method definitively confirms nor diagnoses a patient with an environmental allergy, because both methods can have false positive and false negative test results. The results should be considered as a guide of potential causes but must be interpreted in context with the horse’s

clinical signs, region where it lives, seasonality, abundancy of the allergen in the environment and severity of the allergenic reaction. Avoidance to suspected allergens can be impractical and nearly impossible in some circumstances, because most pollens or allergens are ubiquitous or can travel great distances in the air. To use an oak allergy as an example, unless you remove every oak tree for 100 miles around, then removal of oak trees from the pasture where the horse is housed is futile. Finally, the testing modality does not determine future treatment success. To date, studies have not shown one method provides better results when used to guide desensitization therapy (allergenspecific immunotherapy or allergy shots).

The main reason for performing allergy tests is to identify possible allergens for inclusion in allergen-specific immunotherapy. These injections are initially given frequently and then spaced over time as the concentration and amount of the allergens is increased. Allergy shots have been shown in numerous studies to be helpful for alleviating allergic conditions in the horse that are triggered by environmental allergens. Most horses that show a response to therapy do so in the first six to 12 months. As previously stated, the route of testing does not impact therapeutic success, but client adherence to treatment protocol is of utmost importance. Given the importance of client participation with allergen-specific immunotherapy, sufficient time should be spent educating and training owners on how to administer injections and identify adverse reactions and therapeutic responses.

Darren Berger, DVM, DACVD 515-294-8316 djberger@iastate.edu Iowa State University Ames, IA

A PUBLICATION BY THE UNIVERSITY OF KENTUCKY DEPARTMENT OF VETERINARY SCIENCE MAXWELL H. GLUCK EQUINE RESEARCH CENTER FUNDED BY: EQUUS / STANDARDBRED STATION, INC. M&J INSURANCE

The University of Kentucky is an equal opportunity organization.