Voluntary Surveillance Program for Equine Influenza Virus in the United States during 2008-2021.

A voluntary upper respiratory biosurveillance program in the USA received 9740 nasal swab submissions during the years 2008-2021 from 333 veterinarians and veterinary clinics. The nasal swabs were submitted for qPCR testing for six common upper respiratory pathogens:equine influenza virus (EIV), equine herpesvirus-1 (EHV-1), equine herpesvirus-4 (EHV-4), Streptococcus equi subspecies equi (S. equi), equine rhinitis A virus (ERAV), and equine rhinitis B virus (ERBV). Additional testing was performed for equine gamma herpesvirus-2 (EHV-2) and equine gamma herpesvirus-5 (EHV-5) and the results are reported. Basic frequency statistics and multivariate logistic regression models were utilized to determine the associations between risk factors and EIV positivity. The EIV qPCR-positivity rate was 9.9%. Equids less than 9 years of age with a recent history of travel and seasonal occurrence in winter and spring were the most common population that were qPCR positive for EIV. This ongoing biosurveillance program emphasizes the need for molecular testing for pathogen identification, which is critical for decisions associated with therapeutics and biosecurity intervention for health management and vaccine evaluations and development.

Voluntary Biosurveillance of Streptococcus equi Subsp. equi in Nasal Secretions of 9409 Equids with Upper Airway Infection in the USA.

This study aimed to describe selected epidemiological aspects of horses with acute onset of fever and respiratory signs testing qPCR-positive for S. equi and to determine the effect of vaccination against S. equi on qPCR status. Horses with acute onset of fever and respiratory signs from all regions of the United States were included in a voluntary biosurveillance program from 2008 to 2020 and nasal secretions were tested via qPCR for S. equi and common respiratory viruses. A total of 715/9409 equids (7.6%) tested qPCR-positive for S. equi, with 226 horses showing coinfections with EIV, EHV-1, EHV-4, and ERBV. The median age for the S. equi qPCR-positive horses was 8 ± 4 years and there was significant difference when compared to the median age of the S. equi qPCR-negative horses (6 ± 2 years; p = 0.004). Quarter Horse, Warmblood, and Thoroughbred were the more frequent breed in this horse population, and these breeds were more likely to test qPCR-positive for S. equi compared to other breeds. There was not statistical difference for sex between S. equi qPCR-positive and qPCR-negative horses. Horses used for competition and ranch/farm use were more likely to test qPCR-positive for S. equi (p = 0.006). Horses that tested S. equi qPCR-positive were more likely to display nasal discharge, fever, lethargy, anorexia, and ocular discharge compared to horses that tested S. equi qPCR-negative (p = 0.001). Vaccination against S. equi was associated with a lower frequency of S. equi qPCR-positive status.

Pharmacokinetics of a FDA-labeled dose of diclazuril administered orally once weekly to adult horses.

Equine protozoal myeloencephalitis (EPM) has remained a devastating neurological disease of the Americas, especially in young performance horses. Prophylactic treatment strategies with diclazuril have shown to reduce seroprevalence and titer levels to Sarcocystis neurona in healthy horses continuously exposed to the apicomplexan parasite. The goal of this study was to determine if the FDA-labeled dose of 1 mg/kg of 1.56% diclazuril (ProtazilTM) given once weekly to healthy adult horses would achieve steady-state concentrations in plasma known to be inhibitory to S. neurona in cell culture. Five individual diclazuril doses were administered at weekly intervals to 8 adult horses. Blood was collected via venipuncture immediately before (trough concentration) and 10 hours after (peak concentration) each diclazuril administration. Following the fifth dose, additional blood samples were collected every 24 hours after the peak blood collection for 7 days. All plasma samples were analyzed by high-pressure liquid chromatography. The pharmacokinetic analysis was performed using a nonlinear mixed effects model. The mean population-derived peak concentration was 264 ng/mL and the mean terminal half-life was 3.6 days. Thus, the oral administration of an FDA-labeled dose of diclazuril to healthy horses once a week was able to produce steady-state plasma drug concentrations known to inhibit S. neurona in vitro.

Frequency of Detection and Prevalence Factors Associated with Common Respiratory Pathogens in Equids with Acute Onset of Fever and/or Respiratory Signs (2008-2021).

A voluntary biosurveillance program was established in 2008 in order to determine the shedding frequency and prevalence factors for common respiratory pathogens associated with acute onset of fever and/or respiratory signs in equids from the USA. Over a period of 13 years, a total of 10,296 equids were enrolled in the program and nasal secretions were analyzed for the qPCR detection of equine influenza virus (EIV), equine herpesvirus-1 (EHV-1), EHV-4, equine rhinitis A and B virus (ERVs), and Streptococcus equi subspecies equi (S. equi). Single infections with respiratory pathogens were detected in 21.1% of the submissions with EIV (6.8%) and EHV-4 (6.6%) as the two most prevalent viruses, followed by S. equi (4.7%), ERVs (2.3%), and EHV-1 (0.7%). Multiple pathogens were detected in 274 horses (2.7%) and no respiratory pathogens in 7836 horses (76.2%). Specific prevalence factors were determined for each of the six respiratory pathogen groups; most differences were associated with age, breed, and use of the horses, while the clinical signs were fairly consistent between viral and bacterial respiratory infections. Monitoring the frequency of detection of common respiratory pathogens is important in order to gain a better understanding of their epidemiology and to implement management practices aimed at controlling disease spread.

Investigation of the Bi-Weekly Administration of Diclazuril on the Antibody Kinetics to Sarcocystis Neurona in Healthy Horses.

The aim of this study was to determine if bi-weekly administration of diclazuril at half the label dose would reduce seroprevalence and magnitude of titers to S. neurona in healthy horses naturally exposed to the apicomplexan protozoal parasite. 12 healthy adult horses were moved from a low-risk exposure to a farm with high exposure rate to S. neurona in their horse population. The horses were randomly assigned to either a treatment or a control group. Treatment consisted in the administration of half the label dose (0.5 mg/kg) of diclazuril (Protazil) pelleted top dress twice weekly (every 3-4 days) for 12 months. Prior to initiation of treatment and monthly thereafter, blood was collected for the detection of antibodies to S. neurona using a quantitative immunoassay. Further, trough plasma diclazuril levels were determined every 60 days. All 20 horses remained healthy during the entire study period. Seroprevalence to S. neurona decreased initially in the treatment group to 50% at 30 days post-treatment commencement. This was followed by a slow increase in seroprevalence in the treatment group before reaching 100% in both groups by 90 days post-treatment commencement. The seroprevalence remained 100% in both groups from 90 to 360 study days. While titer distribution between the two groups was similar at study commencement, treated horses had significantly lower titers throughout the treatment period (P < 0.05). All treated study horses had detectable plasma trough diclazuril levels at the 6 time points and the levels were above the concentration known to inhibit S. neurona in vitro (1.0 ng/mL). The administration of diclazuril pelleted top dress at half the label dose twice weekly was able to maintain low titers to S. neurona in healthy adult horses naturally exposed to the protozoal parasite. Further, trough diclazuril levels were in excess of the minimal concentration known to inhibit S. neurona.

Diagnostic Approaches to Understanding Equine Limb Wounds.

An accurate and timely diagnosis of the systemic and local tissue influences of a wound are essential to target successful treatment measures and reach the best result for an affected horse. A complete physical examination should be completed for any wounded horse and appropriate systemic therapies instituted. Visual and manipulative examinations aid in the complete understanding of wounded tissues. Imaging and invasive diagnostic techniques also have value in determining the extent of a wound. Considering what tissues are involved from an inside-out perspective can assist in developing a complete diagnosis.

Flexural Limb Deformities of the Carpus and Fetlock in Foals.

Early recognition and treatment of congenital and acquired flexural deformities of the carpi and fetlocks of foals can lead to conformation correction and an athletic future. Treatment is often based on rigid external coaptation assisted by systemic medical treatment. Foals that readily respond to treatment and correct conformation faults can have normal adult athletic expectations.

Ultrasonographic visualization of colonic mesenteric vasculature as an indicator of large colon right dorsal displacement or 180° volvulus (or both) in horses.

Visualization of colonic mesenteric vasculature during transabdominal ultrasonographic examination of horses with colic can be a predictor of right dorsal displacement of the large colon or 180° large colon volvulus, or both. Medical records of 82 horses having had surgical treatment of colic and having received a transabdominal ultrasonographic examination on admission were reviewed. Colonic mesenteric vessels were sonographically identified coursing laterally on the right side of the abdomen in 24 of the 82 cases. Horses with colonic vessels identified on ultrasound were 32.5 times more likely to be diagnosed at surgery with either large colon right dorsal displacement or 180° large colon volvulus than those in which vessels were not seen (P < 0.001). Visualization of colonic mesenteric vessels on ultrasound provided a sensitivity of 67.7%, specificity of 97.9%, positive predictive value of 95.8%, and negative predictive value of 81% for large colon right dorsal displacement or 180° large colon volvulus, or both.

Case report: squamous cell carcinoma of the urinary bladder in a horse.

A 14-year-old Hanoverian gelding was evaluated after a 10-week history of occasional straining during urination and dark red urine production after exercise. Physical examination findings were within normal limits. After 2 weeks of clinical signs, ultrasonography had found no abnormalities in the kidneys or bladder. A freely voided urine sample revealed an elevated protein concentration (500 mg/dL; reference range: <100 mg/dL) and few red blood cells. Vitamin C supplementation was suggested to acidify the urine, as was provision of a salt block to encourage water intake.

Influence of exercise on thermographically determined surface temperatures of thoracic and pelvic limbs in horses.

OBJECTIVE: To determine the amount of time required for surface temperatures of thoracic and pelvic limbs in horses to return to pre-exercise temperatures after high-speed treadmill exercise, as detected via infrared thermographic imaging. DESIGN: Prospective study. ANIMALS: 6 Thoroughbreds. PROCEDURES: All horses had been trained on and conditioned to use of a high-speed treadmill. Baseline thermographic images were obtained 3 days prior to exercise (baseline). Horses were exercised on a treadmill at a walk for 5 minutes, a slow trot (3 m/s) for 5 minutes, a trot (5 to 6 m/s) for 5 minutes, and a slow gallop (6 to 8 m/s) for 5 minutes, then back to a trot for 3 minutes, a slow trot for 3 minutes, and a walk for 3 minutes prior to stopping. Thermal images were obtained immediately after stopping exercise (0 minutes) and 5, 15, 45, and 60 minutes and 6 hours after stopping exercise. Ambient temperature surrounding each horse was recorded. RESULTS: In all regions, significant differences in surface temperatures were detected between thermograms obtained before exercise and those obtained immediately after, 5 minutes after, and 15 minutes after exercise was stopped. There were no significant differences in surface temperatures between thermograms obtained before exercise and those obtained > or = 45 minutes after exercise was stopped. CONCLUSIONS AND CLINICAL RELEVANCE: In horses, images generated via infrared thermography are not influenced by exercise-generated heat > or = 45 minutes after exercise is stopped.

Pharmacokinetics and pharmacodynamics of enrofloxacin and a low dose of amikacin administered via regional intravenous limb perfusion in standing horses.

OBJECTIVE: To evaluate the pharmacokinetic-pharmacodynamic parameters of enrofloxacin and a low dose of amikacin administered via regional IV limb perfusion (RILP) in standing horses. ANIMALS: 14 adult horses. PROCEDURES: Standing horses (7 horses/group) received either enrofloxacin (1.5 mg/kg) or amikacin (250 mg) via RILP (involving tourniquet application) in 1 forelimb. Samples of interstitial fluid (collected via implanted capillary ultrafiltration devices) from the bone marrow (BMIF) of the third metacarpal bone and overlying subcutaneous tissues (STIF), blood, and synovial fluid of the radiocarpal joint were collected prior to (time 0) and at intervals after tourniquet release for determination of drug concentrations. For pharmacokinetic-pharmacodynamic analyses, minimum inhibitory concentrations (MICs) of 16 microg/mL (amikacin) and 0.5 microg/mL (enrofloxacin) were applied. RESULTS: After RILP with enrofloxacin, 3 horses developed vasculitis. The highest synovial fluid concentrations of enrofloxacin and amikacin were detected at time 0; median values (range) were 13.22 microg/mL (0.254 to 167.9 microg/mL) and 26.2 microg/mL (5.78 to 50.0 microg/mL), respectively. Enrofloxacin concentrations exceeded MIC for approximately 24 hours in STIF and synovial fluid and for 36 hours in BMIF. After perfusion of amikacin, concentrations greater than the MIC were not detected in any samples. Effective therapeutic concentrations of enrofloxacin were attained in all samples. CONCLUSIONS AND CLINICAL RELEVANCE: In horses with orthopedic infections, RILP of enrofloxacin (1.5 mg/kg) should be considered as a treatment option. However, care must be taken during administration. A dose of amikacin > 250 mg is recommended to attain effective tissue concentrations via RILP in standing horses.

Septic arthritis, tenosynovitis, and infections of hoof structures.

Infectious diseases of synovial and hoof structures in horses can be devastating to soundness and can result in life-threatening complications. Timely diagnosis and early aggressive treatment can result in successful outcomes and resumption of athletic careers; however, delays in recognition and therapy can be the most costly reasons for failure. Sterilization of affected compartments and tissues requires removal of microorganisms and compromised tissue. Debridement, lavage, and appropriate antimicrobial drug use are the most reliable avenues of treatment. Antimicrobial drugs can be administered by local, regional, and systemic routes. Lavage techniques and debridement typically require surgical manipulations.

Ex vivo strength comparison of bioabsorbable tendon plates and bioabsorbable suture in a 3-loop pulley pattern for repair of transected flexor tendons from horse cadavers.

OBJECTIVE: To test the failure strength and energy of 2 bioabsorbable implants applied to transected deep digital flexor tendons (DDFT) from adult horses. STUDY DESIGN: Ex vivo biomechanical experiment. SAMPLE POPULATION: Twelve pairs of deep digital flexor tendons harvested from the forelimbs of fresh equine cadavers. METHODS: Poly-L-lactic acid tendon plates were custom manufactured for application to the cylindrical surface of an adult equine deep digital flexor tendon. Twelve pairs of DDFTs were transected 2 cm distal to the insertion of the distal check ligament of the deep digital flexor tendon. One tendon of each pair was randomly selected for repair with a biodegradable plate or a 3-loop pulley method. Size 2 polydioxanone suture was used in both repairs. Repairs were tested in tension to failure, with peak force (PF) and total energy (TE) at repair failure recorded in Newtons (N) and Joules (J), respectively. A paired t-test was used for statistical evaluation with a significant level set at P< or = .05. RESULTS: Mean+/-SD PF for failure of plated tendons (1507.08+/-184.34 N) was significantly greater than for sutured tendons (460.86+/-60.93 N). TE was also significantly greater for failure of plated tendons versus sutured tendons. CONCLUSIONS: Plate fixation of transected cadaver DDFTs appear to have superior immediate failure strength than 3-loop pulley repairs. CLINICAL RELEVANCE: Whereas in vivo testing is required, a bioabsorbable tendon plate may provide initial increased strength to support tendon healing and decrease external coaptation requirements.

Abdominal surgery in neonatal foals.

Abdominal surgery in foals under 30 days old has become more common with improved neonatal care. Early recognition of a foal at risk and better nursing care have increased the survival rates of foals that require neonatal care. The success of improved neonatal care also has increased the need for accurate diagnosis and treatment of gastrointestinal, umbilical, and bladder disorders in these foals. This chapter focuses on the early and accurate diagnosis of specific disorders that require abdominal exploratory surgery and the specific treatment considerations and prognosis for these disorders.

Segmental ostectomy of the second and fourth metacarpal and metatarsal bones in horses: 17 cases (1993-2002).

OBJECTIVE: To determine clinical findings in and outcome of horses with fractures of the second or fourth metacarpal or metatarsal bone that underwent segmental ostectomy, leaving the proximal and distal portions of the bone undisturbed. DESIGN: Retrospective case series. ANIMALS: 17 horses. PROCEDURES: Medical records were reviewed, and information on signalment, affected bone, lesion type, surgical procedure, amount of bone removed, and surgical and postsurgical complications was obtained. Follow-up information was obtained through telephone conversations with owners, trainers, and referring veterinarians. RESULTS: One horse had a fracture involving the distal third of the second metacarpal bone; 13 had fractures involving the middle third of the second metacarpal bone (n = 4), fourth metacarpal bone (5), or fourth metatarsal bone (4); and 3 had fractures involving the proximal third of the second (2) or fourth (1) metacarpal bone. Affected portions of the bones were surgically resected, leaving the proximal and distal portions undisturbed. All horses returned to previous performance levels without evidence of lameness. Cosmetic results were good to excellent. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that horses with a complicated injury of the proximal, middle, or distal portion of the second or fourth metacarpal or metatarsal bone may be successfully treated by means of segmental ostectomy of the abnormal portion of the bone.

The effect of perineural anesthesia on infrared thermographic images of the forelimb digits of normal horses.

Infrared thermography is an imaging modality gaining popularity as a diagnostic aid in the evaluation of equine lameness. Anecdotal reports of skin hyperthermia induced by local anesthesia, detected by thermography, have been made; however, no controlled studies have been reported. The purpose of this study was to examine the effects of perineural anesthesia on infrared thermographic images of the forelimb digits in normal horses. After environmental acclimation, infrared thermographs were made at intervals of 0, 5, 10, 15, 30, and 45 min from administration of mepivacaine hydrochloride or phosphate buffered saline in 6 adult horses with no clinical evidence of abnormality of the forelimb digits. The mean limb surface temperatures were compared by 2-factor ANOVA. Results indicated no significant difference between treatments, time after injection, or an interaction of time and treatment. Infrared thermographic imaging apparently can be performed within 45 min of perineural mepivacaine hydrochloride anesthesia without risk of artifactual changes in limb surface temperature.

Osteomyelitis of the pelvis caused by Rhodococcus equi in a two-year-old horse.

A 2-year-old female Quarter Horse was evaluated for hind limb lameness, fever (40 degrees C [104 degrees F]), and lethargy of 2 weeks' duration. Hypoproteinemia characterized by hypoalbuminemia and hyperfibrinogenemia was detected. Abdominal ultrasonography revealed thickening of the right dorsal colon wall. Treatment was instituted for putative right dorsal coliis. Lameness evaluation localized signs of pain to the lumbar vertebrae or pelvis. Radiography performed with the horse standing and nuclear scintigraphy revealed no abnormalities. Ventrodorsal pelvic radiography revealed a focal area of bony lysis and proliferation involving the cranial portion of the pubic symphysis. Aspiration yielded purulent exudate containing Rhodococcus equi, which was susceptible to erythromycin. Treatment included surgical debridement of the abscess and oral administration of erythromycin and rifampin. The horse's hind limb lameness completely resolved within 20 days. Infections of the pubic symphysis should be considered when lameness localized to the pelvis is associated with fever and an inflammatory leukogram.

Tenoscopic-assisted treatment of open digital flexor tendon sheath injuries in horses: 20 cases (1992-2001).

OBJECTIVE: To determine history, physical and diagnostic examination findings, medical treatment, and outcome of horses with open injuries to the digital flexor tendon sheath treated with the assistance of tenoscopy. DESIGN: Betrospective study. ANIMALS: 20 horses. PROCEDURE: Medical records of 20 horses with open injuries to the digital flexor tendon sheath were reviewed. Signalment, history, physical and diagnostic examination results, bacteriologic culture and susceptibility testing results, surgical and medical treatments, and follow-up examination results were determined. Outcome was determined by use of telephone interview or physical examination. RESULTS: All horses were treated with tenoscopic-assisted lavage and debridement. Eighteen horses survived, and 2 were euthanatized during treatment. All horses were either grade-4 or grade-5 lame before treatment. Ten horses returned to previous use. Four horses were considered mildly lame and in athletic use. Three horses were considered mechanically lame and are in use with reduced expectations. One horse was lost to follow-up after being sold. One horse was euthanatized for financial reasons and 1 because of complications from regional sepsis. CONCLUSIONS AND CLINICAL RELEVANCE: Tenoscopy appears to be a useful modality in the treatment of open injury to the digital flexor tendon sheath in horses. Direct viewing, guided debridement, and targeted large-volume lavage are advantages obtained with intrathecal arthroscopy. Tenoscopy, when combined with antimicrobial and anti-inflammatory treatment, appears to offer a good chance of survival for affected horses.

Clinical evaluation of the effects of immobilization followed by remobilization and exercise on the metacarpophalangeal joint in horses.

OBJECTIVES: To evaluate clinical effects of immobilization followed by remobilization and exercise on the metacarpophalangeal joint (MPJ) in horses. ANIMALS: 5 healthy horses. PROCEDURE: After lameness, radiographic, and force plate examinations to determine musculoskeletal health, 1 forelimb of each horse was immobilized in a fiberglass cast for 7 weeks, followed by cast removal and increasing amounts of exercise, beginning with hand-walking and ending with treadmill exercise. Lameness examination, arthrocentesis of both MPJ, single-emulsion radiographic examination, nuclear scintigraphic examination, ground-reaction force-plate analysis, and computed tomographic examination were done at various times during the study. RESULTS: All horses were lame in the immobilized MPJ after cast removal; lameness improved slightly with exercise. Force plate analysis revealed a significant difference in peak forces between immobilized and contralateral limbs 2 weeks after cast removal. Range of motion of the immobilized MPJ was significantly decreased, and joint circumference was significantly increased, compared with baseline values, during the exercise period. Osteopenia was subjectively detected in the immobilized limbs. Significant increase in the uptake of radionucleotide within bones of the immobilized MPJ after cast removal and at the end of the study were detected. Loss of mineral opacity, increased vascular channels in the subchondral bone, and thickening within the soft tissues of the immobilized MPJ were detected. CONCLUSIONS AND CLINICAL RELEVANCE: Results indicate that 8 weeks of enforced exercise after 7 weeks of joint immobilization did not restore joint function or values for various joint measurements determined prior to immobilization.