Subconjunctival autologous muscle-derived mesenchymal stem cell therapy: A novel, minimally invasive approach for treating equine immune-mediated keratitis.

OBJECTIVE: To establish the safety of subconjunctival injections of autologous muscle-derived mesenchymal stem cells (mdMSCs) in healthy horses and to evaluate their effect in four horses (six eyes) with severe chronic equine immune-mediated keratitis (IMMK) that was unresponsive to medical treatments. METHODS: MdMSCs were cultured from minimally invasive muscle biopsies. In the safety group, four healthy horses received two subconjunctival injections of 2.5 and 5 million cells, respectively, at 1-month interval, to the same eye. Ocular side effects were monitored for 1 month following each injection. In the treatment group, six eyes received four to seven subconjunctival mdMSCs injections (2.5 or 5 million cells per injection) every 4 weeks, approximatively. Medical treatment was discontinued 1 week before and throughout the entire treatment period. A scoring system was used to assess the evolution of the ocular lesions. RESULTS: In the safety group, all horses exhibited mild to moderate chemosis and conjunctival hyperemia at the injection site, lasting 24-48 h. In the treatment group, all eyes initially responded positively to therapy, with a reduction in lesion scores observed after the first injection. Four eyes achieved control of the lesions with repeated injections during the 9.2 months of follow-up. CONCLUSION: The first subconjunctival injection of mdMSCs resulted in improvement of the ocular lesions. Repeated injections were found to be safe, minimally invasive and showed promise in managing refractory cases of equine IMMK. Further studies are warranted to demonstrate the long-term benefits of these injections and to optimize the therapeutic protocol.

Equine ulcerative keratitis in Belgium: Associated bacterial isolates and in vitro antimicrobial resistance in 200 eyes.

PURPOSE: To describe bacterial isolates and associated antibiotic resistance from horses with ulcerative keratitis in Belgium. METHODS: Medical records from horses with ulcerative keratitis presented to the ophthalmology service of the Veterinary teaching hospital of Liege, Belgium, between 2014 and 2021 were evaluated. Bacterial isolates were identified and VITEK® 2 (Biomérieux) provided antimicrobial susceptibility testing and resistance detection. RESULTS: Two hundred eyes of 196 horses were sampled. Ninety-seven eyes had a positive bacterial culture (48.5%) and 139 bacterial isolates were identified. Staphylococcus (63/139: 45.3%) and Streptococcus (33/139: 23.7%) were the most frequent genus isolated. Staphylococcus aureus (21/139: 15.1%) was the most frequent species isolated of which half were methicillin-resistant (MRS). Streptococcus equi subsp. zooepidemicus (19/139: 13.7%) was the second most identified bacterial isolate. Only two Pseudomonas species were isolated (2/139: 1.4%). The overall resistance of all bacterial isolates against chloramphenicol (12.4%) and fluoroquinolones (14.3%) was low. Resistance against tobramycin, polymyxin B, gentamicin, fusidic acid, tetracycline, and neomycin ranged from 40.8% to 58.6%. When separating the MRS from the other staphylococci, a significant difference was noted in percentage of resistance to gentamicin (p = .00026) and tetracycline (p = .00015). MRS were highly resistant to gentamicin (75%) and tetracycline (100%), whereas the remaining staphylococci were significantly less resistant to gentamicin (17%) and tetracycline (40.4%). CONCLUSION: Although Pseudomonas species has been rarely cultured, our results are roughly consistent with previous studies. Multiple drug resistance was high and resistance to first-choice antibiotics in ulcerative keratitis was noted. These results warrant continued monitoring of susceptibility profile.

Identification of an ectopic periorbital lymph node in two horses.

Background: To describe the clinical presentation and treatment of an ectopic periorbital lymph node in two young horses. Case Description: Two warm-blood horses were presented at the equine clinic of the University of Liège with a periorbital non-painful mass. Differential diagnosis included neoplasm (lymphoma), (sterile) abscess, cyst, ectopic lacrimal gland tissue, hematoma, adipose tissue, or ectopic lymphoid tissue. Information collected included physical and ophthalmic examination findings, results of the ocular and periocular ultrasound, surgical procedure, histopathology, and follow-up. Masses of 2 × 2 cm and 3 × 2 cm subcutaneous, ovoid, smooth, and firm mass were observed in the zygomatic region of the head. On ultrasound, the mass appeared as a hypoechoic subcutaneous structure. Cytology showed a mixed lymphocytic cell population. No abnormal mitotic activity was observed. Histopathology revealed a chronic markedly reactive lymph node. Conclusion: To the authors' knowledge, this is the first description of periorbital ectopic lymph nodes in veterinary medicine. Ectopic lymph nodes should therefore be included in the differential diagnosis of periocular masses in animals. Surgery was easily performed and was curative.