Case report: Bilateral ulcerative keratitis in a Thoroughbred mare
The mare was presented to the Animal Health Trust with a one-month history of bilateral ulcerative keratitis. A number of other horses at the same stud farm and in the surrounding area had had bilateral ulcerative keratitis but all cases had resolved quickly on topical antibiotic. This case failed to respond to similar therapy so the referring veterinary surgeon took bacterial and fungal conjunctival swabs as well as a cytological smear preparation. The cultures were negative and the cytology revealed neutrophils and epithelial cell debris. After 2 weeks corneal fluorescein uptake was no longer present and topical gentamicin therapy was discontinued in favour of Maxitrol TM . After a further week corneal fluorescein uptake was again present and treatment with plasma in EDTA and gentamicin was instituted t.i.d. Five days later the eyes had deteriorated markedly and a referral was sought.
| Right eye day 2 | Left eye day 2 |
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Bacterial and fungal culture swabs were taken from each eye. Under local anaesthesia corneal scrapes were taken and smears made for cytology. Cytology revealed numerous neutrophils, many of which were degenerate. Bacterial cocci were present, both intracytoplasmic and within proteinaceous debris. No fungal hyphae were seen. This picture was consistent with a bacterial keratitis.
Bacteriology revealed a moderate growth of Streptococcus zooepidemicus from both eyes. Fungal culture revealed no growth.
Intensive topical therapy was instituted in the form of chloramphenicol drops every 2 hours to both eyes. Atropine was used as necessary to control ocular pain from ciliary spasm and pupillary constriction. Gut sounds were monitored as ileus is a recognised side-effect of topical atropine. Analgesia was provided by butorphanol as there was some concern over using NSAIDs in a pregnant mare. Morphine was contraindicated as she was lactating and it is sequestered in milk.
The left eye progressed well and was healed by 10 days post admission.
| Right eye day 11 | Left eye day 11 |
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Gentle debridement of necrotic corneal epithelium in the right was undertaken under local anaesthesia with a cellulose stick swab. The right eye then healed well.
| Right eye day 20 | Left eye day 20 |
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Discussion
Strep. zooepidemicus can be an aggressive pathogen once the epithelium is breached. The route of entry in this case is not clear as there was no traumatic incident reported. The simultaneously bilateral nature of the disease might also suggest a lack of traumatic involvement. The recent outbreak in the area is suspicious and fly vectors could be responsible for its spread. The foal however remained clinically unaffected and conjunctival swabs were bacteriologically negative.
The possibility that the bacterium was introduced by contaminated plasma is strong given the rapid deterioration after introducing this treatment. Plasma or serum is primarily used topically to inhibit the action of matrix metalloproteinases (MMPs) and collagenases responsible for keratomalacia ('melting ulcer') and there is some argument that it may also contain growth factors and other substances of benefit to epithelial healing. It should be autologous if at all possible and should be prepared using a sterile technique. It is best stored in the fridge and discarded after 72 hours. There is a good argument for not dispensing this treatment to the owner and only utilising plasma or serum in the hospital based patient.
Intensive topical antibacterial therapy is warranted and early surgical intervention should be considered where a bacterial ulcer is progressing. Topical steroids are contraindicated in ulcerative keratitis. They can potentiate fungal infections, promote the development of keratomalacia and greatly delay epithelial healing.
References
Brooks D., Andrew S.E., Biros D.J., Denis H.M., Cutler T.J., Strubbe D.T., Gelatt K.N. Ulcerative keratitis caused by beta-haemolytic Streptococcus equi in 11 horses. Veterinary Ophthalmology , 2000: 3 (2/3): 121-125.
Sauer P., Andrew S.E., Lassaline M., Gelatt K.N., Denis H.M. Changes in antibiotic resistance in equine bacterial ulcerative keratitis (1991-2000): 65 horses. Veterinary Ophthalmology , 2003: 6 (4):309-313.
Barnett K.C., Crispin S.M., Lavach J.D., Matthews A.G. Cornea. In: Equine Ophthalmology 2 nd ed . Saunders, Oxford. 2004; 107-147.
Strubbe D.T., Brooks D.E., Schultz G.S., Willis-Goulet H., Gelatt K.N., Andrew S.E., Kallberg M.E., Mackay E.O., Collante W.R. Evaluation of tear film proteinases in horses with ulcerative keratitis. Veterinary Ophthalmology , 2000; 3 (2/3):11
