Case Report: Periocular Conjunctivitis in a group of Laboratory Swine (Sus scrofa)

Submitted by Curtis Rheingold from Tufts University Cummings School of Veterinary Medicine

History & Clinical Presentation
Eight, adult, female, Yorkshire pigs (Sus scrofa) arrived to the University Laboratory Animal Resources at The Ohio State University for use in an Institutional Animal Care and Use Committee (IACUC) approved dermatologic wound-healing research study. Initial visual assessments performed by veterinary technical staff revealed bilateral periocular conjunctivitis. Closer examination performed by facility veterinarian revealed chemosis (OU), mucopurulent discharge (OU), scleral injections (OU), and blepharospasm (Fig 1). No other significant findings were reported upon completion of physical exam. All animals were quarantined into a separate room and started on empirical therapy which involved daily eye flushing using ophthalmic solution eyewash (Medi-First, Medique Products, Fort Myers, FL) BID (OU) and topical neomycin-polymyxin B sufates and bacitracin zinc ophthalmic suspension (Bausch+Lomb, Rochester, NY) TID (OU). A more in depth ophthalmic exam was also scheduled to be performed at each subject’s next experimental anesthetic event. After 72hr of treatment, all subjects were reevaluated. Reexamination revealed no significant improvement of ocular clinical signs. Clinical staff reported difficultly administrating topical ophthalmic medications in subjects.

Within 7-14 days all subjects were anesthetized for study-related events. At this time a more thorough ophthalmic examination was performed. All previously reported clinical signs (i.e., conjunctivitis, chemosis, and mucopurulent discharge) were still present. Both affected eyes were rinsed with ophthalmic eye wash, had conjunctival scrapes performed for cytology interpretation and swabbed with sterile curettes for bacterial culturing and sensitivity testing (aerobic and mycoplasma spp. specific). All samples were submitted to The Ohio State University Clinical Pathology Laboratories, Veterinary Medical Center (Columbus, OH) and Antech Diagnostics (Oak Brook, IL).

Fluorescein staining was also performed using ophthalmic strips (Bio Glo, Fluorescein Sodium 1 mg strips U.S.P., Hub Pharmaceuticals, Rancho Cucamonga, CA)  and revealed no signs of superficial corneal ulceration. At this time, empirical treatment was discontinued, and all subjects were started on a combination of enrofloxacin (Baytril® 100, 100 mg/mL, Bayer, Shawnee Mission, Kansas) and dexamethasone-SP (DexaJect SP, 4 mg/mL, Henry Schein®, Dublin, OH) solution (1:1 ratio) administered subconjunctivally in the bulbar and palpebral regions, while still under general anesthesia (Fig 2). This was performed using a 1 mL syringe with 27 gauge needle attached. Total volume of each injectable solution was 0.15 mL respectively. Additionally, 2-3 drops of topical ophthalmic neomycin-polymyxin B sulfates and dexamethasone suspension (Bausch+Lomb, Rochester, NY) were applied. This therapy regimen was continued until return of all diagnostic testing.

Analysis and findings
Twenty percent of the animals were selected to undergo diagnostic testing in order to capture the overall herd health.

              Cytological findings

Two slides prepared from conjunctival scrapes revealed occasional to modest numbers of intact nucleated cells with minimal hemodilution on a pale eosinophilic background with copious amount of magenta staining, granular material, presumed lubrication or eye ointment. There were occasional anucleate and nucleated squamous epithelial cells that often have a mixed bacterial population consisting of small rods and cocci. Additionally, occasional to modest numbers of variably degenerate neutrophils were present. No overtly neoplastic cells were seen.

Impression

Mild to moderate neutrophilic inflammation with mixed bacterial infection that consistent of small rods and cocci (Fig 3).

Antibiotic sensitivity testing of cultured aerobic bacteria revealed that all species were susceptible to both gentamicin and tobramycin.

Morphologic diagnosis

Mycoplasmic conjunctivitis with associated ocular and conjunctival sequelae.

Post-diagnostic testing: treatment and results
Upon diagnostic findings and results, the current medical therapy was discontinued and subjects were started on gentamicin sulfate (40 mg/mL, APP Pharmaceuticals, Schaumburg, IL) /dexamethasone solution (DexaJect SP, 4 mg/mL, Henry Schein®, Dublin, OH) was injected into the bulbar and palpebral conjunctiva of both eyes in a similar 1:1 ratio as previously described. Two to three drops of topical 0.3% tobramycin ophthalmic solution (Akorn Inc, Lake Forest, IL) was also applied to the globe.

Upon examination 24 hours after treatment, all pigs’ eyes showed significant improvement with reduction in gross clinical signs (Fig 4). Weekly treatment of gentamicin/dexamethasone and tobramycin continued during research-related anesthesia until each pig’s euthanasia endpoint. At euthanasia, final aerobic and mycoplasma cultures from each pig were sent for further diagnostic testing. Culture results from the last pig showed no remaining Mycoplasma spp., approximately two months after initiating treatment.

Discussion:
The conjunctiva of domestic animals is rarely sterile, and the microbial species found in pig conjunctiva are similar to other domestic species. In a study of a commercial swine operation, bacteria were found in 98% of healthy pigs tested (1). The most common bacteria included alpha-Streptococcus spp (89% of pigs), Staphylococcus epidermidis (39%), and Staphylococcus spp (39%). Chlamydia spp. were also identified in 28% of pigs (2). Mycoplasma species were not identified in any of these healthy pigs.

Mycoplasmosis has been implicated in spontaneous conjunctivitis and keratoconjunctivis in swine (3, 4), as well as in other domestic animals such as cats and dogs (5). In our group of pigs, Mycoplasma spp. was the only pathogen identified with reports of causing clinical disease. The recommended treatment in companion animals is tetracycline (5,6). Intramuscular oxytetracycline is typically used in production swine with a 28-day withdrawal period. Our group was limited on treatment options due to the risk of interfering with the approved IACUC study protocol, with systemic antibiotics and tetracyclines not available. Additionally, while we would have normally used diclofenac or a similar non-steroidal anti-inflammatory drug (NSAID) to alleviate inflammation and discomfort associated with the conjunctivis, all NSAIDs were contraindicated by the research protocol as well.

Diseases in research animals present a unique challenge for laboratory animal veterinarians since all diagnostic procedures and medical treatments must be carefully considered as to not interfere with the research protocol. The present case illustrates how coordination between research and veterinary staff can result in improved welfare for research animals. After initial treatment with empirical therapy did not affect any clinical signs, we were able to collaborate with the research group to evaluate and treat the pigs under general anesthesia. Topical ophthalmic administration is not consistently feasible in an awake, active pig.  Since the research protocol involved weekly anesthetic episodes, allowing the veterinary staff to examine and treat the animals while they were still under general anesthesia eliminated the need for additional sedation. With tetracyclines contraindicated by the research group, we elected to treat the susceptible aerobic bacteria with antibiotics recommended by sensitivity testing.

Treating non-research related diseases is vital from both an ethical and a data quality perspective. Preventing and relieving pain and disease is a vital mission for all health-related staff, veterinarians and technical staff alike. The Guide for Care and Use of Laboratory Animals, which sets standards and guidance for NIH-funded animal research, states that, “Pain is a stressor, and if not relieved, can lead to unacceptable levels of stress and distress in animals”. Even though certain treatments may not be possible in the context of a certain study, it is up to the laboratory animal veterinarian to devise a treatment plan that is both usable and effective. Treatment of diseases in research animals also ensures that data collected is free of any confounding factors. A sick or injured animal is drastically different from a healthy animal on many dimensions, including behavior, immune responses, and even gene expression. These differences can affect the reliability or reproducibility of study results and hinder collaboration between research labs.

In summary, a group of laboratory swine presented with periocular conjunctivitis and several other ocular clinical signs. Through collaboration with the research group, diagnostic testing and ophthalamic treatment were successfully conducted without any additional anesthesia or sedation. The present case demonstrates how coordination between veterinary and technical staff can lead to better outcomes for laboratory animals’ health and therefore augment the research process.

References

1. Davidson HJ, Rogers DP, Yeary TJ, Stone GG, Schoneweis DA, Chengappa MM. 1994. Conjunctival microbial flora of clinically normal pigs. Am J Vet Res 55(7): 949-951.
2. Zimmerman JJ, Karriker LA, Ramirez A, Schwartz KJ, Stevenson GW, editors. 2012. Diseases of Swine. Ames (IA): Wiley-Blackwell.
3. Rogers DG, Frey ML, Hogg A. 1991. Conjunctivitis associated with a Mycoplasma-like organism in swine. J Am Vet Med 198(3): 450-452.
4. Friis NF. 1976. A serologic variant of Mycoplasma hyorhinis recovered from the conjunctiva of swine. Acta Vet Scand 17(3): 343-353.
5. Maggs D, Miller P, Ofri R. 2017. Slatter’s Fundamentals of Veterinary Ophthamology, 6^th edition. St. Louis (MO): Saunders.
6. Schaer M. 2009. Clinical Medicine of the Cat and Dog, Second Edition. Boca Raton (FL): CRC Press.