LEAP FORWARD IN EYE TREATMENT TECHNOLOGY
Treating horses with fungal eye infections may be significantly easier in the future thanks to injectable thermogels that slowly release medication to a targeted location for days, weeks or months.
Currently, managing a horse with keratomycosis, a fungal infection of the cornea, can be extremely difficult. “The standard use of antifungal medications in keratomycosis consists of topical application from four to 12 times a day, depending on the clinical signs and stage of the disease,” says Eva M. Abarca, DVM, MS, DACVO, of the University of Bern in Switzerland. “This intensive treatment protocol is challenging in horses due to their lack of tolerance for repeated applications of topical medications, therefore these intensive treatment protocols typically require the placement of an indwelling tubing system through which to administer medications.” Often, horses must be admitted to a clinic for the duration of treatment, greatly increasing the cost.
Seeking to develop a more economical and practical treatment alternative, Abarca is working with her former colleagues from the equine and internal medicine and pharmacy departments at Auburn University to investigate the potential of delivering antifungal medications via thermogels injected under the eye’s conjunctiva.
“Thermogels are polymer solutions that are transformed into gels by changes in temperature,” she explains. “This means that they can be injected as a liquid but form a gel deposit upon reaching body temperature.”
When a medication is mixed with the thermogel, it is slowly released as the polymer breaks down over time. “Depending on the composition of the polymers this drug release may be maintained at the site of administration over days to months,” says Abarca.
In a recent study conducted at Auburn University, the research group analyzed the release rate of a thermogel containing the antifungal drug voriconazole and the degree to which the medication permeated corneal tissue. The data showed that voriconazole was released from the gel over the course of 21 days and diffused through the sclera and cornea of the equine eye. In addition, the researchers determined that upon release from the thermogel, the drug retained its antifungal properties.
These results suggest that a voriconazole-containing thermogel could be used to
simplify the treatment of fungal eye infections in horses: Instead of multiple daily treatments, a single injection could potentially deliver medication for a sustained period. Although more research is needed to test this treatment protocol in living horses with active disease, in the opinion of the authors: “If the proposed thermogel proves effective, the continuous and sustained release of voriconazole within the eye may reduce the frequency, length and cost of treatment required in horses with keratomycosis and thus improve patient comfort, client compliance and clinical outcomes.”
According to a recently published study, a vaccine to protect horses from equine protozoal myeloencephalitis (EPM) failed two separate clinical trials.
Researchers at Ohio State University worked with clinicians at what was then Fort Dodge Animal Health to test a killed-organism vaccine against Sarcocystis neurona, the protozoan that causes EPM. Fort Dodge Animal Health was subsequently acquired by Pfizer.
S. neurona is passed to horses by wildlife through contaminated feed and water. The organism is ubiquitous in many parts of the United States, and many horses are exposed to it without ill effects. When S. neurona crosses the blood-brain barrier, however, it attacks the brain and spinal cord leading to neurological impairment. Why that happens isn’t completely understood, but stress is believed to make some horses more susceptible.
For their vaccine studies, the researchers selected neurologically normal horses that tested negative for S. neurona. In the first experiment, researchers gave the horses either a vaccination followed by a booster injection, or two placebo injections on the same schedule. Thirty-four days after the second injection, the horses were then given feed contaminated with S. neurona sporocysts.
For the second experiment, half the horses received an initial vaccination followed by two booster injections, while the other half received placebo shots at the same intervals. All of the horses were fed sporocysttainted feed 139 days after the third injection. Also, all of the horses were subjected to long trailer rides to increase their stress levels.
The researchers determined that there was no statistical difference in the incidence of neurological signs indicative of EPM between the horses in the vaccinated and placebo groups. Based on the two experiments, researchers conclude that the vaccine against S. neurona did not prevent the development of neurologic signs associated with EPM.
Reference: “Testing the Sarcocystis neurona vaccine using an equine protozoal myeloencephalitis challenge model,” Veterinary Parasitology, November 2017
NO SUCCESS FOR EPM VACCINE The researchers determined that there was no statistical difference in the incidence of neurological signs indicative of EPM between the horses in the vaccinated and placebo groups.