Causative agent: unknown
In cattle, pinkeye is caused by Moraxella bovis. A culture survey for M. bovis demonstrated the bacteria in 12.7% of clinically normal bison eyes (19). In sheep and goats, pinkeye can be caused by Rickettsia, Chlamydia, and Mycoplasma organisms (9). Pinkeye has been seen in bison (19) but the cause has not been identified (19). In cattle the spread of pinkeye is accomplished by face flies (9).
Clinical signs:
One or both eyes may be infected (19). There is increased lacrimation, reddening of the conjunctiva, squinting, and cloudiness of the cornea, which may lead to ulceration of the cornea (19). In severe cases the cornea may become conical in shape (19). Temporary or permanent blindness can result (19).
Diagnosis:
Biopsies of the cornea or swabs of the conjunctival sac can be sent to a diagnostic pathology laboratory for bacterial culture and identification.
Treatment:
Recovery may be spontaneous in many cases (19). Small volumes of penicillin and corticosteroids may be injected into the bulbar conjunctiva or the onjunctiva of the eyelids (19). In cattle, third eyelid flaps or suturing the eyelids closed have been used. Bison will often remove these sutures shortly after they are placed, by rubbing their eyes and head on the ground (19). Large conical shaped corneas may take 6 months to a year to heal, or they may never heal.
Handling bison with pinkeye can be dangerous to the handlers as well as to the animal. Bison that are blind in one or both of their eyes will be unable to protect the affected eye from injury during handling. They will frequently rupture the globe of the affected eye in a handling facility, or a squeeze. Bison that are bilaterally blind from pinkeye are unable to avoid obstacles, fences, or other bison. This predisposes them to serious injury (19).
Prevention:
In cattle, prevention has been aimed at reducing the population of face flies to which cattle are exposed, reducing the spread of the infective agent (9). Insecticide ear tags have not been demonstrated to reduce the incidence of pinkeye in bison (19). Installing insecticide applicator wicks around grain and salt feeders as well as around water sources has been used to reduce the face fly population (19).
There are commercially available pinkeye vaccines on the market. They are designed for use in cattle. Since the etiological agent for pinkeye in bison is unknown, the efficacy of these vaccines in bison is very questionable.