Infectious bovine keratoconjunctivitis (IBK or Pinkeye) is a common ocular condition of cattle, with prevalence peaking in young stock during the summer months. While all breeds are susceptible, those with light heads, such as Hereford and Simmentalers have a higher incidence of the disease.
Clinical signs of IBK include corneal ulceration, corneal oedema, photophobia, blepharospasm, lacrimation and epiphoria. If allowed to progress the severity of symptoms increases which can culminate in rupture of the cornea and permanent blindness.
Corneal scarring occurs during healing of ulcers, this too will negatively affect sight in the long term. Young cattle affected with IBK have poor weight gains. It is believed to be due to ocular pain affecting feed intake.
Moraxella bovis is a gram-negative rod, considered to be the etiological agent responsible for IBK, however M. bovis is a commensal of the eyes of cattle and can be isolated from corneal swabs without ever causing clinical disease. Intrinsic factors play a significant role in the development and spread of IBK within a group of animals. Factors such as UV radiation, flies, foreign bodies or concurrent infection with Mycoplasma spp infection or IBR viral infection are all factors which affect the pathogenicity of M. bovis.
More recently the organism Moraxella bovoculi has been isolated from the eyes of cattle affected with IBK leading to investigation into this bacteria being an additional cause of IBK, however there have been no studies published to date that have shown a direct causal role for M bovoculi in IBK. Mycoplasma spp have been isolated from the eyes of calves with clinical IBK which had no evidence of M bovis which is of interest when determining a treatment protocol. Treatment options are varied for IBK. M. bovis is susceptible to many different antibiotics and via many different routes of administration:
Penicillin is the most common treatment for IBK. Procaine penicillin (2ml – 600 000IU) administered as a subconjunctival injection was found to reach a peak concentration rapidly and had a duration of action of approximately 68hours. When the penicillin dose was reduced to 1ml (300 000 IU) the duration of action reduced to 35 hours. In an alternative study comparing sites of deposition, investigators found that the incidence of IBK was significantly reduced in calves that received the penicillin subconjunctivally in the bulbar conjunctiva when compared to injection into the superior palpebral conjunctiva.
Topical Cloxacillin such as that found in the commercial intra-mammary preparations have been shown to be effective against experimentally induced IBK using a minimum dose of 250mg per eye. In the same study they compared lower doses of 50mg and 125mg per eye and at these doses,the ocular treatment was not found to be effective. While these intra-mammary preparations are cost effective and require little expertise for application, the dose needs careful consideration as many preparations contain in the region of 500mg cloxacillin per 10ml syringe making the routinely advocated 1ml per eye a fraction of the required dosage in order to effectively treat IBK.
Oxytetracycline is a commonly used antibiotic. With parenteral treatment in calves consisting of 2 doses of long acting oxytetracycline (20mg/kg 3days apart) they described a decreased duration of M bovis shedding as well as a reduced period of lacrimation and blepharospasm.
Oxytetracycline (300mg) injected subconjunctivally was compared to parenteral tilmicosin in a study and while it did result in some improvement in clinical signs of IBK, investigators found it inferior to parenteral tilmicosin. It should be noted that injection of long acting oxtetracycline subconjunctivally has been shown to result in conjunctival chemosis and necrosis and is not recommended. Intrapalpebral injection of oxtetracycline hydrochloride (10%) was equally effective as parenteral injection however is associated with transient swelling around the eye which disappeared after 72 hours.
Tulathromycin is the one antibiotic which has a published indication for the parenteral treatment of IBK. A study comparing affected calves receiving a single injection of tulathromycin (2.5mg/kg) to an untreated control group found that the treated animals had significantly shorter healing times, lower corneal lesion scores as well as reduced size of corneal ulcers.
Tulathromycin has the added benefit of being used to treat respiratory infections where Mycoplasma bovis is implicated, While there have been no studies investigating the control of IBK where Mycoplasma is involved it may very well be effective in its control.
Florfenicol administered parenterally has been investigated in 2 studies. One treatment group consisted of 2 doses of florfenicol (20mg/kg IM at 0 and 48 hours) and the second treatment group received 1 dose of florfenicol (40mg/kg SC once). Both treatment groups had better cure rates than the untreated controls with smaller ulcers and faster healing times. The two treatment protocols had comparable efficacy with the 2 doses being only slightly more effective than a single SC dose.
Dexamethasone (1ml; 4mg) was added to penicillin and administered into the palpebral conjunctiva in a comparative study using penicillin on its own. The inclusion of dexamethasone had no effect on ulcer healing time, severity, diameter or surface area. The inclusion of a nonsteroidal anti-inflammatory into the treatment regime is likely to reduce ocular inflammation and improve comfort level thereby reducing the effect of the condition on weight gains.
Non Pharmacologic options such as using serum harvested from the patient as an eye drop has been advocated in animals where the animal can be handled often. The serum provides growth factors and contains anticollagenase activities which may aid corneal ulcer healing. In most cases it is practically impossible to administer serum eye drops as frequently as is published in companion animal literature (every 60minutes) however dosing less frequently will still have some positive effect.
The use of a fabric patch of dark sturdy material to cover a severely affected eye is a useful adjunctive therapy especially in calves being housed in crates or in animals affected only in a single eye. The bottom of the patch should be left unattached to allow drainage. These patches are useful in protecting light sensitive eyes from UV radiation as well as limiting spread of the organism by fly vectors.
The reduction of risk factors may contribute to a reduction in the spread of IBK between animals. M bovis has been shown to be transmitted by flies. Reducing fly numbers at the time of an outbreak will limit spread.
Dust and UV radiation are also risk factors and spraying animal collecting facilities prior to congregating animals prior to milking etc may limit ocular irritation leading to M bovis moving from commensal to pathogen.
As is the case with other infectious diseases of livestock, successful control is through a multi faceted approach of disease diagnosis, rapid treatment and management of herd and environment to limit spread. While there are many different antibiotic regimes that have been investigated for the control of IBK, selection of the appropriate one should include identification of the appropriate route as well as dosage required for maximum efficacy.
- Alexander D, 2010: Infectious Bovine Keratoconjunctivitis: A Review of Cases in Clinical Practice. Veterinary Clinics of North America: Food Animal Practice 26 487-503.
- Brown MH, Brightman AH, Fenwick BW, Rider MA, 1998: Infectious bovine keratoconjunctivitis: a review. J.Vet.Intern.Med. 12 259-266.