Pinkeye is also known as infectious bovine keratoconjuctivitis (IBK) in cattle and as infectious opthalmia in sheep and goats is a highly contagious and infectious disease that happens in epidemics (a disease outbreak where many cases occur in a short time; epizootic). The disease is considered to be of economic importance due to poor thrift in affected animals. Kasimanickam and Parish (2011) agree that the financial loss is due to decreased weight gain, increased treatment costs and market discounts due to eye disfigurement and blindness.
WHAT CAUSES IT
in cattle, it is caused by bacteria called Moraxella bovis.in sheep and goats it is caused byMoraxella(Branhamella) ovis of varying virulence in conjunction with other agents: –Moraxella ovis andchlamydia spp.
According to Mushi et al. (1999) it is clinically characterised by:
- Conjunctivitis – infection of the mucus membrane covering the inside of the eyelids and the visible surface of the eyeball.
- Lachrymation – secretion of tears.
- Photophobia – avoidance of light.
- Corneal opacity – is a disorder of the cornea which is the transparent structure on the front of the eyeball. It occurs when the cornea becomes scarred thereby preventing light from passing hence making it look clouded.
- Ulceration – occurrence of open shallow chronic sore on an inner or outer surface of the body in this case the eye.
OTHER FACTORS PREDISPOSING LIVESTOCK TO INFECTION
Factors that make animals more prone or likely to get the infection are:
- High / increased fly population
- Poor host immune system
- Nutritional deficiencies (vitamin A, Copper and Selenium)
- Increased ultraviolet radiation; ultraviolet (UV) light (sunlight) exposure
- Presence of disease agents and concurrent infections
- Hot months
- Breeds lacking eye pigment
- Young animals
- Pasture conditions that causes eye irritation such as dust, wind, tall grasses, weeds, or any other element creating mechanical injury to the eye.
TRANSMISSION/SPREAD OF THE DISEASE
The disease is more common and more severe in young animals with cattle being the reservoir or main host of the bacteria. Since it is a highly contagious infection, it spreads very rapidly. It can remain on a farm in carrier animals from year to year and Kasimanickam and Parish (2011) warn that it can be transmitted by animal handlers or direct contact with eye and nose discharges of infected animals, contact with fomites (equipment or hands that carry the disease) and most commonly by mechanical vectors. The face fly (Musca autumnalis), the house fly (Musca domestica) and the stable fly (Stomoxys calcitrans) are instrumental in spreading the disease.
HOW INFECTION OCCURS
The pathogenic strain adheres to the cornea and conjunctiva and produce skin destroying toxin, the toxin causes edema (watery swelling under the skin) of the cornea followed by blister formation and subsequent ulcer formation and scarring.
SIGNS OF INFECTION HOW THE DISEASE IS RECOGNISED
- Incubation period is short usually 2-3 days but can extend to a few weeks in extreme cases.
- One or both eyes can be affected.
Can occur in several stages of progression (Kasimanickam and Parish (2011), Mushi et al. (1999), Mushi (1995)):
|Earliest signs of the disease are:
-avoidance of light (photophobia)
-a lot of watery discharge which then later becomes cloudy/ pus like mucus discharge.
-loss of appetite due to pain.
|Within 24-48 hours after the onset of stage1 signs:
-small grey area develops on the center of the cornea and radiates over the whole cornea.
-many blood vessels appear all over the cornea. These blood vessels make the cornea appear pink, hence the name of the disease.
|-ulcers on the cornea.
-Entire cornea will have grey-white to yellow color with deep, central ulceration of cornea within 6 days.
-inflammation then spreads to the inner eye.
In cattle, the bacteria produces pore forming toxin that promotes the development of ulcers on cornea by death (lysis) of corneal epithelial cells.
|-some animals recover spontaneously in a few weeks and ulcers heal and reduce leaving scars.
-some become chronic or severe leading to temporary blindness that could take 1-2 months to resolve while in other cases permanent blindness occurs.
-even after healing, eye may appear cloudy or blue due to blood vessels but may eventually clear.
HOW THE DISEASE IS RECOGNISED
Veterinary assistance is needed for this. Swabs need to be taken from early untreated animals for culture, identification and antibiotic sensitivity.
This disease may be confused with:
- Foreign bodies such as grasses
- Infectious agents such as Thelazia spp., an eye worm that also infects human eyes. Mycoplasma spp., IBR (Infectious Bovine Rhinotracheitis), bovine malignant catarrheal fever.
- Vitamin A deficiency.
Recommended treatment by Kasimanickam and Parish (2011):
- The diseaseis often susceptible to oxytetracycline, ceftiofur, and penicillin. Antimicrobial drugs may be administered by subconjunctival injection or intramuscularly or subcutaneously, depending on the drug.
- Long acting tetracycline. A second dose administered at 48 to 72 hours later may increase the number of cattle that responds to treatment. (Follow Beef Quality Assurance measures when administering injections). Find a tetracycline product that is labeled for Pink Eye treatment.
- Injecting penicillin under the white part of the eye or lid is another option (1 ml procaine penicillin G). This is an extra‐label use of this drug and requires a veterinarian’s prescription and label if used in this manner. It also requires excellent technique because it can be dangerous to the cattle.
- Other antibiotics may be effective but are not labeled for Pink Eye treatment. If a labeled product is not working for you, contact your veterinarian for a new treatment protocol.
- Antibiotic eye ointment. Oil based topical preparations are better than powder.(Mushi et al.,1999).
Note: When treating animals, wash your hands or change gloves between animals to prevent spread of this bacteria.
Eye patches can be glued over the affected eye, after treatment. Eye patches offer protection from any further irritation from dust, flies and sunlight. Protection is probably only of value to an individual animal when there is still a chance of saving sight in the eye. However, preventing flies access to the affected eye will reduce spread of the disease within the herd.
PREVENTION AND CONTROL
- Fly control: Use sprays, pour‐ons, repellents or dust bags early in the fly season and use insecticide impregnated ear tags when there is a heavy fly population. For effective fly control, two ear tags are recommended. Alternate the use of pyrethroids and organophosphates on a yearly basis to help prevent resistance development. A fly control program should focus on egg and larvae control. Multiple methods of control should be employed to achieve good results.
- Grass, weed, and brush control: Clip or graze pastures. Grazing management, brush beating, mowing, and spraying minimize pollen and mechanical irritation to the eyes.
- Hay and/or feed bunk management –avoid overhead hay feeders, spread hay out, do not feed hay containing mature seed heads or cheat grass in overhead feeders or in round bales, and increase bunk space to decrease direct contact.
- Ultraviolet light (sun light) ‐ breed for eyelid pigmentation, provide shade or tree rows with ample room to prevent overcrowding.
- Disease management – provide proper immunization against viral diseases (IBR and BVD), isolate infected animals, and decrease environmental and nutritional stress.
- Vaccination – Commercial and autogenous pinkeye vaccines are available. Reported results by producers and veterinarians have been mixed from their use of these products. Because pinkeye vaccines have not proven to be consistently effective in prevention, check with a local veterinarian about the use of these products in a specific area. It should also be emphasized that vaccination is only part of a disease prevention program.
- Infected animals should be isolated and treated.