Infectious bovine keratoconjunctivitis

Infectious bovine keratoconjunctivitis, or IBK, is a veterinary infection of cattle caused by Moraxella bovis, a Gram-negative, β-haemolytic, aerobic, rod shaped bacterium. It is spread by direct contact or by flies serving as vectors. It is the most common ocular disease of cattle (mostly beef). IBK is similar to human pink eye and causes severe infection of the conjunctiva, edema, corneal opacity and ulceration. This disease is highly contagious and occurs worldwide. Younger animals are more susceptible but recovery with minimal damage is usual, if they are treated early. The disease is also known as pinkeye, New Forest eye or blight.^[1]

Cause

Moraxella bovis is a Gram-negative rod-shaped aerobe. This bacterium is an obligate intracellular parasite of the mucous membranes and can usually be isolated from the respiratory tract, vagina and conjunctiva of healthy animals. Transmission of IBK is through direct contact with mucous membranes and their secretions and indirect contact where flies act as a mechanical vector. Asymptomatic carrier animals can also be source of infection.

Predisposing factors

Ultraviolet (UV) radiation is implicated in cattle with no pigmentation around the eyelids and cattle with prominently placed eyes. Exudate from the sun-burnt skin around the eyes becomes a culture medium for bacteria and attracts flies. UV also directly damages the corneal epithelium leading to a breakdown in host innate immunity.

Dust, dried-up plants, tall vegetation and oversized or incorrectly placed ear tags may cause mechanical damage to the eye and facilitate bacterial colonization.

The disease may be complicated by concurrent infection with viruses such as infectious bovine rhinotracheitis virus (bovine herpesvirus 1) or adenovirus, bacteria such as Mycoplasma boviculi or Listeria monocytogenes, or infestation by Thelazia, a nematode.

Vitamin A deficiency is also implicated.

IBK is most prevalent in summer and early autumn.

A recent Meat & Livestock Australia (MLA) report "estimates that the disease costs Australian beef producers $23.5 million annually in lost production and treatment costs".^[1]

Clinical signs and diagnosis

The bacteria invade the lacrimal glands of the eye, causing keratitis, uveitis and ulceration. Cattle show signs of pain, increased lacrimation, excessive blinking and conjunctivitis.

More severe cases may show systemic signs such as inappetance and weight loss. Chronic untreated cases can become blind.

Diagnosis is usually based on the clinical signs, but the bacteria can be cultured from lacrimal swabs, or visualised on smears of lacrimal secretions.

Treatment and control

Shade, insect repellent impregnated ear tags, and lower stocking rate may help prevent IBK. Early identification of the disease also helps prevent spread throughout the herd. Treatment is with early systemic use of a long-acting antibiotic such as tetracycline or florfenicol. Subconjunctival injections with procaine penicillin or other antibiotics are also effective, providing a "bubble" of antibiotic which releases into the eye slowly over several days.

Anti-inflammatory therapy can help shorten recovery times, but topical corticosteroids should be used with care if corneal ulcers are present.

M. bovis uses several different serotyped fimbriae as virulence factors, consequently pharmaceutical companies have exploited this to create vaccines. However, currently available vaccines are not reliable.

Vaccination

Coopers Animal Health , a division of Schering-Plough, has released a new vaccine "Piliguard" in Australia. The vaccine contains three strains of Morexella bovis (SAH38, FLA 64, EPP 63) pilli antigen. This stimulate antibody production against the bacterial pilli to prevent their attachment and invasion of the conjuntiva. The company claims that the vaccine reduce the incidence and severity of the disease in an individual animal which directly reduce animal suffering and production loss on top of limiting the spread of disease through the herd. This in turn reduces the amount of antibioitcs and fly repellent needed during high-risk seasons. The vaccine is marketed in multidose-vials and have an adjuvant to create a long-term subcutaneous depot. This means that no booster shot is necessary but severe local reaction can be seen in people who accidentally self-inoculate. Calves as young as 1 week old can be treated and there is no meat, milk or export slaughter interval withhold.

References

External links

• Infectious Bovine Keratoconjunctivitis expert reviewed and published by Wikivet at http://en.wikivet.net/Infectious_Bovine_Keratoconjunctivitis accessed 06/10/2011.
• Animal Disease Diagnostic Laboratory