Mycoplasma conjunctivae infection

International Common Names

• English: conjunctivitis in sheep and goats; contagious conjunctivo-keratitis; contagious ophthalmia; contagious ovine ophthalmia; epidemic caprine keratoconjunctivitis; infectious caprine keratoconjunctivitis; infectious keratoconjunctivitis; infectious ovine keratoconjunctivitis; keratoconjunctivitis; kerato-conjunctivitis; mycoplasma conjunctivae keratoconjunctivitis in sheep and goats; ovine infectious keratoconjunctivitis; ovine keratoconjunctivitis; pink eye; pink-eye; pinkeye of sheep and goats
• French: kératoconjonctivite

English acronym

• ICK
• IKC
• IOK

Introduction

Mycoplasma conjunctivae (Mconj) is the cause of infectious keratoconjunctivitis (IKC), or pink-eye, in domestic and wild ovine and caprine species (Jones et al, 1976; Giacometti et al, 1998), although M. arginini and Acholeplasma oculi have also been isolated from sheep with ocular infections (Leach, 1970; Arbuckle and Bonson, 1980). M. agalactiae, the classical cause of contagious agalactia, and some members of the M. mycoides cluster may also cause keratoconjunctivitis (Bergonier et al., 1997). Bacterial causes of the disease include Chlamydia and Rickettsia (Egwu, 1991). IKC is a localized inflammatory condition of the conjunctiva and cornea in domestic and wild small ruminants. In the early stages, the disease may present as a unilateral or bilateral conjunctivitis with hyperaemia of the vessels but untreated cases may progress to mucopurulent keratitis and corneal ulceration resulting in opaque or perforated corneas and transient blindness. IKC with M. conjunctivae may be exacerbated by exposure to sunlight. In Scotland it occurs most frequently in the autumn: black face and Cheviot ewes are equally susceptible (Hosie, 1989). M. conjunctivae may be isolated with some difficulty in most mycoplasma media; it ferments glucose but does not use arginine or urea (Jones et al., 1976). Topical or parenteral administration of tetracyclines has been recommended for treatment (Hosie, 1989) although a report by Waseem Shahzad et al. (2013) indicated topical treatment with a sterile solution of gentamycin at 100mg/ml was suitable in Pakistan.

History

Mycoplasmas from sheep and goats with naturally occurring IKC were characterised biochemically and serologically from samples obtained from two farms in Maryland, USA, in the late 1960s and found to be a different species. They were not related to any known mycoplasmas isolated from sheep and goats with IKC but were similar to some conjunctival strains from Australia and Canada and named M. conjunctivae (Surman, 1968; McCauley et al., 1971; Barile et al., 1972;). IKC progresses slowly and it was not considered economically important at the time. Although a causal relationship between M. conjunctivae and IKC was not firmly established, the disease was subsequently reproduced experimentally (Jones et al., 1976; Trotter et al., 1977; ter Laak et al., 1988; Dagwall, 1993). Further isolations from sheep and Swiss chamois and ibex revealed that the disease was more severe in wild animals in which it caused total blindness (Nicolet and Freundt, 1975; Mayer et al., 1996). The M. conjunctivae genome is 846,214 bases, it has a G+C content of 29% with an estimated 734 genes (Calderon-Copete et al., 2009).

In acute cases of M. conjunctivae infection, the conjunctiva and cornea are infiltrated with large numbers of neutrophils and small numbers of plasma cells and lymphocytes. In one study the neutrophil count rose on the 1st day after inoculation, peaked 8 days afterwards, and decreased subsequently from day 13 to 25 when it was negligible (Dagnall, 1993). Cells scraped from the conjunctival fornix and stained by Giemsa show large numbers of uni-, bi- or tripolar bodies about 250-1100 µm in diameter closely associated with epithelial cells. Specific immufluorescence staining of such cells shows that these bodies are aggregations of M. conjunctivae.

In alpine ibex, the course of infection and pathogenesis (both clinically and histologically) seems to be more severe than in sheep. Mucopurulent and purulent discharges develop more rapidly and mononuclear infiltrates in conjunctival and limbic areas is more progressed. Vascularisation, ulceration and serious disruption of ocular structures are also more apparent (Mayer et al., 1997).

Four clinical stages of disease are recognised in ovine and caprine IKC (and apply for both bacterial and mycoplasmal causes of ocular infections) (Egwu, 1991).

Stage 1: Hyperaemia of the palperbral and the bulbar conjunctival vessels, serous lachrymation, increased blinking and blepharospasm. The corneoscleral junction may show congestion prior to vascular migration (pannus) into the cornea. Most cases do not progress beyond this stage, but regress spontaneously.

Stage 2: Continuation of stage 1, characterised by corneal inflammation with blood vessels and pannus spreading from the corneoscleral margin. Early keratitis causes great irritation and, consequently, the blepahospasm and lachrymation are more obvious. Again spontaneous regression may occur.

Stage 3: Progress from stage 2, to a mucopurulent keratitis with extension of migrating blood vessels and a more purulent lachrymal discharge. Sometimes shallow corneal ulceration is apparent, which affects vision. These cases are very obvious and usually receive treatment.

Stage 4: A corneal ulcer develops and vision is lost. Pus may be present in the anterior chamber of the eye (hypopyon). These cases are slow to resolve, even with treatment. Corneal scarring may persist permanently following resolution. Lymphoid follicle hyperplasia causes the conjunctiva and third eyelid to appear granular and nodular.

Frequently, the disease is less severe in lambs and most cases do not progress through all stages described. Corneal ulceration also is rare in lambs. Relapses in treated and naturally recovering animals commonly occur in keratoconjunctivitis associated with mycoplasmas.

The main reservoirs of M. conjunctivae are populations of domestic sheep. In an infected sheep the organisms can persist for up to 23 weeks, even after clinical recovery (Janovsky et al., 2001). Therefore, domesticated sheep in which the agent is self-maintained, are sometimes considered as reservoirs also for wild animals (Giacometti et al., 2002; Belloy et al., 2003; Egwu et al., 1989). Transmission from animal to animal is presumed to be by physical contact. One study recorded few contacts between wild and domestic animals in the Swiss Alps, and in this case the observation of Muscidid flies from the genera Hydrotaea, Musca, Morellia and Polietes frequenting infected eyes led to the suggestion of a possible role of these flies as vectors of M. conjunctivae (Giacometti et al., 2002). Another study observed that short-distance encounters between free-ranging individuals of different domestic and wild Caprinae species, are not uncommon events in the Alps (Degiorgis, 1998). In a study of wild Caprinae with and without clinical signs of infectious keratoconjunctivitis Mavrot et al. (2012) concluded that the mycoplasma load was significantly lower in eyes from healthy carriers; therefore the presence and severity of signs are related to the quantity of M. conjunctivae in the eyes.

The economic evaluation of IKC is difficult because of the variability of the clinical manifestations. At tupping time the occurrence of IKC was reported to reduce twining and induce toxaemia in affected ewes and temporarily reduce growth in lambs (Axelsen, 1961). Blindness, either unilateral or bilateral, leading to the accidental suffocation with placenta, or trampling of lambs, starvation, weight-loss, death or drowning of adult animals are among the losses ascribed to M. conjunctivae infection. The cost of treatment is probably the most significant economic loss (König, 1983; Hosie, 1988). M. conjunctivae-causing IKC has most severe consequences from blindness for wild chamois and ibex; a welfare concern for conservationists.

The use of corticosteroids is contra-indicated in keratitis especially where ulceration is present because it often antagonises rather than complements ocular defence mechanisms. Ophthalmic preparation of 350 mg of chlortetracycline twice a day for 3 days may eliminate M. conjunctivae. A single intramuscular dose of long-acting oxytetracycline may be used to supplement topical therapy or given on its own (König, 1983; Hosie and Greig, 1989).