CASE NOTES

CONTAGIOUS OPHTHALMIA ASSOCIATED WITH MYCOPLASMA CONJUNCTIVAE IN SHEEP

Laura Kerrison, Veterinary Student, University of Sydney, Bruce Watt, Central Tablelands Local Land Services, Bathurst and Mark Hazelton, Ania Deutscher and Mark Westman, Elizabeth Macarthur Agricultural Institute, Menangle

Posted Flock & Herd November 2020

Introduction

Contagious ophthalmia (infectious keratoconjunctivitis or &squo;pink eye&squo;) is a contagious bacterial infection of sheep, goats and cattle. Clinical signs include inflamed conjunctivae, ocular discharge, corneal opacity and impaired vision, with corneal ulceration and perforation occurring in severe cases (Motha, et al.., 2003). Bacteria commonly associated with this condition include Mycoplasma conjunctivae, Chlamydia pecorum and Moraxella (Branhamella) ovis. However, Colesiota (Rickettsia) conjunctiva and Listeria monocytogenes can also be involved (Abbott, 2018). M. conjunctivae has been identified as the major cause of contagious ophthalmia in sheep (Naglić, et al.., 2000); however, other mycoplasma spp. can be involved, for example Mycoplasma arginini has been isolated (Surman, 1973). Moraxella ovis may be present in infections with contagious ophthalmia, but can also be found as part of the normal conjunctival flora of healthy sheep (Bankemper, et al.., 1990 and Dagnall, 1994) and, therefore, may be the primary pathogen or an opportunist infection.

This report details four cases of contagious ophthalmia in lambs and ewes where M. conjunctivae was detected via PCR, with and without concurrent isolation of Moraxella ovis. This finding supports the view that an antibiotic that is effective against Mycoplasma spp. (such as oxytetracycline) is the preferred option in severe cases of contagious ophthalmia.

History and clinical findings

Four cases of contagious ophthalmia were investigated in the Central Tablelands, NSW, from March to June 2020.

Case 1. In March 2020, ocular disease was noted amongst a total of 2450 Merino, Merino x West Suffolk and Merino Dorset lambs running in several mobs. Approximately 75% of the lambs were affected; however, few had notable visual deficits. The eyes of three lambs were examined, all presenting bilateral or unilateral serous ocular discharge, cloudy oedematous corneas (Figure 1) and peripheral neovascularisation. One had a shallow corneal ulcer (Figure 2).

Case 2. In March 2020, 30 of 300 Merino lambs were noticed to be affected with ophthalmic disease. Some lambs had been treated with topical cloxacillin as benzathine salt (278mg OU; Opticlox, Norbrook) with no noticeable improvement. Six were completely blind. Three lambs and one ewe were examined. The lambs had cloudy, oedematous corneas, red conjunctivae and serous ocular discharge (Figure 3). The ewe had bilateral stromal abscesses, extensive neovascularisation and corneal opacity (Figure 4).

Case 3. In March 2020, a mob of 515 composite ewe lambs, mustered for investigation of ewe infertility, were noted to be affected with mild contagious ophthalmia. From a selection of ten ewes examined closely, four were affected. The affected lambs had serous ocular discharge and some also presented with red conjunctiva and a cloudy cornea.

Case 4. In June 2020, 20 Merino ewe hoggets from a mob of 200 presented with blindness and a high stepping gait. Four were examined, all with bilateral cloudy corneas, superficial corneal erosions, marked neovascularisation and serous ocular discharge.

Figure 1: An affected lamb from Case 1 with a serous ocular discharge and corneal oedema

Figure 2: An affected lamb from Case 1 with diffuse corneal oedema, peripheral neovascularisation and a large corneal ulcer of the left eye

Figure 3: A ewe hogget from Case 2 with conjunctivitis, mild diffuse corneal oedema and serous ocular discharge

Figure 4: An affected ewe from Case 2 with marked neovascularisation, conjunctivitis, a stromal abscess and a seropurulent ocular discharge

Laboratory Findings

Dry eye swabs were collected for all cases and submitted to the EMAI for bacteriology diagnostics. Mycoplasma spp. and Chlamydia spp. PCRs were performed for all cases. Three cases had aerobic culture (sheep blood agar plate incubated at 37°C with 5% CO₂, and MacConkey agar plate incubated at 37°C) performed on all swabs, set up the day after the swabs were collected. One case (Case 3) did not have any culture performed.

Table 1 displays all laboratory results for Cases 1 to 4. Moraxella ovis was cultured in Cases 1 and 4. Mycoplasma spp. were detected via PCR from all cases. Employment of a real-time Mycoplasma spp. PCR for Cases 2-4 revealed that the relative amount of the target sequence was high (cycle threshold [Ct] values between 21-29).

The Mycoplasma sp. detected in all cases was determined to be M. conjunctivae by amplification and sequencing part of the 16S rRNA gene using in-house Mycoplasma-specific primers. Chlamydia spp. were not detected via PCR (individual or pooled) from any of the cases.

Table 1 Summary of laboratory results

Case	Lamb or Ewe	Aerobic culture	Mycoplasma spp. PCR¹	Chlamydia spp. PCR¹
1	1	Sparse mixed growth	D³ (3 swabs pooled) M. conjunctivae	ND (3 swabs pooled)
	2	Sparse mixed growth
	3	Sparse mixed growth including Moraxella ovis²
2	1	Profuse mixed growth	D³M. conjunctivae	ND
	2	Moderate mixed growth	D³M. conjunctivae	ND
	3	Sparse mixed growth	D³M. conjunctivae	ND
	4	No growth	D³M. conjunctivae	ND
3	1	Not performed	D³ (5 swabs pooled) M. conjunctivae	ND (5 swabs pooled)
	2	Not performed
	3	Not performed
	4	Not performed
	5	Not performed
4	1	Sparse mixed growth including Moraxella sp.⁴	D³ M. conjunctivae	ND (3 swabs pooled)
	2	Moderate mixed growth including Moraxella sp.⁴	D³M. conjunctivae
	3	Sparse pure growth of Moraxella ovis²	D⁵

D=detected, ND = not detected
Species determined via amplification and sequencing of the 16S-23S intergenic spacer region.
Species determined via amplification and sequencing part of the 16S rRNA gene using in-house Mycoplasma-specific primers.
DNA amplicon not sent for sequencing.
Unable to determine the species due to a mixed sequence result from sequencing part of the 16S rRNA gene using in-house Mycoplasma-specific primers.

Discussion

M. conjunctivae was detected by PCR from eye swabs from all four cases. M. conjunctivae is a common isolate associated with contagious ophthalmia (Abbott, 2018). Chlamydia spp. were not detected via PCR in any of the four cases.

The concurrent isolation of Moraxella ovis in Cases 1 and 4 may be due to its presence as part of normal conjunctival flora, or as a consequence of colonisation following infection with M. conjunctivae (Bankemper, et al.., 1990 and Dagnall, 1994). There are some reports that suggest concurrent infection with Moraxella ovis and M. conjunctivae may be associated with more severe clinical signs; however, severity may depend on the pathogenicity of the strain of Moraxella ovis (Dagnall, 1994).

In this case series, most lambs were not treated; however, severe cases such as shown in Figure 3 were treated with injectible long-acting tetracyclines. In our experience, severe cases respond to oxytetracyclines rather than antimicrobials that target cell wall synthesis (as expected given Mycoplasmas lack a cell wall).

Almost all of the affected sheep resolved within two weeks, which is consistent with the observations of Abbott, 2018. However, in our experience, severe cases may be refractory to treatment with permanent eye damage. This finding has been observed by others (Motha, et al.., 2003 and Naglić, et al.., 2000). Repeated yarding may exacerbate clinical signs due to increased stress and dust and increased transmission to naïve animals (Abbott, 2018). Animals with severely compromised vision may benefit from being separated to an area with adequate shade and easy access to food and water.

Flies and dust are believed to play a role in the transmission of infection (Toop, 1964, Abbott, 2018). However, on the Central Tablelands this disease often occurs in the colder seasons without predisposing factors such as flies, dust or other causes of eye damage such as grass seeds. While these mostly mild, but occasionally severe, cases all involved young sheep, contagious ophthalmia also occurs sporadically in flocks of mature ewes without obvious predisposing factors. Disease prevalence may be affected by host susceptibility and virulence of the organisms involved (Bankemper, et al.., 1990). Recovery from contagious ophthalmia results in short-term immunity for approximately one year before the sheep become susceptible if re-exposed to the organisms (Toop, 1964).

Acknowledgements

We thank NSW DPI Veterinary Bacteriology and Molecular Biology Diagnostic teams for performing the bacterial cultures and molecular testing.

References

Toop C. Contagious ophthalmia (pinkeye) of sheep. Journal of the Department of Agriculture, Western Australia, Series 4 1964;5:955-957
Motha M, Frey J, Hansen M, Jamaludin R, Tham K. Detection of Mycoplasma conjunctivae in sheep affected with conjunctivitis and infectious keratoconjunctivitis. New Zealand veterinary journal 2003;51:186-190
Abbott K. The Practice of Sheep Veterinary Medicine. 1st edn. University of Adelaide Press, Adelaide, 2018
Barile MF, Del Giudice RA, Tully JG. Isolation and Characterization of Mycoplasma conjunctivae sp. n. from Sheep and Goats with Keratoconjunctivitis. Infection and Immunity 1972;5:70
Naglić T, Šeol B, Hajsig D et al. Epidemiological and microbiological study of an outbreak of infectious keratoconjunctivitis in sheep. Veterinary Record 2000;147:72-75
Surman P. Mycoplasma aetiology of keratoconjunctivitis (&quo;pink-eye&quo;) in domestic ruminants. Australian Journal of Experimental Biology & Medical Science 1973;51
Bankemper KW, Lindley DM, Nusbaum KE, Mysinger RH. Keratoconjunctivitis associated with Neisseria ovis infection in a herd of goats. Journal of Veterinary Diagnostic Investigation 1990;2:76-78
Dagnall G. The role of Branhamella ovis, Mycoplasma conjunctivae and Chlamydia psittaci in conjunctivitis of sheep. British Veterinary Journal 1994;150:65-71