Case-control study to identify the causative agents of ophthalmia and conjunctivitis in goats in Savannakhet province of Lao PDR

Pinkeye is a highly contagious disease of goats with different aetiologies. Surveys in Lao PDR have identified eye lesions typical of pinkeye as a common condition, however, this has not been confirmed diagnostically, and the responsible pathogens have not been identified. A matched case-control study was implemented in 70 goat holdings from Savannakhet province, Lao PDR, to detect agents causing pinkeye and conduct phylogenetic analysis of the identified pathogens. Fifty eye swabs from goats with infected eyes (cases) and 50 paired samples from unaffected cohorts (controls) were collected from 25 holdings. Samples were tested using quantitative PCR assays targeting known pinkeye pathogens at the genus and species levels. The prevalence of pathogens in case and control goats was as follows: Mycoplasma conjunctivae (94% and 74% respectively, P = 0.006, OR = 5.5), Chlamydia pecorum (4%, 10%), Moraxella ovis (30%, 30%), Moraxella bovis (0%, 0%) and Moraxella bovoculi (0%, 0%). M. conjunctivae was present in a high proportion of goats in both groups revealing that Lao goats are carriers of M. conjunctivae. However, the mean log₁₀ genome copy number/µL of DNA extract was significantly higher in case goats than control goats (P < 0.05). Thus, M. conjunctivae is likely the principal causative agent of pinkeye in Lao goats with carrier status converting to clinical infection following corneal damage or other causative factors. M. conjunctivae detected in samples from different goats and districts showed low genetic diversity. Identifying the causes of pinkeye in Lao goats will assist in designing appropriate treatment and control strategies.