In a study published in this week's PLoS Medicine, researchers have found that more than one species of bacteria may be causing the infectious eye disease trachoma.
Six million people – most of whom live in crowded and unhygienic conditions in the developing world – are blind because of the disease and many more are actively infected. The possibility that multiple strains of the Chlamydiceae family of bacteria are involved in trachoma would involve a re-evaluation of vaccines and treatment programmes.
It is accepted that Chlamydia trachomatis (C. trachomatis) causes trachoma. The bacteria, some strains of which are associated with sexually transmitted infections, can also pass between people on hands and clothing; successive infections cause scarring of the inside of the eyelid. As the eyelashes of the infected eyes turn inward they scar the cornea - the transparent tissue covering the front of the eye - leading eventually to blindness. To investigate whether other species of Chlamydiceae also cause human trachoma, Deborah Dean and colleagues from Children's Hospital Oakland Research Institute and the University of California San Francisco conducted their research in the Lumbini Zone of south-western Nepal where the disease is endemic. Obtaining specimens from 146 individuals in 9 households, they found that a third of the people who had trachoma were infected with only C. trachomatis, including not only the type that is typically described in trachoma-infected eyes but also the type usually associated with sexually transmitted diseases. Also, participants with Chlamidiacae infections of the eye were infected only with species previously associated with lung infections: one in five showed Chlamydophilia psittaci (C. psittaci) and one in ten Chlamydophila pneumoniae (C. pneumoniae); infection with these strains was just as strongly linked with severe inflammation of the eyes as was infection with the C. trachomatis bacteria already known to cause trachoma. Additionally, one third of the individuals had a mixed infection with two or three species.
Interventions to prevent trachoma by improving personal hygiene – such as the SAFE initiative promoted by the World Health Organization – have had limited success, and an effective vaccine may also be needed to eliminate the disease. The findings and their distribution by household and age provide evidence that C. psittaci and C. pneumoniae, in addition to C. trachomatis, are involved with trachoma and that these infections are widespread rather than sporadic. The findings would also explain why some people with active trachoma do not have C. trachomatis in their eyes, and suggest that antibiotics used for trachoma may need to be changed or used for longer periods of time to be effective against all three species. If these findings are confirmed in other trachoma-endemic regions, then future vaccines and treatments w ill need to combat all these bacteria and not just C. trachomatis.