Measuring the Immunological Response to Trachoma-Causing Bacterial Antigens in Endemic Zones in Ethiopia: A Case Study

Trachoma is one of the Neglected Tropical Diseases (NTDs) for which the World Health Organization (WHO) has set a goal for elimination by 2020. It is the leading cause of preventable blindness and is caused from the repeated ocular infection with Chlamydia trachomatis (Ct). To achieve trachoma elimination, the WHO Alliance for the Global Elimination of Blinding Trachoma by 2020 (GET2020) recommends using the SAFE strategy comprised of Surgery (to treat trachomatous trichiasis, the late stage of the disease which leads to blindness if untreated), Antibiotics (to reduce bacterial load in communities with azithromycin/tetracycline distribution), Facial cleanliness and Environmental improvements (to reduce infection transmission and promote improved sanitation and hygiene behaviors).

In 1-9 year olds, active trachoma is determined through clinical signs of trachomatous inflammation – follicular (TF), sometimes manifested as trachomatous inflammation – intense (TI). However, the use of TF may not be optimal, especially after mass treatment where the correlation between clinical signs and infection is shown to be low at the community level, with higher levels of TF than active infection. This would also be a problem during surveillance in the long-term. Therefore, antibody testing against Ct antigens could be an alternative, as the antibody response to Ct persists even after infection resolves. Antibodies could serve either as a measure of historical infection or exposure over time.

Random selection

Ethiopia has a higher prevalence of trachoma than any other country, with over 69 million individuals living in areas in need of trachoma intervention. In December 2017, a study was initiated to evaluate antibody responses in several hyperendemic and lower prevalence woredas (district-equivalent) in Oromia - the largest and most populous region in Ethiopia  - using the Pgp3 LFA and Pgp3 ELISA. This study builds off a baseline study conducted in the Gemechis woreda of that region in 2016. Ocular swabs were also collected to test for infection and for possible whole genome sequencing.

Due to political unrest, it was impossible to collect data at the baseline site of Gemechis Woreda. However, data was collected in four hyperendemic districts (Fedis and Babilee) in East Hararge and (Dedo and Mana) in Jimma, as well as a low prevalence district (Halu) in Ilu Ababora with the help of nine teams – each composed of a grader, a laboratory technician, and a recorder. The teams spent three days in each woreda, and were each assigned per day one or two kebeles (the smallest administrative units within a district, often corresponding to villages). As the teams arrived at the kebele, they received a list of all gheres (development units of about 30 households). A ghere was then randomly selected from the list, and the team headed to each household in the selected ghere accompanied with a member from the kebele health bureau (often a health extension worker) and/or a district health bureau employee. Parents and guardians in the gheres often easily consented to have their children participate in the study, and provided assistance in data and specimen collection. Children were also provided with pencils and/or candies at the end of specimen collection, and if a child showed signs of TF/TI, parents were provided with two packs of tetracycline with instructions. Over 8,000 swab and blood spot specimens from over 4,000 children were collected overall from all five districts, and specimens were stored in a laboratory in Adama.


Photos (Credit: Ahlam Awad Mohammed)

Top: A laboratory technician collecting blood spots on filter paper from a young girl

Bottom: Random selection process of a ghere within each kebele (All ghere names put on rolled pieces of paper in a hat with the help of data collection team members and a health extension worker who provided the list.)