Trachoma: how a common cause of blindness can be prevented worldwide
The world has seen a large decline in trachoma, but millions are still at risk. How can we make more progress against it?
Hundreds of thousands of people worldwide are blind because of a disease called trachoma. Trachoma is caused by repeated bacterial infections, and people suffer eye pain for years before they can potentially go blind from the disease.
Records of trachoma date back thousands of years, and it used to be common across Africa, the Middle East, South Asia, and South and Central America.1
Even today, the disease is a major infectious cause of blindness worldwide. But it can be prevented.
Many countries have recently eliminated or substantially reduced the disease through antibiotics, surgery, improved sanitation, clean water and hygiene, and insect control.
This progress is a major success story of public health efforts, and with more effort, the world can entirely eliminate this painful cause of blindness.
What is trachoma?
Trachoma is an eye disease caused by specific strains of the bacterium Chlamydia trachomatis.2
These bacteria are infectious and can spread between people through touching secretions from the eyes or nose or from contaminated items like clothing. It can also be spread via flies, especially some species that are attracted to human eyes.3
The bacteria infect the conjunctiva — the thin, pink, soft inner layer of the eyelids — which leads to inflammation.
If people have many repeated infections, the inflammation scars the eyelids, which begin to turn inwards.4 The eyelashes then turn inwards and scratch the cornea (the clear surface of the eyes). In severe cases, this causes the cornea to become clouded, which eventually results in permanent blindness.5
Trachoma is more common in rural areas and spreads easily between people living together, especially in places with poor sanitation and hygiene.6 While it mainly infects children, the later stages of scarring and blindness develop in adulthood.7
Trachoma is a very painful disease. Aside from the risk of blindness, it causes blurry vision, red and swollen eyes, pain while blinking or sleeping, and vision loss. As a consequence, people are more prone to accidents, have problems with daily life and work, and experience social stigma.
It’s estimated that more than 400,000 people globally were blind as a result of trachoma in 2021. As you can see in the chart below, it is a particularly common cause of blindness in Africa and South Asia.8
Trachoma is preventable
There are several ways to tackle trachoma and blindness.
First, the spread of the Chlamydia trachomatis bacteria can be reduced. With more access to clean water and sanitation, better waste management, and hygiene, it becomes less likely that the bacteria spread between people.9 Insecticides can also help deter flies.10
Second, the disease can be prevented in people who have been infected. For example, antibiotics such as azithromycin and tetracycline can kill the bacteria causing the disease.11
For people who have progressed to later stages of the disease, there are also cheap surgeries, which reshape the patient’s eyelids12 or remove in-turned eyelashes. These help prevent the clouding of the cornea and blindness.13
Trachoma was once seen around the world, but it has declined greatly over time
Trachoma is an ancient disease that has been described in ancient Egypt, China, and Greece. It is less common outside tropical regions, but as recently as the 1950s, the World Health Organization reported that it was found in almost every country in the world.1
Trachoma declined significantly in many richer countries over the twentieth century with improvements in clean water, sanitation, garbage collection systems, insect control programs, and the development of effective antibiotics.14
Although it’s still widespread in poorer countries, great progress has been made against the disease in the last few decades.
The maps below show the prevalence of early stages of trachoma in African children, according to surveys conducted between 1996 and 2021.15
In the first surveys, which were mostly conducted in the early 2000s, more than 10% of children in many areas had trachoma. In some, more than half of children had the disease.
However, by the most recent surveys, the prevalence of trachoma shrunk greatly.
Of all the areas surveyed, 92% had begun using mass antibiotic treatment programs, and 77% of areas managed to reduce the prevalence of trachoma by 50% or more.15
Many countries, including the poorest ones, are making progress
A lot of progress has been made in poorer countries in the last few decades through deliberate public health efforts.
In 1998, the World Health Organization established the “WHO Alliance for the Global Elimination of Trachoma by 2020” (GET2020), which aimed to eliminate trachoma as a health problem by 2020.
Although trachoma hasn’t yet been eliminated, researchers estimate that the number of people at risk of blindness from trachoma worldwide has declined substantially.15
The strategy relied on collecting data — mapping the disease down to the level of neighborhoods in the poorest regions — which would help guide efforts to fight it and track progress over time.
To do this, the “Global Trachoma Mapping Project” was launched in 2012, which was led by Sightsavers and funded by the United States Agency for International Development (USAID) and the Department for International Development (DFID).
Researchers surveyed over 2.6 million people across 35 countries to identify people who were infected or had developed the disease.17
They checked whether people had developed eye symptoms, which helped to understand which regions had higher rates of trachoma and how many people were at risk.18
Using this knowledge, countries could direct antibiotics to populations at higher risk of trachoma. International efforts also provided access to surgery, education on hygiene practices, and generally improved access to clean water and sanitation.19
The chart below shows the number of people living in areas where trachoma is common and the number who have been treated with antibiotics or surgery.
As you can see, over a hundred million people were at risk of trachoma in 2022.
This is lower than it was in the past because the number of people treated with antibiotics has risen over time as the global project scaled up. The chart also shows that the COVID-19 pandemic disrupted treatment programs.
These efforts in controlling trachoma have been very effective.
In many regions, the prevalence of trachoma reduced greatly, as we saw in the previous section.
Eighteen countries were able to reduce the disease sufficiently to eliminate the disease as a public health problem as of 2023. They are shown in blue on the map below.
More progress can be made to eliminate trachoma
There are two remaining challenges to eliminating trachoma.
First, the disease still persists in the world’s poorest areas, and over a hundred million people are still at risk.
Second, continued efforts — such as surgeries — are still needed to treat adults who have reached later stages of the disease.
By using tools more widely — such as antibiotics, surgeries, clean water, sanitation, and insecticides — we could greatly reduce trachoma, especially after disruptions from the COVID-19 pandemic.
Several new technologies could also help eliminate the disease. They include improved rapid tests to diagnose infected people, antibody tests to study immunity toward the disease, new surgical techniques, and vaccines.9
Previous research has shown that vaccines can provide at least short-term protection against the disease, which suggests that effective vaccines could be developed. However, only one trachoma vaccine candidate is in human trials as of 2024.20
As the charts below show, research investments to address trachoma are very limited and have declined recently.21
Our efforts so far — mapping trachoma, providing antibiotics, surgeries, clean water, sanitation, waste management, and insect control — show us that public health initiatives can successfully improve the lives of millions of people. There is a clear path to eliminating this ancient disease; we should decide to take it.
Acknowledgments
I’m very grateful to Kristen Renneker for providing this article's geospatial and survey data. Ed Mathieu, Hannah Ritchie, and Max Roser also provided valuable feedback on this article.
Explore more data on neglected tropical diseases:
Neglected Tropical Diseases
Neglected tropical diseases affect millions of people despite the existence of cheap interventions to control them.
Endnotes
Sidky, M. M., & Freyche, M. J. (1951). World Distribution and Prevalence of Trachoma in Recent Years. Epidemiological & Vital Statistics Report, World Health Organisation, Nov-Dec, Vol. 2(No. 11/12), 230–277.
Allen, S. K., & Semba, R. D. (2002). The Trachoma “Menace” in the United States, 1897–1960. Survey of Ophthalmology, 47(5), 500–509. https://doi.org/10.1016/S0039-6257(02)00340-5
Taylor, H. R. (2008). Trachoma: A blinding scourge from the bronze age to the twenty-first century. Haddington Press.
Different strains of the bacteria cause chlamydia, a genital infection.
Brewer, N., McKenzie, M. S., Melkonjan, N., Zaky, M., Vik, R., Stoffolano, J. G., & Webley, W. C. (2021). Persistence and Significance of Chlamydia trachomatis in the Housefly, Musca domestica L. Vector-Borne and Zoonotic Diseases, vbz.2021.0021. https://doi.org/10.1089/vbz.2021.0021
Robinson, A., Gomes, L. R. D. O., Abdurahman, O. S., Alemayehu, W., Shuka, G., Melese, E., Guye, M., Legesse, D., Elias, E., Temam, K., Koro, K. H., Adugna, D., Seife, F., Aga, M. A., Sarah, V., Lambert, S. M., Walker, S. L., Habtamu, E., Solomon, A. W., … Logan, J. G. (2022). Evaluation of the efficacy of insecticide-treated scarves to protect children from the trachoma vector Musca sorbens (Diptera: Muscidae): A phase II randomised controlled trial in Oromia, Ethiopia. eClinicalMedicine, 49, 101487. https://doi.org/10.1016/j.eclinm.2022.101487
Gambhir et al. (2009) estimate that it takes over a hundred infections per individual, on average, for trichiasis (when the eyelashes begin to scratch the cornea) to develop. This estimate is based on simulations using data on the duration of each infection and infection load and may be revised based on further data.
Gambhir, M., Basáñez, M.-G., Burton, M. J., Solomon, A. W., Bailey, R. L., Holland, M. J., Blake, I. M., Donnelly, C. A., Jabr, I., Mabey, D. C., & Grassly, N. C. (2009). The Development of an Age-Structured Model for Trachoma Transmission Dynamics, Pathogenesis and Control. PLoS Neglected Tropical Diseases, 3(6), e462. https://doi.org/10.1371/journal.pntd.0000462
Solomon, A. W., Burton, M. J., Gower, E. W., Harding-Esch, E. M., Oldenburg, C. E., Taylor, H. R., & Traoré, L. (2022). Trachoma. Nature Reviews Disease Primers, 8(1), 32. https://doi.org/10.1038/s41572-022-00359-5
See here for a grading system used to diagnose it, which lists the different stages of the disease -
Solomon, A. W., Kello, A. B., Bangert, M., West, S. K., Taylor, H. R., Tekeraoi, R., & Foster, A. (2020). The simplified trachoma grading system, amended. Bulletin of the World Health Organization, 98(10), 698–705. https://doi.org/10.2471/BLT.19.248708
Blake, I. M., Burton, M. J., Bailey, R. L., Solomon, A. W., West, S., Muñoz, B., Holland, M. J., Mabey, D. C. W., Gambhir, M., Basáñez, M.-G., & Grassly, N. C. (2009). Estimating Household and Community Transmission of Ocular Chlamydia trachomatis. PLoS Neglected Tropical Diseases, 3(3), e401. https://doi.org/10.1371/journal.pntd.0000401
Burgert-Brucker, C. R., Adams, M. W., Mingkwan, P., Flueckiger, R., Ngondi, J. M., Solomon, A. W., & Harding-Esch, E. M. (2022). Community-level trachoma ecological associations and the use of geospatial analysis methods: A systematic review. PLoS Neglected Tropical Diseases, 16(4), e0010272. https://doi.org/10.1371/journal.pntd.0010272
Gambhir et al. (2009) estimate that it takes over a hundred infections per individual, on average, for trichiasis (when the eyelashes begin to scratch the cornea) to develop. This estimate is based on simulations using data on the duration of each infection and infection load and may be revised based on further data.
Gambhir, M., Basáñez, M.-G., Burton, M. J., Solomon, A. W., Bailey, R. L., Holland, M. J., Blake, I. M., Donnelly, C. A., Jabr, I., Mabey, D. C., & Grassly, N. C. (2009). The Development of an Age-Structured Model for Trachoma Transmission Dynamics, Pathogenesis and Control. PLoS Neglected Tropical Diseases, 3(6), e462. https://doi.org/10.1371/journal.pntd.0000462
Ramadhani, A. M., Derrick, T., Holland, M. J., & Burton, M. J. (2016). Blinding Trachoma: Systematic Review of Rates and Risk Factors for Progressive Disease. PLOS Neglected Tropical Diseases, 10(8), e0004859. https://doi.org/10.1371/journal.pntd.0004859
Flaxman, S. R., Bourne, R. R. A., Resnikoff, S., Ackland, P., Braithwaite, T., Cicinelli, M. V., Das, A., Jonas, J. B., Keeffe, J., Kempen, J. H., Leasher, J., Limburg, H., Naidoo, K., Pesudovs, K., Silvester, A., Stevens, G. A., Tahhan, N., Wong, T. Y., Taylor, H. R., … Zheng, Y. (2017). Global causes of blindness and distance vision impairment 1990–2020: A systematic review and meta-analysis. The Lancet Global Health, 5(12), e1221–e1234. https://doi.org/10.1016/S2214-109X(17)30393-5
Solomon, A. W., Burton, M. J., Gower, E. W., Harding-Esch, E. M., Oldenburg, C. E., Taylor, H. R., & Traoré, L. (2022). Trachoma. Nature Reviews Disease Primers, 8(1), 32. https://doi.org/10.1038/s41572-022-00359-5
Indoor spraying of insecticides and the wearing of insecticide-treated scarves have been found to protect against trachoma infections.
Robinson, A., Gomes, L. R. D. O., Abdurahman, O. S., Alemayehu, W., Shuka, G., Melese, E., Guye, M., Legesse, D., Elias, E., Temam, K., Koro, K. H., Adugna, D., Seife, F., Aga, M. A., Sarah, V., Lambert, S. M., Walker, S. L., Habtamu, E., Solomon, A. W., … Logan, J. G. (2022). Evaluation of the efficacy of insecticide-treated scarves to protect children from the trachoma vector Musca sorbens (Diptera: Muscidae): A phase II randomised controlled trial in Oromia, Ethiopia. eClinicalMedicine, 49, 101487. https://doi.org/10.1016/j.eclinm.2022.101487
Amza, A., Goldschmidt, P., Einterz, E., Huguet, P., Olmiere, C., Bensaid, P., & Bella-Assumpta, L. (2010). Elimination of Active Trachoma after Two Topical Mass Treatments with Azithromycin 1.5% Eye Drops. PLoS Neglected Tropical Diseases, 4(11), e895. https://doi.org/10.1371/journal.pntd.0000895
Amza, A., Goldschmidt, P., Einterz, E., Huguet, P., Olmiere, C., Bensaid, P., & Bella-Assumpta, L. (2010). Elimination of Active Trachoma after Two Topical Mass Treatments with Azithromycin 1.5% Eye Drops. PLoS Neglected Tropical Diseases, 4(11), e895. https://doi.org/10.1371/journal.pntd.0000895
Solomon, A. W., Burton, M. J., Gower, E. W., Harding-Esch, E. M., Oldenburg, C. E., Taylor, H. R., & Traoré, L. (2022). Trachoma. Nature Reviews Disease Primers, 8(1), 32. https://doi.org/10.1038/s41572-022-00359-5
For example, the WHO-recommended bilamellar tarsal rotation (BLTR) surgery cost US$40 as of 2011.
Sightsavers (2011). Elimination of Blinding Trachoma. Available online.
World Health Organization (2015). Investing to overcome the global impact of neglected tropical diseases: Third WHO report on neglected tropical diseases. Available online.
Karun, V., Hotez, P. J., & Rosengart, T. K. (2017). Global surgery and the neglected tropical diseases. PLOS Neglected Tropical Diseases, 11(9), e0005563. https://doi.org/10.1371/journal.pntd.0005563
Habtamu, E., Wondie, T., Aweke, S., Tadesse, Z., Zerihun, M., Zewudie, Z., Kello, A. B., Roberts, C. H., Emerson, P. M., Bailey, R. L., Mabey, D. C. W., Rajak, S. N., Callahan, K., Weiss, H. A., & Burton, M. J. (2016). Posterior lamellar versus bilamellar tarsal rotation surgery for trachomatous trichiasis in Ethiopia: A randomised controlled trial. The Lancet Global Health, 4(3), e175–e184. https://doi.org/10.1016/S2214-109X(15)00299-5
Allen, S. K., & Semba, R. D. (2002). The Trachoma “Menace” in the United States, 1897–1960. Survey of Ophthalmology, 47(5), 500–509. https://doi.org/10.1016/S0039-6257(02)00340-5
Renneker, K. K., Abdala, M., Addy, J., Al-Khatib, T., Amer, K., Badiane, M. D., Batcho, W., Bella, L., Bougouma, C., Bucumi, V., Chisenga, T., Dat, T. M., Dézoumbé, D., Elshafie, B., Garae, M., Goepogui, A., Hammou, J., Kabona, G., Kadri, B., … Ngondi, J. M. (2022). Global progress toward the elimination of active trachoma: An analysis of 38 countries. The Lancet Global Health, 10(4), e491–e500. https://doi.org/10.1016/S2214-109X(22)00050-X
Data and scripts to recreate these maps can be found on Github.
Renneker, K. K., Abdala, M., Addy, J., Al-Khatib, T., Amer, K., Badiane, M. D., Batcho, W., Bella, L., Bougouma, C., Bucumi, V., Chisenga, T., Dat, T. M., Dézoumbé, D., Elshafie, B., Garae, M., Goepogui, A., Hammou, J., Kabona, G., Kadri, B., … Ngondi, J. M. (2022). Global progress toward the elimination of active trachoma: An analysis of 38 countries. The Lancet Global Health, 10(4), e491–e500. https://doi.org/10.1016/S2214-109X(22)00050-X
Strachan, C. (2016). End of Project Evaluation: Evaluation Report. https://assets.publishing.service.gov.uk/media/5a82ce48ed915d74e3403aa2/Evaluation-of-Global-Trachoma-Mapping-Project.pdf
Estimates from these surveys and other surveys in endemic countries were shown above.
Solomon, A. W., Pavluck, A. L., Courtright, P., Aboe, A., Adamu, L., Alemayehu, W., Alemu, M., Alexander, N. D. E., Kello, A. B., Bero, B., Brooker, S. J., Chu, B. K., Dejene, M., Emerson, P. M., Flueckiger, R. M., Gadisa, S., Gass, K., Gebre, T., Habtamu, Z., … Foster, A. (2015). The Global Trachoma Mapping Project: Methodology of a 34-Country Population-Based Study. Ophthalmic Epidemiology, 22(3), 214–225. https://doi.org/10.3109/09286586.2015.1037401
Strachan, C. (2016). End of Project Evaluation: Evaluation Report. https://assets.publishing.service.gov.uk/media/5a82ce48ed915d74e3403aa2/Evaluation-of-Global-Trachoma-Mapping-Project.pdf
In total, four candidate vaccines are in development. However, three are in the pre-clinical stages of research as of 2024.
Policy Cures Research. (2024). The Impact of Global Health R&D: The high return of investing in R&D for neglected diseases. Available online.
Chavda, V. P., Pandya, A., Kypreos, E., Patravale, V., & Apostolopoulos, V. (2022). Chlamydia trachomatis: Quest for an eye-opening vaccine breakthrough. Expert Review of Vaccines, 21(6), 771–781. https://doi.org/10.1080/14760584.2022.2061461
Pollock, K. M., Borges, Á. H., Cheeseman, H. M., Rosenkrands, I., Schmidt, K. L., Søndergaard, R. E., Day, S., Evans, A., McFarlane, L. R., Joypooranachandran, J., Amini, F., Skallerup, P., Dohn, R. B., Jensen, C. G., Olsen, A. W., Bang, P., Cole, T., Schronce, J., Lemm, N.-M., … Follmann, F. (2024). An investigation of trachoma vaccine regimens by the chlamydia vaccine CTH522 administered with cationic liposomes in healthy adults (CHLM-02): A phase 1, double-blind trial. The Lancet Infectious Diseases, S1473309924001476. https://doi.org/10.1016/S1473-3099(24)00147-6
Annual funding for trachoma was only around 2 million USD in 2019. In comparison, the WHO estimates that 2.5 million people had trachomatous trichiasis (the stage when eyelashes touch the eye) in 2019.
That means approximately 1.25 USD was spent annually on research and development against trachoma per person with trachoma.
World Health Organization (2022). R&D funding flows for neglected diseases by disease, year and funding category. Available online. [Accessed 17 May 2024]
World Health Organization (2019). Weekly epidemiological record. 19 JULY 2019. Available online. [Accessed 20 May 2024]
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Saloni Dattani and Fiona Spooner (2024) - “Trachoma: how a common cause of blindness can be prevented worldwide” Published online at OurWorldinData.org. Retrieved from: 'https://ourworldindata.org/trachoma-how-a-common-cause-of-blindness-can-be-prevented-worldwide' [Online Resource]BibTeX citation
@article{owid-trachoma-how-a-common-cause-of-blindness-can-be-prevented-worldwide,
author = {Saloni Dattani and Fiona Spooner},
title = {Trachoma: how a common cause of blindness can be prevented worldwide},
journal = {Our World in Data},
year = {2024},
note = {https://ourworldindata.org/trachoma-how-a-common-cause-of-blindness-can-be-prevented-worldwide}
}
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