Dr Merina Kurian, Junior Doctor

Dr Bayad Nozad, Public Health Consultant

Introduction

Neglected tropical diseases (NTDs) are defined as diseases that mainly affect individuals living in the most deprived populations globally and continue to persist as a consequence of poverty (1). The World Health Organization (WHO) has estimated that greater than 1.7 billion individuals are affected by NTDs, largely in countries of lower to middle-income or low-income (1). Several factors influence the persistence of NTDs including inadequate data regarding the conditions, poor political support, ineffective ways to remove human waste safely, and limited availability of clean water (1,2). There are 20 currently listed NTDs (3). Several NTDs can impact eye health such as blinding trachoma and onchocerciasis (river blindness) which table 1 outlines (3,4). This article provides an overview of the WHO initiatives to manage trachoma and onchocerciasis, two NTDs that can affect the eyes.

Neglected Tropical Disease	Can it affect eye health?
Bilharzia (schistosomiasis)	Yes although rare. For example can cause a subretinal granuloma or uveitis (5)
Blinding trachoma	Yes, can cause inflammation and scarring of the eyelids, as well as trichiasis (6)
Buruli ulcer (Infection of Mycobacterium ulcerans)(7)	Yes, can cause complications following the development of an ulcer (8)
Chagas disease	Yes, for example it can lead to damage of the retinal pigment epithelium (5)
Dengue	Yes, although rare. Can cause anterior uveitis, vitritis, intraretinal haemorrhages and maculopathy (9,10)
Chikungunya	Yes, can cause a range of ocular presentations for example conjunctivitis, keratitis, episcleritis, uveitis and optic neuritis (11–15)
Echinococcosis	Yes, although rare. Can lead to proptosis, corneal ulcers, keratitis, space occupying lesions, optic nerve atrophy, neuritis and orbit wall erosion (5)
Elephantiasis (lymphatic filariasis)	Yes, although rate. Can cause retinal haemorrhages, iritis, eyelid elephantiasis and tears containing microfilaria (16,17)
Leprosy	Yes, leprosy can lead to a range of pathologies including eye lid lesions, lagophthalmos, iridocyclitis, episcleritis, scleritis, corneal scarring, corneal ulceration, corneal anaesthesia and blindness (18,19)
River blindness (onchocerciasis)	Yes, can cause iridocyclitis, optic nerve atrophy, chorioretinitis and sclerosing keratitis leading to vision loss (5)

Trachoma

Trachoma is caused by the bacteria Chlamydia trachomatis (20,21). It is the most common cause of preventable global blindness due to infection, contributing to reduced vision or blindness in approximately 1.9 million individuals (20,21). The number of individuals who are at risk of developing trachoma is believed to be 142.2 million worldwide (22). Trachoma is found across 44 countries with the highest prevalence in the more deprived populations of Asia, Africa, Middle East, Australia as well as Central and South America (20,22). Transmission occurs via spread of eye or nose secretions from an infected individual to a non-infected individual, through direct contact or indirectly, for example, by flies or contaminated items (20,23). Infection is common in children in areas with high prevalence of trachoma (20). The ocular features of trachoma can include conjunctival scarring and trachomatous trichiasis in which the eyelashes scratch the cornea (20,21). Trachoma can cause irreversible corneal damage and blindness (21,23).

There are several social factors which are associated with trachoma. For example, women are at four times the risk of being blinded by trachoma as compared to men (20,24). This is considered to be due to the higher contact with children who have the infection (20). Lack of access to clean water and poor sanitation also affect the transmission of trachoma (25,26). Not only does trachoma have a significant impact on the quality of life of an individual, but also has economic consequences (20). According to the WHO, reduced visual ability and blindness is believed to cost $ 2.9-5.3 billion (US dollars) each year due to the loss of productivity (20).

Examples of WHO initiatives to address trachoma

The 51st World Health Assembly on the global elimination of blinding trachoma, outlined that member states of the WHO should ensure that the SAFE strategy (surgery, antibiotics, facial cleanliness and environment) was applied to help address trachoma. Additionally it advocated for new methods of rapid testing for trachoma in areas of high prevalence and outlined the need for strengthening the collaboration of countries with the WHO (27). The SAFE strategy incorporates (20,23):

• Surgery to treat trachomatous trichiasis. Surgical management of trachomatous trichiasis involves creating an incision on the eyelid’s length and then ensuring that the eyelashes are rotated back to their normal place (28)
• Antibiotics to treat the infection
• Ensuring facial cleanliness
• Improving the environment in which the individual lives, for example improving sanitation and access to clean water

The application of the SAFE strategy was supported by the Alliance for the Global Elimination of Blinding Trachoma by the Year 2020 (GET2020), led by the WHO to work in partnership with countries establishing the SAFE method (27,29). The strategy has been recognised as being one of the contributing factors to the elimination of trachoma in Gambia and Myanmar (30,31).

Progress has been made in helping to address trachoma. For example, over 90,000 individuals had surgical intervention for trachoma in 2019, whilst over 95 million were managed with antibiotics (26). According to the Report of the 19th meeting of the WHO Alliance for the Global Elimination of Trachoma by 2020, since 2014, significant steps have been made in trachoma management (32). These include the mapping of trachoma, and the development of a group of centres for trachoma coordination with the WHO (32).

The Human Eyelid Analogue Device for Surgical Training And skill Reinforcement in Trachoma (HEAD START) is a surgical initiative for the treatment of trachomatous trichiasis, which allows trainees to practice surgical correction of trichiasis on a surgical simulator prior to operating on a patient (28,33).

There are also organisations which work alongside the WHO, for example, the International Trachoma Initiative (ITI) for sharing information (34). Even so, trachoma continues to be a global public health problem (26). Additionally, the COVID-19 pandemic has also impacted programmes for addressing trachoma (35).

Onchocerciasis

The parasitic worm called Onchocerca volvulus is responsible for Onchocerciasis, also known as river blindness (35,36). The parasite is transmitted via blackflies, which produce larvae able to survive in the eyes as well as other organs (36,38). Onchocerciasis can cause a reduction in vision as well as blindness (5,36). It was estimated that of the 20.9 million individuals with Onchocerca volvulus infection globally, over 1 million had loss of vision in 2017 (36). According to the WHO, 99% of those infected with Onchocerca volvulus live in 31 African countries (36,39,40). It also affects individuals living in Yemen and Latin America (36,39,40). The treatment period may be prolonged, with treatment required each year for a minimum of 12 to 15 years to prevent spread in certain regions with onchocerciasis (41).

Examples of WHO initiatives to address onchocerciasis

In the 47th World Health Assembly, the WHO outlined the need for onchocerciasis control via distributing ivermectin. This included establishing national plans to treat onchocerciasis as well as encouraging member states to coordinate with nongovernmental organizations and other agencies (42). In 2003, the 56th World Health Assembly outlined the need for countries to start a Vision 2020 action plan to support the Global Initiative for the Elimination of Blindness (43). Additionally, the WHO requested that countries gather resources which could be used to help eliminate blindness (43). This was further supported by the 62nd World Health Assembly resolution to ensure that states applied a national action plan for preventable visual impairment as well as blindness (44).

The WHO Onchocerciasis Control Programme (OCP) which began in 1974 and ended in 2002, supported the elimination of onchocerciasis in 11 West African countries (45). The strategies of the WHO OCP was in the wide distribution of ivermectin and through the use of insecticides against  the vector black-fly larvae (46). The WHO OCP helped to prevent 600,000 cases of blindness, with 40 million protected from eye infections and lesions (45). Even so, there were challenges posed to the programme by conflict, poor political support and resource limitations (45). Currently, there are region-specific onchocerciasis programmes including the African Programme for Onchocerciasis Control (APOC) and the Onchocerciasis Elimination Program of the Americas (OEPA)(46). Through applying the interventions for several years, many countries have eliminated onchocerciasis including Guatemala in 2016 (41).

Conclusion

There are several NTDs which affect vision, including trachoma and onchocerciasis. Although progress has been made in reducing the global burden of disease of both these conditions by the WHO, challenges still arise in providing care due to the complexity of the factors involved in disease transmission and treatment.

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