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Ending lymphatic filariasis and onchocerciasis in Africa: Reasons for hope

2024; Elsevier BV; Volume: 140; Linguagem: Inglês

10.1016/j.ijid.2024.01.016

1878-3511

Tsitsi Masiyiwa, Moses J. Bockarie,

Parasites and Host Interactions

This year's World Neglected Tropic Diseases (NTD) Day (30 January 2024) comes during a moment of renewed momentum to eliminate NTDs. Two of the NTDs targeted for elimination – lymphatic filariasis (LF) and onchocerciasis (River blindness) – are seeing renewed investment, innovation and importantly, support for local implementing partners. Last December, His Highness Sheikh Mohamed bin Zayed Al Nahyan, President of the UAE, the Bill & Melinda Gates Foundation, and other partners, hosted the Reaching the Last Mile Forum on the inaugural Health Day at the United Nations Climate Change Conference (COP28) held in Dubai, UAE [1]. During the forum, global partners, including African governments and community leaders, joined forces to advance resilient health systems, committing a historic US$ 777 million to combat NTDs and end LF and onchocerciasis in Africa [2]. Lymphatic filariasis and onchocerciasis are parasitic diseases posing a significant public health challenge in Africa and other tropical regions [3]. The filaria parasites responsible for these diseases are transmitted by blood-feeding insects, leading to chronic and prolonged infections that result in disabilities such as hydrocoele, lymphoedema, and elephantiasis in lymphatic filariasis. On the other hand, onchocerciasis is characterized by skin disease and blindness [3]. Over 98% of the people at risk on onchocerciasis live in 31 countries in Africa, where infected blackflies (Simulium spp), that breed along fast-flowing rivers near remote rural villages [4], transmit the disease among local communities. Drugs like diethylcarbamazine, ivermectin, and albendazole are utilized, often in combination, to reduce microfilariae in blood (for LF) and skin (for onchocerciasis). National programs for elimination of NTDs have been operational in almost all disease affected countries in Africa to ensure the consistent delivery of drugs to affected communities, through mass drug administration (MDA) aiming to interrupt disease transmission and ultimately eliminate the public health burden associated with these conditions [5]. In 2020, the World Health Organization (WHO) endorsed the Ending the neglect to attain the Sustainable Development Goals: a road map for neglected tropical diseases 2021-2030, which sets out the path for preventing, controlling and eliminating 20 NTDs [6]. These include discontinuing MDA with ivermectin in at least one focus in 34 countries, in over 50% of the population in at least 16 countries, and in the entire endemic population in at least 12 countries (4, 5). The road map also aims to interrupt onchocerciasis transmission in 12 countries by 2030. Achieving these targets necessitates critical actions, such as establishing a well-coordinated global partnership to connect stakeholders and existing partnerships at all levels [7]. Since 2018, the END Fund, in collaboration with Reaching the Last Mile (RLM) [8], has overseen the RLM Fund, providing support for treatments, preventive care, and health worker training to accelerate the elimination of onchocerciasis and LF in communities lacking access to quality health services [9]. The RLM Fund has supported robust country-led partnerships, demonstrating the feasibility of eliminating river blindness in Africa. A significant announcement during the RLM Forum was the increase of this Fund from US$ 100 million to US$ 500 million [2]. The RLM Fund has made significant strides in sub-Saharan Africa, including providing over 100 million treatments, training 1.3 million health workers, and establishing nine laboratories for NTD surveillance and testing [9]. This expansion is geared towards ending LF and onchocerciasis in Africa, broadening the Fund's coverage from seven to thirty-nine countries across Africa. On Jan 30, 2023, the WHO and partners launched the Global Onchocerciasis Network for Elimination (GONE) to accelerate progress towards onchocerciasis targets set in the NTD road map [7]. The GONE network includes partners that pledged over US $300 million during the RLM event in Dubai in December 2023 including the governments of affected countries like Sierra Leone and Tanzania [2]. Working together on the GONE platform, activities of the funders, stakeholders and implementers will be better coordinated. The network will also serve as an advocacy body, at the national and international levels, to support the ‘last mile’ of elimination efforts [7]. It aims to improve coordination, collaboration, accelerate technical progress, implement a harmonized research agenda, and enhance service delivery. Globally, considerable progress has been made towards the elimination of onchocerciasis, including its elimination in four countries in the Americas – Colombia (2013), Ecuador (2014), Mexico (2015) and Guatemala (2016) [10]. In 2021, Niger, a RLM Fund supported country, became the first country in Africa to compile the requisite information for WHO for verification of elimination onchocerciasis [2]. In February 2023, Senegal, another RLM Fund supported country, announced the interruption of transmission of onchocerciasis a. Challenges to achieving present elimination targets have already been addressed including availability of tools for strengthening national capacity and expertise to implement entomological surveys and a strong partnership among stakeholders to ensure alignment [5]. These milestones are reasons for hope for ending onchocerciasis in Africa. Lymphatic filariasis, which is transmitted by Anopheles mosquitoes across sub-Saharan Africa, is a lower hanging fruit. The Anopheles vectors, which are also the vectors of malaria, are less efficient in transmitting filaria parasites when compared to the Simulium vectors that transmit onchocerciasis [11]. Vector control initiatives targeting malaria are already impacting LF transmission in many countries. The Global Programme to Eliminate Lymphatic Filariasis (GPELF) has achieved more than 43% reduction in the population requiring MDA since it was launched in 2000, and the disease has been eliminated as a public health problem in 17 countries including the African states of Togo and Malawi [12]. The WHO NTD roadmap target is to increase the number of countries validated for elimination as a public health problem to 58 in 2030 (6). The emerging dramatic impact of vector control efforts on LF transmission and the availability of the triple therapy combination of ivermectin (I), diethylcarbamazine (D) and albendazole (A) or IDA for MDA against the disease in certain non-onchocerciasis endemic settings in eastern and southern Africa are very encouraging. Implementation of IDA against LF in certain settings, including in São Tome and Principe have suggested that fewer than three rounds of IDA can reduce microfilaremia below the target threshold in areas where endemicity was low at the start of IDA or fewer than four 2-drug MDA rounds had been delivered previously, and >65% of the total population received IDA [12]. Vector control methods such as residual spraying and using long-lasting insecticidal nets to combat malaria have effectively reduced or eliminated LF transmission by Anopheles mosquitoes in parts of the Solomon Islands, Papua New Guinea, and Togo [13]. A recent survey in the previously LF endemic Gambia, where insecticide-treated bed nets are widely used, found no evidence for active transmission [11]. Lymphatic filariasis is now nearly eradicated along the shores of Lake Victoria, where it was endemic in the 1990s [11]. Residual spraying with dichlorodiphenyltrichloroethane (DDT), a key strategy against African trypanosomiasis (sleeping sickness), has contributed to the absence of LF in areas like southern Uganda, eastern Kenya, and northern Tanzania. The transmission intensity of LF in unmapped regions in Botswana and Zimbabwe may be very low due to extensive spraying efforts in the 1970s and 1980s, covering substantial land areas [11]. Zimbabwe plans to implement MDA with IDA in 2024. The implementation of IDA in low LF transmission zones in eastern and southern Africa will accelerate the interruption of the disease in Kenya, Botswana and Zimbabwe. The global community is heading in the right direction with concerted efforts in the fight against LF and onchocerciasis, which are important components of NTD. With additional funding, new impactful tools like IDA and a platform like GONE for improved coordination and collaboration, Africa ushers in 2024 with hope for ending LF and onchocerciasis. 1.RLM. Reaching the last mile forum 2023. https://www.reachingthelastmile.com/rlm-forum/. 2024; Last accessed 24 January 2024.2.WHO. Global partners pledge US$ 777 million to combat neglected tropical diseases. https://www.who.int/news/item/04-12-2023-global-partners-pledge-usd777-million-to-combat-neglected-tropical-diseases .2023; Last accessed 24 January 2024.3.Taylor MJ, Hoerauf A, Bockarie M. Lymphatic filariasis and onchocerciasis. Lancet. 2010;376(9747):1175-85.4.WHO. Elimination of human onchocerciasis: progress report, 2022–2023. Weekly epidemiological record. 2023; WER No 45(98):572–82.5.WHO. Scoping the needs and gaps of endemic countries in the onchocerciasis elimination programme: findings report, June 2023. https://www.who.int/publications/i/item/9789240075023. 2023; Last accessed 24 January 2024.6.WHO. Ending the neglect to attain the Sustainable Development Goals: A road map for neglected tropical diseases 2021–2030. https://www.who.int/publications/i/item/9789240010352. 2021;Last accessed 24 January 2024.7.Jesudason T. A new key-player for onchocerciasis elimination. Lancet Infect Dis. 2023;23(4):413.8.RLM. Reaching the last mile. https://www.reachingthelastmile.com/. 2024; Last accessed 24 January 2024.9.END Fund. The END Fund celebrates the expansion of the Reaching the last Mile Fund to eliminate River Blindness and Lymphatic Filariasis in Africa https://www.end.org/the-end-fund-celebrates-the-expansion-of-the-reaching-the-last-mile-fund-to-eliminate-river-blindness-and-lymphatic-filariasis-in-africa/. 2024; Last accessed 24 January 2024.10.WHO. Progress in eliminating onchocerciasis in the WHO Region of the Americas: disruption of ivermectin mass drug administration in the Yanomami focus area due to the COVID-19 pandemic. https://www.who.int/publications/i/item/who-wer9639-477-481. 2021; Last accessed 24 January 2024.11.Bockarie MJ, Rebollo MP. Reducing the population requiring interventions against lymphatic filariasis in Africa. Lancet Glob Health. 2016;4(3):e154-5.12.WHO. Global programme to eliminate lymphatic filariasis: progress report, 2022. Weekly epidemiological record. 2023;WER No 41(98): 489-502.13.Bockarie MJ, Pedersen EM, White GB, Michael E. Role of vector control in the global program to eliminate lymphatic filariasis. Annu Rev Entomol. 2009;54:469-87.