Exploring Strategies to Control Neglected Tropical Diseases

In an article published in The Lancet, David H. Molyneux, DSc, from the University of Liverpool, United Kingdom, and colleagues review progress since 2010 in the area of neglected tropical diseases (NTDs), and also discuss strategies used to control them.

According to the authors, NTDs are typically addressed through five strategies: preventive chemotherapy, intensified disease management, vector control, veterinary public health measures for zoonotic neglected diseases, and through improved water and sanitation.

Preventive chemotherapy

The strategy of preventive chemotherapy and transmission (PCT) control is used for NTDs such as lymphatic filariasis, onchocerciasis, schistosomiasis, and soil-transmitted helminthiasis. The main strategy for their control involves periodic administration of effective, safe, and inexpensive (typically donated) drugs to at-risk populations, without first confirming a diagnosis in these individuals. According to the World Health Organization (WHO), more than 1 billion people suffering from NTDs in 88 countries benefited from large scale treatment programs in 2014.

For example, the African Programme for Onchocerciasis Control, which closed at the end of 2015, made epidemiological progress towards nationwide elimination in several African countries. “The African Programme for Onchocerciasis Control delivered more than 1 billion treatments between 1997 and 2014 in 19 countries, built capacity through training or retraining of more than 148,000 health workers and 1.46 million community directed distributors, facilitated use of community structures for other health programmes, and empowered more than 190,000 communities to direct their own ivermectin treatment schedules,” the authors write. A new initiative, the Expanded Special Project for the Elimination of NTDs in Africa, operating as a part of WHO, now continues to tackle onchocerciasis and other PCT-directed NTDs

Intensified disease management (IDM)

In contrast to PCT control, IDM is used for NTDs for which cost-effective control tools are lacking and for which large-scale use of existing tools is limited—including for Buruli ulcer, Chagas disease, human African trypanosomiasis, and leishmaniasis. For example, chemotherapy for Chagas’ disease remains problematic. Less than 1% of affected patients have access to benznidazole; in addition, data from a randomized trial in Chagas’ disease showed that benznidazole did not significantly reduce levels of cardiac clinical deterioration in patients through 5 years of follow-up. As a consequence, these IDM-targeted diseases tend to be more difficult and expensive to manage because of inherent challenges in their diagnosis, treatment, and follow-up.

Vector control

Vector control, in particular, has been an important component of NTD programs for many decades, and effective control strategies have contributed to great success in controlling NTDs such as lymphatic filariasis, visceral leishmaniasis, onchocerciasis, and Chagas’ disease. New strategies for the control of human African sleeping sickness, for example, using selective spraying of cattle to control the acute zoonotic form of disease, have also been effective. However, the authors say that continued development of novel vector control methods will require significantly increased investment if they are to be implemented. In particular, new tools and methods are now high priorities to reduce the spread of Aedes aegypti mosquitoes that transmit Dengue and Chikungunya, especially after the emergence of the Zika virus. In addition, mounting resistance to pyrethoid-based insecticides could jeopardize the lymphatic filariasis elimination program in Africa, the authors add.

Veterinary public health measures

The concept of One Health acknowledges the link between human health, animal health, and the environment. This approach has also been recognized as a major strategy for zoonotic disease control, and has been successfully used in several disease areas: to control rabies in people in Latin America, KwaZulu-Natal, the Philippines, and Bali, using rabies vaccination in dogs; and to control sleeping sickness in people in Uganda, using vector control by spraying cattle to selectively kill the tsetse fly, together with chemotherapy of the cattle reservoir.

Water and sanitation

Clean and safe water, sanitation, and hygiene are critical for control of and elimination of NTDs such as schistosomiasis and soil-transmitted helminthiases. However, provision of clean and safe water in some remote areas where such NTDs are most prevalent is challenging, and help from other sectors is essential. “Engagement of the water, sanitation, and hygiene sector and the inclusion of NTDs within this framework, reflects a holistic policy approach within the SDG goals,” the authors say.

“Increased investment for NTDs will improve the wellbeing of vulnerable groups, which together with improvements in water, sanitation, hygiene, and education, are appropriate links to many of the SDGs [Sustainable Development Goals],” they conclude.

Dr. Parry graduated from the University of Liverpool, England in 1997 and is a board-certified veterinary pathologist. After 13 years working in academia, she founded Midwest Veterinary Pathology, LLC where she now works as a private consultant. She is passionate about veterinary education and serves on the Indiana Veterinary Medical Association’s Continuing Education Committee. She regularly writes continuing education articles for veterinary organizations and journals, and has also served on the American College of Veterinary Pathologists’ Examination Committee and Education Committee.