It’s likely you’ve heard of malaria, HIV-AIDs and tuberculosis. These three diseases continue to have a massive impact on human health across the globe. You may not be familiar, however, with schistosomiasis, Chagas disease, leishmaniasis or trachoma, which fall under the umbrella of “neglected tropical diseases” (or NTDs for short).
What Are Neglected Tropical Diseases?
NTDs comprise a range of illnesses mostly caused by viruses, fungi, bacteria and parasites. Together, these include at least 20 conditions that severely impact the most vulnerable people in the world. Schistosomiasis, for example, is caused by parasitic worms released by freshwater snails. Over 200 million people worldwide are affected by it, according to the WHO, with nearly 12,000 deaths occurring from the disease each year.
Maria-Gloria Basáñez, a professor and chair of neglected tropical diseases at Imperial College London, underlines that these diseases overwhelmingly impact the “bottom billion of the world’s population”.
“They have a disproportionate impact on the most marginalized and vulnerable sections of these populations, namely women and children,” says Basáñez.
How Dangerous Are These Tropical Diseases?
Mortality linked to NTDs is often lower than other diseases, but Basáñez states they can lead to a huge burden of disability, which in turn impacts economies. Trachoma for instance — which is caused by the bacterium Chlamydia trachomatis — can lead to irreversible blindness, and is thought to have impaired the vision of at least 1.9 million people. It’s known as the leading cause of infectious blindness in the world. Onchocerciasis and neurocysticercosis, meanwhile, are caused by parasitic worms, and can lead to epilepsy.
There are 179 countries across the globe that have reported at least one case of NTDs in 2021, but the disease burden is concentrated in just 16 countries. Poverty underpins many of the affected areas, and NTDs can perpetuate that cycle, Basáñez adds.
Why Don't NTDs Get More Attention?
The reasons why NTDs are neglected are complex. Over the last two decades, international organizations, health organizations and governments have increasingly taken notice of tackling these diseases. Yet, despite these efforts, funding, medical support, research and development, as well as awareness, continue to lag behind those of other diseases, Basáñez says.
“I think there is a big gap between awareness and the international commitment, because [NTDs] affect the poorest of the poor,” she adds.
Part of the challenge, Basáñez continues, is that these diseases tend to be endemic — concentrated in specific locations or countries without sudden increases in the number of cases — without much outbreak and epidemic potential, meaning that they tend to fall under the radar.
“It's an example of out of sight and out of mind," says Basáñez. "So, it's really important that we keep the visibility up in all the ways that we can.”
Is Climate Change a Factor?
led by the WHO, international organizations, health authorities, governments and others aim to eliminate NTDs by 2030. Tackling them is ever more important due to climate change, which could result in a geographic spread and change in infection rates, according to researchers. For example, shifting precipitation and temperature are linked to changes in the distribution of diseases such as dengue, chikungunya and leishmaniasis.
How climate change might impact other NTDs is still unclear and a point of active research, notes Basáñez.
“We have two issues: How the ecology of the insects and the snails [and other vectors] that are involved in the transmission of some of these diseases is going to change," she adds. "And how our infrastructure and resources are going to be affected."
How Can We Treat Neglected Tropical Diseases?
Tackling NTDs comes from a range of angles. Fundamentally, many of these diseases are linked to a lack of access to clean water, sanitation and healthcare; addressing these is paramount to reducing their impact. So, too, says Basáñez is ensuring distribution and coverage of preventive treatments for some NTDs, and access to diagnosis, treatment and management for others.
Still, progress is marching forward towards the overall goal of preventing and eliminating NTDs by 2030; around 80 million fewer people required NTD interventions between 2020 and 2021. By the end of 2022, 47 countries across the globe had eliminated at least one of these diseases, according to a recently published global report by the WHO.
New treatments are also under development to help those impacted. In 2021, researchers at the London School of Hygiene & Tropical Medicine identified new compounds that can target the parasitic worms that cause schistosomiasis, raising hopes its elimination could be on the horizon.
“You need to keep the momentum, keep the incentive and the populations engaged with these treatment programs," Basáñez says. "They are going to be needed for a long time."
Eliminating NTDs is still a ways off, with multiple challenges along the way. Researchers like Basáñez remain hopeful that progress can be made with concerted action. “I firmly believe that people should be informed, better acquainted, better engaged at all levels in the population, both in non-endemic countries and endemic countries.”