Millions of people, especially in tropical countries, are infected with neglected tropical diseases (NTDs) every year.

The poorest people in Africa, Asia and Latin America are worst hit. An acute lack of medical care for NTDs not only erodes quality of life for those who fall ill but also harms them economically. 

What is a neglected tropical disease? 

The World Health Organisation (WHO) has classified 20 NTDs as debilitating and sometimes deadly for humans, especially if left untreated. Trachoma, for example, which occurs in many regions of the world, can lead to blindness and lymphatic filariasis (elephantiasis), a painful swelling of the limbs that can cause permanent disfigurement, affects over 120 million people in 72 countries.

Other pathogens such as Chagas disease, transmitted mainly in South America, attacks internal organs, destroys nerve cells and can cause massive heart damage.

NTDs can be easily transmitted via a bug bite, a sandfly sting, or tiny parasites that penetrate the skin of unsuspecting swimmers out for dip in a lake, for instance. 

"The big five" pathogens cause about 90% of all NTD diseases: Lymphatic filariasis (elephantiasis), river blindness (onchocerciasis), trachoma, schistosomiasis — a chronic disease caused by parasite worms — and helminth or worm infections. 

Who is affected by NTDs worldwide?

NTDs affect around 1.7 billion people in 149 countries. Another two billion people are threatened by them, says the German Network against Neglected Tropical Diseases. Half a million people die directly or indirectly from NTDs every year, according to estimates.

NTDs occur in all tropical regions on the planet — from Southeast Asia and the Middle East, and Africa to South America.

"African countries are the most affected," said Jürgen May, who heads Infectious Disease Epidemiology at the Bernhard Nocht Institute for Tropical Medicine in Hamburg.

A researcher on global infections, May added that low-income people are particularly at risk, especially in rural areas isolated from medical care — and where there is often insufficient clean water and food.

"There's a vicious cycle between diseases, chronic infectious diseases and poverty in these countries," May said. The high cost of treating the diseases leads to greater poverty. Meanwhile, infections are exacerbated by problems, like lack of clean water, that go hand in hand with poverty, May added.

Those who are permanently ill often can no longer work and provide for their families. And disabilities caused by NTDs lead to further stigmatization and exclusion.

The illnesses are often worse for women and children, and so far there are no child-friendly medicines for many NTDs.

Why are NTD diseases 'neglected?'

Although billions of people worldwide are at risk from NTDs, the fight against them is still underfunded.

The term "neglected diseases" shows "how difficult it is to create awareness" for NTDs, as well as for the "neglected populations who suffer the most," said May. People in rural areas, as well as residents of poor neighborhoods in urban areas, are often not prioritized by lawmakers. More broadly, there's a lack of awareness that these "diseases are severe" and "chronic."

The COVID-19 pandemic has caused major setbacks in NTD control in many African countries, he said, because millions of doses of medicine could no longer be distributed to those affected. In many tropical countries, the consequences of coronavirus infections have not been as bad as the consequences of NTDs, May added. 

Are tropical diseases spreading because of climate change?

NTDs are most common in tropical regions but climate change and global travel have helped them spread to Europe and North America.

Mosquito-borne dengue fever, for example, is not only found in Africa, Southeast Asia and South America, but has now reached the Mediterranean and southern Europe, May said.

In African countries, too, where the diseases used to affect mostly rural populations, more areas are now at risk.

Rising temperatures caused by man-made climate change has also impacted the insects that transmit pathogens.

May explained how global heating has pushed mosquitoes into higher altitudes where bigger African cities like Nairobi in Kenya, or Addis Ababa in Ethiopia, or Antananarivo in Madagascar, are now seeing the spread of disease.

Cases of tropical diseases are also increasing in North America and Central Europe due to climate change. The West Nile virus is strictly speaking not an NTD, but it has been popping up regularly in Germany since 2018, according to May. It's also spread to the US due to hotter temperatures.

What is the next step in the fight against NTDs? 

By 2030, the WHO wants to largely contain neglected tropical diseases worldwide through international cooperation between aid organizations, medical professionals, governments and the pharmaceutical industry.

"This is certainly an ambitious goal and will be difficult," said May. Experts fear that other crises from the COVID pandemic to the invasion of Ukraine will delay the fight against NTDs.

Yet May added that "we need ambitious goals" to inspire action "to control, eliminate or to eradicate" NTDs. 

Recent successes also give hope, said May. Diseases such as river blindness and trachoma infection-related blindness have become much rarer thanks to improved health education and targeted supply of medicines.

And sleeping sickness, which used to be widespread and deadly, has been almost completely defeated due to the development of a new drug. 

However, in order to develop good diagnostics, drugs and, in some cases, vaccines, more resources and greater commitment from governments are required globally.

Germany, for example, joined the Kigali Declaration on Neglected Tropical Diseases a year ago.

Now aid organizations and health experts are also demanding more money for NTD programs before the climate crisis inflates the devastating impact of these diseases. 

This article originally appeared in German.