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Why scientists should tackle neglected tropical diseases

Abi Perrin

Abi Perrin (Image copyright: Abi Perrin)

Why should researchers study a group of diseases that mainly affect people in developing countries? It’s about reducing human suffering, says MRC PhD student Abi Perrin, but it’s also because studying these ever-changing foe present intellectual challenges, and could lead to insights into other types of infectious disease.  

One billion people are currently suffering from a neglected tropical disease (NTD). These infectious diseases, such as sleeping sickness, elephantiasis and leprosy, are associated with poverty and tend to affect people in developing countries. They have a huge effect on people’s physical and emotional wellbeing, as they are often disabling, disfiguring and stigmatised. And because they prevent people from working and receiving education, NTDs ultimately perpetuate the cycle of poverty.

The worms, parasites, bacteria and viruses which cause NTDs are some of our most ancient enemies. There are references to NTDs in historical documents thousands of years old, including all major religious texts. For example, in Exodus — the second book of the Old Testament — the Israelites are attacked by ‘firey serpents’ as they leave Egypt, and historians believe that these terrible creatures represent parasitic worms.

NTDs have been understudied or ‘neglected’ because they don’t directly affect the developed countries, which have the most resources for infectious disease research. But this is beginning to change. In recent years there has been a huge global research effort to combat HIV, tuberculosis and malaria, the three biggest contributors to Sub-Saharan Africa’s infectious disease burden. This investment has allowed us to develop a clearer understanding of these diseases and design effective interventions. By harnessing this infrastructure and expertise, I hope the research community can make progress in NTDs too.

But there are other reasons for researching NTDs. From my own experience working on malaria, I’ve come to realise that our oldest enemies are some of the most fascinating.

The fact that our bodies have been fighting these diseases for such a long time demonstrates the remarkable ability of these creatures to survive and adapt. Part of their survival secret lies in their ability to live outside of human hosts, in insects, snails and other animals. However the main reason for their success is their incredible capacity to outwit our immune system.

Changing dressings at a leprosy colony (Flickr/Erin Collins)

Changing dressings at a leprosy colony (Flickr/Erin Collins)

Malaria parasites are so efficient at evading the body’s inbuilt defences that people never develop immunity, even if they are repeatedly infected. NTDs and malaria use a number of the same tricks to stay one step ahead of the immune system, including hiding inside human cells and changing their appearance so they aren’t ‘remembered’ by the immune system. Specific NTDs have their own unique ways to survive inside the human body. For example, some parasitic worms are able to disguise themselves by forming a cloak of human proteins. Other parasites are able to engulf or break down the chemicals that the immune system has deployed to destroy them.

We don’t fully understand all the ways that NTDs overcome the body’s defences, but if we did, it would tell us more about how the immune system works and help us to design new ways to treat disease.

We know that allergies are caused by the same mechanisms that the body uses to kill parasites, so studying NTDs could provide some unexpected benefits for patients in the UK. For example, the eggs of parasitic worms have been used successfully to treat people with Crohn’s disease, a painful illness where the immune system attacks its own digestive system. Curing one disease with another is clearly not ideal, but the more we understand the biology of both diseases, the more we can refine treatments and improve patient care.

Discovering the secrets behind these parasites’ evolutionary success could result in truly global benefits to human health. But the path to an NTD-free world is unlikely be smooth. Having outwitted us since antiquity, NTDs are worthy opponents and a fascinating challenge for 21st century researchers.

Abi Perrin

Abi Perrin is an MRC-funded PhD student at the Wellcome Trust Sanger Institute. She is currently completing a policy internship run by the Academy of Medical Sciences in conjunction with the MRC.

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