Trachoma is the world’s leading infectious cause of blindness: there are at least 39 countries where people are at risk from the disease.

It starts off as a bacterial infection that can be easily treated. But if it’s not, over time it can cause the eyelashes to scrape against the eye, causing pain and, eventually, sight loss. Worldwide, it’s thought that 1.5 million people are blind or visually impaired because of the disease.

This parasitic infection causes severe skin irritation and irreversible blindness, but it can be treated with antibiotics to stop it spreading and prevent sight loss.

It’s thought 1.1 million people worldwide are blind because of the disease, which is spread by the bite of infected flies that breed near fast-flowing rivers. This often forces people to move away from fertile river valleys, leaving them unable to grow crops.

This disease, transmitted by mosquito bite, leads to swelling and abnormally enlarged body parts. This can be extremely painful and can lead to permanent physical changes.

The debilitating symptoms mean many people are unable to work, and children miss school to care for family members. It’s thought that 120 million people worldwide are infected, yet medication can protect people to prevent them catching it.

Intestinal worms live in the digestive system, causing malnourishment and leaving people susceptible to illness.

Children aged three to eight are most at risk: the disease can cause them to miss school, damaging their education and development. To prevent this, school children are often given a single dose of medication to treat the disease. Good hygiene can also stop intestinal worms spreading.

Known as ‘snail fever’, schistosomiasis is caused by parasites released by freshwater snails. At first there may be no symptoms, but it can lead to pain, diarrhoea and death.

The disease mainly affects poorer communities that don’t have access to clean drinking water or adequate sanitation, but medication can stop people catching it. It is often treated alongside other neglected tropical diseases.