River Blindness (Onchocerciasis): Prevention and Advice for UK Travellers

Onchocerciasis, commonly known as River Blindness, is a disease caused by the parasitic worm Onchocerca volvulus. It is transmitted to humans through the repeated bites of infected blackflies (genus Simulium). These flies typically breed in fast-flowing rivers and streams, which gives the disease its common name.

According to the World Health Organization (WHO) and the NHS, it is the second leading infectious cause of blindness worldwide. While it is not found in the United Kingdom, it remains a significant concern for British travellers visiting endemic regions, particularly in sub-Saharan Africa. The infection involves larvae entering the skin during a fly bite, where they mature into adult worms, often forming nodules under the skin. These adult worms produce thousands of tiny larvae (microfilariae) that migrate through the skin and eventually reach the eyes.

Symptoms of onchocerciasis do not usually appear immediately after a bite; it can take months or even years for the larvae to reach a level where they cause a reaction. The most common symptoms include:

• Intense itching: Often the first and most distressing sign, which can lead to secondary skin infections.
• Skin changes: You may notice rashes, bumps (nodules) under the skin, or areas of depigmentation often referred to as 'leopard skin'.
• Eye irritation: Early signs include redness, a feeling of grittiness, or light sensitivity (photophobia).
• Vision loss: If left untreated over several years, the migration of larvae into the eye can cause scarring of the cornea and eventually permanent blindness.

When planning your trip through a UK online doctor service, it is important to identify if your destination is endemic for onchocerciasis. Over 99% of infected people live in 31 countries in sub-Saharan Africa. Small pockets of the disease also exist in Brazil, Venezuela, and Yemen. Travellers at highest risk are those visiting rural areas for extended periods, such as aid workers, researchers, or long-term backpackers. Short-term tourists staying in urban centres or far from fast-flowing water sources are generally at a much lower risk.

Currently, there is no vaccine or preventative medication (prophylaxis) available for river blindness. Prevention is entirely focused on avoiding the bites of blackflies, which tend to bite during daylight hours. NICE clinical knowledge summaries suggest the following precautions for tropical travel:

• Wear protective clothing: Opt for long-sleeved shirts and long trousers. Blackflies can bite through thin fabrics, so thicker materials or pre-treated clothing are recommended.
• Use effective insect repellent: Apply repellents containing DEET (diethyltoluamide), Icaridin, or PMD to exposed skin.
• Permethrin-treated gear: Treat your clothing and gear with permethrin for an extra layer of protection.
• Timing: Be particularly vigilant during the day, especially near riverbanks where blackflies are most active.

Speaking to a GP online before you travel is an excellent way to prepare for tropical environments. A travel health consultation via OnlineDoctor24 can provide you with a tailored risk assessment based on your itinerary. While river blindness is rare in short-term UK tourists, an online doctor can help you differentiate between various insect-borne illnesses, such as malaria or dengue fever, which may present with overlapping symptoms like rashes or fever. They can also provide advice on the best repellents to carry and how to manage skin irritations while abroad.

If you return to the UK and suspect you have been exposed to onchocerciasis, a medical evaluation is vital. Diagnosis typically involves a physical examination to look for nodules or skin changes, and sometimes a 'skin snip' biopsy to detect the presence of microfilariae. In the UK, treatment is usually managed by specialists in tropical medicine. The standard treatment is Ivermectin, an antiparasitic medication. This drug kills the microfilariae and relieves skin itching, though it does not kill the adult worms. Therefore, repeat doses may be required over several years until the adult worms die naturally. In some cases, a course of Doxycycline is also used to kill the bacteria (Wolbachia) that the worms rely on to survive.