Filariasis is a group of infectious diseases caused by thread-like worms known as filariae, and the pathogens behind the most common form reach people through mosquito bites, according to a guide published by the German motoring and travel club ADAC on 30 October 2026. The article sets out how the infections are transmitted, what symptoms they can produce and why consistent mosquito protection is the main defence for travellers. ADAC notes that no vaccine against filariasis exists.
Why it matters
The infections occur with varying frequency in tropical and subtropical countries, particularly in Africa, South America and Southeast Asia, depending on where the different worms are found, ADAC reports. The organisation singles out long-term travellers and people who visit affected areas regularly for work as facing a higher risk of being bitten by an infected mosquito. Because an infection can go unnoticed for a long time, the guidance stresses that prevention and awareness matter more than waiting for signs of illness.
Three forms of the disease
ADAC describes several types of filariasis. The most widespread is lymphatic filariasis. A second group, the subcutaneous filariases, affects the fatty tissue beneath the skin and the eyes; river blindness, also called onchocerciasis, belongs to this group. A third form, mansonellosis, often causes no symptoms at all or produces vague complaints such as itching or joint pain.
The transmission cycle is similar across the mosquito-borne forms. Infectious larval stages of the worms enter the body through a mosquito bite and make their way into the lymphatic system, the subcutaneous fatty tissue, the eyes and other organs, according to ADAC. There the worms mature into adults, reproduce and release enormous numbers of microfilariae. When another mosquito bites the affected person, it picks up these circulating microfilariae and can then pass the infection on.
Why diagnosis can take time
An infection may run without symptoms, take an acute course or become chronic, and it often remains undetected for a long period, ADAC writes. Months or even years can pass between infection and the first complaints, and many infected people feel well even though their lymphatic system has already been damaged.
Confirming the infection can also be slow. According to ADAC, the microfilariae of certain worm species appear in blood vessels near the skin surface mainly at night, having adapted over the course of evolution to the activity rhythm of mosquitoes. The time of day therefore matters when a blood sample is taken. Even people who notice no symptoms can carry the disease and help spread it, because mosquitoes that feed on their blood can take up microfilariae and transmit them to others.
From fever to elephantiasis
In the acute phase of lymphatic filariasis, patients experience irregular episodes of fever lasting several days, a pattern ADAC calls filarial fever. In some cases the lymph nodes and lymph vessels become inflamed. That inflammation raises the risk of impaired lymph drainage, which can cause surrounding tissue to swell and lead to lymphoedema, often in the legs.
Once the disease has entered the chronic stage, repeated inflammation leaves the vessel walls scarred and narrowed, so lymph flow is permanently disrupted, according to ADAC. Severe lymphoedema can follow. The legs are most often affected, but swelling may also occur in the arms, breasts and genitals. Skin can thicken permanently, harden and develop deep folds. At this stage, lymphatic filariasis is also known as elephantiasis.
ADAC adds that the folds cause skin surfaces to rub against each other, irritating and damaging the skin. Bacteria and fungi can enter through rough or broken areas, which in turn encourages further inflammation of the skin and lymph vessels.
Treatment and protection
For lymphatic filariasis, drugs directed against the worms are used, ADAC reports. Which active substances are suitable and how long treatment lasts depend on the pathogen and on any other infections the patient has. Compression bandages, manual lymph drainage and physiotherapy can help with swelling, and existing skin folds should be cared for carefully to avoid further complications.
On prevention, ADAC states plainly that there is no immunisation, so rigorous mosquito protection is the most important measure during holidays in the tropics or subtropics. The organisation's guidance is general travel health information and does not replace advice from a doctor.
ADAC based the article on reference works including Pschyrembel online, the MSD Manual and Deximed, with retrieval dates in September 2026. The full guide, including its detailed mosquito-protection recommendations, is available on the ADAC website.
