The Netherlands has recorded its first-ever case of West Nile virus – found in a small migratory bird native to tropical Africa, Arabia, and Pakistan.
The virus was confirmed in a common whitethroat (Curruca communis), a warbler which arrives in Europe in the spring, returning to its home in the autumn.
The bird was trapped and tested as part of the One Health Pact – a research programme from the Dutch institute for public health and environment (RIVM) into setting up an early warning system for the introduction of foreign viruses into the country.
The virus is transported mainly by birds, which then pass it on to the mosquitoes that prey on them. The mosquito acts as a carrier, going on to infect other birds as well as animals and even humans.
Horses are the worst affected, with about 10% suffering an illness requiring treatment. A vaccine exists for horses.
In about eight out of ten cases, humans infected in this way have no symptoms. Most of the remainder suffer a mild fever and flu-like symptoms. In rare cases the virus can lead to encephalitis and meningitis.
However an ongoing outbreak in the province of Cadiz in southern Spain has caused the death of four people, the latest on Monday this week.
All of the fatalities so far concern older people, the latest an 87-year-old woman. Ten others are in hospital in Cadiz and Neighbouring Seville provinces, four of them in intensive care.
The warbler is the first bird to test positive for the active virus in the Netherlands, although others have been found to have antibodies from a previous infection. It is also the first case of the disease being contracted on Dutch soil. There have been cases of infected humans in the past, but those cases were all contracted abroad.
Scientists from the RIVM programme have concluded that the bird probably became infected while in the country, based on how long the bird has been in Europe, and on the fact that it had been tested in the spring and tested negative.
The West Nile virus was originally discovered in Uganda in 1937, and is part of the same family of viruses as dengue, yellow fever and zika.