The Federal Health Office has sounded the alarm after a sharp increase in the number of people developing inflammation of the brain following tick bites.
It said this week 141 cases of tick-borne encephalitis (TBE) had been reported in Switzerland by mid August - 55 per cent more than in the same period last year.
The Health Office is recommending that people living in affected areas get vaccinated against the disease, which can kill.
Regional variations are pronounced, with about 96 per cent of this year's cases involving residents of high-risk areas in German-speaking Switzerland.
Canton Aargau has been particularly hard hit, with large increases also reported in the cantons of Lucerne, Zurich and St Gallen.
About half of those who acquired the disease were bitten by infected ticks while on walks in the forest.
"Data is still lacking on why certain areas have been particularly hard hit," said Hanspeter Zimmermann, a Health Office expert. "It is possible that there are more infected ticks, but we do not know."
According to Zimmermann, between about 0.5 and three per cent of ticks are infected. The weather could be a factor in the increase in cases of tick-borne disease, he told swissinfo.
"Activity of the ticks depends on the climate", explained Zimmermann. "They don't like if it is too hot or too dry."
Encephalitis is a medical term for inflammation of the brain.
Symptoms may include severe headache, stiff neck, fever or vomiting, aversion to bright lights, and sometimes a rash. But not all symptoms need be present.
TBE has to be differentiated from Lyme disease, which is also transmitted by tick bites and affects the skin, the joints, the brain and the heart.
Lyme disease, a bacterial infection, occurs far more frequently than TBE.
Whereas the distribution of TBE is localised, Lyme disease occurs throughout Switzerland, according to the Health Office.
Not everyone who is bitten by an infected tick gets ill, says Zimmermann.
"Some people who are bitten don't have symptoms, others have flu-like symptoms. But it can develop into a dangerous illness, for which there is no specific medicine or treatment," he explained.
In Switzerland between 75 and 80 per cent of those infected require hospitalisation and around one per cent of patients die.
All residents living in at-risk areas should be immunised against TBE, according to the Health Office.
"The vaccine is safe and efficient," said Zimmermann.
An additional concern of the Health Office is that the population in affected regions is insufficiently informed as to the dangers of tick bites.
In addition to being immunised, people in at-risk areas are advised to wear clothing enclosing the arms, wrists and legs when they head into forests or fields.
It is also recommended that they check their body and clothing for ticks after being in the woods, that if ticks are found they are immediately removed, and that the exact time of any tick bite be noted.
Tick-borne encephalitis (TBE) is an inflammation of the brain which can develop after a tick bite.
Symptoms may include severe headache, stiff neck, fever or vomiting, aversion to bright lights, and a rash.
Lyme disease is also transmitted by tick bites and affects the skin, the joints, the brain and the heart.
In compliance with the JTI standards