Some Thai fruit bats carry a strong strain of the Nipah virus, but the bigger danger comes from infected people arriving from countries where there is an outbreak of the disease, health authorities said on Monday.

Officials aimed to prevent Nipah virus outbreaks by banning pig farms from areas where it occurred in bats. This prevented the bats transmitting the virus via pigs to humans.

“There has not been a confirmed case in Thailand. There are concerns in other countries, especially in Bangladesh and West Bengal state in India. Although these countries are far from Thailand, surveillance is necessary because there are direct flights from there to Suvarnabhumi, Don Mueang and Phuket airports,” an official said.

Screening of visitors from infected countries continued at these airports. Officials focussed on passengers who had a fever or showed respiratory symptoms, and on those who had the past 21 days been in an area where there was an outbreak of the disease.

The outbreaks of Nipah disease in Bangladesh and India were under control and there was no sign of the disease in other nearby countries, the official said.

There is no vaccine or medication to cure the disease, the health department said.

Symptoms began with a fever, headache and muscle ache, vomiting, sore throat, dizziness and then drowsiness.