BANGKOK (Reuters) - Thai health officials on Wednesday said 33 new Zika virus cases have been detected in the country as officials step up screening for groups at high risk from the disease such as pregnant women.

A city worker fumigates the area to control the spread of mosquitoes at a temple in Bangkok, Thailand, September 14, 2016. REUTERS/Chaiwat Subprasom/File Photo

“We confirmed 33 new cases last week and have detected the virus in two further provinces,” Ministry of Public Health spokesman Suwannachai Wattanayingcharoenchai told Reuters.

Suwannachai said health campaigns warning travelers about Zika have been increased as many Thais flock to the capital Bangkok to take part in national mourning activities for King Bhumibol Adulyadej, who died on Oct. 13.

“This is a period of movement with people coming to the capital from the provinces to take part in various activities,” he said. “We have to remind them that Zika is a silent disease and some people won’t have symptoms.”

Thailand became the first country in Southeast Asia in September to confirm Zika-linked microcephaly, a condition that results in babies being born with small heads, and has one of the highest number of Zika cases in the region.

Other parts of Southeast Asia have reported dozens of cases of Zika, including city state Singapore where 450 cases have been reported in 2016.

Thailand has reported more than 680 cases of Zika since January but its Department of Disease Control has said the virus is manageable.

In neighboring Myanmar, a pregnant foreign woman was diagnosed with the mosquito-borne virus last month - the first case confirmed in the country.

Zika infections in pregnant women have been shown to cause microcephaly - a severe birth defect in which the head and brain are undersized - as well as other brain abnormalities.

The connection between Zika and microcephaly first came to light in Brazil, which has confirmed more than 1,900 cases of microcephaly.