The number of mosquitoes, flies and rats in Shenzhen, Guangdong province, in-creased in the first three months of this year, posing a growing risk of epidemics, disease control experts say.

The number of rats rose by five or six times from the same period in 2013, according to monitoring re-sults reported by the Shenzhen Center for Disease Control and Prevention.

There is an increased risk of residents catching some new prevailing diseases, such as chikungunya fever and West Nile fever transmitted by mosquitoes, and severe fever from an infectious dis-ease caught from ticks, said Zhao Shaohua, an official with the center.

Zhao said the dramatic increase in rats might be re-lated to subway construction and to less effective measures to kill them in the monitoring areas.

Seventeen cases of epi-demic hemorrhagic fever were reported this year, compared with 10 last year, he said.

Liang Zhuonan, another official at the center, advised people not to use only one type of insecticide, as the insects can develop high re-sistance.