Chikungunya fever: Hong Kong urged to step up mosquito control after rainstorm

Hong Kong should step up efforts to fight mosquitoes after the city recorded its second-longest black rainstorm warning, experts have warned, with data showing the breeding of the pest that can transmit chikungunya fever is “fairly extensive” in 70 per cent of the city’s surveyed areas. A black rainstorm warning lasted 11 hours and 15 minutes on Tuesday, the second-longest on record in Hong Kong. Three days earlier, the city recorded its first imported chikungunya fever case, a mosquito-borne disease, since 2019. “There are more water bodies following heavy rain and they would not evaporate quickly. You would need extra efforts [afterwards] to apply larvicide sand and oil”, said Peter Leung Kwong-yuen, chairman of the Pest Control Personnel Association of Hong Kong. Leung said that more waterlogging would occur after days of thunderstorms, although the heavy rain might curb the breeding of mosquitoes. “We are not worried about the heavy rain, which could wash away the stagnant water,” Leung said, noting that mosquitoes usually prefered to breed in standing water. “Mosquitoes cannot lay eggs in flowing water, and they also have to hide a bit under the heavy rain.” The black rainstorm warning signal on Tuesday was the fourth one issued in eight days. The Hong Kong Observatory also said it had measured 355.7mm (14 inches) of rainfall at its headquarters in Tsim Sha Tsui as of 2pm on the same day, making it the highest daily rainfall recorded for August since records began in 1884. On Saturday, Hong Kong recorded its first imported chikungunya fever case in six years, raising the risk of local transmissions in the city. The case involved a 12-year-old boy who had travelled with his mother to the Shunde district of Foshan city in Guangdong province in the last two weeks of July. The area where the boy visited was experiencing an outbreak of the mosquito-borne disease. Patients usually develop fever and joint pain that can last for a long period. Other potential symptoms include muscle pain, nausea and rashes. The breeding of Aedes albopictus, a type of mosquito that could transmit chikungunya fever and other diseases, in about 70 per cent of the 61 city areas under surveillance in July has reached a “fairly extensive” or higher level, according to the latest available data from the Food and Environmental Hygiene Department. Higher risk areas include Ma Wan, Lam Tin and Sau Mau Ping, Yuen Long Town, Kwai Tsing and Sham Shui Po. The distribution, measured by the so-called area Gravidtrap index, looks at how many specific monitoring devices are found with breeding mosquitoes. “Fairly extensive” refers to areas with the index between 5 and 20 per cent. Ma Wan, in Tsuen Wan, was the only district reaching the level of “extensive” distribution, with a Gravidtrap index of 24.4 per cent. Jackson Chan Chak-shum, chairman of the Hong Kong Pest Management Academic Society, said the surveillance results were still within a normal range but extra effort was necessary for mosquito control. “We must not relax even if the rainfall has flushed away mosquito eggs, and we need to prevent mosquito breeding in our daily lives,” he said. He highlighted that mosquitoes often laid eggs in stagnant water, such as water droplets from air conditioners and water under vases, and urged the public to clean these areas regularly. Dr Wilson Lam, president of the Hong Kong Society for Infectious Diseases, said more stagnant water would be seen after heavy rain, but whether an outbreak of mosquito-borne disease could happen would depend on the efforts dealing with the aftermath. “It would depend on the authorities’ mosquito control work and the public awareness,” Lam said. “It is not a must that there would be an outbreak if we saw more waterlogging.” Taking dengue fever as an example, Lam said areas neighbouring Hong Kong, such as mainland China and Taiwan, had frequent outbreaks, but the city seldom saw a dramatic surge in cases even under rainy weather. Anita Fok Ming-yan, the department’s pest control officer in charge, told a radio show on Tuesday that the mosquito breeding rate in general, measured by the city’s Gravidtrap index, reached its peak from June to September, and saw lower readings from January to March. Past data showed that the average monthly Gravidtrap index for June between 2021 and 2024 was 16.6 per cent, higher than the rate of 9.5 per cent recorded this June.

Chikungunya fever: Hong Kong urged to step up mosquito control after rainstorm

.css-1c6uqr6{color:inherit;font-weight:inherit;font-size:inherit;font-family:inherit;line-height:inherit;overflow-wrap:break-word;}Government data shows mosquito breeding ‘fairly extensive’ in 70 per cent of the city’s surveyed areas

Government data shows mosquito breeding ‘fairly extensive’ in 70 per cent of the city’s surveyed areas