Chikungunya fever

The disease control and prevention authority in Guangzhou, South China's Guangdong Province, added a new feature to its mosquito-borne disease map starting Sunday. The feature alerts users to transmission risks of mosquito-borne diseases in their areas and provides users travel risk reminders, a latest move by the city to combat the spread of Chikungunya fever, an infectious disease transmitted by Aedes mosquitoes with no specific cure.

According to the Guangzhou Center for Disease Control and Prevention, the new function requires users to grant location access. If a mosquito-borne disease outbreak is occurring in the user's area, the system will alert them to the transmission risk and advise them to take preventive measures against mosquito bites, the Guangzhou Daily reported on Monday.

Understanding mosquito density trends plays a role in early warning for mosquito-borne diseases such as dengue fever and Chikungunya fever, and Guangzhou's disease control and prevention center launched the "mosquito-borne disease map" as early as 2023. Internet users can access the map via the center's official website and the drop-down menu on its WeChat public account. 

During seasons when mosquito activity is low, the mosquito surveillance map is updated every two weeks, whereas during the annual peak period of mosquito-borne diseases, the update frequency increases. Since June this year, mosquito monitoring results are updated weekly. 

The latest mosquito surveillance results for the fourth week of July show that among the 120 monitored subdistricts and towns, 45 met the mosquito control standards. There are 24 subdistricts/towns at low risk, 39 at medium risk, and 12 at high risk.

In addition to listing the four risk levels, the map also indicates the corresponding ranges for the Breteau Index (BI) and Mosquito Ovitrap Index (MOI).

The BI is calculated by inspecting the number of small water containers indoors and outdoors and checking for the presence of Aedes mosquito larvae. A higher index indicates greater mosquito density and higher risk of dengue transmission. Generally, a BI above 5 indicates a transmission risk, while a BI above 20 suggests a risk of outbreak.

The MOI is a key indicator for assessing Aedes mosquito density. It is calculated by the proportion of positive Ovitraps (those containing adult mosquitoes or eggs) among the effectively collected traps. An MOI below 5 is the threshold for controlling dengue transmission; above 5 indicates a transmission risk; above 10 suggests an outbreak risk; and above 20 signals a risk of regional epidemic, requiring continuous elimination of breeding sites and adult mosquitoes. 

Chikungunya is primarily transmitted by the bites of Aedes aegypti and Aedes albopictus mosquitoes and is not contagious from person to person.

The mosquito map includes two modules: "overall city situation" and "monitoring site situation." Residents can use the map to understand the overall mosquito density levels in different areas across the city. They can also use the location feature to precisely check the mosquito density at monitoring sites within their own subdistrict or town and surrounding areas, gaining insight into mosquito density trends.

The number of new locally transmitted Chikungunya fever cases declined in Guangdong over the past week, though risks remain, local disease control authorities said on Sunday. A total of 2,892 local infections were reported from July 27 to August 2, with no severe or fatal cases recorded. The majority of cases were found in the city of Foshan, Xinhua News Agency reported. 

Global Times