The relationship between Nagasaki's fire prevention water supply and mosquitoes

The other day, while walking around the city of Nagasaki, I saw the fire prevention canal shown in the photo above. I'm sure there are many people who look at this photo and don't know what it's for. This time, I would like to talk about the surprising relationship between this fire prevention canal and mosquitoes.

The fire irrigation system in the photo was installed in preparation for fires during World War II. At the time, Nagasaki had many wooden buildings, which unfortunately made it a target for air raids using incendiary bombs, so the Air Defense Law required each home to have a fire irrigation system.

This fire prevention water supply brought further tragedy to Nagasaki during the war. The water stored in the fire prevention water supply became a perfect breeding ground for mosquitoes, causing an outbreak of Aedes albopictus, a vector of dengue fever. At that time, Nagasaki was a port of call for merchant and military ships, and there were many returnees from the southern battlefields and occupied territories, where dengue fever was prevalent. This led to a major dengue fever epidemic in Nagasaki from 1942 to 1945. In 1942 , 23,338 dengue fever patients were recorded in Nagasaki City. Similar dengue fever epidemics also occurred in Hyogo, Osaka, and Sasebo, which were also major ports of call for merchant and military ships, causing the world's largest outbreak in a temperate region, with the number of patients reaching 200,000 .

After the war ended, the use of water for fire prevention decreased, and fortunately, no cases of dengue fever have been confirmed in Nagasaki Prefecture since 1946 .

The water source for fire prevention, which was once installed for the purpose of war and even caused a dengue fever epidemic, no longer serves that purpose and now symbolizes the end of the war and the peace of Nagasaki.

Responsible for the text: Naoki Matoba@London

References

• Hotta, S. A consideration of dengue fever vector mosquitoes: The significance of Aedes albopictus and Aedes aegypti in the dengue fever epidemics in mainland Japan from 1942 to 1944 , Hygienist, 49 ( 4 ) : 267-274 , 1998 .
• National Institute of Infectious Diseases: Response and Countermeasures Guide for Local Governments in the Event of a Domestic Dengue Fever Infection (1st Edition), September 2014 (URL as of August 2024: https://www.niid.go.jp/niid/images/vir1/div2/dengue_taio_jichitai.pdf)