[News Terms] 'Wolbachia Bacteria' Spreading Infertile Mosquitoes

'Wolbachia bacteria' is a representative parasitic bacterium that coexists with nematodes and arthropods. Many species of Wolbachia bacteria cannot reproduce or survive without symbiosis with nematodes or arthropods, and they are mainly found infecting the testes or ovaries of their hosts.

In 1924, Marshall Hertig from Minneapolis, USA, and Simeon Burt Wolbach from Harvard Medical School first discovered Wolbachia bacteria in Culex pipiens mosquitoes, and the bacteria were named Wolbachia after Simeon Burt Wolbach.

Dengue fever patients are receiving treatment at a hospital in Dhaka, the capital of Bangladesh. The Bangladesh Health Services Department reported that as of last month, the number of confirmed dengue cases this year has exceeded 200,000, with 1,006 deaths.
[Photo by Dhaka AFP/ Yonhap News]

They were studying a microorganism called 'Rickettsia,' an intracellular parasitic bacterium widely spread among arthropods, when they observed an intracellular bacterium that infected only the ovaries and testes of mosquitoes. However, since this bacterium was similar to Rickettsia, the causative agent of Rocky Mountain spotted fever studied by Wolbach, and was found unrelated to disease, it was initially ignored. It was only in 1936, twelve years later, that Hertig re-examined this bacterium and brought it to attention.

Wolbachia bacteria are always found in infected mature eggs but are absent in mature sperm. Therefore, only infected females can transmit their Wolbachia bacteria to their offspring. Transmission mainly occurs through the eggs of infected females. This characteristic of Wolbachia bacteria is utilized in nature releases to control mosquitoes that transmit various viruses.

In November 2017, the U.S. Environmental Protection Agency (EPA) approved the natural release of genetically modified male mosquitoes infected with Wolbachia bacteria developed by the bio-venture company MosquitoMate. Released males mate with wild females, but the eggs laid do not hatch. Also, when Wolbachia-infected female mosquitoes lay eggs, the hatched mosquitoes are also infected with Wolbachia bacteria. Eventually, only Wolbachia-infected mosquitoes remain, and wild mosquitoes that transmit viruses such as Dengue fever, Yellow fever, and Zika gradually disappear.

Researchers are classifying mosquitoes at the Gyeonggi-do Institute of Health and Environment in Gwonseon-gu, Suwon-si, Gyeonggi-do.
[Photo by Yonhap News]

The nonprofit organization 'World Mosquito Program (WMP)' has conducted small-scale experiments releasing Wolbachia-infected male mosquitoes in some cities in Australia, Brazil, Colombia, Indonesia, and Vietnam over the past decade to prevent Dengue fever and other diseases, all of which have been successful. The largest experiment conducted in Yogyakarta, Indonesia, reduced the incidence of Dengue fever by about 77%. In 2016, a county in California, USA, also released Wolbachia-infected mosquitoes, reducing the mosquito population by about 95%.

According to the Jakarta Post and others on the 24th (local time), the Bali government plans to release 200 million Wolbachia-infected mosquito eggs in collaboration with the WMP. In Indonesia, more than 131,000 Dengue fever patients were reported last year, with 1,135 deaths. As of the end of October this year, 69,000 Dengue fever patients have been reported nationwide, with about 500 deaths.

The Indonesian Ministry of Health stated, "This year, we released Wolbachia mosquitoes in three cities: Semarang in Central Java, Bontang in East Kalimantan, and Kupang in East Nusa Tenggara," adding, "Next year, we plan to start the Wolbachia project in West Jakarta and Bandung in West Java."

However, Bali residents oppose the release of Wolbachia mosquitoes due to concerns that the mosquito population will surge with the mass release. They worry that a sudden increase in mosquito swarms in the popular tourist destination of Bali could cause discomfort to tourists and lead to a decline in tourism revenue.