Natural bacteria could wipe out dengue-carrying mosquitoes, Australian research suggests
Populations of mosquitoes, which spread dengue fever, zika and other viruses, dropped by 80% after being infected with Wolbachia bacteria
Infecting dengue-carrying mosquitoes with a strain of naturally occurring bacteria can drastically reduce their numbers, new Australian research has found.
In a trial in three north Queensland communities, researchers dramatically suppressed the populations of the Aedes aegypti mosquito which spreads dengue fever, Zika, chikungunya and other viruses.
The trial was carried out with local approval in the towns of Mourilyan and South Johnstone in far north Queensland, as well as in Goondi Bend, an outer suburb of Innisfail.
Over 20 weeks, Queensland scientists, in collaboration with Verily Life Sciences – a research firm owned by Google parent company Alphabet – released 3 million male mosquitoes that had been infected with bacteria known as Wolbachia.
Across the three trial sites, mosquito populations subsequently dropped by more than 80%.
In Mourilyan, where the suppression was most successful, the team returned the following year to find the mosquitoes had virtually been wiped out, with a 97% reduction in population.
The trial began in 2018 and has been documented in a study published on Tuesday in the peer-reviewed journal PNAS.
CSIRO scientist Nigel Beebe, the study’s lead author, said infecting male Aedes aegypti mosquitoes – which do not bite – with the bacteria appeared to alter some component of their reproductive biology.
Wild female mosquitoes that mate with infected males consequently lay eggs that never hatch.
“Wolbachia is one of these bacteria that you find in lots of insects,” said Beebe, who is also an associate professor at the University of Queensland. “It makes a really good sterility agent; it doesn’t affect the fitness of the mosquito very much.”
Aedes aegypti – also known as the yellow fever mosquito – arrived in Australia more than a century ago. It is largely confined to Queensland, although earlier this year the mosquito was detected in the Northern Territory.
Suppressing its numbers was unlikely to have any major negative ecological effects, Beebe said.
“It only exists in urban landscapes. It preferentially bites humans, like 95% of the time. The urban landscape is a pretty artificial ecosystem, so removing a mosquito from that ecosystem is probably not going to be a problematic issue.”
The Aedes aegypti mosquito is found in tropical areas in more than 120 countries and infects millions of people globally with viruses each year. The number of dengue cases reported to the World Health Organization has increased by more than eight-fold globally over the past two decades.
Researchers have previously infected Aedes aegypti mosquitoes with different strains of Wolbachia bacteria to reduce the mosquitoes’ likelihood of transmitting viruses that affect humans.
A World Mosquito Program trial in Indonesia last year found that infecting mosquitoes with the bacteria reduced the number of dengue infections in Yogyakarta city by 77% compared to untreated areas. An earlier trial in Townsville found the technique was successful in preventing dengue outbreaks.
In those studies, both male and female mosquitoes were infected with the bacteria.
Wolbachia is unlikely to have any effect if a human is bitten by an infected female mosquito, Beebe said. “There’s experimental evidence and observation evidence that these Wolbachia [bacteria] cannot invade human cells.”
The team plans to use a similar technique to suppress the virus-spreading Asian tiger mosquito, Aedes albopictus, an “incredibly pestiferous” species that has established itself in the Torres Strait Islands since 2004.
“We want to build our own sterile male system so that when this mosquito gets on to the mainland, we can kick it off,” Beebe said.
Mosquito suppression programs are also under way for other species in French Polynesia and the Hunter region of New South Wales.
News Credit: www.theguardian.com