Mosquitoes infected with virus-fighting bacteria reduce dengue fever by more than 75 percent

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Mosquitoes infected with a unique bacteria have caused a staggering decline in dengue fever in a region of Indonesia, researchers say.

Between 2017 and 2020, scientists in Yogyakarta, Java, released millions of mosquitoes injected with Wolbachia, a bacterium that prevents them from transmitting the dengue virus.

The team found that infections were 77 percent lower in treated neighborhoods, compared with areas not exposed to the infected insects.

Dengue, a tropical virus that causes high fever and pain, infects some 400 million people every year and kills up to 25,000.

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Dengue, a tropical virus that causes high fever and pain, infects some 400 million people every year and kills up to 25,000.  It is carried by Aedes aegypti, a mosquito that thrives in tropical climates and breeds in standing water

Dengue, a tropical virus that causes high fever and pain, infects some 400 million people each year and kills up to 25,000. It is carried by Aedes aegypti, a mosquito that thrives in tropical climates and breeds in standing water

In a pilot program coordinated by the World Mosquito Program, mosquitoes infected with Wolbachia were released into 12 randomly selected areas in Yogyakarta, a city of more than 300,000 people, while 12 other neighborhoods were selected as controls.

In a study published this week in The New England Journal of Medicine, researchers have confirmed that dengue was diagnosed in only 2.3 percent of people living in neighborhoods where the modified mosquitoes had been released, compared with 9.4 percent of those in control districts.

The study, which involved more than 8,000 individuals, also found that dengue cases requiring hospitalization were reduced by 86 percent in the treated areas.

“This is a great success for the people of Yogyakarta,” said study co-author Adi Utarini, a public health researcher at the University of Gadjah Mada. ‘Indonesia has more than 7 million cases of dengue every year. The success of the trial will allow us to expand our work across the entire city of Yogyakarta and into adjacent urban areas.”

More than 8,000 residents were tested in a total of 24 neighborhoods in Yogyakarta, Java.  Not only were dengue rates 77 percent lower in the areas where the infected mosquitoes were infected, but cases requiring hospitalization were 86 percent lower.

More than 8,000 residents were tested in a total of 24 neighborhoods in Yogyakarta, Java. Not only were dengue rates 77 percent lower in the areas where the infected mosquitoes were infected, but cases requiring hospitalization were 86 percent lower.

Scientists in Yogyakarta, Indonesia, are infecting mosquitoes with Wolbachia, a bacterium that prevents them from transmitting dengue fever.  Neighborhoods where the infected insects were released reported 77 percent fewer cases

Scientists in Yogyakarta, Indonesia, are infecting mosquitoes with Wolbachia, a bacterium that prevents them from transmitting dengue fever. Neighborhoods where the infected insects were released reported 77 percent fewer cases

The bacteria also affect reproduction, causing the insects to have only Wolbachia-infected offspring.

The result is a growing population of insects that do not transmit the virus – Utarini said she could see a day when cities in Indonesia were free of the virus.

BUGGING OUT: THE THREAT OF DENGU FEVER

Dengue is a viral infection spread by mosquitoes.

It is caught by people visiting or living in Asia, the Caribbean, and North, South, or Central America.

Mosquitoes in the UK do not spread the virus.

In most cases, the infection is mild and clears up in about a week.

Symptoms usually include:

  • Fever
  • Severe headache
  • Pain behind the eyes
  • Muscle and joint pain
  • Nausea and vomiting
  • Widespread rash
  • Stomach ache
  • Loss of appetite

There is no cure or specific treatment.

Patients can relieve their symptoms by taking pain medications, staying hydrated and resting.

In rare cases, dengue symptoms can develop into severe dengue.

Older patients or those with other medical conditions are most at risk.

Serious symptoms of dengue fever can include:

  • Severe skin bleeding with blood spots on and under the skin
  • Blood in the urine and stool
  • Respiratory problems – when the lungs cannot supply the vital organs with sufficient oxygen
  • organ failure
  • Changes in mental status and unconsciousness
  • Dangerously low blood pressure

Severe dengue is usually treated through a blood and platelet transfusion, IV fluids for rehydration, and oxygen therapy if levels are low.

According to the World Health Organization, nearly 400 million people are infected with dengue fever, which is transmitted by mosquitoes, every year, mainly in tropical parts of developing countries.

In Indonesia alone, there are more than 7 million cases annually.

The disease causes high fever, severe headaches and joint pain and can lead to fatal complications that kill up to 25,000 people each year.

The WHO reports that dengue cases have increased 30-fold over the past 50 years as humans invade mosquito habitats and contribute to climate change.

A 2018 trial of Wolbachia-infected mosquitoes in Australia also saw a sharp drop in dengue fever rates, but the effects were not compared with control areas.

A subsequent test in Vinh Luong, Vietnam, resulted in an 86 percent drop in dengue levels compared to a nearby resort town.

Scientists have called the Yogyakarta experiment a “gold standard” trial.

“This is the result we’ve been waiting for,” Scott O’Neill, microbiologist and director of the World Mosquito Program, said in 2020, when the results were first counted.

‘We have evidence that our Wolbachia method is safe, sustainable and reduces the risk of dengue fever.’

The Indonesian trial ended a few months earlier due to the coronavirus pandemic, but O’Neill said the results were encouraging enough to start applying the strategy “globally in large urban populations.”

Wolbachia occurs naturally in about 60 percent of all insect species, including dragonflies, fruit flies and moths.

Scientists first discovered it in mosquitoes living in the drainage system beneath Harvard University in the 1920s.

Aedes aegypti, the mosquito that carries dengue fever, thrives in tropical climates and breeds in standing water.

It also carries yellow fever, Zika, and the chikungunya virus.

Typically, lands infested by the pests spray insecticide, but this only keeps them away temporarily and the insects can also develop resistance.

Adapting mosquitoes to fight infectious diseases has become an increasingly popular tactic around the world, but it is not widely accepted.

In April 2021, residents of the Florida Keys protested plans to release nearly a billion gene-hacked Aedes aegypti over a two-year period.

The project, a collaboration between the Florida Keys Mosquito Control District and Oxitec, a British biotech company, aims to reduce the number of Aedes aegypti by altering their DNA to pass on a particular protein.

When they mate, the protein ensures that female offspring do not survive the next generation.

With fewer females in each generation, the hope is that the overall mosquito population will decline, along with transmission rates of mosquito-borne diseases.

A worker sprays for mosquitoes in Singapore.  Insecticides only keep mosquitoes away for a few days and insects can develop resistance

A worker sprays for mosquitoes in Singapore. Insecticides only keep mosquitoes away for a few days and insects can develop resistance

The modified mosquitoes are all male and Oxitec states that because only female mosquitoes can bite, the program poses no risk to humans.

But, says Barry Wray of the Florida Keys Environmental Coalition, “People here in Florida are not condoning genetically engineered mosquitoes or human experimentation.”

Dana Perls, food and technology program manager at Friends of the Earth, called the program a “dark moment in history” and demanded that the EPA “stop this live experiment immediately.”

Other residents say the EPA did not require peer review or preliminary trials for GE mosquitoes before they were released into the wild.

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