Mosquitoes infected with a unique bacterium have led to a staggering decline in dengue fever in one 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 in treated neighborhoods were 77 percent lower than in areas not exposed to the infected insects.
Dengue, a tropical virus that causes high fever and pain, infects approximately 400 million people each year and kills up to 25,000 people.
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Dengue, a tropical virus that causes high fever and pain, infects approximately 400 million people each year and kills up to 25,000 people. It is carried by Aedes aegypti, a mosquito that thrives in tropical climates and breeds in stagnant water
In a trial program coordinated by the World Mosquito Program, mosquitoes infected with Wolbachia were released in 12 randomly selected areas in Yogyakarta, a city with more than 300,000 inhabitants, while twelve other neighborhoods were selected as controls.
In a study published this week in the New England Journal of Medicine, researchers confirmed that only 2.3 percent of people living in neighborhoods where the modified mosquitoes were released were diagnosed with dengue, compared with 9.4 percent in the control districts.
The study, which enrolled more than 8,000 people, also found that dengue cases that required hospitalization were reduced by 86 percent in the treated areas.
“This is a great achievement for the people of Yogyakarta,” said co-author Adi Utarini, a public health researcher at Gadjah Mada University. “There are more than 7 million cases of dengue in Indonesia each year. The success of the experiment enables us to expand our work to the entire city of Yogyakarta and neighboring urban areas. ‘
In Yogyakarta, Java, more than 8,000 residents in a total of 24 districts were tested. In the areas where the infected mosquitoes were infected, not only were dengue rates 77 percent lower, but the cases that required hospitalization were 86 percent lower
Scientists in Yogyakarta, Indonesia, infected 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 and ensure that the insects only have Wolbachia-infected offspring.
The result is a growing population of insects that do not pass the virus on – Utarini said she could see a day when cities in Indonesia would be free of the virus.
BUGGING OUT: THE DENGUE FEVER THREAT
Dengue is a viral infection that is transmitted by mosquitoes.
It is captured by people who visit or live in Asia, the Caribbean, and North, South or Central America.
Mosquitoes in the UK do not transmit the virus.
In most cases, the infection is mild and lasts about a week.
Symptoms usually include:
- Strong headache
- Pain behind the eyes
- Muscle and joint pain
- Nausea and vomiting
- Widespread rash
- stomach pain
- Loss of appetite
There is no cure or specific treatment.
Patients can use pain relievers to relieve their symptoms, stay hydrated, and rest.
In rare cases, dengue symptoms can progress to severe dengue.
Elderly patients or those with other medical conditions are most at risk.
Serious symptoms of dengue fever can include:
- Profuse skin bleeding with blood stains on and under the skin
- Blood in the urine and stool
- Shortness of breath – when the lungs cannot supply the vital organs with sufficient oxygen
- Organ failure
- Changes in mental state and loss of consciousness
- Dangerously low blood pressure
Severe dengue fever is usually treated with blood and platelet transfusions, IV fluids for rehydration, and oxygen therapy for low levels.
Mosquito-borne dengue fever infects nearly 400 million people annually, mainly in tropical parts of developing countries, according to the World Health Organization.
There are more than 7 million cases each year in Indonesia alone.
The disease causes high fever, severe headache and joint pain, and can lead to fatal complications, killing up to 25,000 people annually.
The WHO reports that dengue cases have increased 30-fold in the past 50 years as humans invade mosquito habitats and contribute to climate change.
A 2018 study of Wolbachia-infected mosquitoes in Australia also saw a decrease in dengue rates, but the effects were not compared to control areas.
A subsequent test in Vinh Luong, Vietnam resulted in an 86 percent decrease in dengue fever compared to a nearby resort town.
Scientists have called the Yogyakarta experiment a “gold standard” study.
“This is the result we’ve been waiting for,” said Scott O’Neill, microbiologist and director of the World Mosquito Program, in 2020 when the results were added up for the first time.
“We have evidence that our Wolbachia method is safe, sustainable and reduces the incidence of dengue.”
The Indonesian trial ended a few months early because of the coronavirus pandemic, but O’Neill said the results were encouraging enough that the strategy should be deployed “globally in large urban populations”.
Wolbachia occurs naturally in around 60 percent of all insect species, including dragonflies, fruit flies, and moths.
Scientists first discovered it in the 1920s in mosquitoes that lived in the drainage system below Harvard University.
Aedes aegypti, the mosquito that transmits dengue fever, thrives in tropical climates and breeds in stagnant waters.
It also carries yellow fever, zika, and the chikungunya virus.
Typically, the countries plagued by the pests spray insecticides, but this only keeps them away temporarily and the insects can also develop resistance.
Modifying mosquitoes to control infectious diseases is an increasingly popular tactic around the world, but it has not met with widespread acceptance.
In April 2021, residents of the Florida Keys protested plans to release nearly a billion 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 specific protein.
When mating, the protein ensures that female offspring do not survive the next generation.
With fewer females in each subsequent generation, there is hope that the total mosquito population will decline along with the rates of transmission of mosquito-borne diseases.
A worker sprays against 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 claims the program poses no threat to humans as only female mosquitoes can bite.
But, says Barry Wray of the Florida Keys Environmental Coalition, “The people here in Florida don’t approve of genetically engineered mosquitoes or human experiments.”
Dana Perls, program manager for food and technology at Friends of the Earth, called the program a “dark moment in history” and urged the EPA to “stop this live experiment immediately”.
Other local residents say the EPA did not require any peer review or preliminary testing for genetically modified mosquitoes before it was released into the wild.