How mosquitoes spread disease

Mosquitoes pick up viruses by biting infected people. When they bite again, they can transmit the virus to the next person. This is how mosquito-borne diseases spread.

Mosquitoes do not naturally carry viruses – they can only get them from infected people. 

Since only female mosquitoes bite humans, only female mosquitoes can transmit viruses.

The Aedes aegypti mosquito is the main transmitter of dengue, Zika, chikungunya and yellow fever viruses.

Aedes aegypti

Aedes aegypti mosquitoes originated in Africa, but they have spread through tropical and subtropical regions around the world.

Aedes aegypti mosquitoes first spread outside Africa during the slave trade between the 15th and 19th centuries. They also spread through trade with Asia during the 18th and 19th centuries, and then again following troop movements in World War II.

child in hospital with yellow fever, Indonesia

The number of people affected by mosquito-borne diseases is rapidly growing.

In recent years, population growth, the movement of people from rural areas to cities, more international travel and climate change have all increased the spread of Aedes aegypti mosquitoes. 

And subsequently, the number of people affected by mosquito-borne diseases has also increased.

Dengue fever is now considered the most critical mosquito-borne viral disease in the world, according to the World Health Organization. It’s also the most rapidly spreading, with a 30-fold increase in global incidence over the past 50 years.

What is Wolbachia?

Wolbachia are extremely common bacteria that occur naturally in 50 per cent of insect species, including some mosquitoes, fruit flies, moths, dragonflies and butterflies.

Wolbachia are safe for humans and the environment. Independent risk analyses indicate that the release of Wolbachia-infected mosquitoes poses negligible risk to humans and the environment.

Wolbachia live inside insect cells and are passed from one generation to the next through an insect’s eggs. Aedes aegypti mosquitoes don’t normally carry Wolbachia, however many other mosquitoes do.

Staff in prepare larve

How our Wolbachia method works

Our Wolbachia method is simple. 

We discovered that when Aedes aegypti mosquitoes carry Wolbachia, the bacteria compete with viruses like dengue, Zika, chikungunya and yellow fever.

This makes it harder for viruses to reproduce inside the mosquitoes. And the mosquitoes are much less likely to spread viruses from person to person.

This means that when Aedes aegypti mosquitoes carry natural Wolbachia bacteria, the transmission of viruses like dengue, Zika, chikungunya and yellow fever is reduced.

So, at the World Mosquito Program, we breed Wolbachia-carrying mosquitoes. Then, in partnership with local communities, we release them into areas affected by mosquito-borne diseases.

Which means less risk of disease in communities where Wolbachia is established in the local mosquito population.

Wolbachia community education Sri Lanka

Is it safe?

Three independent risk assessments have been conducted on our Wolbachia method.

The results concluded that there is negligible risk associated with the release of Wolbachia-carrying mosquitoes. This is the lowest possible rating. 

The risk assessments found that Wolbachia is safe for people, animals and the environment. 

The World Mosquito Program has received regulatory approval from relevant government bodies in all the countries where we are releasing Wolbachia-carrying mosquitoes. In addition, we don’t release Wolbachia mosquitoes without community support.

field staff member in FIji

Our method is unique and effective

Unlike most other techniques that aim to prevent mosquito-borne diseases, our Wolbachia method is natural and self-sustaining

Our method does not suppress mosquito populations or involve genetic modification (GM), as the genetic material of the mosquito is not altered. 

Long-term monitoring shows that our natural Wolbachia method is self-sustaining in almost all international project sites, with the first mosquitoes released in 2011.

How our method comparesOur self-sustaining method

Far-north Queensland is now essentially a dengue-free area for the first time in well over 100 years.

 Dr Richard Gair

Director and Public Health Physician, Tropical Public Health Services, Cairns

Dr Richard Gair

WMP community

How we release Wolbachia mosquitoes

Together with communities around the world, we’ve released Wolbachia-carrying mosquitoes into many towns and cities.

We started our first trials in Australia and, once we proved the method could work, started doing small trials around the world.

We always work with the approval of communities that are affected by mosquito-borne diseases. 

We work closely with local governments, health authorities and community groups before we release any mosquitoes. 

We spread the word about our Wolbachia method through local events, TV, radio, newspapers, social media and word of mouth.

Then we survey the community to make sure there’s support for the project to go ahead.

Each student received a special kit containing Wolbachia mosquito eggs

Once the project is understood and supported by the community, we breed Wolbachia-carrying mosquitoes.

Then, when we have enough, we release them.

This is a team effort! Lots of volunteers get involved for mosquito releases, including individuals, schools, universities and local community groups.

Because mosquitoes don’t fly very far, we usually release a handful of mosquitoes every 50 metres across the target area.

The release period usually lasts for 12 to 20 weeks.

How we deploy our mosquitoes

WMP in Vanuatu

How do we know it works?

We monitor both the Wolbachia-carrying mosquito population and incidence of diseases before, during and after releasing Wolbachia-carrying mosquitoes. 

We have strong evidence showing the effectiveness and safety of our Wolbachia method. 

We have set up projects in 12 countries and our Wolbachia-carrying mosquitoes have reached more than 10 million people (as at June 2022).

In areas where Wolbachia is self-sustaining at a high level, dengue transmission has been significantly reduced.

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