Climate change, chemicals on your skin put you at greater risk of mosquitos

By Joshua Boscaini, ABC

Climate change and extreme weather have the potential to increase cases of mosquito-borne diseases and push the insects into new areas of Australia, according to medical and research science experts.

A "unique signature" of chemicals on the skin can also make people more susceptible to mosquito bites, with these experts highlighting the need to protect yourself from bites.

Australia experienced an outbreak of the mosquito-borne Japanese encephalitis virus recently - a diseases that is usually confined to Asia and the Torres Strait.

What impact could climate change have on mosquitoes?

Experts say climate change could lead to an increase in mosquito numbers and transmission of mosquito-borne diseases, such as Japanese encephalitis.

Tom Burkot from the Australian Institute of Tropical Health and Medicine told the ABC that some species of mosquitoes thrive in warmer climates.

Professor Burkot said warmer temperatures in southern Australia, fuelled by climate change, could cause some mosquito species to migrate south.

"A mosquito like Aedes aegypti, which is a classic and primary dengue vector worldwide, is very much a tropical mosquito," Professor Burkot said.

"As global temperatures increase, temperatures in Australia increase, that will make the climatic conditions more favourable for aegypti to move south."

In 2022, southern Australia experienced an outbreak of Japanese encephalitis cases - a disease that is usually transmitted in Asia and the Torres Strait.

Australia's acting chief medical officer declared the outbreak a Communicable Disease Incident of National Significance, according to Australia's Department of Health and Aged Care.

Research published in the The Lancet Plenatary Health in 2021 found between 4 to 6 billion additional people could be at risk of malaria or dengue fever by 2070 because of climate change.

CSIRO principal research scientist Prasad Paradkar said global warming could increase the transmission of mosquito borne diseases.

Dr Paradkar said warmer temperatures and rainfall created the perfect conditions for mosquito breeding.

"Climate change … has a direct impact as well as some indirect impact [on] mosquitoes, as well as diseases that they will carry," Dr Paradkar said.

"It can also shorten the incubation time for pathogens inside mosquitoes they can carry. So the mosquitoes can become infected more quickly."

Dr Paradkar said extreme weather events, such as cyclones, could transport new species of mosquitoes to new areas, increasing the risk of disease transmission.

"We have seen it happen in, for example, Europe, where we now see dengue transmission cases in areas which previously was really unthinkable," he said.

What mosquitoes do we need to be aware of?

Mosquito-borne diseases kill more than 1 million people and infect about 700 million each year, according to the World Mosquito Program.

Professor Burkot said researchers were monitoring the emergence of the Asian tiger mosquito, or Aedes albopictus, in the Torres Strait.

Aedes albopictus was capable of carrying dengue fever, chikungunya and zika virus, he said.

The World Health Organisation said zika virus can cause infants to be born with microcephaly - a condition where a baby's head grows smaller than expected.

"The only place in Australia where it's present is in the Torres Strait and so there's always a risk of this mosquito being introduced into mainland Australia," Professor Burkoit said.

"If it should get into Australia … it could spread along the entire eastern seaboard of Australia and it would therefore put it at risk of dengue transmission again."

Professor Burkot said it was likely the mosquito's resilient eggs arrived in the Torres Strait attached to synthetic materials on ships.

"They lay their eggs on the sides of small containers, like buckets and tyres and things that can hold water, often times are made of artificial materials like rubber and plastic," he said.

"[Their eggs] can dry out and still be viable … but if it rains and those eggs get wet, the larvae can hatch.

"It's a mechanism they have that makes it really easy for them to be invasive mosquitoes, to be transported great distances and then to populate new geographic areas."

Can mosquitoes be attracted to some people more than others?

Professor Burkot said mosquitoes were first attracted to the carbon dioxide that humans or animals emit when they breathe.

"There's body temperature and there's chemical cues as well. So when the mosquito actually lands on you, it's actually sort of tasting you with its feet," he said.

"On the surface of our body we have a vast array of chemicals that are present. A lot of these are produced by bacteria that are growing on our skin."

He said people had a "unique signature" of chemicals on their skin that could either be more or less attractive to mosquitoes.

"These chemicals are much more attractive to mosquitoes and the concentration of the chemicals is important too."

Dr Paradkar said lactic acid in someone's sweat or dark clothing sometimes made people more attractive than others.

"Some people sweat more or there's lactic acid in the sweat of mosquitoes which is a really good attractant for mosquitoes," he said.

Those chemicals were used in mosquito traps, according to Professor Burkot.

"A lot of the things that we're now using as lures in mosquito traps are really based on some of these things, things like lactic acid is attracted to certain mosquitoes," he said.

"A chemical called octantal is attracted to other mosquitoes and oftentimes it takes a combination."

How do we protect ourselves?

Insect topical repellents containing DEET were best to protect yourself against mosquito bites, Professor Burkot said.

He said spatial repellents, that release anti-mosquito vapour into the air, were also effective.

"You can often put these outside your patio doors and it'll keep the mosquitoes entering your house because they create this mosquito free zone around your house," he said.

Dr Paradkar said wearing long sleeves and pants could also protect you from getting bitten, as well as avoiding going outside early evening.

He said mosquitoes could breed in just a little water, so it was important to ensure bowls, pot plant saucers and buckets were emptied or covered

"Just check for any or empty out any water bowls for pets, bird parts, pots … pot plant saucers, buckets," he said.

"Check your rainwater tank … make sure there's a good mesh to cover the top because mosquitoes can breed in rainwater if there's holes in your mesh."

-ABC