La Ni帽a will give us a wet summer. That's great weather for mosquitoes
The return of the weather pattern will see a wetter spring and summer in many parts of Australia.
We know mosquitoes need water to complete their life cycle. So does this mean Australia can expect a bumper mozzie season? How about a rise in mosquito-borne disease?
While we've seen more mosquitoes during past La Ni帽a events, and we may well see more mosquitoes this year, this doesn't necessarily mean we'll see more related disease.
This depends on a range of other factors, including local wildlife, essential to the life cycle of disease-transmitting mosquitoes.
What is La Ni帽a?
La Ni帽a is a phase of the , a pattern of ocean and atmospheric circulations over the Pacific Ocean.
While is generally associated with hot and dry conditions, La Ni帽a is the opposite. La Ni帽a brings slightly cooler but wetter conditions to many parts of Australia. During this phase, northern and eastern Australia are particularly likely to .
The Bureau has confirmed that has formed in the tropical Pacific, with climate models suggesting it's likely to remain until at least the end of 2020.
鈥� Bureau of Meteorology, Australia (@BOM_au)
Read more in our Climate Driver Update:
Australia's most recent significant La Ni帽a events were in .
Why is wet weather important for mosquitoes?
Mosquitoes lay their eggs on or around stagnant or still water. This could be water in ponds, backyard plant containers, clogged gutters, floodplains or wetlands. Mosquito larvae (or "wrigglers") hatch and spend the next week or so in the water before emerging as adults and buzzing off to look for blood.
If the water dries up, they die. But the more rain we get, the more opportunities for mosquitoes to multiply.
Mosquitoes are more than just a nuisance. When they bite, they can transmit viruses or bacteria into our blood to make us sick.
While Australia is free of major outbreaks of internationally significant diseases such as dengue or malaria, every year mosquitoes still cause debilitating diseases.
These include transmission of , and the potentially fatal .
What happens when we get more rain?
We've know for a long time floods provide plenty of water to boost the abundance of mosquitoes. With more mosquitoes about, there is a of mosquito-borne disease.
The amount of rainfall each summer is also a key for seasonal outbreaks of mosquito-borne disease, especially Ross River virus.
Inland regions of Queensland, New South Wales and Victoria, especially within the , are particularly prone to "boom and bust" cycles of mosquitoes and mosquito-borne disease.
In these regions, the El Ni帽o-Southern Oscillation is thought to play an important role in of mosquito-borne disease.
The hot and dry conditions of El Ni帽o aren't typically ideal for mosquitoes.
But historically, major outbreaks of mosquito-borne disease have been associated with extensive inland flooding. This flooding is typically associated with prevailing La Ni帽a conditions.
For instance, outbreaks of Murray Valley encephalitis in the 1950s and 1970s had on human health and occurred at a time of .
Over the past decade, when La Ni帽a has brought above average rainfall and flooding, there have also been outbreaks of mosquito-borne disease.
These have included:
- Victoria's record breaking epidemic of in 2016-17 after extensive inland flooding
- southeast Queensland's outbreak of Ross River virus in 2014-15, to an increase in mosquitoes associated with freshwater habitats after seasonal rainfall
- eastern Australia's major outbreaks of mosquito-borne disease associated with extensive flooding during two between 2010 and 2012. These included and mosquito-borne illness caused by the closely related West Nile virus (Kunjin strain).
We can't say for certain there will be more disease
History and our understanding of mosquito biology means that with the prospect of more rain, we should expect more mosquitoes. But even when there are floods, predicting outbreaks of mosquito-borne disease isn't always simple.
This is because of the role wildlife plays in the transmission cycles of Ross River virus and Murray Valley encephalitis virus.
In these cases, mosquitoes don't hatch out of the floodwaters carrying viruses, ready to bite humans. These mosquitoes first have to bite wildlife, which is where they pick up the virus. Then, they bite humans.
So how local animals, such as kangaroos, wallabies and water birds, respond to rainfall and flooding will play a role in determining the risk of mosquito-borne disease. In some cases, flooding of inland wetlands can see an .
How can we reduce the risks?
There isn't much we can do to change the weather but we can take steps to reduce the impacts of mosquitoes.
Wearing insect repellent when outdoors will help reduce your chance of mosquito bites. But it's also important to tip out, cover up, or throw away any water-holding containers in our backyard, at least once a week.
Local authorities in many parts of Australia also undertake surveillance of mosquitoes and . This provides an early warning of the risk of mosquito-borne disease.
Provided by The Conversation
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