A look at the current status of some of the most prevalent mosquito-borne diseases.
We are fortunate in Australia in that we do not have a high incidence of mosquito-borne diseases. The most commonly reported diseases being Ross River fever (5000 cases per year), Barmah Forest virus (2400 cases per year, the majority in Queensland), and dengue fever (in Queensland and the Torres Strait). Less common are Murray Valley encephalitis and Kunjin virus (a local variant of West Nile virus).1 Here we share un update on mosquitoborne diseases in Australia and overseas.
Sentinel chickens – an early warning system in Australia
In Australia, State Governments have mosquito surveillance programs in place, not just to detect incursions of invasive mosquitoes at ports and airports, but to detect the spread of mosquitoes around the country and to monitor for potential disease outbreaks. Populations of sentinel chickens around the country have their blood tested regularly for mosquito-borne viruses. These chickens are in areas of high mosquito activity so any virus outbreak is likely to be detected in these birds first, acting as an early warning system. The West Australian Government issued a press release in October stating that mosquito-borne viruses had been detected in sentinel chickens in the Kimberley region. The exact virus had yet to be identified but is from the family that includes Murray Valley encephalitis, Kunjin and Japanese encephalitis.
With the changing climate, which is likely to result in increased mosquito numbers, the spreading of mosquitoes into new parts of Australia means the spreading of disease. Pest managers should learn about the mosquito diseases in Australia and indeed protect themselves when operating in areas of high mosquito pressure.
Eastern Equine Encephalitis outbreak in Massachusetts, USA
Eastern Equine Encephalitis (EEE) is worth a mention as it has been in the news this year, with a recent outbreak in Massachusetts, USA. EEE is a rare but lethal mosquitoborne disease. Much like the mosquito-borne diseases in Australia, the symptoms include diarrhoea, fever, headache, seizures and vomiting. Although a vaccine is available for horses, no vaccination or treatment is available for humans, meaning 30% of patients that develop severe symptoms die, with survivors often suffering brain damage.
EEE was first detected in horses in 1938 in the USA, which is how it got its name, but the main hosts of the virus are birds. EEE is spread by bird-feeding mosquitoes (Culiseta), typically in swamp environments. It is endemic to the Americas, primarily in the more tropical areas, but appears in more temperate regions during summer, following the arrival of migratory birds. Other mosquitoes that feed on both birds and mammals will transfer and infect mammals such as horses and humans with the virus. Although the infected mammals will be affected, they often do not circulate enough virus to infect other mosquitoes and spread the virus.
Fortunately, there is no evidence that EEE is present in Australia even though Culiseta mosquitoes are found here. However, a range of mosquitoes in Australia transmit similar viruses, such as Ross River Fever and Barmah Forest virus.

Egypt declared malaria free
A good news mosquito story: Egypt has been declared malaria free by the World Health Organisation. Malaria kills approximately 600,000 people a year, primarily in Africa. A country is certified malaria free after it has demonstrated no transmissions for three consecutive years and has an action plan in place to prevent the re-establishment of transmission.
The process of eradication began in 1926, following the banning of rice cultivation and agricultural crops near residential areas. Spikes in malaria numbers occurred during the Second World War (three million cases) and during the construction of the Aswan dam. But with a rigorous surveillance and vector control program in place, malaria cases continued to decrease. Having free malaria diagnosis and treatment is also a key element of the program, as is surveillance and co-operation at the borders to prevent re-establishment through migrants entering the country.
Mosquitoes found across Scotland
Scotland is renowned for its biting midge populations, but a recent surveillance study also detected 16 different mosquito species, much to the surprise of researchers. This included Culex pipiens – the common house mosquito or Northern house mosquito, which is a known vector of West Nile virus in Europe. Whilst this was the first benchmarking study of its kind in Scotland, the results were surprising nonetheless. With mosquitoes already well established, the researchers noted that warming temperatures are likely to increase mosquito numbers and the potential threat from mosquito-borne diseases.
Mosquito outbreak in western Sydney
Residents in areas of western Sydney, in particular Chipping Norton, are currently experiencing plague levels of mosquitoes. Mosquito numbers are so high that residents cannot go outside and the number that are getting inside buildings is significant. Local supermarkets have sold out of personal insect repellents and mosquito control products. Investigations led by Dr Cameron Webb from the University of Sydney identified the mosquito as the brown house mosquito, Culex quinquefasciatus, and have uncovered the origin of the outbreak.
A wastewater facility in Liverpool has been identified as the source. The oxidation pool had become overgrown with frogbit weed, allowing mosquito larvae numbers to increase un-noticed. To deal with the problem, it was necessary to remove the weed before larvicide treatments could be applied.

Two weeks after the initial clean-up efforts and treatment saw a 98% reduction in mosquito larvae numbers. Whilst the treatment will take care of the larvae and stop new adults emerging, the current population of adults will take a few weeks to die. Professional pest treatments including fogging and surface spray applications would provide some relief, but such are the numbers it is likely residents will not be able to enjoy outdoor areas until Christmas (hopefully!)
1 Ong, O.T.W et al. (2021). Mosquito-Borne Viruses and Non- Human Vertebrates in Australia: A Review. Viruses 13(2):265. doi: 10.3390/v13020265