Mosquito borne disease and mosquito management in South Australia
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An overview of mosquito ecology, mosquito borne diseases, monitoring tools and techniques and Integrated Mosquito Management
Flaviviruses are arthropod-borne positive-strand RNA viruses. Murray Valley encephalitis virus (MVEV), Dengue virus, Kunjin strain of West Nile virus (KUNV) and Japanese encephalitis virus (JEV) are known to be transmitted in Australia and are of major significance to human health. Other flaviviruses known to be transmitted in Australia include Alfuy, Kokobera, Edge Hill, Stratford and New Mapoon viruses, although only Kokobera virus has been shown to cause human disease (very rarely)1.
MVEV and KUNV are endemic in birds in northern Australia with occasional cases occurring in humans. MVEV and KUNV rarely occur in southern Australia. JEV is endemic in the Torres Strait, but until February 2022 had not been acquired in southern Australia.
Many people infected with MVEV/KUNV/JEV are asymptomatic or have mild symptoms such as fever, headache, nausea, vomiting, myalgia and arthralgia.
Less than 1% of people develop meningitis or encephalitis and symptoms may include: increasing confusion, headaches, neck stiffness, tremors, drowsiness and seizures. Other patients may present with aseptic meningitis or acute flaccid paralysis and have no encephalopathic features. Patients may present with a syndrome similar to Parkinson's disease, with dull faces that are mask-like and wide unblinking eyes, tremor, and cogwheel rigidity. In infants and young children meningitis or encephalitis may present as irritability or floppiness.
If infection occurs during pregnancy there may be a risk of miscarriage and other complications,
These flaviviruses are transmitted to humans by a bite from an infected mosquito. Mosquitoes acquire infection from biting infected animals such as water birds or pigs. Humans are a dead-end host. Pigs are an amplifying host for JEV.
Consider flavivirus infection in persons with encephalitis/meningoencephalitis and discuss suspected cases with an infectious disease physician. Undertake usual testing to evaluate for other causes of encephalitis/meningoencephalitis (e.g., HSV, VZV, enteroviruses).
Test for flaviviruses in persons with suspected encephalitis/meningoencephalitis without identified cause. Flaviviruses can be diagnosed on PCR of CSF, blood or urine, or by serology. Flaviviruses IgM antibodies can cross-react, especially between MVEV and JEV.
Send the following to SA Pathology requesting “Flavivirus investigation” on the form.
It is suggested any positive results are discussed with a virologist or infectious diseases physician.
Tests for flaviviruses often need to go to reference laboratories interstate, so results can take time.
There is no specific treatment for flaviviruses. Cases who become severely unwell may need supportive treatment in ICU.
Notify suspected and confirmed cases of flavivirus infection to the Communicable Disease Control Branch on 1300 232 272.
Immunisation plays an important role in protecting against JEV. Two JEV vaccines with different modes of action are available for use in Australia. Imojev (live vaccine) is recommended for use in people aged ≥ 9 months and is given as a single dose. JEspect (inactivated vaccine) is recommended for use in people ≥ 2 months and is given as a two-dose schedule, 28 days apart. It can be used when live vaccine is contraindicated e.g. pregnancy and immunocompromise. As at March 2022, there is a limited supply of JEV vaccines in Australia, so populations at higher risk will be prioritised Communicable Disease Network Australia for vaccination.
There are no available vaccines for MVEV/KUNV.