What is being tested?
Arbovirus (arthropod borne virus) testing detects viral infections that are transmitted from mosquitoes and other blood-sucking insects to humans. Found throughout the world, arboviruses are an important cause of viral meningitis and encephalitis. In temperate climates, they tend to cause occasional seasonal epidemics. In tropical climates, they may be found year-round, whenever mosquitoes are active.
There are hundreds of different arboviruses, but most are not common. The most widely recognised arboviruses in Australia include the Dengue viruses, Ross River virus, Barmah Forest virus and Murray Valley encephalitis virus. Dengue virus infections most commonly occur in travellers returning to Australia from endemic areas, while other arboviruses of concern to Australian travellers include Yellow Fever, Japanese Encephalitis virus and Chikungunya.
These viruses are spread when a mosquito, or sometimes another insect carrier (vector) such as a tick or sandfly, bites an infected bird or other small animal and becomes infected, then bites a human and passes it on. Arbovirus infections are not directly passed from person-to-person but can be passed from human-to-mosquito-to-human when the level of virus in the blood of the infected human is high. Rarely, an infection may be transmitted through a blood transfusion, organ transplant, or from a mother to child through breast milk.
Arbovirus testing is used along with a person's signs, symptoms and history of exposure and travel to detect and confirm an acute arbovirus infection and to distinguish between an infection and other conditions that may cause similar symptoms. Testing measures either antibodies produced by the body's immune system in response to a specific arbovirus infection or it detects the virus's genetic material.
Depending on the virus causing the infection, people infected by an arbovirus may have only mild to moderate flu-like symptoms that resolve within a few days to a few weeks. In some cases, a sudden onset of high fever may be accompanied by a rash (dengue fever), jaundice (yellow fever), or severe joint pain and debilitating symptoms. Depending on the virus, a person may develop severe symptoms that may be life-threatening and require hospitalisation.
Examples of arboviruses include:
|VIRUS/ILLNESS||INSECT CARRIER||FOUND IN|
|Dengue Fever||Mosquito||South America, Asia, tropical tourist destinations, Caribbean|
|Ross River Virus||Mosquito||Australia, Solomon Islands, New Guinea|
|Japanese Encephalitis||Mosquito||Southeast Asia, New Guinea|
|Barmah Forest Virus||Mosquito||Australia|
|Kunjin Virus||Mosquito||Australia, Asia|
|Murray Valley Encephalitis Virus||Mosquito||Australia, New Guinea, Indonesia|
|Eastern Equine Encephalitis (EEE)||Mosquito||Eastern U.S.|
|Western Equine Encephalitis (WEE)||Mosquito||Western U.S.|
|Venezuelan Equine Encephalitis (VEE)||Mosquito||South and Central America, rarely U.S|
|Chikungunya Fever (CHIKV)||Mosquito||Africa, Asia, some in Southern Europe|
|Yellow Fever||Mosquito||South America, Africa, rare epidemics in U.S|
|West Nile Virus||Mosquito||Throughout U.S.|
|St. Louis Encephalitis||Mosquito||Throughout U.S|
|LaCrosse Virus||Mosquito||South America, Central America, Asia, Central and Eastern U.S.|
|Rift Valley Fever||Mosquito, Tick, Sandfly||Africa and Middle East|
|Zika Virus||Mosquito||Africa, South and Central America|
|Cremean- Congo Haemorrhagic Fever||Tick||Asia, Africa, Europe|
How is it used?
Arbovirus testing is used to determine whether a person with symptoms and a recent history of potential exposure to a specific arbovirus has been infected. Testing can help diagnose the cause of meningitis or encephalitis, distinguish an arbovirus infection from other conditions causing similar symptoms, such as bacterial meningitis, and can help guide treatment. Testing may be performed on blood to detect antibodies to the viruses and/or may be performed on a sample of cerebrospinal fluid (CSF) to determine if an infection is present in the central nervous system.
Typically, the individual test ordered is specific for a particular arbovirus, such as Ross River Virus or dengue fever, depending on the person's symptoms and likely exposure. Sometimes, a panel of tests may be used to determine which arbovirus is causing the infection.
Most often, testing involves the measurement of specific arbovirus antibodies produced in response to an infection. In certain cases, testing may involve direct detection by testing for virus antigen in blood or the genetic material (nucleic acid) of the virus.
Antibody testing is primarily used to help diagnose a current or recent infection. There are two classes of arbovirus antibodies produced in response to infection: IgM and IgG. IgM antibodies are produced first and are present within a week or two after infection. Levels in the blood rise for a few weeks, then taper off. After a few months, IgM antibodies fall below detectable levels. IgG antibodies are produced after IgM antibodies. Typically, the level rises with an acute infection, stabilises, and then persists long-term.
IgM antibody testing is the primary test performed on the blood or cerebrospinal fluid of symptomatic people. IgG tests may be ordered along with IgM testing to help diagnose a recent or previous arbovirus infection. Sometimes testing is done by collecting two samples 2 to 4 weeks apart (acute and convalescent samples) and measuring the IgG level (titre). This may help determine whether antibodies are from a recent or past infection.
Antibody tests may cross-react with viruses in the same family, so a second test that employs a different method, such as a neutralisation assay or another specific test, is used to confirm positive results. These confirmatory methods are specialised tests that must be performed by a second arbovirus reference laboratory. Confirmed cases are reported to the Department of Health and Ageing (DoHA) in Australia.
The NS1 antigen test is used to detect a current infection with Dengue virus through detection of the non-structural protein 1 (NS1) of the dengue viral genome. The NS1 antigen is detectable in blood before antibodies to dengue are detected in blood.
Nucleic Acid Amplification Test
A nucleic acid amplification test (NAAT) amplifies and measures the genetic material of the arbovirus to detect the presence of the virus. This type of testing is done at specialised laboratories. It can detect a current infection with the virus, often before antibodies to the virus are detectable, but there must be a certain amount of virus present in the sample in order to detect it. For most arboviruses, virus levels in humans are usually low and do not persist for very long.
Nucleic acid testing may be used to test the tissues of a person who has died (post mortem) to determine whether a specific arbovirus may have caused or contributed to their death.
Testing can also be performed on suspected host animals and mosquito pools to detect the presence and spread of an arbovirus in the community and region. This information can be used to help investigate outbreaks, identify and monitor infection sources, and to guide efforts to prevent the spread of the infection.
When is it requested?
Antibody tests are primarily ordered when a person has signs and symptoms suggesting a current arbovirus infection, especially if the person lives in or has recently travelled to an area where a specific arbovirus is endemic.
An arbovirus infection may be suspected when symptoms arise, often during mid to late summer.
Some signs and symptoms may include:
A small percentage of people, especially the young, elderly, and immunocompromised, may have more serious symptoms associated with meningitis and encephalitis. These symptoms may include:
Antibody tests may be ordered within the first week or two of the onset of symptoms to detect an acute infection. An additional blood sample may be collected 2 to 4 weeks later to determine if the antibody level is rising. When an infection of the central nervous system is suspected, antibody testing may be performed on CSF as well as blood.
Antigen and nucleic acid amplification testing (NAAT) is not ordered as frequently as antibody testing but may sometimes be ordered when a person has symptoms of an arbovirus infection.
What does the result mean?
Results of arbovirus testing require careful interpretation, taking into consideration the individual's signs and symptoms as well as risk of exposure.
Antibody tests may be reported as reactive (positive) or non-reactive (negative), or may be reported as less than or greater than a certain titre. For example, if the established threshold is a titre of 1:10, then a result less than this is considered non-reactive while a titre greater than this is considered reactive.
If IgM or IgG antibody is detected in the CSF, it suggests that an arbovirus infection is present in the central nervous system. If a CSF antibody test is non-reactive, then it suggests that there is no central nervous system involvement or the level of antibody is too low to detect.
If IgM and IgG arbovirus antibodies are detected in an initial blood sample, then it is likely that the person became infected with the arbovirus within the last few weeks. If the IgG is positive but the IgM is low or non-reactive, then it is likely that the person had an arbovirus infection sometime in the past. If the arbovirus IgG antibody titre increases four-fold between an initial sample and one taken 2 to 4 weeks later, then it is likely that a person has had a recent infection.
If the tests are negative for IgM and/or IgG antibodies, the person may still have an arbovirus infection – it may just be that it is too soon after initial exposure to the virus and there has not been enough time to produce a detectable level of antibody. A negative result may also suggest that symptoms may be due to a different cause, such as bacterial meningitis.
The following table summarises results that may be seen with antibody testing:
|IGM RESULT||IGG RESULT||POSSIBLE INTERPRETATION|
|Low or non-reactive or not tested||Four-fold increase in samples taken 2-4 weeks apart||Recent infection|
|Low or non-reactive||Reactive||Past infection|
A reactive result on an initial test for IgM arbovirus antibody in blood or CSF is considered a presumptive positive since antibodies to viruses in the same family may cross-react. It suggests a diagnosis, but it is not definitive. A reactive result on a second test using a different method (neutralisation assay) confirms the diagnosis.
Nucleic Acid Amplification Testing (NAAT)
If a NAAT blood, CSF, or tissue test is positive for an arbovirus, then it is likely that that specific virus is present in the sample tested. A positive NAAT for arbovirus in an animal or mosquito pool sample indicates that the virus is present in the geographic location where the sample was collected.
A NAAT may be negative for an arbovirus if there is no virus present in the sample tested or if the virus is present in very low (undetectable) numbers. A negative test cannot be used to definitely rule out the presence of an arbovirus.
Is there anything else I should know?
The presence of arbovirus antibodies may indicate an infection but cannot be used to predict the severity of an individual's symptoms or their prognosis.
Other tests, such as viral cultures may be used in some instances. NAAT and viral cultures may be used in research settings and by the medical community at a national and international level to identify and study the strains of arboviruses causing infections. Different strains have been isolated and associated with regional epidemics.
In general, there is no need. Most people who become infected have few to mild symptoms and are only exposed to those arboviruses that are present in the areas where they live or travel. Testing is not usually done on asymptomatic people.
Every region in the world has its own health concerns and it is prudent to read about the areas where you will be travelling and to talk to your doctor about the risks for infection. There is an increased risk of an arbovirus infection when travelling to a tropical location or to an area that has seasonal outbreaks. A person's likelihood of exposure will be influenced by their planned activities and by the preventive measures that they take. (For more on the specific diseases related to your travels, visit the Destinations page on the CDC web site. For general travel advice, visit the travel advice page on smartraveller.gov.au)
Protection begins with preventing mosquito bites. Measures may include wearing long-sleeved shirts and pants when outdoors, using insect repellent, and staying indoors at dawn and dusk when mosquitoes are most active. Around your home, you can eliminate standing water sources that attract mosquitoes. Communities can take preventive measures by monitoring the seasonal risks and spraying for mosquitoes as warranted.
There are vaccines for Yellow fever and Japanese encephalitis for humans and there are several vaccines for the equine encephalitis viruses that have been developed for horses. Research in this area continues.
Testing is performed in clinical laboratories, who will refer samples to a reference laboratory.
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