Summary

• Hendra virus is a rare but serious viral infection that is carried by flying foxes (fruit bats) and can be passed on to horses.
• Rarely, it can spread from infected horses to other animals and people.
• There have been very few cases in people and all of them have resulted from very close contact with the bodily fluids of infected horses.
• There is no evidence that Hendra virus spreads from flying foxes to people or from one person to another. 
• Diagnosing Hendra virus needs two tests: PCR, a genetic test which detects the bacteria’s DNA, and serology, which detects antibodies made by your immune system as part of your body’s defence.
• Hendra virus testing is performed at specialist, high-containment government reference laboratories in Queensland and Victoria.
   

What is Hendra virus?

Hendra virus is a rare but serious viral infection that mainly affects horses but can affect people. It can spread:

• from flying foxes (fruit bats) to horses
• from horse to horse and horse to dogs
• and, very rarely, from infected horses to people.

There is no evidence that Hendra virus spreads:

• directly from flying foxes to people
• from dogs to people
• from the environment to people
• from people to horses
• from one person to another
• through the air over long distances

Flying foxes (fruit bats) are the natural carriers of Hendra virus. They usually do not become ill. Horses are thought to become infected when they eat or drink feed or water that has recently been contaminated with the urine, saliva or birth fluids of an infected flying fox. Although the exact route of infection is not fully understood, horses may also become infected by sniffing contaminated material.

An infected horse can spread the virus to other horses through close contact with its body fluids, especially respiratory (nasal) secretions. A horse may begin shedding small amounts of virus a few days before it appears sick.

People can become infected only through close contact with the blood or body fluids of an infected horse. The few human cases in Australia all occurred after people had high-level exposure while caring for, treating or performing a post-mortem examination on an infected horse without appropriate personal protective equipment (PPE).

Hendra virus does not survive well outside the body. It is easily destroyed by heat, drying
and cleaning with ordinary detergents and disinfectants.

Since Hendra virus was first identified in Brisbane in 1994, no one has developed Hendra virus after lower-risk activities such as feeding, grooming or patting an infected horse. People with these types of exposures have been tested, and none showed evidence of infection.

In that time, more than 90 horses are known to have been infected. These animals have either died as a direct result of their infection or have been euthanised. Several hundred people have been exposed to Hendra virus infected horses but have not been infected. However, 7 people have been confirmed to have Hendra virus infection following high levels of exposure to infected horses. Four of these people died, the most recent being in 2009.
 

Symptoms

In the seven reported cases of Hendra virus, symptoms have developed between five and 21 days after exposure to an infectious horse.

The documented human cases to date have presented with: 

• self-limiting influenza-like illness (two cases)
• influenza-like illness complicated by severe pneumonia contributing to death (one case)
• aseptic meningitis (inflammation of the lining around the brain, but no infection of this lining) with apparent recovery, then death from inflammation of the brain (encephalitis) 13 months later (one case) 
• acute influenza-like illness followed by encephalitis, followed by recovery (one case) and death (two cases).

Testing

If Hendra virus is suspected, your doctor will arrange testing and notify the public health authorities. Hendra virus testing is performed at specialist, high-containment government reference laboratories in Queensland and Victoria.

Two types of tests are used to diagnose Hendra virus. They work in different ways. They are:

• polymerase chain reaction (PCR) tests (genetic testing)
• serology tests (antibodies)

PCR tests (direct testing)

PCR detects the genetic material (RNA) of the virus. It is the main test used to diagnose Hendra virus. It can be performed on samples such as blood, nose and throat swabs, urine, cerebrospinal fluid (CSF) or tissue.

Serology (antibody) tests (indirect testing)

These are tests that look for the antibodies your immune system makes to fight the virus. Your immune system protects you by making antibodies to attack substances that are foreign to your body and could be harmful to you. This includes infections like viruses and bacteria.  

It does this by targeting marker antigens which are found on the surfaces of most cells. Cells with marker antigens that are different from your own can be attacked. Each antibody is made to recognise and attach to only one particular target antigen, or a very small group of closely related targets.

Antibodies take time to develop. Your immune system usually starts producing antibodies after symptoms begin. Serology tests look for these antibodies rather than the virus itself. In the first few days of illness, there may not yet be enough antibodies to detect, so an antibody test result can be negative even if you are infected.

Why are both tests used?

PCR can detect the virus earlier because it looks directly for the virus rather than the body's immune response. However, a negative PCR result cannot rule out Hendra virus infection. The virus may not be present in the sample in high enough amounts to be detected, especially if taken too early (too soon after exposure) or too late (after the virus has been cleared from the blood).

Serology testing also has limitations. It takes time after you are infected before antibodies develop. In the first few days of illness, there may not yet be enough antibodies to detect, so an antibody test can be negative even if you are infected.
 

Having the test

Sample
Blood, nose and throat swab, urine, cerebrospinal fluid (CSF) or tissue (such as kidney, or lung).

Any preparation?
None
 

Results

A diagnosis of Hendra virus is made through a positive result from PCR genetic testing followed by confirmatory serology testing.

Serology testing looks at two Hendra virus-specific antibodies:

• IgM antibodies. These are the first antibodies made by the immune system and suggest a recent infection.
• IgG antibodies appear shortly after IgM antibodies and become the main long-term antibody. They can remain detectable for months or years after infection.

Unlike many viral infections where IgG appears a week or more after IgM, Hendra virus IgM and IgG often develop within a similar timeframe, so some laboratories have reported the appearance of ‘total antibodies’ rather than separate IgM and IgG timelines.

There are only a small number of documented cases (only seven confirmed human infections), so the antibody timeline is based on limited clinical experience. Unlike many viral infections, there is no well-defined IgM and IgG timeline.

For example, in two reported human cases, IgG seroconversion (the point at which IgG first becomes detectable) occurred on day 5 after symptom onset in one patient and day 11 in another.

Two blood samples need to be collected and tested repeatedly throughout the course of the illness.  
 

Questions to ask your doctor

The choice of tests your doctor makes will be based on your medical history and symptoms. It is important that you tell them everything you think might help.

You play a central role in making sure your test results are accurate. Do everything you can to make sure the information you provide is correct and follow instructions closely.

Talk to your doctor about any medications you are taking. Find out if you need to fast or stop any particular foods or supplements. These may affect your results. Ask:

• Why does this test need to be done?
• Do I need to prepare (such as fast or avoid medications) for the sample collection?
• Will an abnormal result mean I need further tests?
• How could it change the course of my care?
• What will happen next, after the test?
  
   

More information

Pathology and diagnostic imaging reports can be added to your My Health Record. You and your healthcare provider can now access your results whenever and wherever needed.
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