Arbovirus Infections

What is an arbovirus?

The word arbovirus is a contraction of arthropod-borne virus.  In Australia the principal vectors for these viruses are mosquitoes. 

The major arboviruses of concern in Australia are:

• Dengue
• Ross River Virus
• Barmah Forest Virus
• Japanese Encephalitis
• Murray Valley Encephalitis
• Kunjin  
  

 Four types of reactions to arboviruses are recognised based on clinical criteria:

• A mild fever: causes illness, sometimes with a rash
• A long term fever: persistent arthritic symptoms, often with a rash
• Haemorrhagic fever: serious, often fatal
• Encephalitis: associated with central nervous system (specifically with an inflammatory response in the brain); often with severe symptoms, death.  Survivors may suffer permanent brain damage.
  

Most of these viruses have reservoir hosts.  The encephalitic viruses (including Kunjin) are mainly associated with waterfowl, but also mammals.  Ross River Virus and Barmah Forest Virus have marsupial reservoir hosts, but the former may persist in the eggs of vector mosquitoes.  In the case of dengue, only humans are hosts in Australia.


Symptoms of arbvoviruses relevant to Queensland

Classical dengue	Severe. Often symptoms appear without warning.  Fever lasts five to seven days; may fluctuate in severity.  Symptoms include an intense headache, rash and retro-orbital pain.  Muscular movement causes considerable pain.  Often causes diarrhoea. Not fatal.
Haemorrhagic Fever	Similar to classical dengue initially. Body temperature increases after about four days.  Extensive internal bleeding (due to haemorrhaging) occurs throughout the body causing the skin to become mottled blue and red. Patients bleed through the nose and gums and blood appears in the urine. Vomiting expels dead (black) blood cells.  Blood pressure drops occur.
Ross River Virus & Barmah Forest Virus	These viruses are grouped together as symptoms are similar. Symptoms may persist for 6 weeks to a year or longer. The first sign of infection is given by symptoms of a mild viral illness. This often persists longer than most viruses, but advanced symptoms differ quite dramatically from person to person. Infections can produce polyarthritis, true arthralgia, decreased mobility, swollen joints, a rash, fatigue, headaches, hot and cold sensations, muscle pain and dizziness. Symptoms usually become more severe with increasing age of the patient. Not fatal.
Japanese Encephalitis	Symptoms are often mild or absent.  However, typical viral fever symptoms develop in some patients, including vomiting, nausea and fatigue.  The subsequent affect on the brain is more significant.  More than half of those that develop symptoms either do not survive or suffer severe brain damage and/or paralysis
Murray Valley Encephalitis	Causes Australian Encephalitis. Typical fever symptoms like Japanese Encephalitis, often with a severe initial fever that may include seizures.  Can cause permanent brain damage in some people and is fatal in about one third of clinical cases.
Kunjin	Generally begins with typical viral symptoms and often causes lethargy and can affect behaviour.  May cause encephalitis (swelling in the brain), but outcomes are generally less severe than in Murray Valley Encephalitis and Japanese Encephalitis