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:


 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


 
Reference

Benenson, A. S. (Ed.) (1985).  Control of communicable diseases in Man.  Fourteenth Edition.  American Public Health Association.

 Links

http://www.arbovirus.health.nsw.gov.au/areas/arbovirus/viruses/rossriverbarmahforest.htm
http://www.dhs.vic.gov.au/phb/hprot/inf_dis/bluebook/arbo.htm
http://www.uq.edu.au/vdu/Arbovirus.htm



Dengue viruses

Type of virus: Flavivirus

Distribution: Found in many tropical countries around the world.  Not endemic to Australia.  Epidemic outbreaks are dependent on the distribution of Aedes aegypti and Ae. albopictus (Ae. albopictus is not native to Australia, but has been identified from shipments into the Northern Territory).  

Prevalence: Four major outbreaks since 1990 in north Queensland. 

Mosquito vectors: Aedes aegypti is the vector for transmission of dengue in Australia.

Notes: Three of the four strains of the virus have been recorded in Australia leading to two cases of haemorrhagic fever.



Ross River Virus

Type of virus: Alphavirus.

Distribution: Throughout Australia, the Solomon Islands and New Guinea.

Prevalence: More than 3000 cases per year in Qld.

Mosquito vectors: Isolated from Coquillettidia linealis, Anopheles amictus, An. annulipes, An. farauti, Ochlerotatus notoscriptus, Oc. alternans, Oc. bancroftianus, Oc. eidsvoldensis, Oc. flavifrons, Oc. kochi, Oc. normanensis, Oc. procax, Oc. sagax, Oc. theobaldi, Oc. tremulus, Oc. vigilax, Verrallina carmenti, Ve. funerea, Ve. lineata, Culex annulirostris, Cx. gelidus, Cx. quinquefasciatus, Cx. sitiens, Mansonia semptempunctata and Ma. uniformisCo. linealis, Oc. notoscriptus, Oc. vigilax, Ve. funerea and Cx. annulirostris are recognised as important vectors for Ross River Virus in Qld.  Oc. camptorhynchus is also a significant vector, but it is a temperate species that does not occur in Queensland.

Notes: May persist in the environment in the eggs of Ochlerotatus spp., which are resistant to desiccation.  Natural hosts are native mammals.



Barmah Forest Virus

Type of virus: Alphavirus.

Distribution: All reported cases have been restricted to mainland Australia.

Prevalence: Only recently recognised.  It is less often reported than the Ross River Virus, but many cases of BFV may be misidentified as Ross River Virus, as symptoms are similar. 200 cases were confirmed during an outbreak in New South Wales in 1995.

Mosquito vectors: Ochlerotatus procax, Oc. vigilax, Verrallina funerea, Coquillettidia linealis and Culex annulirostris.  Also isolated from Oc. bancroftianus, Oc. eidsvoldensis, Oc. normanensis and Oc. pseudonormanensis and Cx. quinquefaciatus.

Notes: Outbreaks usually associated with parallel outbreaks of the Ross River virus.  Reservoir (natural) hosts not known, possibly native mammals such as possums.



Japanese Encephalitis

Type of virus: Flavivirus.

Distribution: Southeast Asia and New Guinea.  May already be present in northern Queensland

Prevalence: A small number of cases have been confirmed from the Torres Strait.

Mosquito vectors: Culex annulirostris, Oclerotatus notoscriptus, Oc. vigilax, Culex gelidus, Cx. quinquefasciatus and Cx. sitiens are capable of transmitting the virus in Australia.  Also isolated from Mansonia semtempunctata.

Notes: Virus isolated from pigs in northern Australia.  May spread if pigs are a reliable reservoir host.  Another possible host is the Nankeen Night Heron.



Murray Valley Encephalitis

Type of virus:
Flavivirus

Distribution:
The headquarters of the virus appears to be Western Australia, the Northern Territory and possibly north Queensland.  Cases have been reported from all mainland states.  Also New Guinea and possibly Indonesia.

Prevalence:
25 cases since 1990.

Mosquito vectors:
Culex annulirostris.  Also isolated from Oclerotatus eidsvoldensis, Oc. normanensis, Oc. pseudonormanensis, Oc. tremulus, Cx. bitaeniorhynchus, Cx. quinquefasciatus and Mansonia uniformis.

Notes:
Principal reservoir hosts are water birds.



Kunjin Virus

Type of virus: Flavivirus.

Distribution: Across the Australian mainland, mostly from Western Australia and the Northern Territory.  There have been no recent reports from Queensland.

Prevalence: Eight cases since 1990.

Mosquito vectors: Culex annulirostris.  Also isolated from Oc. tremulus and Cx. squamosus.

Notes: Hosts are most likely to be water birds