MARC

Mosquito and Arbovirus Research Committee

Public health

MARC scientists work closely with local and state governments and industry to develop better ways of preventing human diseases caused by Ross River Virus (RRV), Barmah Forest Virus (BFV) and Dengue viruses.

Mosquito-borne viral diseases

Ross River Virus

Ross River virus is the largest cause of mosquito-borne disease in Australia.

Over the last 11 years, between 1,447 and 7,783 notifications have been received by Australian health departments annually. In 2014-2015, Australia saw the largest Ross River outbreak in 20 years, and Queensland reported 5,155 cases.

There are still major gaps in knowledge regarding Ross River virus transmission, including:

  • identification of important non-human vertebrate reservoirs
  • implication of mosquito vectors in local enzootic and epizootic transmission cycles.

Barmah Forest Virus

Since the commencement of national reporting of Barmah Forest Virus (BFV) disease in 1995 (except for the Northern Territory which commenced reporting in 1997), there has been an average of 830 cases each year, of which 43-69% have been reported from Queensland.

Although BFV is considered to be endemic in Queensland, there has been considerable variation in the numbers of cases reported each year (between 310 and 870 cases each year).

In 2012-2013, there appeared to be a spike in BFV cases, approximately 4 times historic averages in some areas, but there is now consensus that some of those excess notifications were diagnostic issues.

Dengue fever

Dengue fever has historically been reported in the Northern Territory, New South Wales and Queensland, however, it is currently limited by the distribution of its vector, Aedes aegypti, to north Queensland.

Outbreaks of dengue in Queensland have increased in frequency and intensity since the early 1990s.

In 2003 and 2004, there were six outbreaks of dengue in north Queensland with a combined total of nearly 900 cases reported in Cairns, Townsville and the Torres Strait. Two Torres Strait Island residents were hospitalised with severe and life-threatening symptoms of dengue haemorrhagic fever (DHF). There were also the first two recorded fatalities in Australia in more than a century.

Again in 2008 and 2009 over 1,000 cases were reported in north Queensland - the worst dengue outbreak in Queensland for 50 years. This, combined with increasing detections of exotic dengue vectors (Aedes aegypti, Aedes albopictus) in international airports and seaports throughout Australia, highlights the public health risk posed to Queensland communities.

Other arboviruses

Other arboviruses that are in Australia include Murray Valley Encephalitis (MVE) virus, Kunjin virus and Japanese Encephalitis Virus (only in north Queensland).

Although the MVE virus is occasionally found as far south as New South Wales, it is much more common in the north of Western Australia and the Top End of the Northern Territory. In these areas it appears in most years during the wet season (from February onwards) when mosquitoes are abundant. During very extensive and heavy wet seasons the virus occasionally extends further south from these areas, for example into central Australia.

Although Gan Gan and Trubanaman viruses are associated with human infection, they are not thought to cause any severe disease.

Malaria

Australia was declared 'malaria free' by the World Health Organization in 1981. However, the number of cases imported to Australia has increased dramatically since the 1960s.

Although there have been several episodes of locally acquired malaria cases on the Australian mainland, all of these were linked to introduction of Plasmodium vivax in an infected human or mosquito. The most recent outbreak occurred at Noah Beach near Cape Tribulation in north Queensland in November 2002. Seven locally acquired cases were reported.

Given that the conditions suitable to maintain endemic malaria transmission exist only in areas in northern Australia (North of 19°S), together with health surveillance systems and drug therapy of cases, there is little real threat of significant malaria transmission in Australia.

Chickungunya

Chikungunya virus (CHIKV) is emerging as a significant vector borne disease in many regions across the world.

Since 2004, Chikungunya has caused large epidemics in many regions. These outbreaks have had a severe impact on individuals, communities and public health resources. The principle vectors identified are Ae. aegypti and Aedes albopictus.

Currently Ae. aegypti is endemic in parts of north Queensland and has been identified in some areas of central and southern Queensland.

Ae. albopictus is currently (July 2016) endemic in the islands of Torres Strait and poses a serious risk of extending its range to mainland Australia.

Despite a relatively low notification rate of imported CHIKV to date, the risk of further imported cases and hence the distinct possibility of local transmission in CHIKV receptive areas has heightened in recent years.

Zika Virus

Zika virus (ZIKV) has received a considerable amount of media attention since 2015, when an outbreak in Brazil was first connected to an increase in severe birth defects, particularly microcephaly, in infants born to Zika-infected mothers.

Like Dengue and Chikungunya, Zika virus is primarily transmitted through the bites of Ae. aegypti mosquitoes, although there are other known vectors as well (e.g. Ae. albopictus, Ae. hensilli). In rare cases, Zika virus is known to be transmitted sexually, so some local transmission is possible even in the absence of mosquito vectors.

Australia-wide, there have been over 60 imported cases of Zika virus since 2012 (as of July 2016), so the importance of limiting the spread of Ae. aegypti within Queensland and preventing the establishment of Ae.albopictus in mainland Australia is even more important.

Human filariasis

Human filariasis (caused by Wuchereria bancrofti) was endemic in Queensland until the 1940s, but has since been eliminated and is no longer a medical concern in Australia.

Dog heartworm

Dog heartworm (caused by Dirofilaria immitis) has been an increasing veterinary problem in recent decades and human infections are occasionally reported with eye, lung, and skin involvement.

Local mosquitoes, including species in southern Queensland (Ochlerotatus notoscriptus and Culex annulirostris) have been shown to be highly susceptible to infection and have close contact with dogs in domestic and peridomestic urban and rural situations.

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