Dengue virus disease

Notification requirement for dengue

Dengue is a ‘routine’ notifiable condition and must be notified by medical practitioners and pathology services in writing within 5 days of diagnosis.

This is a Victorian statutory requirement.

Primary school and children’s services centre exclusion for dengue

Exclusion is not required.

Infectious agent of dengue

Dengue virus is a flavivirus. There are four serotypes of dengue virus: dengue 1, 2, 3 and 4.

Dengue has been recognised since the latter part of the 18th century as causing epidemics in tropical and subtropical regions throughout the world. Dengue was first recognised in Townsville late in the 19th century and early in the 20th century. Outbreaks occurred in an area from the coast of Western Australia to the Northern Territory, and down through high-rainfall areas of Queensland and New South Wales.

At that time, Aedes aegypti mosquitoes were widely distributed in northern Australia; they occurred as far south as the Victorian border in eastern Australia and south of Perth in Western Australia. By the 1970s, Aedes aegypti (and therefore dengue cases) were restricted to a small area of northern Queensland. Epidemic dengue returned to north Queensland in 1981–82. Other outbreaks occurred there in the 1990s, when Aedes aegypti mosquitoes were spreading westwards from Queensland to the Northern Territory border and towards the New South Wales border.

Identification of dengue virus disease

Clinical features

Dengue fever (break-bone fever)

Dengue fever classically presents as an acute febrile illness of sudden onset. It is extremely debilitating, with fever lasting 3–5 days, myalgia (particularly backache), arthralgia (thus ‘break-bone’), retro-orbital pain, anorexia, gastrointestinal disturbance, rash and increased vascular permeability. There is a high subclinical rate of milder disease in children compared with adults and a low fatality rate compared with dengue haemorrhagic fever in both children and adults. Recovery from infection with one serotype of dengue virus results in homologous immunity but does not provide protection against infection with other serotypes.

Dengue haemorrhagic fever

Dengue haemorrhagic fever (DHF) is a severe complication of dengue virus infection. It occurs mainly in children and is characterised by abrupt onset of fever, haemorrhagic phenomena and thrombocytopaenia. In its severest form, it may result in shock (dengue shock syndrome [DSS]), which has a high fatality rate. The rate of death from DHF without DSS is usually quoted as 1–5 per cent. Death from DHF is believed to be caused by immune enhancement when a person with dengue antibodies due to a previous infection is subsequently infected by a dengue virus of a different serotype.

Diagnosis

Diagnosis may be determined with the following tests:

• isolation of dengue virus
• detection of dengue virus by nucleic acid testing
• detection of dengue non-structural protein 1 (NS1) antigen in blood
• IgG seroconversion, or a significant increase in antibody level, or a fourfold or greater rise in titre to dengue virus, proven by neutralisation or another specific test
• detection of dengue virus-specific IgM in cerebrospinal fluid, in the absence of IgM to Murray Valley encephalitis, West Nile/Kunjin or Japanese encephalitis viruses.

Confirmation of laboratory results by a second arbovirus reference laboratory is required if the case occurs in previously unaffected areas of Australia. North Queensland is currently the only area with the potential for indigenous (epidemic) dengue fever in Australia.

NS1 antigen testing can be done from illness onset up to 9 days post-onset for dengue. Early diagnosis (within 5 days of illness onset) can be readily done through polymerase chain reaction (PCR) testing; later diagnosis (5 days or more after illness onset) can be through IgM detection and a second blood test to check for IgG seroconversion.

Incubation period of dengue

The incubation period is usually short but varies from 3 to 14 days.

Public health significance and occurrence of dengue virus disease

Dengue is not an endemic disease in Australia, and the outbreaks that have occurred have been due to importations of the virus by a viraemic tourist or returning resident. It is important to rapidly diagnose the disease in returning residents and tourists to prevent local spread in receptive areas. Spread or introduction of Aedes aegypti from its present distribution in Queensland must be closely monitored.

Aedes aegypti is predominantly a day-biting mosquito whose larvae may be found almost exclusively in clean water in artificial containers such as water barrels, rainwater tanks, wells, vases, tyres, bottles, tins and other water-holding containers found in the domestic environment.

Although the species is currently restricted to Queensland, there are past records of Aedes aegypti being found in New South Wales, the Northern Territory and Western Australia. In 2013, Western Australia recorded a locally acquired case in Point Samson, about 55 kilometres north-east of Karratha in the Pilbara region. The exact mechanism of transmission has not been ascertained.

Of great concern has been the repeated detection of imported Aedes albopictus mosquitoes in various parts of Australia, dating from 1975 in Townsville. Ae albopictus – also known as the Asian tiger mosquito – is responsible for transmitting dengue overseas. Since 1975, it has been detected at various times and in various carriers on ships, in machinery and in car tyres in South Australia, Perth and Darwin. It was trapped on a wharf in Cairns in 1998 and on a wharf in West Melbourne in 2002. Occasional detections of Ae albopictus continue to occur with movements of cargo from around the world. Surveillance strategies are in place to detect exotic mosquitoes through inspection of international cargo and carriers.

In 2008–09, more than 1,000 cases of dengue, encompassing all four serotypes, were locally acquired in north Queensland. The presence of multiple serotypes in parts of Queensland allows for the possibility of DHF or DSS occurring in residents of these areas due to repeated infection with different serotypes.

Preventing the introduction and establishment of Aedes albopictus remains a high priority because this mosquito has the potential to spread widely over Australia, including southern areas. Local transmission has not been reported for Victoria for decades; however, dengue does occur in travellers returning from endemic areas.

Reservoir of dengue

Humans are the only vertebrate hosts of the virus. There is a jungle cycle between monkeys and mosquitoes, but this plays no role in human disease.

Mode of transmission of dengue

Humans are the only vertebrate hosts of the virus. Dengue is not transmitted directly from person to person. Only infected mosquitoes transmit dengue virus. It is thought that the mosquito contracts the virus when it bites an infected person. The mosquito is then infective for the rest of its life and can spread the virus every time it bites someone.

Period of communicability of dengue

There is no evidence of person-to-person transmission. However, theoretically there may be sexual transmission during the case's viraemic period. Humans are infective for mosquitoes during periods of high viraemia, from shortly before the febrile period to its end. This is usually 3–5 days.

Susceptibility and resistance to dengue

Recovery from infection with one serotype of dengue virus provides lifelong immunity to that serotype but does not provide protection against infection with other serotypes. It is therefore possible to contract dengue four times. A person who has had dengue once is at increased risk of DHF or DSS if they are infected again.

Control measures for dengue

Preventive measures

Dengue can be prevented by:

• mosquito control measures
• personal protection measures, such as wearing long, loose-fitting, light-coloured clothing
• using personal repellents containing diethyl toluamide (DEET) or picaridin
• avoidance of mosquito-prone areas.

Control of case

• Investigate the source of infection.

Control of contacts

Not applicable.

Control of environment

If a person is found to have acquired their illness in Victoria, the following measures may be put into place:

• Search for, and eliminate, breeding sites of Aedes aegypti in the urban area.
• Educate via mass communication.
• Use mosquito repellents, mosquito nets and other methods of personal protection.
• Control Aedes aegypti near airports.
• Prevent importation of new vectors, such as Aedes albopictus.

Outbreak measures for dengue virus disease

Not applicable.