What is Dengue? (Mosquito Transmitted Diseases)
Published: 06 December 2020
Published: 06 December 2020
Dengue is not endemic in Australia (QLD DoH 2020a). However, it became nationally notifiable in 1991. Until 2009, there were typically less than 100 notifications a year, many of which were imported from Papua New Guinea (Moore et al. 2017). Since then, however, there has been an upward trend to as many as 1200 imported cases a year, mainly from travellers who visit Indonesia (NAMAC 2015).
North Queensland experiences outbreaks of dengue every year from returning travellers (Healthdirect 2019). The largest recent outbreak in Australia was in 2016 where there were over 2000 confirmed cases, including many from Western Australia, Victoria and New South Wales (Butt 2017).
While outbreaks were contained, constant surveillance is needed.
Dengue is a mosquito-transmitted virus that causes dengue fever, a flu-like illness (QLD DoH 2020; Healthdirect 2019).
There are at least four genotypes of dengue virus (known as DENV-1, DENV-2, DENV-3 and DENV-4). A person infected with dengue will generally develop a lifelong immunity to the particular genotype they contracted, however, they will still be susceptible to the others (NSW DoH 2016).
Dengue is most commonly transmitted through a bite from an Aedes aegypti mosquito, but Aedes scutellaris and Aedes katherinensis are also thought to be carriers. Aedes albopictus, which is found in the Torres Strait, is another vector for dengue, however, it is not found on the Australian mainland (QLD DoH 2020a; Better Health Channel 2018). Despite this, Aedes albopictus still poses a threat to Australia as it is a significant vector in Asia and has been introduced to several countries through motor vehicle tyres and other containers (Russell & Doggett n.d.).
Aedes aegypti mosquitoes feed predominantly on humans, breed in small man-made areas that contain water, rest inside buildings and are usually found in close proximity to human habitation (within 50 metres). They are therefore highly effective at transmitting disease (NSW DoH 2016).
Aedes aegypti mosquitoes can only be found in Queensland, however, they once lived in New South Wales, the Northern Territory and Western Australia as well (CSIRO 2017).
Mosquitoes acquire dengue by feeding on blood from an infected human. The virus requires an incubation period of 8 to 12 days inside the mosquito before it can be transmitted to another human. Once infected, the mosquito will carry and transmit the virus until it dies (WHO 2020).
Dengue can also be transmitted through blood transfusions, tissue or organ transplants, needlestick injuries and mucous membrane contact with infected blood (NSW DoH 2016).
Dengue symptoms may vary from mild or even unnoticeable (more often in children) to fatal (QLD DoH 2020b).
Typically, 3 to 14 days after a mosquito bite, the patient will experience a sudden onset of symptoms that may include:
(QLD DoH 2020b; NSW DoH 2016; WHO 2011)
Depending on the clinical presentation and patient history, dengue may need to be differentiated from other illness including chikungunya, hantavirus, measles, rubella, enteroviruses, influenza, hepatitis A, meningococcal disease, scarlet fever, typhoid, leptospirosis, rickettsioses or malaria (WHO 2009).
Definitive diagnosis is by a variety of blood tests. In Australia, this will probably involve the use of commercial antibody kits; however, these are not specific and need to be confirmed by nucleic acid testing or a specific antigen test (CDNA 2015).
Treatment is rest, plenty of fluids and paracetamol for pain (not aspirin or non-steroidal anti-inflammatory medicines (NSAIDs), which increase the risk of bleeding) (NSW DoH 2016). Dengue usually resolves in one to two weeks, but lethargy and depression may persist (Better Health Channel 2018; SA Health 2020).
In some cases, especially in babies and young children, dengue may progress to severe dengue (also known as dengue haemorrhagic fever) (Healthdirect 2019). Some 3 to 7 days after the initial symptoms, someone with severe dengue will experience a decrease in fever but onset of symptoms including:
(NSW DoH 2016; Healthdirect 2019)
The patient may also experience liver and heart problems. Loss of plasma causes a concentration of haemoglobin in the blood, while deficiency of thrombocytes promotes bleeding (Samanta & Sharma 2015).
In extreme cases, severe dengue may progress to dengue shock syndrome, in which severe bleeding leads to circulatory failure and hypotension progressing to profound shock (no measurable blood pressure), agitation, coma and death (Better Health Channel 2018).
In these cases, rapid volume replacement may be required (Smith 2019).
Prevention of dengue is mainly achieved through mosquito control. This involves getting rid of breeding sites (any open container that holds water around homes and workplaces) and using surface spray insecticides in homes. Personal protection is also important, especially when travelling to endemic areas (QLD DoH 2020b).
A number of live vaccines are currently being tested. A novel approach being tried is to infect mosquitoes with Wolbachia bacteria, which prevents the virus infecting the mosquito (Dorigatti et al. 2018).