Dengue fever, also known as ‘break bone fever’, results from infection by one of four types (and many strains) of virus from within the flavivirus genus. The four dengue viruses, DEN-1, DEN-2, DEN-3 and DEN-4, are found in most tropical and subtropical regions of the world, and are transmitted by certain Aedes sp mosquitoes.
Dengue affects 40% of the world’s population, infecting some 390 million people each year.
All 4 serotypes of endemic DENV have evolved independently from ancestral sylvatic viruses and have become both ecologically and evolutionarily distinct. In the 1950’s dengue, a previously benign disease, developed a mysterious new fatal form (dengue hemorrhagic fever) which is expanding its global terrain in 2015.
In their history dengue and yellow fever seem to display a tendency toward mutual exclusiveness, consistent with the geographical and experimental evidence.
The Aedes aegypti mosquito is endemic in North Queensland. Bites occur during daylight hours.
The incubation period is usually 5 to 8 days.
Many cases are subclinical, but others experience a sudden high fever, headache, weakness, muscle pain, sacral pain and sometimes a rash resembling scarlet fever. The disease is usually self-limiting after about 6 days, producing a degree of immunity to the strain of virus involved.
Secondary infection with another strain may, in rare instances, cause serious complications such as dengue haemorrhagic fever (DHF) or dengue shock syndrome (DSS), which may be fatal.
In Victoria, dengue fever is a Group B notifiable disease and must be reported within 5 days.
Dengue in pregnancy
The effects of dengue in pregnancy have been unclear in the past, but a recent literature review concluded:
- Symptomatic dengue infections in pregnancy may be associated with adverse fetal outcomes, most commonly preterm birth and low birth weight but also miscarriage and stillbirth.
- Severe dengue infections may be associated with stillbirth.
- Pregnant travellers should be advised of possible fetal risk, but with current evidence there is no case for advising against travel to dengue endemic areas.
From Travax Alert Service
Dengue fever is common in travellers, and hemorrhagic complications occur in the absence of the WHO criteria for dengue hemorrhagic fever (DHF). High liver enzyme levels, severe thrombocytopenia, and serological evidence of a second dengue infection may be better markers of risk of bleeding in the individual patient than the WHO criteria for DHF.
A Torres Strait Island woman died of DSS early in 2004. This was the first dengue-related death in Queensland since 1905. While DHF is a serious disease, it is more serious for children than for adults.
Extensive outbreaks of dengue have occurred in North Queensland in 1992-93 and in 2003-04. Lesser outbreaks occurred in 2005, 2006 and 2008.
In early 2009, all four strains of dengue were discovered in North Queensland. 798 cases (types 2 and 3) were reported from Cairns and 72 (types 1 and 3) from Townsville. 12 cases of type 4 were reported from Innisfail.
From Communicable Diseases Intelligence
According to predictions made using the CSIRO climate matching software CLIMEX, ® Ae. albopictus could become established elsewhere in Australia, including southern Australia, and lead to these areas becoming receptive to dengue infections—a condition that currently does not exist because the vector Aedes aegypti is confined to Queensland and no species in southern Australia is known to be capable of transmitting dengue.
The US Centers for Disease Control and Prevention has billed dengue as the most important mosquito-borne viral disease affecting humans — ahead of malaria and encephalitis — with an estimated 2.5 billion people at risk worldwide.
All over Asia, governments are scrambling to halt the spread of the disease, with the agenda topped by efforts to educate the public on the disease and control of mosquito-breeding areas, as there is no known cure for dengue.
There are currently no vaccines offering protection against the dengue virus. However, several companies are close to producing effective vaccines.
In the US, scientists from The National Institutes of Health have reported initial success from a vaccine known as TV003. The world’s first dengue vaccine, produced by Sanofi and known as Dengvaxia has been approved in 2015 in Mexico, but its safety remains under review.
The normal precautions such as use of tropical strength insect repellents (containing DEET or Picaradin) and the wearing of long sleeves and long trousers if you are outside during the day or in the evening, are recommended. General avoidance of mosquitoes bites is suggested.
Travellers are advised to practice daytime insect precautions in affected regions.
Pregnant travellers should be advised of the possibility of adverse effects of dengue on pregnancy, especially late pregnancy, and advised to be meticulous in taking anti-mosquito measures, especially during daylight hours.