Prompt action by local authorities may have prevented a larger outbreak of Dengue

Published:14 June 2019

The mosquito responsible for transmitting dengue is Aedes aegypti.

By Professor Andrew Taylor-Robinson

A confirmed case of the mosquito-transmitted viral infection dengue is something which has had the potential to happen in Rockhampton for a long time, but which required the perfect storm of overlapping causal events. This is what happened in late May in the Park Avenue suburb, to which Rockhampton Regional Council and Central Queensland Public Health Unit enacted a full outbreak response. As it is thought that the flight range of the culprit mosquito, Aedes aegypti, is no further than 200 metres, the local authorities in Rockhampton, with good reason, focused their mosquito control efforts in and around the house in which the dengue-infected person lives.

This individual has, we are led to believe, not travelled outside the locality in the last few weeks and, importantly, has no history of travel overseas or to north Queensland, where occasional dengue outbreaks are known to occur. Neighbouring residents were warned to take precautions and their properties checked, and if need be, treated for mosquito infestation.

In the couple of weeks since the first confirmed case of dengue was reported, several others were initially diagnosed. Symptoms can range from mild to severe and include sudden onset of fever, extreme tiredness, intense headache, muscle and joint pain. While the precise numbers of people now confirmed to be affected has been downsized from seven to three after follow-up testing (with five others still probable), there does appear to be a clustering of infection across a small area. This represents a very localised outbreak hotspot.

In order to confirm a diagnosis of dengue two consecutive positive blood tests results are required between 10 and 14 days part. Following the door-to-door home checks, no further cases have come to light, so the vigilance of the local authorities may have prevented a larger scale outbreak. Of the 580 households that were inspected and sprayed with insecticide, Ae. aegypti was detected at 47 of those, highlighting the potential for further spread within the Park Avenue community if prompt action had not been taken.

Professor Andrew Taylor-Robinson is an expert in mosquito-borne viruses in Australia.

So where did the dengue virus come from? We know that the mosquito which infected the original confirmed patient could not have flown far. Ae. aegypti prefers to live in and around domestic dwellings. Does this imply that it had previously bitten someone who had dengue and was themselves infectious extremely close by? A family member, friend, visitor to the house … a  neighbour?

It is plausible that there were hitherto undetected cases of dengue in Rockhampton; possible if a person is not sufficiently ill, does not attend a GP or hospital, or whose symptoms are misdiagnosed. Alternatively, and more probable, this infected ‘mystery person’ (or conceivably, someone a step or two down the track of transmission) would have acquired infection further afield, most likely on a recent trip overseas. Ae. aegypti is commonly found in the tropics, where dengue is prevalent, including those favourite Australia holiday destinations of Bali and Koh Samui.

This outbreak of dengue is the first in Central Queensland for almost 30 years – but we may not wait so long for the next. While it looks to be contained, the fact that favourable conditions exist for the virus to be maintained in the community is cause for public health concern. Epidemiologists predict that dengue could pose a growing risk to our State in coming years. This is due in no small measure to climate change providing an increasingly suitable environment for dengue-transmitting Aedes mosquitoes to become a feature of our backyards.

Vigilance is therefore needed by well-informed householders to stop these pests from breeding in stagnant water that collects in upturned vessels, discarded tyres and the like, as well as in uncovered water tanks. As the saying goes, prevention is better than cure – never more so than in the case of this nasty, but preventable, mosquito-borne infectious disease.Andrew Taylor-Robinson March 2019

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