Mozzie viruses tightening grip on Pacific, say researchers

By Laurie Sullivan

The Pacific is in the grip of an ‘unprecedented epidemic wave’ of the mosquito-borne dengue, Chikungunya, and Zika viruses. And, the pattern of disease is likely to continue for years, experts say.
The grim assessment was outlined in a study published by Eurosurveillance, a European scientific journal covering communicable diseases.
The report should serve as a warning to Australians holidaying, working or returning to visit family and friends in the region to take special care to avoid mosquito bites, said Dr Eddy Bajrovic, Medical Director of Travelvax Australia.
He said the diseases pose a risk for all travellers – even cruise ship passengers taking day trips ashore – because the mosquitoes that spread the nasty trio breed and feed around port buildings and in nearby urban areas tourists might visit.

‘Perfect storm’ of conditions

The Eurosurveillance study states that the Pacific region is in the early stages of an epidemic wave that began building in 2012 and ‘is likely to continue for several years’.
The researchers rate the chances of the three viral diseases spreading further as ‘high’.
“Firstly, it’s likely that there is little immunity to these diseases,” the reports states.
“DENV-3 (dengue type 3) had not been circulating in the region since 1995 and prior to the current wave, the CHIKV and Zika viruses were limited to 2 documented outbreaks.
“Secondly, competent vectors (mosquitoes) are present in the region, mainly Aedes aegypti and Ae. albopictus, but also other local mosquitoes such as Ae. polynesiensis or Ae. hensilli are known to transmit these viruses. 
“Thirdly, the large human population mobility and airline travel facilitate the spread.”

Changing pattern of Pacific’s epidemics

The researchers found that epidemics of the Pacific’s mosquito-borne viral diseases have become more frequent and diverse.
Since January 2012, the region has been hit by 28 outbreaks of dengue (18 outbreaks), Chikungunya (7), and Zika (3) – the highest number in the past 40 years. Official figures put the number of people affected at 120, 000, a figure which the authors say is likely to be ‘substantially under reported’.
They added that improved surveillance and response measures are needed to ease the already-heavy burden on Pacific island health systems and limit further spread of outbreaks to other parts of the world.
As if on cue, French Polynesia announced an outbreak of Chikungunya virus disease that has soared from a single case in the island of Tahiti on October 10 to hundreds of confirmed and suspected cases on another 3 islands – Tubuai, Raiatea, and Apataki Atoll – less than a fortnight later. Reports say that in some of Tahiti’s small communities, half the population are experiencing Chikungunya’s severe arthritic pain.

Remote nations not spared

More remote locations haven’t been spared. One of the Pacific’s smallest nations, Tokelau (pop. 1400) comprises three tiny coral atolls with a total area of just 10 square kms in the Western Pacific. This week the islands announced a health emergency following a spate of Chikungunya – possibly brought in from the nearby Cook Islands.
Dr Bajrovic said mosquito-borne diseases were becoming more widespread – not just in the Pacific, but throughout the world’s tropical and sub-tropical regions. The Chikungunya outbreak that emerged last December in the tiny Caribbean island of St Martin has now swept through the entire Caribbean Basin and is now making inroads into South, Central and North America, infecting 772, 069 confirmed or suspected cases to date.
Australians visiting any tropical and sub-tropical area must guard against complacency – regardless of how long they intend to stay.
“Longer stays hold more chance of infection – in part because people become complacent,” he said.
“But a short stay doesn’t mean you can dismiss the potential risk. As we’ve seen with travellers returning with dengue from Asia, a high proportion of them were only on holiday for a week.”

Apply repellent (and carry it)

Dr Bajrovic said cruise ship passengers making brief stopovers in Pacific ports can’t afford to be blasé.
“If a cruise passenger was to go ashore for even a few hours, there is certainly the potential for them to be bitten and infected if any of the viruses are circulating,” Dr Bajrovic said.
“Passengers need to prevent mozzie bites.
“The easiest way is to apply an effective personal insect repellent before leaving the ship, and then carry it with them if they need to reapply it – especially if they're not returning to the ship until late in the day.” 
Dr Bajrovic urged intending travellers to call Travelvax Australia’s free travel health advisory service (1300 360 164) to learn if any outbreaks had been reported recently.

Protect yourself - Ask our experts

They could ask our travel health experts about the range of bite-prevention measures they could take, such as:
– Moving inside at peak mosquito feeding times – especially around dusk.
– Using insect repellent containing an effective active ingredient (DEET, Picaridin (KBR 3023), oil of Lemon Eucalyptus/PMD, or IR3535) and is use as directed. (If you will also be using sunscreen, apply it BEFORE you apply insect repellent.) 
– Wearing loose, long-sleeved shirts, long pants, and shoes and socks when outdoors in the early morning and the evening (the peak times when mosquitoes feed).
– Aedes mosquitoes will breed in tiny amounts of fresh water. On day one of your stay conduct a thorough search of your yard and gardens to find anything that may hold even a small amount of water and either remove it or turn it over so it doesn’t become a nursery for mozzie larvae.
– Soak your clothing and bed net in permethrin.

Permethrin creates lethal bug barrier

Permethrin is an inexpensive way to create a lethal barrier against all biting bugs. Although it should not be applied directly to skin, it is safe to use in clothing, hats, and your bed net.
“It’s a simple process to make a solution in a bucket and soak anything from the hats, clothes, even socks you will be wearing during the day, to the bed net you’ll be sleeping under at night,” Dr Bajrovic said.
“The protection lasts even if the item is washed a few times.
“A bed net is a must-take accessory if you will be in budget accommodation that may not be well screened, or if you’ll be staying in local homes.”

‘Worrying’ trend of severe illness

The new European study provides an insight into the three mosquito-borne diseases and their impact on Pacific communities in recent years.
In the past, one of the 4 types of dengue swept through the region every 3-5 years. However, in 2012 there were outbreaks of all 4 DENV serotypes documented for the first time in a single year.
Since then, DENV-1 dominated in 2012 and early 2013, causing the largest documented outbreak ever in New Caledonia. Five people died among the 10,978 confirmed cases over 12 months.
Chikungunya and Zika are becoming more firmly established, too. 
Chikungunya was reported in the Pacific for the 1st time in a small tightly controlled outbreak in New Caledonia in 2011. Since then, the largest epidemic has been in Papua New-Guinea, involving cases ‘in the tens of thousands’, the researchers said. Both African and Asian ‘lineages’ of the disease have been detected in the smattering of Pacific outbreaks.
The Zika virus was first documented in Yap Island in 2007 before the Asian lineage of the virus reappeared in French Polynesia in October 2013. It has since caused large outbreaks in New Caledonia (1400 confirmed cases), Cook Islands (900-plus), and Easter Island. 
Of greater concern was the incidence of neurological complications suffered by 42 French Polynesians with Zika between last November and February this year. The severe cases of what had been considered a milder disease are a ‘unique and worrying’ development warranting urgent investigation, the researchers say.