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Australian Scientists Tackling Dengue Fever



An explosion of dengue fever in Thailand since the start of the year has health officials warning occurrences of the disease, already up 75 percent over the same period last year


Hopes that dengue fever may one day be eradicated have been raised by scientists who have discovered how to stop mosquitoes carrying the disease.

Groundbreaking experiments in Queensland have found a common insect bacteria – wMel Wolbachia – can dramatically reduce the presence of dengue fever in mosquitoes.

If the number of mosquitoes carrying dengue can be cut, far fewer people could end up with the disease, which infects about 50 million people worldwide each year.

In the past decade, there have been 2400 cases of dengue fever reported during 36 outbreaks in Australia, mainly in northern Queensland and the Torres Strait.

Lead researcher and dean of science at Melbourne’s Monash University, Professor Scott O’Neill said while it was too early to say if the experiments heralded the end of dengue fever, it was a major step towards that goal.

‘I think it’s early days, but at the moment we are very hopeful,’ he told reporters.

‘People are very tired of dengue fever and very fearful of it and really don’t think there are good control measures available at the moment.

‘(What the experiments have shown is that) this strain of Wolbachia when it is put into mosquitoes … really reduces the ability of the (dengue) virus to grow in the mosquito and if it can’t grow, then it can’t get transmitted in people.’

Dengue fever has become endemic in tropical regions, where it is spread by a specific type of mosquito that becomes infected after biting humans with the disease.

Infected mosquitoes then spread the disease by biting other humans, who develop severe flu-like symptoms.

Despite millions of people being infected with dengue each year, there is currently no way of stopping its rapid spread either by vaccines or controlling mosquito populations.

Australian scientists have taken on the challenge and begun trials to see if infecting the mosquito breed that spreads the disease, known as A.aegypti, with the Wolbachia bacteria can stop them developing and spreading dengue fever.

While Wolbachia is carried by about five million insect species, it is not naturally present in A.aegypti.

As a result, the scientists had to breed genetically modified A.aegypti mozzies in a laboratory at James Cook University in Cairns.

Armed with the bacteria, the laboratory mosquito colony was fed dengue-infected blood meal.

As they continued to breed in an enclosed replica of a Queensland backyard, the number of mozzies carrying the Wolbachia bacteria increased while those with dengue fell.

The experiments marked the first time scientists succeeded in transforming a wild insect population to stop their ability to transmit human diseases.

Buoyed by their success, the scientists in January released about 300,000 laboratory mosquitoes over 10 weeks in the northern Queensland towns of Yorkeys Knob and Gordonvale to see if they would breed with local wild A.aegypti.

Tests carried out five weeks after the release program stopped showed almost all of the local A.aegypti mozzies carried the protective Wolbachia bacteria.

‘We expect these regions now to have a much reduced risk of dengue transmission within them,’ Prof O’Neill said.

The researchers plan to expand their study and carry out more tests in the Cairns region during this summer’s wet season, when mozzie numbers soar.

Travelers to Thailand are being reminded to exercise extreme vigilance against mosquitoes, with the country experiencing a five year high in dengue fever cases.

Thailand´s Ministry of Public Health said last week there has been 41,136 reported cases and 38 deaths from January 1 to July 20, compared to 22,969 infections and 19 deaths in the same period last year.

Of particular concern is an increasing number of reports of a virulent strain of dengue hemorrhagic fever (DHF) cutting a swath through towns and villages in the north and northeastern provinces, with Chiang Mai, Chiang Rai, Mae Sai, and Surrin all reporting hospitals filled to capacity and deaths.

The situation is not much better in the south of the country, with the Phuket Provincial Public Health Office (PPHO) saying the number of dengue fever cases there is soaring, while Thailand´s five southern border provinces have recorded more than 6,500 cases and 13 deaths between the start of the year and July 29.

DHF is particularly dangerous, with patients exhibiting higher fever, and variable hemorrhagic phenomena, including bleeding from the eyes, nose, mouth, and ear into the gut, and oozing blood from skin pores.

Also known as the bone-crusher disease, dengue is transmitted to humans by the female Aedes aegypti mosquito, which feeds exclusively during daylight hours.

Provincial hospitals are urging residents and concerned agencies to help clean up breeding sites of house mosquitoes in order to control the spread, and also advising people to seek immediate medical attention if they suspect they are infected.

In June Thailand Travel News reported on the early wet season emergence of dengue (see: Tourists urged to take precautions as dengue fever cases rise) and plans by the PPHO to mount a concerted effort on the island of Phuket to bring the disease under control.

There is no tested and approved vaccine for the dengue flavivirus and a classic dengue fever infection can last between two to seven days, with a smaller peak of fever at the trailing end of the disease.

Symptoms are very similar to influenza and can very in intensity, but include fever, bad headaches, muscle and joint pains, skin rashes, and overall weakness in the body.

Due to the risk of bleeding with DHF, people in dengue fever areas who exhibit symptoms should not be given aspirin, but paracetamol is okay, and should seek immediate medical treatment.

Tourists visiting regions prone to dengue fever should be particularly vigilant during daylight hours and wear long-sleeved clothes and long trousers when going outdoors. The use of good quality insect repellents containing DEET on clothes and exposed parts of the body is highly recommended.

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