Why Are Dengue Cases Surging in Asian Countries This Monsoon?

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Dengue is one of the world’s leading mosquito-borne illnesses and infects as many as 100 million people annually. Dubbed as the “break bone fever”, dengue typically occurs in and around the monsoon season in sub-tropical and tropical countries.

Its symptoms typically begin three to fourteen days after infection. This may include a high fever, headache, vomiting, muscle and joint pains, and a characteristic skin rash. The dengue virus has five different types, each of increasing severity. Infection with one type gives lifelong immunity to it and short-term immunity to the other types. The dengue virus isn't contagious and can't be spread from person to person. Recovery generally takes around two to seven days. However, if the disease is not diagnosed and treated on time, it may turn out to be fatal in nature.

About half the planet’s populations live in at-risk areas, mainly in Asia, Latin America and Africa. Explosive outbreaks have ravaged Southeast Asia this year, with around 670,000 infected and more than 1,800 people dead in the region, according to national and World Health Organisation data.

Experts say an outbreak of the mosquito-borne disease in Southeast Asia is the worst in years. At least 622 have died in the Philippines so far this year, cases in Vietnam, Laos and Singapore have tripled, and hospitals are overrun in Malaysia, Myanmar and Cambodia as governments struggle to contain the untreatable virus. Experts say it’s the worst outbreak in years. But one group of scientists is rolling out trials to breed dengue-resistant bugs, raising hopes that the disease could finally be beaten.

Infections have steadily climbed across the globe since the 1970s due to rising temperatures and irregular monsoon rains linked to climate change, which allow for ideal mosquito breeding conditions.

A massive boom in international travel and trade has also expanded dengue’s footprint, allowing the virus to be carried across the globe in a matter of hours and unleashed in new communities.

Experts say the widespread adoption of plastic is also to blame – storage containers, discarded takeaway boxes, backyard pools, plant pots and cooking urns all collect water – a problem made worse during dry spells.

“When you have a drought, people collect water in containers. That is one place the dengue mosquito loves to breed,” said Gawrie Loku Galappaththy, a dengue specialist with the World Health Organisation in the Philippines.

The disease is cyclical – dramatic outbreaks occur every few years – but climate change is believed to have contributed to a spike in cases in 2019, with July clocked as the warmest on record.

“Extremely warm temperatures we’ve seen this year [likely facilitated its spread],” said Rachel Lowe, assistant professor at the London School of Hygiene & Tropical Medicine, noting that mosquitoes thrive in warm weather climates.

Several European countries, where dengue was once marginal have seen outbreaks. Latin American countries, on the other hand, are tackling a surge in cases.

In Southeast Asia, insecticide fogging is commonly used to kill mosquitoes off, but they usually return after a few days, and insects can quickly become resistant to the chemicals.

The World Mosquito Program (WMP) has pioneered a method where male and female Aedes Aegypti mosquitoes are infected with the disease-resistant bacteria called Wolbachia before being released into the wild. In a matter of weeks, baby mosquitoes are born carrying Wolbachia, which acts as a disease buffer for the bugs — making it harder for them to pass on not only dengue, but Zika, chikungunya and yellow fever.

Several countries are also trialing the Wolbachia method, and although it is too early to say if the approach works on a large scale, early results are promising.