Mosquito. Photo: Eli Christman, Attribution license, Creative Commons.

What is dengue fever?

Dengue fever is an infectious tropical disease caused by the dengue virus and transmitted by Aedes mosquitos.  Contrary to common misconception, dengue fever is an urban disease – people living in urban and suburban areas are at greatest risk for infection.

In some, dengue fever can progress to more deadly forms of the disease known as Dengue Hemorrhagic Fever and Dengue Shock Syndrome. The World Health Organization (WHO) estimates that anywhere from 50-100 million people are infected every year.  Approximately three out of every 100 dengue infections are fatal.

What are the symptoms?

Symptoms can range from mild to life threatening. Headaches, fever, pain behind the eyes, skin rashes, nausea, vomiting, joint and muscle pain are most common, but in some patients, the virus interferes with blood to clotting causing internal bleeding that can be seen under the skin and from the nose and gums.  According to the WHO, if fever plus any other two of the above occur, seek medical attention immediately.

How many cases and fatalities have there been so far in Malaysia this year?

From January to 4 December 2014, there have been 98,128 cases compared with 37,698 cases in 2013. From January to 13 September 2014, there were 136 deaths – more than triple the same period last year.

Why is the rate so high in Selangor?

Apparently, dengue cases in Selangor have doubled this year with 48,691 cases in 2014 compared to over 20,209 last year. This accounts for nearly half of all cases nationwide. This is likely to be because the mosquitoes have adapted to the conditions of dense urban areas. After Selangor, the state with the second highest number of cases is Kelantan.

Why is the rate increasing so fast?

The current theory among dengue researchers is that a human population is more vulnerable to attack when immunity to the virus falls below a certain threshold. We are less vulnerable just after a large epidemic.

This rise and fall in the number of dengue cases produces a seasonal cycle that peaks every four to five years. Unfortunately, 2014 appears to be following that seasonal trend as a peak year – the last peak occurred in 2010 when there were 134 deaths in Malaysia.

Is it true that there’s a new strain of Dengue? 

Yes! Until October of 2013 when the discovery was announced, only four distinct strains of dengue virus were known to science.  Researchers screening samples from a 2007 outbreak in Sarawak, Malaysia, stumbled upon a dengue virus that was so different from known form of dengue that it was deemed a separate, fifth strain.

What do these different strains mean to us?  If you’ve recently recovered from a dengue infection, you have gained immunity only to the strain that made you sick and you can still be infected by any of the four remaining strains – sorry.  It also means that all dengue vaccines currently in development will have to go back to the drawing board to include a fifth strain.

What precautions can people take?

The best way to prevent infection is to protect against the bites of the mosquitoes that transmit the virus and minimize sites where mosquitoes can breed.  This involves using insect repellent (those containing DEET are most effective), wearing clothing that fully covers the skin while outdoors, using mosquito netting, and eliminating any sites with standing water in and around the home (where mosquitoes breed).

There is still no vaccine and no cure.  The best way to survive dengue fever is to get to a hospital as soon as symptoms suggest an infection.

Will Stuebing has performed laboratory research on dengue virus at Universiti Sains Malaysia.

First published February 2014. Updated July 2014 and December 2014.