This blog post originally appeared on the Dengue Vaccine Initiative Blog

So far this year the number of dengue cases in Singapore has already surpassed the number of cases reported in 2012, and it looks like it will just keep rising.  As of last week, Singapore was reporting over 6,000 cases, while 2012 saw around 4,600.

Early last month reports began to trickle in of high numbers of dengue cases, and April saw a rapidly growing number of cases. Channel News Asia reported 510 cases in the week ending 20 April, citing it as the highest weekly number recorded since Singapore saw a major outbreak in 2005, in which a total of 14,000 people fell sick. The numbers are only expected to grow, as Singapore’s high season for dengue doesn’t start until May, and typically runs until late summer or early fall.

"Dengue epidemics in Southeast Asia are cyclical. There are very bad epidemic years and there are more-mild years," said Anna Durbin, an associate professor at the Johns Hopkins Bloomberg School of Public Health and a Dengue Technical Expert for DVI, in a Wall Street Journal article on the outbreak.

Dengue can be caused by one of four serotypes, three of which are currently circulating in Singapore. Den-1, which has not been seen in Singapore in many years, appears to be the main serotype present in this latest outbreak.  In YahooNews Singapore, Dr Jenny Low, Senior Consultant at the Department of Infectious Disease, Singapore General Hospital (SGH) explains, “Those that contract dengue develop an immunity to the particular strain that infected them. However as the Den-1 strain has stayed low key for several years in Singapore, most do not have immunity to it..”

Ooi Eng Eong, an associate professor of emerging infectious diseases at Duke-NUS Graduate Medical School in the city-state, offers another suggestion for the high numbers in a recent Bloomberg article, suggesting that, “a significant proportion of our population’s made up of people who may not have been born in dengue-endemic regions so they are immunologically naive and therefore susceptible to infection.”

In response to the outbreak, the government has stepped up dengue control measures, kicking off public awareness campaigns and calling on residents to help slow the outbreak. Prime Minister Lee Hsien Loon launched the “Do the Mozzie Wipeout” campaign.  The initiative involves both government and grassroots groups, as well as volunteers going door to door to get the message out. As part of these control efforts, inspectors from the National Environment Agency have broken in to homes with suspected dengue breeding grounds.

Leo Yee Sin, director of Tan Tock Seng Hospital’s communicable disease center, said that, unabated, dengue infections may total as high as 23,000 this year.

Singapore skyline photo by William Cho.