The health ministry reported Aug. 27 that a teenager in Saitama Prefecture with no record of overseas travel had been infected with dengue fever — the first domestic infection of the disease in almost 70 years. The infection has since spread nationwide, with the number of patients reaching 133 as of Thursday.
It is now safe to assume that an outbreak of dengue fever somewhere in Japan could be possible every summer. The central and local authorities should carefully watch future developments and take necessary steps such as eliminating mosquitoes, which spread the virus, and providing information for people on how to cope with the disease.
Since 2010, about 200 Japanese were found to have been infected with dengue fever each year after traveling overseas, but infections among people with no record of traveling abroad have not been confirmed since 1945. The latest outbreak of the viral disease reflects its global spread. The number of dengue fever patients worldwide increased from some 16,000 annually in the 1960s to roughly 2 million in 2011.
Dengue fever is common in Taiwan, Southeast Asia, Central and South America and Africa, but the disease is no longer limited to tropical and subtropical areas as global travel becomes commonplace.
The dengue virus is transmitted by tiger mosquitoes — whose habitat in Japan ranges as far north as Tohoku. If they bite infected people, the virus multiplies inside them and gets transmitted to other people when the mosquitoes bite them.
Sufferers of dengue fevers are attacked by a sudden fever that continues three to seven days, accompanied by head and muscle pains and a rash.
While most patients have only mild symptoms, some may suffer bleeding gums or nosebleeds.
There are also many people who are infected with the dengue virus but do not develop symptoms. The World Health Organization warns that 40 percent of the world population face the risk of dengue virus infection.
A German woman who traveled in Japan in August 2013 developed symptoms of the disease after arriving back home. Japan’s health authorities may not have noticed an outbreak in this country at the time.
The first several patients of the latest outbreak in Japan are known to have visited Yoyogi Park in Tokyo. Doctors who find cases of dengue infection are obliged to alert public health authorities. Repeated news reports about becoming infected in the popular park, where weekly large-scale events attract visitors even from overseas, apparently roused people’s interest and led to reports of more cases of infection.
Yoyogi Park may have provided an optimum environment for an outbreak, but it is not the only park where mosquitoes and people gather.
The spread of dengue fever to more temperate areas of the Earth can be attributed to global warming, population increases and urbanization in many countries, as well as the rise in international travel.
It may be difficult to contain future outbreaks in Japan, but there is no need to panic. The life span of tiger mosquitoes is 30 to 40 days, and they die off in late October. The virus that has entered them dies while the mosquito’s eggs winter over.
The best defense against dengue fever is for municipalities to take steps to reduce mosquito populations. Residents can do their part by eliminating containers in their yard where water can collect, as standing water provides a breeding ground for mosquitoes.
People should also make a point of using mosquito repellent before spending time outdoors.
Finally pharmaceutical companies and researchers should step up their efforts to develop a vaccine against the dengue virus and to improve treatment of patients with dengue fever.