The health ministry has confirmed the first domestic dengue fever case in Japan in nearly 70 years. A Saitama Prefecture teen girl was found Wednesday to have contracted the virus through a mosquito in Japan, followed by news that two more people — a man and a woman in Tokyo — have also been infected.
More than 200 dengue cases are reported in Japan each year, but those are of patients who contracted dengue virus abroad. The World Health Organization estimates the number of infections across the globe to be 50 million to 100 million per year.
While the news has led to widespread fears that a pandemic outbreak might have arrived, experts are quick to deny such a scenario, while offering some advice on what measures people can take to minimize their exposure. Following are some basic questions and answers regarding the infectious disease and measures that can be taken to prevent infection.
What is dengue fever and what causes it?
Dengue fever is a tropical viral disease, also known as dengue hemorrhagic fever or break-bone fever, which is caused by dengue virus.
It is said that dengue fever can be caused by any of the four closely related types of dengue virus: DEN-1, DEN-2, DEN-3, and DEN-4.
So far, it is not clear which of the four types that the three latest patients in Japan contracted, though the three probably came down with the same virus type, according to Koichi Morita, professor of virology at the Nagasaki University’s Institute of Tropical Medicine.
While its origin remains unclear, the disease was named “dengue” as early as in 1801, according to Scitable, an online science education portal run by the Nature Publishing Group.
The word dengue is Spanish for “affectation,” “careful,” or “fastidious,” and was probably used to describe the cautious, stiff movements of patients suffering from the muscle, bone and joint pains, Scitable said.
How is the virus transmitted?
Dengue viruses are carried and transmitted to humans by several species of female mosquitoes.
The Aedes aegypti mosquito, which is found mainly in tropical and sub-tropical climates, is deemed the primary vector of dengue. It can be transmitted by Aedes albopictus, also called the Asian tiger mosquito, which is prevalent in Japan.
Although the viruses cannot be transmitted directly from humans, transmission is possible through the bite of an infected mosquito.
What are the symptoms?
The main symptoms observed in patients diagnosed with dengue fever are high fever, joint and muscle pain and rash. They can be accompanied by headache, weakness, nausea, vomiting and bleeding.
The incubation period ranges from two or three days to two weeks, but in most cases symptoms develop within a week after being bitten by an infected mosquito. Because the symptoms are often confused with those caused by influenza or other viral infections, milder symptoms in patients can go unnoticed, Morita said.
A 46-year-old woman from Tokyo, who was diagnosed with dengue fever about 20 years ago upon returning from a trip to Thailand, said it is vital for people who travel abroad not to neglect symptoms and, upon their return, to undergo quarantine checks at the airport in Japan if they are feeling sick.
Because she waited until she came back to Japan to see a doctor, she said she suffered from severe symptoms and needed to receive a blood transfusion. She said she now regrets not visiting a doctor in Thailand while she was there.
What treatments exist?
Currently no vaccines or effective drugs exist, and most patients are only given drugs to lower their fever.
Morita said, however, the recovery from infection by one of the virus’ serotypes provides lifelong immunity against that particular serotype.
If patients are left unattended, they could later develop more severe symptoms, such as internal bleeding, low levels of blood platelets and blood plasma leakage.
What are the measures to prevent from infection?
Given the significant increase in dengue infections worldwide plus the number of imported cases, Morita emphasized the importance of defending against dengue-carrying mosquitoes on an individual basis.
Because transmission is likely in all areas of the country, it is important to protect one’s skin with long-sleeved shirts and full length pants, or by using insect repellent.