Global brief on vector-borne diseases
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Officially Japan hasn’t seen a locally acquired case of Dengue since the late 1940s, although in January of this year the journal Eurosurveillance published a reports on a German tourist who was diagnosed with the disease upon returning home from a trip to Japan (see Autochthonous dengue virus infection in Japan imported into Germany, September 2013).
Today, however, the Japanese Ministry of Health is reporting the local acquisition of the virus by a teenage girl (without travel history outside the country) residing in in Saitama prefecture, adjacent to Tokyo (see AP report Japan sees 1st local dengue case in over 60 years).
Japan, like the United States, sees hundred of imported dengue cases each year – carried by travelers coming from areas of the world where the virus is endemic.
If an infected traveler is viremic (currently producing large quantities of virus in the blood) - and is bitten by a local mosquito capable of vectoring the disease - it is possible to introduce the virus to a new region. In 2009 Dengue returned to the South Florida after a 60 year absence, and since then we’ve seen a handful of locally acquired cases each year (see MMWR: Dengue Fever In Key West).
In order to spread, Dengue requires the right mosquito vector. And the two species best suited to transmit the virus are the Aedes aegypti and Aedes albopictus mosquitoes, which also can spread such diseases as West Nile, Malaria, Yellow Fever, and Chikungunya.
While the Aedes Aegypti isn’t a problem in Japan, the Aedes Albopictus (`Asian Tiger’) mosquito is.
After World War II advances in insecticides and massive mosquito control programs practically eliminated Dengue in all but a few tropical ports. But over the past 40 years - between the explosion of world travel, a rise in insecticide resistance, and lapses in mosquito control – the incidence of dengue around the world has literally exploded.
The World Health Organization estimates 100 million people are infected with Dengue each year, and 500,000 are sickened enough to require hospitalization. The WHO considers Dengue to be the most rapidly spreading mosquito borne viral disease in the world, and increasingly it is posing a threat to Europe and North America.
Countries at risk for Dengue Transmission
The detection of a single autochthonous Dengue infection in Japan hardly constitutes a public health emergency, but it is another sign that this mosquito borne virus continues to encroach into new regions around the world, and that even places previously thought immune are becoming increasingly vulnerable.
And since they share a common mosquito vector, that probably holds true for Chikungunya as well.