81 dengue fever cases reported in 15 prefectures

81 dengue fever cases reported in 15 prefectures

Does that make Yoyogi Park a potential red herring?

Yoyogi Park has a lot to answer for........

The ministry is working with Tokyo metropolitan government health officials to spray insecticide in three parks in Tokyo

I suppose no one cared to tell these folks that mosquitoes are airborne insects and may not necessarily stay in Yoyogi park... I suppose we have to spray insecticide over the whole country....

That did not take long to spread over 15 Prefectures! Or was it detected but the recipients were not " celebrities " so not news worthy, or perhaps the spraying spread the Mosquitos to 15 other prefectures?

@farmboy:

Here ya go: Yoyogi Park, Shibuya Ward, Tokyo, Japan | Dengue | Humans Tokyo Metropolis, Japan | Dengue | Humans Osaka Prefecture, Japan | Dengue | Humans Aomori Prefecture, Japan | Dengue | Humans Niigata Prefecture, Japan | Dengue | Humans Yamanashi Prefecture, Japan | Dengue | Humans Ehime Prefecture, Japan | Dengue | Humans Kanagawa Prefecture, Japan | Dengue | Humans Ibaraki Prefecture, Japan | Dengue | Humans Chiba Prefecture, Japan | Dengue | Humans Okayama Prefecture, Japan | Dengue | Humans

unfortunately doesn't show detailed locations.

@Farmboy, this map shows where the cases were reported - in Japan and around the world:

http://www.healthmap.org/dengue/en/

Where I'm from, dengue is a year-long threat, and for many people a right of passage. I had it when I was a teen. It was like having the worst flu mixed with bad acid. We had insecticide trucks roams the streets spraying gawd-knows-what in the air everyday. It doesn't work! The number of cases never dropped. Emptying pools of stagnant water is the only way to curb mosquitos from breeding. I'm disappointed that j-media have not made it a point to teach this simple method. However small, if you see something (e.g. trash) collecting rainwater, dump it before it becomes a mosquito orgy. Perhaps if there wasn't so much trash around this would not be an issue.

Besides, mosquito season is nearly over so suck it up Japan.

Mirai HayashiSep. 09, 2014 - 01:42PM JST I suppose no one cared to tell these folks that mosquitoes are airborne insects and may not necessarily stay in Yoyogi park... I suppose we have to spray insecticide over the whole country....

... no. The problem here is the people, not the mosquitoes.

Come on people, connect the dots. What has just happened? Obon. That means a lot of Tokyo people went back home to their home prefectures.

Let's take a hypothetical, Taro. Taro visits Yoyogi park and contracts Dengue fever, but it is misdiagnosed as influenza. Taro then goes home for Obon in Kanagawa and is bitten by a mosquito there, which bites 10 more people, one of whom contracts Dengue, let's call that person Yuki. Yuki is then bitten by 5 more mosquitoes who now become carriers.

And this is how diseases spread. People are the main problem in this scenario, not the mosquitoes.

Killing the mosquitoes will not help, they die every winter across most of Japan anyway. The problem is that the infected humans are still around next summer, and they reinfect the mosquitoes.

Unfortunately, mosquito larva can survive the winter season. Since the mosquito season is almost over, the dengue cases will drop and we won't hear another word about until next summer when they all hatch. The only way to prevent a future epidemic is by destroying their breeding grounds: standing water. Dengue is typically carried by tropical mosquitos, not those native to Japan. This is something entirely new and could potentially be an epidemic next year if not taken seriously. The "hundreds of people" that come to Japan every year that may or may not have an infectious disease is a mute point if dengue has infiltrated Japan'e native mosquito.

chikvSep. 09, 2014 - 07:58PM JST Yes, humans have only the virus in the blood for a few days and after that its cleared and no more transmission is possible. What Frungy may be referring is that every year hundreds of people come to Japan infected with the virus, and since mosquitoes reappear every year after dying in the winter there will be other outbreaks in the future.

Yeah, sorry for my ambiguous response. Japan is close to several areas where Dengue fever is wide-spread (most of SE Asia), and with travelers (both Japanese and foreign) coming into to Japan it just takes one person who has the virus and likes walking around at night.

Robert NishimuraSep. 09, 2014 - 09:04PM JST Unfortunately, mosquito larva can survive the winter season.

Vertical transmission (female mosquito to larvae) is possible, but is extremely rare (about 1 in 2000 to 1 in 4 000 depending on which study you're looking at - if you want to read more google "transovarial transmission dengue"). A single mosquito lays 100 to 200 eggs at a time, but in her lifespan can lay up to 3000... which means that a single infected female mosquito will probably only produce a single successor that is also infected.

The primary problem is infected humans infecting more mosquitoes.

It is a good idea to control the mosquito population, because they're vectors for several nasty diseases. The good news is that Asian tiger mosquitoes are the laziest on the planet and only fly a couple of hundred meters at best, so eliminating free-standing water sources in towns and for a couple of hundred meters around towns will do the trick.

... and there's no need to use DDT or other drastic measures. For small sources of standing water like buckets, simply empty them. For larger sources, like water reservoir tanks for air conditioning, simply spray a thin film of oil across the top, thereby suffocating the larvae when they come to the surface to breathe.

chikv: In the case of Japan that is not possible, there is a absolute minimum temperature that have to be kept in order for the eggs, larva or females to survive. Outside of Okinawa the winter is just too cold to have any significant number of infected mosquitoes surviving.

Wondered this before, from someone else's post, but you might actually know the answer: where do the mosquitoes in Tokyo come from if the eggs don't overwinter?

chikvSep. 09, 2014 - 11:06PM JST In the case of Japan that is not possible, there is a absolute minimum temperature that have to be kept in order for the eggs, larva or females to survive. Outside of Okinawa the winter is just too cold to have any significant number of infected mosquitoes surviving. (meaning that the probability of getting a mosquito infected by imported human cases is still much higher than the probability of an infected mosquito surviving.)

Thank you for your post.

I think the phrasing in your post is somewhat ambiguous. At 0C about 95% of adult female Aedes aegypti (Asian tiger mosquitoes) die, and for those that survive their total life expectancy plummets to about 5 days (source: http://www.parasitesandvectors.com/content/6/1/351) . This is about as cold as it gets in Tokyo, with Tokyo rarely experiencing sub-zero temperatures.

What this means in practical terms is that a single female Asian tiger mosquito that experiences winter in Tokyo will wake up when it gets warm enough and die a few days later, having probably only laid a couple of hundred eggs. Since only 1 in 2000 to 4000 eggs will carry the virus this means that naturally winter in Japan will completely eliminate the virus within a couple of years IF we take humans out of the equation.

If you put humans back into the equation then one mosquito infects a human who likes night walks, and ten other mosquitoes feed on that human, and suddenly you're not looking at one female producing 200 eggs, but 11 infected females producing 2200 eggs, which means there's 50/50 odds that another Dengue virus carrying mosquito will be born next year, repeating the cycle.

The answer is that humans need to take basic precautions against mosquitoes. This means keeping screen doors closed and in good condition, using an insect repellant, and avoid going out when mosquitoes are most active, at night.

There is way too much focus in this case on the mosquitoes, and too little focus on humans modifying their behaviour.

In the case of the Tiger mosquito even running water is a proper breeding ground, so its materially impossible to destroy them all (you would have to drain all rivers)

This I did not know, thank you. However it is worth noting that this is a simplification. Running water contains predators like fish that reduce the chances of larvae survival, which is why standing water is preferred. Eliminating mosquitoes is never possible, the goal is to reduce the population.

fortunately for now overwintering is not a real possibility but a few more degrees of temperature can change that.

With all due respect, the data doesn't support that position. The difference in survival rates between 2 degrees and 5 degrees is a matter of about 5% survival and 7% survival. That isn't a major factor.

For now the only real way to bring Dengue to Japan every year is by imported human cases, there is no possibility of mosquito persistent infection and Dengue have no other known animal reservoir so every winter Dengue is again eradicated from the country, if Japan closed it borders the risk of Dengue would disappear but of course that is not a real option.

However recommending people wear insect repellant, do not open unscreened windows, and asking people to please stay indoors at night if possible are realistic and reasonable measures, and would cut down on infection rates significantly.

Plus dealing with standing water where larvae are less likely to die.

At the end of the day this is a numbers game, and no single thing is going to deal with the problem. But there's absolutely no hope if people continue to act in the same fashion and ignore the risk entirely. Is it really too much to ask for people to put on some insect repellant before going out at night?

Face it, mosquitoes are ubiquitous, even in Shinjuku. That dengue is getting this far north is just part of the normal cycle of a warmer winter, in general. Best to cover up in the evenings. Dengue is supposed to be miserable.

Thank you papigiulio and Fish Forest for your information!! Really appreciate it!

** papigiulioSep. 09, 2014 - 02:18PM JST @farmboy:Here ya go: Yoyogi Park, Shibuya Ward, Tokyo, Japan | Dengue | Humans Tokyo Metropolis, Japan | Dengue | Humans Osaka Prefecture, Japan | Dengue | Humans Aomori Prefecture, Japan | Dengue | Humans Niigata Prefecture, Japan | Dengue | Humans Yamanashi Prefecture, Japan | Dengue | Humans Ehime Prefecture, Japan | Dengue | Humans Kanagawa Prefecture, Japan | Dengue | Humans Ibaraki Prefecture, Japan | Dengue | Humans Chiba Prefecture, Japan | Dengue | Humans Okayama Prefecture, Japan | Dengue | Humans

unfortunately doesn't show detailed locations.

** FishForestSep. 09, 2014 - 04:04PM JST @Farmboy, this map shows where the cases were reported - in Japan and around the world:

http://www.healthmap.org/dengue/en/

The german news already reported in January about a german tourist who returned home with dengue fever after a trip to japan.

I live in the caribeean. most of us have had dengue. But we have 3 types of dengue. Nobody dies from that.

and avoid going out when mosquitoes are most active, at night.

Well, I learned that the little beasts that are flying around at night are not tiger mosquitos but some other, "normal" type which can't transfer the dengue virus. You can get dengue only from tiger mosquitos which are only flying during daytime (I was bitten by one in April and that was definitely around noon). So protecting yourself at night will keep you only from being bitten by normal mosquitos, but it will not protect you from the tiger mosquitos. So you need to use long clothes and repellants during daytime, while at night you are relatively safe. Or is that information wrong and they are active at night as well?