I'm wondering, because I know that the Japanese traded with the Dutch from the 17th century onward, but otherwise trade and travel was closed to the rest of Europe. When their ports were forced open and Europeans visited, why weren't they wiped out like the Native Americans were? The Japanese were an island nation with no immunity built up from raising livestock!
The reason for this is that Japan, unlike the Americas, is not part of a different landmass. Instead of thinking of the Dutch as Europeans, think of them as part of the Afro-Asian continents. This is the same continent as Japan and therefore they share diseases.
For example, the plague originated in Asia. It was in China and Europe. The Japanese would have had contact with this disease through contact with the Chinese.
Edit: Due to the increase in views and interest on this question, I am going to add some sourcing and other information.
I have assured myself of my correct memory of Sino-Japanese relations long prior to 1492 by referring to Fernand Braudel's A History of Civilizations pages 277-300. In it he writes, "This was the beginning of the Japan known to history, with its hierarchy, its scribes, its chronicles and its embassies to the Emperors of China, the first being accredited in 607."
You can read about disease exchange in Alfred Crosby's The Columbian Exchange.
Changed to "Afro-Asian" and "continent"
However, syphilis did arrive in Japan, just as it did arrive in Europe through the Colombian exchange. And it killed many people, like Tokugawa Ieyasu's second eldest (at the time eldest surviving) son.
The Japanese were an island nation with no immunity built up from raising livestock!
...Why do you think the Japanese weren't raising livestock?
Edit: New World populations were separated from the Old World for 10,000 years or more. Japan has been trading regularly with Korea and China for at least 1500 years. It's little more isolated than the British Isles. A couple hundred years of near-isolation, with livestock, wouldn't change that.
Zoonosis is the process of a pathogen crossing over from animals to humans, and its how lots of diseases begin. Livestock, for example are reservoirs of germs, some of which cross over and make people sick (think influenza or TB). Since the Eurasian continent has been fairly connected for most of history (not directly but germs hop around easily), the Japanese would have plenty of exposure to chickens, and pigs, and all the germs you might find throughout Eurasia.