There are so many parasites living in tropical regions of Africa, South America, or Asia, but very few in Europe or North America.
Is this due to climate, or are there other reasons?
Many of the tropical diseases and parasites are transmitted by insects, such as flies and mosquitoes. Well there are flies and mosquitoes in Europe as well.
There might be malaria-transmitting mosquitoes in the very south of Europe, and there is encephalitis transmitted by ticks. But that's it. Why don't the hundreds of different parasitic species from Africa spread to Europe ?