What makes vector borne diseases so sexy? Well, let's start with the basics. It takes a fair amount of evolutionary genius to manage to infect one host without killing it, so that you can infect another host to propagate your lifecycle. Additionally, many of these viruses or parasites have multiple infectious strains that have different properties and can exchange nucleotides with each other to increase the biodiversity of the pathogen.
Let's take Dengue Fever virus for example. Spread by the Aedes Aegypti mosquito, dengue fever can be caused by four different strains. You get one strain, you have lifelong immunity. BUT if you get infected with another strain, you could have haemorrhagic fever (like ebola). So, Dengue is made up of 4 segmented strands of RNA and they do a tango and dos-e-doe, and then they make new variations. And you think you need a central nervous system to be smart...Don't get me started on African Trypanosomiasis...that little parasite is just too cool for school.