Yes, it turns out that mosquitoes are our worst enemies -- even worse than other humans. Gates writes:
What makes mosquitoes so dangerous? Despite their innocuous-sounding name-Spanish for "little fly"-they carry devastating diseases. The worst is malaria, which kills more than 600,000 people every year; another 200 million cases incapacitate people for days at a time. It threatens half of the world's population and causes billions of dollars in lost productivity annually. Other mosquito-borne diseases include dengue fever, yellow fever, and encephalitis.
Gates used this as a jumping-off point to introduce Mosquito Week, a campaign to raise awareness for mosquito-borne diseases and parasites: