Depression increases your risk of a number of diseases and other conditions by, for example, increasing levels of stress hormones such as cortisol or adrenaline. Depression can affect the immune system, making it harder for your body to fight infection. Vaccinations are even less effective in people with depression.
The total surface area of the Earth is about 7008510000000000000â 510 million km2 (197 million sq mi). Of this, 70.8%, or 7008361130000000000â 361.13 million km2 (139.43 million sq mi), is below sea level and covered by ocean water.
The total land area of the earth is about 57 million square miles, so I'll bump that down to 50 million square miles of land habitable to mosquitoes (probably an overestimate, but I'm just looking for ballpark here). Next one would have to estimate how many mosquitoes inhabit each square mile on average. I've seen some areas where the mosquito density was upwards of 1 mosquito per 2-3 square feet, but I think that's a gross overestimate of the world as an average.