They're coming. 

It's not a matter of if. It's a matter of when. An invasion is taking place. Bloodthirsty armies are cropping up everywhere. You can't hide from them. They can track you. Gunfire won't kill them; neither can swords or knives. They're hungry, but they don't want your canned goods or your MREs. You see, they don't want your food because, to them, you are the food. And no, I'm not talking about space aliens. 

I'm talking about parasites.

Fleas, ticks, and mosquitoes, to be precise. Prosperous societies have seemingly reduced these pests from threat level status to little more than an inconvenient, occasional nuisance. However, history says that once prosperity fades, these pests come back with a vengeance. And when that happens, that "nuisance" fast becomes a danger. 

Infections transmitted by a parasite can kill you.

One only needs to crack open a history book to see the devastating, chilling effects that parasites can inflict on us. Bubonic plague killed an estimated ? of Europe alone in the 1300s. Malaria, dengue, West Nile, Lyme disease, typhus, and Rocky Mountain spotted fever are responsible for a number of fatalities each year, and sometimes even cause permanent damage to the body if you survive the initial infection. New, deadly diseases could emerge in the future, the spread of which can likely be aided by fleas, ticks, and mosquitoes. 

The conveniences, cleanliness, readily available medical treatment, and technological advances that modern society has to offer have made many people forget the threat that these parasites have posed and still pose to us. Even in a slow-burning SHTF situation, hindrances with garbage removal can leave trash uncollected, gradually piling up in people's yards. Raw, untreated sewage can leak into the environment as companies cut corners to try to fight rampant inflation. Shortages of important medicines, such as antibiotics, fever reducers, and common medical supplies, can become more scarce. A lack of doctors, nurses, and hospital workers can prolong wait times for urgent emergency care.