Solving the problem of overpopulation on Earth by terraforming Mars using Moss and Cockroaches sounded like a good idea on paper. Unfortunately, like many other theories, this plan completely ignored that evolution is a thing that happens, and thus, 500 years after the original plan was created, we ended up with not only giant humanoid cockroaches on Mars but also a new viral DNA, the Alien Engine Virus, that has a death rate of 100%. In the hopes of finding a cure, the Annex I mission was sent to the red planet to collect some cockroaches because they believe that they carry the A.E. virus in a form that can help mankind to create a vaccine. And that’s when things got more complicated because two previous missions to Mars had managed to make sure that the cockroaches would be very hostile to mankind.

This particular entry is so low on the list because while the virus and the epidemic are very important to the plot, they are usually on the background of the story. We’re far more worried about the fate of the latest mission to Mars –especially given the huge mortality rates of the other two missions- and the characters that we see dying for the chance to find a cure. But still, if there was no epidemic, there would be no story, and that is why Terra Formars is the tenth choice on our list.

Five prisoners wake up in an empty building. We don’t know much about them, except very short glimpses at what they did to end up in jail, with one newspaper also talking about a terrible pandemic. However, this is so fast, we don’t know the details. All we know is that the five prisoners are alone with a cat and a seemingly dead old man. It’s when the old man wakes up that things start getting really interesting, as the others figure out that they’re much farther away from home than they thought originally and that only one of them can escape from their prison while all the others will die.

At first glance, Norageki! may seem a bit of a departure from the other anime on the list because none of the main characters show any signs of being sick. However, the mention of the pandemic is not gratuitous, and soon, we find out that -once again- everything in the story happened because the Earth Government is trying hard to make sure a horribly unstable virus, called the Undone Virus, can be destroyed. Again, the Virus may not be an active threat to our main characters, but without it, we wouldn't have a story, and thus, Norageki! remains in the ninth place on our list.

Takashi Komuro was having a very bad day already when the dead decided to rise from their graves. He was bored with his life, his friends, and his family, but he never expected to have to fight for his life next to his childhood friend Rei Miyamoto, or with past classmates; Kouta Hirano, Saya Takagi, Saeko Busujima, and their school nurse, Shizuka Marikawa. Still, that’s what he had to do in order to escape his now zombie-infested school and, later, the city that has been apparently abandoned by the defense forces.

In Highschool of the Dead, we can clearly see the consequences of a terrible epidemic with no real cure and with a 100% contagion rate. While the story itself never reveals what exactly made the dead rise, it is treated like a disease that has no cure. It only spreads through bites, at least as far as the anime and manga went, which makes it a bit easier to avoid as long as one doesn’t end up surrounded by zombies. Still, because of the obvious decay of society and how deadly this particular virus seems to be, HighSchool of the Dead climbs to the eighth place on our list.

The worst thing that can be done when a virus is threatening to destroy mankind is to avoid researching it. At least that’s what Ikoma thinks, but he is just a young steel smith that works to maintain the trains that go from fortress to fortress to protect what remains of mankind after the Kabane appeared, not someone with authority. The Kabane look human, and they were once people, but upon being infected by a bite from another Kabane, they become metal-covered zombies, hungry for flesh. People have decided that the only solution to this is to kill the bitten before they turn into Kabane, but Ikoma is not sure that it’s the best route and wants to research the virus more. Which comes in handy when he is bitten during an attack and has to find a way to keep his mind.

Unlike other Zombie Apocalypse stories, in Koutetsujou no Kabaneri the virus makes it even harder to kill the zombies, and due to the time that has passed since it first appeared and the secrecy that surrounds it and the Kabaneri, those who are not quite immune to the virus but at least don’t become mindless ghouls when infected, have resulted on the fact that the virus and the Kabane have overrun most of the Earth’s surface. There’s also the fact that the little research done means that when the virus seemingly evolves, people aren’t prepared to deal with those changes. And because of those surprises, Koutetsujou no Kabaneri rides all the way to the seventh place on our list.

The most terrifying viruses are the ones that have a slow process. The Apocalypse virus can be quite fast, but it still has, at the very least, four very distinct stages that make the disease even more frightening. While stages 1 and 2 give the infected a few extra abilities and could even be considered useful, once it reaches stage 3 and the person starts growing crystalline structures that will slowly but surely cover all the victim’s body, things get ugly really fast. So fast, that in order to control the epidemic on a night known as the Lost Christmas, Japan gave up their independence in order to get a vaccine and save what was left of their population.

Although the story takes place 10 years after the Lost Christmas, and it’s mostly about the fight of an underground resistance group that wants to return Japan’s independence, it still shows the effects that the epidemic had on society and the continuous attempts by scientists at finding a cure, or at least a way to contain the virus. We see many of the victims, as well as how the virus is still active both in Japan and around the world. As we see people fighting for their lives and, thanks to flashbacks, the origin of the virus all the way down from patient zero, Guilty Crown earns the sixth place on our list.

Another virus that forced humanity to live in small, walled cities trying to defend themselves from the infected and have a life as normal as possible, is the Gastrea virus. It infects people and turns them into horrible monsters. Sure, the walls in these particular cities are made of Varanium, an element that can hurt Gastrea, but once they reach a certain evolution stage, even Varanium walls can’t stop them from entering the cities known as Monoliths. To make things even worse, there are certain children whose blood is infected with the virus and, sooner or later, will turn into Gastrea’s abominations, but in the meantime, are used as weapons to protect mankind.

This is another series where it seems that science has given up on trying to understand how to fight the virus and is rather interested in how to try to protect those who are still uninfected. While it may seem like a defeat for mankind, the truth is that it's a reasonable attempt at trying to preserve civilization against an unbeatable enemy. At some points, the attitude against the “Cursed Children”, the ones who slowly are turning into Gastrea monsters, can make one feel quite uncomfortable. Even more so when one considers that many of those "Cursed" are quite young. Still, because it shows quite clearly how a disease can destroy a civilization, Black Bullet lands right in the fifth place on our list.

After any natural disaster, one of the very first things that have to be restored for the sake of the population is the health service. After all, with no doctors or medicine, even the common cold can be deadly for those injured. At first, Mirai Onozawa, a thirteen-year-old girl who was with her younger brother Yuuki at an artificial island when an 8.0 earthquake hit, doesn’t really notice that there are no doctors around because she and her brother managed to survive unscathed, but as they start the journey back to try to find their parents, she sees more and more how dangerous a small injury can become when there are no easy ways to reach a hospital.

Unlike most of the shows on the list, Tokyo Magnitude 8.0 doesn't dwell on the different illnesses that can crop after a natural disaster like an earthquake. Instead, we just witness what happens in the background while we follow Mirai and Yuuki’s journey. And this is quite realistic for the situation, as sometimes, people who aren't sick tend to ignore how bad an epidemic can get until it really hits them close to home. Because of this realism, Tokyo Magnitude 8.0 more than deserves the fourth place on our list.

Despite what some people may believe, not all bacteria are dangerous. In fact, some of them can be quite useful to mankind. Tadayasu Souemon Sawaki, the son of a yeast maker, knows this first hand. Not just because of his father’s profession, but also because he has the very unique ability to touch and talk to bacteria that surrounds everyone. While this creates a lot of trouble for him, it also allows him to interact with the world in a way that can be helpful when dealing with both good and harmful bacteria.

This is not a good anime for germophobic viewers, as it shows a lot of the daily contact we have with millions of microscopic bacteria, microbes, and viruses. While it is not as dramatic in effect as the other entries on the list, Moyashimon is one of the most realistic in the way in which we interact with those organisms and how not all of them are immediately harmful. This is why we give the series the third place on our list.

The city Number 6 is a beautiful utopia. After all, it’s of the six cities that house the remains of mankind after a world war, and the government in city-state does everything possible to keep their inhabitants happy and healthy. But Shion soon realizes that it’s not that wonderful when he and his mother are stripped of all their privileges because Shion dared to help Nezumi, a fugitive that came from beyond the walls. Now that he has no protection, Shion witnesses first hand how a parasitic wasp species is starting to kill the poorest inhabitants of No. 6.

Here, we see a completely different disease from the titles on our list so far: Parasites are not an illness you can cure, and while there are some methods in real life to kill parasites without harming the host body, people in No. 6 don’t have that particular technology at hand. Even if they had the technology, it would be useless, as there are no symptoms to be observed before the wasps come out of their bodies, killing them, so there’s practically no time to save the victims. And because of that particular nightmarish scenario, No. 6 reaches the second spot on our list.

Before medicine, the first line of defense our body has against illness are our own cells. The specialized cells that fight against any external threat are the white cells, but they also receive help from other cells such as the Killer T Cells, the Monocytes, the Lymphocytes, and the B Cells. Most common illnesses, such as the common cold, food poisoning, and even small scratches, can be defeated by these hard-working cells who work with the circulatory system and the nervous system to keep us alive. Sure, there's a particular red cell, AE 3803 who tends to lose her way quite often, and a white cell, U-1146, who seems to run into more trouble than his companions, but that doesn't mean the rest of the immune systems and working cells don't do their job to keep their body alive and well.

Given that the whole concept of Hataraku Saibou is to watch how our body fights against the possible dangers of the outer world, it’s no surprise that every episode has to do with a different illness. From Pneumococcus to Influenza, from Dengue Fever to even Cancerous Cells, the brave Immune System fights them all with the same fervor. Sometimes, it requires a bit of help from others, like the cute Platelets, but in the end, it’s the immune system cells who keep fighting for our health. And because this series is completely dedicated to that fight, it more than deserves the first place on our list.