Special rooms, terrain and the hazards in the tissue.
When people get sick they take antivirals (like Tamiflu or tenofovir), get vaccines and boosters, or are given interferon, a signalling protein that puts cells into an antiviral state.
In the game
Once Detection is 75 or higher, the host may feel sick enough to take a treatment (a 30% chance every 10 seconds). A warning flashes, and about 2 seconds later a big swarm floods the room: an antiviral dose (drug capsules, antibodies, neutrophils; you also fire 20% slower everywhere while it lasts), a vaccine booster (vials, antibodies, B cells, plasmablasts; every cell takes 20% less damage) or an interferon shot (NK cells, antibodies, neutrophils, monocytes; every hit on you does 25% more). After a dose there is at least a 2-minute break (40 seconds longer after each dose) before another can come, and each dose this run is much stronger than the last. It also grows with the immune system's level (the L number by the detection bar). Survive it and the leftovers drop nucleotides and materials; leave the room and you escape it, but lose the reward. Tip: Keep Detection under 75 to avoid it entirely. During the warning, step away from the middle or toward a door; kill drug capsules and vaccines first since they weaken you or protect the others.
Fun fact: Interferons were discovered in 1957 because cells infected with one virus resisted infection by a second one; they 'interfere' with viruses.
Appears inTreatments & Vaccines
Tissues are not solid: there are gaps, ducts and spaces between cells, and particles can be swept away by fluids and mucus.
In the game
Bottomless gaps in the tissue. Falling in costs about a third of your max HP and you climb back out at the edge; it only kills you if that takes you to 0. Cells (and knockback) can push you toward them. Tip: Dash over them; you can't fall while dashing.
Fun fact: Your nose and airways clear about a litre of mucus a day, sweeping trapped microbes to be swallowed.
Appears inTissue Hazards & TerrainHazards, Pits & Shafts
The lungs end in about 480 million alveoli, tiny air sacs where oxygen crosses into the blood. Together they'd cover roughly half a tennis court.
In the game
Alveoli on the walls swell, then exhale a gust that blows you and cells away and clears enemy shots. Step out of the way when one swells up.
Fun fact: Flu viruses that reach the alveoli cause pneumonia, much more dangerous than an infection of the nose.
Appears inTissue Hazards & TerrainHazards, Pits & Shafts
The liver makes bile, a detergent that breaks up fats. It also dissolves the fatty envelope of viruses like flu and HIV.
In the game
Ducts in the walls spray a jet of bile straight across the room after a flashing warning line. It burns cells far worse than it burns you.
Fun fact: That's why most viruses that spread through the gut, like norovirus and hepatitis A, have no envelope at all.
Appears inTissue Hazards & TerrainHazards, Pits & Shafts
Airway cells are covered in cilia, tiny hairs that beat about 15 times a second in coordinated waves, sweeping mucus and trapped microbes up and out (the mucociliary escalator).
In the game
A carpet of beating hairs carries anything on it the way the arrows point: you, cells, everything. Dash to cross against it, or let it sweep cells into pits.
Fun fact: Smoking paralyses cilia, which is one reason smokers get more chest infections.
Appears inTissue Hazards & TerrainHazards, Pits & Shafts
Tissues seal themselves with barriers: thick mucus layers, and tight junctions that zip neighbouring cells together so nothing slips between them.
In the game
A door sealed by the host (a mucus plug or tight junction). It won't open until you carry this area's gene. Tip: Explore this area to find its gene room.
Fun fact: Some viruses open tight junctions to spread; others are stopped cold by them.
Appears inKey Guardians & GenesSealed Doors & Genes
Sensory nerve endings line the airways. When something irritates them, the trigeminal nerve in the nose triggers a sneeze and the vagus nerve in the lungs triggers a cough, blasting irritants (and viruses) out at high speed.
In the game
Glowing nerve fibers in the walls of the Nasal Passage and Lungs. Linger on one and it glows hotter, then fires a reflex: a sneeze in the nose, a stronger cough in the lungs. The blast flings you and every cell nearby away from the wall, hurts everything caught in it, and raises Detection if you set it off. Cells flung into an abyss die. It recharges after 7 seconds. Tip: Shoot a nerve when cells crowd around it: it fires at once, blasts them away, and the host doesn't blame you.
Fun fact: A sneeze can launch droplets at over 30 m/s and spread them several metres, which is exactly how flu hitches a ride to the next host.
Appears inTissue Hazards & TerrainHazards, Pits & Shafts
Bone marrow holds stem-cell niches, pockets where blood stem cells divide into every kind of blood cell, including white blood cells.
In the game
A pod of young blood cells. Burst it (touch or shoot) to heal 12% HP, but two fresh neutrophils pour out.
Fun fact: The marrow makes about 100 billion new neutrophils every day.
Appears inTissue Hazards & TerrainHazards, Pits & Shafts
Peristalsis is the wave of muscle contraction that pushes food along the gut. It also flushes out microbes that can't hold on to the lining.
In the game
Every few seconds the gut wall clenches and a wave sweeps across the room, carrying everything with it. Watch for the flashing band, then dash through it.
Fun fact: Many gut viruses, like rotavirus and norovirus, cause diarrhoea that speeds things up even more, spreading new virions.
Appears inTissue Hazards & TerrainHazards, Pits & Shafts
Red blood cells are the most common cells in the body, around 25 trillion of them, carrying oxygen in haemoglobin. Their dimpled disc shape lets them squeeze through capillaries.
In the game
Solid cells drifting with the blood flow. They shove you around and soak up shots from both sides; three of your shots burst one.
Fun fact: Red blood cells have no nucleus, so most viruses can't infect them; malaria parasites can.
Appears inTissue Hazards & TerrainHazards, Pits & Shafts
Lymph nodes are held together by a mesh of reticular fibres. Immune cells crawl along them like roads while scanning for invaders.
In the game
Fibres strung across the node. Touching one slows you to under a third of your speed, and cells get snagged too. Two shots snap a fibre.
Fun fact: HIV can get trapped on the fibre network's dendritic cells, which keep it on display for months.
Appears inTissue Hazards & TerrainHazards, Pits & Shafts
Viruses spread between organs through airways, blood and lymph: flu can move from the nose down into the lungs, and HIV travels through the blood to lymph nodes.
In the game
A drop shaft. Walk in to fall through. You land in a freshly reshuffled layout of this same area, safe for a moment, and hunting Killer T cells lose your trail. Tip: Grab your drops first: anything left on the floor stays behind.
Fun fact: Inhaled droplets small enough can bypass the nose entirely and land deep in the lungs.
Appears inTissue Hazards & TerrainHazards, Pits & ShaftsInfect Game Mode
Neurons talk at synapses with electrical spikes and chemical signals. Some viruses, like rabies and herpes, travel along neurons from synapse to synapse.
In the game
Two neurons that fire an electric arc between them every few seconds, after a flickering warning. The arc hurts cells; shoot a neuron to fire it early.
Fun fact: Rabies moves through nerves at a few centimetres a day toward the brain.
Appears inTissue Hazards & TerrainHazards, Pits & Shafts
Evolution is full of trade-offs. A mutation that makes a virus more aggressive can also make it easier for the immune system to spot, or less stable outside the body.
In the game
Altars, each offering a trade-off: a strong boost that costs you something. You can take only one. Examples: −25% max HP for +40% damage, a full heal that raises Detection by 30, or 40 nucleotides that raise Detection by 25. Tip: Read both sides; walking away is fine.
Fun fact: Viruses that kill their hosts too quickly often spread worse; many evolve to become milder over time.
Appears inSpecial Rooms
Mutagens like radiation and some chemicals raise mutation rates. Some antivirals, like molnupiravir, work by pushing viruses into so many mutations they collapse.
In the game
A mutagenic pool. Step in to bathe. It costs 20% of your current HP and grants a random trait with better odds of a rare tier. One use. Tip: Only bathe while you have health to spare.
Fun fact: This is called 'error catastrophe': too many mutations and the virus can no longer make working copies.
Appears inSpecial Rooms
Viruses carry genes for tools that break host barriers, like neuraminidase that cuts through mucus, or fusion peptides that merge viral and cell membranes.
In the game
A gene cassette you can pick up. It opens this area's sealed doors (mucus plugs or tight junctions) and gives a passive bonus, such as mucus no longer slowing you. Tip: Grab it early; sealed doors often hide shortcuts and rewards.
Fun fact: Neuraminidase is the target of Tamiflu: block it, and new flu virions get stuck to the cell they came from.
Appears inKey Guardians & GenesSpecial Rooms
A virus can't copy itself on its own. It hijacks a host cell's machinery to make new virions, and lytic viruses then burst the cell open to release them.
In the game
The doors seal around 9 host cells. You have 18 seconds to burst them. Burst them all for a chest and a mutation orb. Each host cell drops nucleotides (and can drop RNA in Pandemic Game Mode). If time runs out, the rest escape. Tip: Piercing and explosive shots burst several cells at once.
Fun fact: One infected cell can release thousands of new flu virions before it dies.
Appears inSpecial Rooms
Viruses enter cells by binding receptors: proteins on the cell surface. Flu binds sialic acid; HIV needs CD4 plus a co-receptor (CCR5 or CXCR4), engaged in the right sequence.
In the game
Receptor pads on the floor. Either step on them in the order they light up, or hold them in sync. Solve it for a reward (sometimes a Ribozyme in Endless Game Mode or RNA in Pandemic Game Mode). Mistakes trigger an alarm that raises detection and can call cells in. Tip: Clear the room's enemies first so you can focus.
Fun fact: Some people carry a CCR5 mutation (Δ32) that makes them highly resistant to most HIV strains.
Appears inSpecial Rooms
Some viruses hide inside cells without making new copies (latency). HIV hides in resting immune cells as a 'reservoir' that drugs can't reach.
In the game
A quiet host cell you can slip into. One use. It heals half your HP, drops detection by 30 and makes every hunting cell lose track of you. Tip: Save it for when you're hurt or the Killer T is close.
Fun fact: Herpes viruses go latent in nerve cells for life; that's why cold sores come back.
Appears inDetectionSpecial Rooms
When an infection is detected, the immune system recruits waves of white blood cells to the site, guided by chemical signals called chemokines.
In the game
The doors seal and waves of immune cells pour in for 22 seconds. Survive the timer and the remaining cells retreat, leaving a chest and a mutation orb. Tip: Stay mobile near the middle; you don't have to kill everything, just survive.
Fun fact: Inflammation (redness, swelling, heat) is largely caused by immune cells flooding into infected tissue.
Appears inSpecial RoomsExtra LivesThe HUDThe Codex
Viruses mutate constantly as they copy themselves. Most mutations are harmful, but a few give an advantage and spread through the population.
In the game
A mutation orb. Touch it to choose 1 of 3 traits for this run. Traits roll a tier from common to mythic; picking the same trait again stacks it. Tip: Build around one or two strong traits rather than spreading out.
Fun fact: RNA viruses like flu make roughly one copying error per genome they replicate.
Appears inSpecial Rooms
Cancer is the host's own cells dividing out of control after mutations break their brakes. Some viruses (HPV, Epstein-Barr, hepatitis B) can help cause it.
In the game
A cancer grows here, and every area has its own: a carcinoma shielded by nodules, a growing lung tumor that spreads metastases, leukemia, lymphoma, colon carcinoma, liver cancer, multiple myeloma or glioblastoma. The doors stay open. Destroy it and the whole tumor collapses: about 30 nucleotides (more in later areas), a chest, a mutation orb, materials and, in Pandemic Game Mode, often RNA. Take too long and it keeps spreading. Tip: Deal with whatever is making it spread first.
Fun fact: Oncolytic viruses are engineered to infect and burst cancer cells; T-VEC, a modified herpes virus, is approved for melanoma.
Appears inTumors & MetastasisTumor RewardsSpecial Rooms
Infected cells and immune sentinels release alarm signals (interferons and cytokines) that warn neighbours and call in the immune system.
In the game
The eye meter (top right) tracks how aware the immune system is of you. Being spotted, getting hit, Shift and every kill raise it, and each kill adds more the more you've killed this run. At 35, 60 and 80 hunter squads arrive, each bigger than the last; at 100 a Killer T cell is sent after you. It cools down slowly once nothing has alarmed it for 5 seconds, twice as fast while you stand still. Tip: Ambush unaware cells: they deal 2.5× damage and their kills only count half.
Fun fact: Many of the symptoms of being sick, like fever and aches, are caused by these alarm signals, not by the virus itself.
Appears inDetectionThe HUDLineage & GenerationsHosts & Genome
Cytokines are signalling proteins that recruit and activate immune cells, steering them to where an infection is.
In the game
Cytokines have called in a squad of cells that already know where you are. They come through the far door and hunt you directly. Nothing they do raises Detection, but more squads come if it keeps climbing. Tip: Fight near a doorway or retreat to cleared rooms to spread them out.
Fun fact: An overreaction, a 'cytokine storm', can do more damage than the infection itself.
Appears inDetection
