It's staggering how many games feature a malady of some kind. Here's the best of the worst...

#10
Game:
The Elder Scrolls IV: Oblivion
Disease:
Vampirism (Porphyric Haemophilia)
Risk factors:
Hanging out with Vampires
Being a virgin
Symptoms to look out for:
Biteyness.
Negativity toward days at the beach.
Tendency to become bat-like*
A strong dislike of Italian food.
Friends often complain to you of anaemia.
Bed is all soily.
Always insist on being ‘Noughts’.
Celebration of your 300th Birthday.
Unreasonable fear of Buffy.
Takes longer to brush teeth.
*Like a bat.
What to do if you think you have vampirism:
Avoid churches. Consult your physician immediately. At night. And tell him to come alone. Also remember to ask permission before entering houses.
Prognosis:
There is no known cure for Vampirism’s antisocial symptoms. However, if you manage to find an old woman called Draklowe in a tumbledown house in the countryside, a cure may well be on your horizon. Despite the difficulty of obtaining said cure, however, Vampirism is not fatal. In fact, Vampirism is the only disease that can cure all other known diseases.

At least with vampirism in Oblivion you won't be short of friends.

#9
Game:
Theme Hospital
Disease:
Bloaty Head (Bloatius Noggis)
Risk factors:
Egotism
Wearing a low-pressure hat
Symptoms to look out for:
A bloaty head.
What to do if you think you have bloaty head:
Theme Hospital recommends immediate popping. Ensure you use a clean needle or stylus.
Prognosis:
As long as your head is popped manually before bloatiness leads to involuntary poppage, the outlook is good.

#8
Game:
Super Mario Bros.
Disease:
Fungal Infection (Candidosis)
Risk factors:
Living in the Mushroom Kingdom
Possession a mushroom-related name, such as Toad*
Redirecting plumbers.
Symptoms to look out for:
A mushroom-like body shape
A very wide head (Not to be confused with Bloaty Head)
Vaginal itching
What to do if you think you have a Fungal Infection:
Escape the Mushroom Kingdom and if possible, apply an over-the-counter remedy such as Canesten or an industrial fungicide, such as OMACIDE IPBC 30.
Prognosis:
If symptoms have progressed unhindered all the way to the stage where to all intents and purposes you are a mushroom, it’s probably too late. Best you can hope for is to try to find somewhere dark and moist and stay there.

*Okay, it’s frog-related really, but they mean it like Toad-as-in-toadstool. Nintendo obviously couldn’t have just called him Stool, since that again, has an entirely different set of connotations.

#7
Game:
Far Cry 2
Disease:
Malaria (Plasmodium Falciparum)
Risk factors:
Spending time in these parts of the world.
Hot humid conditions and standing fresh water, which are fundamental to the breeding of mosquitoes.
Symptoms to look out for:
Blurring of vision during intense battle scenarios
Need to trek back twenty minutes to find more pills
Ability to carry only three pills at a time
Extreme frustration
Staggering while being shot at
Death
A ruined videogame
What to do if you think you have malaria:
Visit a priest for pills. Then visit him again. Then either repeat until dead, or simply eject the disc.
Prognosis:
Not good. Occupying the unenviable position of this list’s most irritating and pointless malady, malaria will stay with you until the bitter end. Oh joy.

… continued