It took me a long time to work out how to do Fungus on Brutal, let alone Mega Brutal; once you understand it, though, it's quite easy. As you will know, getting it to infect is the hard thing, but getting it spread around early does help (ps, Brutal can be done with only 2 spore bursts!). Please note, I play on my tablet, I don't know how well this strategy will work on Xbox One or other devices.
Here's how I did it:
Start in Brazil
Don't forget - if any symptoms mutate before the cure is found, devolve them immediately (to get the points and to keep it unnoticed). Do so even after the cure has started, as it still gives you a point or two.
Order of play:
All Spore Bursts (SB) in one circle, including the Spore Eruption (SE)
(2 at a time to make sure you can pop them all!)
All Spore Bursts in the second circle, EXCEPT FOR SE.
Cold Resistance (CR) 1
Drug Resistance (DR) 1
Around now the disease should be noticed - make sure you have 29 points for Genetic Hardening 1 & 2. It's imperative to get these as soon as possible, as they really slow the cure down.
Extreme Bioaerosol (EB)
After you've put all these in play, give it a bit longer, then look to see which countries are still not infected. If there are a few that don't have land near them (like Greenland, the Phillipines, the Caribbean, New Guinea), do the second Spore Eruption. The others will get infected anyway. Be patient and you shouldn't need to get Spore Hardening, thus saving yourself 5 points. You might even get away with not getting the second SE.
Get Pulmonary Fibrosis
The last time I did this route, the cure was at 55% when the last person was infected. It definitely shouldn't be any higher than this if you're going to win!
Immediately the last person is infected:
Devolve EB, Air 2, CR 1 and CR 2 - 6 points refunded
Get Total Organ Failure (TOF).
If the cure is over 65%, which it soon will be, get Genetic Reshuffle (GRes) 1, then GRes 2 and GRes 3 the minute you can - shouldn't be too hard because the points roll over really quickly on Fungus once you've got TOF going.
I needed Coma and Paralysis to make sure the cure didn't beat me.
I finished it with the cure on 86%, with 8680 points.