EDIT 2: Added rarity. ;P
EDIT: Added cure since many asked. :3

So, I was exploring with my king, right? And I come across the familiar elephant dung pile; we pull out a feather and all of a sudden, this thought came to me.
'What if they added parasites to this game, to make it more dangerous/interesting?'

If the admins DID add parasites, I'd think it should be something like this (and yes, I did research parasites in Africa that'd affect lions):

Babesia/Babesiosis
This parasite is transmitted through ticks. These ticks can be found anywhere where domestic dogs come in(so, everywhere). These little buggers will bite a exploring lion and have a 50/50 chance of contracting the disease, Babesia. This disease can be spread by the ticks hitching rides on the lions and infecting their pridemembers OR any lion's den(page) they visit.
'You start to notice Cub is itching alot these past couple days. Perhaps you should help them, or you should finish snacking on this gazelle...
Yep, you'll just finish this gazelle.'
'Cub is starting to get ill with a fever. You try to give them a herb to slow their fever, but they claw you and you get a nasty cut on your lip. Ouch.'
'Cub is getting skinnier as the weeks that go by. They crawl to you and cuddle with you, while you look at them with pity. D'aww.'
'Cub has sadly passed on due to complications.'

Trypanosoma/Trypanosomes
These parasites are transmitted through tsetse flies. They can be found anywhere on the map, but are more common around the Marshlands and Waterhole. When infected, the lion will soon go into a 'sleeping sickness', where they will sleep ALL day, but have insomnia at night. Since lions are known to sleep throughout the day, your king will brush it aside, posing a danger to the infected lion.
'You trot up to a grumpy looking Cub. As you nudge them to ask what's the matter, they snarl and swat at you in the face. You back off, leaving the steaming furball to simmer down.'
'Cub is starting to sleep more than usual, but you brush it aside, since that's what everyone is doing these days.'
'Cub's neck is getting more swollen through the days. You comfort them with snuggles and licks. Not weird. Not weird at all. *cough* creep *cough*'
'Cub has passed in their sleep.'

Theileria
This parasite is transmitted through ticks. The Theileria is similar to Babesa, but has less symptoms. This parasite is dangerous, in the way, the infected lion has a high chance of getting anorexia.
'You start to notice Cub is itching alot these past couple days. Perhaps you should help them, or you should finish snacking on this gazelle...
Yep, you'll just finish this gazelle.'
'Cub is starting to eat less and less, making them skinnier. Or maybe they're just getting slimmer from those extra patrols you're putting them on. Heheheh.'
'You catch Cub barfing up their meal on the ground behind a bush. You gently comfort the lion with a pat on the head as they stalk off afterwards, angry you caught them.'
'Cub has started to get weaker by the day, and they smile at you as you comfort them by your presence.'
'Cub has passed from anorexia.'

Cure:
This is a cure for ALL parasites. At only 50 SB, you can cure any lion, and even yourself. (Maybe it should be called 'Sky Gift' or 'Hell Destroyer'?) This has 10 uses.

Rarity:
Each disease is rare to get, at least every 2 out of 10 members' lions will get infected; so no need to totally stress! ^^

COMMENT BELOW IF YOU HAVE ANY EXTRA IDEAS FOR THIS