Stream of Blight seems like a spell designed to be used against players.
Black Fever: Meters? In D&D5E? Has a strange feel to me. Americans and fantasy worlds should use imperial. You know, for fun, or to make fun of. *giggle*
For reference: 100 meters ~~ 328 feet.
Now for every 100 meters and each hour effected the target takes 1d6 damage. I recon I can walk between 2 and 5 km in 1 hour, depending on terrain. So I'd arguably would have to roll between 21 and 51 d6 per hour. That's a lot of damage.
Catalapsy: Prone? Spend half movement to get up? Does this effect start combat? DC10 saving throws to end seizure each round? I mean this potentially happens during travel, out of combat... Feels very strange to me to count rounds and such.
I don't know. I find it strange to punish out of combat overworld travel. I'd be in favor of limiting such an effect to short and long rests. Maybe change the effect so the target would have to save a roll and on a fail they lose X temporary HP until they find someone who can cure diseases. (Instead of a professional in a near town. It can mean the same, or a player with an appropriate spell.)
Not sure if I made a coherent argument. Am pretty tired. Will check back tomorrow!