Congo's health ministry says unknown disease is severe malaria

Does Plasmodium do that? Sure was news to me!

I guess the main question then becomes, is it spreading in a highly unorthodox manner, by respiratory droplets, or are the familial clusters etcetera just an artifact of similar exposure to infected mosquitos?

I can see how it might not take a whole lot of mutations to get a strain with elevated affinity for the lungs, and it's not like they take an insignificant share of the blood-flow at any given time in the first place.

No, it does seem to be known actually. Wikipedia has a fair bit about it under "Complications" https://en.wikipedia.org/wiki/Malaria#Complications (as well as some under "Cause") and links Walter et al. (2012) "Respiratory Manifestations of Malaria" https://journal.chestnet.org/article/S0012-3692(12)60464-4/a...

Okay, still horrible for the afflicted, but almost certainly not anything explosively contagious then, and well understood as well as generally treatable and preventable, unless e.g. severe lack of resources prevents that.