Malaria is caused by a parasite in your blood stream.
Back then when you had it, it would regularly symptomatically flair up once contracted it. You don’t get immune, like mumps or measles. It was a very bad thing,
BTW - World War II: Many troops had to suffer casualties by inflicted malaria even in World War II. Gen. Douglas MacArthur’s predicament in May 1943 is very clear: “This will be a long war if for every division I have facing the enemy I must count on a second division in hospital with malaria and a third division convalescing from this debilitating disease!” It appears that the general was not at all worried about defeating the Japanese, but was greatly concerned about the failure to defeat the Anopheles mosquito! 60,000 U.S. troops died in Africa and the South Pacific from malaria. U.S. Forces could succeed only after organising a successful attack on malaria.
“..it would regularly symptomatically flair up once contracted it.”
Interesting. I did some work in Papua New Guinea and one of our local workers didn’t show up. His friend said he had malaria. I had this worried look on my face and his friend said “No problem, he should be back to work next week”. So perhaps this was not so much him “getting” malaria, but just the symptoms showing up again.