https://www.who.int/news-room/fact-sheets/detail/malaria
One question that gets asked is "have you traveled to another country?" When the answer is "no", then doctors no longer consider diseases that exist in other countries. So that is why they did not understand the parasitic infection until it was too late.
Some of the early symptoms resemble a bad cold.
The parasite that causes malaria (literally "bad air") can only survive in certain species of mosquitos. Those skeeters don't live in Germany. They used to live in the state I live in, but they were exterminated back in the 1950s & 1960s (thanks DDT!). And people from West Africa were naturally/genetically resistant, which was why slaves from that region were preferred over every other race in the southern US where malaria existed until the 1950s & 1960s. If you have 0 copies of the gene then you usually die (of malaria) before puberty. If you have 2 copies of the gene, then you die from sickle cell anemia (usually by your teen years). If you have 1 copy of that gene (another commenter used the term "heterozygote") then the parasite can't live in some of your red blood cells, so you survive to have children.
Germany never had it, and reported being malaria free in 1964. America, in 1970.
https://www.who.int/teams/global-malaria-programme/eliminati...