What made you want to look up mean? Please tell us where you read or heard it (including the quote, if possible).
Malaria - and its cousin, yellow fever - had significant implications during the war and the debilitating consequences of the disease were already certain before the Civil War had started in earnest and well before its final history had been written.
In this article. Yellow fever is a viral infection transmitted by a bite from infected mosquitoes most commonly found in parts of South America and Africa. When transmitted to humans, the yellow fever virus can damage the liver and other internal organs and be potentially fatal. The World Health Organization estimates there are 200,000 cases of yellow fever worldwide each year, resulting in 30,000 deaths.