From The Day of Battle: The War in Sicily and Italy, 1943-1944, Volume Two of the Liberation Trilogy, by Rick Atkinson (Henry Holt, 2007), Kindle pp. 145-146:
In 1740, the writer Horace Walpole noted “a horrid thing called mal’aria” that afflicted Italy every summer. Before the war, the Rockefeller Foundation had published a sixteen-volume study on where the disease, which killed three million people each year, was most prevalent; Italy, infested with the mosquito Anopheles maculipennis—soon shortened to “Ann” in GI slang—had the highest malaria rates in the Mediterranean. Quinine had been used for centuries to suppress malaria’s feverish symptoms, but U.S. supplies came almost exclusively from cinchona trees in the East Indies, now controlled by the Japanese. American scientists seeking a substitute examined fourteen thousand compounds, including dozens tested on jailhouse volunteers; the best replacement proved to be a substance originally synthesized by the German dye industry and given the trade name Atabrine.
Soldiers detested the stuff, which they dubbed “yellow gall.” It tasted bitter, upset the stomach, turned the skin yellow, and was rumored to cause impotence and even sterility. Many soldiers stopped taking it, prophylactic discipline grew lax, and proper dosage levels were misunderstood. Moreover, some malaria control experts failed to reach Sicily until weeks after the invasion. Soldiers also grew careless about covering exposed skin in the evening. Protective netting was in short supply, and insect repellent proved ineffective: troops agreed “the mosquitoes in Sicily enjoyed it very much.”
More than a thousand soldiers afflicted with malaria in North Africa on the eve of HUSKY had been left behind when the fleets sailed. On July 23, doctors detected the first case contracted in Sicily. By early August thousands of feverish, lethargic soldiers had been struck down. Ten thousand cases would sweep through Seventh Army, and nearly twelve thousand more in Eighth Army. (The swampy Catania Plain was particularly noxious.) All told, the 15th Army Group sustained more malaria casualties than battle wounds in Sicily. A medical historian concluded that “the disease record of the Seventh Army on Sicily was one of the worst compiled by any American field army during World War II.” With soldiers also suffering from dengue, sandfly, and Malta fevers, distinguishing one malady from another became so difficult that many patients were diagnosed simply with “fever of unknown origin,” soon known to soldiers as “fuo.”