Video from 2016.
"Today in the west, most people have forgotten how deadly malaria used to be, although there were serious malarial epidemics in many parts of Italy as recently as the 1950s. But each year, mainly in Africa, it still kills over two million people, most of them children. While there are several mentions of a disease sounding very similar to malaria in historical documents from Roman times, there has never been any hard evidence of its presence ... "But last year , for the first time, a British scientist proved conclusively that the most dangerous type of malaria was a killer in imperial Rome."" Source: BBC (2011).
Note: The evidence shows that a serious malaria epidemic swept through Italy around the same time as the collapse of the western Roman empire. For instance, some researchers believe that Alaric, the famous king of the Visigoths who sacked Rome in 410 AD, died of malaria:
According to Forbes (2016), "Alaric could have become infected with malaria anywhere in his Italian travels, even in Rome while he was sacking it. The disease was well known in ancient times and wasn't fully eradicated from Italy until 1970. But Calabria, in Italy's toe where Alaric died, 'was classified as the most affected region, with active transmission foci concentrated especially along the coasts and the valleys of its broad streams,' the researchers write. 'A fatal form of malaria contracted during his stay in Calabria seems to be the most probable cause of the king's death.'"
Comment: Malaria outbreaks could have had a major effect on the readiness of Roman legions during the barbarian invasions, but the empire had already been seriously weakened by decades of civil war, political corruption, religious upheavals, administrative division and general mismanagement. By the fifth century, the money and power had already been transferred to the east and the western half of the empire was just a rotten husk waiting to collapse. It wouldn't have taken much to bring it down.