Anyone who wants to understand southern Italy should read "Il Gattopardo" (The Leopard) by one of the last peers of Sicily.

Not sure about the malaria cause, but it is true that the South of Italy has traditionally been far less free and far more dependent on agriculture than the north. It has a history of being conquered over and over again by different foreign powers which led many times to extractive regimes (and inevitably less innovation - some parallels to the American south before the abolition of slavery). Such an environment led to them invent something even worse than a disfunctioning state, namely the mafia.

Until reunification in the 1860s Italy had a bunch of city-states in the North, tight fisted control by the Church in center Italy, and an extractive / agriculturally dominant economy in the south ruled by the aristocracy.