NEW ORLEANS (AP) — Louisiana's health department says a seriously ill Caldwell Parish resident is the first person this season to be diagnosed with West Nile virus.

State epidemiologist Raoult Ratard says it's a very late start. He says the cool spring apparently kept mosquito populations down.

The case confirmed Monday is the most serious form of the disease, affecting the nervous system.

By this time last year, 31 such "neuroinvasive" cases had been diagnosed. There were 160 last year, plus 191 cases of flu-like West Nile fever. Another 46 people were diagnosed without any symptoms, 34 of them after giving blood. It was the worst season since 2002.

About 90 percent of all cases are asymptomatic. About 10 percent develop West Nile fever.

Copyright 2013 The Associated Press.