NEW ORLEANS (AP) — Louisiana and Mississippi are leading the nation in the number of people who have become seriously ill from West Nile virus this year. State health departments are warning residents to take precautions against mosquitoes, which spread the virus.

The Centers for Disease Control and Prevention says that as of Aug. 21 , Louisiana had 18 cases of West Nile encephalitis or meningitis, out of a national total of 133. Mississippi had 15 “neuroinvasive” cases, Texas 14 and California 12.

South Dakota had nine, Iowa seven, Nebraska six and Alabama and Pennsylvania five each.

CDC figures lag behind state reports. Louisiana reports there have been 31 residents with dangerous nervous system infections and 13 cases of flu-like West Nile fever. Mississippi has reported 25 total cases.

Louisiana’s state epidemiologist says the number of cases depends on local factors.