Two more West Nile virus deaths have been reported in North Texas. Health officials said Tuesday that a Fort Worth man in his late 70s with underlying medical conditions is the sixth death related to the virus in Tarrant County this year.  Dallas County health officials say a man in his 60s also with underlying medical conditions is the 15th such death in the county.  That brings the 2012 West Nile death toll in Texas to at least 50. Federal health officials say this is the nation's worst year for the mosquito-borne virus since it was discovered in New York 13 years ago. Texas has about half of the U.S. deaths from the illness.  Several Texas counties have been spraying pesticide to help reduce the mosquito population.