( CNN ) -- Cases of West Nile virus are up 25 % over the past week and are expected to rise further over the next several weeks , the U.S. Centers for Disease Control and Prevention said Wednesday . As of Tuesday , 1,993 reported cases of West Nile virus have been reported in humans , including 87 deaths . Last week , the CDC said there were 1,590 cases with 66 deaths . `` As we expected , the number of humans with West Nile virus disease continues to rise in the United States , '' said Dr. Lyle Petersen , director of the CDC 's Division of Vector-Borne Diseases . `` We expect this increase to continue for the next several weeks , probably until October . '' The number of West Nile cases is the highest reported to the CDC through the first week in September since 1999 , when the mosquito-borne virus was first detected in the United States . Fast facts on West Nile virus . More than 70 % of cases are in six states : Texas , South Dakota , Mississippi , Michigan , Oklahoma and Louisiana , officials said . Texas bears the brunt of the outbreak , with nearly 45 % of cases . Wednesday 's briefing focused on how Hurricane Isaac may have affected the outbreak and how Texas is managing its high number of cases . `` As of now , 2012 is the worst year in the state of Texas for West Nile disease , '' said Dr. David L. Lakey , commissioner of the Texas Department of State Health Services . He says that before this , 2003 was the worst year for the virus . Although Petersen did not give any specific numbers associated with states affected by Hurricane Isaac , he stressed that the CDC is working with state and local officials in those areas to offer assistance on managing infestations . Experience with natural disasters such as hurricanes has shown that West Nile virus cases do not tend to increase in their wake , he said . However , people who spent more time outdoors because they were displaced from their homes or during recovery efforts may be more likely to contract the virus . Who 's at risk for West Nile virus ? Aerial spraying has sometimes been used to control mosquitoes after hurricanes , Petersen said . In Texas , spraying has been effective in areas that utilized it , Lakey said . A 93 % reduction was seen in the density of mosquitoes in areas that received two consecutive sprays , he said . Unsprayed areas showed increases in virus-carrying mosquitoes , and places that were not sprayed consecutively showed smaller reductions in mosquitoes . Protection against mosquito bites is the best defense against West Nile virus , Petersen said . He recommended wearing long pants and sleeves during dusk and dawn -- prime mosquito times -- to prevent bites . In addition , he said , wear insect repellent when you go outdoors ; install or repair screens on doors and windows ; use air conditioning if possible ; empty standing water from outdoor containers and objects that collect water ; and support local mosquito control programs .
Cases of West Nile virus are up 25 % in the past week . Officials say they expect cases to rise for several more weeks . There have been 87 deaths from the mosquito-borne virus .