When it rains, it pours. That’s especially true in Texas, where some much-needed moisture came with something absolutely unneeded—a West Nile outbreak of emergency proportions.

A Dallas County judge declared a public health emergency on August 10 after 175 cases of West Nile were reported in the county, according to CNN. The declaration allowed the county to receive state and federal assistance in stanching the virus' spread, including a controversial aerial spraying campaign to eliminate mosquitoes carrying the disease.

While Texas leads the nation in 2012 West Nile occurrences (537 human infections and 19 deaths, according to Centers for Disease Control and Prevention numbers released Tuesday), experts weren’t inclined to simply label the outbreak local.

“With this huge outbreak in Texas, the jury is still out on what’s going to happen with the rest of the country,” Lyle Petersen, director of the CDC Division of Vector-borne Infectious Diseases, told the New York Times last week. “But in Chicago, we’ve already observed high numbers of West Nile virus-infected mosquitoes. This is looking like a large regional event. We don’t know if the number of cases is going to drastically increase, but we do expect more cases.”

Since then the number of reported cases nationwide has shot up to 1,118, according to the CDC, with 75 percent located in five states—Texas, Mississippi, Louisiana, South Dakota, and Oklahoma. Those numbers point to one of the worst outbreaks on record, with mosquitoes likely to be active through October.

“[These] are the highest numbers of West Nile virus disease cases reported to CDC through the third week in August since West Nile virus was first detected in the United States in 1999,” Petersen said in a press conference Wednesday (the full transcript of which is available online). “In comparison, one month ago, there were only 25 people with West Nile virus disease reported to the CDC.”

More than half of all West Nile cases this year have been reported in Texas, Peterson said. The next hardest hit state is Mississippi with 79 cases. Last year, California led the nation with 158 cases reported. In 2010, it was Arizona with 167 cases, and Texas led with 115 cases in 2009.

There’s no definitive answer for the uptick in West Nile cases this year, but factors such as hot weather can contribute to increased mosquito populations while at the same time making transmission of the virus easier, Petersen said in the press conference. Local conditions also weigh in heavily.

“Oftentimes West Nile virus is a very local disease, you can have a lot of cases in one area and it has a lot to do with the local ecology of that area,” he said. “How many birds might be susceptible? The particular population of mosquitoes … frankly, [the factors] are difficult to predict and know why outbreaks occur in certain areas and not others.”

In places like Indiana and Texas, officials are treating the outbreaks with the same tactics they would any other disaster.

“One of the lessons that we learned from our disaster experiences we have to have a very organized response,” said Texas Commissioner of Health David Lakey at the CDC press conference. “We set up what we call Incident Command using our emergency management system several weeks ago so that we could have that type of coordination between the local government, state government, federal government, public health emergency management all working together.”