West Nile virus is back on the rise in Minnesota after a four-year lull.

So far, 18 cases have been reported this year, with some severe complications requiring hospitalization, according to the Minnesota Department of Health.

The numbers have not reached Texas-size proportions -- where an outbreak of 200 cases prompted Dallas' mayor to declare a state of emergency and order aerial pesticide spraying.

In Minnesota, however, it's the first time that the number of West Nile cases has hit double digits since 2008, when 10 were reported.

"Cases have been rising quite a bit and we expect them to continue to rise," said Melissa Kemperman, a Health Department specialist in mosquito-borne diseases. She said this season may be on track to match the higher numbers of the early 2000s, when cases ranged from 34 to 148 a year.

Symptoms include fever, headache, nausea, pain and fatigue. About one in 150 people infected will develop severe complications, such as encephalitis, a brain infection.

Kemperman said that although several patients have been hospitalized in Minnesota this year, no deaths have been confirmed.

Health officials are urging the public to take precautions against mosquito bites, including using insect repellent.

This year's dry, hot weather may be contributing to the spread of the disease, officials say, because it's especially conducive to the type of mosquitoes that carry West Nile virus. In such conditions, the insect's life cycle accelerates, which speeds replication of the virus. And during a drought, standing water can quickly turn stagnant when it's not flushed away by rain or runoff.

In several states, the West Nile outbreak is shaping up as the worst on record.

Nearly half of all U.S. cases have occurred in Texas, where the virus has killed 10 people and sickened at least 230 others, according to the U.S. Centers for Disease Control and Prevention.

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Includes material from the Associated Press. Maura Lerner • 612-673-7384