Texas is reeling from Hurricane Harvey, with thousands of residents displaced by flood waters and a climbing death toll. But the dangers go beyond the rising waters, as the storm brings an array of public health dangers, from mosquitoes to mold.

Here are five public health threats facing authorities in Houston.

Contaminated water

Huge swaths of Houston are submerged in water — as much as 30 percent of Harris County, which includes the city and surrounding towns. In addition to the floods, which will take time to recede, the water also poses problems from contamination.

Experts say all sorts of chemicals are likely to be in the water.

“Pick a toxin, that's going to be in the water,” said Dr. Georges Benjamin, executive director of the American Public Health Association. “Oil and grease and chemicals.”

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Houston is a major center for the oil and gas industry, adding to those worries.

Exxon Mobil Corp. said Tuesday that two of its refineries were damaged and released pollutants. The full extent of the damage was not yet clear.

Contaminated water could lead to rashes, burns or a range of other symptoms.

A chemical plant owned by the company Arkema is also in danger. Executives said they had no way or preventing the chemicals from exploding after the plant flooded.

Mosquitoes

The stagnant water will also provide new pools for mosquitos to breed, bringing with them diseases.

Houston was already “the mosquito capital of the United States,” said Dr. Peter Hotez, dean of the National School of Tropical Medicine at Baylor University in Waco, Texas.

Now, the number of mosquitoes is only expected to grow. Flooding may wash away some of the breeding pools, but once the waters recede mosquitoes will recover.

“We're gonna have an explosion of mosquitoes because there's so much standing water, which is all breeding sites,” Dr. David Persse, director of Houston’s Public Health Authority, told CBS.

Mosquitoes carry diseases like the West Nile virus, Zika virus, chikungunya and dengue. And the effects are likely to last.

“The impact on mosquito-borne illnesses could be around for another year,” Hotez predicted.

Lost medicines

In addition to a range of new health dangers, the storm makes it harder for people to treat health conditions they already had.

Many of the thousands of people who had to leave their homes behind could be without access to the prescription drugs they take.

Benjamin said it would be a “real nightmare” getting people the medication they need, noting that many seniors do not know the names of all the drugs they take.

Some people also need access to medical equipment, such as those who need dialysis.

Health and Human Services Tom Secretary Price told reporters that his department is working to find people places for dialysis treatment and to help people who need other equipment, like oxygen machines.

“What HHS does is identify where those people are or who they are, and then, in concert with the local government, let them know and so somebody can go out to the house or the apartment and make certain that they're doing all right,” Price told reporters.

Mold

Mold is a longer-term issue that evacuees may not realize is a problem until after the flood waters recede.

According to The Washington Post, investigators with the Centers for Disease Control and Prevention found mold in the walls in half of 112 water-damaged homes two months after Hurricane Katrina hit New Orleans in 2005.

“The amount of water they have had, you can’t avoid the mold. It will happen in homes that will be underwater for a longer period of time,” said Maureen Lichtveld, professor and chair of the department of global environmental health sciences at Tulane University School of Public Health and Tropical Medicine.

She advised residents who return to previously flooded homes to gut the interiors and rebuild, rather than wasting time and money to test for mold that’s almost an inevitability.

Mold can trigger allergic reactions and asthma attacks. In some extreme cases, exposure to mold can cause death.

“Mold is a really big problem as people go back into their homes,” Benjamin said.

Spread of infectious diseases

With thousands of people crowding into shelters after their homes were evacuated, the risks for disease to spread due to close contact will spike.

“There's going to be infectious diseases,” Benjamin said, naming the common cold and norovirus as the most frequent.

The Federal Emergency Management Agency says that more than 30,000 people are in 230 shelters across Texas, providing plenty of opportunities for disease to spread from person to person.

“The solution is good hygiene and handwashing,” Benjamin added.

Any health problems will be more dangerous for the most vulnerable — such as the elderly and the poor, said Lichtveld.

But beyond the physical ailments, she said, mental problems will be much longer lasting.

Long term, depression and mental health concerns “linger much longer than physical consequences. We’re still seeing that 12 years after Katrina,” Lichtveld said.