A 5-year-old Wright County boy is fighting for his life after contracting a strain of E. coli that killed his younger sister earlier this week.

Kade and Kallan Maresh were sickened by a shiga toxin-producing bacteria on July 9, eventually sending them into acute kidney failure. State health officials are investigating the source for the E. coli that eventually led to hemolytic uremic syndrome (HUS), a complication of the bacterial infection.

On their CaringBridge site, parents Joseph and Tyffani Maresh said the toxin from the bacteria attacked their 3-year-old daughter's kidneys and her neurological system. "Her brain and heart were being damaged," the family said. "Our sweet sweet little girl lost the battle. … Kade is still fighting." Kallan would have turned 4 next month.

"We were able to give Kallan a bath and put her favorite jammies on her," her parents wrote in a journal entry on Sunday. "We got to hold her free of tubes and snuggle and kiss her. She is the most amazing little girl in the world. Our hearts are aching with the deepest sadness."

Deaths resulting from HUS, which causes kidneys to stop working and red cells to be destroyed, are very rare, said Joni Scheftel, supervisor of the zoonotic diseases unit at the Minnesota Department of Health. Children and the elderly are most at risk, she said.

In an "abundance of precaution," the animals at a petting zoo the children recently visited were taken off display, she said.

But the children could have been infected with E. coli from any number of other sources that health officials are investigating, she said.

Besides petting zoos, E. coli can be found in contaminated meat or produce, swimming pools or lakes contaminated with feces.

Health officials may be able to zero in on the source by next week once lab results are in, Scheftel said. So far, no other similar cases have been reported, she said.

The family said their son has had blood transfusions and is on kidney dialysis. "He has a long road to recovery and we hope and pray the toxins stay away from his brain and heart and other organ systems," the family said.

Most types of E. coli are normal and harmless, according to a Mayo Clinic website. But other strains — including those that cause HUS — are responsible for serious foodborne infections.

Although health officials are in the early stages of their investigation, Scheftel said the children's infection was what's called an STEC, a group of E. coli that produces a toxin. One of the best known STECs is called E. coli O157:H7.

Last year, 326 cases of STEC were reported in Minnesota, including 122 E. coli O157:H7 cases and 14 HUS cases, Scheftel said. The last fatal pediatric HUS case was in 2014, she said.

HUS, which is a serious condition, usually develops in children after five to 10 days of diarrhea — often bloody — caused by infection with certain strains of E. coli bacteria, according to Mayo. Timely and appropriate treatment usually leads to a full recovery for most people, especially young children, according to the Mayo website.

The family said on CaringBridge that the two children began suffering from nonstop bloody diarrhea and vomiting a week earlier. After several visits to the emergency room, the two were rushed by ambulance to Children's Hospital at the University of Minnesota.

On Monday, the parents said Kade's blood work has not yet shown improvement.

"He got a special visit from some of his closest friends and family today and it was so fun to see him smile and be so talkative," they wrote. "We have not got to see that in a long time."

By Tuesday afternoon, a gofundme page had raised more than $45,000, double its $20,000 goal, to help the family with medical expenses.

Mary Lynn Smith • 612-673-4788