Riley Olsheski

Riley Olsheski had a heart transplant as a baby. He's unable to receive the measles vaccine and depends on others around him being immunized. (Mallory Olsheski)

Measles cases in southern Ontario are a worry to an Ottawa-area mother whose three-year-old son can't be vaccinated.

Mallory Olsheski's son, Riley, had a heart transplant at five months of age. He's on immune-suppressing medications so he won't reject the heart and is unable to receive the measles vaccine, which contains live virus.

"Measles could be deadly to someone like Riley," Olsheski said Thursday after health officials in Toronto announced a fifth case in the city.  One adult case was reported in Niagara.

"I do shelter him more, especially if there's an outbreak."

The Pembroke mother said her son has a hospital appointment in Toronto in March and it's nerve-racking to think of potential exposures.

Toronto Public Health said a total of five lab-confirmed cases of measles have been reported. The cases include two children under age two and three adults, all from separate families.

Olsheski urges parents opposed to measles vaccination to research the seriousness of the illness. Complications can include encephalitis and seizures.

5 babies at Chicago daycare infected

In the U.S., five babies at a suburban Chicago daycare centre have been diagnosed with measles, adding to a growing American outbreak.

Officials are investigating the cluster of measles cases at KinderCare Learning Center in suburban Palatine, the Illinois and Cook County health departments said.

All the children are under 1 year old and therefore would not have received routine measles vaccination, which begins at 12 months.

Public health officials have reported that more than 100 people across the United States have been infected with measles, many of them traced to an outbreak that began at the Disneyland theme park in Anaheim, Calif., in December.

Decades ago, when measles was common, people were more aware of how devastating the infection could be, especially for young and vulnerable children, said Dr. David Goldfarb, a pediatric infectious disease specialist at McMaster University in Hamilton.

"The best way to protect them is by making sure that you are also protected," through vaccination, Goldfarb said.

In Toronto, pediatrician Dr. Marvin Gans is receiving more calls from parents.

"There's an increasingly big pool of susceptible children," Gans said.

Measles is a highly contagious respiratory disease that causes fever, red and sore eyes, runny nose, cough and a characteristic rash.

With files from Reuters