Story highlights Four young children in two provinces have been identified with paralysis caused by polio infection

The World Health Organization is boosting monitoring, testing and immunization efforts

(CNN) Two separate outbreaks of polio have been reported in remote parts of the Democratic Republic of Congo, a setback for large-scale efforts to eradicate the highly infectious and potentially fatal disease.

There is a high risk of the disease spreading across the country, though not beyond its borders, the World Health Organization (WHO) warned Tuesday in a statement

Four cases have been reported in children between 17 and 36 months old in the provinces of Haut Lomami and Maniema, both in the center of the country.

All four children are paralyzed and are being monitored, the WHO said. Their families also are being monitored and getting tested regularly to see if they become infected.

"This is not unusual; it is usually the very young who are most at risk," said Oliver Rosenbauer, WHO Global Polio Eradication Initiative spokesman. "It further underscores the risk, how quickly polio can re-emerge in polio-free areas."

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