NAIROBI, Kenya (AP) – Kenya announced its first polio infection in 20 years on Wednesday, after a 4-year-old girl was diagnosed with the disease along the country’s remote border with Sudan.

“In a country free of polio, when you make a diagnosis of one case of polio the definition is an outbreak,” said Dr. David Okello, country representative of the World Health Organization. For every child paralyzed by polio, there are about 200 other asymptomatic cases who can spread the disease to others.

Okello said they were investigating a second case in Lokichoggio, 900 kilometers (560 miles) north of the capital city of Nairobi, where an infant had shown symptoms of the disease.

“Really we are not sure, there may be other cases,” said Okello.

Polio is an infectious disease that mainly strikes children under five. It is spread primarily by the feces of an infected person getting into the food chain. It causes paralysis and can be fatal.

In 2006, two refugees escaping the war in Somalia were diagnosed with the disease at the Dadaab refugee camp at Kenya’s eastern border with Somalia. That outbreak was contained before it spread.

Okello said the disease may have spread from south Sudan, where a polio outbreak occurred in early January.

He said many Kenyan children were not immunized due to postelection violence in 2008, which left more than 1,000 people dead and 600,000 people displaced from their homes. Many have still not returned home.

Okello said coverage of the immunization campaign was 100 percent before the violence but has dropped to 60 percent.