Washington, D.C. — Nigerian presidential candidate Umar Yar'Adua is undergoing medical treatment in Germany and is in "good health and is stable," a diplomatic source in Germany told allAfrica Wednesday.

Muktar Meimaje, Yar'Adua's campaign chief of staff, said from Nigeria that Yar'Adua developed a cough. He said the candidate "has been working on a very intense schedule since the primaries" often "working 18-hour days" and decided to visit his doctors in Germany "for a checkup."

"He has been going to the doctors in Germany for a long while," said Meimaje. "There is nothing wrong with having a medical checkup," Meimaje said in a telephone interview with allAfrica. "I see no reason why - if you are comfortable with certain doctors and you can afford it - you should not go."

Countering reports of Yar'Adua's death, Meimaje said "all the rumors are just that – rumors."

The campaign will continue on schedule and Yar'Adua is expected to return to Nigeria by the end of the week, he said.

Yar'Adua, candidate for the ruling PDP and governor of Katsina state, is considered the front-runner in elections scheduled for April.