LONDON (AP) -- With a field that features five of the seven fastest men's marathoners in history, Sunday's race in London shapes up as a showcase of Kenyan distance running.
Yet, the specter of doping is casting a shadow over the London Marathon following a spate of positive tests by athletes from the sport's long-distance heartland in recent years -- notably Rita Jeptoo, winner of women's marathons in Boston and Chicago.
Wilson Kipsang, the 2014 winner in London, acknowledged that Kenya's reputation in athletics has been damaged by the positive doping tests, even though he says 99 percent of its athletes are clean.
"We have people taking advantage of the ignorance of some guys mainly to kill the sport," Kipsang said, referring to coaches in Kenyan athletics.
A German TV documentary in 2012 alleged doping was common in Kenya.
"There is no awareness," Kipsang said. "Some athletes use some medication because they go to hospital, they are sick, they are prescribed some medicines, but they are given substances that are banned by the World Anti-Doping Agency."
Kipsang is in top form after winning his last three races in the World Marathon Majors series and is looking to become the fourth man to win London three times.
There was even talk of the world record being broken, even though the twisty nature of the London course makes that difficult.
Kipsang's biggest rival is set to be Dennis Kimetto, who set a world record of 2 hours, 2 minutes, 57 seconds in Berlin last year, and is making his first appearance in London. They are racing against each other for the first time.
The Kenyan presence is bolstered by Stanley Biwott, second in London last year; 2011 winner Emmanuel Mutai, who ran the second-fastest time of 2:03:13 behind Kimetto in Berlin; Geoffrey Mutai, who has won marathons in Boston (2011) and New York (2011, '13); and Eliud Kipchoge, who won the Chicago and Rotterdam Marathons in 2014.
"Sometimes it is more interesting to have guys like this all racing together," said Kipsang, who is predicting a tactical race. "My main aim is not to break the world record but to retain the title."
Kenyans should also dominate the women's race, with defending champion Edna Kiplagat facing her biggest challenges from countrywomen Mary Keitany, Florence Kiplagat and Priscah Jeptoo. Ethiopia's Aselefech Mergia is also a threat after winning the Dubai Marathon in January in 2:20:02.
Keitany is the fastest woman in the field and bidding to become the third woman to win the London Marathon three times. In that exclusive club is Britain's 41-year-old Paul Radcliffe, who is taking part in her last marathon and will be running with the masses rather than in the elite field.