By Tom Miles
GENEVA (Reuters) - The World Health Organization's battle to eradicate Guinea worm is being hampered by conflict and infections in dogs but cases have fallen to just 17 so far in 2016, the doctor leading the fight told Reuters on Wednesday.
The debilitating parasite afflicted 3.5 million people 30 years ago but is now endemic in only four countries: South Sudan, Chad, Ethiopia and Mali.
"Globally we have never been so close to Guinea worm eradication as now," Dieudonné Sankara said. "It will be a colossal achievement."
Victory over the worm, which grows up to a meter long before emerging through the skin and which lays its eggs in water, has been repeatedly delayed. But Mali has had no cases this year, while South Sudan has had five, Ethiopia two and Chad 10.
Although the decline in the global number of cases has leveled off, one worm can cause 80 new cases after its incubation period of 10-14 months, so keeping cases low signals the battle is being won.
But the security situation in the endemic countries is a complicating factor, as health workers and volunteers often venture hundreds of kilometers into lawless areas, said Ashok Moloo, a WHO information officer.
Another challenge was the discovery that dogs - mainly around the Chari river in Chad, but also in the other countries - were picking up Guinea worm infections too.
That required a new fight, to control the disease among the dog population. In 2015, more than 500 dogs in Chad, 13 in Ethiopia, and one each in Mali and South Sudan, were reported with emerging Guinea worms.
Moloo said WHO was optimistic that the dog problem had peaked, although the incubation period meant it was premature to be sure, and the new challenges were unexpected.
"People warned us a few years ago: 'You're moving fast, but you will see'," said Sankara. "And now we are seeing."
(Reporting by Tom Miles; Editing by Catherine Evans)