"If your immune system is very efficient, it will try to attack the dead worms" that the medicine kills, Katabarwa explained. "The itchiness that will be triggered is incredible. It happens within 10 minutes."
But most of the reaction subsides after two days. During that time, other biting insects such as mosquitoes, lice and bedbugs also die if they attempt to bite the treated patient.
Because of the observed benefits of treating river blindness, infected people agree to take the medication despite the side effects, Katabarwa said.
"When people see you with that skin, they don't want to be near you," Katabarwa said.
How disease creates outcasts
One patient who made a big impression on Katabarwa was Semanza from the Rukungiri district of Uganda. In 1992, Semanza's skin looked like it was covered in dried mud, and flies swarmed around him. No one from his village wanted to be near him and he lived in a hut behind his family's home, separated from everyone else.
"He was really forgotten," Katabarwa said. Semanza's skin was so thick, because of river blindness, that it could break a needle.
Katabarwa told the local health workers to give Semanza a dose of ivermectin every three months, which is more often than the standard distribution.
Years later, when Katabarwa visited again, a man approached him and hugged him, smiling. "Who are you?" Katabarwa asked. It was Semanza. Two years later, they reunited again, and Semanza revealed that he had married and wanted many children.
Katabarwa also remembers educating a particular community in northwest Uganda in 1993, which had all the right conditions for black flies that transmit river blindness to breed.
A group of women in the community told Katabarwa that because of river blindness, people from surrounding areas did not want to marry anyone from their village. As a result, marriages had to happen within the community, including among relatives. Incest was strictly forbidden in their culture, but because of river blindness, it happened quietly, Katabarwa said.
When Katabarwa returned five years later, the skin of infected individuals had greatly improved, and marriages with outsiders were happening again.
"These are stories of sadness, but after a few years there is hope," Katabarwa said.
Katabarwa has taken the approach of making use of Ugandan villages' kinship structures to assist with health care.
People in villages often live on the land that belonged to their families several generations back, and do not move away in adulthood. This means that cousins live near each other, too, and will help with care for family members who are absent when health workers visit.
It is easier and more efficient to distribute medications when tapping into these large family structures, Katabarwa said. Through this approach, many more women have joined the effort to distribute the medicines because they are comfortable working among their family members.
Elimination in 2020 is the goal for Uganda, but river blindness is harder to control in some parts of the country because of environmental and political factors, Unnasch said.
There are places where insecticide resistance is a problem with a particular species of black fly that also moves around a lot, he said, especially on the border with South Sudan and the Democratic Republic of the Congo.
Doing any kind of river blindness control in Democratic Republic of the Congo is problematic because of safety issues, he said. A lack of government structure also makes it hard for health workers to coordinate efforts. But the flies don't respect the border between DRC and Uganda, and people belonging to the same tribe in both countries migrate across, too.
"If you're controlling it on the Ugandan side, and doing nothing on the DRC side," Unnasch said, "you're never going to really eliminate it until you deal with these cross-border issues, and get an effective program going."
Unnasch commended the work that the Carter Center has been doing. He and Katabarwa travel together to Uganda every year. They are both part of an expert committee on river blindness through the country's Ministry of Health.
"When summertime rolls around, and the rains start to come and the flies go out, that's when we need to be there," Unnasch said.