* Guatemala program virtually eradicates river blindness
* Parasite affects 18 million people worldwide
WASHINGTON, March 30 (Reuters) - Dogged education and distribution of an anti-parasitic drug have virtually eradicated river blindness in badly affected parts of Guatemala, researchers reported on Monday.
And a second study showed that treating family members with antibiotics helped stop the spread of trachoma, another common cause of blindness.
The two studies in the Public Library of Science journal PLoS Neglected Tropical Diseases show it is possible to end the misery caused by common but not usually fatal diseases, the researchers said.
"In a few short years, with continued hard work and increased political will, river blindness will never threaten the Americas again," Dr. Frank Richards of the non-profit Carter Center's River Blindness Program said in a statement.
His international team of researchers found that a program by the Guatemalan government and the Onchocerciasis Elimination Program of the Americas to give Merck and Co's (MRK.N) drug ivermectin to 85 percent of the at-risk population in Escuintla, Guatemala, virtually stopped the epidemic.
River blindness, known medically as onchocerciasis, is caused when the roundworm Onchocerca volvulus is transmitted to humans by the bite of an infected black fly.
The parasite causes eye damage that can lead to blindness and skin disease. It affects 18 million people worldwide and has made 300,000 blind.
None of the children in the community aged 7 or younger were infected and none of the nearly 15,000 black flies tested carried the parasite, the researchers report in the study, available online here
In a second study, a team led by Isobel Blake of Imperial College London found they could greatly reduce transmission of trachoma, the most common cause of blindness, by focusing on households in Tanzania and Gambia.
Trachoma, which infects 84 million people globally and has affected the vision of 8 million, is caused by the bacteria Chlamydia trachomatis and can be treated with antibiotics.
"We have shown that within-household transmission ... accounts for almost three quarters of new infections across the four communities we studied," David Mabey of the London School of Hygiene and Tropical Medicine, who worked on the study, said in a statement.
"Failure to treat all infected members of a household during the mass administration of antibiotics is likely to lead to the rapid re-infection of that household, followed by a more gradual spread across the community."
Household spread is the same as for any infectious disease, added Blake. "This happens through contact with an infected person's hands, or with objects like towels and clothing that have picked up the bacteria, or with flies, which transfer the bacteria from person to person," she said.