Contact lenses might harbour pathogens

October 21st, 2008 - 1:28 pm ICT by IANS  

Washington, Oct 21 (IANS) Most contact lenses are contaminated with acanthamoeba, increasing the risk of infection that can cause blindness. Acanthamoeba is one of the most common types of protozoa in soil and is often found in fresh water. Most Acanthamoeba species eat bacteria and some can cause infections in humans.

One of the diseases caused by Acanthamoeba is called amoebic keratitis, which is an infection of the eye. Around 85 percent of all amoebic keratitis cases occur in people who use contact lenses.

The infection is very painful and can cause blindness. As the amoeba can be found in chlorinated swimming pools and domestic tap water, people who wear lenses while swimming or use tap water to rinse their lenses have an increased risk of infection.

“The prevalence of this infection has risen in the past 20 years worldwide, mainly because more people are wearing contact lenses,” said Basilio Valladares from the University Institute of Tropical Diseases and Public Health of the Canary Islands, University of La Laguna, according to a release of the Society for General Microbiology.

“When people rinse their contact lens cases in tap water, they become contaminated with amoebae that feed on bacteria. They are then transferred onto the lenses and can live between the contact lens and the eye,” he said.

The scientists looked at 153 contact lens cases, 90 containing lenses, from people in Tenerife who were showing no symptoms of infection. About 66 percent of the cases and lenses were contaminated with pathogenic Acanthamoeba and 30 percent of the identified amoebae were highly pathogenic.

“We tested the effect of two standard drugs on the amoebae. We found that the antibiotic ciprofloxacin and the antiseptic chlorhexidine both kill Acanthamoeba. However, the concentrations of chlorhexidine found in contact lens maintenance solutions are not high enough to kill pathogenic strains, so most lens solutions do not protect against amoebic keratitis,” said Valladares.

“At the moment, we are developing a contact lens maintenance solution that can kill pathogenic Acanthamoeba species,” said Valladares.

The new research will be published in the November issue of the Journal of Medical Microbiology.

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