Contact Lenses Could Harbor Pathogenic Amoebae

A high percentage of contact lenses are contaminated with infection-causing pathogenic protozoa that cannot be killed by normal contact lens solution, claims a new study.

Researchers at the University of La Laguna (Tenerife, Canary Islands, Spain) examined 153 contact lens cases and 90 contact lens containers from people in Tenerife who were showing no symptoms of infection. The researchers found that 65.9% of the containers and lenses were contaminated with pathogenic Acanthamoeba, and that 30% of the amoebae identified were highly pathogenic. No pathogenic strains were found in daily contact lenses but several pathogenic amoebae were isolated from monthly and bimonthly lenses. The two-year-use lenses that were analyzed contained a high percentage of pathogenic amoebae due to a lack of hygiene and poor care of the lenses. The researchers then tested the effect of two standard drugs on the amoebae, and found that the antibiotic ciprofloxacin and the antiseptic chlorhexidine both kill Acanthamoeba; however, the concentrations of chlorhexidine found in standard contact lens maintenance solutions was not high enough to kill the pathogenic strains. The study was published in the November 2008 issue of the Journal of Medical Microbiology (JMM).

"Studies have shown that these amoebae are more common among contact lens users in Tenerife than in Scotland, perhaps because of the warmer climate,” said lead author Basilio Valladares, Ph.D., a professor of parasitology and director of the Tenerife Institute of Tropical Diseases and Public Health. "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. This is particularly worrying because commercial contact lens solutions do not kill the amoebae.”

Acanthamoeba is one of the most common types of protozoa in soil and is often found in fresh water. One of the diseases caused by Acanthamoeba is an infection of the eye called amoebic keratitis, and an estimated 85% of all amoebic keratitis cases occur in people who wear 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.

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University of La Laguna