Contact lens cases are often contaminated with Acanthamoeba which cannot be killed by normal contact lens solution, according to a new Spanish study.
Published in the Journal of Medical Microbiology, the study report describes Acanthamoeba as one of the most common types of protozoa in soil, which is often found in fresh water.
The researchers behind the study say that most species eat bacteria, and some can cause infections in humans.
According to them, about 85 per cent of all amoebic keratitis cases occur in people who wear contact lenses.
The team say that people who wear lenses while swimming or use tap water to rinse their lenses have an increased risk of infection, as amoeba is usually present in chlorinated swimming pools and domestic tap water.
"The prevalence of this infection has risen in the past twenty years worldwide, mainly because more people are wearing contact lenses," said Dr Basilio Valladares from the University Institute of Tropical Diseases and Public Health of the Canary Islands, University of La Laguna.
"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," the researcher added.
For their study, the researchers examined 153 contact lens cases, 90 containing lenses, from people in Tenerife who were showing no symptoms of infection.
They observed that 65.9 per cent of the cases and lenses were contaminated with pathogenic Acanthamoeba, and 30 per cent of the amoebae identified were highly pathogenic.
While no pathogenic strains were found in daily contact lenses, several pathogenic amoebae were isolated from monthly and bi-monthly lenses.
The two-year use lenses that were analysed contained a high percentage of pathogenic amoebae due to a lack of hygiene and poor care of the lenses.
"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 Dr. Valladares.
"At the moment, we are developing a contact lens maintenance solution that can kill pathogenic Acanthamoeba species.
"Studies have shown that these amoebae are more common among contact lens users in Tenerife than in Scotland, perhaps because of the warmer climate. Contact lens users are at greater risk of infection here and we hope we will be able to prevent and treat the diseases caused by these amoebae more effectively in the near future," the researcher added.