The microorganism that causes rare but severe eye infections has been detected in New South Wales coastal areas, prompting warnings about the risk to swimmers wearing contact lenses.
New research has identified the microorganism Acanthamoeba, which can cause an extremely rare but potentially sight-threatening eye infection, in seawater at four NSW coastal sites.
The new research is published in Science of The Total Environment, and is a collaboration between UNSW Sydney, University of Technology Sydney (UTS) and the University of the West of Scotland.
Swimmers should take off contact lenses before entering the water to avoid picking up an Acanthamoeba infection, according to the researchers.
Infection is difficult to eradicate due to the absence of drugs that can kill Acanthamoeba in both its cyst and trophozoite life stages.
Rare but Sight-Threatening
Acanthamoeba keratitis (AK) occurs when Acanthamoeba infects the cornea. The microorganism feeds on bacteria and corneal cells, leading to inflammation and damage to the cornea.
Infection is difficult to eradicate due to the absence of drugs that can kill Acanthamoeba in both its cyst and trophozoite life stages. This can lead to vision loss, with around one quarter of AK patients ending up with less than 25% of vision or becoming blind.
AK is very rare, estimated to affect 10–40 Australians per year. But it is important to educate contact lens wearers about the risk. Acanthamoeba from the environment can get trapped between the contact lens and the eye, leading to infection.
“Wearing contact lenses is the leading risk factor, particularly if people mix their contact lenses with contaminated water,” said first author Binod Rayamajhee, from UNSW Medicine & Health.
UNSW researchers previously found that around one third of the tap water in bathroom sinks in greater Sydney contains Acanthamoeba. Washing contact lenses in tap water is a major risk factor for AK, as well as showering and swimming with contact lenses.
“There have been two previous studies, one in Sydney and another in Melbourne, suggesting that nearly 20% of patients acquired AK after swimming in seawater or fresh water with their contact lenses,” Mr Rayamajhee said.
However, levels of Acanthamoeba in Australian aquatic environments have not been studied until now.
Wearing contact lenses is the leading risk factor, particularly if people mix their contact lenses with contaminated water
Testing NSW Coastal Waters
During the study, the researchers collected water samples from four NSW coastal sites. These locations are used for recreational activities like swimming or kayaking, and water quality is monitored regularly for safety.
“We chose coastal sites to look for the presence of Acanthamoeba species that we knew experienced high levels of seasonal variability in environmental conditions, as well as intermittent impacts from stormwater and sewage contamination. We aimed to identify any links between environmental factors and the presence of the organism,” said co-author Professor Justin Seymour, who leads the Ocean Microbiology Group at UTS.
The researchers collected multiple samples from each site between August 2019 and July 2020. They measured water characteristics including temperature, dissolved oxygen concentration, pH, and salinity.
In addition, the researchers extracted DNA from the water, which allowed them to measure the levels of Acanthamoeba and bacterial communities.
Detection of Acanthamoeba
Acanthamoeba was present in water samples from all four coastal sites, with 38% of the water samples overall testing positive.
The prevalence of Acanthamoeba varied across the sites. For the most highly urbanised site, more than half the samples tested positive. In contrast, for the least urbanised site, 32% of the samples contained Acanthamoeba.
The study found a positive correlation between the presence of Acanthamoeba and elevated levels of the intl1 gene in the water samples. The intl1 gene serves as an indicator of contamination in aquatic habitats due to human activity.
Taken together, these results suggest that urbanised coastal sites could be impacted by contaminants like sewage, animal faeces, and stormwater, potentially creating a better environment for Acanthamoeba.
The researchers also found that Acanthamoeba was more prevalent in the water during the summer months. They also found a weak positive correlation between water temperature and presence of Acanthamoeba.
“When we look at global data, there are more AK cases during summer, when recreational activities are likely to be at their highest,” Mr Rayamajhee said.
“With rising temperatures and increased stormwater runoff due to climate change promoting algal blooms in seawater, urbanised coastal waterways could potentially become favourable habitats for Acanthamoeba. However, further investigation is crucial to accurately determine the prevalence of Acanthamoeba in the region.”
This paper highlights the risk of eye infections while swimming in contact lenses and calls for reminder signs at pools and recreational water facilities
Avoiding AK infection
According to the researchers, these findings highlight the widespread prevalence of Acanthamoeba in the environment, and the importance of public awareness. While AK infections are extremely rare in Australia and worldwide, they can lead to serious vision loss.
“Many public health messages about swimming safety focus on microbes that cause gastrointestinal infections. This paper highlights the risk of eye infections while swimming in contact lenses and calls for reminder signs at pools and recreational water facilities to remove contact lenses before swimming,” said senior author Associate Professor Nicole Carnt from UNSW Medicine and Health.
Contact lens wearers should not panic or avoid swimming altogether, but they should be careful to avoid developing AK. They should also monitor for early symptoms such as eye pain and redness, blurred vision, light sensitivity, and excessive tearing.
“For people planning to do water activities in these areas, it’s strictly advisable to take off your contact lenses before getting in the water,” Mr Rayamajhee said.