Free-living amoebas, or single-celled organisms that do not require a host to live, pose a dangerous threat to humans. They are notoriously difficult to kill and can also harbor other pathogens.
The “widespread presence” of amoebas poses “significant exposure risks through contaminated water sources, recreational water activities and drinking water systems,” a team of environmental and public health scientists said in a paper published in the journal Biocontaminant. While most species are harmless, there is a subset that can have serious public health consequences, like the brain-eating amoeba Naegleria fowleri.
Other amoebas can “cause painful eye infections, skin lesions in people with weakened immune systems and rare but serious systemic infections affecting organs,” Manal Mohammed, a medical microbiology lecturer at the University of Westminster, said at The Conversation. The level of human exposure to amoebas is “likely substantially underestimated,” said the study, as “amoebic infections are prone to clinical misdiagnosis.”
Free-living amoebas can thrive in even the most inhospitable environments, including high temperatures and amid strong cleaning chemicals. Along with their resilience, amoebas “act as hidden carriers for other harmful microbes,” Shenyang Agricultural University said in a news release on the paper. “By sheltering bacteria and viruses inside their cells, amoebae can protect these pathogens from disinfection and help them persist and spread.” Known as the Trojan horse effect, this process can contribute to the prevalence of antibiotic resistance.
Most water systems are “not routinely checked for free-living amoebas,” said Mohammed. The problem is likely to worsen due to climate change, with rising temperatures “expanding the geographic range of heat-loving amoebae,” said the release. | 
