Pathogenic waterborne free-living amoebae: An update from selected Southeast Asian countries.

Nongyao Sawangjaroen,Tooba Mahboob,Joon Chuah,Narong Jaturas,Wai Lynn Aung,Yvonne A L Lim,Kyaw Nyein Aye,Tzen-Yuh Chiang,Brandon G J Mong,Atipat Yasiri,Mohamad Azlan Abdul Majid,Tan Tian-Chye,Alan D Ziegler,Panomphanh Mahaphonh,Anusorn Phimphila,Veeranoot Nissapatorn,Reena Leeba Richard

doi:10.1371/journal.pone.0169448

Abstract

Data on the distribution of free-living amoebae is still lacking especially in Southeast Asian region. The aquatic environment revealed a high occurrence of free-living amoebae (FLA) due to its suitable condition and availability of food source, which subsequently causes infection to humans. A total of 94 water samples consisted of both treated and untreated from Laos (31), Myanmar (42), and Singapore (21) were investigated for the presence of pathogenic FLA. Each water sample was filtered and cultured onto non-nutrient agar seeded with live suspension of Escherichia coli and incubated at room temperature. Morphological identification was conducted for both trophozoites and cysts via microscopic stains (Giemsa and immunofluorescence). The presence of Naegleria-like structures was the most frequently encountered in both treated and untreated water samples, followed by Acanthamoeba-like and Vermamoeba-like features. To identify the pathogenic isolates, species-specific primer sets were applied for molecular identification of Acanthamoeba, Naegleria, and Vermamoeba. The pathogenic species of Acanthamoeba lenticulata and A. triangularis were detected from untreated water samples, while Vermamoeba vermiformis was found in both treated and untreated water samples. Our results suggested that poor water quality as well as inadequate maintenance and treatment might be the cause of this alarming problem since chlorine disinfection is ineffective in eradicating these amoebas in treated water samples. Regular monitoring and examination of water qualities are necessary in order to control the growth, hence, further preventing the widespread of FLA infections among the public.

Highlights

Free-living amoebae (FLA) belonging to the genera Acanthamoeba, Balamuthia, Naegleria, Sappinia, and Vermamoeba (= Hartmannella) are potentially pathogenic to humans [1,2]
In Myanmar, Vermamoeba was the only pathogenic FLA found in treated water samples with high nitrate concentration (2.13±6.03 mg/L; confidence intervals (CIs): 3.34)
In Laos, Acanthamoeba was detected in untreated water samples with high level of nitrite (0.38±0.20 mg/L; CI: 0.13) and Vermamoeba was detected in treated water samples with high level of ammonia (2.05±5.36 mg/L; CI: 3.10)

Summary

Introduction

Free-living amoebae (FLA) belonging to the genera Acanthamoeba, Balamuthia, Naegleria, Sappinia, and Vermamoeba (= Hartmannella) are potentially pathogenic to humans [1,2]. They are known as amphizoic amoeba due to the ability to exist within a host or in the environment as ‘free-living’. Many species under the genus of Acanthamoeba are reported to be the causative agent of keratitis in healthy individuals, often among contact lens wearers. Vermamoeba (= Hartmannella) vermiformis seems to be the potential causative agent of human keratitis [12] and it can serves as a host to pathogenic bacteria, Legionella pneumophila [13,14]

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Conclusion