Emerging Waterborne Pathogens-The Serious Threat To Public Health

Gaurav Saxena, Praveen Kishan and Ram Naresh Bharagava, Department of Environmental Microbiology (DEM), School for Environmental Sciences (SES), Babasaheb Bhimrao Ambedkar University (A Central University), Vidya Vihar, Raebareli Road, Lucknow 226 025 Utt

2017-02-28 10:44:39

Credit:  .bvwater.co.uk

Credit: .bvwater.co.uk

Water is essential for all life forms. A clean and safe drinking water supply may be the norm in European and North American countries, but in developing countries, the assessment of both clean and safe drinking water is not, the rule and hence, waterborne illness outbreaks are common. In Asian and African countries, diarrheal diseases transmitted through contaminated drinking water primarily affect children below 5 years of age. It is also reported that around two and half billion people have no access to clean and safe drinking water and more than 1.5 million children die each year from diarrheal diseases. This is due to the contamination of drinking water with different types of pathogenic microorganisms present in urban sewage, and feces of infected humans and animals.

Today, the global burden of infectious waterborne disease has become a matter of serious concern because waterborne pathogens have created a serious threat to the safety of public health. The emerging waterborne pathogens pose major health hazards in both the developed and developing countries. An emerging pathogen can be a microorganism that is totally new (e.g., human immuno-deficiency virus: HIV), one that was previously known, but only recently identified as a pathogen (e.g., Helicobacter pylori), or one that is old, but has undergone some changes (e.g., resistant microbes). Emerging pathogens have potential to be spread through the supply of drinking water, but their presence in water environment does not correlate with the presence of E. coli or other indicator microorganisms such as coliforms, which are commonly used in different countries as a tool to monitor the microbiological quality of drinking water. However, the current indicator microorganisms have no more space for their improvement. In most cases, there is no perfect indicator microorganism to indicate the presence of emerging waterborne pathogens because of some serious limitations such as:

a.      Sensitive to inactivation through wastewater treatment processes and sunlight exposure.

b.      Short survival period as compared to microbial pathogens.

c.       Not indicative of exclusive faecal source.

               d.      Ability to multiply in some natural environments.

e.       Inability to recognize faecal contamination source (point or non-point).

f.       Less correlation with the presence of pathogens.

The clinical illnesses associated with the emerging waterborne pathogens may be more severe, transmitted more rapidly or widely within the population or more difficult to prevent or treat as compared to other closely related pathogens. The primary mode of transmission is faecal-oral route and consumption of contaminated water and vegetables that has been irrigated with contaminated water. Recently, several “new or emerging” pathogens have arisen or arising as a continuing problem in drinking water due to the rapid emergence of waterborne pathogens. A complex relationship between host, pathogens and natural environment play a central role in the emergence of pathogens.

The microbial agents, which may qualify as emerging waterborne pathogens include environmental mycobacteria, aeromonads (Aeromonas sobria, A. caviae and A. hydrophila), Legionella pneumophila, Vibrio sp. (V. cholerae O139 and V. cholerae O1), pathogenic E. coli (enteroinvasive E. coli, enteropathogenic E. coli, enteroaggregative E. coli and shiga toxin producing E. coli), Yersinia enterocolitica, Helicobacter pylori, multi-drug resistant Pseudomonas aeruginosa, Klebsiella pneumoniae, Campylobacter jejuni and some viruses such as Enteroviruses, Noroviruses, Hepatitis A and E viruses, Adenoviruses, Influenza viruses etc.

The rapid and continuous emergence of waterborne pathogens may be due to the following reasons:

a.   Increase in sensitive populations.

b.   Globalization of trade and travel.

c.    Lack of suitable techniques for their detection and source tracking.

d.   Changes in drinking water treatment technologies.

e.    Changes in food production processes and supply.

f.    Changes in climatic conditions and weather.

g.   Molecular evolution (genetic re-assortment).

h.   Multi-drug resistance (MDR) amongst the pathogens.

i.     Lack of public health awareness and services.

However, the rapid emergence of waterborne pathogens has created a serious threat to public health and therefore affects the economy of the world. Hence, there is an urgent need to develop the strategies for identification of these potentially emerging waterborne pathogens. Moreover, the development of microbial source tracking (MST) has allowed the identification of contamination sources of these waterborne pathogens. MST includes a group of molecular techniques particularly nucleic acid amplification methods that provide the sensitive, rapid and quantitative means for the detection of specific pathogens of public health concern including newly emerging pathogenic strains. These techniques are used to evaluate the microbiological quality of drinking water and pathogens removal efficiency of drinking and wastewater treatment plants. These molecular techniques include:

a.      Ribotyping.

b.      Amplified Ribosomal DNA Restriction Analysis (ARDRA).

c.       Ribosomal RNA Intergenic Spacer Analysis (RISA).

d.      Pulse-field Gel Electrophoresis (PFGE).

e.       Denaturing-gradient Gel Electrophoresis (DGGE).

f.       Terminal-restriction Fragment Length Polymorphism (T-RFLP).

g.      Fluorescent in-situ hybridization (FISH).

h.      Quantitative Polymerase Chain Reaction (qPCR).

i.        Multiplex Polymerase Chain Reaction (mPCR).

j.        Repetitive DNA sequences (Rep-PCR).

k.      Length heterogeneity-Polymerase Chain Reaction (LH-PCR).

l.        Host-specific 16S rDNA analysis.

m.    Nucleic Acid Microarrays.

n.      On-chip technology.

However, the best way to combat the newly emerging pathogenic microbes is to avoid the initial exposure because the exposure routes are the common sources of human infection such as food, water and direct human contact. Further, it is also important to follow the precautionary guidelines for the safe handling of food, adequate water treatment and good personal hygiene. In addition, the general strategies should also be used at personal level to minimize the spreading of waterborne pathogens effectively like chlorination and boiling. However, waterborne pathogens promise to continue emerging as we recognize their presence in water environments. Improved or adequate treatment of source water supply is only one option for their control, but maintaining the constant water quality throughout the distribution system is a major challenge. Moreover, the adequacy of guidelines and standards are also required to be reassess and tightened for the safety of drinking water at both local and national level.

Further, there is a need to expand and coordinate the surveillance systems for the early detection and tracking of emerging waterborne pathogens at local and national level to identify the cause of illness outbreaks and also to understand the environmental factors contributing to these illness outbreaks. Further, the development of new, simple and quick molecular techniques is also required for the detection of pathogens in order to determine the extent of fecal contamination, types of pathogens involved and the correlation between pathogens and environmental factors.

Nevertheless, the progress made in water and wastewater treatment technologies, emerging waterborne pathogens will always be a serious concern for public health in both developed and developing countries. Further, more studies are also required to understand the behavior and ecology of waterborne pathogens, so that their true potential as emerging waterborne pathogens could be evaluated for the safety of human health.