Waterborne Pathogens. Detection Methods and Applications

395 Pages·2013·17.848 MB·English

by  Helen Bridle (Eds.)

CHAPTER ONE
Introduction
Helen Bridle
Heriot-Watt University, Institute of Biological Chemistry, Biophysics and Bioengineering, Riccarton,
Edinburgh, Scotland
Access to potable water is essential to life. It is a right enshrined in the
Universal Declaration of Human Rights and it is critical to meeting all of
the Millennium Development Goals.1 This is also recognized by the United
Nations (UN) General Assembly, which recently stated that safe and clean
drinking water and sanitation are a human right that is essential to the full
enjoyment of life. They designated the period from 2005 to 2015 as the
International Decade for Action, “Water for Life”.
Due to population growth, increased industrialization and climate
change, the scarcity of safe, pollutant-free drinking water sources is a
major problem. Numerous countries around the world already face
severe water shortages, and many more are considered water-stressed (see
Fig. 1.1). It is estimated that 60% of the population of the world will suf-
fer water scarcity by 2025. In terms of waterborne contaminants, which
include inorganic and organic chemicals as well as pathogens/microbes,
the World Health Organisation (WHO) considers that microbial hazards
remain the primary concern in both developing and developed coun-
tries.2
Safe drinking water poses no significant risk during a lifetime of con-
sumption. Globally, in 2012, nearly a billion people still lacked access
to safe drinking water. This is despite the announcement on March 6,
2012 that the Millenium Development Goal of halving the proportion
of people without access to an improved water source had been achieved.
In addition to acknowledging that numerous people are still without
access to safe drinking water, the WHO press release recognized that an
improved source of drinking water was not necessarily an assurance of
water quality and that work is still needed to ensure that these sources are,
and remain, safe.
Contaminated drinking water is one of the most significant environ-
mental contributors to the human disease burden. It is responsible for an
estimated 1.9 million deaths each year, predominantly in children under
Waterborne Pathogens © 2014 Elsevier B.V.
http://dx.doi.org/10.1016/B978-0-444-59543-0.00001-3 All rights reserved. 1
2 Helen Bridle
Figure 1.1 Map of the world indicating areas of water stress. Source: http://www.grida.
no/graphicslib/detail/water-scarcity-index_14f3# (For color version of this figure, the
reader is referred to the online version of this book.)
Figure 1.2 Illustration of the worldwide mortality impacts of waterborne patho-
gens. Source: http://www.who.int/heli/risks/water/en/wshmap.pdf accessed on
29/09/12 (For color version of this figure, the reader is referred to the online version
of this book.)
5 years old. Although most of this disease impact occurs in low income coun-
tries, where it is estimated that more than 3000 children die each day from
diarrheal diseases, waterborne disease is still a threat to citizens in the devel-
oped world (Fig. 1.2). For example, one of the largest recent outbreaks was the
cryptosporidiosis outbreak in Milwaukee in 1993, in which approximately
Introduction 3
400,000 people were infected.3 Additionally, it has been estimated that
10% of all the hospital patients in the United States contract diseases due to
poor water, significantly increasing morbidity, mortality and the financial
burden.
Waterborne pathogens also have a significant economic impact. One
such cost, although it is very necessary, involves the building, upgrading and
maintaining of water treatment plants to remove pathogens from the water
supply. Therefore, it has been suggested that catchment management strate-
gies, which attempt to reduce the pathogen load entering the water source,
is a more cost-effective strategy than adopting more and more advanced,
and expensive, treatment technologies. However, it has been shown that, in
some regions, investment in the provision of water treatment returns a net
economic benefit through alleviation of health-related effects. The health
impact of waterborne pathogens is considerable in terms of both health care
costs and lost productivity. This is true for both outbreaks and endemic dis-
ease. For example, the above outbreak example in Milwaukee was estimated
to cost US$96 million.3 An Escherichia coli O157:H7 outbreak in Canada in
2000 killed seven, infected 2300 residents and cost $155 million.4 Overall,
in the United States lost productivity due to waterborne diseases is esti-
mated at $20 million per year.5
An overview of the most important types of microbial contamination
that pose risks to health is given in Chapter 2. Based on a List of Relevant
Pathogens published by the WHO, this chapter describes in detail the most
problematic waterborne pathogens, focusing upon those for which trans-
mission occurs via ingestion of water, e.g. via drinking water.
In order to alleviate the problems associated with waterborne patho-
gens, the WHO recommends adoption of a Water Safety Framework (WSF)
approach, tailoring the design of Water Safety Plans (WSPs), which nations
or regions design to suit the relevant environmental, social, economic and
cultural conditions. Further information on the WSF and WSPs is given in
Chapter 3, where the role of monitoring and detection of pathogens in the
delivery of a WSF is also considered.
Monitoring for pathogens is important for many reasons:
• Investigative monitoring allows for an analysis of the source water,
which enables the selection of appropriate barriers (e.g. catchment
management or particular water treatment technologies) to remove
the identified type of pathogen from the water. Another example of
investigative monitoring is the identification of sources of an out-
break, which contributes to halting and preventing the reoccurrence
4 Helen Bridle
of an outbreak. Furthermore, analysis of patient samples contributes
to an understanding of the disease burden and to setting appropriate
health targets. The key important factor in this type of monitoring is
the delivery of sufficient information to quantify and characterize the
pathogen load.
• In contrast, operational monitoring is undertaken to provide timely
indications of the performance of any implemented drinking water
treatment process, enabling the possibility of taking appropriate action
to remediate any potential problems. The key factor here is rapid mea-
surements, i.e. delivering information in time for action to be taken.
According to the WHO, monitoring for pathogens is of limited use
for operational purposes as existing methods of detection take too
long.2
• Surveillance or verification monitoring provides information to assess
the functioning of adopted WSPs and contributes to the effective man-
agement and rational allocation of resources to improve water supplies.
Chapter 3 provides a brief overview of existing, widely adopted methods
for pathogen detection, including their advantages and disadvantages. Gen-
erally, the problem with existing techniques is that the use of fecal indicator
organisms is not always correlated with pathogen presence. Therefore, while
a test may be negative for the fecal indicator, pathogens may still be present.
Additionally, while culture-based methods are cheap and easy to perform,
they are also time-consuming.
The main focus of this book is on alternative, developing and emerging
technologies, which are presented in Chapters 5–10. This main detection
section of the book gives background information along with an explana-
tion of how the various methods and techniques work, followed by a com-
prehensive literature review detailing how each method has been applied
to the detection of waterborne pathogens. Performance evaluation accord-
ing to a range of criteria (e.g. detection limit, ability to determine species
or viability, etc.) is provided based on information that was reported in
the literature, and at the end of each chapter a summary and comparison
are given. The introduction to this detection section explains the rationale
behind the chapter division and discusses the essential considerations for
any detection technology in this application. Chapter 11 builds on this by
considering what is required for a technology to translate from success-
ful laboratory results to widespread adoption by the water sector. A final
summary of the state-of-the-art and a future outlook are provided in
Chapter 12.
Introduction 5
Finally, it is important to remember that sample processing is an impor-
tant part of any monitoring strategy. As more direct detection methods are
developed, specific sample enrichment techniques suitable for returning
particular pathogens with a high recovery rate are essential. An explana-
tion of existing procedures and a review of the latest literature are given
in Chapter 4. Consideration is also given to how different sample pro-
cessing approaches may be required depending upon the chosen detection
technology.
Several commentators have presented the idea of a distributed network
of sensors that continuously reports on water quality within a catchment
area, enabling appropriate operational decisions. Back in 2001 when Rose
and Grimes summarized the view of a colloquium panel of water experts,
they reported that “water quality monitoring is mired in the past” and they
envisioned a future in which pathogen detection will be performed in real-
time feeding into operational decision making. This book will examine the
progress that has been made toward delivering novel monitoring technolo-
gies that meet the needs of the water sector, and comments will be made on
directions for future work.
REFERENCES
1. Rahman A. Towards an arsenic safe environment in Bangladesh. BCAS; 2010.
2. World Health Organisation. Guidelines for drinking-water quality. 2011.
3. Corso PS, Kramer MH, Blair KA, Addiss DG, Davis JP, Haddix AC. Cost of illness in
the 1993 waterborne Cryptosporidium outbreak, Milwaukee, Wisconsin. Emerging Infectious
Diseases 2003;9(4):426–31.
4. Meinhardt PL. Recognizing waterborne disease and the health effects of water contami-
nation: a review of the challenges facing the medical community in the United States.
Journal of Water and Health 2006:27–34.
5. Straub TM, Chandler DP. Towards a unified system for detecting waterborne pathogens.
Journal of Microbiological Methods 2003;53(2):185–97.
CHAPTER TWO
Overview of Waterborne
Pathogens
Helen Bridle
Heriot-Watt University, Institute of Biological Chemistry, Biophysics and Bioengineering, Riccarton,
Edinburgh, Scotland
Waterborne pathogens can be divided into three main categories: viruses,
bacteria and parasites, the latter of which are comprised of protozoa and
helminths. Such pathogens reach water sources when infected people or
animals shed microbes in feces. For example, untreated, undertreated or
accidental release of sewage allows pathogens to enter water sources. An
alternative mechanism is through runoff to source water or permeation
into groundwater from animal feces or sewage utilized as fertilizer. Many
waterborne pathogens are zoonotic, i.e. they are capable of infecting both
humans and animals (Fig. 2.1).
The persistence of pathogens in the environment depends upon many fac-
tors. For example, pathogens may be removed from the water supply due to set-
tling in lakes, possibly augmented by interactions of pathogens with sediment.
Furthermore, inactivation by light, temperature or chemical conditions, such as
salinity or ammonia, can occur (Fig. 2.2).1 Understanding the fate and transport
of pathogens in the environment is essential for risk management. However, the
survival and transport of pathogens is beyond the scope of this book and the
reader is referred to other articles2 and books for more on this topic. It is suffi-
cient to note that some of the pathogens discussed in this book remain infective
in the environment for long periods of time (from months to years).
As waterborne pathogens are transported through the environment, they
are often diluted to low concentrations. However, while these low concen-
trations may prove challenging for detection purposes, they may still present
a considerable public health risk, as several of the pathogens discussed here
have extremely low infectious doses.
One final factor, in addition to environmental persistence and infectious
dose, which renders some waterborne pathogens particularly problematic is
their resistance to disinfection methods. Most viruses, the spores or a veg-
etative phase of a bacterium, and the cysts, oocysts or ova of parasites are
capable of some degree of resistance to chlorination.3
Waterborne Pathogens © 2014 Elsevier B.V.
http://dx.doi.org/10.1016/B978-0-444-59543-0.00002-5 All rights reserved. 9
10 Helen Bridle
Figure 2.1 Transmission pathways of fecal-oral disease. Source: Reproduced from Figure
16.1 from Ref. 1.
UV deactivation
Inflow
Temperature
deactivation Temperature (ºC)
Advection
Outflow
Resuspension
Depth
Settling
Figure 2.2 Schematic indicating fate and transport of pathogens in a reservoir. Source:
Reproduced from Figure 8 from Ref. 2. (For color version of this figure, the reader is referred
to the online version of this book.)
The World Health Organisation (WHO) has compiled a List of Rel-
evant Waterborne Pathogens, which considers the risk represented by the
three factors discussed above.4 An adaptation of this list forms the basis of
this chapter. Each category of waterborne pathogen is discussed in turn,
with examples given of those pathogens considered most problematic.
Overview of Waterborne Pathogens 11
In general, the focus is on those pathogens for which the route of disease
transmission occurs through ingestion of water. This chapter is divided into
sections according to the main categories of pathogens.
Environmental Persistence
Environmental persistence refers to the length of time a pathogen is able to sur-
vive in the environment and retain infectivity.
Host-dependent pathogens gradually lose viability and the ability to infect
after they are shed from a host. Pathogens with low persistence are unlikely to be
spread by drinking water since they would be nonviable or noninfectious by the
time they were able to reach a new host. Some waterborne pathogens are capable
of growth in water. For example, Legionella, Vibrio cholerae and Naegleria fowleri
will grow in warm water that contains relatively high amounts of biodegradable
organic carbon, which can occur in some surface waters or water distribution sys-
tems. Other pathogens, e.g. norovirus (NoV) or Cryptosporidium, are unable to mul-
tiply in water but are robust enough to survive for a considerable length of time.
The persistence of pathogens in water is influenced by many factors, includ-
ing temperature, exposure to sunlight (UV) or certain chemical conditions (e.g.
salinity or ammonia), all of which could inactivate pathogens and result in set-
tling or interaction with sediment in surface waters.
In this chapter and the WHO list, the persistence in water is defined as short
for survival periods of less than one week and moderate for times between a
week and a month, with high persistence being assigned to those pathogens
capable of survival in the environment for periods of greater than one month.
Microbiology Definitions
Virus: Viruses are the smallest of the microorganisms, typically 20–300 nm, and the
only living organisms not to have a cell membrane; they consist of a small amount
of nucleic acid (DNA or RNA) coated with and protected by a layer of protein.
Bacteria: Bacteria are prokaryotic microorganisms with a typical size of a few
micron; prokaryotes are cells with little intracellular organization that reproduce
asexually via cell division to give two daughter cells.
Protozoa: Protozoa are a diverse group of unicellular eukaryotic organisms,
including sporozoa (intracellular parasites), flagellates (which possess tail-like
structures for movement), amoeba (which move using temporary cell body pro-
jections called pseudopods) and ciliates (which move by beating multiple hair-
like structures called cilia).
Helminth: Helminths are worms, with the name coming from the Greek word
for worm.
Continued
12 Helen Bridle
Microbiology Definitions—cont’d
Genera: A taxonomic category ranking used in biological classification that
is below a family and above a species level, and includes group(s) of species
that are structurally similar or phylogenetically related. In binomial nomencla-
ture, the genus is used as the first word of a scientific name. The genus name is
always capitalized and italicized, e.g. Cryptosporidium. In order for a genus to
be descriptively useful, it must have monophyly, reasonable compactness, and
distinctness.
Species: A taxonomic category subordinate to a genus (or subgenus) and
superior to a subspecies or variety, e.g. Cryptosporidium parvum. An exact defini-
tion is difficult but could be thought of as populations of organisms with a high
degree of genetic similarity. In terms of sexually reproducing organisms, a spe-
cies could be thought of as a group of organisms that could potentially inter-
breed and produce fertile offspring.
Strains: A simple definition is that a strain is a genetic variant or subtype of
a microorganism. According to the first edition of Bergey's Manual of Systemic
Bacteriology, “A strain is made up of the descendants of a single isolation in pure
culture and usually is made up of a succession of cultures ultimately derived from
a single colony.” For a more detailed discussion, see Ref. 5.
Spores: A dormant, reproductive cell formed by certain organisms. It is
thick-walled and highly resistant, enabling it to survive under unfavorable con-
ditions so that when conditions revert to being suitable they give rise to a new
individual.
Cysts/oocysts: A resting or dormant stage of a microorganism/the encysted
zygotic stage in the life cycle of some sporozoans. Encystment helps the microbe
to disperse easily, from one host to another or to a more favorable environment.
When the encysted microbe reaches an environment favorable to its growth and
survival, the cyst wall breaks down by a process known as excystation.
Prokaryotic: This cell type is a simple structure and is confined to the bacteria.
They are typically less than 5 µm long and 1 µm wide and have little structural
organization within the cell. The single DNA molecule is in direct contact with the
cytoplasm. Prokaryotes reproduce asexually by division.
Eukaryotic: This cell type is more complex than the prokaryote, contain-
ing several distinct intracellular compartments. These structures are known
as organelles, e.g. a nucleus, and are surrounded by membranes, enabling the
maintenance of chemical conditions within the organelles, which is different
from cytoplasm. There is no such thing as a typical eukaryotic cell as they exhibit
considerable diversity. Eukaryotes can reproduce sexually or asexually.
Culture: With regard to microorganisms, this term refers to in vitro culti-
vation of cells. Culturing of microorganisms requires specific culture media
Overview of Waterborne Pathogens 13
containing the nutrients and growth factors necessary for microorganism
growth; this is highly specific to different microorganisms, thus allowing selec-
tive growth of certain microorganisms from a mixed sample. However, many
microorganisms are nonculturable, meaning it is not possible to grow them in
the laboratory.
Self-limiting: This term is used to describe some of the diseases resulting from
infection with microorganisms. In self-limiting cases, the immune response of the
human body will eventually kick in, thus preventing further multiplication of the
pathogen and a return to health.
For more details, the reader is referred to standard microbiology textbooks.
Infectious Dose
The infectious dose does not refer to a minimum threshold value above which
infection occurs. Every single pathogen ingested has the possibility to initiate
infection. However, among the different pathogens, the probability that a single
organism will initiate infection can vary widely. The infectious dose attempts to
characterize this by providing a probability of infection. The infectious dose can
therefore be thought of as the dose above which the probability of infection
exceeds a certain value. The probability for illness to develop following infection
depends upon the degree of host damage and whether this is sufficient to result
in clinical symptoms.
Sometimes, clinical or epidemiological data are available from previous out-
breaks. Alternatively, in order to determine the infective dose, dose–response
experiments can be undertaken with healthy adult volunteers to determine the
probability of infection at different dose levels. These data are not available for all
pathogens and they do not indicate susceptibility of vulnerable subpopulations
to any of the studied pathogens. Additionally, experiments are often performed
with laboratory strains of pathogens, which may differ from the wild-type. How-
ever, these studies provide strong evidence that the infective dose of many
waterborne pathogens is very low.
In this chapter, and the WHO list, the relative infectivity is categorized as
low if the infective dose is greater than 104 pathogens, moderate for doses
between 102 and 104 and high for doses between 1 and 102. There is no indica-
tion in the WHO list of what probability of infection this infective dose repre-
sents.