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Imbalance of Ecosystems and Its Effect on Public and Livestock Health

Imbalance of Ecosystems and Its effect ondisease remains endemic in India, Bangladesh,
Public  and  Livestock  healthand Africa. Vibrio cholerae has also been
found in the United States-in the Gulf Coast
Dr.Kedar Karki M.V.St. (Preventive veterinaryregion of Texas, Louisiana, and Florida; the
Medicine)Chesapeake Bay area; and the California
coast.
Central  Veterinary  Laboratory  Tripureshwor
The increase in prevalence of V. cholerae has
The health of humans, like all livingbeen strongly linked to degraded coastal
organisms, is dependent on an ecosystem thatmarine environments. Nutrient-enriched warmer
sustains life. Healthy ecosystems are thecoastal waters, resulting from a combination
sine qua non for healthy organisms. Yet thereof climate change and the use of fertilizers,
is abundant evidence that many life-supportprovides an ideal environment for
systems are far from healthy, placing anreproduction and dissemination of V.
increased burden on human health. In somecholerae. Recent outbreaks of cholera in
areas of the world, gains in life expectancyBangladesh, for example, are closely
and quality of life made during the twentiethcorrelated with higher sea surface
century are at risk of being reversed in thetemperatures. V. cholerae attach to the
twenty-first century. The consequences ofsurface of both freshwater and marine
ecosystem degradation to human health arecopepods (crustaceans), as well as to roots
numerous, and include health risks fromand exposed surfaces of macrophytes (aquatic
unsafe drinking water, polluted air, climateplants) such as the water hyacinth, the most
change, emerging new diseases, and theabundant aquatic plant in Bangladesh.
resurgence of old diseases owing toNutrient enrichment and warmer temperatures
ecological imbalances. Reversing this damagegive rise to algae blooms and an abundance of
is possible in some cases, but not in others.macrophytes. The algae blooms provide
Prevention of ecological damage is by far theabundant food for copepods, and the
most  efficient  strategy.increasing copepod and macrophyte populations
provide V. cholerae with habitat. Subsequent
DEFINING  ECOSYSTEMSdispersal of V. cholerae into estuaries and
fresh water bodies allows contact with humans
An ecological system may be defined as awho use these waters for drinking and
community of plants and animals interactingbathing. Global distribution of marine
with each other and their abiotic, orpathogens such as V. cholerae is further
natural, environment. Typically, ecosystemsfacilitated by ballast water discharged from
are differentiated on the basis of dominantvessels. Ballast water contains a virtual
vegetation, topography, climate, or somecocktail of pathogens, including V. cholerae.
other criteria. Boreal forests, for example,
are characterized by the predominance ofTwo other examples of how ecological
coniferous trees; prairies are characterizedimbalances lead to human health burdens
by the predominance of grasses; the Arcticconcern the increased prevalence of Lyme
tundra is determined partly by the harshdisease and hantavirus pulmonary disease.
climatic zone. In most areas of the world,Lyme disease, sonamed because it was first
the human community is an important and oftenpositively identified in Lyme, Connecticut,
dominant component of the ecosystem.is a crippling arthritic-type disease that is
Ecosystems include not only natural areastransmitted by spirochete-infected Ixodes
(e.g., forests, lakes, marine coastalticks (deer ticks). Ticks acquire the
systems) but also human-constructed systemsinfection from rodents, and spend part of
(e.g., urban ecosystems, agro-ecosystems,their life cycle on deer. Three factors have
impoundments). Human populations arecombined to increase the risk to humans of
increasingly concentrated in urbancontracting Lyme disease, particularly in
ecosystems, and it is estimated that, by theNorth America: (1) the elimination of natural
year 2010, 50 percent of the world'sdeer predators, particularly wolves; (2)
population  will  be  living  in urban areas.reforestation of abandoned farmland has
created more favorable habitat for deer; and
A landscape comprises a mosaic of ecosystems,(3) the creation of suburban estates, which
including towns, rivers, lakes, agriculturalthe deer find ideal habitat for browsing. The
systems, and so on. Precise boundariesnet result is a rising deer population, which
between ecosystems are often difficult toincreases the chances of humans coming into
establish. Often regions slide into onemore  contact  with  ticks.
another gradually, over a protracted
"transition" zone, as for example between theBy 1995, in the southwestern United States,
boreal forest and the Taiga regions ofhantavirus infection was confirmed in
Canada.ninety-four persons in twenty states, with 48
percent mortality. Variants of the strain
ECOSYSTEM  HEALTHthat causes hantavirus pulmonary syndrome
have also been found in other areas of the
It is important to recognize the inherentcountry, as well as in Asia and Europe. The
difficulties in defining "health," whether atvirus is apparently asymptomatic in rodents,
the level of the individual, population, orand it is transmitted in their saliva and
ecosystem. The concept of health is somewhatexcreta. In humans it has a flu-like
of an enigma, being easier to define in itspresentation, which is followed by acute
absence (sickness) than in its presence.respiratory distress syndrome. The primary
Perhaps partially for that reason, ecologistsreservoir in the Four Corners area of the
have resisted applying the notion of "health"southwestern United States is the deer mouse.
to ecosystems. Yet, ecosystems can becomeClimatic disturbances, which in recent years
dysfunctional, particularly under chronicare thought to be exacerbated by human
stress from human activity.Example for thisactivity (e.g., global warming), appear to
can be cited the discharge of nutrients fromset up conditions that trigger outbreaks. In
sewage, industrial waste, or agriculturalthe early 1990s, ENSO events initially caused
runoff into lakes or rivers affects thedrought conditions to develop in the
normal functioning of the ecosystem, and cansouthwestern United States. This led to a
result in severe impairment. Excessivedecline in plant and animal populations,
nutrient inputs from human activity was oneincluding natural predators of the deer
of the major factors that severelymouse. Heavy rains followed the drought in
compromised the health of the lower1993, resulting in a bumper crop of piñon
Laurentian Great Lakes (Lake Erie and Lakenuts, a major food supply for the deer mouse.
Ontario) and regions of the upper Great LakesSubsequently the deer mouse population
(Lake Michigan). Unfortunately, degradedgreatly increased, bringing about increased
ecosystems are becoming more the rule thancontact with humans and triggering the
the  exception.outbreak  of  hantavirus.
The study of the features of degradedAntibiotic Resistance and Agricultural
systems, and comparisons with systems thatPractice Antibiotic resistance is a growing
have not been altered by human activity,threat to public health. Antibiotic resistant
makes it possible to identify thestrains of Streptococcus pneumoniae, a common
characteristics of healthy ecosystems.bacterial pathogen in humans and a leading
Healthy ecosystems may be characterized notcause of many infections, including chronic
only by the absence of signs of pathology,bronchitis, pneumonia, and meningitis, have
but also by signs of health, includinggreatly increased in prevalence since the
measures of vigor (productivity),mid-1970s. In some regions of the world, up
organization,  and  resilience.to 70 percent of bacterial isolates taken
from patients proved resistant to penicillin
Vigor can be assessed in terms of theand other b-lactam antibiotics. The use of
metabolism (activity and productivity) of thelarge quantities of antibiotics in
system. Ecosystems differ greatly in theiragriculture and aquaculture appears to have
normal ranges of productivity. Estuaries arebeen a key factor in the development of
far more productive than open oceans, andantibiotic resistance by pathogens in farm
marshes have higher productivity thananimals that subsequently may also infect
deserts. Health is not evaluated by applyinghumans. One of the most serious risks to
one standard to all systems. Organization canhuman health from such practices is
be assessed by the structure of the bioticvancomycin-resistant enterococci. The use of
community that forms an ecosystem and by theavoparcin, an animal growth promoter, appears
nature of the interactions between theto have compromised the utility of
species (both plants and animals).vancomycin, the last antibiotic effective
Invariably, healthy ecosystems have moreagainst multi-drug-resistant bacteria. In
diversity of biota than ecologicallyareas where avoparcin has been used, such as
compromised systems. Resilience is theon farms in Denmark and Germany,
capacity of an ecosystem to maintain itsvancomycin-resistant bacteria have been
structure and functions in the face ofdetected in meat sold in supermarkets.
natural disturbances. Systems with a historyAvoparcin was subsequently banned by the
of chronic stress are less likely to recoverEuropean Union. Another example is the use of
from normal perturbations such as droughtofloxacin to protect chickens from infection
than those systems that have been relativelyand thereby enhance their growth. This drug
less  stressed.is closely related to ciprofloxacin, one of
the most widely used antibiotics in the year
Healthy ecosystems can also be characterized2000. There have been cases of resistance to
in economic, social, and human health terms.ciprofloxacin directly related to its
Healthy ecosystems support a certain level ofveterinary use. In the United Kingdom,
economic activity. This is not to say thatciprofloxacin resistance developed in strains
the ecosystem is necessarily self-sufficient,of campylobacter, a common cause of diarrhea.
but rather that it supports economicMulti-drug-resistant strains of salmonella
productivity to enable the human community tohave  been traced to European egg production.
meet reasonable needs. Inevitably, ecosystem
degradation impinges on the long-termFood and Water Security. Agricultural
sustainability of the human economy that ispractices are also responsible for a growing
associated with it, although in thenumber of threats to public health. Some of
short-term this may not be evident, asthese are related to inadequate waste
natural capital (e.g., soils, renewablemanagement, which has resulted in parasites
resources) may be overexploited andand bacteria entering water supplies. Others
temporarily enhance economic returns.are of entirely different origins and involve
Similarly, with respect to social well-being,apparent transfer across species of pathogens
healthy ecosystems provide a basis for andthat affect both animals and humans. The most
encourage community integration.recent and spectacular example is mad cow
Historically, for example, native Hawaiiandisease, known as variant Creutzfeldt-Jakob
groups managed their ecosystem through adisease in humans, a neuro-degenerative
well-developed social cohesiveness thatcondition that, in humans, is ultimately
provided a high degree of cooperation infatal. The first case of Bovine Spongiform
fishing  and  farming  activity.Encephalopathy (BSE), the animal form of the
disease, was identified in Southern England
Another reflection of ecosystem health liesin November 1981. By the fall of 2000, an
directly in the public health domain. Inoutbreak had also occurred in France, and
spring 2000, a deadly strain of the bacteriumisolated cases appeared in Germany,
E-coli (0157:H7) entered the public waterSwitzerland, and Spain. More than one hundred
supply in Walkerton, Ontario, Canada, causingdeaths in Europe were attributed to what has
seven deaths and making thousands sick. Thiscome  to  be commonly called mad cow disease.
small town, with a population of five
thousand, is in a farming community.Improper manure management was the likely
Inadequate manure management from cattlesource of the outbreak of E. coli 0157:H7 in
operations was the likely source of thisWalkerton, Ontario, Canada. Other health
tragedy.risks associated with malfunctioning
agroecosystems include periodic outbreaks of
HOW  HEALTHY  ECOSYSTEMS  BECOME PATHOLOGICALcryptosporidiosis, a parasitic disease that
is spread by surface runoff contaminated by
Stress from human activity is a major factorfeces of infected cattle. This parasite
in transforming healthy ecosystems to sickcauses fever and diarrhea in immunocompetent
ecosystems. Chronic stress from humanindividuals and severe diarrhea and even
activity differs from natural disturbances.death  in  immunocompromised  individuals.
Natural disturbances (fires, floods, periodic
insect infestations) are part of the dynamicsECOSYSTEM  RESTORATION
of most ecosystems. These processes help to
"reset" ecosystems by recycling nutrients andEcosystem pathology in some cases can be
clearing space for recolonization by biotareversed simply by removing the source of
that may be better adapted to changingstress. In cases, for example, where
environments. Thus, natural perturbationsecosystem degradation is the result of
help keep ecosystems healthy. In contrast,point-source additions of nutrients or toxic
chronic and acute stress on ecosystemschemicals, removal of these stresses may
resulting from human activity (e.g.,result in considerable recovery of ecosystem
construction of large dams, release ofhealth. A classic case is Lake Washington
nutrients and toxic substances into the air,(near Seattle, Washington). This lake had
water, and land) generally results inbecome highly anoxic (oxygen-depleted) owing
long-term  ecological  dysfunction.to a sewage outfall entering the lake.
Redirecting the sewage outfall away from the
Five major sources of human-inducedlake reversed many of the signs of pathology.
(anthropogenic) stresses have been identified
by D. J. Rapport and A. M. Friend (1979):In cases where it is not feasible to remove
physical restructuring, overharvesting, wastethe source of stress, more innovative
residuals, introduction of exotic species,engineering solutions have been tried. For
and  global  change.example, in the Kyrönjoki and Lestijoki
Rivers in western Finland, spring and fall
Physical Restructuring. Activities such asrunoff leads to sharp pulses of acidity.
wetland drainage, removal of shoals in lakes,Spring runoff from snowmelt, which releases
damming of rivers, and road constructionacid from tilled or dug soils, has been
fragment the landscape and alter and damageparticularly damaging to fish, during the
critical habitat. These activities alsocritical time of year for spawning. Fish
disrupt nutrient cycling, and cause the lossreproduction is severely curtailed, if not
of  biodiversity.all together eliminated in highly acidic
water. Further there have been massive fish
Overharvesting. Overexploitation iskills resulting from the highly acidic
commonplace when it comes to harvesting ofwaters. One possible remedy is to replace the
wildlife, fisheries, and forests. Over longoriginal drains which take runoff from the
periods of time, stocks of preferred speciesland to the rivers with new limed drains that
are reduced. For example, the giant redwoodscan neutralize the acidity. This solution has
that once thrived along the California coastbeen implemented on an experimental basis and
now exist only in remnant patches because ofappears to substantially reduce acidic
overharvesting. When dominant species likerunoff.
the giant redwoods (arguably the world's
tallest tree-one specimen was recorded at 110More radical treatments for damaged
meters tall with a circumference of 13.4ecosystems involve "ecosystem surgery." In
meters) are lost, the entire ecosystemsome cases, invading exotic vegetation (such
becomes transformed. Overharvesting oftenas mangroves in Hawaii) have been removed
results in reduced biodiversity of endemicfrom regions, and native vegetation has been
species, while facilitating the invasion ofreplanted. In areas of North America where
opportunistic  species.wetlands have been severely depleted owing to
farming, urbanization, and industrial
Waste Residuals. Discharges from municipal,activity, efforts have been made to establish
industrial, and agricultural sources into thenew  wetlands.
air, water, and land have severely
compromised many of the earth's ecosystems.More often than not, however, reversing
The effects are particularly apparent inecosystem pathology is not possible. Efforts
aquatic ecosystems. In some lakes that lack ato restore the indigenous grasslands in the
natural buffering capacity, acidJornada Experimental Range in the
precipitation has eliminated most of the fishsouthwestern United States provide an
and other organisms. While the visual effectexample. Overgrazing by cattle has severely
appears beneficial (water clarity goes up)degraded the landscape and has lead to
the impact on ecosystem health isreplacement of the native grasses by largely
devastating. Systems that once contained ainedible shrubs, dominated by mesquite.
variety of organisms and were highlyErosion by wind and episodic heavy rains have
productive (biologically) become devoid ofleft areas between shrubs largely bare, and
most lifeforms except for a few acid-tolerantsubsequently underlying sands have developed
bacteria  and  sediment-dwelling  organisms.in dune-like fashion over a large part of the
area. The resulting mesquite dunes have
Introduction of Exotic Species. The spread ofproven highly resistant to efforts to restore
exotics has become a problem in almost everythe native grasslands, although almost every
ecosystem of the world. Transporting speciesintervention has been tried, including highly
from their native habitat to entirely newtoxic defoliants (Agent Orange), fire, and
ecosystems can wreck havoc, as the newbulldozing.
environments are often without natural checks
and balances for the new species. In theEven where it has been possible to restore
Great Lakes Basin, the accidentalsome of the ecological functions of degraded
introduction of two small pelagic fishes, theecosystems, and thus improve ecosystem
alewife and the rainbow smelt, combined withhealth, the restoration seldom results in
the simultaneous overharvesting of naturalreestablishment of the pristine biotic
predators, such as the lake trout, led to acommunity. The best that can be achieved in
significant decline in native fish species.most cases is reestablishment of the key
The introduction of the sea lamprey, anecological functions that provide the
eel-like predacious fish that attacks largerrequired ecosystem services, such as the
fish, into Lake Erie and the upper Greatregulation of water, primary and secondary
Lakes further destabilized the native fishproductivity, nutrient cycling, and
community. The sea lamprey contributed to thepollination. In all such efforts, key
demise of the deepwater benthic fishindicators of ecosystem health (vigor,
community by preying on lake trout,productivity, and resilience) are essential
whitefish, and burbot. This contributed to ato monitor progress. Standard ecological
shift in the fish community from one that hadindicators can be used for this purpose
been dominated by large benthics to one(e.g., measures of productivity, species
dominated by small pelagics (fish found incomposition, nutrient flows, soil fertility)
the upper layers of the lake profile). Thisalong with socioeconomic and human health
shift from bottom-dwelling fish (benthic) toindicators.
surface-dwelling fish (pelagic) has now been
partially reversed by yet another accidentalExperience in efforts to restore highly
introduction of an exotic: the zebra mussel.damaged ecosystems suggests that
As the zebra mussel is a highly efficientecosystem-health prevention is far more
filter of both phtyoplankton and zooplankton,effective than restoration. For marine
its presence has reduced the available foodecosystems, setting aside protective zones
in the surface waters for pelagic fish.that afford a sanctuary for fish and wildlife
However, while the benthic fish community hashas considerable promise. Many countries are
gained back its dominance, the preferredadopting policies to establish such areas
benthic fish species have not yet recoveredwith the prospect that these healthy regions
owing to the degree of initial degradation.can serve as a reservoir for biota that have
Overall, the increasing dominance by exoticsbecome depleted in the unprotected areas. Yet
not only altered the ecology, but alsothis remedy is not without its limits.
reduced significantly the commercial value ofRestoring ecosystem health is not simply a
the  fisheries.matter of replenishing lost or damaged biota.
It is also a matter of reestablishing the
Global Change. Rapid climate change (orcomplex interactions among ecosystem
climate warming) is an emerging potentiallifeforms. Having a ready source of healthy
global stress on all of the earth'sbiota that could potentially recolonize
ecosystems. In evolutionary time, there havedamaged ecosystems is important, but it is
of course been large fluctuations in climate.only  part  of  the  solution.
However, for the most part these fluctuations
have occurred gradually over long periods ofPREVENTION  OF  ECOSYSTEM  DISRUPTIONS
time. Rapid climate change is an entirely
different matter. By altering both averagesGiven the difficulties in reversing ecosystem
and extremes in precipitation, temperature,degradation, and the many associated human
and storm events, and by destabilizing the Elhealth risks that arise with the loss of
Niño Southern Oscillation (ENSO), whichecosystem health, the most effective approach
controls weather patterns over much of theis simply the prevention of ecosystem
southern Pacific region, many ecosystemdisruption. However, like many common-sense
processes can become significantly altered.approaches, this is easier said than done. In
Excessive periods of drought or unusuallyboth developed and developing countries there
heavy rains and flooding will exceed theis a strong inclination to continue economic
tolerance for many species, thus changing thegrowth, even at the cost of severe
biotic composition. Flooding and unusuallyenvironmental damage. Apart from selfish
high winds contribute to soil erosion, and atmotivations, the argument is made that
the same time add to nutrient load in riverseconomic growth has many obvious health
and  coastal  waters.benefits, such as providing more efficient
means of distributing food supplies,
These anthropogenic stresses have compromisedproviding more plentiful food, and providing
ecosystem function in most regions of thebetter health services and funding for
world, resulting in ecosystem distressresearch to improve standards of living.
syndrome (EDS). EDS is characterized by aThese are indeed benefits of economic
group of signs, including abnormalities indevelopment, and have led to substantial
nutrient cycling, productivity, speciesincreases  in  health  status  worldwide.
diversity and richness, biotic structure,
disease prevalence, soil fertility, and soHowever, at the dawn of the twenty-first
on. The consequences of these changes forcentury, the past is not necessarily the best
human health are not inconsiderable.guide to the future. The human population is
Impoverished biotic communities are naturalat an all-time high, and associated pressures
harbors for pathogens that affect humans andof human activity have led to increasing
other  species.degradation of the earth's ecosystems. As
ultimately healthy ecosystems are essential
ECOSYSTEM  HEALTH  AND  HUMAN  HEALTHfor life of all biota, including humans,
current global and regional trends are
An important aspect of ecosystem degradationominous. Under these circumstances, a
is the associated increased risk to humantradeoff between immediate material gains and
health. Traditionally, the concern has beenlong-term sustainability of humans on the
with contaminants, particularly industrialplanet may be the only option. If so, the
chemicals that can have adverse impacts onsolution to sustaining human health and
human development, neurological functions,ecosystem health becomes one of devising a
reproductive functions, and that appear to benew politic that places sustaining life
causative agents in a variety of carcinomas.support systems as a precondition for
In addition to these serious environmentalbetterment  of  the  human  condition.
concerns (where the remedies are often
technological, including engineeringBIBLIOGRAPHY
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