Imbalance of Ecosystems and Its Effect on Public and Livestock Health

Imbalance of Ecosystems and Its effect on Public and				cholera involved more regions than at any previous
Livestock health				time in the twentieth century. The disease remains
Dr.Kedar Karki M.V.St. (Preventive veterinary Medicine)				endemic in India, Bangladesh, and Africa. Vibrio
Central Veterinary Laboratory Tripureshwor				cholerae has also been found in the United States-in
The health of humans, like all living organisms, is				the Gulf Coast region of Texas, Louisiana, and Florida;
dependent on an ecosystem that sustains life. Healthy				the Chesapeake Bay area; and the California coast.
ecosystems are the sine qua non for healthy				The increase in prevalence of V. cholerae has been
organisms. Yet there is abundant evidence that many				strongly linked to degraded coastal marine
life-support systems are far from healthy, placing an				environments. Nutrient-enriched warmer coastal
increased burden on human health. In some areas of				waters, resulting from a combination of climate change
the world, gains in life expectancy and quality of life				and the use of fertilizers, provides an ideal environment
made during the twentieth century are at risk of being				for reproduction and dissemination of V. cholerae.
reversed in the twenty-first century. The				Recent outbreaks of cholera in Bangladesh, for
consequences of ecosystem degradation to human				example, are closely correlated with higher sea
health are numerous, and include health risks from				surface temperatures. V. cholerae attach to the
unsafe drinking water, polluted air, climate change,				surface of both freshwater and marine copepods
emerging new diseases, and the resurgence of old				(crustaceans), as well as to roots and exposed
diseases owing to ecological imbalances. Reversing				surfaces of macrophytes (aquatic plants) such as the
this damage is possible in some cases, but not in				water hyacinth, the most abundant aquatic plant in
others. Prevention of ecological damage is by far the				Bangladesh. Nutrient enrichment and warmer
most efficient strategy.				temperatures give rise to algae blooms and an
DEFINING ECOSYSTEMS				abundance of macrophytes. The algae blooms provide
An ecological system may be defined as a community				abundant food for copepods, and the increasing
of plants and animals interacting with each other and				copepod and macrophyte populations provide V.
their abiotic, or natural, environment. Typically,				cholerae with habitat. Subsequent dispersal of V.
ecosystems are differentiated on the basis of				cholerae into estuaries and fresh water bodies allows
dominant vegetation, topography, climate, or some				contact with humans who use these waters for
other criteria. Boreal forests, for example, are				drinking and bathing. Global distribution of marine
characterized by the predominance of coniferous				pathogens such as V. cholerae is further facilitated by
trees; prairies are characterized by the predominance				ballast water discharged from vessels. Ballast water
of grasses; the Arctic tundra is determined partly by				contains a virtual cocktail of pathogens, including V.
the harsh climatic zone. In most areas of the world, the				cholerae.
human community is an important and often dominant				Two other examples of how ecological imbalances
component of the ecosystem. Ecosystems include not				lead to human health burdens concern the increased
only natural areas (e.g., forests, lakes, marine coastal				prevalence of Lyme disease and hantavirus pulmonary
systems) but also human-constructed systems (e.g.,				disease. Lyme disease, sonamed because it was first
urban ecosystems, agro-ecosystems, impoundments).				positively identified in Lyme, Connecticut, is a crippling
Human populations are increasingly concentrated in				arthritic-type disease that is transmitted by
urban ecosystems, and it is estimated that, by the year				spirochete-infected Ixodes ticks (deer ticks). Ticks
2010, 50 percent of the world's population will be living				acquire the infection from rodents, and spend part of
in urban areas.				their life cycle on deer. Three factors have combined
A landscape comprises a mosaic of ecosystems,				to increase the risk to humans of contracting Lyme
including towns, rivers, lakes, agricultural systems, and				disease, particularly in North America: (1) the elimination
so on. Precise boundaries between ecosystems are				of natural deer predators, particularly wolves; (2)
often difficult to establish. Often regions slide into one				reforestation of abandoned farmland has created
another gradually, over a protracted "transition" zone,				more favorable habitat for deer; and (3) the creation
as for example between the boreal forest and the				of suburban estates, which the deer find ideal habitat
Taiga regions of Canada.				for browsing. The net result is a rising deer population,
ECOSYSTEM HEALTH				which increases the chances of humans coming into
It is important to recognize the inherent difficulties in				more contact with ticks.
defining "health," whether at the level of the individual,				By 1995, in the southwestern United States, hantavirus
population, or ecosystem. The concept of health is				infection was confirmed in ninety-four persons in
somewhat of an enigma, being easier to define in its				twenty states, with 48 percent mortality. Variants of
absence (sickness) than in its presence. Perhaps				the strain that causes hantavirus pulmonary syndrome
partially for that reason, ecologists have resisted				have also been found in other areas of the country, as
applying the notion of "health" to ecosystems. Yet,				well as in Asia and Europe. The virus is apparently
ecosystems can become dysfunctional, particularly				asymptomatic in rodents, and it is transmitted in their
under chronic stress from human activity.Example for				saliva and excreta. In humans it has a flu-like
this can be cited the discharge of nutrients from				presentation, which is followed by acute respiratory
sewage, industrial waste, or agricultural runoff into				distress syndrome. The primary reservoir in the Four
lakes or rivers affects the normal functioning of the				Corners area of the southwestern United States is the
ecosystem, and can result in severe impairment.				deer mouse. Climatic disturbances, which in recent
Excessive nutrient inputs from human activity was one				years are thought to be exacerbated by human
of the major factors that severely compromised the				activity (e.g., global warming), appear to set up
health of the lower Laurentian Great Lakes (Lake Erie				conditions that trigger outbreaks. In the early 1990s,
and Lake Ontario) and regions of the upper Great				ENSO events initially caused drought conditions to
Lakes (Lake Michigan). Unfortunately, degraded				develop in the southwestern United States. This led to
ecosystems are becoming more the rule than the				a decline in plant and animal populations, including
exception.				natural predators of the deer mouse. Heavy rains
The study of the features of degraded systems, and				followed the drought in 1993, resulting in a bumper crop
comparisons with systems that have not been altered				of piÃ±on nuts, a major food supply for the deer
by human activity, makes it possible to identify the				mouse. Subsequently the deer mouse population
characteristics of healthy ecosystems. Healthy				greatly increased, bringing about increased contact
ecosystems may be characterized not only by the				with humans and triggering the outbreak of hantavirus.
absence of signs of pathology, but also by signs of				Antibiotic Resistance and Agricultural Practice Antibiotic
health, including measures of vigor (productivity),				resistance is a growing threat to public health. Antibiotic
organization, and resilience.				resistant strains of Streptococcus pneumoniae, a
Vigor can be assessed in terms of the metabolism				common bacterial pathogen in humans and a leading
(activity and productivity) of the system. Ecosystems				cause of many infections, including chronic bronchitis,
differ greatly in their normal ranges of productivity.				pneumonia, and meningitis, have greatly increased in
Estuaries are far more productive than open oceans,				prevalence since the mid-1970s. In some regions of the
and marshes have higher productivity than deserts.				world, up to 70 percent of bacterial isolates taken from
Health is not evaluated by applying one standard to all				patients proved resistant to penicillin and other b-lactam
systems. Organization can be assessed by the				antibiotics. The use of large quantities of antibiotics in
structure of the biotic community that forms an				agriculture and aquaculture appears to have been a
ecosystem and by the nature of the interactions				key factor in the development of antibiotic resistance
between the species (both plants and animals).				by pathogens in farm animals that subsequently may
Invariably, healthy ecosystems have more diversity of				also infect humans. One of the most serious risks to
biota than ecologically compromised systems.				human health from such practices is
Resilience is the capacity of an ecosystem to maintain				vancomycin-resistant enterococci. The use of
its structure and functions in the face of natural				avoparcin, an animal growth promoter, appears to
disturbances. Systems with a history of chronic stress				have compromised the utility of vancomycin, the last
are less likely to recover from normal perturbations				antibiotic effective against multi-drug-resistant bacteria.
such as drought than those systems that have been				In areas where avoparcin has been used, such as on
relatively less stressed.				farms in Denmark and Germany, vancomycin-resistant
Healthy ecosystems can also be characterized in				bacteria have been detected in meat sold in
economic, social, and human health terms. Healthy				supermarkets. Avoparcin was subsequently banned
ecosystems support a certain level of economic				by the European Union. Another example is the use of
activity. This is not to say that the ecosystem is				ofloxacin to protect chickens from infection and
necessarily self-sufficient, but rather that it supports				thereby enhance their growth. This drug is closely
economic productivity to enable the human community				related to ciprofloxacin, one of the most widely used
to meet reasonable needs. Inevitably, ecosystem				antibiotics in the year 2000. There have been cases of
degradation impinges on the long-term sustainability of				resistance to ciprofloxacin directly related to its
the human economy that is associated with it, although				veterinary use. In the United Kingdom, ciprofloxacin
in the short-term this may not be evident, as natural				resistance developed in strains of campylobacter, a
capital (e.g., soils, renewable resources) may be				common cause of diarrhea. Multi-drug-resistant strains
overexploited and temporarily enhance economic				of salmonella have been traced to European egg
returns. Similarly, with respect to social well-being,				production.
healthy ecosystems provide a basis for and				Food and Water Security. Agricultural practices are
encourage community integration. Historically, for				also responsible for a growing number of threats to
example, native Hawaiian groups managed their				public health. Some of these are related to inadequate
ecosystem through a well-developed social				waste management, which has resulted in parasites
cohesiveness that provided a high degree of				and bacteria entering water supplies. Others are of
cooperation in fishing and farming activity.				entirely different origins and involve apparent transfer
Another reflection of ecosystem health lies directly in				across species of pathogens that affect both animals
the public health domain. In spring 2000, a deadly strain				and humans. The most recent and spectacular
of the bacterium E-coli (0157:H7) entered the public				example is mad cow disease, known as variant
water supply in Walkerton, Ontario, Canada, causing				Creutzfeldt-Jakob disease in humans, a
seven deaths and making thousands sick. This small				neuro-degenerative condition that, in humans, is
town, with a population of five thousand, is in a farming				ultimately fatal. The first case of Bovine Spongiform
community. Inadequate manure management from				Encephalopathy (BSE), the animal form of the disease,
cattle operations was the likely source of this tragedy.				was identified in Southern England in November 1981.
HOW HEALTHY ECOSYSTEMS BECOME				By the fall of 2000, an outbreak had also occurred in
PATHOLOGICAL				France, and isolated cases appeared in Germany,
Stress from human activity is a major factor in				Switzerland, and Spain. More than one hundred deaths
transforming healthy ecosystems to sick ecosystems.				in Europe were attributed to what has come to be
Chronic stress from human activity differs from natural				commonly called mad cow disease.
disturbances. Natural disturbances (fires, floods, periodic				Improper manure management was the likely source
insect infestations) are part of the dynamics of most				of the outbreak of E. coli 0157:H7 in Walkerton, Ontario,
ecosystems. These processes help to "reset"				Canada. Other health risks associated with
ecosystems by recycling nutrients and clearing space				malfunctioning agroecosystems include periodic
for recolonization by biota that may be better adapted				outbreaks of cryptosporidiosis, a parasitic disease that
to changing environments. Thus, natural perturbations				is spread by surface runoff contaminated by feces of
help keep ecosystems healthy. In contrast, chronic and				infected cattle. This parasite causes fever and
acute stress on ecosystems resulting from human				diarrhea in immunocompetent individuals and severe
activity (e.g., construction of large dams, release of				diarrhea and even death in immunocompromised
nutrients and toxic substances into the air, water, and				individuals.
land) generally results in long-term ecological				ECOSYSTEM RESTORATION
dysfunction.				Ecosystem pathology in some cases can be reversed
Five major sources of human-induced (anthropogenic)				simply by removing the source of stress. In cases, for
stresses have been identified by D. J. Rapport and A.				example, where ecosystem degradation is the result
M. Friend (1979): physical restructuring, overharvesting,				of point-source additions of nutrients or toxic chemicals,
waste residuals, introduction of exotic species, and				removal of these stresses may result in considerable
global change.				recovery of ecosystem health. A classic case is Lake
Physical Restructuring. Activities such as wetland				Washington (near Seattle, Washington). This lake had
drainage, removal of shoals in lakes, damming of rivers,				become highly anoxic (oxygen-depleted) owing to a
and road construction fragment the landscape and				sewage outfall entering the lake. Redirecting the
alter and damage critical habitat. These activities also				sewage outfall away from the lake reversed many of
disrupt nutrient cycling, and cause the loss of				the signs of pathology.
biodiversity.				In cases where it is not feasible to remove the source
Overharvesting. Overexploitation is commonplace				of stress, more innovative engineering solutions have
when it comes to harvesting of wildlife, fisheries, and				been tried. For example, in the KyrÃ¶njoki and
forests. Over long periods of time, stocks of preferred				Lestijoki Rivers in western Finland, spring and fall runoff
species are reduced. For example, the giant redwoods				leads to sharp pulses of acidity. Spring runoff from
that once thrived along the California coast now exist				snowmelt, which releases acid from tilled or dug soils,
only in remnant patches because of overharvesting.				has been particularly damaging to fish, during the critical
When dominant species like the giant redwoods				time of year for spawning. Fish reproduction is
(arguably the world's tallest tree-one specimen was				severely curtailed, if not all together eliminated in highly
recorded at 110 meters tall with a circumference of				acidic water. Further there have been massive fish kills
13.4 meters) are lost, the entire ecosystem becomes				resulting from the highly acidic waters. One possible
transformed. Overharvesting often results in reduced				remedy is to replace the original drains which take
biodiversity of endemic species, while facilitating the				runoff from the land to the rivers with new limed drains
invasion of opportunistic species.				that can neutralize the acidity. This solution has been
Waste Residuals. Discharges from municipal, industrial,				implemented on an experimental basis and appears to
and agricultural sources into the air, water, and land				substantially reduce acidic runoff.
have severely compromised many of the earth's				More radical treatments for damaged ecosystems
ecosystems. The effects are particularly apparent in				involve "ecosystem surgery." In some cases, invading
aquatic ecosystems. In some lakes that lack a natural				exotic vegetation (such as mangroves in Hawaii) have
buffering capacity, acid precipitation has eliminated				been removed from regions, and native vegetation has
most of the fish and other organisms. While the visual				been replanted. In areas of North America where
effect appears beneficial (water clarity goes up) the				wetlands have been severely depleted owing to
impact on ecosystem health is devastating. Systems				farming, urbanization, and industrial activity, efforts have
that once contained a variety of organisms and were				been made to establish new wetlands.
highly productive (biologically) become devoid of most				More often than not, however, reversing ecosystem
lifeforms except for a few acid-tolerant bacteria and				pathology is not possible. Efforts to restore the
sediment-dwelling organisms.				indigenous grasslands in the Jornada Experimental
Introduction of Exotic Species. The spread of exotics				Range in the southwestern United States provide an
has become a problem in almost every ecosystem of				example. Overgrazing by cattle has severely
the world. Transporting species from their native				degraded the landscape and has lead to replacement
habitat to entirely new ecosystems can wreck havoc,				of the native grasses by largely inedible shrubs,
as the new environments are often without natural				dominated by mesquite. Erosion by wind and episodic
checks and balances for the new species. In the Great				heavy rains have left areas between shrubs largely
Lakes Basin, the accidental introduction of two small				bare, and subsequently underlying sands have
pelagic fishes, the alewife and the rainbow smelt,				developed in dune-like fashion over a large part of the
combined with the simultaneous overharvesting of				area. The resulting mesquite dunes have proven highly
natural predators, such as the lake trout, led to a				resistant to efforts to restore the native grasslands,
significant decline in native fish species. The introduction				although almost every intervention has been tried,
of the sea lamprey, an eel-like predacious fish that				including highly toxic defoliants (Agent Orange), fire, and
attacks larger fish, into Lake Erie and the upper Great				bulldozing.
Lakes further destabilized the native fish community.				Even where it has been possible to restore some of
The sea lamprey contributed to the demise of the				the ecological functions of degraded ecosystems, and
deepwater benthic fish community by preying on lake				thus improve ecosystem health, the restoration seldom
trout, whitefish, and burbot. This contributed to a shift in				results in reestablishment of the pristine biotic
the fish community from one that had been dominated				community. The best that can be achieved in most
by large benthics to one dominated by small pelagics				cases is reestablishment of the key ecological
(fish found in the upper layers of the lake profile). This				functions that provide the required ecosystem
shift from bottom-dwelling fish (benthic) to				services, such as the regulation of water, primary and
surface-dwelling fish (pelagic) has now been partially				secondary productivity, nutrient cycling, and pollination. In
reversed by yet another accidental introduction of an				all such efforts, key indicators of ecosystem health
exotic: the zebra mussel. As the zebra mussel is a				(vigor, productivity, and resilience) are essential to
highly efficient filter of both phtyoplankton and				monitor progress. Standard ecological indicators can be
zooplankton, its presence has reduced the available				used for this purpose (e.g., measures of productivity,
food in the surface waters for pelagic fish. However,				species composition, nutrient flows, soil fertility) along
while the benthic fish community has gained back its				with socioeconomic and human health indicators.
dominance, the preferred benthic fish species have not				Experience in efforts to restore highly damaged
yet recovered owing to the degree of initial				ecosystems suggests that ecosystem-health
degradation. Overall, the increasing dominance by				prevention is far more effective than restoration. For
exotics not only altered the ecology, but also reduced				marine ecosystems, setting aside protective zones
significantly the commercial value of the fisheries.				that afford a sanctuary for fish and wildlife has
Global Change. Rapid climate change (or climate				considerable promise. Many countries are adopting
warming) is an emerging potential global stress on all of				policies to establish such areas with the prospect that
the earth's ecosystems. In evolutionary time, there				these healthy regions can serve as a reservoir for
have of course been large fluctuations in climate.				biota that have become depleted in the unprotected
However, for the most part these fluctuations have				areas. Yet this remedy is not without its limits.
occurred gradually over long periods of time. Rapid				Restoring ecosystem health is not simply a matter of
climate change is an entirely different matter. By				replenishing lost or damaged biota. It is also a matter of
altering both averages and extremes in precipitation,				reestablishing the complex interactions among
temperature, and storm events, and by destabilizing the				ecosystem lifeforms. Having a ready source of
El NiÃ±o Southern Oscillation (ENSO), which				healthy biota that could potentially recolonize damaged
controls weather patterns over much of the southern				ecosystems is important, but it is only part of the
Pacific region, many ecosystem processes can				solution.
become significantly altered. Excessive periods of				PREVENTION OF ECOSYSTEM DISRUPTIONS
drought or unusually heavy rains and flooding will				Given the difficulties in reversing ecosystem
exceed the tolerance for many species, thus changing				degradation, and the many associated human health
the biotic composition. Flooding and unusually high winds				risks that arise with the loss of ecosystem health, the
contribute to soil erosion, and at the same time add to				most effective approach is simply the prevention of
nutrient load in rivers and coastal waters.				ecosystem disruption. However, like many
These anthropogenic stresses have compromised				common-sense approaches, this is easier said than
ecosystem function in most regions of the world,				done. In both developed and developing countries there
resulting in ecosystem distress syndrome (EDS). EDS				is a strong inclination to continue economic growth,
is characterized by a group of signs, including				even at the cost of severe environmental damage.
abnormalities in nutrient cycling, productivity, species				Apart from selfish motivations, the argument is made
diversity and richness, biotic structure, disease				that economic growth has many obvious health
prevalence, soil fertility, and so on. The consequences				benefits, such as providing more efficient means of
of these changes for human health are not				distributing food supplies, providing more plentiful food,
inconsiderable. Impoverished biotic communities are				and providing better health services and funding for
natural harbors for pathogens that affect humans and				research to improve standards of living. These are
other species.				indeed benefits of economic development, and have
ECOSYSTEM HEALTH AND HUMAN HEALTH				led to substantial increases in health status worldwide.
An important aspect of ecosystem degradation is the				However, at the dawn of the twenty-first century, the
associated increased risk to human health. Traditionally,				past is not necessarily the best guide to the future.
the concern has been with contaminants, particularly				The human population is at an all-time high, and
industrial chemicals that can have adverse impacts on				associated pressures of human activity have led to
human development, neurological functions,				increasing degradation of the earth's ecosystems. As
reproductive functions, and that appear to be				ultimately healthy ecosystems are essential for life of
causative agents in a variety of carcinomas. In addition				all biota, including humans, current global and regional
to these serious environmental concerns (where the				trends are ominous. Under these circumstances, a
remedies are often technological, including engineering				tradeoff between immediate material gains and
solutions to reduce the release of contaminants), there				long-term sustainability of humans on the planet may
are a large number of other risks to human health				be the only option. If so, the solution to sustaining
stemming from ecological imbalance.				human health and ecosystem health becomes one of
Ecosystem distress syndrome results in the loss of				devising a new politic that places sustaining life support
valued ecosystem services, including flood control,				systems as a precondition for betterment of the
water quality, air quality, fish and wildlife diversity, and				human condition.
recreation. One of the major signs of EDS is increased				BIBLIOGRAPHY
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Imbalance of Ecosystems and Its Effect on Public and Livestock Health

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