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Imbalance of Ecosystems and Its Effect on Public and Livestock Health

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