Water Is Necessary For Life Biology Essay

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Water is necessary for life. Over 70 of the surface of the Earth is water. Of this, only 3 is freshwater found in glaciers, lakes, groundwater, and rivers, and in the atmosphere. Water means different things to different people, and is used as a food resource; as a means of power; as a coolant, cleanser, and dilutant; for navigation; for recreational purposes; as a source of tranquil aesthetic enjoyment; as a transporter of disease; as a container for nuisances; and finally, as the once unlimited area for disposal of society's waste products.

Aquatic environments are vast in quantity and varied in quality. They consist of small streams from snow-capped mountains, brooks, lakes, small and great rivers, coastal estuaries, and oceans. All aquatic environments are affected by their altitude, latitude, area, mean depth, maximum depth, area of different depth zones, volume of different depth strata, length of shoreline, slope, drainage area, runoff rate, average inflow and outflow, detention time, water level fluctuation, number of islands or other masses present within the water, physical composition of the water bed, physical nature of the surrounding terrain, area geology, and untold number of uses and reuses by humans, animals, insects, worms, fish, plants, and trees. Water quality is affected by temperature, amount of dissolved oxygen (DO) present, pH, light flow of water, amount of silt, oil, major nutrients, and contaminants. Water quality affects humans through their direct use of water. It also affects the aquatic life contained in the water.

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Ecosystem

The earth is divided into the lithosphere, or land masses, and the hydrosphere, or the oceans, lakes, streams, and underground waters. The hydrosphere includes the entire aquatic environment. Our world, both lithosphere and hydrosphere, is shaped by varying life forms. Permanent forms of life create organic matter and, in combination with inorganic materials, help establish soil. Plants cover the land and reduce the potential for soil erosion - the nature and rate of erosion affects the redistribution of materials on the surface of Earth. Organisms assimilate vast quantities of certain elements and molecules, such as carbon and oxygen. Animals, through respiration, release carbon dioxide into the atmosphere - carbon dioxide affects the heat transmission of the atmosphere. Organisms affect the environment and in turn are affected by it.

Two environments, biotic (living) and abiotic (nonliving), combine to form an ecosystem. An ecosystem can also be subdivided by more specific criteria into the following four categories: (1) abiotic, the nutrient minerals that are synthesized into living protoplasm; (2) autotrophic, the producer organisms (largely the green plants) that assimilate the nutrient minerals using energy and combine them into living organic substances; (3) heterotrophic, the consumers, usually the animals, that ingest or eat organic matter and release energy; and (4) heterotrophic reducers, the bacteria or fungi that return the complex organic compounds to their original abiotic state and release the remaining chemical energy. The biotic group in the ecosystem complex is essentially composed of the autrotophs, or producer organisms that synthesize organic substances, and the heterotrophs, or consumer or reducer organisms that decompose labile organic substances. The ecosystem is important when considering the food chain, which is in effect a transfer of energy from plants through a series of organisms that eat and, in turn, are eaten. Eventually, decay will start the process all over again.

The biosphere is that part of Earth - lithosphere and hydrosphere - in which life exists. However, this definition is not complete, because spores may commonly be found in areas that are too dry, too cold, or too hot to support organisms that metabolize. The biosphere contains the liquid water necessary for life, it receives an ample supply of energy from an external source, which is ultimately the Sun, and within it liquid, solid, and gaseous states of matter interface. All the actively metabolizing organisms operate within the biosphere. The operation of the biosphere depends on photosynthesis, during which carbon dioxide is reduced to form organic compounds and molecular oxygen. Oxygen, the by-product of photosynthesis, replenishes the atmosphere and most of the free water, which contains dissolved oxygen.

Hydrologic Cycle

The hydrologic cycle consists of inflows, outflows, and storage. Precipitation from the clouds comes to the earth in the form of rain, snow, sleet, dew, fog, and hail. When the precipitation falls, a part of it may evaporate and return immediately to the atmosphere. Precipitation that is in excess of the amount that wets a surface, or evaporates, is a potential source of water. Plants, trees, or other green materials also resupply the clouds through transpiration. Additional moisture evaporates from rivers, lakes, streams, and other bodies of water. The water that arrives on the ground either may replenish the soil moisture that is needed by growing plants, and then eventually returned to the atmosphere by transpiration, or may penetrate below the root zone and fill voids within the earth to form a zone known as the zone of saturation or it may run off the ground into streams, rivers, and oceans. When the water in the hydrologic cycle penetrates the subsoil and goes into the water table, it may be taken out by wells or springs, and utilized in homes. It then carries waste material. The water portion eventually comes back to the streams, rivers, oceans, and clouds. The underground water may also flow into underground rivers, which may surface at some point, or may simply stay in the ground until the water is ready to be utilized.

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Human Impact on Water Cycle

Although Earth's water supply remains constant, people are capable of altering the cycle. The increase in population, rising standards of living, and growth of industry have made greater demands on the environment. The activities of people may affect the quantity, quality, and availability of natural water resources in any given area. A large population not only uses more water but also discharges more wastewater. Water supplies are overloaded with hazardous chemicals and bacteria from domestic; agricultural, and industrial waste, where intensive use of pesticides, herbicides, fertilizers, and industrial chemicals are utilized. Poor irrigation increases soil salinity and evaporation. The previous factors reduce the availability of potable water. Large cities accompanied by large suburban areas affect local climate and hydrology. Urbanization accelerates drainage of water through road drains and cities sewer systems, also causing an increase in urban flooding. The rates of infiltration, evaporation, and transpiration are altered from the natural setting, reducing the replenishment of groundwater aquifers. All these factors have very negative consequences for river watersheds, lake levels, aquifers, and environment in general.

Water Problems

Natural water pollution is created through the silt that washes down along water beds due to rain or snow carrying dust, dust particles, and other material into the water. Artificial pollution, until recently, was mostly created by domestic and industrial waste. The pollution problems were usually of a local nature and needed a local solution. However, as the national growth has increased, the production of goods has increased sharply and with it the production of common industrial waste has increased sharply. Further, new processes in manufacturing have produced new complex wastes that have not been easily handled by the current control technologies. The increased use of commercial fertilizers and the wide use of large number of pesticides have contaminated many of our waters. Radioactive materials have entered waters by means of precipitation from the radioactive dust created by nuclear explosions. At present, long stretches of interstate streams have become polluted and are continuing to be polluted.

Pollution usually is classified as either point source or nonpoint source. Non-point source pollution results from a vast variety of human activities, either within or outside the urban area. This includes wastewater from homes, drainage from landfills, and so on. In the rural areas, drainage comes from agricultural practices, croplands, and also any of the vast uses of pesticides. Point source pollution has come form specific industrial operations where specific materials have been dumped into the receiving waters.

Industry uses an enormous amount of water for cooling and processing. The largest amount of water utilized, which is over 90%, is for cooling purposes. The major amount is used to condense steam is thermal electric power stations. Excluding electrical utilities, industry still uses twice as much water for cooling as for processing and other purposes. Although most of the water used for cooling does not have any significant contaminant, these may be added through treatment chemicals, use of direct contact condenses, or leakage of the process into the water.

A definite problem occurs when the blowdown from an open recirculating system containing considerable hexavalent chromium or other compounds enters the water supply. Chromates and phosphates are used to control corrosion. Bromine, chlorine, copper, mercury salts, and quaternary amines are used to inhibit biological growths. The blowdown water comprises 0.5 to 2.0% of the total water used in the recirculation system. Another problem that is created in the cooling water is thermal pollution occurring as a result of the heat that has been absorbed by the water during the cooling process.

Water is used in the following ways and contains some potentially hazardous materials, such as a reactant in a chemical reaction in the production of acetylene, calcium carbide, or phosphoric acid; or such as a reaction medium to facilitate the mixing and contact of all compounds in the chemical pulping or sulfite process or in metal finishing baths. As a solvent, water is considered the universal solvent. Examples of this use include hot water extraction of glues and gelatin from skin and bones, leaching or metallic ores by acid and alkaline materials, and extraction or removal of inorganic salts from crude oils. Water is also used for cleaning and washing of products, such as in the washing of fruits and vegetables, pulp washing after digestion, pulp washing after bleaching, or washing and soaking of any material where dirt, salts and blood are to be removed; and an intermediate and final rinse, such as in the rinsing of parts after plating or pickling, or after alkaline cleaning and metal finishing. Water is also used for washing equipment that contains grease, flour, sugar, or vast numbers of impurities; for quenching hot coke, glass furnace slag, or hot metals; for scrubbing of gases and carrying off any impurities that would have escaped from the smokestack; for transporting, thereby receiving all the contaminants of the material transported; as a processing medium, such as the flotation of ores and wet grinding; and as control of temperature at critical stages in industrial processes, such as in the nitration of toluene to produce trinitrotoluene (TNT). As a result of these uses and various additional uses, a tremendous number of potential or actual wastewater sources enter the water stream.

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Environmental Problems and Human Health

Water, our most precious resource, is used to sustain life, support the growth of food, develop business and industry, and provide recreation. Despite these essential human needs, individuals, municipalities, industries, commercial establishments, and agriculture continue to pollute our water supply. Historically many of our worst epidemics have been caused by contaminated water.

Chemical pollution has also created new hazards. Mercury has caused food poisoning. Oil spills have caused the deaths of birds and fish, and have befouled once lovely beach areas. Insecticides have caused millions of fish to die and could well cause serious harm to people. Fertilizers are helping destroy our streams and lakes by transforming them into open sewers.

Potable water used for drinking and swimming may be unsafe because of physical, chemical, and bacteriologic hazards. Physical deficiencies exist because of inadequate groundwater sources, inadequate design of treatment plants, inadequate disinfection capacity, inadequate system capacity, improper design of swimming pools, and inadequate training of water plant and swimming pool operators. Poor outmoded, unsafe plumbing can easily lead to contamination of potable water by nonpotable water through cross connection and submerged inlets.

Infants are susceptible to methemoglobinemia caused by the ingestion of nitrates or nitrites with drinking water. Chemicals may also affect the CNS during postnatal development, affecting particularly the cerebrum. Lead poisoning in children produces irreparable brain damage, permanent retardation, and eventual death. The frequency of occurrence of waterborne disease is increasing. In addition to water-borne infections, an increasing number of deaths occurred due to chemical poisoning through the ingestion of water. In the reuse of water, problems are created by the presence of microorganisms and toxic minerals, which ordinarily are not found in the initial pure water supply.

Public Health Aspects of Water Pollution

Pollution is any undesirable change in the physical, chemical or biological characteristics of air, water or land. Pollution can harm the health and threaten the survival or activities of human beings and other living organisms "The earth has become a very sick planet and urgently needs a cure. A disaster is looming around. Unless otherwise checked, the whole planet would become uninhabitable" (Fig. 10.6). Whereas microbiological hazards used to be the major concern associated with water quality, today the situation has become much more complex. Water treatment plants and the chlorination process have eliminated many of the past waterborne outbreaks of disease due to microbiological factors. However, the potential for disease due to microorganisms is ever present, with actual disease outbreaks continuing to occur. From time to time, new organisms seem to create a new potential of disease.

Biological Hazards

Bacteria

Organisms associated with intestinal waste from warm-blooded animals found in wastewater may be of major pathogenic concern. Those of major pathogenic concern include Campylobacter jejuni, which may also be found in a nonhuman reservoir of cattle, dogs, cats, and poultry; Escherichia coli (pathogenic strains); Leptospira spp., which may also be found in domestic and wild mammals and rats; Salmonella paratyphi; S. typhi; Salmonella spp., found in domestic and wild mammals, birds, and turtles; Shigella sonnei, S. flexneri, S. boydii, and S. dysenteriae; Vibrio cholerae; Yersinia enterocolitica, also found in wild and domestic birds and mammals; and Y. pseudotuberculosis.

Pathogenic bacteria of minor concern as transported through sludge include Aeromonas spp., Bacillus spp., Clostridium perfringens, Coxiella burnetii, Enterobacter spp., Erysipelothrix spp., Francisella tularensis, Klebsiella spp., Legionella pneumophila, Listeria monocytogenes, Mycobactrium tuberculosi, Mycobacterium spp., Proteus spp., Pseudomonas aeruginosa, Serratia spp., Staphylococcus aureus and streptococcus spp.

Many of these organisms in themselves are major problems, depending on the route of entry into the body and the mode of transmission. Campylobacter jejuni causes acute gastroenterities with diarrhea. It may be as prevalent as salmonella and shigella. The pathogenic strains of E.coli are of three types. They are enterotoxigenic, enteropathogenic, and enteroinvasive. All produce acute diarrhea, but by different mechanisms. The fatality rates may range up to 40% in newborns. Outbreaks occur occasionally in nurseries and institutions, and are commonly found among travelers in developing countries. Leptospira spp. are bacteria excreted in the urine of domestic and wild animals. Rats are the primary source of the Leptospira to enter municipal wastewater. Leptospirosis is a group of diseases caused by the bacteria that gives the symptoms of fever, headache, chills, severe malaise, vomiting, muscular aches, and conjunctivitis; and occasionally meningitis; renal insufficiency, hemolytic anemia, and skin mucous membrane hemorrahage.

Routinely, tests are taken of the bacteriological quality of water by measuring the indicator groups, such as coliform and certain subgroupings, fecal streptococci and certain subgroupings, and other miscellaneous indicators of pollution. If these organisms are present, it is assumed that the water has been contaminated by warm-blooded animals and therefore may be a hazard to humans.

The term enteric bacteria includes all those facultative bacteria whose natural habitat is in the intestinal tract of humans and animals, including members of several different families. These bacteria are all Gram-negetative, non-spore-forming rods. The Enterobacteriaceae family includes the Escherichieae, made up of Escherichia, Edwardsiella, Citrobacter, Salmonella, and Arozona; the Klebsielleae, made up of Klebsiella, Enterobacter, Hafnia, and Serratia; the Proteae, made up of Proteus; Yersinieae, made up of Yersinia; and Erwinieae, made up of Erwinia. Obligate anaerobic bacteria, which constitute 95 to 99% of the intestinal flora, are usually not included in the term anaerobic bacteria. The term total coliform defines the indicator that is looked for as an indication of contamination of the water.

Pathogenic bacteria found in the feces of infected persons, including the following, are of great concern:

 Campylobacter jejuni

 Escherichia coli (enteropathogenic strains)

 Salmonella paratyphi (A, B, C)

 S. typhi

 Salmonella small species

 Shigella sonnei, S. flexneri, S. boydii, S. dysenteriae

 Vibrio cholerae

 Yersinia enterocolitica, Y. pseudotuberculosis

Fecal streptococci are excellent indicators of human waste pollution. These organisms are also called enterococci, group D streptococci, and streptococcus fecalis. Fecal streptococci are associated with human feces and therefore could be good indicator organisms. However, the difficulty with using these organisms is that a special medium is needed for the growth of all the varieties of streptococci that fall into the fecal strep group. The pH range of the fecal strep must be dept at 4 to 9, and the samples must be analyzed as quickly as possible. Storm water and combined sewers are known to carry a variety of fecal strep in substantial numbers. Generally, if surface waters contain fecal strep and few or no other warm-blooded animals are present, the problem can be attributed to humans.

Shigellosis or bacillary dysentery, is rarely fatal, but it can create a serious hazard to the young, very old, or debilitated, and of course can create a carrier state in the individual. Shigellosis may be caused by a variety of shigella, including Shigella dysentriae, S. sonnei, S. flexneri, and others. Humans are the reservoir for the infectious spread of this disease for a period of up to 1 to 2 years.

Paratyphoid fever caused by Salmonella paratyphi and other salmonella comes from humans through urine or feces.

Although the actinomycetes and the filamentous iron bacteria do not cause disease, they do cause odors that are annoying in water supplies. They may create accumulations, which cause taste, odor, and color problems, and also clog piping systems or wells.

Bacteria are commonly found in water when it either rains or snows. The rain washes the bacteria out of the air and into the water supply. The bacterial content varies with the amount dust and the total bacteria count in the air. Large numbers of bacteria enter the water from runoff from various lands. The bacteria may act in unpredictable manners, depending on the quantity of nutrients present and the amount of bacteria available plus temperature, pH, speed of the stream, presence of predators, amount of sedimentation, antibiotics and toxins in the water, salinity, turbidity, and presence of industrial waste.

Viruses

A variety of potential viral diseases may also be transmitted through water from human feces. At times, small but very intense outbreaks of infectious hepatitis have been traced to drinking water from contaminated wells, ponds, or streams. Any of the enteric viruses may exist in the water, and therefore may create potential hazards to humans. The organisms causing outbreaks of water borne disease are assumed to be viral in nature, but have not been tracked down adequately. Adenoviruses that produce acute respiratory diseases and eye infections have been associated with chlorinated swimming pools. It is known from laboratory studies that several viruses classified in the enteric group have survived storage in certain cold waters from 6 to 7 months. These apparently can then become a source of potential disease hazards.

Human enteric viruses may be present in wastewater and sludge. These viruses include the enteroviruses, such as polio virus, coxsackie virus A, coxsackie virus B, and echovirus. Also found in human waste are the hepatitis A virus, rotavirus (duovirus, reovirus-like agent), adenovirus, reovirus, astrovirus, calcivirus, and coronavirus-like particles.

When the viruses enter into the alimentary tract if they are not inactivated by the hydrochloric acid, bile, acids, salts, and enzymes, they may multiply within the gut. Occasionally after continued multiplication in the lymphoid tissue of the pharynx and gut, viremia may occur. In viremia, the virus enters the bloodstream, leading to further virus proliferation in the cells of the reticuloendothelial system and finally the involvement of the major target organs.

Polioviruses cause poliomyelitis, an acute disease that may range from fever to aseptic meningitis, muscle weakness, or complete paralysis. The weakness and paralysis are caused by the destruction of motor neurons in the spinal cord. Although polio is rare today, it may be found in nonimmunized populations in the rest of the world. There does not appear to be any reliable evidence that the poliovirus is spread by wastewater at this time.

Coxsackie viruses may cause aseptic meningitis, myocarditis, pericarditis, pneumonia, rashes, common colds, fever, hepatitis, and infant diarrhea. The echoviruses may cause aseptic meningitis, paralysis, encephalitis, fever, rashes, colds, pericarditis, myocarditis, and diarrhea. The enteroviruses may cause pneumonia, bronchitis, acute hemorrhagic conjunctivitis, aseptic meningitis, encephalitis, and hand, foot, and mouth disease.

Hepatitis A virus causes infectious hepatitis that may range from an inapparent infection, especially in children to fulminating hepatitis and jaundice. Childhood infections are most common and tend to be asymptomatic.

Rotaviruses cause acute gastroenteritis with severe diarrhea, sometimes resulting in dehydration and death in infants. These viruses are the most important cause of acute gastroenteritis in infants and young children, and can be affect older children and adults.

Norwalk-like agents cause epidemic gastroenteritis, diarrhea, vomiting, abdominal pain, headache, and malaise. The disease is generally mild and self-limiting. Sporadic outbreaks of this disease occur in school children and in adults.

Adenoviruses are primarily the cause of respiratory and eye infections transmitted by the respiratory route. However, several of these may be enteric and be important causes of sporadic outbreaks of gastroenteritis in young children.

Reoviruses have been isolated from the feces of patients with a variety of diseases. However, no clear etiologic relationship has been established at this point. Reovirus infections may be common in people, but they may be mild or have clinical manifestations. Papovaviruses have been found in urine. Astroviruses, calciviruses, and coronavirus-like particles may be associated with human gastroenteritis, producing diarrhea. These diseases are poorly understood.

Viruses are not normal inhabitants of the gastrointestinal tract or regular components, even in feces. Therefore, the use of coliforms and fecal streptococci as indicators of the potential viral contamination to the environment is useful. Viruses in wastewater do not behave the same as bacteria. Viruses are less easily removed by treatment processes and during passage through the soil. Removal of the polio virus varies from 0 to 69%; coxsackie virus, from 90 to 94%; and other viruses, from 53 to 71%. The concentration of viruses in unaffected people is normally zero.

The survival time of viruses at a sludge application site is primarily of concern, because the longer the viruses survive at the surface, the greater the opportunity they have for moving through the soil toward the groundwater.

There seems to be little reliable information concerning viruses getting into groundwater beneath sludge application sites. Once enteric viruses do get into groundwater, however, they can survive for long periods of time ranging from 2 to 180 days. Enteroviruses have been found at depths of 54 to 201 ft (1645 to 6126 cm) from a septic tank leach field in shallow sandy aquifer.

Human polio viruses, coxsackie viruses, echoviruses, and reoviruses have been recovered from, or found to produce, an infection in dogs, cats, swine, cattle, horses, and goats. Dogs and cats were found to be involved in the majority of these infections, probably because of their intimate association with people in the household. Information is insufficient at this point to determine the effect of virus transmission in animals and its relationship to transmission in people.

In contrast to bacteria where a large number of bacterial cells are usually needed to produce an infection, a few virus particles may be able to produce an infection under favorable conditions.

Because viruses do not regrow in foods or other environmental media as bacteria sometimes will, the risk of infection is totally dependent on exposure to an effective dose immediately transmitted to the material.

Fecally polluted vegetable garden irrigation water has been found to contain polio viruses and coxsackie viruses, and has been associated with epidemics among the people consuming the garden products. It is thought that epidemiological techniques are probably not sensitive enough to detect the low levels of viral disease transmission that might occur from a modern land application of sludge.

Protozoa

Protozoa and helminths (worms) are often grouped together as parasites. However, helminths are discussed in another subsection immediately following this one. Because of the large size of protozoan cysts and helminth eggs compared with bacteria and viruses, it is likely that they are present in either aerosols or groundwater at the land application sites.

The most common protozoa found in wastewater and sludge are:

 Entamoeba histolytica of the protozoan class Amoeba

 Giardia lamblia of the protozoan class Flagellate

 Balantidium coli of the protozoan class Ciliate

 Toxoplasma gondii of the protozoan class sporozoan (Coccidia)

 Dientamoeba fragilis of the protozoan class Amoeba

 Isospora belli of the protozoan class sporozoan (Coccidia)

 I. hominis of the protozoan class sporozoan (Coccidia)

Entamoeba histolytica causes amoebiasis or amoebic dysentery, an acute enteritis, with symptoms ranging from mild abdomical discomfort with diarrhea to fulminating dysentery with fever, chills, and bloody or mucoid diarrhea. Although most infections are asymptomatic, in severe cases abscesses appear in the liver, lungs, or brain, and death may result. The cysts are transmitted by contaminated water or blood.

Giardia lamblia causes giardiasis, which is often an asymptomatic infection of the small intestine. This may be associated with chronic diarrhea, malabsorption of fats, abdominal cramps, bloating, fatigue, and weight loss. The disease is transmitted by cysts that have contaminated water or food, or may be spread person to person by contact.

Balantidium coli causes balantidiasis, which is a disease of the colon characterized by diarrhea or dysentery. Infections are often asymptomatic, and the incidence of disease in people is very low. The disease is transmitted by cysts that contaminate water. This is particularly true of water contaminated by pigs.

Toxoplasma gondii causes toxoplasmosis, which is an asymptomatic disease that rarely gives rise to critical illness. However, it can damage the fetus if a woman is infected and congenital transmission occurs during pregnancy. The infection is probably transmitted by cysts in cat feces or the consumption of cyst contaminated inadequately cooked meat of infected animals.

The active stage of protozoans in the intestinal tract of infected individuals is the trophozolite. The trophozolites after a period of reproduction may form precysts, which secrete tough membranes to become environmentally resistant cysts. The cysts are then excreted in the feces. The types and amounts of protozoan cysts found in wastewater depend on the levels of disease in the human population and on the degree of animal contribution to the system.

The protozoan cysts are sensitive to drying, and therefore should die off rapidly when exposed to the air or when deposited on the surfaces of plants. However, under poor management of the human food supply, cysts of Entamoeba histolytica and Giardia lamblia have been found on irrigated fruits and vegetables where wastewater has been used as the source of irrigation. A low infected dose of protozoan cysts may cause disease. It is, therefore, important that humans maintain minimum contact with any active land application of sewage and sludge.

Helminths

The pathogenic helminths whose eggs are of major concern in wastewater and sludge are divided into two categories. They are the nematodes or roundworms, and cestodes or tapeworms.

The nematodes of concern are:

 Enterobius vermicularis is the pinworm that causes enterobiasis

 Ascaris lumbricoides is the roundworm that causes ascariasis

 A. suum is the swine roundworm that causes ascariasis

 Trichuris trichiura is the whipworm that causes trichuriasis

 Necator americanus is the hookworm that causes necatoriasis

 Ancylostoma duodenale is the hookworm that causes ancylostomiasis

 A. braziliense is the cat hookworm that causes cutaneous larva migrans.

 A. caninum is the dog hookworm that causes cutaneous larva migrans

 Strongyloides stercoralis is the threadworm that causes strongyloidiasis

 Toxocara canis is the dog roundworm that causes visceral larva gimrans.

 T. cati is the cat roundworm that causes visceral larva migrans.

The cestodes or tapeworms are as follows:

 Taenia saginata is the beef tapeworm that causes taeniasis

 T. solium is the pork tapeworm that causes taeniasis

 Hymenolepis nana is the dwarf tapeworm that causes an intestinal infection

 Echinococcus granulosus is the dog tapeworm that causes unilocular hydatid disease

 E. multilocularis causes alveolar hydatid disease.

Enterobius vermicularis, which is the pinworm, causes itching and discomfort in the perianal area. This occurs particularly at night when the female lays her eggs on the skin. The eggs are not usually found in the feces but are spread by direct transfer from person to person. These pinworms live for only a few days.

Ascaris lumbricoides, the large roundworms, produce numerous eggs that require 1 to 3 weeks for embryonation. After the embryonated eggs are ingested, they hatch in the intestine, enter the intestinal wall, migrate through the circulatory system to the lungs, enter the alveoli, and migrate up to the pharynx. During the passage through the lungs, they may produce ascaris pneumonitis of Loeffler's syndrome. Loeffler's syndrome consists of coughing, chest pains, shortness of breath, fever, and eosinophilia, which can be especially severe in children.

The larval worms are then swallowed and they complete their maturation in the small intestine. Small numbers of worms usually do not produce symptoms. Large numbers of worms may cause digestive and nutritional disturbances, abdominal pain, vomiting, restlessness, disturbed sleep, and occasionally intestinal obstruction. Adult worms may cause death if they migrate into the liver, gallbladder, peritoneal cavity, or appendix.

Trichuris trichiura, the human whipworm, lives in the large intestine with the anterior portion of its body threaded superficially through the mucosa. Ingestion of the eggs causes an infection in the mucosa of the cecum and possibly in the proximal colon. Light infections are often asymptomatic. Heavy infections may cause intermittent abdominal pain, bloody stools, diarrhea, anemia, low of weight, or rectal prolapse in the case of very heavy infections. Human infections have been reported with T. suis, the swine whipworm, and T. vulpis, the dog whipworm. Ascaris, Trichuris, and Toxocara are most frequently found in municipal wastewater sludge.

Necator americanus and Ancylostoma duodenale, the human hookworms, live in the small intestine by attaching themselves to the intestinal walls. The eggs are passed out in the feces and developed into the infective stage in 7 to 10 days in warm, moist soil. The larvae penetrate the bare skin of the foot and pass through the lymphatics and bloodstream to the lungs, enter the alveoli, migrate up the pharynx, are swallowed, and reach the small intestine. The larvae may also be swallowed in food or water. Light infections usually result with few clinical effects, but heavy infections can result in iron-deficiency anemia. This happens because the secreted anticoagulant causes bleeding at the site of attachment. The disease especially affects children and pregnant women.

The threadworm lives in the mucosa of the upper small intestine. The eggs hatch within the intestine and reinfection may occur. Noninfective larvae can usually pass out in the feces. The larvae in the soil may develop into the infective stage or a free-living adult, which can produce infective larvae. Infective larvae penetrate the skin, usually the foot, and can complete their life cycle in a manner that is similar to hookworms. Intestinal symptoms include abdominal pains, nausea, weight loss, vomiting, diarrhea, weakness, and constipation. Massive infections and autoinfection can lead to wasting and death in patients who are receiving immunosuppressive medication. (Table 10.11).

Water Borne Diseases

Diseases transmitted by water where water acts as a passive vehicle for infecting agent.

(a) Viral

Poliovirus Poliomyelitis

Echovirus Meningitis, Gastro-enteritis

Coxsackie virus Pharyngitis, Respiratory

AI-22, 24 Disorders, Meningitis, Stomatitis

HAV Viral Hepatitis A

HEV Viral Hepatitis E

Human Rota virus Infantile diarrhoea

Adeno Virus Respiratory diseases, Conjunctivitis

Astro Virus Gastro-enteritis, Neonatal necrotising enterocolitis

Papilloma Virus Plantar warts

(b) Bacteria

Salmonella Gp Typhoid, Paratyphoid

E coli Diarrhea/Dysentry

Shigella Dysentry

Vibrio cholerae Cholera

(c) Protozoa

Entamoeba histolytica Amoebiasis

Giardia lamblia Giardiasis

Cryptosporidium Gastric upsets

Balantidium coli Gastric upsets

(d) Helminthic

Round worm PEM, urticaria, intestinal obstruction

Thread worm Pruritis periani, salpingitis, nocturnal enuresis

Hydatid worm Hydatid disease

(e) Leptospiral

Weil's disease

Water Washed Diseases

These are the diseases caused due to lack of water. Poor personal hygiene favours spread. Examples are:

Scabies

Skin Sepsis

Yaws

Lice

Trachoma

Water Based Diseases

Diseases transmitted by agents whose essential part of the life cycle takes place in an aquatic animal. e.g.

Schistosomiasis - in Snail

Guinea worm disease - in Cyclops

Eating Uncooked Food from Water

Diphylobothrium latum

Fasciolopsiasis