We shall examine common examples of pathogenic disease where water pollution is responsible in part or in whole.
The diseases include infection by one of four major categories of organisms:
1. Enteric viruses,
3. Protozoans, and
1. Viral Infections:
Viruses are properly identified as obligate, intracellular parasites. This means that, while they can survive in the Free State, they cannot reproduce unless they are within the restrictive environment of their specific host. They are composed mostly of high molecular weight proteins and nucleic acids and are essentially inert in the Free State.
They are ultramicroscopic and are more than an order of magnitude smaller than bacteria. Infection occurs when the virus adsorbs onto a complementary site of the host’s cell or nucleus. The nuclear material is then injected into the host.
From 1978 to 1982, there were 18 outbreaks of waterborne disease caused by viruses with 5,700 cases, as reported in the Federal Register. Although these numbers are low, it is reasonably safe to say that many more cases, labeled as unknown, are probably due to viruses.
As related to waterborne disease associated with groundwater, it is convenient to group viruses as shown in Table 16.1, which also provides the associated disease. In all but one of the classifications, human waste is believed to be the primary source of the associated disease. In that one case, the Reoviruses, animal waste in addition to human waste is considered to be a source. Each group or subgroup consists of different serological types so that there are more than 100 different human enteric viruses recognized.
Groundwater probably accounts for about half of the waterborne-related illnesses in the United States. This number may be lower in other countries depending on how extensively they depend on groundwater as a source of potable supply. Viruses, not bacteria, are probably implicated in causing most of the outbreaks in the United States.
Viruses and bacteria survive longer in groundwater than surface water. This is because the quality and characteristics favor their preservation. Conditions such as low constant temperature, no ultraviolet light, lack of oxygen and little biological antagonism support their survival.
Viruses have been proven to travel further in the subsurface saturated environment than first thought. At the Brookhaven National Laboratory, viruses were proven to travel more than 200 feet from a septic tank to an observation well. This is disturbing because the New York State standard for separation is 100 feet. Viruses are also unaffected for the most part by conventional wastewater treatment methods.
Infectious hepatitis may be the most important enteric viral disease associated with contaminated water. There are about 76 outbreaks in the United States documented during 1930 through 1984, mostly related to gross contamination of small water supplies. Probably one of the single largest outbreaks in history occurred in Delhi, India, in 1955-56.
The Jamuna River received raw sewage downstream of the city. A reversal of the river’s direction of flow resulted in the contaminated wastewater being transported upstream, where it was taken up into the potable water treatment plant. As many as 50,000 cases of hepatitis were reported. This is despite the fact that increased chlorination kept other diseases in check, and it attests to the chlorine resistance of viruses.
Because pathogenic viruses are not a normal part of human intestinal flora, they are readily excreted by infected individuals. Some removal of viruses may be accomplished by conventional wastewater treatment, but it is very limited. Additionally, some protection is afforded by dilution, natural deactivation, and water treatment. However, the potential for epidemics from massive sewage contamination of a water supply does exist.
Another threat from infectious hepatitis exists from eating raw contaminated shellfish. Because shellfish, such as oysters and clams, filter feed, they provide an excellent means for bioaccumulation of viruses. Shellfish harvested from contaminated beds and sold illegally is a common way in which the public is threatened. Beds can be contaminated by runoff, sewage treatment plant discharges, and poorly designed or faulty septic systems.
Most other viral-related diseases are associated with non-specific gastroenteritis. These are often associated with droughts, when dry conditions may assist by concentrating the viruses in surface waters. One epidemic occurred during a drought in 1959-1960 in the Ruhr Valley in Germany where non-bacterial gastroenteritis affected 5% to 10% of the population, mostly children.
There have only been two possible waterborne outbreaks of poliomyelitis reported in the United States and Canada. It is interesting to note that the survival time of the poliovirus in water is estimated to be around 20 days. Other enteroviruses may survive as long as several months.
Bacterial-related waterborne disease is usually related to human waste but also can result from improperly disposed-of medical waste and sometimes animal sources. Because bacteria are much larger than viruses and can be easily filtered out or destroyed by conventional wastewater treatment, they are easily amendable to control.
Problems can result from cross-contamination of water and sewer lines, poorly designed and operated water wells, treatment plant malfunctions and breakdowns, and direct discharges of untreated wastes, for example, by combined sewer overflows (CSOs).
The bacteria of most concern in the United States are the Salmonella types (more than 2,000) most commonly associated with food contamination. Bacteria that cause cholera, tuberculosis, and leptospirosis are not a particular threat in the United States anymore. This is not the case for other countries, particularly developing ones. For example, Leptospira Pomona, causing leptospirosis, is important in Brazil but not in the United States.
The salmonella-type infections cause both acute gastroenteritis and salmonellosis, typhoid fever (Salmonella typhosa), and paratyphoid fever (Salmonella paratyphi). The largest recorded outbreak of salmonellosis in this country was recorded in 1965 in Riverside, California.
It is estimated that more than 16,-000 people were infected by drinking water contaminated with Salmonella typhimurium. The case was interesting because total coliform bacteria were not found prior to the outbreak and only measured 1.4 per liter during the outbreak. Other incidences of salmonellosis outbreaks reported are shown in Table 16.2.
Salmonella typhosa, causing typhoid fever, is a potentially fatal disease that is usually spread by drinking contaminated water or washing in it. Today it is more commonly spread by contaminated food handled by a carrier of the disease.
In the United States at the turn of the century, as many as 27,000 Americans died of typhoid fever. With the construction of treatment plants and public water supply systems, this number was quickly reduced. The etiology of waterborne typhoid outbreaks in the United States is listed in Table 16.2.
A case in 1937 in London is typical of the scenarios resulting in outbreaks of the disease. A well shaft laborer, who was infected with Salmonella typhosa, did not obey the sanitary rules and contaminated the water supply. The incident resulted in 341 reported cases with 43 dead.
Another example occurred in 1940 in Rochester, New York, when a worker inadvertently opened a valve serving an emergency connection between a polluted industrial water supply and the city’s potable supply. This resulted in 30,000 cases of mild enteritis and five cases of typhoid fever.
In developing countries, the incidence of typhoid fever is much higher than in the United States. Due to the absence of safe water and sanitation, estimates for developing countries are on the order of a million outbreaks per year with 25,000 deaths.
Shigellosis is caused by the bacterium Shigella dysenteriae and related types that cause bacillary dysentery. In 1965 in Madera, California, Shigella and Salmonella were implicated in an outbreak of 2,500 cases resulting from waterborne contamination.
The outbreak was linked to a 370-foot-deep well contaminated when an adjacent pasture was irrigated with unchlorinated wastewater effluent. Shigella can survive for up to a month in wastewater and some groundwaters. The etiology of shigellosis, as related to waterborne disease outbreaks, is given in Table 16-2.
Cholera is caused by Vibrio cholerae, and is a bacterial colonization of the small intestine. It is generally characterized by massive diarrhea with depletion of extra cellular fluids and electrolytes and can be fatal. Its source is human waste, but it does not survive long in water.
Carriers of cholera are not common; polluted water is the most common disseminator of the disease. In the late summer of 1978 an outbreak occurred in Louisiana. It was traced to ingestion of inadequately cooked crabs with 11 cases of cholera resulting.
One other outbreak, with 17 cases, was reported in the early 1980s. Cholera is endemic in Asia, India, and Pakistan. There have been seven pandemic outbreaks since 1817. In endemic areas, it is known as the disease of children. In Bangladesh, the attack rate is 10 times higher for 1-5 year olds than it is for those over 14. In non-endemic areas, the attack rate between children and adults is about the same.
One of the most famous cases is sometimes credited with the beginnings of the field of epidemiology. In 1854 in London, an outbreak of Asiatic cholera occurred in a main area of the city. During the 17-week epidemic, more than 700 people died in the St. James district, far more than surrounding districts. One member of an inquiry committee that had formed to investigate the matter was John Snow.
His plotting of the pattern of the disease led to a communal water source, the Broad Street pump, as the probable source. It was eventually confirmed that the infection had been transmitted underground from the defective cesspool of an infected family to the public water supply pump.
A different species of the same genus, Vibrio vulnificus, represents a health threat not related to cholera. The species occurs in less than 10% of shellfish and does not normally affect healthy people. However, for that percentage of the population with chronic liver disease or impaired immune systems, the threat is significant.
This is typified by a recent case. In the summer of 1993, a man with chronic hepatitis died six days after eating oysters in Brevard County, Florida. The Florida Department of Health and Rehabilitation Services responded with proposed health warning requirements for display at restaurants to alert high-risk individuals. Louisiana and California had already adopted this practice.
Leptospirosis, also called hemorrhagic jaundice or Weil’s disease, has been associated with swimming or wading in polluted canals, streams, ponds, and lakes. Leptospira pomona is an important pathogen in Brazil. Dogs, pigs, and rodents all have been traced to carrying the serum spirochetes that cause a fairly large group of associated diseases.
Symptoms include chills, fever, headaches, muscle and joint pain, and in 10% or more of the cases, kidney damage, jaundice, and anemia. Only one outbreak was recorded in the United States in the late 1940s, with nine cases resulting.
Several other types of bacteria have been associated to some degree with water- borne illnesses. Legionella pneumophila and associated species cause legionellosis, an acute respiratory illness associated with thermal pollution of drinking water and cooling water systems.
Tuberculosis, caused by Mycobacterium tuberculosis, is suspected as being capable of being waterborne. E. coli is referred to in the literature as being non-pathogenic, which is generally true. However, enteropathogenic and enterotoxigenic strains do exist and can cause gastroenteritis. Five outbreaks and 1,200 cases have been reported in the past 25 years.
A number of single-celled animals belonging to the Phylum Protozoa are known to cause certain waterborne related diseases. They are often spread when someone eats or washes in a contaminated water supply. Irrigation with contaminated water as well as cross-connections of piping and back-flow into potable water systems also has been reported to cause illnesses.
Amoebic dysentery, caused by species such as Entamoeba histolytica, is probably the most common type of waterborne protozoan disease. It can survive up to two months in water where its encysted form protects it. In the past 60 years, there have been about seven outbreaks, with about 1,500 cases and a little more than 100 deaths in the United States.
It is estimated that up to 10% of the United States population are carriers of amoebic cysts. The reported incidences of waterborne amoebic dysentery have been very low in the past 20 years. This is attributable to the relatively small number of cysts excreted by carriers, and the fact that the cysts’ size and weight makes them easy to settle or filter out in treatment systems.
Another species of amoeba-like pathogens is Naegleria fowleri. This species is associated with thermal pollution. It has been found in cooling canals at power plants and also was found in warm natural springs originally used as Roman baths in England. The species may enter through the mucous membranes and cause meningoencephalitis, which can be fatal.
In the past 30 years, the flagellate protozoan Giardia lamblia has been identified and become important as a waterborne pathogen (Figure 16.2). From 1961 to 1984 there have been 90 outbreaks reported with almost 24,000 cases. The disease is characterized by diarrhea, cramps, nausea and general weakness, and is non-fatal.
It takes up to eight weeks before the organism has a population that can result in noticeable symptoms. The organism has two nuclei and four pairs of flagella. The ventral surface is equipped with a suction disc that enables it to attach on the surface of the small intestine.
The species has a highly motile stage called a trophozoite, which is a few microns in size. It also has an encysted stage that is used when it is not parasitizing its host. Transmission occurs when the cyst is excreted and becomes waterborne. Its numbers can be so high that they prevent the intestine from performing absorption, in particular fat absorption.
Transmission is by ingestion of water contaminated with the cyst. The cyst may be resistant to chlorination, and filtration may be the only effective process. This fact has recently received attention in upstate New York and elsewhere. Here, small or private water systems with little or no treatment, which are contaminated by human or animal waste, appear to be the source. Beavers may well be the most common animal source, although coyotes, muskrats, dogs, cats, and even cattle can host the parasite.
The most recent of the protozoan parasites to be linked to human pathology is a minute coccidian, (i.e., a member of the protozoan Order Coccidia), that can be found in the intestinal tracts of vertebrates, including reptiles, birds and mammals. The genus is Cryptosporidia. It was first discovered in 1907 in a mouse at Harvard University, and has long been known as a cause of diarrhea in animals. It was identified as a human parasite in 1975, and in 1984 it was linked to contamination of drinking water supplies.
A severe outbreak of infection occurred in April 1993 in Milwaukee, Wisconsin. The potable water system was responsible for the dissemination of the organism, which affected more than 300,000 people. Almost one of every four residents on the system was affected, and one person with an impaired immune system died. It required about three weeks and the complete disinfection of one city water treatment plant to rectify the situation.
Analysis of the cause pointed to improper watershed management and the water intake system. Numerous dairy farms are located near and in the watershed to the
Milwaukee River and cattle are common carriers of the parasite. The river feeds into Lake Michigan near the water intakes.
An important characteristic of the parasite is that it is very resistant to chlorination disinfection, with the only effective counter- measure being filtration. The water treatment facility did not employ this practice, and so the parasite passed through the treatment process.
Symptomology includes severe diarrhea, abdominal cramps and pain, fever, and a variety of other non-specific symptoms. The disease runs its course in a few weeks and is rarely fatal. Outbreaks of Cryptosporidia also have been recorded in Carollton, Georgia, in 1987, and Jackson County, Oregon, in 1992.
One last protozoan parasite is deserving of attention. The parasite itself is not waterborne but the intermediate host, i.e., the mosquito larva, is. Man creates environmental conditions, predominantly stagnant water through construction and other activities (such as drainage ditches), that foster the infection and spread of the disease.
The disease is malaria and has long been a scourge of man. In fact, it may have factored into man’s evolution, habitation and development. DDT and other pesticides have been, and still are, used to kill mosquitos. Some 50 or more species of the anopheles mosquito can carry the parasite.
Oil has often been used as a larvacide to control the developing mosquito larva in the water. A light oil is applied directly to the water surface creates surface tension, which prevents the mosquito larva from obtaining oxygen with its siphon.
The generalized life cycle of Plasmodium, which is the genus of several species causing malaria, is described in the following list:
1. Man becomes infected by the bite of a mosquito carrying a stage of Plasmodium called the sporozoite. The mosquito harbors the sporozoite in its salivary glands, and secretions carry it into the capillary of the host when bitten.
2. The circulatory system of the host carries the sporozoite to the liver where the liver cells are invaded.
3. The sporozoite undergoes multiple fission or schizogony, to form cryptozoites, which re-invade the liver cells and reproduce.
4. After about a week, they leave the liver cells and invade red blood cells.
5. In the red blood cells they again undergo schizogony and form merozoites, which escape and re-invade the red blood cells. This activity is typically synchronized, for example, at 48-hour intervals, and yields the characteristic chills and fever of malaria.
6. Some of the merozoites become transformed into gametes.
7. If a mosquito bites an infected person, it in turn becomes infected with the gametes.
8. In the gut of the mosquito, the gametes form a zygote, which imbeds itself in the stomach wall and encysts. Inside of the encysted zygote the sporozoites are formed.
9. The sporozoites escape from the cyst and migrate to the salivary gland of the mosquito, where they are ready to infect a new host with the mosquito’s bite.
A number of different species of worms, representing several different phyla which parasitize man, have life cycles involving aquatic systems. In these cases the use of the term “parasitism” is most appropriate. The dependency on the host for completion of a life cycle and survival is generally detrimental to that host.
We will examine two phyla, one with two classes that pose a threat to man, although many others also could be included. The parasitic worms representing the phyla are principally intestinal, and use eggs and larva in transmission to and from what are often multiple hosts.
The parasitic worms may not normally exist in an aquatic system; however, it is not uncommon that they are introduced and cause sporadic outbreaks. This can happen in grossly unsanitary conditions, mismanagement of treatment systems, and accidents or system failures.
Often, worm infections occur as the result of floods or storms with excessive runoff. Using contaminated water for irrigation of crops that are eaten raw may transmit any one of a number of intestinal worms. Irrigation of grasslands with contaminated water may infect cattle or other species, and through them, man.
The first phylum we will discuss is “Platyhelminthes” or the flatworms. There are three classes, two of which are parasitic. The first class is Turbellaria, and it contains about 3,000 species of free-living flatworms. The second class is the Trematoda or flukes; the last is the Cestoda or tapeworms. We also shall address the phylum Nematoda or roundworms, which contains many thousands of species, about half of which are parasitic on many different creatures. Only a few are specifically related to water pollution.
This class of parasitic flatworms called “flukes” has a non-ciliated epidermis and a pumping pharynx used in obtaining nutrition. The body is covered by a cuticle for protection against a host’s enzymes. They are hermaphroditic, which means that their bodies contain both male and female reproductive organs and are capable of self-fertilization. The class can be further broken down to orders “Monogenea” and “Digenea” depending on the number of hosts in the life cycle, i.e., one or two, respectively.
The genus Schistosoma is comprised of several species commonly referred to as blood flukes. Their life cycle is somewhat typical of the flukes. The disease schistosomiasis is one of the great scourges of mankind, and in its severe form can be fatal. It is believed that more than 200 million people are affected yearly, primarily in developing countries, with some 500,000 to 1 million fatalities.
Man has greatly facilitated the spread of the species by construction of slow-moving water bodies and structures such as drainage ditches. These environments foster the proliferation of the parasite’s intermediate host. There is an extremely high rate of infection for those who live in the vicinity of the Aswan High Dam in Egypt. This is caused by a combination of a large amount of human activity related to agriculture and the slow-moving irrigation waters made available by the dam, which support the intermediate host.
The eggs of the parasite are passed from the primary host in waste, and if water is contaminated by it, the eggs hatch. A free swimming, ciliated larval form called the “miracidium” results. This stage penetrates an aquatic snail, its secondary host, and inside the snail the miracidium lose their cilia and become “sporocysts”. The sporocysts develop into a stage called the “cercariae,” which leaves the snail. It has a forked tail and can be an active swimmer. One miracidium can give rise to many cercariae.
The cercariae actively seek the primary host, which can be man. Infections may occur during bathing, washing, or wading. Species that parasitize man enter the circulatory system upon penetration, hence the name blood flukes. They have a sucker at one end that is used for attachment to the walls of blood vessels.
In the primary host the fluke then matures to the adult stage. Liver and urinary disease are often a common result. Sexual reproduction results in the production of eggs, which are deposited in the host’s waste for transmission outside the body.
A variation in this cycle can take place. The motile cercarid stage is sometimes not that specific in its selection of the primary host, and occasional penetration of the wrong host takes place. Because parasite life cycles are highly specific, a cercarid stage entering the wrong host precludes the normal life cycle of the parasite.
With some species of Schistosoma, whose primary host is not a human, this situation results in only the penetration of the host’s outer skin layers. The parasite is therefore unable to complete its life cycle, remaining in the skin. This gives rise to skin irritation commonly referred to as “swimmers itch.”
Other species of flukes have life cycles involved with water pollution and hosts that are aquatic organisms. The Chinese liver fluke, Opisthorchis sinensis, is an example of a parasitic fluke with two intermediate hosts. The first is a snail that eats the eggs of the parasite.
Miracidium hatch from the eggs and penetrate the snail’s tissue. They develop into resistent sporocysts that produce redia internally and that leaves the tissue and form cercariae. The cercariae, upon leaving the snail, penetrate the second intermediate host, which is a fish. An additional life stage called the “metacercaria” is employed. This stage encysts, and through consumption of infected fish by the primary host, when eaten raw or partially cooked, the cycle is completed.
Another fluke of interest is Paragonimus westermani, which can result from eating uncooked crabs or lobsters. It is referred to as a pulmonary fluke because it parasitizes the lungs. The eggs are coughed up and swallowed and excreted. If this occurs in cool, clear water, the eggs will hatch and the miracidium will enter a snail. The second intermediate host is a crustacean, i.e., the crab or lobster, and consumption of the infected crustacean by man completes the cycle.
The class “Cestoda” is commonly called the tapeworms. The body (stro-bilia) of a tapeworm can be very long, composed of a large number of attached segments called proglottids, and ends in a small head region called the scolex. The rostrum of the scolex is equipped with attachment structures such as hooks for anchoring themselves onto the gut or intestinal walls. Each of the proglottids contains male and female reproductive organs capable of self-fertilization. Thousands of eggs can be produced in a day.
Untreated waste or direct contamination by an infected human is probably the most common means of contamination. The eggs or the free-swimming ciliated larval stage, called the coracidium, may be eaten by a copepod. Inside the copepod, the parasite further develops in the body cavity.
If the copepod is eaten by a fish, the parasite will eventually migrate to the fish’s muscle tissue. If man then eats the fish raw or improperly cooked, it will result in the parasite attaching to the walls of the intestine. The eggs can then be passed in the waste and the cycle is completed.
The fish tapeworm Dibothecocephalus latus (also known as Diphyllobothrium latum) represents a typical life cycle. The species has been known for a long time in the Baltic Sea area, but during the decline of the Roman Empire it was spread throughout Europe. It now occurs in Africa, Australia, Japan, South America, and in the United States and Canada.
It has a whitish color and can be up to 30 feet long with 4,000 segments (proglottids) that function only for reproduction. Terminal proglottids fall off after degeneration. Its scolex is about a millimeter or two in size with suckers for attachment. Eggs are about 40 to 70 microns in size and develop in 11 to 15 days after reaching cool, fresh water.
If tapeworm eggs passed in human wastes contaminate water, they must hatch and be eaten within one-half day by zooplankton copepods such as Cyclops or Diaptomus. If a small plankton-eating fish consumes the infected crustacean, the larval form is carried to the muscle or connective tissue.
A larger fish will be infected from consumption of this smaller fish. If man then eats the infected fish, raw or improperly cooked, the tapeworm will mature and take up residence in the small intestine. The proglottids of this tapeworm continuously produce eggs which are deposited in the waste ready for transmission.
The phylum “Nematoda” is commonly called the roundworms. It contains a great number of species, about half of which are parasitic. Several of these are related to water pollution. Roundworms are covered by a smooth protective cuticle and are characterized as having no special external features to distinguish them.
They are often described by the effects they cause or by the organ or structure in the body that the worm principally parasitizes. They successfully exploit many modes of transmission, including drinking water supplies.
A massive infection of the population of Darmstadt, Germany, occurred in 1947 with Ascaris lumbricoides. The vegetable crops were spray-irrigated with contaminated water. It is the largest roundworm of the human intestine with the female reaching up to 20 inches. They have a very high reproductive rate, typical of nematodes.
They also tend to wander about the body, boring through internal tissues causing much damage. This is also typical of the roundworms. Poor hygiene practices and lack of clean water for washing are known to assist in the spread of ascarid roundworms.
Another species of interest is Dracunculus medinensis, the guinea worm. In some parts of the world, the freshwater copepod Cyclops has been known to ingest the larva of the worm. The worm develops in the hemocoel of the crustacean. If the water is ingested without treatment, the parasite then infects man. It also has been suggested that the worm larva can infect a common algae, which can then be ingested in drinking water.
Dracunculus will bore through the intestinal wall and migrate to connective tissue. The males die after fertilization, and the gravid females migrate to just under the skin. They create an ulcerous sore or blister, and when the skin is submerged in water for bathing or washing, the female releases the developed young larva to the water. Surgical techniques are required to remove the worm, the females of which may attain a length of up to four feet.