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Giardia was the first of these organisms to be widely associated with human disease, and there have been many documented cases of waterborne giardiasis since the s. Cryptosporidium emerged as a threat to water supplies in the s, particularly in the United States and the United Kingdom, and since that time other countries have had recognised outbreaks of waterborne cryptosporidiosis.

Cyclospora has only been documented as a significant human pathogen since the early s. It has been recognized in developed countries as a causative agent of gastrointestinal outbreaks associated primarily with fresh unprocessed food produce, particularly soft fruits and leafy vegetables. Mobile section navigation: Menu. Page navigation: Research. Areas of research. Arcobacter, Campylobacter, Helicobacter pylori. Bacteria vary in size from 0. Pathogenic bacteria, which represent only a small fraction of total bacteria in the environment, can be divided into two major groups based on their cell wall structures, which influence their Gram stain reaction: gram-positive and gram negative.

Gram-positive bacteria appear purple-violet and gram-negative bacteria appear pink after Gram staining. Most of the bacteria that cause waterborne illnesses are gram-negative bacteria include Aeromonas, Arcobacter, Campylobacter, pathogenic E. Note: examples of pathogenic gram-positive bacteria are Bacillus and Staphylococcus aureus however these are not fecal-oral and are not considered waterborne pathogens. The diseases are described in Table 3. Bacteria separate Kingdom prokaryotes with simple structure, grow via division and range in size from 0.

Wybo et al. Gastroenteritis, septicemia, meningitis, pneumonia, haemolytic uraemic syndrome acute renal failure and haemolytic anaemia. Some pathogenic bacteria such as Aeromonas , pathogenic members of E.

Members of the genus Aeromonas are ubiquitous in water environments both freshwater and seawater and wastewater. Certain pathogenic strains of Aeromonas cause diseases in human, ranging from subclinical conditions such as gastroenteritis to severe conditions including wound infections and septicemia. Aeromonas has also been shown to be a cause of infections associated with natural disasters such as hurricanes, tsunamis and earthquakes Janda and Abbott, Both pathogenic E.

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Vibrio cholerae , with strains that cause cholera, still remains a global threat to public health and is usually restricted to developing regions where drinking water and feces or wastewater treatment and disposal are poor. But Vibrio also has an environmental reservoir in the marine environment and can replicate in zooplankton. Cholera is characterized by an acute diarrheal infection and dehydration usually in epidemic outbreaks Barzilay et al. Vibrio cholera is usually found in water or food sources in areas where the disease is endemic and have been contaminated by feces from an individual infected with cholera.

This includes fecal coliforms, E. These fecal indicator bacteria are usually non-pathogenic and are natural inhabitants of the gastrointestinal tracts of humans and other warm-blooded animals.

They are released into the environment with human and animal feces. Protists are eukaryotic organisms which means they actually belong to the animal kingdom. Their DNA is enclosed in a nucleus inside the cell.

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They have organelles and can undergo either simple replication growing and splitting or complex sexual replication. They are diverse in form and examples include plant-like protists the algae , fungus-like protists the slime molds and animal-like protists the protozoa. Many protists, particularly protozoa are pathogens that are obligate parasites that must infect other organisms to survive and propagate. Most protozoa transmitted via water are gastrointestinal pathogens that cause nausea, abdominal cramps, vomiting, diarrhea and fever Table 4.

Chronic disease sometimes occurs, characterized by intermittent diarrhea, cramping rectal pain, nausea and vomiting. Blastocystosis, diarrhea, abdominal pain. The role of Blastocystis in causing disease is unclear, a natural component of the human intestinal microbiota.

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  • The most prevalent protozoan parasites associated with waterborne disease are Cryptosporidium parvum and Giardia lamblia. They form hardy oocysts Cryptosporidium and cysts Giardia that can survive outside a host and are excreted in the feces of infected individuals.

    Worms (parasitic helminths)

    Oo cysts are very persistent in water and resistant to the disinfectants commonly used in drinking water treatment. Cryptosporidium along with enterotoxigenic E. Microsporidia are obligate spore-forming parasitic fungi with the spore is the only environmentally stable and infective form. Although microsporidia are associated primarily with infections of the intestinal tract, dissemination to ocular, genitourinary and respiratory tracts may occur in immunocompromised individuals Didier et al.

    Disease: Protozoan Pathogens - A-level Biology - OCR, AQA, Edexcel

    Cyclospora cayetanensis and Toxoplasma gondii are parasitic protozoa which the oocysts unlike other parasitic protozoa such as Cryptosporidium are not infectious upon excretion and require a maturation phase in the environment that is on the order of days. Toxoplasma gondii has wild and domestic felines as its host but can also infect humans and other animals due to the ingestion of oocysts from feline feces Figure 2.


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    Figure 2. They can end up in sewage and sludge if cat feces are disposed of to the toilet. Can be associated with runoff into waterways from cat defecation. Unsporulated oocysts are shed in cat feces every weeks. Oocysts take days to become infective in environment. Exposure occurs when infective oocysts are ingested by humans, as accidental hosts, via hands, food and water due to contamination with cat feces.

    Sources of Infection & Risk Factors

    Other transmission routes are blood transfusions, organ transplants, consumption of uncooked intermediate hosts and from mother to fetus transplancentally. Inside the human host: the parasite forms cysts in the tissues which include skeletal muscle, myocardium, brain and eyes and may stay with the host for life. Cats then become infected after consuming intermediate hosts harboring tissue cysts or directly ingesting sporulated oocysts. Helminths, also commonly known as parasitic worms, are multicellular complex organisms containing organ and tissue.

    They belong to the Kingdom Animalia and include cestodes tapeworms , nematodes or roundworms and trematodes or flukes. The classification of helminths is based on the external and internal morphology of egg also referred to as ova , larval and adult stages and their life cycles.

    Cestodes are flat, hermaphroditic, having both male and female reproductive organs, worms that colonize the human gastrointestinal tract. Adult tapeworms are 5 to 10 m long. Some cestodes are primarily human pathogens such as Taenia spp. Nematodes are cylindrical in structure and bisexual.

    Examples of nematodes include Toxocara spp. Trematodes are leaf-shaped flatworms and vary in length from a few millimeters to 8 cm. Trematodes are hermaphroditic, except blood flukes Schistosoma spp. Other examples of trematodes include Fasciola spp. Helminths infect a large number of people and animals worldwide, particularly in developing regions where sanitation and hygiene conditions are poor De Silva et al. Adverse health effects due to heavy helminth infestations include abdominal pain, diarrhea, blood and protein loss, intestinal blockage, rectal prolapse, and impairment of physical and mental development in children Sobsey, Table 5.

    Several helminths including Echinococcus spp. Schistosoma spp. Helminths classified as various type of worms which produce eggs which are excreted in the faeces, multicellular organisms, vary in length from 2 to 3 mm to 10 m, are visible to the naked eye in their adult stages, infect definitive hosts.

    Diphyllobothriasis, diarrhea, weight loss, vitamin B12 deficiency with pernicious anemia, cholecystitis. Cystic echinococcosis as a cyst in liver or lung , alveolar echinococcosis as a pseudo-tumor in liver. Di Comite et al. Chronic phase after months to years of infection : painful liver enlargement, obstructive jaundice, chest pain, weight loss, cholelithiasis, hepatic lesions, fibrosis and chronic inflammation of the bile ducts. Echinostomiasis diarrhea, abdominal pain, catarrhal inflammation , heterophyiasis diarrhea, colicky abdominal pain.

    Intestinal schistosomiasis hepatosplenomegaly, fever, abdominal pain, bloody diarrhea , urinary schistosomiasis dysuria, haematuria. Liver fibrosis, portal hypertension, bladder cancer, renal failure, anaemia, malnutrition, impaired growth and poor cognition in children. Itching and a localized rash, abdominal pain, diarrhea, loss of appetite, weight loss, fatigue, anemia.

    Ocular toxocariasis vision loss, eye inflammation or damage to the retina , Visceral toxocariasis fever, fatigue, coughing, wheezing, or abdominal pain. Rectal prolapse, severe anemia, growth retardation and impaired cognitive development in children. Nematodes such as Trichuris trichiura , Ascaris spp.

    The fecally excreted eggs mature in the soil and this takes days to weeks depending on the helminth and environmental conditions.


    Human can expose to the helminths by either penetrating of mature helminth larvae to the skin when come in contact with contaminated soil or by ingesting of mature eggs in contaminated food and water. Many other helminths are regarded as agents of water-based disease because they have life cycles involving water, although the final transmission to humans is primarily through the consumption of uncooked or undercooked food such as fish.

    Schistosoma species are parasitic flukes that have a life cycle involving only water. Many factors affect the ability of a pathogen to be transmitted through the environment that represents a potential risk of host exposure, infection and disease. First, the pathogen must enter the environment and for water-associated pathogens, they enter the environment via human or animal feces urine for Leptospira and Schistosoma deposited on land or in water.

    Thus the loading and concentrations of pathogens are of great importance. Once the pathogen is in the environment, several factors affect the ability of the pathogen to be transmitted to a human or animal host. The pathogen must infect new susceptible hosts by entering their body in order to survive.