Chapter IV -Medical Biology - Ecology 2023-2024 PDF

Exercise 4. Topic: The hydrosphere and lithosphere as a source of pathogenic agents for humans. Glossary: Allochthonous organisms - organisms that do not naturally occur in a specyfic environment, migratory organisms Autochtonic organisms - native organisms in a given environment. Biological index (...

Exercise 4. Topic: The hydrosphere and lithosphere as a source of pathogenic agents for humans. Glossary: Allochthonous organisms - organisms that do not naturally occur in a specyfic environment, migratory organisms Autochtonic organisms - native organisms in a given environment. Biological index (biotic index, Bi) - the index showing the numerical ratio of different types of microscopic organisms found in a representative sample of water from the reservoir. Clostridium perfringens titer - the smallest soil mass in which C. perfringens spores are still present. Faecal coliform titer - the smallest soil mass or the lowest volume of water (ml) in which faecal coliforms are still present. Flotation methods - concentration methods of parasitic developmental forms separation in which solutions of higher density (specific gravity) than the forms of these organisms are used. Geophagia - intentional practice of consuming soil. Helminths - multicellular parasites, including tapeworms, flukes, nematodes. Helmintological examination - searching for developmental stages of helminths. Water eutrophication - the process of a gradual increase in the concentration of bigenous elements (e.g. nitrogen, phosphorus) in aquatic ecosystems, resulting in an increase in the biomass of algae and plants. Hydrosphere - all the waters on the earth including underground, surface waters, ice and snow. Indicator organisms - organisms that allow to monitor the condition of the ecosystem, only occur under certain conditions. Lithosphere – the rigid external shell of the earth covering the earth's crust and the upper part of the earth's mantle (the intermediate layer of the Earth, having an average thickness of about 75 km). Sedimentation methods - in parasitology, diagnostic concentration methods, which use solutions of lower density than parasitic developmental forms, allow the separation of parasites from fecal particles. Water-borne infections - infections or invasive diseases transmitted through contact with or consumption of microbially polluted water. Hydrosphere Hydrosphere is a discontinuous layer of water at or near the earth’s surface; it includes all liquid and frozen (glaciers, icebergs) surface waters, groundwaters held in soil and rock, and atmospheric water vapour. All water resources on the Earth constitute about 1.5 billion km3. Over 95% of resources are found in the oceans, and only approx. 3% (35 million m3) are fresh water resources. It is estimated that about 70% of freshwater is trapped in glaciers and snow cover, which significantly reduces the amount of fresh water useful for humans. 3 Providing a population with the right amount and quality of water is one of the basic conditions for sustainable development. For human populations, inland waters are the main water resources used as a source of drinking water, as well as for economic and recreational purposes. Water pollution refers to the contamination of lakes, oceans, rivers, aquifers, and groundwater and it often results from human activity (Table 1). Table 1. Water pollutants depending to human activity. Activity Agriculture Sewage discharge Industrial discharge Aquaculture Oil and fuel terminals Shipping, including bunkering and harbour dredging Pollutants Nutrients Pesticides Suspended matter Biological Oxygen Demand Nutrients Organics Bacteria and viruses Turbidity Heavy metals Pesticides Other synthetic chemicals Heavy metals Organics Synthetic chemicals Thermal pollution Nutrients Suspended matter Organics Petroleum Hydrocarbons Anti-fouling chemicals Petroleum Hydrocarbons Suspended matter Heavy metals Nitrogen and phosphorus compounds are the most important in the process of enriching water reservoirs with nutrients. These compounds can enter surface waters from internal sources (bottom sediments and organisms) and external waters such as municipal (e.g. some soaps and synetic detergents) and industrial wastewater, as well as surface runoff (e.g. agricultural fertilizers). The excess of nitrogen compounds (ammonium nitrogen = ammonia, nitrates, nitrites) and phosphorus compounds (soluble phosphates) in water reservoirs cause eutrophication, increase the amount of plant and algae growth - can cause harmful algal blooms, reduce dissolved oxygen, may exerta toxic effect on aquatic organisms (hypoxic conditions – dead zones). Also, nitrogen compouds reduce the effectiveness of chlorination (disinfection), which in turn limits the possibility of reusing water for consumption. High nitrate (V) concentration in drinking water has a negative impact on human health. Nitrites lead to methemoglobinemia and are precursors of nitrosamines that have carcinogenic, mutagenic and teratogenic effects. Phosphates are not toxic to people or animals unless they are present in very high levels. Because of this, no drinking water standards have been established for phosphorus. Digestive problem could occur from extremely high level of phosphate. These compounds contained in water may indirectly influence human health through their role in the eutrophication of fresh and salt waters. In e.g. coastal and marine ecosystems, it leads to algal blooms and is associated with shellfish poisoning. Under favorable lighting and nutritional conditions, some species of cyanobacteria produce toxic secondary metabolites known as cyanotoxins. Their consumption with contaminated drinking water, direct contact, inhalation and / or consumption during recreational activities can cause a variety of effects on human health: hepatotoxic, neurotoxic and dermatotoxic. Directive 2008/105/EC of the European Parliament and of the Council of 16 December 2008 on environmental quality standards in the field of water policy provides a detailed list of basic pollutants that have a significant impact on water quality. Other legal acts of the European Community concern the regulation of the gradual reduction of pollutants (especially the so-called priority substances) and the cessation or gradual elimination of emissions and discharges of hazardous substances. Apart from physical contaminants (solids, suspended matter and insoluble substances) and chemical (inorganic or organic chemicals / substances) of surface waters, there are also biological contaminants that pose a significant threat to human health. Biological contamination Microorganisms occurring in water reservoirs can be divided into two groups: - autochthonic (species for which water is a natural habitat of living and development) - mainly autotrophic bacteria; photoand chemosynthetic (nitrifying, sulphuric, iron); - allochtonic (migratory) - getting into the water from the air, soil, with industrial and communal sewage - mainly saprobionts and pathogenic microorganisms. Water-borne infectious and invasive diseases Water borne infections - infectious and invasive diseases affecting humans; their etiological factors occur in water, and infection/invasion occurs most often: - through the consumption of contaminated water, - direct contact during the use of water recreation spots (swimming pools, swimming pools), - when using water for hygienic and economic purposes. Pathogens present in water belong to different taxonomic groups (viruses, bacteria, fungi, protozoa, helminths), for some of them, water is the natural environment of existence (free living amoebae, e.g. Acanthamoeba spp.) and for other the space of development (eg. Schistosoma spp., Diphyllobothrium latum, Fasciola hepatica). However, a majority of pathogenic microorganisms are allochthonous microbiota of water reservoirs to which they get along with municipal sewage (Escherichia coli, Salmonella spp., Shigella spp.). Table 2. Selected etiological factors of infectious and invasive diseases occurring naturally or contaminating the aquatic environment. 5 Pathogen type viruses bacteria fungi protozoa helminths Examples Coxackievirus, Enterowirus, Norovirus, Rotavirus, Adenovirus, Poliovirus, Hepatitis-A and E Escherichia, Salmonella, Shigella, Campylobacter, Clostridium, Enterococcus, Leptospira, Listeria, Mycobacterium, Pseudomonas, Vibrio, Yersinia Aspergillus, Penicillium, Exophiala, Fusarium, Mucor, Rhizopus, Candida, Rhodotorula, Trichosporon Toxoplasma gondii, Giardia, Cryptosporidium, Acanthamoeba, Negleria fowleri, Balamuthia mandrillaris, Entamoeba histolytica Schistosoma mansoni, Ascaris, Trichuris, Dracunculus Factors conducive to the occurrence of water-borne parasitic diseases: - pollution of surface and groundwater (human and animal waste); - irregularities in the course of the water treatment process; - properties of the parasite: wide host specificity (e.g. human and over 80 mammal species are the hosts of Cryptosporidium parvum), high invasiveness (a small number of cysts of intestinal protozoa causes invasion, e.g.C. parvum - 10 to 100 oocysts can initiate an infection), small size of dispersive forms (cysts/oocysts - it is necessary to use filters with appropriately small pores; C. parvum - cysts are 4.5-5.5μm in diameter of and can penetrate through sand filters), resistance to environmental factors and disinfectants (e.g. conventional chlorination of water destroying intestinal bacteria is insufficient to destroy cysts C. parvum, Giardia intestinalis and Entamoeba spp.). Most species of the genus Cryptosporidium may pose a threat to humans by causing cryptosporidiosis (Cryptosporidium hominis and C. parvum species are of greatest epidemiological significance). Symptoms usually appear 5 to 7 days after infection and include watery diarrhoea, abdominal pain, nausea, vomiting, fever and malaise. Most cases of cryptosporidiosis are reported in children under five years of age, mainly due to immaturity of the gastrointestinal tract and mucosal immunity. Cryptosporidiosis outbreaks are more common than epidemics caused by other biological factors. Analysis of 89 waterborne intestinal disease outbreaks recorded in England and Wales, including 4,321 cases, confirms the dominance of Cryptosporidium (69%) among the diagnosed etiological factors. According to the Center for Disease Control and Prevention (CDC), in the years 2000-2014, 493 outbreaks of waterborne infections were reported in the United States; out of 363 outbreaks with confirmed infectious aetiology, 212 (58%) were caused by Cryptosporidium spp. An analysis of waterborne infections epidemics made in the EU in 1990-2005 revealed that out of the 31 outbreaks caused by protozoa present in drinking water in as many as 29 cases, the etiological factor was the genus Cryptosporidium; the most frequent causes of water pollution were failures during water filtration, contamination of water intakes with municipal and agricultural sewage. The reservoir of pathogens and the source of the epidemic may also be water in hospitals. The hospital environment is conducive to pollution caused by pathogens transmitted by water (high water temperature, abiotic surfaces conducive to the formation of biofilms, incorrect maintenance of water systems). Common pathogens transmitted by water are bacteria (Legionella spp., other Gram-negative bacteria, non-tuberous Mycobacterium), less frequently fungi and viruses. Sanitary-epidemiological evaluation of water Physical, chemical and biological indicators are taken into account for assessment of water quality. The biological indicators of water pollution are different species / types of bacteria. Direct detection of absolutely pathogenic bacteria in water samples (e.g.Salmonella, Shigella) is difficult. The most common method is the indirect method of detecting bacteria considered as indicators of sanitary condition. Indicators of faecal pollution are coliform bacteria: Escherichia coli, Citrobacter sp., Enterobacter sp., Klebsiella sp. - Coliform titer is the smallest volume of water (ml) where coliforms are present; for drinking water coliform titer - Coliform index is the quantity of coli group bacteria in 100 ml of water. - Total viable bacteria over 1 ml of the agar medium in temperature 37°C after 24 hours (for drinkable water ≤ 20) and in 22 °C after 72 hours (≤ 100) of incubation. - Membrane filtration - test samples are passed through a membrane filter with a specific pore size (usually 0.45 microns); the microorganisms present in the water remain on the filter surface which is then placed on a selective medium in a petri dish, incubated at a specified temperature for a specified time; and then the number of colonies grown on the filter is counted. A routine bacteriological analysis assessing the sanitary state of water also includes determining the total number of psychrophilic bacteria (they grow at a temperature of -5 to + 30°C, the optimum being 15-30°C) and mesophilic (+15 to + 45°C, the optimum being 37°C; these are mainly pathogenic bacteria). Apart from the microbiological factors, the assessment of water purity also includes hydrobiological methods. The biological indicator Bi can be defined as a quantity relation of different microorganisms in the water reservoir (producers, consumers and reducents) relation between doubled producers’ quantity (P) in 1ml of water and the sum of consumers (C) and reducents’ quantity (R) in 1ml of water. Water quality WHO prepares international norms on water quality and human health in the form of guidelines that are used as the basis for regulation and standard setting worldwide (Table 3). For microbial water quality, verification is likely to be based on the analysis of faecal indicator microorganisms, with the organism of choice being Escherichia coli or, alternatively, thermotolerant coliforms. Escherichia coli provides conclusive evidence of recent faecal pollution and should not be present in drinking-water. Exceptionally, additional indicators, such as bacteriophages or bacterial spores, may be used. 7 Microbial drinking-water safety is not associated with faecal contamination only. Some organisms can grow in piped water of public water distribution systems (e.g. Legionella), whereas others occur in source waters such as rivers, streams, lakes, reservoirs, springs, and ground water) that provide water to public drinking-water supplies and private wells. (e.g. guinea worm - Dracunculus spp.) and may cause outbreaks and individual cases. To purify water intended for consumption, settlers and filters are used. They remove suspensions, and after coagulation, colloidal admixtures and a large part of bacteria, including pathogenic bacteria. If the mechanical-chemical methods of water treatment do not guarantee full removal of microorganisms, water is disinfected using ozone or chlorine compounds. Table 3. Guideline values for bacteriological quality (WHO). Organisms All water intended for drinking - E. coli or thermotolerant coliform bacteria Treated water entering the distribution system - E. coli or thermotolerant coliform bacteria - Total coliform bacteria Treated water in the distribution system - E. coli or thermotolerant coliform bacteria - Total coliform bacteria Guideline value must not be detectable in any 100-ml sample must not be detectable in any 100-ml sample must not be detectable in any 100-ml sample must not be detectable in any 100-ml sample must not be detectable in any 100-ml sample. In the case of large supplies, where sufficient samples are examined, must not be present in 95% of samples taken throughout any 12-month period. Infectious diseases caused by pathogenic bacteria, viruses and parasites (e.g. protozoa and helminths) are the most common and widespread health risk associated with drinking-water. Consumption of contaminated drinking-water represents the greatest risk, but other routes of transmission can also lead to disease. Inhalation of water droplets (aerosols) can lead to infection or invasion with for example Legionella spp., Naegleria fowleri (the cause of primary amoebic meningoencephalitis) and Acanthamoeba spp. (the cause of granulomatous amoebic encephalitis, amoebic keratitis, pulmonary infections). In the European Union countries, for the assessment of the sanitary state of water, the following bacteria are used as indicator organisms of faecal contamination: Escherichia coli, Enterococcus faecalis (all types of waters), Clostridium perfringens (surface waters), Pseudomonas aeruginosa (bottled water). The frequency of sampling of drinking water, test methods used and acceptable values of sanitary and bacteriological indicators must comply with the standards specified in relevant legal acts (Water Framework Directive 2000/60/EC). In countries such as the USA, Ireland and the United Kingdom, apart from faecal bacteria, an obligatory indicator of purity of drinking water is also protozoan Cryptosporidium parvum whose oocysts show high resistance to chlorination and ozonation. The WHO Guidelines for Safe Recreational Water Environments describe the present state of knowledge regarding the health hazards and risks associated with the recreational water use. Recreational waters of natural bathing areas are examined for the presence of faecal streptococci (Enterococcus spp.) and Escherichia coli. The water of inland and sea bathing areas must also meet the visual inspection criteria; it cannot contain large amounts of cyanobacteria, macroalgae, marine phytoplankton, chemical impurities (including tarry materials) or solids (glass, plastics, rubber). Water-borne parasitic invasion For pathogens transmitted by the faecal–oral route, drinking-water is only one vehicle of transmission. Contamination of food, hands, utensils and clothing can also play a role, particularly when domestic sanitation and hygiene are poor. Improvements in the quality and availability of water, excreta disposal and general hygiene are all important in reducing faecal–oral disease transmission. Drinking-water contaminated with soil or faeces could act as a carrier of other infectious parasites, such as Fasciola spp., Echinococcus spp., Ascaris spp., Trichuris spp., Strongyloides spp. and others. Pathogens naturally present in the environment may cause disease in vulnerable subpopulations, i.e.the elderly or the very young, patients with burns or extensive wounds, those undergoing immunosuppressive therapy or those with acquired immunodeficiency syndrome.Examples of such agents are listed in Table 4. Table 4. Characteristics of parasites associated with the aquatic environment. Characteristics Type of organism Geographical occurrence Acanthamoeba castellani protozoa Stage invasive for humans Route of invasion protozoa cosmopolitan, freeliving ameba Hosts Cryptosporidium parvum - cyst trophozoite injured conjunctiva or skin, nasal cavity Fasciola hepatica liver fluke Schistosoma mansonii blood fluke Diphyllobothrium latum broad fish tapeworm fluke fluke tapeworm cosmopolitan cosmopolitan Africa, Arabian Peninsula, South America, Caribbean - mammals, about 150 species, mostly domestic animals - non-biting cyclorrhaphan flies - definitive host – human and other mammals (sheep) - intermediate host – snail Galba truncatula - definitive host – humans and some other mammals - intermediate host – snail of genus Biomphalaria oocyst metacercariae furcocercariae plerocercoid oral cavity through water or food contaminated with feaces, rarely direct contact epithelial cells of intenstine (intracellular parasite) oral cavity throughingestion of water plant or contaminated vegetable active penetration through the skin oral cavity throughraw or undercooked freshwater fish liver inferior mesenteric vein small intenstine Northern Europe, North America, Asia, but cases also Uganda and Chile. - definitive host – mammals feeding with raw fishes, including human - intermediate hosts: 1st – crustacean 2nd – small freshwater fish Localization in human organism eyeball CNS Stage found in human organism – parasitic stage cyst trophozoite trophozoite oocyst adult fluke adult fluke adult tapeworm Pathogenicity - Acanthamoeba keratitis - Granulomatous Amebic Encephalitis - disseminated acanthamoebosis cryptosporidiosis fasciolosis / fasciolasis acute or chronic schistosomiasis diphyllobothriasis Lithosphere 9 Lithosphere supports all the life which exists on the Earth, whether on land or in oceans. It is a large reservoir of useful resources: minerals, metals, fossil fuels: coal, natural gas and petroleum. It provides nutrients to the plants and contains large reservoirs of water like lakes, rivers and oceans which are essential for the existence and survival of life. The uppermost layer of Earth’s crust is named soil. Soil contamination Soil undergo degradation – it is a natural process, but it can also be caused by human activity e.g deforestation, overgrazing, intensive cultivation, forest fires and construction work. The main causes of soil degradation and, consequently, the main threats to its ecological functions are erosion, organic matter decline, loss of biodiversity, pointsource and diffused contamination, pollution, and salinization. Soil pollution occurs when the presence of toxic chemicals, pollutants or contaminants in the soil is in high enough concentrations to be of risk to plants, wildlife, humans. As a result, soil loses its function. Agricultural soil undergoes gradual desertification due to global warming and agricultural fertilizers and pesticides. Contact with contaminated soil may be can be via the digestive system (young children eating soil, or through the consumption of plants or animals that have accumulated large amounts of soil pollutants), or respiratory system by inhaling soil dust particles. It may also result from secondary contamination of water supplies and from deposition of air contaminants. There are two major sources of soil pollutants: - natural/geogenic – “parent rock” can contain heavy metals and radionuclides (arsenic, radon); volcanic eruptions or forest fires may release toxic elements (dioxin-like compounds, polycyclic aromatic hydrocarbons) into the environment; - anthropogenic – energy industry; production and processing of metals; mineral industry; chemical industry; waste management; other business activities (textiles, slaughterhouses, intensive animal breeding, extensive farming); mining; urban and transport infrastructures; waste and sewage disposal; military activities and wars. Soil biology Soil structure, the arrangement of soil particles in various aggregates and the pore spaces between them, largely depends on the amount and composition of microorganisms (bacteria, fungi, algae, protozoa) inhabiting soil layers. Microorganism activities and interactions between them influence soil fertility, decomposition of organic matter and cycling of nutrients in environment. Organisms in soil may be classified as: - autochthonous – an indigenous form of soil microorganisms responsible for chemical processes that occur in the soil under normal conditions (e.g. Actinomycetes, Azotobacter, Rhizobium); - allochthonous – an organism that originates from a place other than that in which it is found, usually a transient member of a community (e.g. Pseudomonas, Clostridium, Salmonella,E. coli). Actinomycetes are a large group of bacteria that constitute 10% of all soil microorganisms. They decompose a wide array of substrates, but are especially important in degrading recalcitrant (hard-to-decompose) compounds, such as chitin and cellulose, and are active at high pH levels. Actinomycetes produce a large amount of compounds with different types of biological activity, including antibacterial, antiviral, anticancer, antifungal and anthelmintic. About 80% of the known antibiotics of natural origin are produced by Actinomycetes, usually 5-10% of their genome are genes responsible for secondary metabolism. The most important medical significance is the cosmopolitan genus Streptomyces (about 500 species) that produces nearly 80% of all bioactive metabolites of Actinomycetes (Table 5). Table 5. Examles of antibiotics produced by Streptomyces spp. Species Antibiotic Antibacterial activity Streptomyces griseus streptomycin Streptomyces aureofaciens tetracycline Streptomyces orientalis vankomycin Antifungal activity Streptomyces nodosus amphotericin Streptomyces noursei nystatin Antitumor activity Streptomyces caespitsus mitomycin Streptomyces antibioticus actinomycin Soil, contaminated with sewage (municipal sewage and slurry, animal waste from slaughterhouses), or directly with human and animal feces, becomes a reservoir of many gastrointestinal parasites, not only bacteria, but also viruses protozoa and helminths. Soil-transmitted parasites live in the intestine and their cysts/eggs are passed in the feces of infected persons directly to the soil. In areas with warm and moist climates where sanitation and hygiene are poor (also in temperate zones) they are the cause of parasite invasions. Sanitary evaluation of soil Sanitary evaluation of soil includes bacteriological and helminthological examination. Bacteriological research allows to determine the intensity and the origin of pollution, the time of contamination, as well as the progress of the process of the soil self-cleaning. The presence of intestinal microorganisms indicates contamination with faeces: - fresh - Escherichia coli and other intestinal bacilli (e.g. Salmonella - up to 3 months, Shigella - up to several days); - older - Enterobacter aerogenes (several months, up to a year); - the oldest - Clostridium perfringens in the form of spores (even up to several years). Coliforms titer or C. perfringens titer is the smallest soil mass in which coliforms or C. perfringens spores are still present. 11 The soil helminthological examination consists in searching, in the tested samples, for developmental stages of parasites classified as helminths (and also some protozoa). Soils in which the presence of such parasitic forms has been detected cannot be used for growing vegetables or fruits consumed in the raw state. Commonly in soil parasitological studies concentration methods (flotation and sedimentation) are used which analyze the differences in the specific weights of cysts, oocysts, parasite eggs and the appropriate fluids. Concentration methods allow the separation of parasites from soil/fecal particles, increase the detectability of parasites by concentrating their developmental forms in the material being evaluated: - sedimentation methods – use of a solution with a specific weight lower than weight of developmental stages of parasites; parasites fall to the bottom of the dish; - flotation methods - use of a solution with a specific weight greater than weight of developmental stages of parasite; parasites rise to the surface. Soil-transmitted parasites – helminths Soil-transmitted helminth infections are among the most common infections worldwide and affect the poorest and most deprived communities. More than 1.5 billion people (about 24% of the world’s population) are infected with soil-transmitted helminths worldwide: - approximately 807-1,121 million with Ascaris; - approximately 604-795 million with whipworm; - approximately 576-740 million with hookworm. Infections are widely distributed in tropical and subtropical areas, with the greatest numbers occurring in Sub-Saharan Africa, the Americas, South and East Asia. Charactericstics of most common soil-transmitted helminths is presented in Table 6. Table 6. Characteristics of soil-transmitted helminths. Characteristics Ascaris sp. - roundworm Trichuris sp. - whipworm Ancylostoma hookworm Geographical occurrence cosmopolitan, more common in tropical countries cosmopolitan cosmopolitan Stages found in soil unfertilized eggs, fertilized eggs eggs eggs, rhabditiform larvae, filariform larvae Period of stay in soil to gain invasiveness 18 days 15-30 days 5-10 days Stages invasive humans fertilized eggs embryonated eggs filariform larvae Route of invasion oral cavity, with soil and vegetables contaminated with feaces oral cavity, with food or soil contaminated with feaces skin, larvae actively penetrate trough undamages skin Localization in human organism larvae – lungs/sputum adult - small intenstine larvae – small intenstine adult - cecum adult - small (duodenum) Pathogenicity ascariosis trichuriosis ancylostomosis for sp. - intenstine Adult worms live in the intestine where they produce thousands of eggs each day. Human can be invade trough: - eggs that are attached to vegetables and are ingested when the vegetables are not carefully cooked, washed or peeled; - eggs are ingested from contaminated water sources; - eggs are ingested by children who play in the contaminated soil and then put their hands in their mouths without washing them. Hookworm eggs hatch in the soil,they release larvae that mature into a form that can actively penetrate the skin. Hookworm infection is transmitted primarily by walking barefoot on contaminated soil. One type of hookworm (Anclostoma duodenale) can also be transmitted through the ingestion of larvae. References: 1. Park J., Kim J.S., Kim S., Shin E., Oh K.H., Kim Y., Kim C.H., Hwang M.A., Jin C.M., Na K., Lee J., Cho E., Kang B.H., Kwak H.S., Seong W.K., Kim J. A waterborne outbreak of multiple diarrhoeagenic Escherichia coli infections associated with drinking water at a school camp. International Journal of Infectious Diseases, 2018, 66:45–50 2. Hlavsa M.C., Cikesh B. L., Roberts V. A., Kahler A. M., Vigar M., Hilborn E. D. et al.. Outbreaks Associated with Treated Recreational Water — United States, 2000–2014. Morbidity and Mortality Weekly Report, 2018, 67(19): 547–551 3. Buczek A.: Parasitology for medical students. Koliber Lublin, Second Edition. 2007 4. Meder S., Windelspecht M.: Human Biology. McGraw-Hill Science/Engineering/Math, Twelfth Edition 2011 5. Murray PR., Rosenthal KS., Pfaller MA. “Medical microbiology”, Elsevier, 2016. 13