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Pathogens and drinking water Professor Nick Gray Centre for the Environment Trinity College University of Dublin © Tigroney Press
Pathogens and drinking water Learning objectives: • To know the main pathogen categories • To be aware the key pathogens in drinking water • Methods involved in monitoring of pathogens
Pathogens and drinking water Disease Classification Water associated diseases are classified according to their mode of transmission and the form of infection as: • Waterborne diseases • Water-washed diseases • Water-based diseases • Water-related diseases All drinking water disease in W. Europe currently classified as waterborne
Pathogens and drinking water Waterborne diseases • Caused by contamination of water by faecal matter and urine • Infection by direct ingestion of water or indirectly by any ingestion of pathogens (e. g. food-Typhoid Mary) • Results in widespread outbreak of disease amongst those using the same source of water • Carriers may be symptomless • Example: Cholera, infectious hepatitis, paratyphoid, tularaemia, typhoid, amoebic dysentery, bacillary dysentery. • Weil’s diseases (leptospirosis) caused by skin contact with infected rat urine found in sewage, flood water and contaminated surface water.
Pathogens and drinking water Water-washed diseases • Caused by poor personal hygiene due to water shortages • Spread of infection reduced by supplying additional water. Microbial quality unimportant as used for cleaning/washing not ingestion • Diseases normally skin infections, mucous membranes and eyes. Non-faecal in origin (e. g. bacterial skin sepsis, scabies, cutaneous fungal infections). • Diseases also include those spread by fleas, ticks and lice (e. g. epidemic typhus, rickettsial typhus and louse-borne fever). • Some water borne diseases can be contracted due to poor personal hygiene (e. g. shigellosis) • Other examples: ascariasis, conjunctivitis, leprosy, skin sepsis
Pathogens and drinking water Water-based diseases • Caused by pathogens that have complex life cycle requiring an aquatic intermediate host • Disease can not be contracted by ingestion or contact with pathogen as excreted by infected person • All caused by parasitic worms with severity of infection dependent on number of worms infecting host • Schistosomiasis caused by trematode Schistosoma spp. Aquatic snails intermediate host, cercarias penetrate skin of humans normally spread via irrigation schemes. Eggs leave humans via urine. >200 million people infected globally. • Other examples: Dracunculus medimensis - guineaworm (nematode) Cyclops spp. intermediate host.
Pathogens and drinking water Water-related diseases • Pathogens carried by insect vectors living near water • Diseases are all severe and difficult to control • Viral diseases • Yellow fever – mosquito Aedes spp. • Dengue – mosquito Aedes aegypti • Protozoan diseases • Gambian sleeping sickness (trypanosomiasis) – river tsetse fly Glossina spp. • Malaria – protozoan Plasmodium sp. Carried by mosquito Anopheles spp.
Pathogens and drinking water Controlling Pathogen transfer Ideally drinking water should be free from all micro-organisms -unattainable goal in practice Barrier approach: (i) Wastewater treatment (ii) Natural self purification (iii) Water treatment Point-of-use techniques Monitoring Barrier approach has been largely successful given huge reductions in outbreaks of primary pathogens.
Pathogens and drinking water
Pathogens and drinking water Monitoring • Far too many pathogens to monitor them all • Use of indicator organisms to indicate contamination • Based on theory that there is a quantifiable relationship between indicator density and potential health risks
Pathogens and drinking water All waterborne pathogens have certain traits that make them so successful: • An ability to be excreted in faeces in large numbers during illness • Failure of conventional sewage treatment to remove them • Survive as an environmentally robust form • Resilience to inactivation while in aquatic environment • Largely resistant to common disinfects used in water treatment • Only require small numbers to elicit infection in host consuming or exposed to water These factors compounded by difficulty in detecting them in resources and effluents.
Pathogens and drinking water EU Drinking Water Directive specifies numerical standards for: • Escherichia coli (0/100 ml) • Enterococci (Faecal streptococci) (0/100 ml) Routine monitoring • Coliform bacteria (0/100 ml) • Clostridium perfringens (0/100 ml) Bottled water • E. coli (0/250 ml) • Enterococci (0/250 ml) • Pseudomonas aeruginosa (0/250 ml) • Heterotrophic bacteria 22 o. C (100/ml) • Heterotrophic bacteria 37 o. C (20/ml) Membrane filtration on m. Enterococcus agar – maroon colonies are enterococci
Pathogens and drinking water Main groups able to survive different periods: Enterococci die quickly outside host indicates recent contamination E. coli can survive for several weeks under ideal conditions – easily detected. Sulphate reducing clostridia survive indefinitely in water – when above are absent indicates remote or intermittent contamination- useful in reservoirs. Heterotrophic bacteria commonly found and reproduce in water- some now considered opportunistic pathogens- not direct indicator of faecal contamination- do indicate potential for pathogen survival and regrowth- EU DWD requires no significant increase above background levels in either tap or bottled water.
Pathogens and drinking water Enumeration techniques Quantitative: Membrane filtration used for all except Clostridium as requires anaerobic conditions (i. e. multiple tube method). Used in EU Presence: absence: Based on enzyme detection- Incubated 24 h at 35 o. C- also quantitative as well as PA – used in US • Total coliforms presence of ß-galactosidaese activity (ONPG) • E. coli presence ß-glucuronidase activity (MUG) Gene probe technology: Allows single cells to be identified.
Pathogens and drinking water Membrane filtration Medium varies with many new ones on the market – specified methods linked to standards
Pathogens and drinking water
Pathogens and drinking water Main Irish/UK pathogens Two protozoan diseases common • Giardia lamblia – giardiasis – backpacker’s disease • Crytosporidium parvum / hominis– cryptosporidiosis Giardia • Lives in wide range of animals lives as trophozoite form (free-living) in intestines • Shed cysts: Oval 8 -14 µm long 7 -10 µm wide • One of the commonest causes of waterborne disease • US 71% raw 17% treated contain cysts • Scotland 48% raw and 23% treated • Symptoms explosive watery foul smelling diarrhoea, gas, nausea • Filter or boil 20 minutes
Pathogens and drinking water Giardia: Top right: schematic of trophozite; Below right: trophozites X 1000, Left: Life cycle
Pathogens and drinking water Cryptosporidium • C. parvum can be differentiated into two distinct genotypes. o Genotype 1 or H (for human) exclusively human now named as C. hominis. Very aggressive and was the cause of the 1993 outbreak in Milawakee. o Genotype 2 or C (for calf) traditional C. parvum which has now been found in over 150 species including humans. • Both genotypes are commonly recorded in water supplies, but it is also readily spread from person to person as well as being auto-infective. • Oocysts ovoid 4 -7 µm diameter; Infected animals and humans shed 1010 oocysts during course of infection; 1 cyst infects • UK 50% and in US 97% surface water affected • 1989 Swindon/Oxford outbreak led to operational changes • Self limiting gastroenteritis, often fatal in immuno-suppressed • Spring/autumn peaks
Pathogens and drinking water Bacteria Primary: major diseases causing gastroenteritis • Salmonella – typhoid, paratyphoid • Shigella – bacterial dysentery • Vibrio cholerae – cholera • Campylobacter – enteritis – dog and pets carry disease • Enteropathogenic E. coli- many strains- traveller’s tummy • e. g. Enterohaemorrhagic E. coli (0157. H 7)- haemorragic colitis leading to kidney disease in children, also associated with food
Pathogens and drinking water Primary pathogen: Cholera (Vibrio cholerae) • Increasingly common due to increased mobility and speed of travel • Healthy symptomless carriers 2 -9% of population • Haemolyic strain 25% carrier • 108 -109 organisms needed to cause illness – not person to person • Primarily water transmitted or food handled by carrier. • Two serotypes 01 and 0139 responsible for epidemic cholera • 0139 responsible for new world wide epidemic (8 th pandemic) • Symptoms sudden diarrhoea with copious watery faeces, vomiting, suppression of urine, rapid dehydration, lowered temperature and blood pressure, collapse. • 60% death rate – death a few hours on first showing symptoms • Rapid treatment death rate reduced to 1%
Pathogens and drinking water Vibrio cholerae 2 um _________
Pathogens and drinking water Factors involved in the spread of cholera is air transport, frequency of natural and man-made disasters exacerbated by climate change. Note: reporting has also improved
Pathogens and drinking water Opportunistic pathogens Part of normal heterotrophic flora of aquatic systems • Not a threat to healthy people • At risk: newborn, elderly, immuno-compromised • List very long – most important: Mycobacteria spp, Legionella pneumopila and Aeromonads spp. • Readily multiply in distribution system and/or household plumbing.
Pathogens and drinking water Legionnaires’ Disease (Legionella pneumophila) • 1976 -American Legion annual conference in Philadelphia hotel • 1985 - 75, 000 cases in US 11, 250 deaths • Bacteria survive and grow in phagocytic cells and multiply in the lungs causing bronchopnemonia and tissue damage • Very dangerous, high death and disability rates • Widespread in nature – readily colonizes supply pipes, resistant to disinfection • Domestic water supplies stored at 20 -50 o. C plus key nutrients (e. g. Fe) and long retention time. • Mode of transmission as aerosols – showers humidifiers, air conditioning. • Problem in hospitals and hotels • Hyperchlorination, thermal eradication, UV sterilizers at point of use
Pathogens and drinking water Mycobacteria spp. • Common in all natural waters • Causes soft tissue damage-especially pulmonary disease and cervical lymphadenopathy • Disseniated mycobacterial disease third most common terminal infection of AIDS patients • Common in all waters, many pathogenic species, can get into system due to poor chlorination, able to colonize and grow in distribution systems (flats, offices, hospitals) due to slow moving water.
Pathogens and drinking water Viruses • 120 distinct types of human pathogenic viruses • In drinking water gastrointestinal illness caused by enteric viruses (e. g. enteroviruses, Rotaviruses, Astroviruses, Calciviruses, Hepatitis A, Norovirus and other small round viruses • Respiratory infections - Reovirus, Coxsackievirus, Echovirus, • Poliomyelitis – common in sewage due to live virus vaccination • Coxsachie B – associated with myalic encephalomyelitis (ME and cardiac disease • US - >20% all wells contaminated with viruses, common in surface water • Most warm blooded animals carry viruses pathogenic to man, especially dogs. Storm water major problem • Georgetown, Texas. 1979 - 79% of population contracted Hepatitis A after sewage washed into groundwater supply by heavy rainfall.
Pathogens and drinking water Conclusions • Pathogens are a continuous major risk to public health via drinking water • Barrier approach used to control pathogen transfer • Disinfection vital to prevent transfer • Detection difficult based on indicator organisms • Large volume of water need to be analysed for protozoa and viruses • Point of use systems best for opportunistic pathogens
Pathogens and drinking water References Percival, S. L. et al. (2014) Microbiology of Waterborne Diseases: Microbiological Aspects and Risk (2 nd Edition), Academic Press, London. Call No. 616. 9 P 42*1 http: //www. cdc. gov/ncezid/dfwed/waterborne/ http: //www. cdc. gov/healthywater/surveillance/ http: //www. who. int/water_sanitation_health/diseases/en/