Ch 2 - Waterborne Pathogens
Canoeist Pathogenic Illness Guide


2 - Waterborne Pathogens
2.1 - Sewage/Waste Related Pathogens
2.2 - Non Sewage/Waste Related Pathogens
2.3 - Indicator Organisms

Forward to Chapter 3 - Epidemiological Research - Early Investigations

2 - Waterborne Pathogens

Microorganisms are ubiquitous in all of nature. Vast numbers of varieties and species of microorganism occur in the natural aquatic environment. The ability of some of these organisms to cause disease to man has been known since the mid 1800s. This chapter aims to list and describe the main pathogenic microorganisms of interest to the recreational water user.

When looking at those water-borne pathogens which can cause problems to canoeists, it is possible to define two main routes of infection. The first category of pathogens are those which are commonly regarded as natural human pathogens, intimately associated with the vast amount of sewage, industrial effluent and agricultural waste which is discharged to the inland waterways of Britain. The other category are those microorganisms which occur naturally in river and lake water, often non-human parasites, which can occasionally cause problems to recreational water users if they can find a route into the human body.

2.1 - Sewage/Waste Related Pathogens

Sewage and many other liquid waste streams are likely to contain pathogenic microorganisms which have been excreted by humans. Although much of this waste receives some treatment before disposal to the river, the treatment is mainly to reduce the level of suspended solids, and to reduce the biochemical oxygen demand (BOD) of the effluent. The levels of bacteria and viruses in treated sewage effluent can still be considerable (House of Commons Environment Committee, 1990).

The risk of sewage derived infection from water is also emphasised by the DOE and Public Health Laboratory Service:

Contamination by sewage or by human or animal excrement is the greatest danger associated with water for drinking - whether it occurs as a result of inadequate treatment or during distribution. This is because sewage from human or animal sources may contain the causative organisms of many communicable diseases such as typhoid fever, bacterial or amoebic dysentery, giardiasis, infective hepatitis and poliomyelitis. If such contamination is recent, and if among the population from which the sewage is derived there are cases or carriers of these or other microbial diseases, some of the living causal agents may be present and the drinking of such water may result in further infections.
Animals and birds may also harbour in their gut various organisms pathogenic to man, and the importance of these sources of pollution must not be overlooked. Gulls in particular now cause a serious problem because they may breed on catchments, feed at refuse tips and sewage treatment works, and subsequently roost on water........(HMSO, 1982. page 5).

Although this reference describes the potential risks from pathogens in the public drinking water supply, the same risks can easily occur to canoeists when in contact with the river or reservoir water from which the drinking water supply is eventually to be taken.

It is thus possible to have human pathogens which have been excreted by one person, which pass unaffected through the waste treatment process, and be present in river water to infect other water users, including canoeists.

2.1 a) - Enteric Bacteria and Viruses

Gastroenteritis has been linked to a range of microorganisms, including bacteria (such as Campylobacter, Salmonella and Shigella species) and protozoa (Giardia and Entamoeba). More recently viral cause have been implicated (mainly enteroviruses such as coxsackle viruses, echoviruses, polioviruses and the norwalk virus). (Philipp. R. 1991). Whilst most cases of gastroenteritis caused by such pathogens are linked to the contamination of food or water supplies, in recent years infection through recreational contact with sewage contaminated water has become recognised as a serious problem.

In epidemiological studies of this problem it can be difficult to distinguish recreational infections from those infections caused by the same pathogens but through other causes, such as food poisoning caused by contaminated food and drinking water.

2.1 b) - Skin, Eye, Ear and Respiratory Tract Infections

Although gastroenteritis is the main disease causing public concern amongst canoeists and other water users, a range of other infections and symptoms can be caused by recreational water contact.

Some symptoms such as headaches, muscle and joint pains or flu-type fevers may be associated with the same organisms that cause the gastrointestianal symptoms of diarrhoea, vomiting and dehydration.

Pseudomonas has been assocoated with follicular dermatitis (an itching, pustular scalp infection) and otitis externa (inflamation of the ear canal commonly called swimmers ear). Skin infections have also been associated with members of the genus Staphylococcus, some of which can invade the body through breaks in the skin and mucous membranes.

Many of these skin infections are more commonly associated with recreational activities such as swimming, where the pathogen is easily passed from person to person in the close confines of a bathing pool or changing room. In a canoeing context it may be possible for pathogens to be passed directly between two recreational participants sharing a site, or via some intermediate route such as a sewage system and river.

2.2 - Non Sewage/Waste Related Pathogens

Whilst the pathogenic microorganisms listed above are related to sewage and human waste, there is a second category of microorganism which occurs naturally in river or lake water in certain conditions, but which will cause problems to recreational water users if they can find a route into the human body.

2.2 a) - Algae

A number of algal species present in both marine and freshwater are capable of producing toxins. Traditionally the main route of human ingestion of these toxins has been through the consumption of contaminated shellfish (Fewtrell L. et al 1994). More recently the presence of toxic algal blooms has become recognised as a problem in fresh water used for recreation.

The causative agents of toxic blooms are blue green algae or cyanobacteria (Fewtrell, L. 1991). Neurotoxins produced by some cyanobacteria can lead to muscle paralysis and respiratory collapse leading to death. Other toxins can lead to gastroenteritis or inflammatory skin effects.

Cyanobacteria grow within the water body. They contain gas vacuoles which control their position vertically in the water column. If the algae are near the surface, wind and wave action can lead to the formation of a concentrated bloom or scum near to or on the shoreline. It is also possible for sub-surface banding or layers to form, which causes concentrations of algae not clearly visible to the naked eye (NRA 1990).

In 1989 ingestion of a beach-side scum lead to the death of several dogs and lambs at Rutland Water. In 1990 two army recruits were admitted to hospital suffering from pneumonia after a canoeing course involving total immersion in Rudyard Lake, Staffordshire. The men were shown to have lung deposits similar to those seen in animals inoculated with algal toxins. A further eight participants had symptoms such as sore throats, headaches, abdominal pains, dry coughs, diarrhoea, vomiting and blistered mouths. Subsequent investigation implicated cyanobacterial poisoning. All survived.

There are a number of incentives for Water Authorities to control algal growth. Many bodies of water used for recreation have their primary use as a water supply reservoir. Uncontrolled algal growth in such reservoirs could lead to dangerous toxins in the public water supply, as well as filter blockages and other mechanical problems in the water treatment works. In the reservoir or other watercourses algal respiration can also absorb excessive amounts of dissolved oxygen. This can lead to the asphyxiation of fish and other marine life.

Algal blooms are slow growing, and only tend to be a problem in still waters, late in the season of a long hot summer. Countermeasures to algal growth primarily include long term strategic measures to reduce water nutrient levels. Such measures include specialised tertiary treatment of sewage and industrial discharges, and controls on agricultural fertiliser use (NRA 1990).

Once a bloom has formed, measures such as physical removal, algicides or localised nutrient reduction are less effective and more expensive. The normal public health response is to ban recreational use water of which is seriously affected by algal growth. If it is possible to induce a flow into the watercourse then this can be beneficial, both by reducing nutrients and removing the algae.

2.2 b) Leptospira spp.

Leptospirosis is a potentially fatal disease caused by infection with pathogenic Leptospira bacteria. The degree of severity of the disease can vary from mild flu-like symptoms with severe headache, to the classic heptorenal failure and meningitis associated with Weil's disease (Fewtrell, L. 1991).

Leptospires are shed in the urine of contaminated animals (mainly rodents and cattle). Animals and humans become infected either directly through contact with contaminated urine, or indirectly, via contaminated freshwater or wet soil. Leptospires can survive for long periods (up to six months) in clean fresh water or damp conditions at neutral pH, but are not tolerant to drying out or to saline conditions. In the UK the bulk of the cases are between July and November, with net environmental water level rather than rainfall being a major factor in determining the spread of infection (Ferguson, I. R. 1990, Elder et al 1986).

Leptospires gain access to the body through cuts and abrasions in the skin, and through the mucosal surfaces of the mouth, nose and conjunctiva.

The incidence of the disease is fairly low compared to the number of persons engaged in recreational watersports. Sensible precautionary measures to reduce the risk are the best means of achieving protection.

Water Authorities, Local Authorities and other land managers discourage rodents with baiting (especially in sewers) and use litter control measures to prevent attracting rodents into waterside areas used for recreation. In addition Sports Governing Bodies, employers, and other agencies carry out education campaigns which cover three main topics:

  1. Covering cuts and scratches with waterproof plasters.
  2. Showering after water contact.
  3. The importance of seeking informed medical help if the symptoms of leptospiral infection are recognised.

See Appendix A - British Canoe Union Guidance on Leptospirosis - 1996

2.2 c) - Trichobilharzia ocellata

Trichobilharzia ocellata is a schistosome parasite of ducks, which requires aquatic snails to complete it's lifecycle. The snails emit a mobile larval stage (cercariae) which attempt to infect vertebrate hosts by skin penetration or ingestion. Cercarial dermatititis (swimmers itch) occurs when the parasites attempt to invade the skin of man. The problem is associated with aquatic snails, which thrive in slow moving weedy rivers, lakes and estuaries. Wet suits give excellent protection, and biological measures such as weed control and the introduction of predatory (snail eating) carp have been found effective (Fewtrell, L. 1994).

2.3 - Indicator Organisms

If there is the potential for any body of water used for recreation or for the public water supply to contain a massive variety of pathogenic microorganisms, then there will be a need to develop tests to indicate whether these organisms are present, and if so whether they are at a concentration which is dangerous to health.

Although it may seem logical to test the water specifically for those microorganisms which are known to have pathogenic effects, this is impracticable for a variety of reasons. Tests for certain agents, such as viruses, are time consuming and costly, and specific tests for certain pathogens are still not yet available to any degree of accuracy. Even if tests were available it would still be impractical and inordinately expensive to test for every known pathogen in every sample used for routine control purposes. It has therefore become standard practise to test the water for certain "indicator species". Originally the development of the use of indicator organisms was associated with the public health problems of protecting drinking water supplies from sewage contamination. The most common indicators are therefore commensal (non pathogenic) intestinal bacteria which are present in the faeces of man and other warm blooded animals. Their presence in the water can be assumed to be indicative of the presence of faecal contamination (typically through sewage), and therefore an indicator of the potential presence of those many other pathogenic microorganisms commonly found in sewage.

Most bacterial indicator tests consist of culturing the microorganisms contained in a known volume of water in a differential medium at a predetermined temperature. Both the temperature of incubation and the chemical content of the medium have been chosen to ensure that only the selected organisms grow and reproduce. Other organisms will die. It is then possible to estimate the number of indicator organisms in the original sample through some measure such as the gas given off, production of acid, or the number of colonies formed.

One key indicator organism is Esherichia Coli. This is the most abundant coliform organism present in the normal human and animal intestine. It is found in numbers approaching one thousand million per gram of fresh faeces, but rarely in soil, vegetation or water in the absence of excremental contamination.

Originally the most common test was for Total Coliform, a group which includes many different genera such as Citrobacter, Klebsiella, and Enterobacter as well as Esherichia coli. The test looked for those organisms that ferment lactose within 48 hours at 370C with the production of acid and gas (HMSO 1982).

Unfortunately it was found that the group included too many coliform bacteria which were not actually human pathogens. Only E. coli was a consistent inhabitant of the human intestinal tract. A second test was developed at an elevated temperature of 440C with a modified medium which selected primarily for Klebsiella and E. coli. This group is normally referred to as Faecal Coliform, or Thermotolerant.

Another class of indicator organisms is Faecal Streptococci, a group which includes a number of different species occurring naturally in man and other animals. Faecal Streptococci are more resistant to disinfection, and have longer survival times, and may therefore be a better indicator species of the risk from viral infections (Phillipp R. ibid). The test for faecal streptococci is similar to that for coliform, but a different medium is in use which includes sodium azide. This is inhibitory to E. coli and other coliforms and Gram negative bacteria.

The test for viruses is more difficult, partly due to the low numbers of viruses in water compared to typical indicator bacteria. Quite often up to twenty litres of water will be collected to provide a sample containing sufficient organisms. The first stage of the test involves procedures to concentrate the virus, such as filtration, floculation and centrifugation. The resulting concentrate can then be enumerated using electron microscopy, or by innocculating the concentrate onto a susceptible cell culture and looking for cytopathic effects which can be measured. Not all enteric viruses will however produce such effects, even if a variety of cell cultures are used.

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