Drinking water cholera

Propagated outbreaks of infection relate to the direct transmission of an infective agent from a diseased individual to a healthy, susceptible one. Mechanisms of such transmission were described in Chapter 4 and include inhalation of infective aerosols (measles, mumps, diphtheria), direct physical contact (syphilis, herpes virus) and, where sanitation standards are poor, through the introduction of infected faecal material into drinking water (cholera, typhoid). The ease oftransmission, and hence the rate of onset of an epidemic (Fig. 16.3) relates not only to the susceptibility status, and general state of health of the individuals but also to the virulence properties of the organism, the route oftransmission, the duration of the infective period associated with the disease. 

One of the foremost global issues regarding water quality is access to safe drinking water. Currently, one-sixth of the world s 6.1 billion people do not have access to a source of clean water, and 40% do not have adequate sanitation facilities. Polluted water is responsible for diseases such as typhoid, cholera, and dysentery. Three million people die annually due to the latter. The discovery that diseases were transmit-... 

In the early 1990s, an anti-water-chlorination campaign in Pern led the government to stop chlorinating the drinking water. Within months there were 1.3 million new cases of cholera resulting in 13,000 deaths. 

An adequate supply of water is essential to the health and well-being of the world s population. Across the planet, biological and chemical pollutants are affecting the quality of our water. An adequate supply of fresh drinking water is needed for everyone on the planet. Lack of availability of fresh water leads to waterborne diseases, such as cholera and typhoid, and to diarrhoea, which is one of the biggest killers across the world. 

Since the fledgling days of industrial chemical practice, the bleaching properties of chlorine have been in demand. Rampant spread of the great killer diseases such as cholera and typhoid was eliminated by the treatment of wastewater and drinking water with small amounts of bleach. Textile manufacturers and the paper industry had established the value of bleach in their operations early on. 

Thousands of people in Britain, and Europe died of cholera during the nineteenth century. At that time there was no known cure and no connection was made between the incidence of cholera and the unsanitary conditions. In the cities human excrement was thrown into open sewers flowing down the streets and into rivers. The rivers were also the source of drinking water. London was known as the city of smells. The disease was thought to be carried by the smells . The conditions were only improved when major underground sewers were built in the 1880s. It was also realized that there were very small organisms such as bacteria and viruses. The bacterium responsible for cholera was discovered by Robert Koch in 1883. 

Waterborne microorganisms are largely responsible for the transmission of diseases such as cholera, typhoid, dysentery, muscular paralysis (e.g., poliomyelitis), infectious hepatitis, gastroenteritis, giardiasis, cryptosporidiosis, and so forth. In a drinking-water potabilization procedure not all the microorganisms present in water need to be killed (sterilization), but only those disease-related (disinfection). Water disinfection can be achieved by chemical, physical, or mechanical action. Agents that provide chemical action for such purposes include ... 

Drinking water has been disinfected with chlorine for approximately 100 years to protect against waterborne infectious diseases. In addition to chlorination, other methods of drinking water disinfection include the use of chlorine dioxide (either alone or in combination with chlorine), the addition of ammonia to chlorine to form chloramines, ozone treatment, oxidation with potassium permanganate, and ultraviolet radiation. Chlorination, however, is by far the most widely used method. Treatment with chlorine has virtually eliminated cholera, typhoid, dysentery, hepatitis A, and other waterborne diseases)54 ... 

Asia. V. cholerae 0139 also has been isolated from food-production animals in the Netherlands. Four mechanisms for transmission have been proposed, including animal reservoirs, chronic carriers, asymptomatic or mild disease victims, and water reservoirs. A relatively large inoculum of 10 to 10 is required for infection if water is the vehicle and 10 to 10" if the vehicle is food. Approximately half the people infected with V. cholerae 01 are symptomatic, whereas only 1% to 5% of those infected with V. cholerae 0139 manifest symptoms. The hallmark of cholera is the production of watery diarrhea, and severe dehydration may develop within a few hours, causing death within 24 hours. An estimated 25% to 50% of cases are fatal if left untreated. The prevention of cholera transmission depends on the provision of clean drinking water and public sanitation, which is difficult in impoverished developing countries. ... 

Bacterial infections are the other common neglected diseases. They comprise leprosy and trachoma, which are controlled by antibiotic treatments, Buruli ulcer, managed by surgery and antibiotics, cholera, caused by Vibrio cholerae living in contaminated drinking water, and for which antibacterials and isotonic fluid replacement therapy are recommended. 

Before leaving this sub-section on chlorine as a disinfectant, we should note that the majority of the Asian cities still do use chlorine to disinfect drinking water. The benefits in term of protection from water-borne diseases in Asia far overweigh the possible hazard from, for example, 10 or 20 ppb of trihalomethanes. Disinfection with chlorine may possibly pose a cancer risk in old age no disinfection in the Asian region does mean a substantial chance of dying from typhoid fever or cholera as a child or young adult. However, as we have seen in Table 1, there are different methods of disinfection and we consider some of these alternatives to chlorination. 

V. cholerae epidemics are associated with unsanitary conditions affecting the drinking water supply and are rare in the United States. However, these bacteria grow well under the alkaline conditions found in seawater and attach to chitin in shellfish. Thus, sporadic cases occur in the southeast United States associated with the ingestion of contaminated shellfish. 

Up to the advent of the twentieth century, the fight against microbes was devoted to disinfecting external wounds and to sanitizing drinking water. Since Pasteur s works, the objective was to treat infectious diseases cholera, tuberculosis, diphtheria, etc. Some vaccines were already available, but only for smallpox and rabies. 

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