Public Health & Preventive Medicine Lecture 4 PDF

Public Health & Preventive Medicine Lecture 4 Prof. Reham Elkased Milk Microbiology  Milk and milk products are rich in nutritional benefits. Raw milk (unpasteurized milk), can harbor dangerous microorganisms that can cause serious health risks. excellent medium for...

Public Health & Preventive Medicine Lecture 4 Prof. Reham Elkased Milk Microbiology  Milk and milk products are rich in nutritional benefits. Raw milk (unpasteurized milk), can harbor dangerous microorganisms that can cause serious health risks. excellent medium for microbial growth due to: high water and nutrient content (proteins, lipids, carbohydrates, vitamins); moderate pH (6.4–6.6). Milk-borne diseases are any diseases caused by the consumption of milk or dairy products infected or contaminated by pathogens. microbes release certain metabolites like acids, gases, enzymes & toxins leading to milk spoilage. Milk spoilage can take the form of discoloration, gas production, lactic acid production/souring, proteolysis and lipolysis. Sources of milk contamination 1- Animals microbes causing these diseases may be transmitted to milk either directly during milking process or indirectly through the infected body discharges that may drop into milk. diseases such as tuberculosis, anthrax, and Campylobacter infections. 2- Handlers diseased persons may transmit diseases by contaminated hands or by coughing, sneezing, and talking during milking or subsequent handling of milk at the farm level. diseases such as typhoid fever, dysentery, scarlet fever and diphtheria 3- Environment Dairy farm environment may also introduce pathogens into milk products. Contaminated water, unclean vessels and containers used for handling milk and other unhygienic conditions at farms and factory may significantly contribute to microbial growth in milk. Group A Streptococci, Mycobacterium tuberculosis, and some viruses of respiratory origin. How to Prevent Milk-Borne Infectious Diseases? Milk should be produced from physically healthy livestock in a standardized environment. Pasteurization of milk: Milk is heated to a high temperature (72 ℃ for 15 seconds) to kill pathogens, followed by rapid cooling. Then, milk should be tested to confirm that the number of pathogens is controlled to an acceptable level. Coolers are needed for transporting fresh milk to keep the milk temperature at 4 ℃ or lower. Hygiene in milk transportation, handling, and storage. Avoid unpasteurized milk and dairy products. Keep dairy products refrigerated within the expiration date marked on the package. Water and water supplies Importance of water is the body's principal chemical component and makes up about 50% to 70% of body weight. body depends on water to survive. Every cell, tissue and organ in the body needs water to work properly. Gets rid of wastes through urination, perspiration and bowel movements. Keeps body temperature normal. Lubricates joints. Protects sensitive tissues. ✓ Water is essential for domestic, agricultural and industrial purposes. ✓ Safe water supply is essential for satisfactory public health. Daily requirements of fluid intake (3.7 liters) a day for men (2.7 liters) a day for women fluids include water, beverages and food. About 20% of daily fluid intake usually comes from food and the rest from drinks. U.S. National Academies of Sciences, Engineering, and Medicine International human rights law obliges countries to work towards achieving universal access to water and sanitation for all, without any discrimination. The key elements of the rights to water and sanitation are: availability; sufficient and continuous accessibility; physically accessible affordability; affordable to all quality and safety; safe and free from threats to person’s health acceptability; all facilities should be culturally acceptable and appropriate and sensitive to privacy requirements  Water supplies 1. Atmospheric water: (Rain and snow) it is very pure, however, it may pick some impurities from the atmosphere or storage tank. 2. Surface water: (Rivers, streams, and lakes) is highly liable to pollution by human and animal wastes as well as industrial wastes. Surface water must be purified before use. 3. Underground water: (Wells and springs) a. Shallow wells: Water collected above the first layer; is liable to contamination. b. Deep wells: Water collection below the first layer; it is pure but hard water (high in minerals). c. Springs: Natural holes in the earth and source of water are higher than the earth’s level. Water impurities: 1. Gases such as Co2 and H2S during rainfall. 2. Minerals such as Ca and Mg are dissolved during filtration in soil and usually leads to hardness. 3. Microorganisms are derived from the environment or from sewage. 4. Suspended substances from agricultural, industrial, or animal sources. Diseases associated with water: 1. Waterborne infections: e.g. typhoid, dysentery, cholera, infective hepatitis, and poliomyelitis. 2. Diseases due to chemical constituents: ▪ Lead poisoning: affects the kidney and nervous system. ▪ Arsenic long term consumption: affects the bladder, kidneys and lungs and may lead to cancer. ▪ High fluoride content: may affect teeth and bones. ▪ high content of nitrite: interferes with the oxygen-carrying capacity of the blood. Purification of water Water for drinking must be soft and free from dangerous chemicals and pathogenic M.O. It should be also free from visible suspended matter, odor, taste, or color. Some natural sources could be considered safe for drinking as they are purified by the effect of sunlight, sedimentation (in lakes), or filtration through the soil in deep wells. However, surface water is considered unsafe until it is subjected to artificial purification. Hard water is water that has high mineral content (calcium, magnesium). The hardness of water can be classified into two types: - Temporary Hardness Presence of magnesium and calcium bicarbonates in water. - Permanent Hardness Presence of salts of magnesium and calcium in the form of chlorides and sulfates in water. 1- Removal of hardness Temporarily hardness calcium and magnesium is easily removed by boiling. Soluble bicarbonates are converted into insoluble carbonates by boiling which is then removed by filtration. Permanent hardness is removed by ion exchange resin (Ca++/Mg++ ions are exchanged with Cl–, and SO4-2 ions). Demineralized water is formed in this process. 2- Removal of gross matter Screening: to remove floating matter. Sedimentation: to remove large suspended matter when water is left in tanks for hours. Tanks may be aerated to remove odor. Coagulation: to remove fine suspended particles using aluminum sulfate, forming insoluble colloidal substances entrapping fine suspended matter and precipitating it. All precipitates are removed mechanically.  C) Removal of microorganisms:- Microorganisms treatment is approached in two ways: removal processes and/or inactivation (disinfection) processes. - Storage of water in tanks for days may purify water from human pathogens, as they have relatively short life in water. - Filtration Using either: 1- Slow sand filter ▪ Slow sand filtration involves passing water through a sand filter by gravity at a very low filtration rate, without the use of coagulation pretreatment. ▪ The filter typically consists of a layer of sand supported on a layer of graded gravel. ▪ As water passes within 2-3 days, an effective slimy layer of algae, diatoms, and bacteria is formed on the surface, which is very useful in removing bacteria and oxidizing organic matter. However, over time this layer becomes very thick and so the water flow rate decreases, so periodically such layer is cleaned. 2- Rapid sand filter Consist of coarse or crushed quartz deep filters. It is preferable that coagulant is added before or during filtration to form colloidal aluminum hydrates, which settle on the top and so improve filtration. The unfiltered water flows through the filter medium under gravity or under pumped pressure and the floc material is trapped in the sand matrix. When deposit impurities become too thick, compressed air is passed in the reverse direction and by agitation washes the filter clean. 3- Membrane filtration In membrane filtration, a thin semipermeable film (membrane) is used as a selective barrier to remove contaminants from water. The membrane processes most commonly used to remove microbes from drinking water are microfiltration (MF), and ultrafiltration (UF). MF can remove protozoa, algae, and most bacteria very effectively. UF membranes are small enough to remove some viruses in addition to bacteria and protozoa.  Disinfection by Chlorination Is the most widely used method for the chemical disinfection of water. may be used in the form of chlorine gas, bleaching powder, liquid bleach, or hypochlorite. Chlorine gas is preferred when large-scale disinfection is required. Chlorine gas and water react to form free chlorine, which is extremely reactive with numerous components of the bacterial cell. Super chlorination is sometimes required during epidemics or in presence of iron salts. Ozone or ultraviolet may be also used. Domestic purification of water Boiling, bleaching powders or the use of ceramic filters  Measurement or analysis of water quality 1- Physical quality: Color, turbidity odor and taste but these do not indicate safe water. a- Color: Pure water is colorless. any type of color appearance in water indicates water pollution. Color in water may be caused by the presence of minerals such as iron and manganese or by substances of vegetable origin such as algae and weeds. b- Turbidity Turbidity in water is because of suspended solids and colloidal matter. It may be due to soil or due to the growth of microorganisms. High turbidity makes filtration expensive. c- Odor and taste Odor and taste are associated with the presence of living microscopic organisms; or decaying organic matter including weeds, algae; or industrial wastes containing ammonia, phenols, halogens, hydrocarbons. 2- Chemical quality 1. Chloride ion: Water normally contains chloride ions but its concentration is very low. Its concentration increases in the case of urine and sewage-contaminated water. High concentration of chloride ion gives a salty taste and corrodes water pipelines. 2. Ammonia: Ammonia comes from the decomposition of organic matter like proteins. In water Ammonia (NH3) is first oxidized into nitrite and then into nitrate. Therefore by measuring the concentration of NH3, nitrite, and nitrate, we can predict the time of contamination of organic matter in water. In recent contamination, the concentration of NH3 is higher than nitrite and nitrate. 3. Nitrate: It is the most stable oxidized form of nitrogen. nitrate comes from organic matter decomposition. Nitrate should not exceed 3mg/l in drinking water, because nitrate can be reduced into nitrite in the gut of infants and causes nitrite poisoning. 4. Dissolved Oxygen (DO): DO is a source of oxygen for aquatic organisms. If organic content is high, microorganisms utilize DO for its oxidation causing depletion of dissolved oxygen level. If DO is absent in water, the aquatic organisms cannot survive. The total absence of DO in water facilitates the anaerobic decomposition of organic compounds. 5. pH: Water becomes alkaline due to the presence of NH3, OH-, Ca++, Mg++, etc. in alkaline water certain minerals are deficient. Water becomes acidic due to the presence of dissolved acids and dissolved carbon dioxide. Acidic pH corrodes pipelines. Similarly, certain minerals are more than excess in acidic water. The pH of drinking water should be around 6.5-8.5 3- Microbiological quality Drinking water must be free from pathogens which are generally due to fecal pollution. The organisms of prime concern are the intestinal pathogens, particularly those that cause typhoid fever and bacillary dysentery. Since human fecal pathogens vary in kind and number, it would be impossible to test each water sample for each pathogen. Instead, it is much easier to test for the presence of nonpathogenic intestinal organisms such as E. coli. E. coli is a normal inhabitant of the intestinal tract and is not normally found in freshwater. Therefore, if it is detected in water, it can be assumed that there has been fecal contamination of the water. The presence of this organism in a water supply is evidence of recent fecal contamination and is sufficient to order the water supply closed until tests no longer detect E. coli.