Foods of animal origin are perishable foodstuffs which need special attention during processing, preparation, transportation and storage to avoid them becoming contaminated and causing ill health to the consumer. In this session you will learn how to inspect and assure the quality of food items of animal origin, and how to keep and handle them safely, without contamination. You will also learn about diseases caused by contaminated perishable foods. We will look in turn at meat, fish, milk and eggs.
When you have studied this session, you should be able to:
12.1 Define and use correctly all of the key words printed in bold. (SAQ 12.1)
12.2 Describe the public health importance of diseases derived from foods of animal origin. (SAQs 12.2, 12.6 and 12.7)
12.3 Describe meat inspection procedures. (SAQ 12.2)
12.4 Describe the procedures for meat and butchery hygiene. (SAQs 12.2 and 12.3)
12.5 Describe the criteria for assessing fresh fish. (SAQ 12.4)
12.6 Describe the procedures for milk hygiene and quality control. (SAQs 12.5 and 12.6)
12.7 Describe the procedures for poultry and egg hygiene. (SAQ 12.7)
Meat is among the most highly nutritious foods. It is a good source of protein, fat and minerals. It is also a highly perishable product because cooked and especially raw meat (Figure 12.1) is a good substrate (underlayer) for the growth and multiplication of harmful microorganisms. As a result, several diseases may be transmitted to humans through the consumption of meat or meat products.
What are the most common perishable food items?
Common perishable foods are meat, milk, fish and vegetables.
Meat is the flesh of an animal used for human consumption. In this text ‘meat’ refers mainly to the flesh of bovine animals i.e. cattle and oxen, generally known as beef, although of course there are other types such as sheep meat (mutton), goat meat, and pig meat (pork).
Diseases transferred to humans from animals are known as zoonotic diseases. One route of transmission of zoonotic diseases is by the consumption of infected meat.
The most common zoonotic diseases found in Ethiopia are:
Tapeworm infections are discussed in detail in Part 4 of the Communicable Diseases Module.
Which of these diseases are caused by parasites?
All of them except the first three.
Taenia saginata infection or beef tapeworm has been known in Ethiopia for many centuries. The disease is locally known as kosso and is related to the cherished tradition of eating raw beef, a common practice in most parts of the country (Figure 12.2). The disease is closely linked to its cure so the traditional taeniacide (agent that kills Taenia) is also known as kosso. Kosso is an Amharic word that describes both infection (beef tapeworm) and the treatment. The name comes from the tree (Hagenia abyssinica) whose flowers are active against tapeworm (Figure 12.3).
The major factors contributing to the continuing existence of beef tapeworm infection in Ethiopia are lack of proper slaughtering practices and eating raw beef. Open defecation also spreads the disease. Open field defecation practices are widespread in rural areas and small urban centres. This means that if a person infected with kosso defecates on open fields, the infected faeces contaminate the environment, especially pastoral lands used for cattle grazing. The cattle then become infected. Once inside the animal, the larval stages of the tapeworm form cysts, also known as cysticerci, in the muscles and some other organs. The contaminated meat containing the cysts will infect people who eat it if it is not thoroughly cooked (see Figure 12.4).
The lack of proper slaughtering facilities and the absence of meat inspection in some slaughterhouses (abattoirs) means that contaminated meat can be sold, and people eat the infected meat. This practice results in a high frequency of tapeworm occurrence.
The bacterium that causes anthrax is called Bacillus anthracis. It is capable of producing very durable and long-lived spores which can cause disease by coming in contact with skin, by being inhaled and by being consumed. The three forms of disease are:
The control measures for anthrax are to advise people not to eat raw meat from sick and dying animals like cows, oxen, sheep, camels and goats, and to only eat thoroughly cooked meat and meat that has been inspected and approved for consumption. Even handling hides and skins from these dead animals may result in cutaneous anthrax.
Abattoirs, also known as slaughterhouses, are establishments where livestock are killed prior to human consumption. Slaughterhouses should be subject to inspection to ensure that the meat they produce is safe to eat. This includes inspection of live animals and also of the slaughtered animal carcasses. Before slaughter, the animals should be observed to check for any abnormalities in their appearance or behaviour that could indicate sickness. After slaughter, animal carcasses should be inspected by a qualified meat inspector who knows the signs of specific types of disease and which organs they may be found in. If the carcass passes the inspection it will be stamped with safe, indelible ink to indicate it has been approved for human consumption.
The carcass should be transported soon after slaughter, in a special vehicle, to a butchery or distribution centre. If such customised vehicles are not available, every precaution should be taken to avoid contamination of the meat during transportation. Even if the meat travels in a wheelbarrow it should be kept absolutely clean.
Butcher’s shops are the link between the inspected and approved safe meat, and meat products and the consumer. Therefore the hygienic practices used for handling meat in these shops determine the health of the meat consumer. For this reason, butcher’s shops need licences to operate, confirming that they meet all the handling specifications that ensure the safety of the meat. For example, the licensed premises must have adequate working space. The walls and floor should be constructed of durable material and be smooth, impermeable, easily cleanable and light-coloured. There should be adequate ventilation and natural light. The utensils should be clean and kept in an appropriate place. The butcher should wear a clean white gown, preferably with an apron and a white hair cover (Figure 12.5). Importantly, an approved means for the disposal of meat waste should be provided inside or outside the butchery.
Suggest why waste meat needs to be disposed of carefully.
The waste will attract insects, rodents and other animals, increasing the risk of contaminating the shop and its surroundings.
As noted above, meat is highly perishable, so it must be preserved properly. One way of doing this is to chill the meat in a refrigerator. Temperatures for refrigeration of meat should be lower than the usually recommended 10ºC and should be below 7ºC for carcasses and below 3ºC for offal. For long-term storage, meat should be frozen. However, since most rural people do not have a refrigerator or freezer, they should use traditional preserving methods.
You learned in Study Session 10 about some meat preservation methods used in rural communities in Ethiopia. What are they?
Common methods are smoking, salting and drying to prepare quanta.
Ethiopia is a country with a lot of raw meat consumption and a high prevalence of tapeworm. Two rules must be enforced, and educating the community about them is an essential part of your role:
Additionally there are measures that you can recommend in the community. Abstaining from eating raw or inadequately cooked meat is a good control measure. The Ethiopian dishes of kitfo or lebleb kitfo are not safe to eat. However, there are strong cultural reasons for this practice, so people may not take your advice.
The best control measure against meatborne zoonotic diseases is to cook the meat thoroughly before consumption. Exposing meat to a temperature above 56oC inactivates any cysticercus bovis (beef tapeworm cysts) present. Organised and strict meat inspection practices in abattoirs can ensure that meat is free from tapeworm infection as well as other meatborne diseases.
Finally, avoiding open defecation is a major control measure for zoonotic – and other – faeco-oral diseases.
Globally, fish are a popular food item (Figure 12.6). With the abundant rivers, ponds and lakes in Ethiopia, fish is among the commonest foods in many parts of the country.
Fish are generally considered clean and fresh, but several environmental factors can make fish unfit for consumption. The factors relate to the food of the fish itself – the fish is what it eats – and to the cleanliness/safety of the water body. Fish can also be contaminated by poor handling at any stage from being caught to being eaten.
Water bodies can be contaminated by:
Bioaccumulation is the gradual build-up of chemicals such as pesticides in the bodies of living organisms.
Fish is a perishable and potentially hazardous food item if not handled properly. There are many fishborne diseases associated with the environment in which the fish is grown, and with the way it is handled after it is brought out of the water, particularly if it is kept at room temperature.
Why does temperature affect the condition of the fish?
Microbes and autolytic enzymes are more active at higher temperatures, so deterioration proceeds faster.
Do you remember what autolytic means?
Autolytic means ‘self-destroying’. Autolytic enzymes are naturally occurring proteins in an animal that cause its cells and tissues to break down automatically after death.
Some of the zoonotic fishborne diseases include the following:
If you want to know whether fish is fresh, there are a number of signs you should look out for (Figure 12.7). Fresh fish has bright, convex (bulging) eyes with a dark pupil. The flesh of a fresh fish is translucent (almost transparent), but as it ages it gets darker and more opaque (you cannot see through it).
A fresh and sound fish shows the following typical characteristics:
A fish that is not fresh and is starting to rot shows changes in all these signs. For example, the gills may be open and discoloured, and the skin slimy and malodorous. The eyes are opaque and sunken, the scales can be removed easily and the carcass floats in water. The flesh falls easily from the bones and is easily broken up.
There are traditional and modern ways by which fish can be preserved, such as chilling, freezing, smoking, drying, salting and canning. In all cases fish should be properly gutted, washed and chilled immediately upon removal from the water, and kept cold until consumed.
Milk is an important food, supplying us with proteins, fat, carbohydrates, minerals and vitamins (Figure 12.8).
The provision of a safe supply of milk is of great importance for public health, with the following objectives:
Disease organisms in milk are derived from the dairy animal itself, the human handler or the milk-handling environment.
What human behaviours might result in milk contamination?
Poor personal hygiene by the food handler including activities such as coughing, sneezing or scratching over the milk, and allowing objects, particularly fingers, to come into contact with the milk.
In terms of the environment, the milking and milk-handling processes must be carried out hygienically, avoiding contamination with soil, manure, animal hair or dirt from the cowshed. The milk containers must be clean and disinfected.
Bovine tuberculosis (bovine TB) is a very common infection of cattle. It is caused by the bacterium Mycobacterium bovis. Infection may be acquired by drinking raw milk from a cow that has bovine TB. The disease may reach the milk by contamination with faeces or from the coughs of infected cows. Diseased humans can also contaminate the milk during handling. Milk, therefore, should always be pasteurised or sterilised before drinking. Raw milk is the usual cause of the forms of human TB that affect parts of the body other than the lungs.
Brucellosis is an infectious disease characterised by a high fever. It is caused by bacteria belonging to the Brucella genus, mostly Brucella melitensis (a disease of goats) and also Brucella abortus (a disease of cattle) and Brucella suis (a disease of pigs). It occurs mostly as a result of ingestion of contaminated milk and dairy products (such as cheese) from animals infected with Brucella. Brucellosis can also be transmitted by blood, urine or tissues of sick animals, so good hygiene must be maintained at all times around animals.
Q fever is an infection caused by the bacteria Coxiella burnetii (formerly Rickettsia burnetii). Its name derives from the time when the cause of the fever was unknown – the ‘Q’ stands for ‘query’. Only one bacterium is needed to cause the Q fever infection! The disease is transmitted through drinking the raw milk of infected cattle, goat or sheep, and it can also be transmitted in airborne droplets.
As you read earlier, anthrax is usually caused by spores of the bacterium Bacillus anthracis. The spores can remain in soil and dust for a long time and they can infect milk. The spores usually reach the milk via infected blood contaminating the milk, or by dust from the animal’s coat or the environment.
Milk sanitation, i.e. the protection of milk from dirt and contamination, is essential to prevent milk infection. Clean milk (with a low number of bacteria) is a necessity, and is possible by using good milking hygiene (Figure 12.9).
The essential steps in hygienic milk production are summarised in Box 12.1.
Remember that raw milk should not be consumed without treatment to protect consumers from milkborne diseases. The following methods are recommended:
This is the most widely practised domestic method of making milk safe. Milk must be boiled for 30 minutes and then cooled to below 10ºC. It must be protected from contamination by flies, dust, etc. Boiling in this way can prevent the transmission of bovine TB and brucellosis.
This method ensures that all microorganisms and their spores are killed, but it also affects the nutritional quality of the milk as the process destroys vitamins, especially vitamin C. Sterilisation is carried out by raising the temperature to between 110ºC and 130ºC for at least 20 minutes.
In the drying process all the water is removed by evaporation and what remains is solid, dry milk (powdered milk). The powder is not sterile, but once dry, it can be stored for extended periods.
Why does drying make it safe to store powdered milk?
Bacteria and other microorganisms need water to survive. Drying prevents the growth and reproduction of microorganisms that could contaminate the milk. But it must also be stored correctly. It must be kept in an air-tight container to ensure it remains dry and free from dust and dirt.
What is pasteurisation?
Pasteurisation is a process of heat treatment of food that kills most pathogenic micoorganisms without altering the nutritional value.
Pasteurisation is not sterilisation but it is a process in which all pathogenic microorganisms, many other non-spore forming bacteria and many enzymes in the milk are destroyed or inactivated without much affecting the nutritive value and the chemical nature of the milk. In practice one expects to find no faeco-oral bacteria and not more than 10,000 microorganisms of any type per millilitre of pasteurised milk. You learned the details of pasteurisation in Study Session 10.
Poultry consumption has greatly increased in recent years (Figure 12.10). Due to poor hygiene, poultry and poultry products are responsible for a number of foodborne illnesses including salmonellosis, staphylococcal food poisoning and botulism. Other, less common diseases include psittacosis or ornithosis, also known as parrot fever, which is a zoonotic disease caused by the bacterium Chlamydophila psittaci, and ‘bird flu’, which is a viral disease that can affect both poultry and people.
From your general knowledge, what symptoms may occur following the consumption of raw eggs if they are contaminated with Salmonella?
Common effects are diarrhoea, fever and headaches, which may be signs of salmonellosis.
Correct sanitation procedures involve all stages in the operation from live poultry pens to retail establishments, including processing, packing, storage and transportation. Whether in large-scale commercial production or domestic poultry keeping, the poultry handlers must be healthy and maintain food handlers’ hygienic practices.
In the poultry farm, the housing, feed and water supply must be safe. The plant and equipment must be cleaned daily. In particular, any dead birds must be removed from coops. During processing, hygienic methods of killing and dressing must be used.
Although most freshly laid eggs are sterile inside, the shells soon become contaminated by faecal matter from the hen and the lining of the nest. When collecting eggs, any visible dirt should be rubbed off the shells. During handling, contamination can also arise from washing water and from any packing material. However, some eggs will be spoiled on the inside, generally because of cracks in the eggshell through which bacteria can enter. It is important to test for egg spoilage, and this can be done in the following ways.
Eggs should first be inspected for cracks, leaks, stains or dirt on the exterior and general bloodiness or translucent spots in the yolk when candled (see below). You are looking for freshness, soundness, size and cleanliness of the shell (Figure 12.11).
A fresh egg makes no sound, but a stale (bad) egg makes a sound when shaken.
This is performed by holding the egg between the eye and a light such as a candle flame or the sun. As the shell is translucent, you can assess the internal quality and the size of the yolk.
Fresh eggs usually sink to the bottom of a bowl of water, whereas spoiled eggs float and can be removed. Floating occurs because, in spoiled eggs, the air cavity is bigger, which makes the egg more buoyant. The problem with this method is that the water may penetrate through the eggshell pores so it is important to use clean water, change it frequently and not to leave eggs in the water.
In this test, around 10 eggs out of 100 are taken randomly and checked for spoilage by breaking them open to see what is inside. This is the most accurate testing method but it is not cost-effective, so is only used when the other methods are not exercised – for example, in large-scale operations.
Since eggs are perishable food items, they need proper storage. They should be kept cool and dry. Maintenance of the egg’s internal quality depends on the time and conditions of storage, especially the temperature and the presence of tainting substances in the storage environment. Eggshells are porous and eggs can quickly absorb foreign odours which will taint the contents. It is therefore advisable to avoid storing strong-smelling and volatile materials such as kerosene or varnish near egg stores.
In Study Session 12, you have learned that:
Now that you have completed this study session, you can assess how well you have achieved its Learning Outcomes by answering these questions. Write your answers in your Study Diary and discuss them with your Tutor at the next Study Support Meeting. You can check your answers with the Notes on the Self-Assessment Questions at the end of this Module.
What is kosso?
Kosso is a tree (Hagenia abyssinica) whose leaves contain a taeniacide (tapeworm-killing agent). It is also the common Ethiopian name for the tapeworm disease that occurs through eating raw beef.
Explain why eating raw beef is inadvisable and how the risks can be minimised.
Raw beef could be infected with Taenia saginata and people who eat it could get beef tapeworm disease. Raw meat should not be eaten, but risks can be minimised by only eating meat from cattle that have been kept on pasture free of faeces or other contaminants. The cattle should then be slaughtered in a licensed abattoir where the meat is inspected and stamped as safe. The meat should be transported and stored hygienically unitil it is eaten.
Outline the main steps in abattoir inspection and explain why inspection is important for food safety.
Animals should be inspected before and after slaughter at the abattoir. Live animals should be observed for any signs of illness. Animal carcasses should be closely examined by experienced inspectors who can identify the visible signs of contamination such as tapeworm cysts. If the meat is healthy it will be marked with an indelible stamp to indicate it is safe for human consumption. The inspection process is important to ensure the health of anyone who eats the meat and to prevent the spread of disease.
You bought some fish today but you will not eat it until tomorrow. Describe a. how you will keep it overnight and b. how you will tell if the fish is safe to eat tomorrow.
Your brother has just bought two cows and wants to sell the milk to his neighbours. What advice would you give him so that everyone can be sure of the milk’s safety?
Your brother should be advised to keep his cows clean and healthy, in a hygienic environment. He must milk the animals in a clean place, wiping the udder and teats before he starts and using disinfected utensils. He must only milk the cows if he is healthy and clean himself. After milking, the milk should be kept cold and sold as quickly as possible.
In a nearby community, it is common to drink raw milk from goats and there is a frequent problem of coughing among children and older people. Outline your advice to the community to help them avoid this illness.
There are many possible causes of coughing as a common problem in a community, so you should consider other possible options as well as the raw milk. Raw milk is a source of many diseases that affect the lungs, including TB, brucellosis and Q fever. This community should not drink raw milk but should treat it in some way. If there is no local treatment plant available, they should boil the milk for 30 minutes, then cool it quickly and keep it cold until it is drunk. They may not want to comply with this as boiling alters the flavour of the milk, but it does destroy the pathogens so is better for them.
There is an outbreak of an unknown bird disease, killing many chickens in your village. As a Health Extension Practitioner for your local community, what advice would you give in this situation?
Poultry and their eggs should only be eaten if the animals are healthy. The sick animals should not be eaten, but should be disposed of by burning the carcasses. Good attention must be paid to the cleanliness of the poultry coops, and handlers should avoid approaching healthy birds after handling sick ones. Veterinary care should be given to the chickens if possible.