4.1 What are germs?Germs are tiny animals which are so small they cannot be seen without the help of a special instrument called a microscope. The microscope allows the germs to be seen by making them look a lot bigger. Many of these germs will cause disease in humans and other animals.
There are two main types of germs which can cause disease in humans and animals. These are bacteria and viruses. Bacteria are larger than viruses.
All animals need warmth, moisture and food in order to live. Germs are no different. They can get all of these things from many places. For example, faeces (guna, shit), rubbish, food scraps and even from our bodies.
There are many germs inside the human body which may not cause disease. There are even some germs which help parts of the body to work properly. The gut, for example, cannot digest food properly without the help of certain ‘good’ bacteria.
There are other germs in the environment which do good things, for example, the Lactobacillus germ which turns milk into yoghurt, or the many types of germs which help break down vegetable matter into compost.
Fig. 1.2: Germs seen through a microscope
Germs and DiseaseThere are, however, some germs which can make people sick if they enter their bodies, for example, hepatitis A and Salmonella germs.
Other germs which usually stay in certain parts of the body where they do not cause disease, will make a person sick if they find their way to another part of the body. For example, Escherichia coli (which is also sometimes known as E. coli) lives in the gut and helps digest food. However, if it gets outside the gut, E. coli can cause sickness such as bladder infection.
Food, water or air can be made dangerous to humans and other animals by things which are living in it or mixed into it. When this happens, it is said to be contaminated or polluted. Food and water can be contaminated by disease-causing germs.
Germs can get into the body through the mouth, nose, breaks in the skin, eyes and genitals (privates). Once disease-causing germs are inside the body they can stop it from working properly. They may breed very quickly and in a very short time a small number of germs can become millions.
Germs can cause disease by upsetting the way the body works. They do this when they:
- produce toxins (poisons)
- increase their number greatly by breeding and they can stop parts of the body from working properly, or
- attack and damage a particular part of the body
Diseases caused by bacteria germs are called bacterial diseases, and those caused by virus germs are called viral diseases.
Fig. 1.3: Some medicines help the body fight germs.
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4.2 Diseases caused by germsScientists have discovered many thousands of different types of germs. However, only some of these cause sickness in humans. Some of these diseases happen because poor environmental health standards make it easy for disease-causing germs to live and breed and for humans to get the germs into their bodies. The more common of these diseases are described below.
Hepatitis AThis disease is caused by a virus germ. It may last from a few days to several months and can range from being a mild illness to a very serious illness. It causes fever, nausea and stomach cramps and sometimes death. It is a disease of the liver and can make the skin and whites of eyes turn yellow. A person with this disease may take many months to fully recover.
The germ which causes hepatitis A is commonly found in the faeces of people who are already infected. The germ can be passed directly from person to person, or indirectly, by food or water which has hepatitis A virus germs in it.
Gastrointestinal illnesses - Food poisoning, gastroenteritis and acute diarrhoeaFood poisoning is usually caused by bacterial germs. There are different kinds of bacterial germs which can cause food poisoning, for example, Salmonella, Staphylococcus, Clostridium, Shigella, Campylobacter and Bacillus. Some viruses also cause food poisoning.
Food poisoning can result from eating or drinking germ contaminated food or water. Different types of germs take different lengths of time between being ingested (taken into the body) in food or water and the onset (start) of the disease.
Gastroenteritis (gastro) is a disease caused by a virus germ in faeces. People can become infected with this germ when they eat food or lick fingers or use eating equipment, such as knives, forks, plates and cups, which are contaminated with the germ.
Acute diarrhoea (runny tummy) is commonly experienced by people with food poisoning and gastroenteritis but may also be caused by infection with the bacterial germ Escherichia coli (E. coli). It can be a useful germ when it stays in the bowel of a person because it helps to digest food.
The E. coli germ of one person may differ slightly from that of another person. This means that if the E. coli germs from one person get into the stomach and bowel of another person it could cause that other person to get acute diarrhoea. This disease is particularly dangerous to babies, very young children, the elderly or the sick because they can quickly become dehydrated.
Gastrointestinal diseases can cause all or a few of the following conditions:
- frequent watery bowel movements, known as diarrhoea or runny tummy. (This can be very serious. If it continues untreated for more than a day, the bowel movements remove too much water from the body and the person gets dehydrated. When this happens to babies, young children, the elderly or the sick it is especially dangerous because they may lose so much water that they die)
- nausea (person feels as though he/she wants to vomit)
- stomach cramp or pains
- fever (high body temperature)
Infections of the skin and earBacteria germs can get into sores, cuts and broken skin and into the ears and cause pus sores. These germs can be of many different types, but not all the germs that reach these places will cause infection.
Germs can get into cuts, sores and broken skin when these places come into direct contact with things which have the germs on them, such as:
- flies and other insects
Colds and flu
These diseases are caused by virus germs which infect the respiratory (breathing) organs (nose, throat and lungs). The signs of these diseases are:
- coughs and sneezes
- dry or sore throat
- blocked and runny nose
- muscle or joint aches and pains
- nausea, vomiting and diarrhoea
TrachomaThis is a disease caused by a bacterium germ which gets into the eyes. This infection can cause scars to form on the eyelid. Reinfection by the trachoma germ can cause serious scarring which affects the eyesight and may cause blindness.
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Murray Valley encephalitis (Australian encephalitis)Murray Valley encephalitis (also known as Australian encephalitis) is caused by a virus germ which is transmitted from animals to people by a number of different types of mosquitoes. It is mainly a problem in northern Australia, but occasionally it extends further south. It is a very dangerous disease which causes inflammation (swelling) of the brain and can result in brain damage and death.
The signs (symptoms) of this disease include:
- very severe headache
- coma (unconsciousness)
- convulsions and tremors (shakes)
- paralysis (unable to move parts of the body)
Ross River virus diseaseRoss River virus disease is caused by a virus germ which is transmitted from animals to people by a number of different types of mosquitoes. Ross River virus can occur in most areas of Australia. A number of different types of mosquitoes can transmit this virus, including ones that breed in marshes, billabongs, drains and backyards. This disease can cause a kind of arthritis, which affects the bone joints of the body and may last for weeks, months or even longer. It does not cause death. The signs of this disease include:
- severe joint pain
- skin rash (in some people)
- fever and headache
Barmah Forest virus diseaseBarmah Forest virus disease is caused by a virus germ similar to Ross River virus, and can occur in most areas of Australia. The mosquitoes that carry it and the animal hosts are similar to those for Ross River virus. The signs of this disease are also similar to those for Ross River virus.
Tetanus (lockjaw)This is a serious disease caused by poison produced by the bacterial germ Clostridium tetani. This germ can be in human and animal faeces. It can get into the soil and onto other objects on the ground if faeces are left lying around. The germ and its poison can last in the soil and on objects for a long period of time.
People get this disease when the tetanus germ gets into the body through a cut, sore or other kind of break in the skin which comes into contact with something, such as a rusty tin or nail, soil, or human faeces, which is contaminated with the germ.
Tetanus is a serious disease which can cause:
- very painful muscles
- severe spasms (cramps) in the muscles of the face, neck and trunk (body) which stop a person being able to control his/her movements
MelioidosisMelioidosis is a serious disease with a high mortality rate that occurs in the Kimberley region of Western Australia, Top End of the Northern Territory and far north Queensland.
Melioidosis is caused by bacteria that usually live deep in the soil during the dry season but are found in surface water and mud after heavy rainfall.
People most at risk of developing melioidosis are those with poor health and underlying conditions that impair the immune system, like diabetes, heavy alcohol intake, cancer, advanced age, kidney or lung disease and long term steroid therapy medicines.
Bacteria enter the body directly through small cuts and sores on the hands and feet or by inhalation. This can cause a variety of symptoms such as skin ulcers or sores that fail to heal, abscesses, unexplained fevers, weight loss, fatigue, cough, shortness of breath, abdominal pain, urinary symptoms and occasionally neurological problems such as headache and confusion.
People with risk factors are advised to stay indoors during periods of heavy wind and rain. People who work with the soil such as gardeners and people in the building trade should always wear protective clothing as healthy people can get the disease if they work in or are exposed to muddy soil or water in pooled muddy areas.
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4.3 The spread of germsGerms live anywhere they can find warmth, food and moisture. This could be:
- inside people's bodies or on their skin
- inside or on the bodies of other animals
- in sewage systems
- on food
- on rubbish of any kind
- on the ground
- in unclean water
- in the air
Below are some of the methods by which ‘vehicles’ can help spread germs to people.
Hands spread germsWhen a person goes to the toilet, he/she may get some germs from the faeces onto their hands. If the hands are not washed after going to the toilet, these germs will stay on them. The germs will then get onto whatever the person touches, such as food, his/her face or other people. Examples of germs spread in this way are hepatitis A and Shigella.
This way of spreading germs is called the faecal/oral (mouth) route
Fig. 1.3: Some medicines help the body fight germs
Droplets in the air spread germsWhen a person coughs or sneezes, small droplets of water are released into the air. If this person has a throat or lung disease, the germs will also be in these droplets. If these droplets then come into contact with or are breathed in by other people, they too can get the disease. Examples of germs spread in this way are colds and flu.
Fig. 1.5: Germs can be carried in droplets
Water can spread germsSome germs can be carried in drinking water. Examples of germs spread in this way are hepatitis A and Salmonella.
Fig. 1.6: Germs can be carried in water
Sharing clothes and towels can spread germsA person who has a disease such as trachoma or an infected skin rash may get these germs onto his/her clothes or towel. If that person then shares his/her clothes or towel with someone else, it is likely that the other person will catch the disease. An example of a germ spread in this way is trachoma.
Fig. 1.7: Sharing towels can spread germs
Insects can spread germs directly to peopleGerms can be carried from one person to another by insects. Examples of germs spread in this way are Murray Valley encephalitis and trachoma.
Fig. 1.8: Insects spread germs
Insects and rodents can spread germs to foodInsects, such as flies and cockroaches, and rodents, such as rats and mice, can spread germs to food when they crawl or walk over it. If people then eat the contaminated food the germs can make them sick. Examples of germs spread in this way are Salmonella and Staphylococcus.
Animals such as rats, mice, and flies which act as ‘vehicles’ for carrying disease-causing germs are called vectors.
Fig. 1.9: Flies spread germs from faeces to food