Diseases Caused by Microorganisms

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Harmful Microorganisms

 Some microorganisms are harmful to humans, animals and plants because they cause diseases. They can also result in food turning bad and rotten. This may lead food poisoning if the food is consumed. Microorganisms that cause diseases are called pathogens. Pathogens consist of viruses, bacteria, fungi and protozoa.

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Pathogens are classified as parasites or saprophytes. Parasites live inside a living organism called the host, for example a human being or a cow. Saprophytes live on dead tissues such as decaying plants and animals. Some bacteria turn food rotten and unsafe for consumption. These microorganisms decompose food and release toxins (poison) which result in food poisoning. Signs and symptoms of food poisoning are vomiting, stomach ache and diarrhea.

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Bacteria found in the mouth can cause tooth decay and gingivitis. Bacteria act on carbohydrates (glucose) found in food remnants and change them into lactic acid which dissolves the enamel layer of the teeth, causing small holes (caries). The action of bacteria can also release a certain poison which causes the gums to swell and bleed.

Diseases Caused by Microorganisms

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Pathogens attack and kill cells and tissues of the host directly or indirectly by producing toxins. Microorganisms such as bacteria, fungi and protozoa can reproduce inside and outside a host while viruses can only reproduce inside a living host. Specific diseases are caused by specific microorganisms and show specific signs and symptoms.

Signs are external evidences, for example, swelling or fever due to a disease while symptoms are internal and cause a change in the normal functions of the body.

Diseases Caused by Bacteria

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Tuberculosis or commonly known as TB a) it is caused by the Bacillus bacteria which enter the human body through the nose or mouth b) the bacteria attack and destroy the lung tissues, lymph nodes, bones and joints of the patient c) the symptoms take time to show. The patient first suffers from a dry cough and feels weak and tired. The cough is continuous and becomes more severe. The patient then coughs out yellowish-green sputum containing blood. The patient also loses weight because of a loss of appetite d) an X-ray film of a tuberculosis patient’s chest shows black spots on the lungs.

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Cholera a) it is caused by the vibrios bacteria which contaminate drinking water and food. Hence the bacteria enter the human body through the alimentary canal b) the bacteria reproduce very fast inside the intestines and digest the mucous lining of the intestinal walls c) the symptoms of this disease are vomiting, diarrhea and severe muscle cramps d) this results in the patient suffering from dehydration due to the excessive loss of water and this can cause death if not treated early.

Sexually Transmitted Diseases a) sexually transmitted diseases are diseases which spread through sexual activities and infect both the male and female reproductive systems b) two examples of such diseases are gonorrhea and syphilis.

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c) Gonorrhea is caused by the cocci bacteria i) a male patient will suffer pain when urinating. His penis will excrete a thick white liquid or pus. His testes become swollen. If not treated, the person may become sterile ii) A female patient suffers from the inflammation of the urethra, uterus and cervix. Sometimes the Fallopian tubes become blocked and may lead to sterile.

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d) Syphilis is caused by the spiral bacteria. The symptoms appear in three stages i) first or early stage – ulcer and red spots appear around the vagina or penis ii) second or middle stage – rashes occur on the skin of the body, ulcers appear in the mouth and throat, loss of appetite and loss of weight as well as pain in the muscles, bones and joints iii) third or final stage – the nervous system becomes infected and internal organs such as the heart and brain may be damaged.

Diseases Caused by Viruses

 Viruses are parasitic pathogens. They only reproduce inside a living host. Each type of virus only infects the cells of a specific host. Examples of diseases caused by viruses are influenza (the common cold), dengue fever, hepatitis and the Acquired Immune Deficiency Syndrome (AIDS).

Influenza a) the virus which causes influenza or the common cold is found in the air b) when a patient coughs or sneezes, the virus attacks the membrane lining of the respiratory tract c) the patient suffers from blocked nasal cavities and excretes excessive mucus from the nose d) the early symptoms of influenza are the abrupt onset of a fever, chills, headache, pain in the muscles and joints, coughing and a sore throat d) influenza may develop into pneumonia and other serious complications if it is not treated quickly and effectively.

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Dengue Fever a) this is dangerous and infectious disease caused by the dengue virus b) it is spread by a vector, the Aides mosquitoes c) the symptoms are fever for about 5 to 7 days, severe pain throughout the body especially in the muscles, joints, bones and eyeballs. There is often an intense headache and rashes on the skin d) in the more serious hemorrhagic dengue fever there is bleeding in the nose, mouth and internal organs which may result in death e) there is no antibiotic to treat dengue fever hence prevention is the best way to control the disease.

Hepatitis a) there are two main types of hepatitis, hepatitis A and B which are caused by different viruses b) the virus attacks liver cells. In severe cases, it leads to cirrhosis of the liver as well as cancer of the liver c) the virus can be transmitted through contaminated food or through the use of contaminated syringes. Table below shows a comparison between the two types of hepatitis.

Acquired Immune Deficiency Syndrome (AIDS) i) AIDS is caused by the human immune –deficiency viruses (HIV-1 and HIV-2) ii) the virus attacks and kills white blood cells and paralyses the immune system of the body iii) the virus is found in body fluids of the patient like the saliva, blood, semen, mother’s milk and secretions from the vagina iv) the incubation period for this disease varies from a few months to a few years before any symptoms appear v) the symptoms are loss of appetite, fever, candidacies in the mouth and throat as well as inflammation of the lymph nodes vi) since the patient’s immune system is weak, the patient can easily contract other diseases such as pneumonia which can lead to death.

Diseases Caused by Fungi

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Fungi grow and multiply quickly in warm and moist environments. Fungi grow and spread easily in the folds of human skin because it is warm and damp from sweat. Examples of fungal diseases are tine and ringworm. Tine (Athlete’s foot) a) this disease is caused by filamentous and round fungi b) the skin infected with tine appears bright with white spots c) it is usually appears on the face, body, hands and legs.

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Ringworm a) ringworm infection usually occurs in the gaps between the fingers and toes, armpits and the area below the breasts b) the infected areas appear red in color. Wounds and bleeding occur sometimes when the skin peels off c) if it grows on the head, it may cause hair to drop off.

Diseases Caused by Pathogenic Protozoa

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Protozoa which cause diseases are parasites which live inside the body of hosts. An example of a disease caused by protozoa is malaria. Malaria a) it is caused by the protozoan Plasmodium which is carried by the female Anopheles mosquitoes b) Plasmodium enters the human body through mosquito bites and is then carried by the bloodstream to the liver c) The parasite attacks the liver and red blood cells d) the incubation period of this diseases varies from 12 to 30 days depending on the protozoan species e) the disease begins with an ill feeling and a rapid rise in body temperature. There is profuse sweating with intermittent fever. Headache and nausea are common f) in advanced stages of the disease, there is enlargement of the spleen g) malaria can lead to anemia.

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Malaria comes from the Italian word ‘Mala-aria’ which means bad air or air from marshy land. A French army surgeon in Algeria in 1880 described the presence of the malarial parasite in fresh human blood. Major Ronald Roses, a doctor in India, discovered the malarial parasite in the stomach of the Anopheles mosquito in 1987. He was awarded the Nobel Prize for his discovery which laid the foundation for the control of malaria.