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Understanding the Causes of Infectious Diseases

Learn about the different types of pathogens that cause infectious diseases, including bacteria, viruses, rickettsias, protozoans, and fungi. Discover how these pathogens invade the body and the various ways in which infectious diseases are spread. Understand the importance of the immune system in defending against these diseases.

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Understanding the Causes of Infectious Diseases

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  1. Chapter 28 Lesson 1 – What Causes Infectious Diseases??

  2. Causes • Every infectious disease is caused by one of several types of microscopic organisms known as ~ PATHOGENS • PATHOGENS invade the body and attacks its cells and tissues. • Most PATHOGENS are parasites which mean they are organisms that live in or on another organism to survive.

  3. Forms PATHOGENS can take • I. BACTERIA – Single Celled micro-organism that can virtually live anywhere. They are abundant in: • Air • Soil • Water Some produce poisons that are harmful to human cells.

  4. How do BACTERIA work? • Most diseases caused by bacteria begin when the micro-organisms not usually present in the body INVADE IT!!! When this happens, they multiply by cell division at a rate of every 20 minutes. After just 15 hours, more than 4 BILLION bacteria can be present.

  5. DON’T GET WORRIED • This cell division rarely happens – WHY?? • 1. In order for this to happen, perfect conditions in which bacteria thrive would have to be present and this is rare in humans. • 2. The human immune system destroys the invading bacteria.

  6. II. Viruses – This is the smallest known type of infectious agent which are about ½ to one hundredth the size of the smallest known bacteria. • Viruses are our worst enemies because we have not found no known cure for them.

  7. VIRUSES – CONT…… • Viruses ARE NOT LIVING CELLS….. • Consist of a inner core of genetic material surrounded by a protective protein shell and are ENTIRELY dependent on a living thing to survive. • Viruses invade all known life forms but are HIGHLY specific in the types of cells they invade. Some can only invade animal cells while others can only invade human cells.

  8. Viruses – CONT………………. • When a virus enters the body, it attaches itself to a cell which is called the HOST. It then injects its genetic material into that cell which enables the virus to be able to make copies of itself time and time again…. • This process continues on into other cells until the virus runs its course and eventually destroyed by the immune system.

  9. Rickettsias • Organisms that resemble small bacteria, but like viruses are not able to multiply without the help of another life form. • Most are found in intestinal tracts of insects, most notably FLEAS as well as in MICE, TICKS, and MITES. • The bacteria enter the body through a bite by the insect. • Diseases caused by RICKETTSIAS are TYPHUS and ROCKY MOUNTAIN SPOTTED FEVER

  10. PROTOZOANS • Single celled organisms that are larger than bacteria and have a more complex cell structure. • Most are harmless, but about 30 different types cause disease in humans. • Most Protozoans are common in tropical areas that have poor sanitation.

  11. FUNGI • Single-celled organisms that cannot make their own food. • Many are SAPROPHYTES which feed off dead animals, insects and leaves. • They prefer dark, damp environments. • The most common invade deep tissues of the hair, nails, and skin and cause infections of the scalp or feet such as ringworm and athlete’s foot.

  12. How Infectious Diseases are Spread • Tranmission which means to SPREAD. • Direct Contact such as with an infected person, animal or contaminated object.

  13. PEOPLE • People can spread diseases such as DIRECT or INDIRECT contact. • DIRECT CONTACT such as sex, bites, touching, and a pregnant mom to her unborn child. • INDIRECT CONTACT – enters either through the lungs if droplets are exhaled, coughed or sneezed and a person inhales the droplets.

  14. ANIMALS • Bites from animals and insects is the most common way diseases are spread. • A mosquito bite or an animal bite can lead to serious diseases.

  15. CONTAMINATED OBJECTS • Eating utensils, razors, glasses or toothbrushes and even needles with intravenous drug users.

  16. THE ENVIRONMENT • Food, Water, Soil and even air we breath carry pathogens that can make us sick. • Examples include toxic waste that is illegal dumping, air pollution, and careless handling of food we eat that is prepared in restaurants.

  17. How our body defends against infectious diseases • Pathogens are everywhere, so much that it is hard to comprehend. Then why are we not sick all the time????? • IMMUNITY which is the bodies natural defense against infection.

  18. THE IMMUNE SYSTEM • Our bodies are exposed to literally millions of pathogens each day. • Our bodies are able to stay free of infections because of our IMMUNE SYSTEM. • The IMMUNE SYSTEM provides two distinct types of MAIN DEFENSES

  19. TWO MAIN DEFENSES • INNATE IMMUNE SYSTEM – which is our inborn defenses and provides NONSPECIFIC RESISTENSE. • ADAPTIVE IMMUNE SYSTEM – which provides SPECIFIC RESISTENCE. • Both systems work in conjunction with one another to help keep our bodies from harmful and deadly pathogens.

  20. NONSPECIFIC RESISTENCE • Also known as GENERAL DEFENSE • Includes PHYSICAL and CHEMICAL barriers, body cells, and the inflammatory response.

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