Infection, Detection, Prevention... A disease is any change that disrupts the normal function of one or more body systems. Non infectious diseases are typically caused by exposure to chemicals or are inherited. (These don't spread from person to person.) Other, infectious diseases are caused by microbes, called pathogens. These can be transmitted or spread from one organism to another. Viral Diseases Viruses can not only cause illnesses like polio, smallpox, influenza (flu), measles, meningitis, and AIDS; but also contribute to about 15% of all human cancers, like cervical cancer, caused by the human papilloma virus. Viruses cause disease by damaging or killing cells when the virus attaches to a healthy cell and then injects its DNA or RNA inside the cell. Once inside, the virus can make many more copies of itself through viral replication, by tricking the cell to make the virus. HIV Influenza HPV 1
Bacterial Diseases Bacteria also are pathogens, causing diseases like cholera, diptheria, food poisoning, Lyme disease, stomach ulcers, typhoid, tetnaus, tuberculosis, and pneumonia. Most bacteria cause diseases by producing toxins that disrupt the way a cell works. Antibiotics do help control some bacteria by killing them or slowing their growth. However some bacteria have become resistant to antibiotics which means they cannot be killed by those drugs. This makes them difficult to treat, and more dangerous. A recent example of a resistant bacteria is MRSA, methicillin resistant staphlococcus aureus, which can begin as skin infections and progress to infections of the bloodstream, damaging organs. Bacteria can be a threat to human health because of how quickly they multiply. Under ideal conditions, a bacterial cell can divide as often every 30 minutes. Assuming just 2 bacteria infect an individual, look how quickly this can increase in one day! and a bacterial infection usually involves thousands of bacteria to start with... Time Number of Bacteria Start (0 min) 2 30 min 4 1hr 8 2hr 32 Click here to see how quickly bacteria divide 4hr 512 8 hr 131,072 16 hr 8,589,934,592 24 hr 562,929,940,000,000 Luckily, conditions usually aren't "ideal" for bacteria... Otherwise, we'd be overrun! 2
Diseases Caused by Protists (Protozoa) Some diseases caused by protists are caused by parasites (an organism that gets its nourishment or habitat from the tissues or fluids from another organism). Parasites don't always kill the host, but they may weaken or sicken it. Protozoa is another name for animal like protists. Both African sleeping sickness and malaria are examples of protist diseases, where the protist destroys red blood cells. Another example is amoebic dysentary, where the amoeba in contaminated food and water is ingested and lives in the intestine, causing ulcers and diarrhea. Diseases Caused by Fungi Most fungi that cause disease in humans are made of only one cell. Candida, a group of yeasts can cause anything from skin infections t severe bone, lungs, or heart infections. More common diseases caused by fungi are Ringworm and Athlete's foot. The athlete's foot fungus grows in moist places, like locker room showers. It grows between the toes, where the skin is warm and moist, and the fungus parasitically feeds on skin and nail cells. Molds are another type of one celled fugi, and can cause problems when the mold or spores (reproductive cells) are inhaled into the lungs. In the lungs, they can cause allergic reactions, asthma attacks, and pneumonia. 3
How Diseases Spread Vectors are organisms that help diseases spread. (i.e. water contaminated with bacteria carrying a disease or protists). Insects also often serve as vectors for many diseases. A carrier is an organism that is infected with and can transmit a disease causing microbe to another living thing, even though the carrier shows no symptoms of illness or disease (like "carriers" of genetic diseases). Epidemics are major outbreaks of disease in a local area. Health officials will try to trace the outbreak back to the source, to learn what caused the epidemic. A pandemic is a world wide epidemic. How Diseases Spread, cont. A contagious disease is one that can be spread from one person to another, not always by direct contact. Contagious diseases can be spread through the air, or from using an object that has been touched by an infected person. Ex. Disease Pathogen How Disease is Spread Athlete's Foot Fungus Contact with contaminated objects Lyme disease Bacteria Bite from infected tick Influenza Virus Contact with infected person or contaminated objects. Botulism Bacteria Eating contaminated food Hepatitis Virus Contact with bodily fluids of infected person 4
Preventing and Treating Diseases Antibiotics are drugs that kill bacteria or prevent their reproduction (i.e. penicillin). They are not as effective against viruses and protists. Antimicrobial products are substances designed to kill microbes before they enter your body (i.e. hand sanitizer). Some antibiotics and antimicrobial products are not as effective as they used to be (like penicillin) because bacteria mutate and develop resistance to these products. Antibiotic resistance is when bacteria develop a tolerance to and survive treatment with drugs that once killed them (MRSA). Preventing and Treating Diseases Active Immunity against a disease comes from being exposed to the pathogen. This makes the immune system make antibodies. When antibodies are made, the immune system is ready to quickly respond if the organism is exposed again to that pathogen. Antibodies are chemical substances that help destroy pathogens. A vaccine is a small dose or fragment of a weakened or inactivated pathogen given to an organism to help the immune system make antibodies to destroy that pathogen. Vaccines can prevent some viruses and also bacterial infections, such as tetanus. Vaccines have made some infectious diseases like smallpox and polio much less common or disappear. 5