Infectious Disease. Bacteria: Friend or Enemy? WHAT IS AN INFECTIOUS DISEASE?

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  • Infectious Disease

  • Bacteria: Friend or Enemy?


  • Pathogens:Bacteria, viruses, parasites, and fungi, called pathogens are capable of causing a change that disrupts the homeostasis in the body. Any disease caused by the presence of pathogens in the body is called an infectious disease. The main sources of pathogens are soil, contaminated water, and infected animals, including other people

  • Good Bacteria:Not all microorganisms are pathogenic; your body is host to billions of microorganisms, most of which are bacteria. These microorganisms have a symbiotic relationship with your body helping to keep harmful bacteria and other microorganisms from growing.

  • Good Bacteria:If beneficial organisms are eliminated from your body, pathogens can establish themselves and cause infectious disease. In addition, if beneficial organisms enter areas of the body where they are not normally found, these formerly harmless organisms can become potential pathogens

  • Common Diseases caused by Pathogens:

    DiseaseCauseAffected OrganTransmissionSmallpoxVirusSkinDropletInfluenzaVirusRespiratory systemDirect contactHIV/AIDSVirusImmune systemBody FluidHepatitis BVirusLiverBody FluidTetanusBacteriaNervous systemPuncture WoundStrep ThroatBacteriaRespiratory systemDropletTuberculosisBacteriaRespiratoryDroplet

  • Strep Throat:


  • Carriers:Main source of human disease pathogens is the human body. People may or may not display symptoms of the illness. Animals are the other main reservoir for pathogens, making the eradication of certain pathogens almost impossible.


  • TransmissionPathogens can be transmitted to a host from a reservoir four main ways; By direct contact; exchange of body fluidBy an object; people handle contaminate objects then touch face, nose, eyes, etcThrough the air; person coughs or sneezes spreading droplets which are then inhaledBy a vector; insects such as mosquitos, ticks spread pathogens between hosts or reservoirs

  • Bats are carriers of rabies, an infectious disease:

  • Mosquitoes carry many infectious diseases:

  • Viruses:Shape: multisidedStructure: contains DNA or RNA, no cytoplasm or organelles, Composed of cells: noTreatments: none, only preventions (antiviral, vaccines)Not considered to be alive, must have a host cell; but destroys the cell

  • Examples of diseases: flu, common cold (can mutate into different forms), viral meningitis, HIV-AIDS, polio, chicken pox

    Flu virus

  • Bacteria:Shapes: spheres, rods, spiralsStructure: single celled with a cell wall and and organelles but no nucleiComposed of cells: yesTreatments: antibiotics, Preventions-antibacterial, bacterial vaccines, antimicrobialsFound everywhere, can survive without a host, multiply rapidly and form colonies (100,000 = size of dime), can be helpful

  • Examples of diseases: tetanus, anthrax, rabies, Lyme disease, bacterial meningitisE ColiLyme Disease

  • Fungi:Shape: numerousStructure: multi-cellular wit a cell wall and organelles including a nucleus, but no chloroplastsComposed of cells: yesTreatments: antifungals, antimicrobialsCannot make their own food, grown on and feed off of organic matter; some kinds are beneficial, but others are harmful

  • Examples of diseases: athletes foot, ringworm, yeast infectionsAthletes FootRingworm

  • Parasites:A parasite is an organism that lives on or in a host and gets its food from or at the expense of its host. Parasites can cause disease in humans. Some parasitic diseases are easily treated and some are not.Major types-protozoa, helminths or worms, and arthropods.

  • Treatment:antibiotics prevention: drugs that can be taken as a barrier to certain parasites. improving sanitary conditions of water and food sources, proper cooking techniques, education about personal hygiene, and control of intermediate and vector host organisms.

  • ProtozoaSingle-celled organisms More than 45,000 species of protozoa are known, many of which are parasitic. Cause of more suffering and death than any other category of disease causing organisms.dysentary

  • Helminths:Wormlike organisms including nematodes (roundworms), cestodes (tapeworms), and trematodes (flukes). Leeches and heartworms are also helminths.


  • Arthropods:Organisms characterized by exterior skeletons and segmented bodies. Examples include the crustaceans, insects, and arachnids. Serve as carriers of bacterial and viral diseases, as intermediate hosts for protozoan and helminth parasites, and as parasites themselves.Mosquitoes, flies, fleas, ticks, mites