Module 14

• "path" 


  It refers to disease
• Pathogenicity


  It means the ability to cause disease.
• Pathogenesis


  It refers to the steps or mechanisms involved in the development of a disease.
• Infectious disease


  It is a disease caused by a microbe, and the microbes that cause infectious diseases are collectively referred to as pathogens.
• Infection


  It is commonly used as a synonym for infectious disease.
• Infection 


  Colonization by a pathogen
• Antibacterial factors


  May be present at the site where the pathogen lands.
• Localized infection


  Once an infectious process is initiated, the disease may remain localized or it may spread; examples of localized infections are pimples, boils, and abscesses.
• Systemic (or generalized) infections


  When the infection spreads throughout the body.
• Acute disease 


  It is one that has a rapid onset, and is usually followed by a relatively rapid recovery; examples are measles, mumps, and influenza.
• Chronic disease 


  It has a slow onset and lasts a long time; examples are tuberculosis, leprosy, and syphilis.
• Subacute disease 


  It is one that comes on more suddenly than a chronic disease, but less suddenly than an acute disease; an example would be bacterial endocarditis.
• Symptom of a disease


  It is defined as some evidence of a disease that is experienced by the patient⎯something that is subjective; examples are aches or pains, ringing in the ears, blurred vision, nausea, dizziness, etc.
• Sign of a disease 


  It is defined as some type of objective evidence of a disease
• Latent infections 


  Are infectious diseases that go from being symptomatic to asymptomatic, and then, later, go back to being symptomatic.
• Primary Syphilis 


  (Stage of Syphilis) Hardened, painless chancre develops about 3 weeks after exposure.
• Secondary syphilis 


  (Stage of Syphilis) Chancre curls inward and a rash develops about 4 to 6 weeks after exposure; rash resolves within weeks to 12 months.
• Latent Syphilis

  (Stage of Syphilis) No symptoms; may last for weeks to years; sometimes continues throughout life.
• Tertiary Syphilis 


  (Stage of Syphilis) CNS, cardiovascular, and other symptoms occur 5 to 20 years after exposure.
• Virulent 


  It is sometimes used as a synonym for pathogenic.
• Virulent strains 


  Are capable of causing disease.
• Avirulent strains 


  Are not capable of causing disease.
• Virulence 


  It is used to express the measure or degree of pathogenicity.
• Virulence factors 


  Are attributes that enable pathogens to attach, escape destruction, and/or cause disease. These are phenotypic characteristics that are

  dictated by the organism’s genotype.
• Adhesins (ligands)


  Are special molecules on the surface of pathogens, are considered to be virulence factors because they enable pathogens to recognize and bind to particular host cell receptors.
• Pili (bacterial fimbriae) 


  Are considered to be virulence factors because they enable bacteria to attach to surfaces, such as tissues within the human body.
• Obligate intracellular pathogens 


  Pathogens that must live within host cells in order to survive and multiply.
• Intraleukocytic pathogens


  Live within white blood cells, causing diseases known as ehrlichiosis and anaplasmosis.
• Plasmodium spp. (which cause malaria) and Babesia spp. (which cause babesiosis) 


  Are examples of intraerythrocytic pathogens; they live within red blood cells.
• Facultative intracellular pathogens 


  Are capable of both an intracellular and extracellular existence
• Capsules and flagella


  These are considered to be virulence factors.
• Flagella 


  Are virulence factors because they enable flagellated bacteria to invade aqueous areas of the body.
• Toxins 


  Are poisonous substances released by various pathogens.
• Endotoxins


  • Part of the cell wall structure of Gram-negative bacteria

  • Can cause serious, adverse physiologic effects such as fever and shock
• Exotoxins


  • Poisonous proteins secreted by a variety of pathogens

  • Examples: neurotoxins, enterotoxins, exfoliative toxin, erythrogenic toxin, and leukocidins
• Antigenic variation 


  Some pathogens evade the immune system by changing their surface antigens⎯antigenic variation; examples, Neisseria gonorrhoeae and Borrelia recurrentis.
• Camouflage and molecular mimicry


  Some organisms conceal their foreign nature by coating themselves with host proteins⎯like camouflage.
• Destruction of antibodies


  Some pathogens produce IgA protease, an enzyme that destroys some of the host’s antibodies.