1、Introduction to infectious diseasesGang XINDepartment of Microbiology and Immunologygxinstu.edermsInfectiology Infection Infectious diseasesInfectiologist Infectious diseases are caused by pathogenic microorganisms, such as bacteria, viruses, parasites or fungi; the disease can be sprea

2、d directly or indirectly, form one person to another.Infectious diseasesCommunicable diseasesWound infectionlung infectionpathogenhostOutline Pathogen Host Pathogenesis of infection Classification of infection Clinical manifestations Laboratory diagnosis of infectious diseases Treatment and preventi

3、onpathogenTypes of pathogenseu-, Good; well; true pro-, before karuo-, nut or cell nucleus Types of pathogensSubcelluarProkaryotic Viruses, prionBacterial, chlamydiae, rickettsiae, mycoplasmasEukaryotic Protozoa, fungi, helminthes, arthropodsprionA prion is an infectious agent composed of protein in

4、 a misfolded form Disease:Bovine spongiform encephalopathyMadcow disease(MCD)VirusesThe term virion (plural virions) is also used to refer to a single, stable infective viral particle that is released from the cell and is fully capable of infecting other cells of the same type A virus is a small inf

5、ectious agent that can replicate only inside the living cells of organisms. Bacteria (singular: bacterium)chlamydiaechlamyd-, mantle (a cloak) Chlamydia infectionchlamydia conjunctivitisor trachoma rickettsiaeThe genus Rickettsia is named after H. T. Ricketts (18711910), who studied Rocky Mountain s

6、potted fever, and eventually died of typhus after studying that disease. rickets, vitamin D deficiency Disease:spotted fever, typhus and scrub typhus Tick hemolymph cells infected with R. rickettsii. From the CDC.Symptoms of Scrub typhus fever headache muscle pain cough gastrointestinal symptoms hem

7、orrhaging and intravascular coagulation. maculopapular rash, eschar焦痂, splenomegaly and lymphadenopathies are typical signs. huajx/news/Detail/13203.htmlMycoplasmamykes (fungus) and plasma (formed)SpirochetesyphilisSaddle nose Fungi (singular: fungus)Tinea (=ringworm ) of skinTinea pedisTinea manusT

8、inea crurisGroup of extremely small single cell (unicellular) or acellular organisms that are found in moist soil or water. They tend to exist as parasites, living off other life forms. Protos (First) and zoon (animal)protozoa (singular: protozoon)helminths are worm-like organisms (Parasitic worms)

9、that live and feed off living hosts, receiving nourishment and protection while disrupting their hosts nutrient absorption, causing weakness and disease. helminthsHelmins = wormHookworms attached to the intestinal mucosa.arthropods Greek arthron, joint, and pods foot, which together mean jointed fee

10、tCulex MosquitoAedes MosquitoTicksPathogen factorspathogenicityvirulenceis the ability of a pathogen to produce an infectious disease in an organism. The virulence factors of bacteria Methods by which bacteria cause disease AdhesionColonizationInvasionImmune response inhibitorsToxins12345The virulen

11、ce factors of bacteria Adhesion. Many bacteria must first bind to host cell surfaces. Colonization. Some virulent bacteria produce special proteins that allow them to colonize parts of the host body. Invasion. Some virulent bacteria produce proteins that either disrupt host cell membranes or stimula

12、te endocytosis into host cells. These virulence factors allow the bacteria to enter host cells and facilitate entry into the body across epithelial tissue layers at the body surface. Immune response inhibitors. Many bacteria produce virulence factors that inhibit the hosts immune system defenses. To

13、xins. Many virulence factors are proteins made by bacteria that poison host cells and cause tissue damage. Methods by which bacteria cause disease invasionminimum lethal dose (MLD) the smallest amount of toxin that will kill an experimental animal.Minimum infective dosemedian infective dose (ID50) t

14、he amount of pathogenic microorganisms that will cause infection in 50 per cent of the test subjects. infective dose that amount of pathogenic organisms that will cause infection in susceptible subjects.Host factorssusceptibilitydispositionImmune systemAntibody, immunoglobulinIceberg concept of infe

15、ctionInfectious disease spectrum If a large number of individuals are equally exposed to an infectious agent, they do not all respond in the same manner. In fact, there may be a broad range of responses: Some do not become infected at all Some become infected but develop no symptoms Some become infe

16、cted and develop mild or moderate symptoms Some become infected and develop severe symptoms Some die as a result of their infectionPathogenesis of infectionClinical manifestations of infectious diseasesNon-specificOrgan system-basedFeverAnorexiaFatigueMuscle achesSkin rasha state of physical and/or

17、mental weakness Loss of appetite Mary Mallon was an asymptomatic carrier of typhoid fever. Over the course of her career as a cook, she infected 53 people, three of whom died.Host-Pathogen Interactions: Symbiotic RelationshipsMutualismCommensalismParasitismNeutralismA symbiotic relationship in which

18、 both species benefit A symbiotic relationship in which one organism derives benefit and the other is unharmed A symbiotic relationship in which one species, the parasite, benefits at the expense of the other, the host The state of being neutral; neutrality prefix, a variant of syn- before b, p, and

19、 m=Together = Life; living organism airborne infection droplet infection vector-borne infection waterborne infection bloodborne infectionMode of infectionSneezing can spread the flu virus to other people. airborne infection one that is contracted by inhalation of microorganisms or spores suspended i

20、n air on water droplets or dust particles. droplet infection infection due to inhalation of respiratory pathogens suspended on liquid particles exhaled by someone already infected (droplet nuclei) . vector-borne infection infection caused by microorganisms transmitted from one host to another by a c

21、arrier, such as a mosquito, louse, fly, or tick. waterborne infection infection by microorganisms transmitted in water.Classification of infections 1Type of the pathogenDegree of involvementBacterial, viral, fungal, parasiticLocal/focal, generalizedManner acquiredCommunity, hospital/nosocomialClassi

22、fication of infections 2Type of occurrenceEndogenous vs. exogenousAutoinfection vs. cross-infectionSuperinfection vs. reinfectionsepsisOpportunistic infection an infection caused by an infectious agent that is already present in the body, but has previously been inapparent or dormant. an infection t

23、hat develops from bacteria normally outside the body that have gained access to the body an infection caused by a disease agent that is already present in the body an infection by an organism that does not ordinarily cause disease but becomes pathogenic under certain circumstances (e.g., impaired im

24、mune responses). the transmission of a communicable disease from one person to another because of a poor barrier protection an infection following a previous infection, especially when caused by microorganisms that have become resistant to the antibiotics used earlier a second infection by the same

25、microorganism, either after recovery or during the original infection 12345678 a bacterial infection in the bloodstream or body tissues Cross-infectionExogenous infectionEndogenous infectionOpportunistic infectionReinfectionSuperinfectionAutoinfection Sepsis Laboratory diagnosis of infectious diseas

26、esGold standard testproceduresMicroscopy and Staining proceduresCulture and sensitivitySerologic testStaining procedures Urinalysis and fecalysis Specimen smear (blood, stool) Gram Staining Zeihl-Neelson stain KOH (potassium hydroxide) test for fungiGram Staining Gram stain a staining procedure in w

27、hich microorganisms are stained with crystal violet, treated with strong iodine solution, decolorized with ethanol, and counterstained with a contrasting dye; those retaining the stain are gram-positive, and those losing the stain but staining with the counterstain are gram-negative.Zeihl-Neelsen stain The Ziehl-Neelsen stain, also known as the acid-fast stain, was first described by two German doctors; Franz Ziehl (1859-1926), a bacteriologist and Friedrich Neelsen (1854-1898), a pa