Fig. 9.1 Examplesofviralinclusions.(A)Cytomegalovirusinfectioninthelung.Infectedcellsshowdistinctnuclear(long arrow) andill-definedcytoplasmic(short arrows) inclusions.(B)Varicella-zostervirusinfectionintheskin.Herpessimplexvirusandvaricella-zostervirusbothcausecharacteristiccytopathologicchanges,includingfusionofepithelialcells,whichproducesmultinucleatecellswithmoldingofnucleitooneanother(long arrow), andeosinophilichaloednuclearinclusions(short arrow). (C)HepatitisBviralinfectioninliver.Inchronicinfections,infectedhepatocytesshowdiffusegranular(“ground-glass”)cytoplasm,reflectingaccumulatedhepatitisBsurfaceantigen(HBsAg).
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Table 9.2 Selected Human Viral Diseases and Their Pathogens
AIDS, Acquiredimmunodeficiencysyndrome;HIV, humanimmunodeficiencyvirus.
others can survive and replicate both outside and inside of host cells (facultative intracellular bacteria such as mycobacteria), and some grow only inside host cells (obligate intracellular bacteria, such as rickettsia).
Bacteria cause a range of infections from common pharyngitis and urinary tract infections to rare diseases such as leprosy (
Table 9.3 ). Chlamydia and Rickettsia are obligate intracellular bacteria that replicate inside membrane-bound vacuoles in epithelial and endothelial cells, respectively. These bacteria get most or all of their energy source, ATP, from the host cell. Chlamydia trachomatis is a frequent infectious cause of female sterility (by scarring and narrowing of the fallopian tubes) and blindness (by chronic inflammation of the conjunctiva that eventually causes scarring and opacification of the cornea). Rickettsiae injure the endothelial cells in which they grow, causing a hemorrhagic vasculitis, often visible as a rash, but they also may injure the central nervous system (CNS), with potentially fatal outcome, as in Rocky Mountain spotted fever and epidemic typhus. Rickettsiae are transmitted by arthropod vectors, including lice (in epidemic typhus), ticks (in Rocky Mountain spotted fever and ehrlichiosis), and mites (in scrub typhus).
Mycoplasma and the related genus Ureaplasma are unique among extracellular bacterial pathogens in that they do not have a cell wall. These are the tiniest free-living organisms known (125 to 300 nm).
Fungi are eukaryotes with thick cell walls composed of complex carbohydrates such as beta-glucans, chitin, and mannosylated glycoproteins. Calcofluor-white, a
Immune-evasion protein (e.g., M protein) (e.g., protein F) Teichoic acid
Fig. 9.2 Moleculesonthesurfaceofgram-negativeandgram-positivebacteriainvolvedinthepathogenesisofinfection.
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Table 9.3 Selected Human Bacterial Diseases and Their Pathogens
ActinomycetalinfectionsNocardia asteroides complex Pulmonarydisease,brainabscessActinomyces israelii Headandneckabscess