Infectious Diseases




(1)
Department of Dermatology, University of Pennsylvania, Penn Presbyterian Medical Center Medical Arts Building, Philadelphia, PA, USA

 



11.1 Bacterial

11.1.1 Gram Positive Bacteria

11.1.2 Gram Negative Bacteria

11.2 Treponemes and Spirochetes

11.3 Fungal

11.3.1 Superficial Fungal

11.3.2 Subcutaneous Fungal

11.3.3 Deep/Systemic Fungal Infection

11.4 Mycobacteria

11.4.1 Typical Mycobacteria

11.4.2 Atypical Mycobacteria

11.5 Viral

11.5.1 DNA Viruses

11.5.2 RNA Viruses

11.6 Sexually Transmitted Infections (STIs)

11.7 Congenital Infections: TORCHeS

11.8 Parasites

11.8.1 Protozoa

11.8.2 Helminths (Worms)

11.9 Infestations

11.9.1 Arthropods (Insects)

11.9.2 Arachnids

11.10 Other Bites and Stings


Abstract

Many types of infection can affect the skin. In this section, infectious skin diseases are categorized by the type of infectious agent. Some listed infectious diseases may not typically have skin findings, but are included for clarity in understanding the categories of infectious diseases.


Keywords
Skin infectionBacterial infectionViral infectionFungal infection



11.1 Bacterial



11.1.1 Gram Positive Bacteria



11.1.1.1 Staphylococcus and Streptococcus




I.

Local cutaneous infection

A.

Impetigo (Staph >> Strep)



  • Aka impetigo contagiosa


  • Can cause post-Strep glomerulonephritis (? if also rheumatic fever)


1.

Bullous impetigo (Staph)



  • Staph exfoliative toxin A, from Staph group 2, phage 71 against dsg1


  • Can be considered a localized form of SSSS


  • MRSA (methicillin-resistant Staph aureus) is thought to have developed resistance via mutations in the mecA gene (which then produces an altered penicillin-binding protein PBP2a)

 

2.

Non-bullous impetigo

 

 

B.

Ecythema



  • Ulcerated form of non-bullous impetigo in which the early lesion extends into the dermis to produce a shallow ulcer

 

C.

Bacterial folliculitis



  • Aka Impetigo of Bockhart (Staph)


  • See also Acneiform Diseases: Folliculitis

 

D.

Furunculosis (follicular abscesses)



  • Deep folliculitis at bulb, usually Staph


  • Mnemonic: Furuncle involves one hair Follicle, carbuncle involves Combination of follicles


  • See also Acneiform Diseases: Folliculitis

 

E.

Cellulitis

1.

Erysipelas



  • Aka “St. Anthony’s fire”


  • Most common cause = group A Strep


  • Painful, often on face, though more on lower extremities

 

 

F.

Necrotizing fasciitis



  • Type 1: polymicrobial (including Clostridium)


  • Type 2: group A Strep (~10%)


1.

Fournier’s gangrene



  • Necrotizing fascititis of the perineum and groin


  • DDx Meleney gangrene (progressive bacterial synergistic gangrene, may be associated with Staph)

 

 

G.

Blistering distal dactylitis



  • Usually solitary on fat pad of finger

 

H.

Felon (Staphylcoccal whitlow)



  • Painful abscess on fingertip

 

I.

Botryomycosis



  • Chronic granulomatous infection, mostly Staph but also Pseudomonas


  • Splendore-Hoeppli phenomenon = eosinophilic, pseudomycotic structures composed of necrotic debris and immunoglobulin

 

J.

Lymphangitis



  • Ascending red streaks

 

K.

Perianal Strep (perianal cellulitis)

 

 

II.

Systemic infection

A.

Toxic shock syndrome

1.

Staph



  • From phage group 1, many types


  • TSST-1 (toxic shock syndrome toxin-1), was originally associated with superabsorbent tampons

 

2.

Strep



  • From Group A Strep


  • Clindamycin may inhibit Strep toxin

 

 

B.

Staphylcoccal scalded skin syndrome (SSSS)



  • Aka Ritter’s disease


  • See primarily in children < 5


  • Can see in adults in context of renal failure (unable to clear toxin) or immunosuppression


  • Can present with erythroderma, scarlatiniform eruption


  • Caused by Staph exfoliative toxin A, from Staph (group 2, phage 71) against dsg-1


  • Path: granular layer split (unlike apoptotic keratinocytes in TEN, in entire epidermis)


  • See also Vesiculobullous:Subcorneal blisters and Vascular:Toxic Erythema:Drug Eruptions:Scarlatiniform

 

C.

Scarlet fever



  • From Group A Strep


  • See also Vascular:Toxic erythema:Scarlatiniform eruptions

 

D.

Rheumatic fever



  • From Strep pharyngitis (not from impetigo, linked to glomerulonephritis)


  • Erythema marginatum (ephemeral figurate erythema) in 11%


  • JONES criteria (J = Joints, O = heart/carditis, N = subcutaneous Nodes, E = Erythema marginatum, S = Syndenham chorea aka St. Vitus’s dance)

 

E.

Endocarditis



  • In native valves, often from Strep viridans (enterococci) > Staph


  • In prosthetics, usually from Staph epidermidis; IVDU: S. aureus


Clinical Findings



  • Splinter hemorrhages (but remember, most commonly from trauma)


  • Osler’s nodes = tender, erythematous papules/nodules with white centers on finger pads


  • Janeway lesions = painless, small hemorrhagic macules on palms/soles, from embolization of organism

 

 


11.1.1.2 Other Gram Positive Bacteria




I.

Corynebacterium (diphtheroid gram positives)

Note: “The triad” are the first three

A.

Erythrasma



  • C. minutissimum, coral-red fluorescence from coproporphyrin III


  • Path: North/South stranding (vs. East–west of tinea versicolor) in stratum corneum

 

B.

Pitted keratolysis



  • Kytococcus sedentarius, does not fluoresce

 

C.

Trichomycosis axillaris



  • C. tenuis (Mnemonic: tenuously hanging on hair)


  • Superficial infection of axillary and pubic hair, cylindrical sheaths and beading of the axillary hairs


  • Ddx white piedra

 

D.

Propionobacterium acnes (formerly Corynebacterium)

 

E.

Diphtheria

 

 

II.

Bacillus anthracis

A.

Anthrax



  • Black eschar (painless, unlike brown recluse bite), can have sporotrichoid spread


  • Need three factors for full virulence: protective, edema, and lethal factors


  • Protective factor + edema factor = edema toxin


  • Protective factor + lethal factor = lethal toxin


  • Edema toxin = impairs neutrophil function, affects water homeostasis, leading to edema


  • Lethal toxin = causes release of TNF-α and IL-1β


  • Tx = ciprofloxacin (for suspected systemic disease, does not affect cutaneous disease, which self-resolves), may use doxycycline for emergency prophylaxis

 

 

III.

Clostridium perfringens

A.

Gas gangrene

 

B.

Necrotizing fasciitis, polymicrobial type

 

 

IV.

Others



  • Mnemonic SNAP for treatments of Nocardia and Actinomyces: sulfa (Bactrim) for Nocardia, Actinomyces tx with penicillin


A.

Actinomyces israelii (Actinomycosis)



  • An anaerobic or microaerophilic gram positive, non-acid-fast organism that can cause suppurative abscesses, granulomas, sinuses


  • Cervicofacial actinomycosis (“lumpy jaw”) usually from poor dental hygiene, injury, or procedure


  • Can also involve pulmonary, GI


  • Treatment = penicillin G

 

B.

Nocardia (Nocardiosis)



  • A filamentous, gram-positive, acid-fast organism


  • In immunocompromised can cause systemic disease, in immunocompetent, usually just skin


  • N. asteroides most cases in US


  • N. brasiliensis tropical/subtropical


  • Tx = Bactrim


1.

Actinomycotic mycetoma/ Madura foot



  • Mostly caused by N. brasilensis and Actinomadura madurae

 

2.

Lymphocutaneous nocardiosis



  • Crusted papule or abscess after trauma


  • Can see sporotrichoid spread of nodules, tender LAD

 

3.

Superficial cutaneous nocardiosis

 

4.

Systemic nocardiosis



  • Can see chest wall abscesses, usually fatal

 

 

C.

Erysipelothrix rhusiopathiae (Erysipeloid)



  • Found in fisherman or people who prepare shellfish, meat, poultry, or fish; usually on hands


  • Tx = PCN

 

D.

Listeria



  • Can be associated with extramedullary hematopoiesis (blueberry muffin syndrome), abscesses

 

 


11.1.2 Gram Negative Bacteria



11.1.2.1 Common Gram Negative Bacteria




I.

Neisseria meningitides

A.

Meningococcemia



  • Can cause purpura fulminans


  • Neisseria grows on chocolate agar with CO2


1.

Waterhouse-Friderichsen syndrome



  • DIC, purpura, adrenal hemorrhage causing adrenal insufficiency

 

 

 

II.

Neisseria gonorrhoeae



  • Aka “the clap”


A.

Disseminated gonorrhea/ gonococcemia



  • Can cause tenosynovitis, monoarticular arthritis, pustule over joint, septic vasculitis


  • Cannot find organisms on gram stain, check blood cultures


  • Specific culture requirements = chocolate agar with CO2

 

 

III.

Pseudomonas aeruginosa



  • Green pigment from pyocyanin


  • Can colonize wounds, can also cause angioinvasive infection


A.

Ecthyma gangrenosum



  • Macule/ulcer/eschar, an embolic lesion, usually on extremity (from septicemia)


  • Path: necrotic hemorrhagic vasculitis


  • Often in immunosuppressed, HIV, hematologic malignancy

 

B.

Otitis externa (“Swimmer’s ear”)



  • Malignant otitis externa usually in diabetics, unresponsive to local tx

 

C.

Hot tub folliculitis

 

D.

Botryomycosis



  • Chronic granulomatous infection

 

 

IV.

Bartonella



  • First line tx = erythromycin


A.

Cat scratch diseaseBartonella henselae



  • Sporotrichoid spread

 

B.

Bacillary angiomatosisBartonella henselae and quintana



  • See more in HIV


  • Clinically can resemble Kaposi’s


  • Parinaud’s ocular/glandular syndrome; when affects liver, can cause peliosis (more with henselae) = hepatic blood-filled cavities

 

C.

Trench feverBartonella quintana



  • Vector = pediculosis corporis

 

D.

Bartonellosis (Carrion’s disease)



  • B. bacilliformis (endemic to Peru), transmitted by Lutzomyia (sandfly)



    • Two biphasic forms:

      1.

      Oroya fever



      • Fever, acute hemolytic anemia

       

      2.

      Verruga peruana (Peruvian wart)



      • Eruption of angiomatous lesions, chronic

       

 

 

V.

Klebsiella pneumoniae

A.

Rhinoscleroma



  • Klebsiella rhinoscleromatis (subspecies)


  • Granulomatous infection of nose and upper respiratory tract


  • Path: parasitized histiocytes = non-lipidized “foamy” macrophages with small pyknotic nuclei/large vacuolated histiocytes with intracellular bacteria = Mikulicz cells (His GiRl Penelope)


  • Also Russell bodies (large eosinophilic homogeneous immunoglobulin-containing inclusions)


  • Tx = tetracycline (first line)

 

 

VI.

Calymmatobacterium (Klebsiella) granulomatis

B.

Granuloma inguinale (Donovanosis)

 




  • Chronic indurated red fleshy ulcer/destructive infection, usually painless


  • Also nodular, cicatricial, and hypertrophic types


  • Most common sites = prepuce, glans penis

 

VII.

Vibrio vulnificus



  • Usually in older men with chronic liver disease, DM, or immunosuppression


  • From raw seafood ingestion or skin injury exposed to seawater, causes hemorrhagic bullae of the leg/cellulitis

 

VIII.

Yersinia pestis “bubonic plague”



  • Vector = Rat flea, Xenopsylla cheopis


  • First line tx = streptomycin

 

IX.

TularemiaFrancisella tularensis



  • Sporotrichoid spread, can have eschar


  • Most common form = ulceroglandular (punched out indurated ulcer and LAD); worst strain = A1b


  • Can resemble plague


  • Associated with rabbit contact, mostly from deer fly and tick


  • Concern about potential use in bioterrorism


  • Vectors: Dermacentor andersoni (American wood tick), Amblyomma americanum (Lone Star tick)


  • First line tx = streptomycin > gentamicin

 

X.

Haemophilus ducreyi (Chanchroid)



  • Purulent, painful, usually multiple ulcers, soft undermined edges


  • Path: “School of fish”


  • Hard to culture, so usually dx of exclusion


  • Tx = one dose of azithromycin or ceftriaxone

 

XI.

Other gram negative bacteria

A.

Salmonella



  • S. typhi (typhoid fever) “rose spots”

 

B.

Brucella (undulant fever)



  • Can get from raw milk

 

C.

Burkholderia mallei (Glanders)



  • See only in people with horse contact


  • Can have sporotrichoid spread

 

D.

Burkholderia pseudomallei (Melioidosis or pseudo-Glanders)



  • Mostly in SE Asia, Australia


  • Treatment difficult, broad spectrum abx

 

E.

E. coli (>Pseudomonas > Proteus)

1.

Malakoplakia



  • Chronic bacterial granulomatous accumulation in immunocompromised hosts


  • Michaelis-Gutmann bodies = calcified


  • intracytoplasmic phagolysosome


  • von Hansemann cells = ovoid histiocytes with fine eosinophilic cytoplasmic granules


  • Non-specific clinical appearance

 

 

 


11.1.2.2 Rickettsial Diseases


Tx: drug of choice = doxycycline; however, chloramphenicol in pregnancy (and no doxy for kids <8 years old); sulfa drugs can exacerbate



  • Pathologically, affects endothelial cells; it follows that rickettsial diseases may cause vasculitis


  • Can be divided into spotted fever, typhus, scrub typhus, and other groups (see below).




  • Spotted fever group:

    I.

    Rickettsia rickettsiiRocky Mountain spotted fever (RMSF)



    • Purpuric eruption, begins on wrists/ankles, moves centripetally (can involve palms/soles)

      Vectors: Major vector in most of US, not in mountains but in eastern states like NC = Dermacentor variabilis (American dog tick); In Rocky Mountains = Dermacentor andersoni (American wood tick); also, Amblyomma americanum (Lone Star tick)

     

    II.

    Rickettsia akariRickettsialpox



    • Infected via mite (Liponyssoides sanguineus) of Mus musculus (house mouse)


    • On path may see “squiggle cells” = banded lymphocytes (non- specific)


    • Tache noir = eschar


    • Endemic to New York City (Bronx, Queens)


    • Recent report of R. parkeri causing rickettsialpox

     




  • Typhus group:

    III.

    Rickettsia prowazekiiEpidemic louse-bourne typhus



    • Brill-Zinsser disease = milder second episode


    • Vector = pediculosis corporis


    • Reservoir = flying squirrel

     

    IV.

    Rickettsia typhiMurine (endemic) typhus (flea-borne)



    • Transmitted by cat and rat fleas

     




  • Scrub typhus group:

    V.

    Rickettsia tsutsugamushiScrub typhus

     




    • Aka Tsutsugamushi fever


    • From chigger (Trombiculid mite)




  • Other rickettsial diseases:

    VI.

    Coxiella burnetiiQ fever



    • Transmitted by inhalation of aerosols

     

    VII.

    Ehrlichia chaffeensisEhrlichiosis



    • Major vector = Amblyomma americanum (Lone Star tick), but also Ixodes (Lyme vectors)


    • Organisms grown in small membrane-bound vacuoles in which they form colonies called morulae; can be seen on peripheral blood smears

      A.

      Human monocytic ehrlichiosis

       

      B.

      Anaplasmosis (human granulocytic ehrlichiosis)

       

     


11.2 Treponemes and Spirochetes






  • The spirochetes, which include treponemes and others, are all gram negative bacteria


  • Mnemonic for spirochetes = rat eating a BLT (rat-bite fever and Borrelia, Leptospirosis, Treponemes)

    1.

    Treponemes

    (a)

    Treponema pallidum = Syphilis



    • Aka Lues disease (pronounced [Louie’s])


    • Path: psoriasiform and lichenoid dermatitis, thin rete ridges, usually increased plasma cells


    • Stain with silver stains (Warthin-Starry), T. pallidum stain


    • RPR = 91 % sensitive, 95 % specific; FTA-ABS 92 % sensitive, 96 % specific


    • In prozone phenomenon (e.g. with high Ab titer as in HIV), may get false negative, so should request further dilutions


    • Screen with RPR/VDRL(sensitive), confirm with FTA- ABS/T. pallidum antibody (specific)


    • RPR: 1:8 or less = false positive (usually)


    • Acute false positive = pregnancy, SLE, mono, leprosy


    • Chronic false positive (>6 months) = Lyme


    • Treatment = benzathine penicillin


    • Jarisch-Herxheimer reaction = febrile inflammatory reaction to release of endotoxins shortly after receiving therapy


    • Successful treatment measured by four-fold difference in RPR titer (this also determines re-infection if increased × 4)


    I.

    Primary syphilis



    • Primary chancre, erosion at site of primary inoculation, classically on coronal sulcus of penis


    • 90 % on genitals, 10 % extra-genital, appears 9–90 days after primary contact, usually 3–4 weeks


    • Could use dark field microscopy for definitive dx


    • Serology positive 2–4 weeks after chancre


    • Non-tender painless, regional non-tender bubo (LN)

     

    II.

    Secondary syphilis



    • Skin eruption with or without lymphadenopathy


    • Occurs 6 weeks to 6 months (average 9 weeks) after chancre


    • Can go into latent syphilis (only serologically positive)


    • Of secondary syphilis, 2/3 develop latent syphilis, 1/3 develop tertiary syphilis

      Clinical manifestations of secondary syphilis:



      • Papulosquamous eruption that may resemble pityriasis rosea or psoriasis; classically involves palms and soles


      • Condyloma lata = papillomatous papules/plaques, look like condyloma, resolve in 2–6 weeks, has the most spirochetes—teeming


      • Split papules = fissured papules seen on angles of mouth, base of earlobe, etc.


      • Mucous patches, “moth-eaten” alopecia, palm and sole papules and plaques (including “copper penny” spots) with collarette of scale (collarette of Biett), sparse eyebrows (madarosis), large annular syphilid, iritis


      • Why not do a dark field on a mouth lesion? Because there are non-pathogenic treponemes naturally in our mouths (will be false-positive)


      • Cervical, inguinal, and epitrochlear lymphadenopathy (easiest to palpate on exam, by elbows)

     

    III.

    Tertiary syphilis



    • Gummas, neurosyphilis, or cardiovascular disease


    • Occurs months to years (4–20 years) after primary infection


    • 1/3 of those infected with syphilis get tertiary


    • Of this 1/3, 15–17 % get cutaneous involvement (gummas); these can affect skin, bones, viscera (but not GI or GYN) and can appear as plaques, nodules, ulcers


    • Gummas = “gummy,” granulomatous lesions, no organisms found, from delayed hypersensitivity?


    • Can see nasal destruction (saddle nose); ddx TB, syphilis, leprosy, rhinoscleroma, Wegener’s, BCC


    • Arteritis in 10 % of tertiary syphilis (aneurysms)


    • Aortic aneurysm (widened mediastinum on CXR)


    • Also, syphilitic glossitis, Charcot joints (enlarged knee with no sensation, osteitis, trauma)


    • Neurosyphilis: tabes dorsalis; tabes = “decay”; this is “decay” of the posterior columns


    • Argyll Robertson pupil = accommodates, but does not react (like a prostitute)


    • Three main forms of neurosyphilis:

      A.

      Asymptomatic neurosyphilis = only positive serology, would need to check LP

       

      B.

      Meningo-vascular = endarteritis leading to focal neurologic signs, stroke

       

      C.

      Parenchymatous = actual decay of brain or posterior columns; tabes dorsalis, “general paresis” = demented, optic atrophy

       

     

    IV.

    Congenital syphilis

    Note: Hutchinson’s triad = interstitial keratitis, Hutchinson incisors (small, notched, widely spaced), sensorineural deafness (CN VIII)

    A.

    Early signs



    • Parrot’s pseudoparalysis, pneumonia alba, snuffles, syphilitic pemphigus, rhagades, Wimberger’s sign

     

    B.

    Late signs



    • Clutton’s joints, ‘Mulberry’ molars, saber shins, saddle nose

     

     

     

    (b)

    Treponema pertenue = Yaws (Framboesia tropica)



    • Can present with “amber yellow” crust; primary = “Mother yaw”


    • Nasal/palate perforation in tertiary yaws = gangosa


    • Species/name mnemonic = “y’all is pertinent”

     

    (c)

    Treponema carateum = Pinta



    • Endemic to rural Central and South America


    • May cause hypopigmented and hyperpigmented patches


    • Species/name mnemonic Pinto car

     

    (d)

    Treponema pallidum endemicum = Bejel or endemic syphilis



    • Most prevalent in northern African and Middle East

     

     

    2.

    Borrelia



    • Note: Borrelia is thought to play a role in the etiology of many primary cutaneous B-cell lymphomas; also associated with pseudolymphomas


    (a)

    Borrelia burgdorferi Lyme disease

    Vector = Ixodes ticks

    I.

    Lyme disease



    • Causes erythema migrans, ddx Southern tick-associated rash illness (STARI)


    • Nerve defects (Bell’s palsy in 10 %), Cardiac (AV block in 5 %), arthritis (in 60 %, preferentially knee)


    • Caused by Borrelia burgdorferi (U.S.), Borrelia afzelii and Borrelia garinii (Europe)


    • Vector = I. scapularis (aka dammini) (US East coast), I. pacificus (West coast), I. ricinis (Europe)


    • Natural hosts = white-footed mouse, white-tailed deer


    • B. garinii associated with neurologic symptoms, B. afzelii associated more with cutaneous disease


    • Tx = doxycycline; in kids/pregnancy: amoxicillin, alternative cefuroxime; in disseminated disease, tx with ceftriaxone

     

    II.

    Acrodermatitis chronica atrophicans



    • Hastened aging to atrophy of acral skin from chronic borrelial infection); ddx morphea


    • Caused by Borrelia afzelii

     

    III.

    Pseudolymphoma (Borrelial lymphocytoma)



    • VBorrelia recurrentis relapsing fever


    • Vector = pediculosis corporis

     

     

     

    3.

    Leptospira interrograns (leptospirosis)



    • Increased in flooding (e.g. post-Hurricane Katrina outbreak)

     

    4.

    Rat-bite fever



    • Fever, rash, arthritis; tx with PCN


    • From rat bite or ingestion of rat-contaminated food or drink

      (a)

      Spirillum minusMostly in Asia



      • Sodoku manifests 2–4 weeks after bite (milder)

       

      (b)

      Streptobacillus moniliformis



      • Haverhill fever 1–3 weeks after bite

       

     


11.3 Fungal



11.3.1 Superficial Fungal




(a)

Candida



  • Budding yeast and pseudohyphae on KOH


I.

Cutaneous candidiasis



  • Markedly erythematous or erosive areas, may have fine white pustules, satellite papules/pustules, often in dependent or occluded areas


  • Predisposed by DM, occlusion, systemic abx


  • Ddx pustular psoriasis, AGEP

 

II.

Oral candidiasis (thrush)

 

III.

Erosio interdigitalis blastomycetica



  • Mostly caused by Candida


  • Finger/toe webspace superficial fungal infection

 

IV.

Granuloma gluteale infantum

 

V.

Angular cheilitis



  • Ddx vitamin B deficiency

 

VI.

Immunodeficiency disorders associated with candidiasis

A.

APECED syndrome



  • Autoimmune PolyEndocrinopathy Candidiasis and Ectodermal Dystrophy


  • Hypoparathyroidism seen in 90 %


  • Can be associated with vitiligo


  • From defects in AIRE (auto immune regulator), encodes a transcription factor

 

B.

IPEX syndrome



  • Immune dysregulation, Polyendocrinopathy, Enteropathy and X-linked


  • Caused by mutations in FOXP3 gene → will lack FOXP3+ regulatory T cells (Treg)

 

 

 

(b)

Dermatophytes



  • Trichophyton, Microsporum, Epidermophyton


  • T. rubrum most common


  • Divided based on natural reservoir (humans, animals, soil): anthropophilic, zoophilic, geophilic


  • Septated hyphae on KOH


  • In tinea capitis, think T. tonsurans (#1 in US) > M. canis (#1 in world)


  • Trichophyton tonsurans = grows on thiamine-enriched medium


  • A few species with unusual nutritional requirements:

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Oct 6, 2016 | Posted by in Dermatology | Comments Off on Infectious Diseases

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