Infections of the skin, soft tissue, muscle and associated systems                

p. 349-381

Introduction

•      Skin is main defense system Intact skin is an excellent defense against microbes

•      Role of normal flora in both defense and infection

•      fig. 26.1

Infections of the skin

•             three lines of attack

–         breach of intact skin (fig. 26.2, fig. 26.3, fig. 26.5)

–        Infection (damage) from outside (Fig 26.2)

–         skin manifestations of systemic infections (fig. 26.4)

–        Spread by blood from an infected focus

–         toxin-mediated skin damage

–        Due to toxin production

Infections of the skin

•             anatomic classification of infection

–          abscess formation

–         Boils and carbuncles

–          spreading infection

–         Impetigo – yellow crusted lesions

–         Erysipelas – spreading erythematous inflammation

–          necrotizing infection

–         Fasciitis – may result in gangrene and myonecrosis

•              common causative organisms

–          Staphylococcus aureus

•          most common cause of skin infections

•          causes minor to major infections

•         Boils and abscesses à post-operative infections

•          may be self-inflicted or by contact

•          diagnosed clinically with laboratory confirmation

•         Boils, Isolation and identification

•          Treatment

•         Drainage and antibiotic treatment

•          scalded skin syndrome in babies (fig. 26.7)

•         Due to toxin – “exfoliatin”.

•          toxic shock (fig. 26.8)

•         Caused by exotoxin

•         fever, hypotension, and macular erythematous rash followed by desquamation of palm and soles.

–            Streptococcus pyogenes (group A strep)

•            causes minor to major infections

•            infection is usually by contact

•           With people with infected skin lesions

•           Risk factors à Fig. 26.9

•            infections are acute

•            M proteins

•           Antigenic surface proteins à inhibit opsonization

•           can cause acute glomerulonephritis

•            diagnosed clinically with laboratory confirmation

•           Gram stain of pus

•            Treatment

•           Penicillin, erythromycin and cephalosporin

•            can co-infect with Staphylococcus aureus

•               Cellulitis (acute spreading skin infection)

–            Caused: Strep. pyogenes and Staph. aureus + other microbes

–            culture from a variety of sites

–            anaerobic cellulitis

•           Foul-smelling discharge, swelling and gas in tissue

•               synergistic bacterial gangrene

–            Cause: streptococci and S. aureus

–            Treatment: removal of necrotic tissue and systemic antibiotic therapy

•               necrotizing fasciitis

–            Resembles synergistic bacterial gangrene

–            Caused by Strep. Pyogenes (“flesh-eating” bacteria)

•              Clostridium tetani

•            Get in through trauma to skin

•            disease is due to toxin damage (tetanospasmin)

•              Clostridium perfringens

•            primary cause of gas gangrene

•           Infection of areas of body with poor blood supply (anaerobic)

•           Damage due to lecithinase (alpha toxin)

–        hydrolyzes lipids in cell membranes à cell lysis and cell death à spread

•            Amputation

•           Excision of infected tissue to prevent spread

•           Treatment

–        hyperbaric oxygen chamber

–        Antibiotic treatments

•              Propionibacterium acnes (fig. 26.19)

•            causes acne

•          Increased sebum production

•          Treatment:

•         oral antibiotics (tetracycline or erythromycin)

•         Skin care and vitamin A

•              Mycobacterium leprae

•            acid fast bacteria

•            causes leprosy

•           Transmission: direct contact, aerosol inhalation, arthropod vectors

•            cannot be grown on artificial culture media

•           Genome is fully sequenced – missing many genes

•           Grows intracellularly

•            cell-mediated response determines clinical features

•           Tuberculoid leprosy

•           Lepromatous leprosy

•            Treatment

•           With multidrug regimen: Dapsone + other antibiotics

•              Other Mycobacteium that also cause skin infections:

•            M. marinum, M. ulcerans and M. tuberculosis

•              Propionibacterium acnes (fig. 26.19)

•            causes acne

•          Increased sebum production

•          Treatment:

•         oral antibiotics (tetracycline or erythromycin)

•         Skin care and vitamin A

•              Mycobacterium leprae

•            acid fast bacteria

•            causes leprosy

•           Transmission: direct contact, aerosol inhalation, arthropod vectors

•            cannot be grown on artificial culture media

•           Genome is fully sequenced – missing many genes

•           Grows intracellularly

•            cell-mediated response determines clinical features

•           Tuberculoid leprosy

•           Lepromatous leprosy

•            Treatment

•           With multidrug regimen: Dapsone + other antibiotics

•              Other Mycobacteium that also cause skin infections:

•            M. marinum, M. ulcerans and M. tuberculosis

•              Propionibacterium acnes (fig. 26.19)

•            Hormonal changes during puberty can result in acne

•          Increased sebum production

•          P. acnes multiply and act on sebum à fatty acids and peptides which lead to inflammation à acne

•          Treatment:

•         oral antibiotics (tetracycline or erythromycin)

•         Skin care and vitamin A

•              Mycobacterium leprae

•            acid fast bacteria – nasal scrapings and lesion biopsies

•            causes leprosy

•           affects millions of people worldwide

•           Transmission: direct contact, aerosol inhalation, arthropod vectors

•            cannot be grown on artificial culture media

•            cell-mediated response determines clinical features

•           Tuberculoid leprosy

•           Lepromatous leprosy

•            Treatment

•           multidrug regimen - Dapsone + other antibiotics

•              Other Mycobacteium that also cause skin infections:

•            M. marinum, M. ulcerans and M. tuberculosis

Fungal infections of the skin

•      Superficial and Cutaneous mycoses - Localized to hair, skin, nails

–    Ringworm (Tinea), Candida infections

•      Subcutaneous mycoses - Beneath skin

–    Thorn or bite à sporotrichosis in gardeners and farmers

•      Systemic mycoses - Deep within body

–    Begin in lungs à other tissues (skin lesions)

•    Blastomycosis

•    Coccidiodiomycosis

•    Crytococcosis

•      Opportunistic mycoses

–    Yeast infections – vaginal or as thrush

Parasitic infections of the skin

•      Enter body through:

–   Direct penetration

–   Injected by blood-sucking vectors

•      Leishmaniasis:

–   cutaneous, skin papule

–   Mucocutaneous: invade skin and mucous surfaces (nose, mouth) à disfiguring condition.

•      hookworms:

–   Larvae penetrate skin, migrate via blood to intestine à cause dermatitis where penetration occur

–   In some host, larvae will migrate parallel to skin à itchy inflammatory trails

Parasitic infections of the skin

•      Arthropod infections:

–  Dipterous flies

–  Ticks, lice, and mites

•   Saliva, excreta à skin irritation

•   Prolonged feeding à lesions

•   Host inflammatory response

Mucocutaneous lesions caused by viruses

–            lesions divided into two groups (fig. 26.39)

•            virus restricted to body surface

•            virus causes lesions after spreading systemically and are divided into:

–         lesions at sites of virus infection (infectious)

–         lesions are non-infectious and immunologically mediated

–            Papillomavirus infections

•            about 70 types can infect humans

•            generally cause warts (skin papillomas)

•            types are site specific

•           Different types are adapted to different body sites:

•         HPV 6, 11, 16, 18 – infect genital area and transmitted sexually

•         HPV 1, 4 – cause plantar warts (sole of feet)

•         HPV 2, 3, 10 – causes warts on knees and fingers

•           Transmitted by direct contact

•           Infect and multiply in mucosa à infected cells form papilloma

•            diagnosis is clinical

•           HPV DNA detection

•            treatment varies

–           cervical cancer

–         Molluscum contagiosum

–        Umbilicated lesion caused by poxvirus

–        Transmission: direct contact with infected hosts or contaminated fomites.

–        infect only humans

–         Orf caused by poxvirus

–        Contagious pustular dermatitis

–        Acquired from direct contact with infected sheep and goats

–            Herpes simplex virus infections

•            Universal

•           Two types: HSV-1 and HSV-2

•           Causes intraepithelial vesicles

•            usually occurs in early childhood

•            various sites for primary infection

•           Eye – causes conjunctivitis and keratitis

•           Fingers – cause herpetic whitlow (abscess)

•           Other skin sites

•           Genital tract

•            virus practices latency (fig. 26.43)

•           Virus lays dormant in dorsal root ganglion for life

•           Can reactivate

•            reactivation due to a variety of factors

•            virus is easily cultured à from saliva, lesion

•            treatment is acyclovir

•           Topical (cold sores) or systemic (encephalitis)

–           Varicella zoster virus

–          causes chickenpox and shingles

–          mild in children, more severe in adults

–          Predisposition for shingles:

–        advancing age, immunocompromised, trauma or tumor affecting brain and spinal cord

–           Coxsackieviruses and echoviruses

–          Causes a variety of skin rashes

–          Also sores in mouth and tongue

–           Human erythrovirus (formerly parvovirus) B19

–          Causes slapped cheek syndrome – characteristic rash on face

–           Human herpesviruses 6 and 7

–          HHV6 – shed in saliva of 85% of adults and causes exanthem subitum (roseola infantum) – accompanies high fever in young children

–          HHV7 – infection occurs later than HHV6 (present in 75% of adults)

Smallpox

•             Cause by poxvirus

•             Spread by direct contact or respiratory tract

•             global eradication

•           Using vaccinia vaccine, last case in 1977

•           Eradication was possible because:

–         no subclinical infections – disease easily identified

–         no carriers

–         Humans are only host, no animal reservoir

–         effective vaccine

Measles

Special features:

•             All infected become unwell

•            Transmitted via respiratory droplets

•             Disease clinically identifiable

•            Characteristic rash on face and trunk

•             one antigenic type of measles virus

•            Paramyxovirus

•             complete protection after infection

•             highly infectious – infects all susceptible

•            No treatment, prevention is vaccine (MMR)

•            Plans for total eradication by 2010

•             nutritional effect (fig. 26.51)

•            Malnourished results in more severe disease

Rubella

•       Spread via air droplets

–   Main impact on fetus when it gets into blood

–   Invades different body tissues causing different diseases (fig. 26.55)

–   Rubella is diagnosed serologically (IgM abs)

–   No treatment, prevented by vaccination (MMR)

•      Other infections

–   Bacterial, fungal, and rickettsial infections à skin rashes and lesions

•      Kawasaki syndrome

–   Acute vasculitis caused by superantigen toxins of Staph. aureus or Strep. pyogenes

Rubella

•       Spread via air droplets

–   Main impact on fetus when it gets into blood

–   Invades different body tissues causing different diseases (fig. 26.55)

–   Rubella is diagnosed serologically (IgM abs)

–   No treatment, prevented by vaccination (MMR)

•      Other infections

–   Bacterial, fungal, and rickettsial infections à skin rashes and lesions

•      Kawasaki syndrome

–   Acute vasculitis caused by superantigen toxins of Staph. aureus or Strep. pyogenes

Viral infections of muscle

•             primarily coxsackieviruses

•            Causes myocarditis and myalgia

•             some influenzae may be implicated

•            Pain and tenderness in muscle - due to invasion by virus?

•             myositis

•             myocarditis

•             myalgias

•             post viral fatigue syndrome (Chronic fatigue syndrome)

•            Chronic and severe muscle weakness

•            Severe tiredness

•            Depression, headache and anxiety

•            Etiology uncertain: coxsackie B viruses, Epstein-Barr virus, HHV6 or other viruses

Parasitic infections of muscle

•      Trypanosoma cruzi

–   protozoan, causes Chagas’ disease

–   Transmitted by blood-sucking insects

–   May invade and destroy heart muscle à enlargement of heart

•      Taenia solium

–   Larvae invades body tissues, forms cyst which becomes calcified

•      Trichinella spiralis

–   Larvae invade striated muscle

–   Causes inflammatory reactions

–   Becomes life-threatening when heavily infected

Joint and bone infections

•             Joints - become infected via blood, by trauma or surgery, or immunologically mediated

•             fig. 26.57 reactive arthritis, arthralgia and septic arthritis – caused by enteric bacterial infections

•             localized infection following systemic

•            Concentrate in joints à fever, pain, swelling

•            Most common cause – S. aureus

•             Osteomyelitis

•            Cause by S. aureus from neighboring site or blood

•            Results in painful, tender bone lesion and fever

•            Treated with antibiotics and surgery

Infections of the hemopoietic system

•             Infectious agents causing changes in circulating blood cells (fig. 26.59)

•             Bordetella pertussis - lymphocytosis

•             EBV and CMV - mononucleosis

•             Plasmodium spp. – anemia and thrombocytopenia

•             HTLV I and HTLV II (human T cell lymphotropic virus)

•           Transmitted by maternal milk, sexual intercourse, contaminated needles by drug users

•           Infects T cells à T cell leukemia