Post on 14-Jul-2015
Microbial disease of the skin and wound
Bacteria, viruses, fungi, protozoa, and arthropods are involved in skin disease
Normal microbiota of the skin Staphylococccus
S. epidermidis S. aureus
Micrococcus
Diphtheroids
Corynebacterium xerosis
Propionibacterium acnes
Malassezia furfur (yeast)
Disease of the skin
Staphylococcus aureus causes a variety of disease
Grapelike arrangement of staphylococci
Virulence factors include enzymes, structures to evade phagocytosis, and toxins
Staphylococcal Scalded Skin Syndrome
Certain strains of S. aureus secrete exfoliative toxins (toxemia) that cause dissolution of epidermal desmosomes
Cause staphylococcal scalded skin syndrome (SSSS), in which the epidermis peels off in sheets
Person-to-person spread
The bacterium penetrates cuts and abrasions
Susceptible patients
Infants, elderly, immunosuppressed patients
Fluid in blisters does not contain S. aureus
Impetigo (Pyoderma)
Contagious skin disease caused by S. aureus or Streptococcus pyogens
Red patches pus filled vesicles (from which bacteria spread – vesicles of impetigo are diagnostic) honey-colored crusts
Epidemics of impetigo in nurseries are of particular concern
Person to person contact or via contaminated fomites
Invade through scratches, abrasions, cold sores
Necrotizing Fasciitis
Commonly caused by S. pyogenes (“flesh eating strep”), the bacterium digests muscle fascia
Person-to-person contact Bacteria enter through breaks in
the skin Intense pain and swelling at
the site of infection Rapid destruction of tissue
within hours
Removal of necrotic tissue Immediate intravenous broad-
spectrum antimicrobial drugs
About 15% of patients die
Burn patients and Pseudomonas aeruginosa infection
The surface of almost two-thirds of burn victims develops infection by this opportunistic pathogen
Pyocyanin discoloration indicates massive infection caused by P. aeruginosa
Treatment requires debridement Administration of a combination of antimicrobial drugs
Rocky Mountain Spotted Fever
Tick
Transmitted by infected tick from salivary glands
Caused by Rickettsia rickettsii (Gram negative, obligate intracellular rod-shaped bacterium) Rickettsia infects cells lining small
blood vessels where it replicates
Infected cells release Rickettsia (Genus: Dermacentor)
Non-itchy, spotted rash on the trunk and appendages, soles, palms
Can develop into petechiae (subcutaneous hemorrhages)
Rocky Mountain Spotted Fever
Damage to blood vessels
Blood escapes, causing low blood pressure, insufficient oxygen and nutrients to the body’s organs
~ 5% of patients die even with treatment
Life-threatening acute RMSF may involve paralysis and secondary infection by Clostridium perfringens
Number of cases of Rocky Mountain spotted fever in the U.S., 1999-2009
Prevention involves protection against the tick (especially in spring and summer)
Gas Gangrene
Clostridium species - C. perfringens
Dead tissue from a traumatic event infected with endospores
Endospores will germinate
Toxins released by cells kill the surrounding tissue - necrosis (muscle and connective tissue), providing anaerobic conditions/nutrients
Blackening of the infected muscle/skin and gas production
Death can follow within a week of infection (Shock/coma)
Removal of dead tissue, antitoxins, antibiotics (and oxygen!)
(~40% mortality rate)
Cutaneous Anthrax and zoonosis
Antrax has three clinical manifestations Cutaneous Inhalation Gastrointestinal
Bacillus anthracis endospores shed by an infected animal come in contact with wounded skin (i.e., farmers) Painless, swollen, black, crusty ulcers called eschar(s)
Cells in the infected area die
Treated cutaneous antrax is rarely fatal (60 days of antibiotics) Prevention involves control of disease in animals (vaccination)
Viral diseases
Viral diseases are systemic
Spread by oral/respiratory routes, or contact (person-to-person contact/contaminated fomites)
Manifest signs and symptoms in the skin Smallpox (Variola virus) Herpes viruses (Herpes simplex virus) Papillomavirus (Warts) Chickenpox and shingles (Varicella zoster virus) German measles (Rubella) Red measles (Morbillivirus)
Poxyviruses (Smallpox)
In 1980 natural smallpox was declared eradicated
Concern about smallpox, It could be reintroduced accidentally from storage or through
bioterrorism Most people would be susceptible to smallpox epidemics
since regular vaccination was discontinued decades ago
Smallpox virus - dsDNA
Smallpox (Variola virus)
Transmitted by inhalation of virus in
droplets (aerosol) or dried crusts
The person is not contagious during the incubation period (12-14 days)
pox Stages of lesions of poxviral skin infections Also used to describe lesions
of other viral infections
Smallpox (Variola virus)
Immediate immunization of people exposed to smallpox virus prevents the disease from developing
No treatment exist once smallpox develops High fever Malaise Delirium Prostration
Herpes simplex viruses (dsDNA)
Human herpes virus HHV-1 and HHV-2
Infection occurs when viruses
invade the mucous membranes of lips, genitalia, broken skin of finger
Viruses may remain latent in nerve cells
Recurrent lesions
Cold sore (fever blister)
Primary HHV-1 infections typically occur during childhood Most HHV-2 infections are acquired between the age of 15-29 as a
result of sexual activity
The virus can cross the placenta infecting the fetus/more likely that a baby is infected at birth
No cure exist but drugs (acyclovir) can shorten outbreaks
Herpes simplex viruses
Active lesions are a source of infection
Papillomaviruses (dsDNA) – many different strains
Papillomaviruses cause warts (epithelial growth of the skin or mucous membranes)
Transmitted via direct contact (including sexual intercourse), childbirth, and fomites
Papilloma virus of genital warts has been linked to cervical cancer (vaccine)
Prevention of genital warts is possible by mutual monogamy
Chickenpox and shingles
Varicella-zoster virus (dsDNA) causes both chickenpox and shingles
Inhalation of virus, infection begins in the respiratory tract, spreads via blood (viremia) to skin
Viruses are shed before/during appearance of signs (droplets-aerosols and lesions)
Characteristic lesions on the
back/trunk, face/neck Macule, papule, vesicle, crust
CDC recommends vaccination
Chickenpox (Varicella) and shingles
Chickenpox virus can become latent
Stress, aging, immunosuppression can reactivate the virus
Producing a painful skin rash known as shingles or herpes zoster (15-20% of adults)
Chickenpox in adults is more severe, it may require hospitalization A person can acquire chickenpox from a shingles patient
Rubella - (Also known as German measles) -ssRNA
Mild rash (macula) in children
Infections in adults are more severe (arthritis/encephalitis)
The virus crosses the placenta
Rubella infections of pregnant women during the first months results in birth defects, including deafness, blindness or mental retardation
Live, attenuated vaccine against rubella is part of the MMR
Measles - (rubeola or red measles) – Morbillivirus - ssRNA
Transmitted by respiratory route
Lesions called Koplik’s spots
on the mucous membrane of the mouth provide a diagnosis of measles
Macopapular skin lesions spread over the body, which gradually turn brown
Live, attenuated vaccine (MMR)
Complications include SSPE: progressive disease of the central nervous system, which
begins 1-10 years after the initial infection, resulting in death Afflicts less then 7 patients/1 million as a result of childhood
immunization
Measles - (rubeola or red measles) - Morbillivirus
Superficial Mycoses
Affect outer skin layers, hair shafts Direct contact with hyphae/spores of opportunistic fungi
Black piedra – Piedra hortae
Hyphae and spores on hair shafts
Cutaneous mycoses
Cutaneous infections caused by fungi that grow in the skin Keratin in dead layers of skin, nails, hair is used as a nutrient Rarely become systemic
Athlete’s foot
Tineas (ring worm) Pityriasis versicolor caused by Malassezia furfur, interference with melanin production
Oral Candidiasis
Factors include: antibiotic therapy, an immunocompromised condition (AIDS), diabetic patients ….
Caused by Sporotrix schenckii introduced into the skin by thorn pricks or wood splinters (gardeners, farmers, and artisans)
Enters lymphatic system near the site of a primary lesion, it remains in subcutaneous tissues and it does not enter the blood
Topical applications of potassium iodide for months
Lymphocutaneous sporotrichosis
Sporotrichosis, subcutaneous mycoses
Diagnosis Patient’s history Clinical signs Dimorphic nature
of Sporotrix
Transmitted via prolonged bodily contact or by sharing clothing ….
Sexual transmission is common
Scabies is caused by a mite called Sarcoptes scabiei
Epidemics: people in crowded conditions such as hospitals, nursing homes, prisons
Treatment: mite-killing lotions, cleaning of contaminated items (hot water and hot dryers )
Prevented only by good personal hygiene!!
Intense itching and rash
Disease of the nervous system
The CNS is an axenic environment, it has no normal microbiota
Pathogens can gain access to the nervous system Breaks in the bones/meninges Medical procedures (spinal taps) Penetration of the blood-brain barrier leading to
meningitis
Pathogens Can infect cells of the nervous system Release toxins that affect neurons
Nervous system
Diseases of the nervous system
Bacterial diseases Bacterial meningitis Neurological diseases caused by bacterial toxins
(botulism and tetanus)
Viral diseases Viral meningitis (enteroviruses) Poliomyelitis Rabies Arboviral encephalitis
Fungal disease (yeast)
Cryptococcosis (cryptococcal meningitis)
Respiratory droplets from infected individuals
Streptococcus pneumoniae pneumococcal meningitis
Neisseria meningitidis meningococcal meningitis
Haemophilus influenzae, type b
Newborns-passage through an infected birth canal
Streptococcus agalactiae
Contaminated food (unpasteurized milk, cheese, raw vegetables or meat) – Transfer to fetuses
Listeria monocytogenes listeriosis
Bacterial Meningitis
Bacterial Meningitis
Bacteria spread to the meninges via blood (bacteremia)
Bacterial meningitis is characterized by High fever and inflammation of the meninges (cranial/spinal) High number of white blood cells in the CSF Severe headache, nausea/vomiting, pain Drowsiness, confusion
If the brain becomes infected (encephalitis), it can lead to deafness,
blindness, coma or death
Bacterial Meningitis
Rapid treatment reduces mortality below ~ 15% of cases
CDC recommends vaccination of children against H. influenzae type b, S. pneumoniae, N. meningitidis
Diagnosis involves detection of pathogens in CSF (spinal tap) – High number of leukocytes
Treatment: Intravenous administration of antibiotics
Viral Meningitis
Viral meningitis (aseptic meningitis) is the most common form of meningitis
Mostly caused by enteroviruses (RNA viruses - cytolytic)
Spread via the bloodstream (viremia) to the meninges Coxsakie A virus Coxsakie B virus Echovirus
Transmission: Fecal contamination of food, water, or hands
(intestinal tract)/Respiratory droplets (lungs) 1/1000 develop viral meningitis
Diagnosis: Signs/symptoms characteristic of meningitis but absence of bacteria in CSF - No specific treatment exist for viral meningitis
Cryptococcosis affects healthy people and immunocompromised hosts (AIDS patients)
Signs and symptoms common to bacterial meningitis - with a high mortality rate
Cryptococcus neoformans is an encapsulated yeast
Transmitted by inhalation of dried, contaminated droppings (pigeon/chicken)
Diagnosis/treatment involve detection of antigens in CSF and serum/Antifungal drugs
Cryptococcal meninigitis
Arboviral (Arthropod-born viruses) encephalitis
Transmission of six encephalitis arboviruses
Zoonotic diseases, typically affect birds, horses, rodents
Seasonal incidence related to the mosquitos
Arboviral (Arthropod-born viruses) encephalitis
WEE-Western equine encephalitis EEE-Eastern equine encephalitis VEE-Venezuelan WNV-West Nile virus St. Louis encephalitis California encephalitis
Diagnosis involves detection of arboviral antigens in the CSF
Signs and symptoms are similar to those of bacterial meningitis
Treatment No specific treatment exist for
arboviral encephalitis but supportive care
Human West Nile virus encephalitis in the US Can be transmitted between people (blood transfusion and
transplanted organs) Treatment is supportive/No human vaccines approved Limiting contact with mosquito (many different species!!)
Neurological diseases caused by bacterial toxins
Botulism is caused by Clostridium botulinum
Foodborne botulism (intoxication) Ingestion of botulism toxin in contaminated food
Wound botulism Growth of the bacterium in dead tissue following introduction of
endospores into wounds
Death: 10% of hospitalized patients
Neurological diseases caused by bacterial toxins
The neurotoxins prevents muscular contraction (skeletal muscle cells), leading to flaccid paralysis
Neurological diseases caused by bacterial toxins
Infant botulism (usually infants under 6/12 months of age) - most common cause in US
Treatment of botulism includes: administration of immunoglobulins that neutralize the toxin (BIG-IV), washing of intestinal tract to remove Clostridium, antimicrobial drugs to kill the bacterium
Death rate: less than 1% of hospitalized children
Neurological diseases caused by bacterial toxins
Tetanus is caused by Clostridium tetani
Endospores enter through breaks in the skin - cuts or punctures
Cells release a toxin called tetanospasmin
Axonal transport carries the toxin to the CNS
Initial diagnostic sign is the tightening of the jaw and neck muscles Progression involves continuous muscle contraction Contraction of the diaphragm leads to final inhalation
“Lollipop” endospores
Tetanus is caused by Clostridium tetani
Treatment Cleansing of wounds to
remove spores Passive immunotherapy
with HTIG Active immunization with
tetanus toxoid (DTaP vaccine)
Antibiotics
Widespread immunization has led to a decline in tetanus incidence in US
Poliomyelitis is caused by an enterovirus called Poliovirus
Most often transmitted by drinking contaminated water
Poliovirus travels to infect neurons of the CNS
Asymptomatic infections – almost 90% of cases
Minor polio – nonspecific symptoms
Nonparalytic polio – muscle spasms and back pain
Bulbar poliomyelitis A form of paralytic polio The brain stem is infected Paralysis of respiratory
muscles or of muscles in the limbs
Complete recovery or paralysis that is lifelong
“Iron lungs” – before 1955
Viral disease of the nervous system - Poliomyelitis
The disease has spread in recent years beyond the borders of endemic Countries (India, Nigeria)
Viral disease of the nervous system – Rabies (ssRNA)
Rabies is a zoonosis, transmitted to human via a bite/breaks in the skin or mucous membranes - viruses are secreted in the saliva
Reservoirs include dogs and cats, foxes, skunks, raccoons, bats
Replicates in skeletal muscle cells, travels to the CNS: function of the brain/spinal cord degenerates
Neurological manifestations characteristic of rabies include Hydrophobia Hallucinations Paralysis (respiratory paralysis
is associated with death)
Viral disease of the nervous system – Rabies
Postmortem laboratory tests include identification of aggregates of rabies viruses in cells of the cerebellum
Postexposure prophylaxis (PEP)/Treatment: immediate cleansing of the wound, passive immunization, and active immunization before onset of clinical symptoms
Control involves immunization of people who regularly come in contact with wild animals