Chapter 19
Infectious Diseases Affecting the Skin and Eyes
19.1 Structure and Function of the Skin
• The skin protects underlying tissues from microbial colonization
• Each layer performs specific activities
• Epidermal dendritic (Langerhans) cells
• Antigen-presenting cells
• Macrophages
• Sebaceous glands
• The skin harbors endogenous microbes
• The human resident microbiota of the skin helps protect deeper tissues
from infection
• “Coryneforms”
• Propionibacteria
• Species associated with nosocomial infections
• Dimorphic fungi
19.2 Skin Infections Caused by Endogenous Microbiota
• Acne is the most common skin disease in the world
• Acne is a chronic inflammatory condition involving Propionibacterium
acnes
• Endogenous microbiota can form biofilms
• Skin wounding through surgery can introduce endogenous microbes
• Other skin infections can result from resident microbiota
• Warm, humid climates can lead to endogenous skin infections
• Pityriasis versicolor
19.3 Skin Diseases Caused by Bacteria
• Staphylococcal contact diseases
have several manifestations
• Localized skin infections
• Abscess
• Furnuncle
• Impetigo
• Toxin generated diseases
• Scalded skin syndrome
• Toxic shock syndrome (TSS)
• Streptococcal diseases can be mild to severe
• Group A streptococci attach to cells and secrete toxins
• 2 classification systems
• Hemolytic groups
• Alpha-hemolytic
• Beta-hemolytic
• Gamma-hemolytic
• Variants of cell wall carbohydrates
• Group A streptococci (GAS)
• Group B streptococci
•
Group A streptococci
• Streptococcal pharyngitis
• Strep throat
• Cellulitis
• Erysipelas
• Streptococcal toxic shock syndrome
• Necrotizing fasciitis
• Other wounds also can cause skin infections
• Traumatic wounds to the skin surface can lead to localized infections
• Gangrene
• Gas gangrene or myonecrosis
• Cutaneous anthrax
• Wound cellulitis
• Animal bites can puncture the skin
• Bacterial disease can arise from animal bites or scratches
• Pasteurellosis
• Cat-scratch disease (CSD)
• Rat-bite fever
19.4 Diseases of the Skin Caused by Herpesviruses
• Human Herpes Simplex Infections Are Widespread and Often Recurrent
• Cold sores are contagious sores caused by HSV-1
• After primary infection, the viruses become latent in sensory
ganglia
• Recurrence of cold sores occurs when viruses are reactivated and
move to the epithelium
• Chickenpox Is No Longer a Prevalent Disease in the United States
• A vaccine using attenuated viruses became available in 1995
• It is a highly communicable disease caused by the varicella-zoster virus
(VZV)
• It is transmitted by skin contact and respiratory droplets
• A red, itchy rash spreads across the entire body and turns into fluid-filled
vesicles
• The itchy vesicles break open and yield highly infectious virus-laden fluid
• The most common complication is bacterial infection of the skin
• Pneumonia, encephalitis, or Reye syndrome may also occur
Shingles is an adult disease caused by the same virus as chickenpox
• After infection, VZV can remain in nerve cells for many years
• If they are reactivated, they can travel to the body trunk and cause blisters
and patches of red
• It can also cause facial paralysis and severe “ice-pick” pains
• It can occur repeatedly
• Postherpetic neuralgia is the persistence of shingles pain
for years after the blisters have disappeared
• Human Herpesvirus 6 Infections Primarily Occur in Infancy
• It causes roseola infantum, marked by
• high fever
• subsequent red rash
• It is spread through
contact with respiratory
secretions or saliva
• Many bone barrow transplant recipients suffer an HHV-6 viremia after
transplantation
• Some researchers believe the virus lies dormant for years and may be
associated with multiple sclerosis later in life
• A Few Herpesvirus Infections Are Oncogenic
• The Epstein-Barr virus (EBV) and the human herpesvirus-8 (HHV-8) are
oncogenic
• Kaposi sarcomic is an angiogenic tumor of the blood vessel walls
• It is most commonly seen in immunocompromised individuals,
such as AIDS patients
• It is caused by HHV-8, forming dark or purple skin lesions
19.5 Other Viral Diseases of the Skin
• Paramyxovirus Infections Can Cause Typical Childhood Diseases
• Measles (rubeola) is a highly contagious disease caused by a member of the
Paramyxoviridae family
• Transmission occurs through respiratory droplets
• Koplik spots are red patches with white grain-like centers that
appear along the gum line
– They appear 2–4 days after the onset of symptoms
• The characteristic red rash begins as maculopapules at the hairline,
spreading to the
– face
– trunk
– extremities
• Complications include
– bacterial disease in the respiratory tissue
– panencephalitis
• Vaccine is given in the measles-mumps-rubella (MMR)
inoculation
• Rubella (German Measles) Is an Acute, Mildly Infectious Disease
• It is caused by a virus of the Togaviridae family
• It is transmitted by respiratory droplets or contact
• Symptoms of rubella include an occasional fever and pale-pink
maculopapular rash
• Recovery is usually prompt, but relapses can occur
• Congenital rubella occurs when the fetus is infected through the placenta
• Children may be born with problems in the
– eye
– ear
– heart
• Fifth Disease (Erythema Infectiosum) Produces a Mild Rash
• It is caused by a member of the Parvoviridae
•
•
Transmission occurs through respiratory droplets
Symptoms include a fiery red rash on the cheeks and ears, and trunk
• It disappears within a few days
• Adults can experience symptoms similar to those of rheumatoid arthritis
• Some Human Papillomavirus Infections Cause Warts
• Common warts are usually benign skin growths resulting from a specific
strain of HPV
• Plantar warts occur on the soles of the feet
• They can be transmitted by contact with
– an affected person
– a contaminated object
Poxviruses Have Had Great Medical Impacts
• Smallpox (variola) is contagious and sometimes fatal
• Pink-red macules appear on the face and trunk
• They then become papules and fluid-filled vesicles
• The vesicles become pustules that break open and emit puss, leaving pitted
scars (pocks)
• Vaccinations ceased in the United States in 1972 after eradication
occurred, so many people are not immune
• Smallpox is one of the most dangerous weapons of bioterrorism
19.6 Skin Diseases Caused by Fungi Parasites
• Dermatophytosis is an infection of the skin, hair, and nails
• Sporotrichosis is an occupational hazard
• Sporothrix schenkii forms subcutaneous lesions
• Leishmania can cause cutaneous infections
19.7 Structure and Function of the Eye
• Ocular infections involve external structures or internal sites
• The major defense mechanisms are tears and the conjunctiva
• The eye may contain an endogenous microbiota
• An ocular microbiota may help protect the eye from infection
19.8 Infectious Disease of the Eye
• Some bacterial eye infections can cause blindness
• Bacterial eye infections can involve the eyelid, cornea, or conjunctiva
• Bacterial conjunctivitis
• Trachoma
• A few viruses and parasites are associated with eye infections
• Viral and parasite eye infections involve the conjunctiva or cornea
• Viral pink eye
• Acute conjunctivitis
• Pharyngoconjunctival fever
• Acanthamoeba keratitis (AK)
• Ochocerciasis
– Intermediate host
– Definitive host
• River blindness