Ch 19: Infections of the Skin and Eye

Skin

• The largest human organ

• 16-22 square feet

• effective barrier for blocking microbial access to deeper tissues

Epidermis

• Superficial

• Five layers

• Consist of dead keratinocytes

• Keratinocytes make the structure protein—keratin

Dermis

• deep layer

• connective tissue

• blood vessels, nerves, hair follicles, sweat glands

Skin rash

• change in color and texture of the skin

• usually caused by an infectious agent, such as a virus, and represent a reaction to a toxin produced by the organism, damage to the skin by the organism, or an immune response

Exanthem

Widespread skin rash accompanied by systemic symptoms (fever, malaise, headache)

Enanthem

Rash on mucous membranes

Macular rash

• flat and red

• less than 1 cm in diameter

Papular rash

small, solid, and elevated lesion called a papule

Pustular rash

a papule filled with pus

Maculopapular rash

a reddened papule

Vesicular rash

small blisters are formed

Mucous membranes

• epithelial

• serve as a barrier (protection)

• Line the inside of the body

• Continuous with the skin in several places

• Not all produce mucous

External structures of the eye

• eyelids, cornea, lens, iris, pupil, sclera

• covered with conjunctiva

Internal structures of the eye

retina, macula, vitreous humor

Measles/Rubeola/first disease

• Viral infection of the skin

• Negative-sense, single stranded RNA virus

• very contagious (8-10 day incubation period)

Measles/Rubeola/first disease portal of entry

• respiratory or conjunctiva

• Replicates in the lungs

  • moves to regional lymph nodes

  • produces a viremia (virus in blood) that spreads throughout the body

Measles/Rubeola/first disease symptoms

• prodromal period starts with cold/flu-like symptoms

• high fever (104 F)

• Koplik’s spots: white spots on the buccal mucosa (inner cheeks), only in measles

• maculopapular rash

• tiredness, low appetite, conjunctivitis, descending rash

German Measles/Rubella/Third Disease

• Viral infection of the skin

• Also called 3-day measles, rash similar to measles

• pronounced eliminated from the US in 2004 but still endemic in many parts of the world

German Measles/Rubella/Third Disease portal of entry

• inhalation of aerosolized respiratory particles

• replicates in the cytoplasm of cells lining the nasopharynx and nearby lymph nodes

• viremia ensues during the 12-23 day incubation period

German Measles/Rubella/Third Disease symptoms

• Pinpoint maculopapular pink rash caused by host immune response

  • appears on head and spreads to the body and extremities

  • does not darken or scab over

  • spreads fast

  • short duration of 1-3 days

• Low grade fever

• enlargement of head and neck lymph nodes

• mild, subclinical, and self limiting

  • more difficult in adults and can lead to joint pain, bacterial superinfections, birth defects

• MMR vaccine

Fifth Disease/Erythema Infectiosum

• Viral infection of the skin

• Human parvovirus B19

Fifth Disease/Erythema Infectiosum portal of entry

• respiratory tract

• viral attachment to and replication in erythrocyte progenitor cells

• viremia within 7-10 days

• bind P antigen (globoside, on the surface of RBCs and their progenitors

• The body responds by producing antibodies and cytokines (TNF-a, IFN-y, and interleukins 2-6)

Fifth Disease/Erythema Infectiosum Symptoms

• Prodromal symptoms coincide with viremia

  • mild fever, flu-like symptoms, arthralgia (joint pain)

• initial rash is pathogenomic (specific to fifth disease)

• Often described as a slapped-cheek rash

• rash followed by a red or gray papular enanthem on the palate or throat

• Third stage is a maculopapular rash that forms on body and limbs

  • looks like lace (reticular rash)

Roseola Infantum/Sixth Disease

• viral infection of the skin

• human herpes virus 6/7 (HHV-6; HHV-7)

• young children usually under 3 years

Roseola Infantum/Sixth Disease Transmission

• respiratory secretions or saliva

Roseola Infantum/Sixth Disease Symptoms

• 3-5 days of very high fever (over 104 F)

• Fever followed by sudden macular or maculopapular red rash that blanches (turns white) when touched

• Latent (hidden) in most people

Chickenpox

• viral infection of the skin

• Herpesviridae family

• Varicella-Zoster virus (VZV)

• initial exposure=chickenpox

  • virus remains latent in the dorsal root ganglia and re-emerges later in life in about 20% of patients which causes shingles (herpes zoster)

• Shingles occurs more often in older people because their cell-mediated immunity decreases

• Chickenpox and shingles are usually diagnosed clinically, but antibody and DNA tests can also be used to detect the virus

Chickenpox portal of entry

• inhalation of infected particles from skin lesions

• virus replicates in nasopharynx and infects the regional lymph nodes, leading to viremia

• 2nd round of replication occurs in liver and spleen followed by a secondary viremia 14-16 days postinfection

• VZV invades capillary endothelial cells in the deepest layer of epidermis which produces fluid accumulation and vesicle formation

Chickenpox symptoms

• usually no prodromal symptoms

• itchy rash on the face, back, chest, and belly

• maculopapules, vesicles, pustules, and scabs

Chickenpox latency

• can be life-threatening in immunocompromised patients

• latency established when viral DNA integrates into host DNA

• can last for decades

• virus infects the nerve endings of the skin

• travel along nerves to the ganglia where they lie in a dormant state

• Latent Virus reactivation: virus particles travel along the sensory nerves of the skin to produce a localized, painful, dermatomal rash known as shingles

Chickenpox treatment

• antihistamines, oatmeal baths, and calamine lotion to reduce intense itching

• acetaminophen to reduce pain and fever

• Acyclovir: used to treat shingles and severe cases of chickenpox

• Varicella vaccination: routine immunization in childhood, live attenuated form of VZV

• People 60 years and older should be vaccinated with zoster vaccine to prevent shingles

Cold sores and genital herpes