Chapter 18 INFECTIOUS DISEASES AFFECTING THE SKIN AND EYES

The diagnostic test for the enzyme __________ differentiates the staphylococci, which produce it, from the streptococci, which do not.

catalase, an enzyme that breaks down hydrogen peroxide accumulated during oxidative metabolism

The dermis is mainly composed of ___________ tissues

connectiveThe skin, together with the hair, nails, and sweat and oil glands, forms the integument

The general term for fungal infections of the skin, hair, or nails is __________

tinea; All these conditions have different names that begin with the word tinea (tin′-ee-ah), which derives from the erroneous belief that they were caused by worms.

Secondary infection of chicken pox skin lesions should be

treated with an antibiotic

Roseola is caused by __________.

Roseola is caused by a human herpesvirus called HHV-6.

A __________ agent causes damage to the developing fetus.

teratogenic; Rubella is a strongly teratogenic virus

Infections of the hair follicle.

Folliculitis, carbuncles, and furuncles (boils) are all infections of the hair follicle and are mainly caused by Staphylococcus aureus, although other microbes may be involved

Prevention of dermatophyte infections is most effectively accomplished by

-keeping susceptible areas dry -avoiding contact with dermatophytes

Signs and symptoms of Measles

-Dry cough, fever, swollen lymph nodes -Pharyngitis ("sore throat") -Conjunctivitis ("pinkeye") -Koplik's spots (red, irregular spots with blue-white centers on the oral mucosa) -Red, maculopapular rash; rash often starts at head/neck, then progresses to trunk and extremities -In a small number of cases, children develop laryngitis, bronchopneumonia, and BACTERIAL SECONDARY INFECTIONS such as ear and sinus infections. -The most serious complication is subacute sclerosing panencephalitis (SSPE), a progressive neurological degeneration of the cerebral cortex, white matter, and brain stem. Its incidence is approximately one case in a million measles infections, and it afflicts primarily male children and adolescents. The pathogenesis of SSPE appears to involve a defective virus, one that has lost its ability to form a capsid and be released from an infected cell.

In addition to transmission via direct contact, HPV can be trasmitted through _________, transfer from one part of the body to another.

autoinoculation

Cutaneous anthrax is caused by the bacterium _________ ___________

Bacillus anthracis.

Which skin layers are usually involved in Cellulitis?

Cellulitis is a condition caused by a fast-spreading infection in the DERMIS and in the SUBCUTANEOUS TISSUES below.

Describe fever seen in roseola?

Children exhibit a high fever (up to 41°C, or 105°F) that comes on quickly and lasts for up to 3 days. Fever precedes the rash.

The Gram-positive anaerobic endospore-former that causes gas gangrene is

Clostridium perfringens

What causes SSPE to occur in some cases of measles?

Defective virus that cannot for a capsid

Describe the virus that causes chickenpox and shingles

Enveloped DNA virus

In __________, bacteria enter the skin through a small break and cause blisters or swollen lesions accompanied by fever, shaking, and chills.

Erysipelas; Streptococcus pyogenes is the main cause of cellulitis, impetigo, and erysipelas.

Low _________ immunity, along with crowding, inadequate medical care, and malnutrition are factors that contribute to measles epidemics.

Herd immunity

SSSS is most effectively diagnosed through __________ examination of tissue from a __________

Histological; lesion

__________ is a superficial bacterial infection that causes the skin to flake or peel off.

Impetigo

Signs and Symptoms: Measles

In a small number of cases, children develop laryngitis, bronchopneumonia, and bacterial secondary infections such as ear and sinus infections

The smallpox rash begins in the __________, spreads to the __________, and processes to the __________.

Infection begins with fever and malaise; later, a rash begins in the pharynx, spreads to the face, and progresses to the extremities.

A large pustular lesion caused by protozoa and transmitted by sandflies is __________

LEISHMANIASIS, a zoonosis transmitted among various mammalian hosts by female sand flies. This infection can express itself in several different forms depending on which species of the protozoan Leishmania is involved.

Sebum protects the skin by inhibiting the growth of microorganisms because of its:

LOW PH; The sebaceous glands' secretion, called sebum, has a low pH, which makes the skin inhospitable to most microorganisms. Sebum is oily due to its high concentration of lipids. The lipids can serve as nutrients for normal microbiota, but breakdown of the fatty acids contained in lipids leads to toxic by-products that inhibit the growth of microorganisms not adapted to the skin environment. This mechanism helps control the growth of potentially pathogenic bacteria

Once infected with HHV-3, individuals will have _________ immunity to the virus due to memory B and T cells, although the virus persists in nerve ganglia.

Lifelong; Some people experience subclinical cases of the disease, meaning that lesions never appear. They will still develop lifelong immunity and will likely harbor the virus in their ganglia, making them subject to shingles in the future.

Which components of S. pyogenes allow it to adhere to host tissue?

M-protein and other proteins, Lipoteichoic acid (LTA), and a hyaluronic acid capsule

Measles, rubella, fifth disease, and roseola are classified as

Maculopapular Rash Diseases

The sloughing of the stratum __________ contributes to the protection of the skin by removing microbes with the dead cells.

Millions of cells from the stratum CORNEUM slough off every day, and attached microorganisms slough off with them.

Impetigo (Epidemiology)

Most common group to get Impetigo infections is children because they are not exactly vigilant about washing their hands as they run about. S. aureus and S. pyogenes can spread through direct contact with the lesions or on fomites. Highly contagious.

Infection with smallpox confers __________ immunity

People who have survived any form of smallpox nearly always develop lifelong immunity.

The Gram reaction for Staphylococcus aureus is Gram-__________

Positive

These positively charged chemicals reduce the number of pathogens on the skin by disrupting their cell membranes

Small molecules called antimicrobial PEPTIDES have been identified in epithelial cells. These are positively charged chemicals that act by disrupting (negatively charged) membranes of bacteria. There are many different types of these peptides, and they seem to be chiefly responsible for keeping the microbial count on skin relatively low.

Causative agent of SSSS

Staphylococcus aureus

Possible causative agents of impetigo?

Streptococcus pyogenes and Staphylococcus aureus

How does sweat defend the skin against pathogens?

Sweat is inhibitory to microorganisms because of both its LOW PH and its HIGH SALT CONCENTRATION. LYSOZYME is an enzyme found in sweat (and tears and saliva) that specifically BREAKS DOWN PEPTIDOGLYCAN, a unique component of bacterial cell walls; -It contains an enzyme that breaks down peptidogylcan in the cell walls of bacteria -It causes the skin pH to be too low to support most bacterial growth. -It causes the skin to have a high salt concentration which inhibits bacterial growth.

Hand, foot, and mouth disease is transmitted through direct contact

TRUE

The causative agent for Fifth disease if __________ __________

The causative agent is parvovirus B19

The variola virus, a member of the Orthopoxvirus genus, is a(n):

The causative agent of smallpox, the variola virus, is an orthopoxvirus, an ENVELOPED DNA VIRUS.

In addition to observation of clinical presentation of symptoms, measles is diagnosed using __________.

The disease can be diagnosed on clinical presentation alone; but if further identification is required, an ELISA test is available that tests for patient IgM to measles antigen, indicating a current infection.

The incubation period for warts is

The incubation period can be from 1 to 8 months. Almost all nongenital warts are harmless, and they tend to resolve themselves over time.

Causative Agent: Measles

The measles virus is a member of the Morbillivirus genus. It is a single-stranded, enveloped RNA virus in the Paramyxovirus family.

What is the role of staphylococcal exotoxins A and B in causing impetigo?

The most important virulence factors relevant to S. aureus impetigo are exotoxins called exfoliative toxins A and B, which are coded for by a phage that infects some S. aureus strains. At least one of the toxins ATTACHS A PROTEIN THAT IS VERY IMPORTANT FOR EPITHELIAL CELL-TO-CELL BINDING IN THE OUTERMOST LAYER OF THE SKIN. Breaking up this protein leads to the characteristic blistering seen in the condition.

What are four methods often used to determine the causative agent in dermatophyte infections.

The presenting symptoms of a cutaneous mycosis occasionally are so dramatic and suggestive of these genera that no further testing is necessary. In most cases, however, direct MICROSCOPIC EXAMINATION and CULTURING are required. Diagnosis of tinea of the scalp caused by some species is aided by use of a long-wave ultraviolet lamp that causes infected hairs to fluoresce. Samples of hair, skin scrapings, and nail debris treated with heated potassium hydroxide (KOH) show a thin, branching fungal mycelium if infection is present.

Ringworm (Cutaneous Mycoses): A group of fungi collectively termed dermatophytes causes a constellation of integument conditions. These mycoses are strictly confined to the nonliving epidermal tissues (stratum corneum) and their derivatives (hair and nails).

The presenting symptoms of a cutaneous mycosis occasionally are so dramatic and suggestive of these genera that no further testing is necessary. In most cases, however, direct microscopic examination and culturing are required

What populations are most at risk for hand, foot, and mouth disease?

This disease is most common in babies and children under the age of 5

Mode of transmission: Fifth Disease

This infection is very contagious. It is transmitted through RESPIRATORY DROPLETS or even DIRECT CONTACT. It can be transmitted through the placenta (VERTICAL TRANSMISSION), with a range of possible effects from no symptoms to stillbirth. There is no vaccine and no treatment for this usually mild disease.

MRSA (methicillin-resistant Staphylococcus aureus)

This red, raised, tender, hot to the touch lesion with pus is typical of lesions caused by

The smallpox vaccine is based on the _________ virus.

To this day, the vaccination for smallpox is based on the VACCINIA virus

Shingles develops abruptly after the __________ virus is reactivated by stimulus such as psychological stress, X-ray treatments, immunosuppresive or other drug therapies, surgery, or a developing malignancy.

Varicella

The peeling of the epidermal tissue layers in SSSS is referred to as

desquamation

Impetigo is most commonly transmitted by __________ and __________.

direct contact; fomites

In gas gangrene, a low-oxygen environment stimulates

endospore germination

What are the established mechanisms by which microbes enter the body to cause cellulitis?

entry through breaks in tow skin caused by athlete's foot; traumatic entry into the dermis layer of skin. Cellulitis generally follows the introduction of bacteria or fungi into the dermis, either through trauma or by subtle means (with no obvious break in the skin). Cellulitis is very common on the lower leg, and it is thought the bacteria can enter through breaks in the skin between the toes caused by fungal infection (athlete's foot).

Fifth disease is more precisely termed __________

erythema infectiosum; Also called "slap-cheek disease" Fifth disease, more precisely called erythema infectiosum, is so named because about 100 years ago, it was the fifth of the diseases recognized by doctors to cause rashes in children.

Prior to its eradication in the 1970's, __________ usually contracted smallpox.

everyone

Like other _________ viruses, HHV-3 is an enveloped DNA virus

herpes

What is the most common age group to experience SSSS infections?

infants; Although children and adults can be affected, SSSS develops predominantly in newborns and babies. Newborns are susceptible when sharing a nursery with another newborn who is colonized with S. aureus.

The skin, together with the hair, nails, and sweat and oil glands, forms the

integument

Methicillin-resistant Staphylococcus aureus is resistant to

multiple antibiotics

The dermis of the skin contains __________, __________ and __________ glands

sebaceous, scent, sweat

The painful, tender rash characteristic of shingles can last for

several months

Zostavax is a vaccine to prevent _________

shingles

Impetigo

superficial skin infection that leads to skin peeling, flaking, or blistering. There are two common gram-positive bacteria that cause impetigo, Staphylococcus aureus or Streptococcus pyogenes. Both S. aureus and S. pyogenes produce a wide variety of toxins and enzymes that can break down the connective tissues. Hyaluronidase, breaks the tight junctions between cells. Adhesion molecules are an virulence factor and S. pyogenes has one specific adhesion molecule called M-protein. This adhesin is unique because it also protects the organism from phaocytosis.