• Viral rashes are often caused by immune reactions to the virus and cell damage caused by the virus.
• A key bacterial cause of rash is Streptococcus pyogenes, which causes Scarlet Fever.

Helpful distinguishers between the viral exanthems:

• We can categorize them by the initial location and pattern of the rash.
  – Three viral exanthems tend to initiate on the face:
  Measles, rubella, and erythema infectiosum.
  – Chickenpox arises on the face/scalp and trunk.
  – Roseola infantum typically first appears on the trunk
  – Hand, Foot, and Mouth disease produces rash on the hands and feet, in the mouth.

Be aware that these are meant to be helpful generalizations, and may not always hold true; for example, hand, foot, and mouth disease can also produce rash on the buttocks.

• Rash types:
  – Multiple rash types can exist at once.
  – Macules are flat, colored spots on the skin.
  – Papules are solid, raised areas; larger papules are called nodules.
  – Vesicular rashes comprise raised “pockets” of fluid in the skin.

• The timing of the rash and presence of other symptoms can also help distinguish among the exanthems.
  – For example, some infections are associated with fever, malaise, and respiratory symptoms.
  – Knowing the time lapse between virus introduction and symptom appearance can also help, although the incubation periods of the various viruses often overlap and may include a wide range.

VIRAL EXANTHEMA

Hand, foot, and mouth disease:

• Usually caused by Coxsackievirus A.
• Average incubation period of 3-6 days.
• Most common in children younger than 5.
• As its name suggests, hand, foot, and mouth disease is characterized by a rash that can be macular, maculopapular, or vesicular on the hands, feet, and in and around the mouth.

Erythema infectiousum, aka, Fifth Disease

• Caused by Parvovirus B19.
• Average incubation period of 7 days
• Tends to affect children 5-15 years old.
• Initial symptoms can include fever, runny nose, headache; diarrhea is also possible.
• These flu-like symtpoms are followed by a malar facial rash that spreads to the trunk and extremities.
  – Facial rash takes on a characteristic “slapped cheeks” pattern, whereas the rash on the extremities often comprises maculopapular rash in a “lacy” pattern.

Roseola infantum, aka, exanthema subitum

• Most commonly caused by Human Herpes Virus 6, and sometimes Human Herpes Virus 7.
• Roseola infantum is also sometimes called “6th disease”, because it was the 6th exanthema identified (erythema infectiosum was the fifth).
• Average incubation period is 9 days.
• Although disease can occur in a wide range of ages, it most commonly affects children younger than 2 years old.
• Initial symptoms include a very high fever (exceeding 104 degrees Fahrenheit/40 degrees Celsius).
  – The fever lasts approximately 3 days, which is why Roseola infantum is sometimes called “3-Day Fever”.
• Macular or maculopapular “blanching rash” arises first on the trunk.
  – “Blanching rash” means that when the skin is pressed upon, often with a clear glass, the rash fades from red to pale.
• Another common finding are red uvulopalatoglossal spots, aka, Nagayama spots,.
• A range of other symptoms, including gastrointestinal, respiratory, ocular, and auditory problems, can occur.
• Febrile seizures are a common complication in roseola infantum.

Chickenpox

• Caused by Varicella-Zoster virus (aka, Human Herpes Virus-3)
• Average incubation period is 16 days.
• Often affects children younger than 5.
• Prior to rash, patients may experience fever, malaise, sore throat, and low appetite.
• Rash is characterized by crops of lesions that pass through macular, vesicular, and crusted phases.
  – Lesions usually first appear on the head/neck, and spread to the rest of the body.
• Clinical correlation: Shingles is an illness that occurs in adults upon reactivation of the Varicella-Zoster Virus; the reactivated virus is called Herpes-Zoster Virus.
  – Whereas the chickenpox rash is often itchy, the shingles rash can be very painful. Vaccination against Varicella-Zoster virus also prevents shingles.

Measles (aka, rubeola)

• Caused by the Measles virus.
• Average incubation period is 14 days.
• Prior to rash, patients often experience Fever and the “Three C’s”: Cough, Coryza (runny nose), and Conjunctivitis.
• These symptoms are followed by a *maculopapular rash that begins on the face and neck and spreads.
• Before the body rash, many patients also develop Koplik spots, which are spots along the palate and internal buccal surfaces (these spots are sometimes calked Koplik’s sign).
• Serious complications from measles virus infection include potentially fatal pneumonia and encephalitis; vaccination helps to prevent these and other complications.

Rubella (aka, German measles)

• Caused by Rubella virus.
• Average incubation period is 14 days.
• Rubella is characterized by the acute onset of a pink maculopapular rash that begins on the face and spreads.
  – The rash lasts about 3 days, so Rubella is sometimes called “3-Day measles” – careful not to confuse this with Roseola infantum, which is sometimes called “3-Day Fever.”
• Some patients also have swollen lymph nodes in the neck area; systemic symptoms, such as headache, are mild if present.
• Congenital rubella, which is contracted during fetal development, is associated with severe birth defects; this form of rubella can also be prevented by the rubella vaccine.