What causes pityriasis rosea and how is it transmitted?

Causes and Transmission of Pityriasis Rosea

Pityriasis rosea is most likely caused by the endogenous systemic reactivation of human herpesvirus (HHV)-6 and/or HHV-7, though it is not considered contagious through direct person-to-person contact. 1, 2

Viral Etiology

• Pityriasis rosea is strongly associated with the reactivation of human herpesviruses, particularly HHV-7 and HHV-6, which have been implicated as causative agents in multiple studies 1, 2
• The disease follows a distinctly programmed clinical course and typically does not recur in most patients, supporting an infectious etiology 3
• The viral load of HHV-6 and HHV-7 in plasma is higher in patients with classic pityriasis rosea compared to those with limited manifestations (herald patch only) 2

Evidence Supporting Infectious Cause

• Temporal clustering of cases has been observed, suggesting an infectious trigger 3
• Seasonal variation in incidence and association with respiratory tract infections provide additional evidence for an infectious etiology 3
• Recent research has identified cases of pityriasis rosea following COVID-19 infection, suggesting that SARS-CoV-2 might trigger the condition either directly or by inducing reactivation of latent herpesviruses 4

Transmission Characteristics

• Despite its infectious etiology, pityriasis rosea is not considered highly contagious through direct person-to-person contact 1
• The condition appears to result from reactivation of latent viruses rather than primary infection 2
• Some epidemiological studies have noted associations with:
  • Unfavorable social and economic backgrounds 3
  • History of contact with other pityriasis rosea patients in some cases, though this is not the predominant pattern 3

Clinical Presentation and Course

• The disease typically begins with a single "herald patch" (larger and more noticeable than subsequent lesions) in approximately 80% of patients 1
• A generalized bilateral, symmetrical eruption develops 4-14 days after the herald patch, with lesions continuing to appear over 12-21 days 1
• Typical lesions are oval or elliptical, dull pink or salmon-colored macules with a delicate collarette of scales at the periphery 1
• The condition is self-limiting with a typical course of 6-8 weeks 1

Risk Factors

• Age: Primarily affects individuals between 10 and 35 years, with peak incidence during adolescence 1
• Recent viral infections: May follow respiratory infections or other viral illnesses 3
• Recent research suggests COVID-19 infection may trigger pityriasis rosea in some individuals 4

Important Clinical Considerations

• A mild prodrome consisting of headaches, fever, malaise, fatigue, anorexia, sore throat, enlarged lymph nodes, and arthralgia is present in about 5% of patients 1
• The condition can be misdiagnosed, particularly when the herald patch is absent or when atypical variants occur 1
• While rare, pityriasis rosea during pregnancy may require closer monitoring and potential treatment due to possible complications 1, 5

Pityriasis rosea remains an interesting dermatological condition where the exact pathophysiological mechanisms are still being elucidated, though the evidence strongly points to viral reactivation rather than a primarily contagious disease transmitted through direct contact.