Herpes simplex virus (HSV)

• Virus that causes cold sores (HSV 1), and genital herpes (HSV 1 or 2).
• Most people infected with HSV are asymptomatic and don’t get recurrences.
• Genital herpes during pregnancy should be discussed with a specialist.

• Genital herpes has been typically associated with HSV 2 infection, however HSV 1 is also responsible for a significant proportion of genital infection.
• HSV 2 tends to recur more frequently than HSV 1, but be less severe.

• Testing recommended for a first episode of genital herpes to establish the diagnosis.
• Testing not required for recurrences of genital herpes, or for cold sores, unless atypical features with a potential differential diagnosis.
• Mimics to consider: syphilis if genital ulcer (although syphilis generally painless).

Request HSV PCR

Viral swab of base of lesion for HSV PCR (need to obtain vesicle fluid or cellular material on swab)

• Good sensitivity – a negative result on an adequately collected sample makes the diagnosis very unlikely
• Excellent specificity – a positive result confirms the diagnosis

Note: swabs run for HSV PCR in our laboratory are run for VZV PCR in parallel, as these viruses can mimic each other.

Serology

• Has a very limited role in the diagnosis of HSV.
• Having positive HSV serology is common in the general population. A positive serological test cannot confirm that a lesion is due to HSV.
• Serology usually takes many weeks to become positive after primary infection, so is not useful for diagnosis in this context.
• The NZ Herpes Foundation recommend education rather than HSV serology in partners of positive patients due to false positive and negative results seen with HSV serology.
• Serology is indicated in pregnant women with a possible first episode of genital herpes from 30 weeks gestation, as it helps inform prophylaxis strategies to prevent neonatal infection.