Hydroa vacciniforme (HV) is a very rare, chronic photodermatitis-type skin condition with usual onset in childhood.

[3] Hydroa vacciniforme is commonly associated with reactivation of a latent Epstein–Barr virus (EBV) formerly acquired by an asymptomatic or infectious mononucleosis-causing infection.

In contrast out of 11 severe patients in this study, 6 had evidence of chronic EBV infection, 5 had hypersensitivity to mosquito bites, 4 had virus-associated hemophagocytic syndrome.

[6] Histology of the affected area commonly shows dense perivascular lymphocytic infiltration with reticulated degeneration of the epidermis.

A study by Iwatsuki et al. detected Epstein–Barr virus (EBV) positive T-cells in the perivascular infiltration on biopsy in 28/29 patients tested.