Many of you might be wondering if herpes zoster or shingles is contagious. We would like to further explain it here. Before we talk about shingles, let me tell you shingles is caused by Varicella Zoster Virus, the same virus that causes chickenpox.
Chicken pox is primary infection cause by varicella zoster virus that is highly contagious and spread rapidly. After the primary attack the virus stays in latent state in ganglion cells of dorsal nerve or cranial nerve roots for several years and is noninfectious. Later when there is decrease cell-mediate immunity, that may be due to old age, trauma, stress, sunburn or any other disease, the virus reactivates to cause secondary infection called as shingles or zoster.
Although less contagious then primary varicella (chickenpox), shingles can still be highly contagious between the periods of rash eruption and crusting and dryness. During this infectious period shingles lesion contains high concentration of VZV that can transmit via airborne route[1,2] and cause chickenpox in susceptible individual (those individuals who have not had chickenpox before, especially child and immuno-compromised patients).
For those who have already had chickenpox during their childhood or at any time, shingles cannot be acquired by contact with other person with chickenpox or shingles. However one may have risk of developing shingles later in their life. The risk of developing shingles is determined by factors that influence the host-virus relationship.
Person with localized zoster are thought to be less contagious if the lesion are covered. After all the blisters are crusted and dried, the virus is no longer contagious and can no longer spread.
References:
1.Josephson A, Gombert ME. Airborne transmission of nosocomial varicella from localized zoster. J Infect Dis 1988;158:238–41
2.Sawyer MH. Chamberlin CJ. Wu YN. Aintablian N. Wallace MR. Detection of varicella-zoster virus DNA in air samples from hospital rooms. J Infect Dis 1994;169:91–4.