Varicella zoster virus
Pathogen: Varicella zoster virus/Human herpesvirus 3, a member of the herpes virus family that also causes chickenpox/varicella.VZV article
Category of pathogen: virus
Disease name: shingles/herpes zoster/zoster
Symptoms: The usual early sign is itching or pain in one particular area on one side of the body. After a few days, a rash of fluid-filled blisters appears in the area of the initial itch/pain.
shingles blisters
In certain cases, there may be pain/itching, but the number of blisters may be small or even absent altogether, making diagnosis more difficult. These cases are known as ‘zoster sine herpete’.
A video showing the development of shingles is here:
The narrow band-like appearance of the shingles rash on one side of the patient’s body often corresponds to one dermatome (an area/zone of the body surface innervated by sensory nerves that originate from a single dorsal root ganglion).
shingles eruption corresponding to one dermatome
Herpes zoster ophthalmicus occurs when re-activated VZV travels down the ophthalmic branch of the trigeminal nerve and involves the eye in addition to the face. In addition to the pain and itching of the rash, loss of vision can occur.
Herpes zoster oticus occurs when VZV re-activation involves the inner, middle, and outer ear. Rash occurs on the outer ear as well as in the auditory canal. Hearing and/or balance can be affected. When facial paralysis in included, the condition is called Ramsay Hunt Syndrome.
For most healthy patients, the shingles rash will clear in a few weeks along with diminishing pain/itch as the lesions heal. However, some people may experience Postherpetic Neuralgia (PHN), pain/itching that persists after the blisters have healed and may last for weeks or months.
Primary host: Humans
Other hosts? None
Route of transmission: During chickenpox, VZV can be transmitted through the air on droplets exhaled from the respiratory system, but not during shingles. Transmission of VZV during shingles can only occur through direct contact of blister fluid (full of shed virus) with the skin of someone not previously exposed to the virus.
Reproductive ratio/Ro: Not applicable, since initiation of shingles begins with reactivation of VZV already present (but latent) in the host nervous system from an initial exposure earlier in life. Regarding initial exposure to VZV, over 90% of the U.S. population has been exposed by adolescence and almost 100% by age 60.
Prevalence: About 1 million new cases per year in the U.S. As a proportion, this = 1/307 = 0.32% of the U.S. population per year, with the highest incidence associated with people > 60 years old (1). Of these new cases, about one-quarter develop herpes zoster ophthalmicus.
Generation time: (Not applicable, for the same reason given for the Rate of increase.)
Mortality rate: In the U.S., as many as 10,000 hospitalizations and 100 deaths per year occur as a result of VZV complications (3).
Morbidity rate: 100%
Is it preventable and how? The likelihood of developing shingles can be significantly reduced through a combination of vaccines. 1) Receiving the vaccine against VZV as a child both reduces the chances of developing chickenpox as well as reducing the severity for those who still develop chickenpox. The vaccine is recommended for children >1year old.
(Get your children immunized against chickenpox. Even though it is not life-threatening, you do not want your child to have to experience this!)
2) Receiving the vaccine against VZV as an adult reduces the chances of developing shingles as well as the severity for those who still develop shingles and its complications (including PHN) by about 50% (5). In the U.S., the shingles vaccine has been FDA approved for adults > 60 years old.
Does long-lasting immunity result? Normally healthy people should not experience re-occurrence of shingles. However, immuno-compromised individuals (HIV-infected, oncology patients, transplant patients) run higher risks of re-activation of VZV and repeated episodes of shingles.
When was the pathogen first described and is there earlier evidence of its existence? VZV was confirmed to cause both chickenpox and shingles in 1953 by Thomas H. Weller, who was able to isolate the virus from tissue of diseased subjects (4). (Along with two other researchers, Dr. Weller received the 1954 Nobel prize in Physiology or Medicine for developing the technique of cultivating viruses using tissue from diseased animals.)
Prior to Weller’s discovery, observations that chickenpox and shingles seemed to arise from the same agent were made throughout the first half of the 20th century. Earlier accounts sometimes mixed up shingles with other diseases that produced skin rashes/lesions: up through the late 18th century, shingles was sometimes confused with smallpox. Up through the late 19th century, shingles was sometimes confused with erysipelas, a type of acute skin infection often caused by strains of the Streptococcus genus (3).
What is the economic impact? According to the Agency for Healthcare Research and Quality, which is part of the U.S. Dept. of Health & Human Services (7):
-Total annual spending to treat shingles or its complications from 2003 – 2005 averaged $566 million.
-The average yearly amount spent per person on shingles treatment from 2003 – 2005 was $525; this included both outpatient visits as well as prescribed medications.
-The amount of lost work time due to shingles averaged 129 hours per person, per year.
The coolest thing about the disease? Because VZV infection is usually limited to the nerves emanating from a single dorsal ganglion root, the shingles rash visually demonstrates how the skin is divided up into adjacent dermatomes.
References:
1) http://www.cdc.gov/mmwr/preview/mmwrhtml/rr5705a1.htm
2) http://www.mayoclinic.com/health/shingles/DS00098
3) Foster, S., Roque, B.L. and M.R. Roque. (2008, October 28). Herpes zoster. Retrieved August 25th, 2009 from http://emedicine.medscape.com/article/1202284-overview
4) http://en.wikipedia.org/wiki/Shingles
5) Oxman, M.N. et. al. (2005, June 2). A vaccine to prevent herpes zoster and postherpetic neuralgia in older adults. New England Journal of Medicine, 352(22): 2271-2284.
6) National Institute of Neurological Disorders and Stroke (July, 2006). Shingles: Hope Through Research (NIH Publication No. 06-307). Retrieved August 25th, 2009 from NINDS website:
http://www.ninds.nih.gov/disorders/shingles/detail_shingles.htm
7) Soni, A. and Hill, S. C. Average Annual Health Care Use and Expenses for Shingles among the U.S. Civilian Noninstitutionalized Population, 2003–2005. Statistical Brief #194. December 2007. Agency for Healthcare Research and Quality, Rockville, MD. Retrieved August 25th, 2009 from http://www.meps.ahrq.gov/data_files/publications/st194/stat194.pdf
(shingles on back picture) http://health.allrefer.com/health/herpes-zoster-herpes-zoster-shingles-on-the-back-1.html
9) (blisters picture) http://www.medicinenet.com/shingles_picture_slideshow/article.htm
10) http://www.vzvfoundation.org
