Download Herpes Simplex Keratitis Ocular Herpes

Herpes Simplex Keratitis
Ocular Herpes
By Lea Hair
General Information
Herpes Simplex Keratitis, also called Ocular Herpes, is an infection of the cornea caused
by the Herpes Simplex Virus 1 (HSV 1). Also called Oral Herpes, HSV 1 is the same virus
which causes cold sores.3
Reservoirs- Infected vertebrates, usually humans 1,3
Historical informationThe earliest mentions of HSV infections were reported by the ancient Greek physician
Hippocrates. Shakespeare also mentions “blister plagues” which many take to be a reference to
HSV. In 1893, Emile Vidal, a French scientist, proved that herpes was transmitted from human
to human. 5
In 1999, the National Eye Institute released a seminal study which changed the way
Herpes was treated. This study, called the Herpetic Eye Disease Study, clearly laid out the
effectiveness of a variety of antiviral medications in treating Ocular Herpes.5
In well developed countries, HSV Keratitis is the is the leading cause of blindness due to
infection.3 In the United States, HSV is also the most common type of infection of the cornea, as
well as the primary reason for corneal transplantation.6
The Virus
From the Family Herpesviridae and the Genus Simplexvirus, this strain of virus is
referred to as the Herpes Simplex Virus 1.1 An alternate strain of the virus, HSV 2, causes the
well-known STI.9 HSV 1 is a doubled stranded DNA virus, surrounded by 162 capsomeres
arranged in an Icosahedron around the nucleic acids. The virus is usually 120 to 200 nm in
diameter. Often, HSV 1 can be found with a spiked envelope, which contributes to its
virulence.1,6 Usually HSV is identified using the signs and symptoms of the disease and not
biochemical tests.4 If required, laboratory testing may include testing for viral antigens, direct
testing for the virus itself, or an application of the Polymerase Chain Reaction to amplify and
isolate any viral DNA.2
The Disease
Transmission
Unlike HSV 2, Ocular Herpes is rarely transmitted sexually.5 Herpes of the eye usually
enters the body through the nose or mouth. A healthy individually can get the disease by coming
into contact with an active cold sore on a friend or partner, or by coming into contact with
someone who has HSV 1 but is asymptomatically shedding the virus. 3
Once contracted, the virus moves to the body’s nervous system. The virus may stay here,
latent and asymptomatic, however, several factors, like fever, exposure to UV light, or trauma,
may activate the virus. Once activated, the virus will travel back to the mouth or nose to produce
cold sores or it will travel to the eye and produce ocular herpes. 3
Signs and symptoms
Ocular Herpes may present in only one eye or in both, though in more than 90% of cases
only one eye will be affected.6 Usual symptoms of an infection include tearing, redness, blurred
vision, light sensitivity, discomfort or foreign body sensation, and cold sores elsewhere on the
face.3,4 Doctors usually identify HSV by looking for a branching ulcer on the cornea. These
ulcers have characteristic shapes with nodes on the ends of the branches. They are called
epithelial dendritic ulcers, as they are found along the dendritic (or nerve) cells of the epithelium,
the outermost layer of the cornea. These lesions easily stain with fluorescein, a florescent drop
often used by Ophthalmology practices. 4,5
It is common for the virus to activate in the eye more than once. Repeated infections can
permanently numb the eye and cause extensive scarring.4 Fever, stress, sunlight, and eye trauma
may trigger a recurrent infection.8 Both new and recurrent cases of Herpes Simplex Keratitis can
affect the lower layers of the cornea as well as the iris.3,4,6 In the stromal or the endothelial layers
of the cornea the most serious symptoms of the disease are possible. In these cases, viral damage,
inflammation, and immune system response may cause severely reduced vision or blindness due
to corneal scarring.6 The corneal scarring is sometimes called an ‘allergic haze,’ as it is believed
that the immune system response to the virus is the primary cause of these symptoms.3,4,5
Treatment
The specific type of treatment administered depends on which layer of the cornea is
affected. No matter the type of infection oral antiviral medications are recommended, especially
for patients with a history of a prior HSV Keratitis episodes.6 Topical corticosteroids should be
used to treat Ocular Herpes of the endothelial and stromal layer of the cornea. Acyclovir or
Valacyclovir, common anti-herpes medications, should be prescribed for infections affecting the
epithelial layers.4,6
Prevention
Currently, the only form of prevention of HSV 1 is the avoidance of contact with an
infected individual.6 However, as can been seen from the incidences figure below, HSV 1 is so
wide spread and easily transmitted that contact avoidance is not a feasible method for preventing
infection.9
While there have been efforts to develop a vaccine, these efforts have been primarily
focused on HSV 2, as this strain of the virus increases an infected individuals possibility of
contracting HIV. The few studies aimed directly at Herpes Simplex Keratitis involved a variety
of approaches, including a subunit vaccine and a live attenuated vaccine. 9
Incidence
Nationally -According to the National Eye Institute, approximately 400,000 to 500,000
Americans are diagnosed with HSV Keratitis, with 50,000 to 60,000 new or recurrent cases each
year. Of these, approximately 25% are the dangerous stromal infections of cornea.6,8,9
Globally - According to a study published in October of 2015, 67% of the global population
under the age of 50 have been infected with HSV 1. This means more than 3.7 billion people
have this virus in their systems.7 Another study done in 2012 found that 1.5 million people are
diagnosed with HSV Keratitis each year. According to the same study, approximately 40,000
people per year loss vision in one eye due to the disease.9
Bibliography
Virus Information
1. Sander, D. "Herpesviruses." The Big Picture Book of Viruses. The Garry Lab, 1997. Web. 6
Dec. 2015. http://www.virology.net/Big_Virology/BVDNAherpes.html
2. Singh, Ameeta. "The laboratory diagnosis of herpes simplex virus infections." National Center
for Biotechnology Information. US National Library of Medicine, Mar. 2005. Web. 7
Dec. 2015. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2095011/
General Disease Information
3. Langston, Deborah. "Herpes Simplex Virus in the Eye." Digital Journal of Ophthalmology.
Massachusetts Eye and Ear Infirmary, 15 Oct. 2002. Web. 7 Dec. 2015.
http://www.djo.harvard.edu/site.php?url=/patients/pi/422
4.Roat, Melvin. "Herpes Simplex Keratitis." Merck Manuals Professional Edition. Merck
Manuals, 1 Sept. 2014. Web. 6 Dec. 2015.
http://www.merckmanuals.com/professional/eye-disorders/corneal-disorders/herpessimplex-keratitis
5. Potter, William. "An Overview of Ocular Herpetic Diseases." Review of Optometry. Jobson
Medical Information LLC, 1 May 2010. Web. 7 Dec. 2015.
http://www.reviewofoptometry.com/continuing_education/tabviewtest/lessonid/106745/
6. Welder, Jeffery. "Herpes Simplex Keratitis." Eye Rounds. The University of Iowa, 31 Dec.
2012. Web. 8 Dec. 2015. http://webeye.ophth.uiowa.edu/eyeforum/cases/160-HSV.htm
Incidence Information
7. Harris, Margaret. "Globally, an Estimated Two-thirds of the Population under 50 are Infected
with Herpes Simplex Virus Type 1." World Health Organization. World Health
Organization, 28 Oct. 2015. Web. 7 Dec. 2015.
http://www.who.int/mediacentre/news/releases/2015/herpes/en
8. "Facts About the Cornea and Corneal Disease." The National Eye Institute. The National Eye
Institute, 1 May 2013. Web. 7 Dec. 2015. https://nei.nih.gov/health/cornealdisease
9. Farooq, Asim. "Herpes Simplex Epithelial and Stromal Keratitis: An Epidemiologic Update."
National Center for Biotechnology Information. US National Library of Medicine, 28
Apr. 2012. Web. 7 Dec. 2015. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3652623/