Rehab Cell

Physical Medicine and Rehabilitation

Varicella zoster virus – causes, symptoms, diagnosis, treatment, pathology

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of pharmacology and clinical reasoning topics. Try it free today. Varicella zoster virus is one of the herpesviruses
and it causes two diseases – varicella or chickenpox, and herpes zoster also known as
shingles. Zoster actually refers to a type of belt used
by ancient Greek warriors because of the belt like appearance of shingles. Now, let’s first talk a bit about the nervous
system – it consists of two parts. The central nervous system which includes
the brain and the spinal cord, and the peripheral nervous system includes the nerves that fan
out from the central nervous system to reach the skin, muscles, and organs. Peripheral nerves that originate from the
brain are called cranial nerves, and they’re in charge of motor and sensory innervation
of the head and neck. A specific cranial nerve, cranial nerve V,
is the trigeminal nerve and it’s responsible for the sensation in the face. Its sensory neurons create a nerve cell cluster
called trigeminal ganglion, located in the bones on the side of the face between the
eyes and ears. The peripheral nerves originating from the
spinal cord are called the spinal nerves. Each nerve is formed by a dorsal and a ventral
root. Ventral roots contains neurons that carry
motor innervation from the spinal cord to the muscles. Sensory information, like touch, temperature,
pain, and pressure from the skin and other tissues travel through 1st order sensory neurons,
in the dorsal root ganglion near the spinal cord, then through the dorsal root, and into
the spinal cord, where it synapses with the 2nd order neurons. Now, each spinal nerve is in charge of the
sensation of a specific area of the skin, called a dermatome. For example, if you step on a lego, the pain
would be carried by the S1 nerve, but if you hit your big toe on a table leg, the pain
would be carried by the L5 nerve. Varicella zoster virus is a double-stranded
DNA virus, protected by a protein coat called capsid, which is enveloped in a lipid membrane. The virus initially enters respiratory epithelial
cells – but eventually spreads to numerous cell types. It gets into all of these cells by fusing
its membrane with the cell membrane and releasing the capsid inside the cell. The capsid binds to the nucleus and injects
it with viral DNA, where it’s copied. The viral genes are transcribed into RNA and
go over to the ribosomes, where they are translated into capsid proteins. The capsid and viral DNA fuse together. They go through the Golgi complex, a cell
organelle in charge of packing proteins, to get their lipid membrane and finally the newly
formed viruses leave the cell. Leaving behind a dead cell. When an infected person sneezes or coughs,
the viruses leaves the lungs and get released into the air. The virus can also be transmitted through
contact with the oral or skin lesions of the infected person. When the virus comes in contact with the respiratory
mucosa or the skin of a new person, it starts replicating in the epithelial cells. It soon gets picked up by nearby immune cells
and gets transported to a nearby lymph node. The virus now causes primary infection called
varicella or chickenpox, and it has two stages – primary viremia and secondary viremia. In primary viremia the virus infects a part
of immune system in the liver and spleen called the reticuloendothelial system, which is made
of phagocytic cells. About two weeks after entering the body, the
virus starts infecting immune cells themselves – specifically T cells – and that is considered
the secondary viremia. Infected T cells start expressing proteins
that bind to receptors on the skin cells. It’s a bit like the virus is hitching a
ride in the T cell to get to the skin. Once the T cells reach the skin, they release
the viruses, which start infecting keratinocytes. The infection spreads through the skin, going
directly from cell to cell. Sometimes the infected keratinocytes start
to fuse together and create giant multinucleated cells called Tzanck cells. Uninfected cells start secreting interferons
alpha and beta, which inhibits viral protein synthesis and protects those cells from getting
infected. As a result, we get tiny lesions on the skin
separated by normal areas of skin. In addition to infecting keratinocytes, the
virus also infects sensory neurons in the skin, and in those neurons it travels retrogradely,
meaning backward through the neuron to the dorsal root ganglia or if it’s on the face,
the trigeminal ganglion. Over time, when the adaptive immune reaction
kicks in, most of the viruses in the body are eliminated, but the ones in the ganglions
are spared and can remain dormant for many years. Most commonly, the virus establishes a latent
state within the trigeminal ganglia and the dorsal ganglia. Later on, if the immune system weakens, due
to aging, stress, or immunosuppressive therapy, the virus can be reactivated. It can then travel back up through the sensory
nerve, anterogradely to the skin and cause an infection in the innervated dermatome – that’s
called herpes zoster or shingles. With both chickenpox and shingles, the most
common complication is a secondary bacterial infection of the skin lesions. So, if the liver becomes infected, hepatitis
can occur. If the virus spreads to the lungs we get pneumonia. If the brain or its protective membrane, called
the meninges, become inflamed, encephalomeningitis could occur. Symptoms of chickenpox begin about 2 weeks
after it enters the body. The infection usually causes a fever, headache
and overall weakness. After a couple days, skin lesions start to
appear on the scalp, face, and trunk. At first, there are flat, red, itchy spots
called macules. Over time, they become elevated and develop
into papules, and then into small fluid-filled vesicles. Within 1 to 2 days the vesicles begin to crust
over and form scabs. After about 5 days the scabs fall off, usually
without leaving a scar. New crops of lesions are continuously forming
in different places on the body every 3 to 5 days, so it’s possible to see lesions
in different phases at the same time. In addition to the itchy lesions, painful
sores can appear on mucosal surfaces like inside the mouth. In shingles there’s typically pain, itching,
or tingling in the area where the rash will develop. The rash itself is usually in a single stripe
of vesicles around either the left or the right side of the body or on one side of the
face. It usually takes 4 weeks for the rash to disappear,
but there can be pain in the affected dermatome which lasts for more than 90 days called postherpetic
neuralgia. Chickenpox and shingles are usually diagnosed
based on the way that the skin lesions appear, but the diagnosis can be confirmed by using
the Tzanck test to look for multinucleated giant cells in the fluid of the vesicles. More commonly, blood test for varicella zoster
antibodies or PCR can be done to look for viral DNA. Chickenpox treatment mainly includes the use
of topical antipruritic medications to help reduce the itching. Also, analgesics and anti-inflammatory medications
can help reduce the fever, but aspirin shouldn’t be used in someone with chickenpox, because
it can trigger Reye syndrome. In Reye syndrome, the liver gets affected
by both varicella zoster virus and aspirin and it leads to a buildup of ammonia in the
body. In immunocompromised individuals, antivirals
like acyclovir, famciclovir, and valacyclovir can be used. In some situations, varicella-zoster immune
globulin or VZIG which are anti-varicella antibodies can be given to treat immunocompromised
or pregnant individuals. Finally, varicella vaccine can be used to
prevent chickenpox by helping the body mount protective immunity against a weakened form
of the virus. Similarly, zoster vaccine can be used to reduce
zoster – which is more common in adults. All right, as a quick recap varicella zoster
virus is a herpesviruses that causes primary infection in the lymph nodes and secondary
infection in the keratinocytes and neurons in the skin. From the neurons in the skin, it travels retrogradely
to the nerve ganglia, where it remains dormant. Chickenpox is characterized by a rash on the
scalp, face, and trunk that contains macules, papules, vesicles and scabs at the same time. Herpes zoster or shingles is caused by the
reactivation of the virus, with vesicles located along one dermatome. Treatment is usually symptomatic, and in some
cases includes antiviral drugs.

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