Herpesviral encephalitis
Encyclopedia
Herpesviral encephalitis is encephalitis
associated with herpes simplex virus
.
Herpes simplex encephalitis
(HSE) is a rare, but severe viral infection of the human central nervous system
. It is estimated to affect at least 1 in 500,000 individuals per year. The majority of cases of herpes encephalitis are caused by herpes simplex virus-1 (HSV-1), the same virus that causes cold sores. 90% of adults are infected with HSV-1, which is spread through droplets and casual contact, though most infected people never have cold sores. About 10% of cases of herpes encephalitis are due to HSV-2, which is spread through sexual contact. About 1 in 3 cases of HSE result from primary HSV-1 infection, predominantly occurring in individuals under the age of 18; 2 in 3 cases occur in seropositive
persons, few of whom have history of recurrent orofacial herpes. Approximately 50% of individuals that develop HSE are over 50 years of age.
HSE is thought to be caused by the retrograde transmission
of virus from a peripheral site on the face following HSV-1 reactivation, along a nerve axon
, to the brain. The virus lies dormant in the ganglion
of the trigeminal cranial nerve, but the reason for reactivation, and its pathway to gain access to the brain, remains unclear, though changes in the immune system caused by stress clearly play a role in animal models of the disease. The olfactory nerve may also be involved in HSE, which may explain its predilection for the temporal lobe
s of the brain, as the olfactory nerve sends branches there. In horses, a single-nucleotide polymorphism is sufficient to allow the virus to cause neurological disease; but no similar mechanism has been found in humans.
Most individuals with HSE show a decrease in their level of consciousness and an altered mental state presenting as confusion
, and changes in personality. Increased numbers of white blood cells can be found in patient's cerebrospinal fluid
, without the presence of pathogen
ic bacteria
and fungi. Patients typically have a fever and may have seizures. The electrical activity of the brain changes as the disease progresses, first showing abnormalities in one temporal lobe
of the brain, which spread to the other temporal lobe 7–10 days later. Imaging by CT or MRI shows characteristic changes in the temporal lobes (see Figure). Definite diagnosis requires testing of the cerebrospinal fluid (CSF) by a lumbar puncture (spinal tap) for presence of the virus. The testing takes several days to perform, and patients with suspected Herpes encephalitis should be treated with aciclovir immediately while waiting for test results.
Herpesviral Encephalitis can be treated with high-dose intravenous Aciclovir
. Without treatment, HSE results in rapid death in approximately 70% of cases; survivors suffer severe neurological damage. When treated, HSE is still fatal in one-third of cases, and causes serious long-term neurological damage in over half of survivors. Twenty percent of treated patients recover with minor damage. Only a small population of survivors (2.5%) regain completely normal brain function. Earlier treatment (within 48 hours of symptom onset) improves the chances of a good recovery. Rarely, treated individuals can have relapse of infection weeks to months later. While the herpes virus can be spread, encephalitis itself is not infectious. Other viruses can cause similar symptoms of encephalitis, though usually milder (human herpes virus-6, varicella zoster, epstein-barr, cytomegalovirus, coxsackievirus, etc).
Encephalitis
Encephalitis is an acute inflammation of the brain. Encephalitis with meningitis is known as meningoencephalitis. Symptoms include headache, fever, confusion, drowsiness, and fatigue...
associated with herpes simplex virus
Herpes simplex virus
Herpes simplex virus 1 and 2 , also known as Human herpes virus 1 and 2 , are two members of the herpes virus family, Herpesviridae, that infect humans. Both HSV-1 and HSV-2 are ubiquitous and contagious...
.
Herpes simplex encephalitis
Encephalitis
Encephalitis is an acute inflammation of the brain. Encephalitis with meningitis is known as meningoencephalitis. Symptoms include headache, fever, confusion, drowsiness, and fatigue...
(HSE) is a rare, but severe viral infection of the human central nervous system
Central nervous system
The central nervous system is the part of the nervous system that integrates the information that it receives from, and coordinates the activity of, all parts of the bodies of bilaterian animals—that is, all multicellular animals except sponges and radially symmetric animals such as jellyfish...
. It is estimated to affect at least 1 in 500,000 individuals per year. The majority of cases of herpes encephalitis are caused by herpes simplex virus-1 (HSV-1), the same virus that causes cold sores. 90% of adults are infected with HSV-1, which is spread through droplets and casual contact, though most infected people never have cold sores. About 10% of cases of herpes encephalitis are due to HSV-2, which is spread through sexual contact. About 1 in 3 cases of HSE result from primary HSV-1 infection, predominantly occurring in individuals under the age of 18; 2 in 3 cases occur in seropositive
Serostatus
Serostatus is a term used to refer to the presence or absence of specific substances in the blood serum. Most commonly, this medical test is looking for specific antibodies in an effort to diagnose a particular disease....
persons, few of whom have history of recurrent orofacial herpes. Approximately 50% of individuals that develop HSE are over 50 years of age.
HSE is thought to be caused by the retrograde transmission
Retrograde infection
Retrograde is defined as "In reverse action", therefore a retrograde infection is an infection that enters or spreads through the body through a means that is usually considered backwards. An example is spreading into the salivary glands through the saliva ducts....
of virus from a peripheral site on the face following HSV-1 reactivation, along a nerve axon
Axon
An axon is a long, slender projection of a nerve cell, or neuron, that conducts electrical impulses away from the neuron's cell body or soma....
, to the brain. The virus lies dormant in the ganglion
Ganglion
In anatomy, a ganglion is a biological tissue mass, most commonly a mass of nerve cell bodies. Cells found in a ganglion are called ganglion cells, though this term is also sometimes used to refer specifically to retinal ganglion cells....
of the trigeminal cranial nerve, but the reason for reactivation, and its pathway to gain access to the brain, remains unclear, though changes in the immune system caused by stress clearly play a role in animal models of the disease. The olfactory nerve may also be involved in HSE, which may explain its predilection for the temporal lobe
Temporal lobe
The temporal lobe is a region of the cerebral cortex that is located beneath the Sylvian fissure on both cerebral hemispheres of the mammalian brain....
s of the brain, as the olfactory nerve sends branches there. In horses, a single-nucleotide polymorphism is sufficient to allow the virus to cause neurological disease; but no similar mechanism has been found in humans.
Most individuals with HSE show a decrease in their level of consciousness and an altered mental state presenting as confusion
Mental confusion
Confusion of a pathological degree usually refers to loss of orientation sometimes accompanied by disordered consciousness and often memory Confusion (from Latin confusĭo, -ōnis, noun of action from confundere "to pour together", also "to confuse") of a pathological degree usually refers to loss...
, and changes in personality. Increased numbers of white blood cells can be found in patient's cerebrospinal fluid
Cerebrospinal fluid
Cerebrospinal fluid , Liquor cerebrospinalis, is a clear, colorless, bodily fluid, that occupies the subarachnoid space and the ventricular system around and inside the brain and spinal cord...
, without the presence of pathogen
Pathogen
A pathogen gignomai "I give birth to") or infectious agent — colloquially, a germ — is a microbe or microorganism such as a virus, bacterium, prion, or fungus that causes disease in its animal or plant host...
ic bacteria
Bacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
and fungi. Patients typically have a fever and may have seizures. The electrical activity of the brain changes as the disease progresses, first showing abnormalities in one temporal lobe
Temporal lobe
The temporal lobe is a region of the cerebral cortex that is located beneath the Sylvian fissure on both cerebral hemispheres of the mammalian brain....
of the brain, which spread to the other temporal lobe 7–10 days later. Imaging by CT or MRI shows characteristic changes in the temporal lobes (see Figure). Definite diagnosis requires testing of the cerebrospinal fluid (CSF) by a lumbar puncture (spinal tap) for presence of the virus. The testing takes several days to perform, and patients with suspected Herpes encephalitis should be treated with aciclovir immediately while waiting for test results.
Herpesviral Encephalitis can be treated with high-dose intravenous Aciclovir
Aciclovir
Aciclovir or acyclovir , chemical name acycloguanosine, abbreviated as ACV,is a guanosine analogue antiviral drug, marketed under trade names such as Cyclovir, Herpex, Acivir, Acivirax, Zovirax, and Zovir...
. Without treatment, HSE results in rapid death in approximately 70% of cases; survivors suffer severe neurological damage. When treated, HSE is still fatal in one-third of cases, and causes serious long-term neurological damage in over half of survivors. Twenty percent of treated patients recover with minor damage. Only a small population of survivors (2.5%) regain completely normal brain function. Earlier treatment (within 48 hours of symptom onset) improves the chances of a good recovery. Rarely, treated individuals can have relapse of infection weeks to months later. While the herpes virus can be spread, encephalitis itself is not infectious. Other viruses can cause similar symptoms of encephalitis, though usually milder (human herpes virus-6, varicella zoster, epstein-barr, cytomegalovirus, coxsackievirus, etc).