Viral meningitis

Viral meningitis characteristically presents with fever, headache and neck stiffness. In contrast to bacterial meningitis, symptoms associated with viral meningitis are often less severe and do not progress as quickly. Nausea, vomiting and photophobia (light sensitivity) also commonly occur, as do general signs of a viral infection, such as muscle aches and malaise. Photophobia is due to meningeal irritation. Infection in the neonatal period may be the result of infection during pregnancy. The pediatric population may show some additional signs and symptoms that include jaundice and bulging fontanelles. Symptoms can vary depending on the virus responsible for infection. Enteroviral meningitis (the most common cause) typically presents with the classic headache, photophobia, fever, nausea, vomiting, and nuchal rigidity. Patients with varicella zoster meningitis may present with herpes zoster (Shingles) in conjunction with classic meningeal signs. Meningitis can be an indication that an individual with HIV is undergoing seroconversion, the time when the human body is forming antibodies in response to the virus. == Causes ==

The most common causes of viral meningitis in the United States are non-polio enteroviruses. The viruses that cause meningitis are typically acquired from sick contacts. However, in most cases, people infected with viruses that may cause meningitis do not actually develop meningitis. ==Mechanism==

Viral Meningitis is mostly caused by an infectious agent that has colonized somewhere in its host. People who are already in an immunocompromised state are at the highest risk of pathogen entry. Some of the most common examples of immunocompromised individuals include those with HIV, cancer, diabetes, malnutrition, certain genetic disorders, and patients on chemotherapy. Immune cells and damaged endothelial cells release matrix metalloproteinases (MMPs), cytokines, and nitric oxide. MMPs and NO induce vasodilation in the cerebral vasculature. Cytokines induce capillary wall changes in the blood brain barrier, which leads to expression of more leukocyte receptors, thus increasing white blood cell binding and extravasation. This leads to elevated intracranial pressure, cerebral edema, meningeal irritation, and neuronal death. ==Diagnosis==

The diagnosis of viral meningitis is made by clinical history, physical exam, and several diagnostic tests. Kernig and Brudzinski signs may be elucidated with specific physical exam maneuvers, and can help diagnose meningitis at the bedside. Most importantly however, cerebrospinal fluid (CSF) is collected via lumbar puncture (also known as spinal tap). This fluid, which normally surrounds the brain and spinal cord, is then analyzed for signs of infection. CSF findings that suggest a viral cause of meningitis include an elevated white blood cell count (usually 10-100 cells/μL) with a lymphocytic predominance in combination with a normal glucose level. Increasingly, cerebrospinal fluid PCR tests have become especially useful for diagnosing viral meningitis, with an estimated sensitivity of 95-100%. Additionally, samples from the stool, urine, blood and throat can also help to identify viral meningitis. CSF vs serum c-reactive protein and procalcitonin have not been shown to elucidate whether meningitis is bacterial or viral. In certain cases, a CT scan of the head should be done before a lumbar puncture such as in those with poor immune function or those with increased intracranial pressure. If the patient has focal neurological deficits, papilledema, a Glasgow Coma Score less than 12, or a recent history of seizures, lumbar puncture should be reconsidered. Differential diagnosis for viral meningitis includes meningitis caused by bacteria, mycoplasma, fungus, and drugs such as NSAIDS, TMP-SMX, IVIG. Further considerations include brain tumors, lupus, vasculitis, and Kawasaki disease in the pediatric population. ==Treatment==

Because there is no clinical differentiation between bacterial and viral meningitis, people with suspected disease should be sent to the hospital for further evaluation. However, if there is initial uncertainty as to whether the meningitis is bacterial or viral in origin, empiric antibiotics are often given until bacterial infection is ruled out. If encephalitis is suspected, empiric treatment with IV aciclovir is often warranted. ==Epidemiology==

From 1988 to 1999, about 36,000 cases occurred each year in the United States. As recently as 2017, the incidence in the U.S. alone increased to 75,000 cases per year for enteroviral meningitis. During an outbreak in Romania and in Spain viral meningitis was more common among adults. While, people aged younger than 15 made up 33.8% of cases. ==Recent research==

It has been proposed that viral meningitis might lead to inflammatory injury of the vertebral artery wall. The Meningitis Research Foundation is conducting a study to see if new genomic techniques can improve the speed, accuracy and cost of diagnosing meningitis in children in the UK. The research team will develop a new method to be used for the diagnosis of meningitis, analysing the genetic material of microorganisms found in CSF (cerebrospinal fluid). The new method will first be developed using CSF samples where the microorganism is known, but then will be applied to CSF samples where the microorganism is unknown (estimated at around 40%) to try and identify a cause. There is also research investigating whether high-throughput sequencing, wherein the investigator does not need to compare DNA results with known genomic sequences, could be used in specifically diagnosing unknown causes of viral meningitis. While there is some emerging evidence that bacterial meningitis may have a negative impact on cognitive function, there is no such evidence for viral meningitis. == References ==