2- Viral meningitis:
Viral meningitis (often referred to as aseptic meningitis) occurs when viral particles invade the fluid around the brain and spinal cord, the CSF, causing inflammation of the lining of the brain and spinal cord, usually following viral infections of the other body parts.
Despite being the most frequent type of meningitis, viral meningitis is less severe than other types, and patients usually get better on their own (without any treatment).
Often no cause is identified; among adult patients with aseptic meningitis, only 50% get a confirmed diagnosis with the following common viruses:
- Non-polio enteroviruses: Accounting for 46% of confirmed cases, it became the most common cause in the last few decades thanks to the mumps, measles, and rubella (MMR) vaccination policies. Enteroviruses infection occurs more often in the late spring or fall, and only a few patients develop viral meningitis.
- Herpesviruses, including Epstein-Barr virus, herpes simplex viruses, and varicella-zoster virus (which causes chickenpox and shingles), are the 2nd common cause.
- Influenza viruses: complicated cases of flu can develop into viral meningitis.
- Mumps and Measles viruses: in infants and children, especially if unvaccinated.
- Arboviruses: they spread by mosquitoes and insects.
- Lymphocytic Choriomeningitis Virus: it spreads by rodents and is a rare cause of viral meningitis.
How do you catch these infections?
Direct contact: Touching contaminated surfaces, objects, or hands of an infected person, then touching the eyes, nose, or mouth without handwashing can transmit non-polio enteroviruses.
Changing diapers of infected children is a common method of transmission of these viruses.
Close contact with patients: Herpesviruses usually spread by direct contact with infected individuals via kissing, sexual contact, or just touching the lesions.
Varicella-zoster virus, influenza viruses, mumps, and measles spread by breathing in tiny droplets of saliva released into the air when an infected person breathes, coughs, sneezes, or speaks. This can occur even if you are 3 meters away from the patient.
Drinking contaminated water: Non-polio enteroviruses can also spread via food and water contamination.
Mosquito bites: Arboviruses, including the West Nile virus, are transmitted via mosquito bites. This is quite common in the continental United States during summer and fall.
Rodents: Exposure to fresh urine, excrement, saliva, or nesting materials from infected rodents can transmit Lymphocytic Choriomeningitis Virus. The bite of an infected rodent is also reported to transmit the infection.
During pregnancy: Some of these viruses are transmitted from infected pregnant women to their babies during pregnancy. This is known as vertical transmission and includes non- polio enteroviruses, Mumps, West Nile virus (WNV), and Lymphocytic Choriomeningitis Virus. However, vertical transmission of these viruses is uncommon.
Most of these viral infections cause viral meningitis under certain conditions; otherwise, they cause other mild diseases.
What makes someone at a higher risk of getting viral meningitis?
› Age: Anybody can develop viral meningitis at any age, but infants and young children (under 5) are most susceptible to viral infections, especially enteroviruses.
› Immunity: People with weakened immunity, for instance, HIV-infected individuals and organ recipients taking immunosuppressive medications.
› Previous infections: Herpes simplex virus (HSV) exists as 2 types (HSV-1 and HSV-2), both closely related antigenically. This means when someone contracts either of the 2 types. They become relatively immune against the other kind. This phenomenon is called (cross-protection).
Since HSV-2 infection is more likely to cause viral meningitis than HSV-1, the declining rates of childhood infection with HSV-1 in the developed countries, the UK, for example, somehow increased the risk of getting HSV-2 infection in the adulthood (genital herpes) and, therefore, increased the risk of Herpes meningitis.
HSV-2 meningitis may also occur in the absence of genital herpes.
Symptoms of viral meningitis are quite similar to those of bacterial meningitis but less severe. It even goes unreported in many cases.
Physical examination, lab investigations, and imaging are required to differentiate from bacterial meningitis.
- General measures: Proper handwashing and avoiding close contact with patients.
- Vaccination: Vaccines are available against measles, mumps, chickenpox, and influenza with adequate protection (up to 97% with measles vaccine).
- Rat and insect control: to avoid Arboviruses and lymphocytic Choriomeningitis Virus infections.