Viral meningitis is more common than bacterial meningitis and cases of unidentified etiology are very few compared to the total number of cases.
Viral meningitis comprises most cases of meningitis in the country. The numbers may be underestimated because many cases go unreported as it is not a serious disease. Of the 15,470 cases of viral meningitis reported throughout Brazil in 2006, the type of virus that caused the disease was isolated in only a minority (52 cases).
The viruses that most often cause meningitis are viruses of the genus Enteroviridae including viruses Echo, Coxsackie, poliovirus and enterovirus from 68 to 71 which account for more than three quarters of cases; other viruses can cause meningitis such as arboviruses, HSV 1 and 2, HIV (acute phase), mumps and lymphocytic choriomeningitis virus.
The enteroviruses (genus Enteroviridae) are most common in summer and early fall causing the disease in young people up to 15 years. In Brazil, apparently enteroviruses 70 and 71 are particularly frequent. THE The transmission is typically fecal-oral and the incubation period is 3 to 6 days.
When a person gets infected with an enterovirus usually by contaminated food, the virus multiplies and reaches the central nervous system via the bloodstream. In the case of mumps virus, the virus causes oropharyngeal infection with contamination of regional nerve ganglia and subsequent progression to the central nervous system.
Symptoms and diagnosis
Viral meningitis is a disease that goes with fever, malaise, body aches, tiredness and weakness. Nausea and vomiting are very common. Most people with meningitis develop meningeal signs.
Meningeal signs are medical examination maneuvers that show the presence of meningitis. One of the signs is known as neck stiffness which is the hardening or stiffness of the neck muscles when the doctor tries to flex the patient's neck. Still another sign is pain when the doctor raises the leg of the lying patient. The movement of raising the legs stretches the inflamed meninges causing pain.
It is important to make a differential diagnosis with bacterial meningitis because the treatment is different. Meningitis can also be confused with the encephalitis that is the Brain infections. In cases of encephalitis, the neurological examination changes allowing the differential diagnosis.
Some encephalitis may develop with involvement of the meninges and in these cases the differential diagnosis is more difficult and imaging may be necessary. However, the most important diagnostic exam is the collection of CSF. In viral meningitis, there is an increase in the number of leukocytes (white blood cells) in CSF, mainly lymphocytes and monocytes.
The treatment of viral meningitis is complicated because often in doubt if it is a bacterial or virus meningitis, the doctor ends up prescribing antibiotics. When in doubt, this is the most appropriate conduct. In viral meningitis the treatment should be supportive, that is, pain medication should be given to improve vomiting and hydration, but there is no specific treatment. In HSV-2 or Herpes Zoster virus meningitis, acyclovir, an antiviral drug, can be used.