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Aseptic meningitis
Aseptic meningitis is one of the most common infections of the meninges. As previously mentioned, if appropriate diagnostic methods are performed, a specific viral etiology is identified in 55-70% of cases of aseptic meningitis. However, aseptic meningitis can also be caused by bacteria, fungi, and parasites (see the Table 1 “Infectious Agents Causing Aseptic Meningitis Syndrome,” below). Importantly, partially treated bacterial meningitis accounts for a large number of meningitis cases with a negative microbiologic workup. Go to Aseptic Meningitis for complete information on this topic. Table 1. Infectious Agents Causing Aseptic Meningitis Syndrome (Open Table in a new window)
Enteroviruses account for 90% of cases of aseptic meningitis. The enteroviruses belong to the family Picornaviridae and are further classified as follows:
The virus is usually spread by fecal-oral or respiratory routes; infection occurs during summer and fall in temperate climates and year-round in tropical regions. The nonpolio enteroviruses (NPEV) account for approximately 90% of cases of viral meningitis in which a specific pathogen can be identified. Echovirus 30 was reported as the cause of an epidemic in Japan in 1991 and also as the cause of 20% of cases of aseptic meningitis reported to the Centers for Disease Control and Prevention (CDC) in 1991. The Herpesviridae family consists of large, DNA-containing enveloped viruses. Eight members are known to cause human infections, and all have been implicated in meningitis syndromes, with the exception of HHV-8 or Kaposi sarcoma–associated virus. HSV accounts for 0.5-3% of cases of aseptic meningitis; it is most commonly associated with primary genital infection and is less likely during recurrences. HSV-1 is a cause of encephalitis, while HSV-2 more commonly causes meningitis. Although Mollaret syndrome, a recurrent, but benign, aseptic meningitis syndrome, is more frequently associated with HSV-2; HSV-1 has also been implicated as a cause. Epstein-Barr virus (EBV, or HHV-4) and cytomegalovirus (CMV, or HHV-5) may manifest as meningitis during the mononucleosis syndrome. Varicella-zoster virus (VZV), or HHV-3, and CMV are causes of meningitis in immunocompromised hosts, especially patients with acquired immunodeficiency syndrome (AIDS) and transplant recipients. HHV-6 and HHV-7 have been reported to cause meningitis in transplant recipients. The most common arthropod-borne viruses are West Nile virus, St. Louis encephalitis virus (a flavivirus), Colorado tick fever virus, and California encephalitis virus (bunyavirus group, including La Crosse encephalitis virus). West Nile virus is the most important arbovirus causing asceptic meningitis in the United States. It is spread largely by infected mosquitoes. According to the Centers for Disease Control and Prevention (CDC), 48 states had reported West Nile virus infections in people, birds, or mosquitoes as of October 23, 2012, and 2,413 cases of neuroinvasive West Nile virus disease (eg, meningitis, encephalitis) in people, including 219 deaths, had been reported to CDC.[8] West Nile fever has a sudden onset. Clinical features typically include malaise, eye pain, headache, myalgia, gastrointestinal discomfort, and rash.[9, 10] A smaller percentage of patients may develop encephalitis, meningitis, or acute flaccid paralysis, and long-term neurologic sequelae are common in more than half of these cases.[11, 12] St. Louis encephalitis virus is a mosquito-borne flavivirus. It may cause a febrile syndrome, aseptic meningitis syndrome, and encephalitis. Other members of the flavivirus group that may cause aseptic meningitis include tick-borne encephalitis virus and Japanese encephalitis virus. California encephalitis is a common childhood disease of the CNS that is caused by a virus in the genus Bunyavirus. Most of the cases of California encephalitis are probably caused by mosquito-borne La Crosse encephalitis virus. Encephalitis can sometimes be difficult to distinguish from meningitis when cultures are negative. LCM virus is a member of the arenaviruses, a family of single-stranded, RNA-containing viruses in which rodents are the animal reservoir. The modes of transmission include aerosols and direct contact with rodents. Outbreaks have also been traced to infected laboratory mice and hamsters. The mumps virus is the most common cause of aseptic meningitis in unimmunized populations, occurring in 30% of all patients with mumps. Following exposure, an incubation period of approximately 5-10 days ensues, followed by a nonspecific febrile illness and an acute onset of aseptic meningitis. This may be associated with orchitis, arthritis, myocarditis, and alopecia. Aseptic meningitis syndrome may be the presenting symptom in a patient with acute HIV infection. This usually is part of the mononucleosis-like acute seroconversion phenomenon. Always suspect HIV as a cause of aseptic meningitis in a patient with risk factors such as intravenous drug use and in individuals who practice high-risk sexual behaviors. Adenovirus (serotypes 1, 6, 7, and 12) has been associated with cases of meningoencephalitis. Chronic meningoencephalitis has been reported with serotypes 7, 12, and 32. The infection is usually acquired through a respiratory route. Go to Aseptic Meningitis for complete information on this topic. Дата добавления: 2015-09-18 | Просмотры: 721 | Нарушение авторских прав |