Wednesday, May 9, 2012


Meningitis Meningitis and encephalitis are potentially life threatening infections especially in children. Meningitis is defined as an inflammation of the meninges, the tough layer of tissue that surrounds the brain and the spinal cord. Aseptic meningitis (AM) is an inflammation of the meninges which is caused mainly by nonbacterial organisms. AM denotes a clinical syndrome characterized by fever , neck stiffness and may be convulsions with a predominance of lymphocytes in the CSF with negative bacterial culture of the CSF. Viral meningitis occurs as an uncommon complication of systemic viral infection that occurs most frequently in infants and children. Morbidity and mortality depend on the infectious agent, age of the child, general health and prompt diagnosis and treatment. Many etiological agents can cause AM .Viruses are the most frequent causes as Enterovirus,Poliovirus , Coxsackievirus ,Echoviruses,Herpes simplex virus (HSV) ,Varicella-zoster virus( VZV) ,Cytomegalovirus (CMV) , Epstein-Barr virus (EBV). Bacterial infections such as tuberculosis , mycoplasma and leptospira can also cause AM. Non infectious causes may include postvaccination with MMR ,rabies and poliomylities vaccines , drugs as nonsteroidal anti-inflammatory drugs (NSAIDs) and antibiotics as amoxicillin, trimethoprim–sulfamethoxazole. Also fungi as Candida , Cryptococcus and parasites as Toxoplasma gondii , Trichinosis , Neurocysticercosis and Naeglari are infrequent causes of AM. Enteroviruses (EVs) especially non polio EVs (NPEV) including echovirus and coxsackie A and B viruses are the most common etiologic agents of AM . EVs meningitis can mimic bacterial meningitis. So, it is important to distinguish AM, meningoen¬cephalitis from bacterial meningitis which demands prompt therapeutic approach and to avoid unnecessary hospitalization and antibacterial treatment in cases AM. Laboratory diagnosis of AM depends on nonspecific tests as macroscopical examination , cell count both total and differential leucocytic count,direct Gram stained ,cell culture and biochemical tests as glucose , protein ,CSF lactate , C-Reactive protein and CSF adenosine deaminase (ADA). The specific tests are virus isolation, virus antigen detection, virus nucleic acid detection and virus antibody detection (serology). Virus isolation is the current method of choice for the diagnosis but it takes several days to be conclusive. However, attempts to isolate virus from CSF are frequently unsuccessful because of the low viral titer in clinical specimens and several types of viruses do not grow well or not at all in tissue culture . Virus antigen detection is more rapid but still manually intensive and relatively insensitive. Virus serology is an indirect approach with many limitations. It is used to assess immune status and to detect the viruses which cannot be cultivated in cell culture.It includes indirect fluorescent antibody testing and enzyme-linked immunosorbent assays (ELISA) which detect antibodies against viruses. The performance of viral serology is useful in the diagnosis of recent, past or chronic viral infections. However , ELISA is not conclusive in the diagnosis of acute EV or HSV meningitis as IgM antibodies may persist for months and it is not unique to the primary phase. There is a great clinical need to develop rapid and sensitive virus diagnostic techniques. Molecular diagnosis may have a significant benefit . PCR is an in vitro method for specific or target cDNA or RNA amplification. The target DNA-or RNA is derived from clinical specimens or a microbial culture. The major advantages of PCR are its rapidity, sensitivity and robustness. But the major disadvantages of PCR are short size,limiting amounts of product and infidelity of DNA replication . The specificity of PCR is based on the sequence of the two primers. This means that any segment of genomic DNA or RNA is a potential target for PCR diagnostic assay. An ideal target sequence should be found in all strains of the virus of interest but not found in any other viruses. Conclusions : * Meningitis is the most common infectious CNS syndrome which is a life – threatening condition especially in children . * Aseptic meningitis is caused mainly by viruses as Enterovirus , Polioviruses , Coxsackievirus ,Herpes simplex virus ,Varicella-zoster virus,Cytomegalovirus.Other causes may include bacterial as tuberculosis , mycoplasma and leptospira or followed MMR ,rabies and poliomyelitis vaccines.Also , drugs as nonsteroidal anti-inflammatory , trimethoprim or fungi as Candida , Cryptococcus and parasites as Toxoplasma gondii , Trichinosis can cause aseptic meningitis. * Enteroviruses are the most common causes of viral meningitis causing appreciable morbidity. * Molecular biological methods as PCR has been developed. It becomes the technique of choice for detecting viral or other pathogen genome. Laboratory Diagnosis of Meningitis Made Ridiculously easy [Kindle Edition] http://www.amazon.co.uk/Laboratory-Diagnosis-Meningitis-Ridiculously-ebook/dp/B007GIXXR6

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