Articles on Medical Diseases and Conditions

Tag: Viral meningitis

  • Viral and Aseptic Meningitis

    Viral meningitis is one component of a syndrome known as aseptic meningitis. The aseptic meningitis syndrome is now usually defined as meningitis with normal CSF glucose levels, normal or elevated protein levels, and elevated cell count with a majority of the cells being lymphocytes. A less common definition is nonbacterial meningitis; a definition no longer used is meningitis with a negative bacterial culture. The CSF findings of aseptic meningitis may be caused by a wide variety of agents, including different viruses, mycobacteria, Listeria, syphilis, Leptospira, Toxoplasma, fungi, meningeal carcinomatosis, and meningeal reaction to nearby inflammatory or destructive processes or to some medications in a few patients. However, viral meningitis is the most common and typical of the conditions that produce this syndrome. The commonest virus group associated with meningitis is enterovirus, which includes ECHO (enteric cytopathic human orphan) virus and coxsackievirus and comprises 50%-80% of viral meningitis patients; the second most common (10%-20%) is mumps. Other viruses include herpes simplex, arbovirus group, herpes zoster-varicella, and lymphocytic choriomeningitis. Although not usually listed, human immunodeficiency virus 1 (HIV-1) (or acquired immunodeficiency syndrome [AIDS]) may be, or may become, one of the most frequent etiologies. There are several reasons for describing the aseptic meningitis syndrome and specifically mentioning viral meningitis. First, it is useful to know what etiologies to expect with this pattern of CSF results. Second, this pattern is not specific for viral etiology. Third, a significant number of patients infected by many of these etiologies do not present with textbook aseptic meningitis findings. This is most true for lymphocytes versus neutrophils as the dominating cell in early enterovirus, mumps, and arbovirus infections. Reports estimate that 20%-75% of patients with viral meningitis have neutrophil predominance in the first CSF specimen obtained. For example, one investigator found that about 50% of enteroviral meningitis patients had more than 10% neutrophils on the first CSF specimen, and about 25% had neutrophils predominating; about 66% had normal protein levels; and about 10% had decreased glucose. Most reports indicate that repeat lumbar puncture in 8-12 hours frequently shows change from neutrophil to lymphocyte predominance, with conversion of the remainder taking place in 24-48 hours. In enterovirus, mumps, herpes simplex, and lymphocytic choriomeningitis, initial CSF glucose is sometimes mildly decreased rather than the expected normal value.

    Differential diagnosis of aseptic meningitis syndrome etiologies generally involves differentiating virus etiology from mycobacterial and cryptococcal infection. CSF culture can be done for all the usual virus possibilities, but viral specimens usually must be sent to a reference laboratory, and the results are not available for several days or even longer. It has been recommended that CSF specimens either be processed in less than 24 hours or be frozen at – 70°C to preserve infectivity. Many viruses lose infectivity when frozen at the usual temperature of – 20°C. Serologic tests are also available but require acute and convalescent serum specimens and thus take even longer than culture. As noted there, herpes simplex type 1 has a predilection for involvement of the temporal lobe of the brain. Cryptococcus and mycobacterial tests have been discussed earlier in this chapter. CSF lactate (lactic acid) has been advocated to separate viral from nonviral etiology but, as discussed earlier, is not always helpful and thus is still somewhat controversial.

  • Viral Diseases

    Viral upper respiratory tract diseases

    Respiratory disease may take several forms, and the predominant etiologies are different in different age groups. Incidence statistics also vary depending on the geographic area and the population selected. Of the known viruses, rhinoviruses are predominantly associated with acute upper respiratory tract disease (including the common cold) in adults, whereas in children, rhinovirus, adenovirus, parainfluenza virus, and the enteroviruses are important. Acute bronchitis in children is most often due to respiratory syncytial virus and parainfluenza virus. In croup, parainfluenza is said to be the most important virus.

    Viral pneumonia

    Respiratory syncytial virus is the predominant cause of pneumonia in infants and young children, beginning at age 1 month with a peak incidence at about age 6 months, followed by adenovirus or parainfluenza virus. In older children or adults, bacterial pneumonia (most often due to Pneumococcus or Mycoplasma pneumoniae) is more common than viral pneumonia. Among viral agents known to cause pneumonia in adults, the most common is probably influenza. In any study, a large minority of cases do not yield a specific etiologic agent.

    Viral meningitis

    Viruses are an important cause of meningitis, especially in children. They typically produce the laboratory picture of aseptic meningitis: the classic cerebrospinal fluid (CSF) findings are variable, but often include mildly increased protein levels, increased cell counts with mononuclear cells predominating, normal glucose levels, and no organisms found on culture. It should be remembered, however, that tuberculous meningitis gives similar findings, except for a decreased CSF glucose level, and likewise shows a sterile culture on ordinary bacterial culture media. Some patients with mumps meningoencephalitis may have decreased CSF glucose levels in addition to CSF lymphocytosis. Enteroviruses are the largest etiologic group causing aseptic meningitis. Among the enteric viruses, poliomyelitis used to be the most common organism, but with widespread polio vaccination programs, echovirus and coxsackievirus have replaced polio in terms of frequency.

    After the enteroviruses, mumps is the most important. A small but significant number of patients with mumps develop clinical signs of meningitis, and a large number show CSF changes without demonstrating enough clinical symptoms to warrant a diagnosis and workup for meningitis. Changes in CSF or the clinical picture of meningitis may occur in patients without parotid swelling or other evidence of mumps. Lymphocytic choriomeningitis and leptospirosis are uncommon etiologies for aseptic meningitis.

    Encephalitis is a syndrome that frequently has CSF alterations similar to those of meningitis. The two cannot always be separated, but the main difference is clinical; encephalitis features depression of consciousness (lethargy, coma) over a prolonged period, whereas meningitis usually is a more acute illness with manifestations including fever, headache, vomiting, lethargy, stiff neck, and possibly convulsions. In severe bacterial infection, encephalitis may follow meningitis. Encephalitis is most often caused by viruses, of which the more common are mumps, herpes simplex type 1 (HSV-1), measles, and the arboviruses. Sometimes encephalitis is a complication of vaccination.

    Viral gastroenteritis

    Viruses are likely to be blamed for diarrhea that cannot be explained otherwise. In most cases, definitive evidence is lacking because enteric virus is present in a significant number of apparently healthy children. Bacterial infection should always be carefully ruled out. Two clinical types of viral gastroenteritis have been described. One type usually occurs in epidemics, more often in older children and in adults, with clinical signs of an acute self-limited gastroenteritis of 1-2 days’ duration. The most commonly associated etiology is the Norwalk-type group of viruses. The other type of illness is sporadic and affects mostly infants and younger children. There is severe diarrhea, usually accompanied by fever and vomiting, which lasts for 5-8 days. Rotavirus is the most frequently isolated virus in these patients. About 5%-10% of gastroenteritis in infants less than 2 years old is said to be caused by adenovirus types 40 and 41

    Viral infections in pregnancy

    By far the most dangerous viral disease during pregnancy is rubella. Statistics are variable, but they suggest about a 15%-25% risk of fetal malformation when rubella infection occurs in the first trimester (literature range, 10%-90%). The earlier in pregnancy that maternal infection occurs, the greater the risk that the fetus will be infected. However, not all infected fetuses develop congenital malformation. When the fetus is infected early in the first trimester, besides risk of congenital malformation, as many as 5%-15% of fetuses may die in utero. Risk of fetal malformation in second trimester infections is about 5%. After the fourth month of pregnancy, there is no longer any danger to the fetus. Cytomegalovirus (CMV) infection is more frequent than rubella, but CMV has a lower malformation rate. Cytomegalovirus damage is more severe in the first two trimesters. Other viruses may cause congenital malformations, but evidence is somewhat inconclusive as to exact incidence and effects. Herpes simplex and the hepatitis viruses are in this group.