Routine immunizations against H. influenzae and S. pneumoniae are recommended for children beginning at 2 months of age. Quadrivalent vaccines against N. meningitidis (serotypes A, C, Y, and W-135) are recommended for adolescents, college freshmen, military personnel, and travelers to highly endemic areas (see Chapter 94), and are licensed down to 2 years of age. Chemoprophylaxis with rifampin, ciprofloxacin, or ceftriaxone to eradicate the carrier state and decrease transmission is recommended both for index cases with N. meningitidis or
H. influenzae and for their close contacts.
Encephalitis is an inflammatory process of the brain parenchyma leading to cerebral dysfunction. It is usually an acute process but may be a postinfectious encephalomyelitis, a chronic degenerative disease, or a slow viral infection. Encephalitis may be diffuse or localized. Organisms cause encephalitis by one of two mechanisms: (1) direct infection of the brain parenchyma or (2) an apparent immune-mediated response in the central nervous system that usually begins several days after the appearance of extraneural manifestations of the infection.
Viruses are the principal causes of acute infectious encephalitis (Table 101-1). The most common viral causes of encephalitis in the United States are the enteroviruses, arboviruses, and herpesviruses. Human immunodeficiency virus (HIV) is an important cause of subacute encephalitis in children and adolescents and may present as an acute febrile illness but, more commonly, is insidious in onset (see Chapter 125).
Enterovirus and parechovirus +++ Herpes simplex viruses (HSV 1, 6, 7) ++ Arthropod-borne viruses (especially West Nile ++ virus, St. Louis, California, LaCrosse, and equine encephalitis viruses) Epstein-Barr virus + Adenovirus + Human immunodeficiency virus + Borrelia burgdorferi (Lyme disease) + Bartonella henselae (cat-scratch disease) + Mycoplasma pneumoniae + Rickettsia rickettsii +
Adapted from Willoughby RE Jr, Long SS: Encephalitis, meningoencephalitis, acute disseminated encephalomyelitis, and acute necrotizing encephalopathy. In Long SS, Pickering LK, Prober CG : Principles and Practice of Pediatric Infectious Diseases, revised reprint, ed 3, Philadelphia, 2008,
Saunders.
Other causes of subacute encephalitis include measles, slow viruses (e.g., JC virus), and prion-associated diseases (e.g., Creutzfeldt-Jakob disease). Encephalitis also may result from metabolic, toxic, and neoplastic disorders.
Acute disseminated encephalomyelitis (ADEM) is the abrupt development of multiple neurologic signs related to an inflammatory, demyelinating disorder of the brain and spinal cord. ADEM follows childhood viral infections (such as measles and chickenpox) or vaccinations and resembles multiple sclerosis clinically.
Arboviral and enteroviral encephalitides characteristically appear in clusters or epidemics that occur from midsummer to early fall, although sporadic cases of enteroviral encephalitis occur throughout the year. Herpesviruses and other infectious agents account for additional sporadic cases throughout the year.