ARBOVIRUS INFECTIONS OF THE NERVOUS SYSTEM: CURRENT TRENDS AND FUTURE THREATS

Systemic viral infections are common. Symptomatic involvement of the nervous system in viral infections is uncommon.1 Encephalitis is the most worrying manifestation of nervous system involvement by viruses. Arthropod-borne viruses (arboviruses) are among the most serious international infectious threats to the human nervous system.2 The neuro-logic diseases that may be transmitted by arthropods to humans include meningitis, encephalitis, myelitis, encephalomyelitis, neuritis (including anterior horn cells and dorsal root ganglia), and myositis.2 Arboviruses are distributed worldwide. Different species, however, have a predilection for different geo-graphical areas. Arboviruses are transmitted to vertebral hosts by blood-feeding arthropod vectors including mosquitoes, biting flies, mites, nits, and ticks.2,3 The table reviews some of the common arboviruses, their vectors, and their geographical distribution. Transmis-sion pattern of arboviruses is climate-dependent and is broadly divided into 2 groups. In tropical areas, viruses circulate throughout the year, often with a broad sea-sonal peak. Pattern is different in temperate climates, where virus is transmitted between the vector and ver-tebrate host species only during the warmer months with no arboviral disease in colder months.4 Arboviruses that affect the nervous system are RNA viruses of several genera of the Togaviridae, Fla-viviridae, Bunyaviridae, Reoviridae, and Orthomyxo-viridae families.2,3,5 These arboviruses replicate in peripheral tissues, produce viremia, enter the CNS, replicate in neurons, and spread outward to other neuron populations, a process that may lead to encephalitis.6 Some of the well-known encephalitides include West Nile encephalitis (WNE), Dengue feve