California Encephalitis, Hantavirus Pulmonary Syndrome, Hantavirus Hemorrhagic Fever with Renal 166 Syndrome, and Bunyavirus Hemorrhagic Fevers Raphael Dolin
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i. Bunyaviridae California Encephalitis, Hantavirus Pulmonary Syndrome, Hantavirus Hemorrhagic Fever With Renal 166 Syndrome, and Bunyavirus Hemorrhagic Fevers Raphael Dolin SHORT VIEW SUMMARY Definition Major Causes of Human Diseases Diagnostic tests are typically performed in } Bunyavirales is a large order of RNA viruses (See Table 166.1) reference laboratories. consisting of 10 families and more than 350 } California encephalitis group: Therapy named species. They are enveloped, } La Crosse virus (LACV) } Treatment is primarily supportive because specific single-stranded RNA viruses with a segmented Jamestown Canyon virus (JCV) } antiviral therapy is not available. Ribavirin has genome. Bunyavirales members can be found Rift Valley fever virus (RVFV) } been studied in some bunyavirus infections, and worldwide and are able to infect invertebrates, Crimean-Congo hemorrhagic fever virus (CCHFV) } data from in vitro and in vivo models hold vertebrates, and plants. Hantaviruses } promise. Ribavirin has shown clinical benefit in Hemorrhagic fever with renal syndrome Epidemiology } HFRS and in CCHF. However, comprehensive (HFRS) } Bunyaviruses are significant human pathogens clinical trials have not been conducted. } Hantavirus pulmonary syndrome with the ability to cause severe disease, } Severe fever with thrombocytopenia syndrome Prevention ranging from febrile illness, encephalitis, and virus (SFTSV) } No specific preventive measures are available, hepatitis to hemorrhagic fever. but experimental vaccines for some With exception of hantaviruses, bunyaviruses Diagnosis } bunyaviruses have been developed and are are transmitted by hematophagous arthropods, In most cases the diagnosis is based on } undergoing study. Individual protective including ticks, mosquitoes, and phlebotomine serologic investigation of acute and early measures, such as arthropod repellents and flies. convalescent sera. Early diagnosis can be insecticide-impregnated mosquito bed nets, Hantaviruses are maintained in nature through based on reverse-transcriptase polymerase } are recommended in endemic areas. persistent infection of rodents. chain reaction assays of blood samples. Bunyaviruses are an extraordinarily diverse and numerous group of VIROLOGY viruses whose taxonomic complexity has led to a recently reorganized Structure,Structure, Replication,R and classification yb the International Committee on Taxonomy of Viruses Antigenic Relationships (ICTV). In 2017 the ICTV reclassified the family Bunyaviridae to that Bunyavirales members are spherical, enveloped RNA viruses, 80 to 120 nm of an order, Bunyavirales, that comprises 10 families: Arenaviridae, in diameter and that display surface glycoproteins of 5 to 10 nm.3 The RNA Cruliviridae, Fimoviridae, Hantaviridae, Mypoviridae, Nairoviridae, is of negative sense or ambisense, and codes for six or fewer proteins. The Peribunyaviridae, Phasmaviridae, Phenuiviridae, and Wupedeviridae. genome consists of two to six segments, although the majority of bunya- The families comprise 35 genera, with more than 350 named viruses viruses studied have a trisegmented genome (Fig. 166.1).3–5 The large RNA identified as ps ecies.1,2 Classification into separate families and species segment (L) encodes an RNA-dependent RNA polymerase; the medium is based on genomic, structural, biochemical, and antigenic chracteristics,3 segment (M) encodes viral glycoprotein precursors, which are cleaved by although limited data are available for a number of these viruses. The the host protease to yield mature glycoproteins, Gn and Gc, that are involved distribution of these viruses is via arthropod-vertebrate cycles or by in receptor binding and endomembrane fusion. The small genome segment chronic infection of vertebrates, which lead to epidemiologic patterns (S) encodes the nucleocapsid proteins.3–5 The molecular weights of the that are ecologically determined and can be focal or diffuse depending proteins and RNAs vary by genus. In general, the Gn or Gc proteins, or on climatic variables. Table 166.1 presents salient features of infections both, are targets for neutralizing antibodies.3 The nucleocapsid protein is caused by Bunyavirales viruses, including vectors, transmission, epide- believed to be the most important source of immunologic relationships miology, and clinical expression. Details of these infections are discussed observed within and across families and genera. In general, the fluorescent further as follows. antibody test is the most cross-reactive, with hemagglutination inhibition 2169 2170 (HI), and although the neutralization tests provide greater specificity, the Virus replication occurs in the cytoplasm, and virions mature by latter is of greatest use in distinguishing individual viruses. Enzyme-linked budding from the Golgi complex and endoplasmic reticulum into vesicles. immunosorbent assays (ELISAs) increasingly are used for diagnosis of Some bunyaviruses are exceptions, such as Rift Valley fever virus (RVFV), s acute or resolving (immunoglobulin [Ig]M) or retrospective (IgG) infections which buds through the outer cell membrane of hepatocytes, and Sin 3 ent (see later). Nombre virus (SNV), which matures at the cytoplasmic membrane. g ic A EPIDEMIOLOGY g EcologyEcology andand DistributionDist With the exception of hantaviruses, all bunyaviruses are transmitted tiolo E by arthropods (mosquitoes, ticks, and sand flies). Hantaviruses are S transmitted through feces from rodent species, such as deer mice or the striped field mouse. L Gn protein California Encephalitis Viruses M Among the California encephalitis (CE) virus group, La Crosse virus Gc protein (LACV) is the most medically significant virus, causing an average of 6 Lipid envelope 79 cases per year, predominantly in children younger than 15 years. Its principal vector is Aedes triseriatus, a forest-dwelling, tree-hole–breed- L protein ing mosquito of the north-central and northeastern regions of the RNP N protein country. LACV is maintained in this mosquito via transovarial transmis- ectious Diseases and Their f sion supplemented by intraspecific venereal transmission and amplifica- In FIG. 166.1 Bunyavirus structure. The three genome segments (L, M, tion during summer by mosquitoes feeding on viremic chipmunks, I and S) are encapsidated by nucleocapsid protein to form ribonucleoprotein 7,8 complexes (RNPs), and together with the viral L protein (RNA-dependent squirrels, foxes, and woodchucks. RNA polymerase) are packaged within a host cell-derived lipid envelope Female mosquitoes infected by any of these mechanisms are capable Part II modified by insertion of the viral glycoproteins Gn and Gc. (Modified from of transmitting virus via a bite. The virus survives during the winter in Elliot RM, Schmaljohn CS. Bunyaviridae. In: Knipe DM, Howley PM, eds. mosquito eggs.9 LACV and human encephalitis were first recognized Fields Virology. Philadelphia: Lippincott Williams & Wilkins; 2013:1245.) in the upper Mississippi and Ohio River valleys. Most cases have TABLE 166.1 Some Characteristics of Severe Diseases Caused by Bunyavirales DISEASE PATTERN GENUS AND TRANSMISSION AND ANNUAL MAJOR CLINICAL DISEASE VIRUSES VECTOR TO HUMANS INCIDENCE FEATURES California encephalitis Orthobunyavirus Aedes triseriatus Mosquito bite Summer-fall; northern Meningoencephalitis, La Crosse Transovarial transmission; United States: 60–130 seizures, cerebral Jamestown Canyon amplification by cases edema chipmunks Rift Valley fever Phlebovirus Aedes mcintoshi Mosquito bite; aerosol Endemic in rainy season Acute febrile illness with Rift Valley fever Transovarial transmission; or contact with fresh sub-Saharan Africa: occasional retinitis, horizontal transmission carcasses, domestic hundreds of cases; hemorrhagic fever, or in other arthropods animals occasional epidemics encephalitis associated with exceptional rainfall Crimean-Congo Orthonairovirus Hyalomma ticks Tick bite, contact with Spring-summer; regions of Severe hemorrhagic fever hemorrhagic fever Crimean-Congo Amplified by hares, blood of humans or former Soviet Union, Hemorrhagic Fever domestic animals domestic animals Middle East, Africa: 50–200 cases Hemorrhagic fever Orthohantavirus Chronic infection of Aerosols from rodent Endemic and epidemic; Fever, shock, bleeding, with renal syndrome Hantaan striped field mouse, excreta season depends on local renal failure Dobrava yellow-necked mouse, conditions. Asia, Seoul rat, or bank vole Europe: 100,000 cases Puumala Hantavirus pulmonary Orthohantavirus Chronic infection of deer Aerosols from rodent Discovered in 1993; Fever, shock, pulmonary syndrome Sin Nombre mouse and other excreta dozens of cases edema Bayou rodents annually in North and Black Creek Canal South America Tropical Fever Orthobunyavirus Biting midge By biting midges Epidemic and sporadic Acute febrile illness with Oropouche Culicoides paraensis disease in tropical areas occasional hemorrhagic of Brazil, Peru, and complications Panama Sand fly fever Phlebovirus Phlebotomus perniciosus, Mosquito bite Circum-Mediterranean Fever, headache, myalgia, Toscana Phlebotomus papatasi distribution in Southern meningitis Sand fly fever Europe Severe fever with Phlebovirus Haemaphysalis longicornis, Tick bites, close Central and eastern Fever, multiorgan thrombocytopenia SFTS Ixodes nipponensis, person-to-person China, South Korea, dysfunction, bleeding syndrome (SFTS) Amblyomma contact western Japan diathesis testudinarium Heartland virus disease Phlebovirus Tick-borne Probably tick-borne Midwestern and southern Fever, headache,