Arthropod-Borne (Arbo) Viral Diseases The arthropod-borne viruses, or arboviruses, are a group of infectious agents that are transmitted by blood-sucking arthropods from one vertebrate host to another. They can multiply in the tissues of the arthropod without evidence of disease or damage. The vector acquires a lifelong infection through the ingestion of blood from a viremic vertebrate. All arboviruses have an RNA genome, and most have a lipid-containing envelope and consequently are inactivated by ether or sodium deoxycholate.

Current taxonomic status of some arboviruses Current Taxonomic Classification Arbovirus Members Togaviridae Genus Alphavirus Aura, Chikungunya, eastern equine encephalitis, Getah, Maygro, Mucambo, Ndumu, O'Nyong-nyong, Ross River, Semliki Forest, Sindbis, Venezuelan and Western equine encephalitis Flaviviridae Genus Flavivirus Dengue, Israel turkey meningoencephalitis, Japanese B encephalitis, Kunjin, Kyasanur Forest disease, Murray Valley encephalitis, Ntaya. Omsk hemorrhagic fever. Powassan, St. Louis encephalitis, tick- borne encephalitis, Uganda S, Wesselsbron, West Nile fever, yellow fever,

Current taxonomic status of some arboviruses Current Taxonomic Classification Arbovirus Members Bunyaviridae Genus Bunyavirus Bunyamwera, Bwamba, C, California, Capim, Guama, Koongol, Patois, Simbu, and Tete; 7 unassigned viruses Genus UukuniemiUukuniemi, Anopheles A, Anopheles B, Bakau, Crimean-Congo hemorrhagic fever, Kaisodi, Mapputta, Nairobi sheep disease, Phlebotomus fever, and Turlock; 8 unassigned viruses Reoviridae Genus Orbivirus African horse sickness, bluetongue, and Colorado tick fever viruses Rhabdoviridae Genus Vesiculovirus Cocal, Hart Park, Kern Canyon, and vesicular stomatitis viruses

Current taxonomic status of some arboviruses Current Taxonomic Classification Arbovirus Members Arenaviridae Genus Arenavirus Junin, Lassa, Machupo, and Pichinde viruses NodaviridaeNodamura virus

Sindbis virus

Structures of Alphaviruses

Principal medically important alphaviruses VirusAntigenic Clinical Syndrome VectorHostDistribution Eastern equine encephalitis Encephalitis (EEE) MosquitoBirdsAmericas Western equine encephalitis Encephalitis (WEE) MosquitoBirdsNorth America Venezuelan equine encephalitis Febrile illness, encephalitis (VEE) MosquitoRodents, horses Americas

VirusAntigenic Clinical Syndrome VectorHostDistribution Chikunguny (CHIK) Africa, Febrile illness, rash, arthralgia MosquitoPrimates, humans India, Southeast Asia O’nyong- nyong (ONN) Febrile illness, rash, arthralgia MosquitoPrimatesAfrica Sindbisc (SIN) Febrile illness, rash, arthralgia MosquitoBirdsNothern Europe, Africa, Asia, Australia Semliki Forest Febrile illness, rare encephalitis MosquitoBirdsAfrica

The scheme of Alphavirus replication

Pathogenesis of alphaviruses

FIGURE Alphavirus transmission. Virus abbreviations: Chik, chickungunya; RR, Ross River; May, Mayaro; ONN, O'nyong-nyong; SIN, Sindbis; EEE, eastern equine encephalitis; VEE, Venezuelan equine encephalitis.

Rubella (German measles) is a common mild disease characterized by a rash. It affects children and adolescents worldwide and can also affect young adults. When rubella virus infects susceptible women early in pregnancy, it may be transmitted to the fetus and may cause birth defects. Therefore, accurate diagnosis is critical in pregnancy. The rubella virus is a member of the genus Rubivirus in the family Togaviridae. Rubellaviruses

Rubella virus

Rash

FIGURE. Clinical findings, virus shedding, and serologic response in postnatally acquired rubella.

Abnormalities Associated with Congenital Rubella Syndrome Type of defectsExamples Ocular defectsCataracts Microphthalmia Glaucoma Retinitis Heart defectsPatent ductus arteriosus Atrial septal defect Ventricular septal defect Peripheral pulmonic artery stenosis Hearing impairmentSensorineural deafness

Abnormalities Associated with Congenital Rubella Syndrome Type of defectsExamples Central nervous systemMental retardation Meningoencephalitis Progressive rubella panencephalitis (rare) Microcephaly OtherGrowth retardation Radiolucent borne disease Hepatosplenomegaly Hemathologic abnormalities: Thrombocytopenia, purpura Pneumonitis Endocrine dysfunction: Insulin dependent diabetes mellitus, thyroididtis

Cataract

Glaucoma

Structure of Flaviviruses

Flavivirus

Tick-born encephalitis virus

Figure 5. The scheme of Flavivirus replication

Virions are formed in perinuclear regions of the cytoplasm in association with Golgi or smooth membranes (Figure 6). Virions appear within cytoplasmic vacuoles and appear to exit the cell as vacuoles fuse with the plasma membrane. Unlike alphaviruses, no evidence of budding has been seen in flavivirus-infected cells, and the mechanisms of virion assembly and release remain obscure. FIGURE 6. Morphogenesis of flaviviruses

VirusAntigenic Clinical Syndrome VectorHostDistribution Dengue (DEN) Febrile illness, rash, hemorrhagic fever, shock syndrome MosquitoHumansTropics, worldwide Yellow fever (YF) Hemorrhagic fever, hepatitis MosquitoPrimates, humans Africa, South America St. Louis encephalitis (SLE) EncephalitisMosquitoBirdsAmericas Principal medically important flaviviruses

VirusAntigenic Clinical Syndrome VectorHostDistribution Japanese encephalitis (JE) EncephalitisMosquitoPigs, birdsIndia, China, Japan, South-East Asia West NileFebrile illness MosquitoBirdsAfrica, Middle East, Europe Tick-borne encephalitis (TBE) EncephalitisTickRodentEuropa, Asia Principal medically important flaviviruses

VirusAntigenic Clinical Syndrome VectorHostDistribution Omsk hemorrhagic fever Hemorrhagic fever TickMuskratsSiberia Kyasanur Forest disease (KFD) Hemorrhagic fever TickRodentsIndia primates Principal medically important flaviviruses

Human infection with both mosquito-borne and tick-borne flaviviruses is initiated by deposition of virus through the skin via the saliva of an infected arthropod (Fig 7). Figure 7. Pathogenesis of flaviviruses.

Tick

Yellow fever virus

Yellow fever

Dengue fever virus

Dengue fever

Bunyaviridae is a family of arthropod-borne or rodent-borne, spherical, enveloped RNA viruses. Bunyaviruses are responsible for a number of febrile diseases in humans and other vertebrates. They have either a rodent host or an arthropod vector and a vertebrate host.

Rift Valley Fever virus

Genus and Group VirusDiseaseVectorDistribution Bunyavirus Anopheles ATacaiumaFeverMosquitoSouth America Bunyamwera FeverMosquitoAfrica GermistonFeverAfrica Bwamba Fever, Rash MosquitoAfrica CApeuFeverMosquitoSouth America Human diseases Caused by Viruses of the Family Bunyaviridae

Genus and Group VirusDiseaseVectorDistribution Bunyavirus CaliforniaCalifornia encephalitis Encepha- litis MosquitoNorth America Snowshoe hare Encepha- litis MosquitoNorth America, Asia TahynaFeverMosquitoEurope SimbuShuniFeverMosquitoAfrica, Asia

Human diseases Caused by Viruses of the Family Bunyaviridae Genus and Group VirusDiseaseVectorDistribution Phlebovirus Phlebovirus fever AlenquerFeverUnknownSouth America NaplesFeverSand flyEurope, Asia, Africa Rift Valley Fever Fever, encephalitis, hemorrhagic fever, blindness MosquitoAfrica SicilianFeverSand flyEurope, Africa, Asia

Human diseases Caused by Viruses of the Family Bunyaviridae Genus and Group VirusDiseaseVectorDistribution Nairovirus Crimean- Congo Crimean- Congo hemorrhagic fever Hemorrhagic fever TickAfrica, Asia Nairobi sheep disease FeverTickAfrica, Asia

Human diseases Caused by Viruses of the Family Bunyaviridae Genus and Group VirusDiseaseVectorDistribution Hantavirus HataanHantaanHFRSRodentAsia PuumalaHFRSRodentAsia SequlHFRSRodentAsia, Europe

Human diseases Caused by Viruses of the Family Bunyaviridae Genus and Group VirusDiseaseVectorDistributi on Genus unassigned BanguiFever, rashUnknownAfrica BhanjaFever, encephalitis TickAfrica, Europa, Asia Issk-kulFeverTickAsia KasokeroFeverUnknownAfrica NyandoFeverMosquitoAfrica TataguineFeverMosquitoAfrica WanowrieFever, hemorrhage TickMiddle East, Asia

FIGURE 3. Pathogenesis of bunyavirus infections. Humans are dead-end hosts of most bunyaviruses; however, the blood of Crimean-Congo hemorrhagic fever patients may be highly infectious.

FIGURE 5. La Crosse encephalitis transmission cycle

Signs of Crimean-Congo Hemorrhagic Fever

Clinics of Hataan virus infection