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Arthropod-borne Viruses

Arthropod-borne Viruses. Arthropod-borne viruses (arboviruses) are viruses that can be transmitted to man by arthropod vectors. The WHO definition is as follows

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Arthropod-borne Viruses

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  1. Arthropod-borne Viruses Arthropod-borne viruses (arboviruses) are viruses that can be transmitted to man by arthropod vectors. The WHO definition is as follows “Viruses  maintained  in nature principally, or to an important extent  through  biological  transmission between   susceptible vertebrate  hosts by haematophagus arthropods or through  transovarian and possibly venereal transmission in arthropods.”

  2. General properties • Haemagglutination with fowl RBC’s • Growth in – Chick embryo fibroblasts, vero cells , mosquito cell lines • Inactivated by lipid solvents & Room Temp • All species are capable of producing encephalitis in suckling mice after intracerebral inoculation

  3. Current taxonomic status of some arboviruses • TogaviridaeGenus Alphavirus • FlaviviridaeGenus Flavivirus • Bunyaviridae GenusBunyavirus • ReoviridaeGenus Orbivirus • RhabdoviridaeGenus Vesiculovirus • ArenaviridaeGenus Arenavirus • Nodaviridae Approximately 80 arboviruses known to cause human disease

  4. Arthropod Vectors Mosquitoes Japanese encephalitis, dengue, yellow fever, St. Louis encephalitis, EEE, WEE, VEE etc. Ticks Crimean-Congo haemorrhagic fever, various tick-borne encephalitides etc. Sandflies Sicilian sandfly fever, Rift valley fever.

  5. Examples of Arthropod Vectors Aedes Aegyti Assorted Ticks Phlebotmine Sandfly Culex Mosquito

  6. Transmission Cycles • Man - arthropod - man • e.g. dengue, urban yellow fever. • Reservoir may be in either man or arthropod vector. • In the latter transovarial transmission may take place. • Animal - arthropod vector - man • e.g. Japanese encephalitis, EEE, WEE, jungle yellow fever. • The reservoir is in an animal. • The virus is maintained in nature in a transmission cycle involving the arthropod vector and animal. Man becomes infected incidentally. • Both cycles may be seen with some arboviruses such as yellow fever.

  7. Animal Reservoirs In many cases, the actual reservoir is not known. The following animals are implicated as reservoirs • Birds Japanese encephalitis, St Louis encephalitis, EEE, WEE • Pigs Japanese encephalitis • Monkeys Yellow Fever • Rodents VEE, Russian Spring-Summer encephalitis

  8. Pathogenesis Insect bite Reticulo endothelial system Viremia CNS Capillary endothelium liver Encephalitis hemorrhagic fevers yellow fever

  9. TOGAVIRUSES • Spherical enveloped viruses • 50 – 70 nm diameter • ss RNA • Alpha virus • Rubivirus – rubella virus

  10. Structures of Alphaviruses

  11. Principal medically important alphaviruses

  12. 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.

  13. Pathogenesis of alphaviruses

  14. Symptoms : EEE • Most people have no symptoms • Central Nervous system symptoms develop 4-10 days after being bitten • Sudden onset of fever, muscle aches, headache • May progress to more severe symptoms such as seizure and coma (encephalitis) • 30 to 50% of patients with encephalitis die of the disease

  15. CHIKUNGUNYA • Aedes aegypti • Fever, Sever joint pains, lymphadenopathy, conjunctivitis, rash • Remission after 1-6 days • Hemorrhagic manifestations in few • No animal reservoir, no vaccine

  16. FLAVIVIRIDAE • Spherical, 40-50nm • Single stranded RNA ENCEPHALITIS VIRUSES • St. Louis encephalitis virus • Ilheus virus • West Nile virus • Murry valley encephalitis virus • Japanese B encephalitis virus

  17. Structure of Flaviviruses

  18. Principal medically important flaviviruses

  19. Principal medically important flaviviruses

  20. Principal medically important flaviviruses

  21. Japanese B Encephalitis • First discovered and originally restricted to Japan. Now large scale epidemics occur in China, India and other parts of Asia. • Transmitted by culex mosquitoes. • The virus is maintained in nature in a transmission cycle involving mosquitoes, birds and pigs. • Most human infections are subclinical: the inapparent to clinical cases is  300:1

  22. Pathogenesis Culex mosquito biting human.

  23. Pathogenesis: • Natural infections in birds (Herons) – Reservoirs • Pigs – amplifier hosts • Other birds, cattle & buffaloes - reservoirs Epidemiology: • China, Japan & south east asia • India – Eastern & southern parts • Karnataka - Kolar

  24. AREA OF HIGH OCCURRENCE IN INDIA • The three southern states of Tamil Nadu (TN), Andra Pradesh, Karnataka were reporting higher incidence. • JE is emerging as a public health problem in Kerala • In a few villages of Cuddalore district of Tamil Nadu, a known JE-endemic area (Chidambaram, Virudhachalam, Thittakudi)

  25. JE clinical features • A Prodromal Stage • An Acute encephalitic Stage • and a late stage

  26. Prodromal Stage • Fever • Rigors • Headache • Nausea • and Vomiting • The Prodromal stage usually lasts for 1 to 6 days. It can be as short as less than 24 hours or as long as 14 days

  27. An Acute Encephalitic Stage: 3rd – 5th day • Convulsions • Altered sensorium, unconsciousness, coma • Mask like face • Stiff Neck • Muscular Rigidity • Tremors in fingers, tongue, eyelids and eyes. • Abnormal movements of limbs • Speech impairment

  28. Late Stage: • the persistence of signs of CNS injury such as,      • Mental impairment.      • Increased deep Tendon reflexes      • Paresis either of the upper or lower motor neuron type.      • speech impairment      • Epilepsy, Abnormal movements, Behaviour abnormalities.

  29. Differential Diagnosis • Cerebral Malaria • Meningitis • Febrile Convulsions • Rey’s Syndrome • Rabies • Toxic Encephalopathy

  30. LAB DIAGNOSIS • Peripheral blood picture shows moderate peripheral leucocytosis with neurophilia and mild anemia. • CSF: (cerbro spinal fluid) analysis: Neutrophils may predominate in early CSF samples but a lymphocytic pleocytosis is typical. • CSF protein is moderately elevated in about 50% of cases.

  31. Serological tests • These are to detect antibodies to viral antigens, which include the plaque reduction virus neutralization test, hemagglutination inhibition, and complement fixation. . • A significant rise in titer should be seen with paired samples from the acute and convalescent stages.

  32. Culture • The virus is isolated from CSF by inoculating into 2-4 day old mice and the virus is identified by haemagglutination inhibition. • Japanese encephalitis virus may also be identified by infection of cell cultures (chicken embryo or hamster kidney cells, or the mosquito cell line C3/36) and by IFA.

  33. Prophylaxis • Formalin inactivated mouse brain vaccine • Nakayama strain • Two doses with 2 weeks interval and 1 booster after 12 months

  34. Yellow Fever • Flavivirus, mainly found in West Africa and S America • Yellow fever occurs in 2 major forms: urban and jungle (sylvatic) yellow fever. Jungle YF is the natural reservoir of the disease in a cycle involving nonhuman primates and forest mosquitoes. Man may become incidentally infected on venturing into jungle areas.

  35. The urban form is transmitted between humans by the Aedes aegypti mosquito • Classically Yellow Fever presents with chills, fever, and headache. Generalized myalgias and GI complaints • Some patients may experience an asymptomatic infection or a mild undifferentiated febrile illness.

  36. Yellow Fever • After a period of 3 to 4 days, the more severely ill patients with a classical YF course will develop bradycardia (Faget's sign), jaundice, and haemorrhagic manifestations. • 50% of patients with frank YF will develop fatal disease characterized by severe haemorrhagic manifestations, oliguria and hypotension.

  37. Diagnosis is usually made by serology • There is no specific antiviral treatment • An effective live attenuated vaccine is available against yellow fever and is used for persons living in or traveling to endemic areas.

  38. Vaccine, Immunization Schedule, Immunogenicity and Protection • Yellow fever vaccine is a live attenuated vaccine, the two vaccine substrains used for production (17D-204 and 17DD) are derived from the 17D strain • The vaccine is produced in embryonated eggs • Immunization schedule: administration of 1 dose for persons 9 months • Seroconversion rate: 95% • A single dose provides protection for at least 10 years, probably for live

  39. Dengue • Dengue  is the biggest arbovirus problem in the world today  with over 2 million cases per year. Dengue is found in SE Asia, Africa and the Caribbean and S America. • Flavivirus, 4 serotypes, transmitted by Aedes mosquitoes which reside in water-filled containers. • Human infections arise from a human-mosquitoe-human cycle

  40. Classically, dengue presents with a high fever, lymphadenopathy, myalgia, bone and joint pains, headache, and a maculopapular rash. • Severe cases may present with haemorrhagic fever and shock with a mortality of 5-10%. (Dengue haemorrhagic fever or Dengue shock syndrome.)

  41. Distribution of Dengue

  42. Dengue • Dengue haemorrhagic fever and shock syndrome appear most often in patients previously infected by a different serotype of dengue, thus suggesting an immunopathological mechanism. • Diagnosis is made by serology. • No specific antiviral therapy is available.

  43. Prevention of dengue in endemic areas depends on mosquito eradication. The population should remove all containers from their premises which may serve as vessels for egg deposition. • A live attenuated vaccine is being tried in Thailand with encouraging results.

  44. Transmitting WNV infection

  45. Symptoms : West Nile virus • Most people do not develop symptoms • An estimated 20% become ill 3-15 days after being bitten • Mild illness: fever, headache, body aches, and sometimes skin rash and swollen glands • An estimated 1 in 150 persons infected develop a more severe form of the disease • West Nile encephalitis: inflammation of the brain, high fever, stiff neck, stupor, disorientation, coma, tremors, convulsions, muscle weakness, and paralysis; few cases have been fatal

  46. Russian spring summer encepahlitis (Louping Ill) • Central & Eastern Europe, Russia • Vector: Ixodid ticks - Tranovarial transmission • Resrvoir: Wild rodents & birds • Hosts: Sheep, Goats & Humans • Transmitted by Tick bites or ingestion of milk of infected goats • Vaccine: Formalin inactivated vaccine

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