1. Chair of Medical Biology, Microbiology, Virology, and Immunology
Arboviruses
Lecturer As. Prof. O.Pokryshko

2. The term ARBO is an abbreviation of "ARthropod BOrne".
"Arbovirus" is the name given to Arthropod-borne viruses, that is, viruses that are transmitted to vertebrates, such as people and mammals, by blood-feeding insects called arthropods. Vertebrate infection occurs when the infected insect bites an animal or person and takes a blood meal.

3. .
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.

4. Current taxonomic status of some arboviruses
Togaviridae Genus Alphavirus
Flaviviridae Genus Flavivirus
Bunyaviridae Genus Bunyavirus
Reoviridae Genus Orbivirus
Rhabdoviridae Genus Vesiculovirus
Arenaviridae Genus Arenavirus
Nodaviridae
Approximately 80 arboviruses known to cause human disease

5. 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.

6. 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

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

8. Diseases Caused
Fever and rash - this is usually a non-specific illness resembling a number of other viral illnesses such as influenza, rubella, and enterovirus infections. The patients may go on to develop encephalitis or haemorrhagic fever.
Encephalitis - e.g. EEE, WEE, St Louis encephalitis, Japanese encephalitis.
Haemorrhagic fever - e.g. yellow fever, dengue, Crimean-Congo haemorrhagic fever.

9. Structures of Alphaviruses

10. Principal medically important alphaviruses
Antigenic Clinical Syndrome
Vector
Host
Distribution
Eastern equine encephalitis
Encephalitis (EEE)
Mosquito
Birds
Americas
Western equine encephalitis
Encephalitis (WEE)
North America
Venezuelan equine encephalitis
Febrile illness, encephalitis (VEE)
Rodents, horses

11. Antigenic Clinical Syndrome Vector Host Distribution Chikunguny (CHIK)
Virus
Antigenic Clinical Syndrome
Vector
Host
Distribution
Chikunguny (CHIK)
Febrile illness, rash, arthralgia
Mosquito
Primates, humans
Africa,
India, Southeast Asia
O’nyong-nyong (ONN)
Primates
Africa
Sindbisc (SIN)
Birds
Nothern Europe, Africa, Asia, Australia
Semliki Forest
Febrile illness, rare encephalitis

12. FIGURE Alphavirus transmission
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. Structure of Flaviviruses

16. Principal medically important flaviviruses
Antigenic Clinical Syndrome
Vector
Host
Distribution
Dengue (DEN)
Febrile illness, rash, hemorrhagic fever, shock syndrome
Mosquito
Humans
Tropics, worldwide
Yellow fever (YF)
Hemorrhagic fever, hepatitis
Primates, humans
Africa, South America
St. Louis encephalitis (SLE)
Encephalitis
Birds
Americas

17. Principal medically important flaviviruses
Antigenic Clinical Syndrome
Vector
Host
Distribution
Japanese encephalitis (JE)
Encephalitis
Mosquito
Pigs, birds
India, China, Japan, South-East Asia
West Nile
Febrile illness
Birds
Africa, Middle East, Europe
Tick-borne encephalitis (TBE)
Tick
Rodent
Europa, Asia

18. Principal medically important flaviviruses
Antigenic Clinical Syndrome
Vector
Host
Distribution
Omsk hemorrhagic fever
Hemorrhagic fever
Tick
Muskrats
Siberia
Kyasanur Forest disease (KFD)
Rodents
India primates

19. Tick-born encephalitis virus

21. Figure. Pathogenesis of 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).
Figure. Pathogenesis of flaviviruses.

22. Japanese Encephalitis
First discovered and originally restricted to Japan. Now large scale epidemics occur in China, India and other parts of Asia.
Most human infections are subclinical: the inapparent to clinical cases is  300:1
In clinical cases, a life-threatening encephalitis occurs.
The disease is usually diagnosed by serology.
No specific therapy is available.
Since Culex has a flight range of 20 km, all local control measures will fail. An effective vaccine is available.

23. Transmitting WNV infection

24. 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

25. Yellow fever

26. 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.
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 (N+V).
Some patients may experience an asymptomatic infection or a mild undifferentiated febrile illness.

27. 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.
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.

28. Dengue fever

29. 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
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.)

30. 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.
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.

31. 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.

33. Human diseases Caused by Viruses of the Family Bunyaviridae
Genus and Group
Virus
Disease
Vector
Distribution
Bunyavirus
Bunyamwera
Fever
Mosquito
Africa
Bwamba
Fever , Rash
California
California encephalitis
Encepha-litis
North America
Simbu
Shuni
Africa, Asia

34. Human diseases Caused by Viruses of the Family Bunyaviridae
Genus and Group
Virus
Disease
Vector
Distribution
Phlebovirus
Phlebovirus fever
Alenquer
Fever
Unknown
South America
Naples
Sand fly
Europe, Asia, Africa
Rift Valley Fever
Fever, encephalitis, hemorrhagic fever, blindness
Mosquito
Africa
Sicilian
Europe, Africa, Asia

35. Human diseases Caused by Viruses of the Family Bunyaviridae
Genus and Group
Virus
Disease
Vector
Distribution
Nairovirus
Crimean-Congo
Crimean-Congo hemorrhagic fever
Hemorrhagic fever
Tick
Africa, Asia
Nairobi sheep disease
Fever

36. Human diseases Caused by Viruses of the Family Bunyaviridae
Genus and Group
Virus
Disease
Vector
Distribution
Hantavirus
Hataan
Hantaan
HFPS (hantavirus pulmonary syndrom)
Rodent
Asia
Puumala
HFPS
Sequl
Asia, Europe

37. Human diseases Caused by Viruses of the Family Bunyaviridae
Genus and Group
Virus
Disease
Vector
Distribution
Genus unassigned
Bangui
Fever, rash
Unknown
Africa
Bhanja
Fever, encephalitis
Tick
Africa, Europa, Asia
Issk-kul
Fever
Asia
Kasokero
Nyando
Mosquito
Tataguine
Wanowrie
Fever, hemorrhage
Middle East, Asia

38. FIGURE. Pathogenesis of bunyavirus infections
FIGURE. 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.

39. Signs of Crimean-Congo Hemorrhagic Fever

40. Diagnosis
Serology - usually used to make a diagnosis of arbovirus infections.
Culture - a number of cell lines may be used, including mosquito cell lines. However, it is rarely carried out since many of the pathogens are group 3 or 4 pathogens.
Direct detection tests - e.g detection of antigen and nucleic acids are available but again there are safety issues.

41. Prevention Surveillance - of disease and vector populations
Control of vector - pesticides, elimination of breeding grounds
Personal protection - screening of houses, bed nets, insect repellants. When possible, wear protective clothing while outdoors.
Vaccination - available for a number of arboviral infections e.g. Yellow fever, Japanese encephalitis, Russian tick-borne encephalitis

42. Treatment No specific therapy
Arboviral encephalitis treated by hospitalization, intravenous fluids, respiratory support, prevention of secondary infections, and good nursing care