This document provides information on arthropod-borne viral diseases. It defines arboviruses as viruses transmitted between vertebrate hosts by blood-feeding arthropods like mosquitoes and ticks. The document discusses the classification, properties, transmission cycles involving vectors and reservoir hosts, pathogenesis and examples of important arboviruses including alphaviruses like Chikungunya virus, flaviviruses like Dengue virus, and bunyaviruses. It summarizes the clinical manifestations and treatment approaches for major arboviral diseases.

1. Arthropod – Borne Viral
Diseases
Dr. Somosree (Ghosh) Mukherjee

2. Definition
• The arthropod-borne viruses or arboviruses, are a
group of infectious agents that are transmitted by
bloodsucking arthropods from one vertebrate host
to another.
• The WHO definition is – Viruses that are maintained
in nature principally, or to an important extent,
through biological transmission between
susceptible vertebrate host by hematophagous
arthropods or through transovarian and possibly
venereal transmission in arthropods.

3. General properties
• They can multiply in the tissues of arthropods
without evidence of disease or damage.
• The vector acquires a life-long infection through the
ingestion of blood from a viremic vertebrate.
• All arboviruses have an RNA genome
• Inclusion in this group is based on ecological and
epidemiological considerations and hence it
contains viruses of diverse physical and chemical
properties.

4. Antigenic Structure
• antigens important in serological studies –
1. Hemagglutinins
2. Complement fixing antigens
3. Neutralizing antigens
• Antigenic cross-reactions occur
• The plague reduction neutralization test (PRNT) shows the greatest
specificity for the identification
• Hemagglutination-
• Most agglutinate RBCs of goose or day-old chicks
• It is influenced by pH and temperature
• Spontaneous resolution does not occur
• Inhibition- 1. specifically- antibody ( used in diagnostic assay)
2. nonspecifically- lipoprotein inhibitors in serum, brain and
other tissues.

5. Resistence
• In general – they are labile
• Inactivated at room temperature
bile salts
ether and other lipid solvents
• Infectivity retained – at -70°C
by lyophilization

6. • 3 important components-
• Virus
• Arthropod vector
• Reservoir / Amplifier Host

7. Arthropod Vectors
• Mosquitoes – Japanese B Encephalitis
Dengue
Yellow fever
Rift valley fever
St.Louis Encephalitis
EEE, WEE, VEE etc
• Sandflies - Sicilian sandfly fever
• Ticks – Crimean-Congo hemorrhagic fever
Kyasunur Forest Disease
Various other encephalitis etc,.

9. Animal Reservoirs
• Reservoirs – amplifying host – no apparent disease
• In many cases the actual reservoirs are unknown.
• The following animals are implicated as reservoirs :
• Birds – Japanese B Encephalitis, St.Louis
Encephalitis, EEE, WEE
• Pigs – Japanese B Encephalitis
• Monkeys – Yellow fever
• Rodents - VEE, Russian Spring Summer Encephalitis

10. Transmission

11. Active / Biological transmission
includes
• Inoculation
• Regurgitation
• Feacal contamination
• Contamination from crushing vector

12. Classification
Arbovirus
Single stranded
positive sense RNA
Single stranded
negative sense RNA
Double stranded
RNA
Family : Togaviridae
Genus : Alphavirus
Family : Flaviviridae
Genus : Flavivirus
Family : Bunyaviridae
Genus : Bunyavirus
Phlebovirus
Nairovirus
Family :
Rhabdoviridae
Genus : Vesiculovirus
Family :
Reoviridae
Genus :
Orbivirus
Coltivirus

13. Arbovirus prevalent in India
Virus Reservior Vector Disease
Chikungunya Monkeys Mosquito Chikungunya fever
Dengue Monkeys, Man Mosquito Dengue
hemorrhagic fever
Japanese B
Encephalitis
Wild birds, Pigs Mosquito Encephalitis
Kyasunur Forest
Disease
Forest birds,
animals
Tick Hemorrhagic fever
Sindbis birds Mosquito Sindbis fever

14. Pathogenesis
infected vector bites a suitable host
Virus is injected into the capillary circulation
Comes in contact with endothelial cells of
capillaries,monocytes, macrophages, cells of RES
Replication
secondary viremia
infection of target organs d/t tissue tropism

16. Clinical manifestations
• Fever with or without rash
• Encephalitis – Japanese B Encephalitis, St.Louis
Encephalitis, WEE, EEE
• Heamorrhagic Fever – Yellow fever, Dengue,
Crimean Congo Heamorrhagic fever
• All arbovirus infections occur with varying degree of
severity. Subclinical infections are the most
common

17. Togavirus
• Virus Properties-
• Spherical
• About 30 viruses
• 70nm in diameter
• Nucleocapsid has 42 capsomeres
• Genome- positive sense ssRNA
• 9.7-11.8kb in size
• Envelope – 2 glycoproteins and lipid
• Replication – Cytoplasm
• Assembly budding through host cell membranes.
• Inactivated by acid pH, heat, organic solvents and detergents.
• Most possess hemagglutinating properties
• RUBELLA VIRUS

18. Taxonomic
classification
Arbovirus Arthropod
vector
Host Distribution Symptoms
Togaviridae
Genus
Alphavirus
Chikungunya Mosquito Humans Africa, India,
Southeast asia
Fever, Rash,
Arthralgia
Eastern equine
encephalitis
Mosquito Birds America Encephalitis
Western equine
encephalitis
Mosquito Birds North America Encephalitis
Venezuelan
equine
encephalitis
Mosquito Rodents,
Horses
America Fever,
Encephalitis
Mayaro Mosquito Monkey,
Marsupial
South America fever
O’Nyong-nyong Mosquito Primates Africa Fever, Rash,
Arthralgia
Ross River Mosquito Smallanim australia fever
Semliki Forest Mosquito Birds Africa Fever, rare
encephalitis
Sindbis Mosquito Birds North Fever, Rash,

19. 1.Chikungunya Virus
• The virus is transmitted by Aedes aegypti
• Chikungunya is the native name for the disease in which the
patient lies ‘doubled –up’ due to severe joint pains
• First reported Tanzania in 1952
• The virus first appeared in India 1963 when it caused
extensive epidemics in Calcutta, Madras, and other areas.
• Outbreaks at irregular intervals along east coast of India and
Maharashtra till 1973
• It remained quiesent and then reappeared in 2006
• Large outbreak in Andhra and Tamil Nadu which spread to
Kerala, Karnataka and Delhi.

20. Re-Emergence Of Chickungunya
• Around 2005-2006, There was a reemergence of the
chikungunya virus in Indonesia, Schyecelles, Reunioun
island of Indian ocean and in India(2006-2007)
• As it was reported from Reunion Island in Indian ocean,
the new virus is also know as Reunion virus.
• This was due to-
• 1. Mutation in the E1 glycoprotein of the virus because
of which the arginine in the 226position was replaced by
valine
• 2. The virus was being taken up and transmitted by
Aedes albopiptus.

22. Man to man infection with Mosquito
bites
• Chikungunya virus requires an agent for
transmission and hence direct human to
human transmission is not possible.
• Usually transmission occurs when a
mosquito bites an infected person and
then bites a non infected person.

23. Cinical manifestations
• Incubation period – 2-3 days
• Adults- full blown disease
• Crippling joint pains. Migratory polyarthritis mainly
affects the small joints of the hands and the wrists
•
• Fever – sudden onset, biphasic with a period of
remission of 1-6 days of fever
• Lymphadenopathy
• Conjuctivities
• Rash and Hemorrhagic tendencies

24. • Investigations-
• Routine Investigations
• Most important – IgM capture Mac ELISA- 4 fold
increase in IgM titre
Remains raised upto 3 weeks
After 3 weeks -IgG titre
• Culture in Cell lines- C6/36 mosquito cell line
• RT PCR - Best

25. • Treatment
• SUPPORTIVE
• Vaccine-
• 5 structural genes of the chickungunya virus is
being incorporated in the measles virus and
vaccine is being prepared
• This is in clinical trial.

26. 2.O’nyong-nyong virus
• First isolated in Uganda
• Transmitted by Anopheles mosquito
• Confined to Africa
• Closely resembles Chikungunya virus
antigenically and causes a similar disease.

27. 3.Semliki Forest virus
• First isolated in 1942 in Uganda
• Transmitted by Aedes mosquito
• Not associated with clinical illness in humans
though neutralising antibodies have been
demonstrated in Africans.

28. 4.Sindbis Virus
• First isolated in Sindbis district of Egypt in 1952
• Transmitted by Culex mosquitoes
• Subsequently recovered from other parts of
Africa, India, Phillipines and Australia.
• Reserviour – birds
• Fever, rash , arthralgia

29. 5.Encephalitis causing Alphaviruses
• Eastern Equine
Encephalitis virus
• Western Equine
Encephalitis virus
• Venezuelan Equine
Encephalitis virus

31. Eastern Equine Encephalitis virus
• Transmitted by Aedes solicitans and Aedes
vexans
• Found in Southern costal regions of America
and Atlantics.
• The mortality rate is highest (about 50-70%)

32. Western Equine Encephalitis virus
• Transmitted by Culex tarsalis
• Found in Pacific, West, central, Southwest parts of
America
• Lower mortality (3-7%)
• In both the incubation period varies from 2-4 days
• First there is a primary viral multiplication either in
the myeloid or lymphoid cells or in the vascular
endothelium followed by CNS invasion and
multiplication.

33. Venezualan Equine Encephalitis virus
• Transmitted by Aedes, Psorophora and Culex
mosquitoes
• Found in South and Central America
• I.P. 24-72hrs
• First there is a primary viral multiplication
either in the myeloid or lymphoid cells or in
the vascular endothelium followed by CNS
invasion and multiplication.

34. In Horses-
• Over 50% horses develop high
fever, depression, diarrhoea,
anorexia and weight loss
• Rest have undifferentiated febrile
illness
• Nonfatal cases – convalescence
• Fatal cases – weakness, loss of
balance and horse dies within 2-
4 days.

35. In humans -
• 97% - influenza-like – high fever, headache,
severe mayalgia.
• 3% - encephalitis.
• Lab diagnosis
• Treatment
• VACCINES are available only for the horses.
• Formalinised vaccine for EEE and WEE
• Live attenuated vaccine for VEE

36. Flavivirus
• Virus Properties-
• Spherical
• 70 viruses
• 45-60nm diameter
• Genome- positive sense ssRNA, 10.7kb in size
• Envelope contains 2 glycoproteins and lipid
• Replication – cytoplasm
• Assembly within endoplasmic reticulum
• Inactivation
• hemagglutination
• HEPATITIS C virus

37. Arbovirus Arthropod
vector
Host Distribution Sumptoms
Flaviviridae
Genus
Flavivirus
Brazilian encephalitis (Rocio
virus)
Dengue Mosquito Man Tropics,
worldwide
Fever,rash,he
morrhagia
,shock
Japanese B encephalitis Mosquito Birds, Pigs India, Japan,
China,
Southeast asia
Encephalitis
Kyassur Forest disease Tick Rodents,
monkeys
India Hemorrhagic
fever
Omsk hemorrhagic fever Tick Muskrats Siberia Hemorrhagic
fever
St.Louis encephalitis Mosquito Birds America Encephalitis
Tick borne encephalitis Tick Rodent Europe, asia Encephalitis

38. West nile fever Febrile illness Mosquito Birds Africa, Middle
east, Europe
Yellow fever virus Mosquito Man, primates Africa, South
America
Hemorrhagic
fever, hepatitis
Louping ill
Murray valley
encephalitis
Powassan
Russian spring
summer
encephalitis

39. Bunyavirus
• Virus Properties-
• *Spherical
• *About 300 viruses.
• *80-120nm diameter
• *Genome – triple segmented, negative sense or ambisense, ss RNA,
11-21kb in size
• *Virion contains a transcriptase
• *Envelope contains 2 glycoproteins and lipid
• *Replication – cytoplasm
• *Assembly – budding on smooth membranes of the Golgi system.
• *Inactivation
• *hemagglutination

40. Arbovirus Arthropod
vector
Host Distribution Symptoms
Bunyaviridae
Genus
Bunyavirus
Bunyamwera Mosquito Man Africa Fever
California Encephalitis
(La Cross)
Mosquito Man North
America
Encephalitis,
Fever
Guama Mosquito Man Africa Fever ,Rash
Simbu(Oropouche) Mosquito Man Africa
Asia
Fever
Turlock virus
Genus
Phlebovirus
Sandfly (Phlebotomus)
fever – Silican and
Naples
Sandfly Man Europe, Asia,
Africa
Fever
Rift valley virus Mosquito Man Africa Fever,
encephalitis,
hemorrhagic
illness,
blindness
Uukuniemi virus

41. Arbovirus Arthropod
vector
Host Distributio
n
Symptoms
Bunyaviridae
Genus Nairovirus Crimean congo
hemorrhagic fever
Tick Man
goat,sheep,
cow
Africa, Asia Hemorrhagic
fever
Nairobi sheep ds. Tick Man, sheep Africa, Asia fever

42. Genus Bunyavirus
• 1.Bunyamwera – Transmitted by Anopheles
mosquito.
• First isolated from Uganda in 1946
• Symptoms – fever

43. 2.California Encephalitis (La Crosse
Encephalitis)
• The California Encephalitis virus complex comprises 14
antigenically related bunya viruses Including the La
Crosse virus
• The zoonotic pathogen cycles between the day time
biting treehole mosquito Aedes triseriatus and
vertebrate amplifier host (chipmunks,tree squirrel) in
deciduous forest habitats.
• Onset – abrupt, typically with a severe bifrontal
headache, a fever of 38-40°C, vomiting, lethargy,
convulsions.
• Less frequently – aseptic meningitis
• Prognosis- excellent.

44. 3.Oropouche Fever
• It is a member of Simbu serologic group of Bunya virus
• It is a major cause of human febrile illness in Brazil.
Other – Amazon and Trinidad.
• 3 syndromes can occur – Febrile illness / fever with
rash / meningitis or meningismus.
• Severely ill – some to the point of prostration
• Confused with MALARIA
• I.P. – 4-8days
• Fever, chills, severe headache, myalgia, arthralgia,
dizziness, photophobia.

45. • Occurs in nature in 2 distinct cycles :
• Jungle cycle -(vector still unknown,
responsible for maintaining virus in nature,
vertebrate hosts- primates, sloths, wild birds)
• Urban cycle -humans are infected who serve
as amplifying hosts ;
2 mosquitoes – Culicoides paraensis (main
vector) and Culicoides quinquefasciatus

46. Genus Phlebovirus – 1.Sandfly fever
• Phlebotomus fever / pappataci fever / 3day
fever
• 20 antigenic types
• Mediterranean sea, Russia, Iran ,Pakistan, India
Brazil
• In humans small bite causes itching papule
• I.P. of 3-6days
• headache, malaise, nausea, fever, photophobia,
conjunctival injection, stiffness of neck and back,
abdominal pain, leukopenia.

47. 2.Rift Valley fever
• Mosquito-borne virus causing enzootic
hepatitis in sheep and other domestic animals
in Africa and Middle-east.
• Human infection resembles Dengue and Yellow
fever ( saddle back type fever), pain in joints,
prostration, G.I.distress, marked leukopenia
• Both killed virus and live attenuated virus
vaccine are available for live-stock

48. Genus Nairovirus
• 1.Crimean Congo hemorrhagic fever virus-
-Main human pathogen in this group
-Transmitted by Hyalomma ticks
-Natural reservoir- Cattle, sheep, goats
- Focal cases are reported in India in 2011 and 2013
-During acute phase, blood is highly infectious and
direct transmission through contact may occur.

49. 2.Nairobi Sheep Disease
• East Africa
• Acute hemorrhagic gastroenteritis in sheep
and goats
• Mild febrile illness in shepherds tending
infected flocks
• Transmitted by Rhipicephalus ticks

50. 3.Ganjam Virus
• Isolated From ticks collected from sheep and
goats in Orissa, India, closely related to
Nairobi sheep virus
• Most recent was found in Pune (2004)
• Accidental infection in laboratory workers
cause mild illness.

51. Rhabdoviridae
• Genus Vesiculovirus- Chandipura virus was
isolated in 1967 from the blood of patients during
an epidemic of dengue-chikungunya fever in
nagpur.
• Found first in Chandipura village, Nagpur
• Transmitted both sandfly and Aedes mosquito
• Children affected
• ENCEPHALITIS
• Outbreaks occur in 2003 in AP and Maharashtra

52. Reoviridae
• dsRNA
• Genus Colti virus –
• 1.Colorado tick fever virus –
-Colorado tick fever / tick fever / mountain
fever
-Self limited mild fever without rash, has deep
occular pain, lumbar pain, joint pain, vomitting
-Caused by coltivirus
-Wood tick Dermacentor andersoni- BOTH
vector and reservior

53. • 2.African horse sickness virus-
• Transmitted by Culicoides causes extensive
disease among army horses and mules in
India
• 3.Palyam, Kasba and Vellore viruses
belonging to Orbivirus group have been
isolated from mosquitoes in India but
pathological significance not known

54. Ungrouped Arbovirus
• Wanowri virus-
- Isolated from Hyalomma ticks in India and
from the brain of a young girl who died after a 2-
day fever in SriLanka
- Virus also present in Iran and Egypt
• Bhanja virus-
- Isolated from Haemophysalis ticks from
goats in Ghanjam, Orissa
- Also present in West Africa and Southeast
Europe

55. Laboratory Diagnosis
• Specimen
• Isolation
• Culture
• Serology

56. Specimen
• BLOOD (viremia)
• CSF (encephalitis)
• Best specimen in encephalitis – Brain
• Serum used in serological purpose.
• Routine investigations- complete blood
counts, bleeding and clotting time.,etc.
• CSF examination

57. Isolation
• Specimens inoculated Intracerebrally in the suckling Mice
• Animals develop fatal Encephalitis
• Intracerebral inoculation in suckling mice – most sensitive
method for isolation
• Can also be grown in –
1. Yolk sac or Chorioallantoic membrane of chick
embryo
2. Tissue cultures of primary cell lines like chick embryo
fibroblasts
3. Continuous cell lines like Vero or HeLa
4. Cultures of appropriate insect tissues- C6/36 Mosquito
cell line. Larval or Adult mosquitoes can be used

58. • Isolates are identified by
• Previously
1. Hemagglutination inhibition
2. Complement fixation
3. Gel Precipitation
4. Neutralization test (PRNT) using appropriate
antisera
At Present-
1.ELISA
2.RT PCR
3.Immunofluoresence
4.Immunochromatography
Serology

59. Serology
• By demonstrating rise in the antibody titre in paired
serum samples.
• Acute infection – IgM ELISA Most Rapid
• Best -RT PCR
• Complications in interpretation due to cross reaction
(sera of patient with prior infection or immunization
with other arboviruses because of broad antigenic
reactivity)

60. Treatment
• Rule out and treat febrile illness
• SUPPORTIVE
• Vital monitoring
• ABC
• IV fluids
• Bed care
• Nutrition
• Treatment of raised ICP ( in encephalitis cases)
• DVT prophylaxis
• Vasopressors or cardiotonic drugs ( hemorrhagic
diasthesis)
• Antiplatelet drugs should be withheld.

61. Prevention and Control
• Surveillance – of the disease and vector
populations
• Control of vector – pesticides, elimination of
breeding grounds
• Personal protection – screening of houses,
bed nets, insect repellants
• Vaccinations – available for few – Yellow fever,
vaccines for horses against Equine
encephalitis.

62. Thank You