1. Arthropod-Borne
Viruses
Part 1 lecture

2. What Is An Arbovirus?
• Arbovirus = arthropod-borne viruses
• Arboviruses are maintained in nature
through biological transmission between
susceptible vertebrate hosts by blood-
feeding arthropods
• Vertebrate infection occurs when the
infected arthropod takes a blood meal

3. Arboviral Infections.
• 100s of Arbovirus,
• Around 100 are Human pathogens,
• Prevalent in Temperate and Tropical
areas.
• Most common in tropics,
• Out of Many 10 are very important.

4. Arthropod-borne Viruses
Arthropod-borne
viruses (arbovirus)
are viruses that can
be transmitted to
man by arthropod
vectors. “

5. 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 trans ovarian and possibly
venereal transmission in
arthropods.”

6. Arbovirus belong to
• Arbovirus belong to three families
• 1. Toga viruses e.g. EEE, WEE, and VEE
• 2. Bunya viruses e.g. Sandfly Fever, Rift
Valley Fever, Crimean-Congo
Hemorrhagic Fever
• 3. Flavivirus e.g. Yellow Fever, dengue,
Japanese Encephalitis

7. Disease Mechanisms of Toga viruses and Flavivirus
Viruses are cytolytic, except for rubella.
Viruses establish systemic infection and viremia.
Viruses are good inducers of interferon, which can account for the flulike
symptoms of infection.
Viruses, except rubella and hepatitis C, are arboviruses.
Flaviviruses can infect cells of the monocyte-macrophage lineage. Non-
neutralizing antibody can enhance flavivirus infection via Fc receptors on
the macrophage.
Flulike Syndrome Encephalitis Hepatitis Hemorrhage Shock
Dengue + + + +
Yellow fever + + + +
St. Louis encephalitis + +
West Nile encephalitis + +
Venezuelan encephalitis + +
Western equine encephalitis + +
Eastern equine encephalitis + +
Japanese encephalitis + +

8. Man-Arthropod-Man Cycle

9. Animal-Arthropod-Man Cycle

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

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

12. 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

13. Major Arboviral Diseases
1.Yellow fever
2.Dengue,
3.Japanese B Encephalitis,
4.St Louis Encephalitis,
5.Russian spring summer encephalitis.
6.Eastren Equine Encephalitis,
7.West Nile Fever,
8.Sand fly Fever

14. Major Arboviruses That Cause
Encephalitis
• Flaviviridae
– Japanese encephalitis
– St. Louis encephalitis
– West Nile
• Togaviridae
– Eastern equine encephalitis
– Western equine encephalitis
• Bunyaviridae
– La Crosse encephalitis

15. http://www.cdc.gov/ncidod/dvbid/arbor/schemat.pdf

17. St. Louis Encephalitis

18. St. Louis Encephalitis
• Flavivirus
• Most common
mosquito-
transmitted human
pathogen in the US
• Leading cause of
epidemic flaviviral
encephalitis

19. Eastern Equine Encephalitis
• Toga virus
• Caused by a virus transmitted to
humans and horses by the bite of
an infected mosquito.
• 200 confirmed cases in the US
1964-present
• Average of 4 cases per year
• States with largest number of
cases – Florida, Georgia,
Massachusetts, and New Jersey.
• Human cases occur relatively
infrequently, largely because the
primary transmission cycle takes
place in swamp areas where
populations tend to be limited.

20. Western Equine Encephalitis
• Toga virus
• Mosquito-borne
• 639 confirmed cases in
the US since 1964
• Important cause of
encephalitis in horses
and humans in North
America, mainly in the
Western parts of the US
and Canada

21. West Nile virus (WNV)
• West Nile virus (WNV) is a
mosquito-borne zoonotic arbovirus
belonging to the genus Flavivirus in
the family Flaviviridae. This flavivirus is
found in temperate and tropical regions
of the world. It was first identified in the
West Nile sub-region in the East African
nation of Uganda in 1937.

22. How the disease manifests
• Approximately 80 percent of West Nile virus infections
in humans are subclinical, which cause no
symptoms. In the cases where symptoms do occur –
termed West Nile Fever in cases without
neurological disease – the time from infection to
the appearance of symptoms (incubation period) is
typically between 2–15 days. Symptoms may
include fever, headaches, fatigue, muscle pain of
aches, malaise, nausea, anorexia vomiting myalgias
and rash. Less than 1% of the cases are severe and
result in neurological disease when the central nervous
system is affected.

23. La Crosse Encephalitis
• Bunya virus
• On average 75 cases per year
reported to the CDC
• Most cases occur in children under
16 years old
• Zoonotic pathogen that cycles
between the daytime biting tree hole
mosquito, and vertebrate amplifier
hosts (chipmunk, tree squirrel) in
deciduous forest habitats
• Most cases occur in the upper
Midwestern state, but recently cases
have been reported in the Mid-
Atlantic region and the Southeast
• 1963 – isolated in La Crosse, WI from
the brain of a child who died from
encephalitis

24. Togaviridae

25. Togaviridae
• The name
Togaviridae
derived from
Toga meaning
roman mantle or
claok refers to
the viral surface

26. TOGAVIRIDAE
Chikungunya virus Infection
• 1952 Epidemic in Tanzania.
• Manifest as Bend Up with Severe
Joint pains.
• Spread from wild primates –
Mosquito-Man
• Appears , reappears,

27. Indian outbreaks
• The virus first appeared in India in
1958 the virus caused large
epidemics in Thailand
• In 1963 India Chikungunya
outbreaks occurred at irregular
intervals along the east coast of India
and in Maharashtra

28. Viral Morphology
• Spherical 50 - 70
nm
• Bears the
Nucleocapsid, 42
capsomeres
• Positive sense ss
stranded RNA

29. Prevalence of Chikungunya

30. Transmission of Infection

31. 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 later bites a non
infected person.

32. Clinical Manifestations
•Crippling Joint pains
•Conjunctivitis
• Lymphadenopathy
•Hemorrhagic
tendencies.

33. Diagnosis
• Isolation of
viruses,
• Serology Ig M
• Nt and HI
tests,

34. Control and Prevention.
• Mosquito control
• No vaccines,
• Other diseases like Chikungunya
1 Onyong Nyong Viruses
2 Simliki Forest Viruses

35. Japanese B Encephalitis

36. Flaviviridae
Genus – Flavivirus,
• Important Diseases,
1. St Louis encephalitis,
2.Ilheus virus
3.West Nile Virus,
4.Murray valley encephalitis,
5.Japanese B encephalitis,

37. Japanese Encephalitis belongs to
Genus Flavivirus
• Flaviviridae
– Flavivirus
• The name is derived from
the Latin ‘flavus’
– Flavus means “yellow”
• Refers to yellow fever virus
• Enveloped
• Single stranded RNA virus
• Morphology not well
defined
Center for Food Security and Public
Health Iowa State University - 2007

38. Japanese Encephalitis
• First discovered and originally restricted to Japan.
Now large scale epidemics occur in China, India and
other parts of Asia.
• Flavivirus, 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 in apparent
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.
• .

39. History
• 1870s: Japan
– “Summer encephalitis” epidemics
• 1924: Great epidemic in Japan
– 6,125 human cases; 3,797 deaths
• 1935: First isolated
– From a fatal human encephalitis case
• 1938: Isolated from Culex
tritaeniorhynchus
Center for Food Security and Public
Health Iowa State University - 2007

40. Genus - Flavivirus
• Japanese B encephalitis
virus is
Spherical, 40 – 60 nm in
diameter
Contain a positive sense
Single stranded RNA, 11 kb
in size
RNA genome is infectious
Several viruses in this group
are related.
Dr.T.V.Rao MD 40

41. Japanese B virus Infection
Infection is caused by a flavivirus, a single
stranded RNA virus. It is transmitted by
the bite of the Culex tritaeniorhynchus
mosquito. The virus multiplies at the site
of the bite and in regional lymph nodes
before viraemia develops. Viraemia can
lead to inflammatory changes in the
heart, lungs, liver, and
reticuloendothelial system.
Dr.T.V.Rao MD 41

42. Structure of Virus
• The outer envelope is
formed by envelope (E)
protein and is the protective
antigen. It aids in entry of
the virus to the inside of the
cell. The genome also
encodes several non-
structural proteins also
(NS1,NS2a,NS2b,NS3,N4a,N
S4b,NS5). NS1 is produced
as secretary form also. NS3
is a putative helicase, and
NS5 is the viral polymerase.
Dr.T.V.Rao MD 42

43. A Flavivirus
• Japanese encephalitis ( previously
known as Japanese B encephalitis is a
disease caused by the mosquito-borne
Japanese encephalitis virus. The
Japanese encephalitis virus is a virus
from the family Flaviviridae. Domestic
pigs and wild birds are reservoirs of the
virus; transmission to humans may occur
Dr.T.V.Rao MD 43

44. INDIAN SCENARIO
• Japanese encephalitis ( previously known
as Japanese B encephalitis is a disease
caused by the mosquito-borne Japanese
encephalitis virus. The Japanese
encephalitis virus is a virus from the
family Flaviviridae. Domestic pigs and
wild birds are reservoirs of the virus;
transmission to humans may occur
D 44

45. History
• 1940-1978
– Disease spread with epidemics in China,
Korea, and India
• 1983: Immunization in South Korea
– Started as early as age 3
– Endemic areas started earlier
• 1983-1987: Vaccine available in U.S. on
investigational basis
Center for Food Security and Public
Health Iowa State University - 2007

46. A leading cause of viral
Encephalitis
• Japanese
encephalitis is the
leading cause of viral
encephalitis in Asia,
with 30,000–50,000
cases reported
annually. Case-
fatality rates range
from 0.3% to 60%
and depends on the Dr.T.V.Rao MD 46

47. Animal-Arthropod-Man Cycle

48. Cycle of Infection in Japanese B Viral
Infection
Dr.T.V.Rao MD 48

49. Transmission
• Vector-borne disease
• Enzootic cycle
– Mosquitoes: Culex species
• Culex tritaeniorhynchus
– Reservoir/Amplifying hosts
• Pigs, bats
• Ardeid (wading) birds
• Possibly reptiles and amphibians
– Incidental hosts
• Horses, humans, others
Center for Food Security and Public
Health Iowa State University - 2007

50. A Vector born- Arbovirus Infection
• Culex tritaeniorhynchus
a rural Mosquito that
breeds in rice fields, is
the principle vector.
In India in 1955 the virus
were isolated from
Culex vishnui
mosquitoes in Vellore
region in Tamil Nadu
Dr.T.V.Rao MD 50

51. Japanese Encephalitis (JE)
• Most important global
cause of arboviral
encephalitis with > 50,000
cases and 15,000 deaths
reported each year.
• Only about 1 in 250 JE
infections result in
symptomatic illness.
• If unrecognized, mortality is up 1 30% with half of
• Primarily affects children to
survivors sustain age. neurological sequelae.
to 15 years of severe
• Incubation period is 5 to 14
days.

52. INCIDENCE
• Leading cause of viral encephalitis in Asia
with 30-50,000 cases reported annually
• Fewer than 1 case/year in U.S. civilians
and military personnel travelling to and
living in Asia
• Rare outbreaks in U.S. territories in
Western Pacific
Dr.T.V.Rao MD 52

53. Dr.T.V.Rao MD 53

54. Cycle of Events in Japanese B
Encephalitis
Dr.T.V.Rao MD 54

55. Pass through two prominent Hosts
• Herons act as reservoir
hosts and pigs as
amplifier hosts.
• Human infection is a
tangential ‘dead end’
and infections are
spread when the
infected mosquitoes
reach high density.
Dr.T.V.Rao MD 55

56. Clinical Manifestations
• The incubation period is 6 to 16 days.
• There is a prodrome of fever, headache, nausea,
diarrhoea, vomiting, and myalgia, which may last for
several days.
• This may be followed by a spectrum of neurological
disease ranging from mild confusion, to agitation, to
overt coma.
• Two thirds of patients have seizures. It is more
common in children, while headache and meningism
are more common in adults.
Dr.T.V.Rao MD 56

57. Common symptoms of encephalitis
Lethargy
Sudden fever
Headache Change in
consciousness
Irritability or
restlessness
Tremors or
Vomiting and
convulsions
diarrhea

58. Can lead to Neurological damage
• Tremor or other involuntary movements
are common.
• Mutism has been described as a
presenting symptom. So has a syndrome
of acute flaccid paralysis.
• Fever resolves by the second week, and
choreoathetosis or extra pyramidal
symptoms develop as the other
neurological symptoms disappear.
Dr.T.V.Rao MD 58

59. Diagnosis of Japanese B Encephalitis
• The isolation of virus from
Blood, CSF, or tissues.
• Detection of Arbovirus specific
RNA in blood,CSF, or Tissue
• However very few reference
laboratories can perform the
isolation in view of the
biosafety considerations
Dr.T.V.Rao MD 59

60. Serology by ELISA
• IgM capture enzyme-linked immunoassay (ELISA) of
serum or CSF is the standard diagnostic test.
Sensitivity is nearly 100% when both serum and CSF
are tested. False-negatives may result if the samples
are tested too early, as in the first week of illness.
• New IgM dot enzyme immunoassays for CSF and
serum are portable and simple tests that can be used
in the field. Compared with ELISA as the gold
standard, the sensitivity and specificity are around
98 and 99% respectively.
Dr.T.V.Rao MD 60

61. Arbovirus Specific RNA detection
• Viral RNA is extracted from serum or from
suspected tissues of the patients or mosquito
homogenates.
• The product is amplified by RTPCR and the
products analyzed by restriction digestion and
determined by nucleotide sequence of PCR
product.
• The identified sequence is compared with
nucleotide sequence found in Gene bank or
other data bases
Dr.T.V.Rao MD 61

62. Japanese Encephalitis B Vaccine
• Japanese Encephalitis B Vaccine has been
produced since 1992. The vaccine is effective
but not without risks and the substantial risks
of the disease and the risks of the vaccine
have to be balanced, especially for stays of
brief duration. These are discussed more fully
in the article on that subject.
As with malaria, prophylaxis must be
supplemented by techniques to avoid being
bitten by mosquitoes.
Dr.T.V.Rao MD 62

63. Preventive measures
• Preventive measures include mosquito control
and locating piggeries away from human
dwellings
• A formalin inactivated mouse brain vaccine
using the Nakayama strain has been employed
in human immunization in Japan – Two doses
at two week’s interval followed by a booster 6
– 12 months later constitute a full course.
• However the immunity was short lived
Dr.T.V.Rao MD 63

64. Emerging Vaccines for JE virus
• Two vaccines are manufactured and distributed
exclusively in People’s Republic of China
– Inactivated vaccine grown in primary hamster kidney cells
– Live attenuated vaccine (SA14-14-2) grown in hamster
kidney cells
• The third is manufactured in Japan and distributed
abroad by arrangement with Sanofi-Pasteur
– Licensed as JE-VAXR and is the only FDA approved vaccine
for use in the U.S.
– Has been in wide use worldwide since the 1960’s
– Three subcutaneous injections over a month with a
booster at 3 years
– 91% efficacy in a large field trial in Thailand

65. Vaccination
• Live attenuated vaccine
– Used in equine and swine
– Successful for reducing incidence
• Inactivated vaccine (JE-VAX)
• Used for humans
• Japan, Korea, Taiwan, India, Thailand
• Used for endemic or epidemic areas
– Recommended for travelers
• Visiting endemic areas for > 30 days
Center for Food Security and Public
Health Iowa State University - 2007

66. Later vaccines
• A live attenuated vaccine has been developed
in China from JE strain SA 14-14-2, passed
through weanling mice
• The vaccine is produced in primary bay
hamster kidney cells.
• Administered in two doses, one year apart,
the vaccine has been reportedly effective in
preventing clinical disease
Dr.T.V.Rao MD 66

67. Prevention
• Vector control
– Eliminate mosquito breeding areas
– Adult and larvae control
• Vaccination
– Equine and swine
– Humans
• Personal protective measures
– Avoid prime mosquito hours
– Use of repellants containing DEET
Center for Food Security and Public
Health Iowa State University - 2007

69. Yellow Fever,
Flaviviridae - Family
• Mosquito Borne disease
• Present in Africa, Central
and South America.
• Absent in India.

71. Flavivirus
• Spherical 40-60 nm in diameter
glycosylated. Diameter,
• Ss-RNA positive sense
• Three or Four structural polypeptides,
Two are glycosylated.
• Replicates in Cytoplasm.
• Produces Councilman bodies

72. Pathogenesis and Pathology
• Mosquito ( Ades aegypti )Through skin-
Lymphatic's, Lymph nodes, circulation liver,
Spleen, Kidney, Bone marrow, Lymph glands.
Necrotic lesions in liver , kidney,
Mid zone – liver
Fatty degeneration – kidney,
Hemorrhages/Circulatory collapse.
Injury to Myocardium

73. Clinical Features
• Incubation period 3-6 days,
• Fever, chills,
• Intoxication, Fever, Jaundice
• Clotting disorders,
• Mortality > 20%
• May recover totally

74. Laboratory Diagnosis
• Intracerebral inoculation,
• Mosquito cell lines,
•PCR
• Serology –
ELISA Ig M Raise of
titers,

75. Immunity and Epidemiology
• Nt Antibodies protects,
• Epidemiology
Urban yellow fever,
Jungle yellow fever. Monkey,
Not Invaded Asia Not present in India.

76. Immunity and Epidemiology
• Nt Antibodies protects,
• Epidemiology
Urban yellow fever,
Jungle yellow fever. Monkey,
Not Invaded Asia Not present in India.

77. Treatment and Prevention.
• No Antiviral drugs,
• Mosquito control
• Vaccine 17 D strain of yellow fever
vaccine.
• A single dose protect 95% of vaccinated.
• Not to be given in infants < 9 months
age.

78. • Programme Created By Dr.T.V.Rao
MD for Undergraduate Teaching in
Medical Sciences
• Email