Chair of Medical Biology, Microbiology, Virology,
and Immunology
Lecturer As. Prof. O.Pokryshko
The term ARBO is an abbreviation of
"ARthropod BOrne".
"Arbovirus" is the name given to Arthropodborne 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.
.
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
 Togaviridae
 Flaviviridae
 Bunyaviridae
 Reoviridae
 Rhabdoviridae
 Arenaviridae
 Nodaviridae
Genus Alphavirus
Genus Flavivirus
Genus Bunyavirus
Genus Orbivirus
Genus Vesiculovirus
Genus Arenavirus
Approximately 80 arboviruses known to cause human
disease
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.
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
Examples of Arthropod Vectors
Aedes Aegyti
Culex Mosquito
Assorted Ticks
Phlebotmine Sandfly
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,
encephalitis, Japanese encephalitis.

Haemorrhagic fever - e.g. yellow fever, dengue,
Crimean-Congo haemorrhagic fever.
St
Louis
Structures of Alphaviruses
Principal medically important alphaviruses
Virus
Antigenic
Clinical
Syndrome
Vector
Host
Distribution
Eastern
equine
encephalitis
Encephalitis
(EEE)
Mosquito
Birds
Americas
Western
equine
encephalitis
Encephalitis
(WEE)
Mosquito
Birds
North
America
Venezuelan
equine
encephalitis
Febrile
illness,
encephalitis
(VEE)
Mosquito
Rodents,
horses
Americas
Virus
Antigenic
Clinical
Syndrome
Chikunguny
(CHIK)
Vector
Host
Distribution
Febrile illness,
rash, arthralgia
Mosquito
Primates,
humans
Africa,
India,
Southeast
Asia
O’nyongnyong
(ONN)
Febrile illness,
rash, arthralgia
Mosquito
Primates
Africa
Sindbisc
(SIN)
Febrile illness,
rash, arthralgia
Mosquito
Birds
Nothern
Europe,
Africa, Asia,
Australia
Semliki
Forest
Febrile illness,
rare
encephalitis
Mosquito
Birds
Africa
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.
Pathogenesis of alphaviruses
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
Structure of Flaviviruses
Principal medically important flaviviruses
Virus
Antigenic
Clinical
Syndrome
Vector
Host
Dengue
(DEN)
Febrile
illness, rash,
hemorrhagic
fever, shock
syndrome
Mosquito
Humans
Tropics,
worldwide
Yellow fever
(YF)
Hemorrhagic
fever,
hepatitis
Mosquito
Primates,
humans
Africa,
South
America
St. Louis
encephalitis
(SLE)
Encephalitis
Mosquito
Birds
Distribution
Americas
Principal medically important flaviviruses
Virus
Antigenic
Clinical
Syndrome
Vector
Host
Distribution
Japanese
encephalitis
(JE)
Encephalitis
Mosquito
Pigs, birds
India, China,
Japan,
South-East
Asia
Febrile
illness
Mosquito
Birds
Africa,
Middle East,
Europe
Encephalitis
Tick
Rodent
West Nile
Tick-borne
encephalitis
(TBE)
Europa,
Asia
Principal medically important flaviviruses
Virus
Antigenic
Clinical
Syndrome
Vector
Host
Distributio
n
Omsk
hemorrhagic
fever
Hemorrhagic
fever
Tick
Muskrats
Siberia
Kyasanur
Forest disease
(KFD)
Hemorrhagic
fever
Tick
Rodents
India
primates
Tick-born encephalitis virus
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.
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.
Transmitting WNV infection
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
Yellow fever
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.
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.
Dengue fever
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.)
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.
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.
Human diseases Caused by Viruses
of the Family Bunyaviridae
Genus and
Group
Virus
Disease
Vector
Distributio
n
Fever
Mosquito
Africa
Bunyavirus
Bunyamwera Bunyamwera
Bwamba
Bwamba
Fever ,
Rash
Mosquito
Africa
California
California
encephalitis
Enceph
a-litis
Mosquito
North
America
Simbu
Shuni
Fever
Mosquito
Africa, Asia
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
Fever
Sand fly
Europe,
Asia, Africa
Rift Valley
Fever
Fever,
encephalitis,
hemorrhagic
fever,
blindness
Mosquito
Africa
Sicilian
Fever
Sand fly
Europe,
Africa, Asia
Human diseases Caused by Viruses of the
Family Bunyaviridae
Genus and
Group
Virus
Disease
Vector
Distribution
Nairovirus
CrimeanCongo
Nairobi
sheep
disease
CrimeanCongo
hemorrhagic
fever
Hemorrhagic
fever
Tick
Nairobi
sheep
disease
Fever
Tick
Africa, Asia
Africa, Asia
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
Rodent
Asia
Sequl
HFPS
Rodent
Asia,
Europe
Human diseases Caused by Viruses of the Family
Bunyaviridae
Genus and
Group
Virus
Disease
Vector
Distributi
on
Genus unassigned
Bangui
Fever, rash
Unknown Africa
Bhanja
Fever,
encephalitis
Tick
Africa,
Europa,
Asia
Issk-kul
Fever
Tick
Asia
Kasokero
Fever
Unknown
Africa
Nyando
Fever
Mosquito
Africa
Tataguine
Fever
Mosquito
Africa
Wanowrie
Fever,
hemorrhage
Tick
Middle
East, Asia
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.
Signs of Crimean-Congo Hemorrhagic Fever
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.
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
Treatment


No specific therapy
Arboviral encephalitis treated by
hospitalization, intravenous fluids, respiratory
support, prevention of secondary infections,
and good nursing care