L4_ARBOVIRUSES & RABIES VIRUSES

Togaviridae

Flaviviridae

Bunyaviridae

Families of arboviruses (TFB)

vectors or biting arthropods (mosquitoes, ticks, midges, sandflies)

Arboviruses are transmitted by

small, roughly spherical, enveloped viruses with ssRNA

shape, capsid, sense, and genome of arboviruses

lipid solvents, detergents and extremes of pH and temperature

arboviruses are fragile and sensitive to

1. Vertebrate

2. Specific type of biting arthropod

for arboviruses; life cycle requires,

Viral encephalitis

arboviruses is responsible for the disease that affects the neurons and neuroglia

1. Vaccination

2. Vector control

3. Prevention of insect bites

Methods of Prevention of arboviruses

Positive (+) ss RNA, nonsegmented; enveloped icosahedral

segment, capsid & symmetry, sense, and genome of arboviruses

cytoplasm

TOGAVIRIDAE replicates in the

mosquito

vector of TOGAVIRIDAE

WEE, EEE, and VEE

TOGAVIRIDAE causes 3 diseases

Alphaviruses (EEs) & Rubivirus (Rubella)

2 groups of togaviridae

Positive (+) ss RNA, nonsegmented; enveloped Icosahedral

segment, capsid & symmetry, sense, and genome of flaviviridae

• Aedes

• Culex

2 mosquito vectors of Flaviviridae viruses

Aedes mosquito

mosquito that causes Yellow and Dengue fevers

Culex mosquito

mosquito that causes : St. Louis and Japanese encephalitis, West Nile encepalitis virus (outbreak in 1937 in Uganda)

Negative (-) ss RNA; segmented (3); Helical

segment, capsid & symmetry, sense, and genome of BUNYAVIRIDAE

Arthropod

Vector of BUNYAVIRIDAE

Hantavirus -exotic virus

Vector of BUNYAVIRIDAE are arthropods except

❖ California encephalitis virus

❖ Rift Valley fever virus

❖ Sandfly fever virus

viruses under the BUNYAVIRIDAE family

Arboviruses

what viruses are very fragile and must be handled with care

True

T/F: Identification procedures are difficult and not practical for arboviruses

False

T/F: Identification procedures are difficult and not practical for arboviruses thus it is referred to tertiary laboratories

False

T/F: Serologic studies for arboviruses can be done because reagents are easy to find

horses

host for EEVs

swamp dwelling mosquitoes

EEVs are spread by

St. Louis Encephalitis Virus

mosquito-borne encephalitis; primarily as viruses of birds (sparrows); Infection occurs in urban areas; (Culex; stagnant water)

3-6 days

Incubation period of yellow fever virus

A. Sylvan (Jungle) Yellow Fever

B. Urban Yellow Fever

2 distinct epidemiological pattern of yellow fever virus

canopy dwelling monkeys and tree-hole mosquitoes

Sylvan (Jungle) Yellow Fever species involved

• Aedes spp in Africa

• Haemagogus spp in S. America

tree-hole mosquitoes responsible for the Sylvan Yellow Fever

Aedes aegypti

vector of urban yellow fever

high fever, slow pulse, toxic phase

Clinical features of urban yellow fever

REC (reticuloendothelial cells) of many organs

Replication site of urban yellow fever

lifetime specific immunity and short-term (<3 mos) cross-immunity

when infected by a DEN it provides two types of immunity

1. Classic Dengue Fever (a.k.a. break bone fever)

2. Dengue Hemorrhagic fever

3. Dengue Hemorrhagic Shock

Three distinct forms/stages of DEN clinical manifestion

Classic Dengue Fever

there is Sudden onset of systemic toxicity, fever, headache, vomiting, severe myalgia or bone pain of escalating intensity; most common clinical manifestation of DEN

3-5 days

Incubation period of Classic Dengue Fever

Maculopapular or morbiliform rash

Classic Dengue Fever rash

3-5

in classic dengue fever, Remittance of fever on day ____ of illness

a. diffuse capillary leak with hemoconcentration (increased vascular permeability)

b. thrombocytopenia

c. disseminated intravascular coagulation (DIC)

Dengue Hemorrhagic fever Results from additional pathogenic processes:

DEN-2

in dengue hemorrhagic fever >90% of cases were previously infected with another serotypes, usually with what serotype?

Dengue Hemorrhagic Shock

Decreased plasma volume resulting from increased vascular permeability which causes clinical shock that if not corrected may lead to hyperkalemia, acidosis, death

• fever

• hemorrhagic manifestations

• excessive capillary permeability

• less than 100,000/mm3 platelets

4 criteria for DHF

• disappearance of fever

• drop in platelets

• increase in hematocrit

Initial warning signals

Neutralization test

test for primary infection for Dengue

False

T/F: Dengue serological tests are easier to interpret in endemic cases

Virus Isolation

laboratory test that uses mammalian or insect cell culture (blood or CSF); new technique involves inoculating a mouse macrophage cell line with patient’s blood + specific antibody to flavivirus

Immunofluorescence staining (2-4 days)

Viral isolation uses what staining and when is the result released?

C6/36

most widely used Mosquito cell lines

1. C6/36

2. AP-61

3. TRA-248-SFG

mosquito cell lines

plaque reduction Nt (Neutralization test)

Identification of cell lines for DEN

Japanese Encephalitis Virus

major cause of encephalitis in Asia; most common cause of arboviral encephalitis in whole world

bullet-shaped

unique shape of rabies virus

enveloped virus with linear, (-) sense ssRNA and a helical nucleocapsid

capsid, sense, and genome of rabies virus

1

how many serotypes does rabies virus have

Rabies

most lethal of all infectious diseases

a. Furious Rabies

b. Dumb Rabies

2 Forms of rabies

Furious rabies

rabies that affects limbic/nervous system

Furious rabies

symptoms include headache, fever, irritability, restlessness, anxiety and muscle pain, salivation and vomiting; hydrophobia → coma

Dumb Rabies

rabies affects neocortex (spinal cord & medulla)

Dumb Rabies

symptoms include depression and paralysis followed by coma; death results from respiratory arrest; difficult to diagnose clinically

3-8 weeks to 1 year

Incubation period of dumb rabies

myocytes

in dumb rabies, Virus remains at bite site and replicates in ?

neocortex

dumb rabies affects the

limbic/nervous system

furious rabies affects the

1. Bite of rabid animal

2. Superficial abrasion of skin

3. Human to human via saliva

Transmission of rabies

head of rabid animal

Sample used for rabies

impression smears

smears to perform for rabies lab diagnosis

Direct Immunofluorescence Assay (IFA)

fastest and most sensitive test for rabies

Rapid Fluorescent Focus Inhibition Test

in vitro cell culture neutralization test that measures rabies neutralizing antibody

suckling or young adult mice

Isolation of rabies uses

murine neuroblastoma and related cell lines, hamster and mouse cell lines

cell lines used for rabies

ELISA

most sensitive serological test for rabies

CSF

rabies spx that is only positive in infected but not in vaccinated individuals

Negri bodies

histological exam of rabies shows what CPE

No treatment for clinical rabies

treatment for rabies

Prophylaxis

Vaccine for rabies that includes Ig

Tissue culture

less painful vaccine for rabies