ST. LOUIS ENCEPHALITIS VIRUS
DATA SHEET – INFECTIOUS SUBSTANCES
SECTION I -
NAME: St. Louis Encephalitis Virus
SYNONYM OR CROSS REFERENCE:
SLE, SLEV, St. Louis encephalitis virus, mosquito-borne encephalitis,
arthropod-borne encephalitis, arbovirus, viral encephalitis (1, 2).
belongs to the family Flaviviridae, genus Flavivirus (formerly grouped
with family Togaviridae) (3, 4) and is a member of Japanese encephalitis virus (JEV) serocomplex (5, 6). SLEV is an arthropod-borne, positive-sense ssRNA, enveloped, icosahedral virus with a genome of approximately
11 Kb (5, 6). They are 40-50 nm in diameter (6).
SECTION II –
Most infections are asymptomatic or result in mild malaise of short duration,
especially in young or middle-aged individuals (1). Clinical disease as a result of infection can include encephalitis, meningoencephalitis,
encephalomyelitis, high fever, altered consciousness, neurologic dysfunction,
aseptic meningitis, stiff neck, headache, myalgia, tremors, nausea, vomiting and
urinary tract infection (1, 3, 7-9). Onset of symptoms is often acute (1, 3, 7), and may resolve spontaneously (1). The severity of clinical illness and fatality rate, but not rate of infection, increase
with age and are most prevalent in the over-60 population (1, 7-13). Hypertension (11, 12) and vascular disease (12) may be risk factors for infection. Based on observations with other members of the Flavivirus genus, immunocompromised individuals may also be at greater risk
of severe illness (14, 15). The fatality rate is 5-20% (1), and acute illness may be followed by prolonged convalescence in 30-50% of
cases (1, 3).
EPIDEMIOLOGY: St. Louis
encephalitis virus is distributed in Northern, Southern and Central America (1). Several outbreaks have occurred, and the average number of reported
cases is slightly more than 100 (16). The greatest number of reported cases was between 1974 and 1976, when more than twelve outbreaks resulted in
more than 2000 officially reported cases in Canada and the United States (10, 16). Cases occur primarily in mid-to-late summer or early fall in temperate areas, and can occur year-round in milder climates (1). Higher temperatures may increase the length of the transmission season, and areas
with the greatest abundance of mosquitoes relative to number of residents (i.e.
rural areas) may be at greater risk of infection (1).
HOST RANGE: Humans, bats, wild birds, domesticated fowl, killer whale, rodents, and possibly other
mammals (1, 2, 6, 8, 12, 15, 17). Wild birds are the primary vertebrate host, and develop an immediate viremic response sufficient to infect the mosquito vector, but do not develop apparent illness following
INFECTIOUS DOSE: Unknown.
MODE OF TRANSMISSION: The primary source of human infections is the
mosquito-wild birds transmission cycle. Infected mosquitoes transmit the virus
by biting an infected animal host and then biting a human host (or other animal
host). Principal mosquito species known to transmit SLE virus are Culex pipiens,
Culex quinquefasciatus, Culex, nigripalpus and Culex tarsalis (1, 9, 10, 13).
INCUBATION PERIOD: 4 – 21
days (1, 9).
transmission has not been documented. Virus is not demonstrated in the blood of
humans after the onset of disease; however, the viremia response in infected
birds is typically detected 1-5 days after infection, depending on the viral
strain and bird species (1, 18). Mosquitoes are infected for life.
SECTION III -
reservoirs are wild birds, domestic fowl, and bats (1, 19). Overwinter survival is possible in bats (19), birds (20), and mosquitoes or mosquito eggs (1).
ZOONOSIS: Yes. SLEV can be
transmitted from infected animals to humans via mosquitoes. Infected animals
are typically asymptomatic (1, 3, 10).
VECTORS: The principal
vectors are mosquitoes of the Culex spp., including C. pipiens, C.
tarsalis, C, quinquefasciatus, C. nigripalpus (1, 10, 13).
SECTION IV – STABILITY
DRUG SUSCEPTIBILITY: No
known drug susceptibility.
DISINFECTANTS: SLEV is susceptible to disinfectants including 3–8%
formaldehyde, 2% glutaraldehyde, 2–3% hydrogen peroxide, 500–5000-ppm available
chlorine, alcohol, 1% iodine, and phenol iodophors (21).
PHYSICAL INACTIVATION: SLEV
is completely inactivated at 56°C for
30 min (22) and is sensitive to UV (23) and gamma (7) irradiation. At 50 °C, 50% of
infectivity is lost in 10 minutes (21) and SLEV is stable at 4°C (22).
SURVIVAL OUTSIDE HOST:
SLEV is stable in liquid aerosol form for at least 6 hours at room temperature
and 23-80% humidity, and in freeze-dried form almost indefinitely at room
SECTION V – FIRST
AID / MEDICAL
SURVEILLANCE: Monitor for
symptoms and confirm by serology. SLEV antibody titre can be determined through
serological testing or lumbar puncture, and seroprevalence rates in free-ranging
birds or sentinel chickens can be useful for monitoring transmission activity (1, 18, 22). Passive surveillance of suspected human SLEV infection, as
well as active monitoring of high-risk populations may provide indications of
human involvement (1). Effective vector control is the only
mechanism for reducing virus amplification and human infections (1).
Note: All diagnostic methods are not necessarily available in
FIRST AID/TREATMENT: There are no vaccines or antiviral agents for SLEV (3). Symptoms and complications as a result of infection are treated with
PROPHYLAXIS: No specific prophylaxis
available; however, measures to reduce the likelihood of mosquito bites may be effective
(i.e. protective clothing, insect repellents).
SECTION VI -
One laboratory-acquired infection by percutaneous exposure was reported in 1950 (24, 25) and another three of non-aerosol source were reported in a
1979 survey of laboratories in the United States (26).
SOURCES/SPECIMENS: Blood (1), CSF (12), urine (17) and exudates (9). Post-mortem, SLEV has been isolated from the CNS, liver, spleen, and
kidney (9, 17, 27-29).
PRIMARY HAZARDS: Exposure
to aerosols of infectious solutions or infected animal blood or urine (i.e.
from animal bedding), accidental perenteral inoculation, or broken skin contact (27).
SPECIAL HAZARDS: None
SECTION VII – EXPOSURE
CONTROLS / PERSONAL PROTECTION
CLASSIFICATION: Risk Group 3 (30).
CONTAINMENT REQUIREMENTS: Containment Level 3
facilities, equipment, and operational practices for work involving infectious
or potentially infectious material, infected animals, or cultures.
PROTECTIVE CLOTHING: Personnel entering the laboratory should remove street
clothing and jewellery, and change into dedicated laboratory clothing and
shoes, or don full coverage protective clothing (i.e., completely covering all
street clothing). Additional protection may be worn over laboratory clothing
when infectious materials are directly handled, such as solid-front gowns with
tight fitting wrists, gloves, and respiratory protection. Eye protection must
be used where there is a known or potential risk of exposure to splashes (31).
OTHER PRECAUTIONS: All activities with infectious material should be
conducted in a biological safety cabinet (BSC) or other appropriate primary
containment device in combination with personal protective equipment.
Centrifugation of infected materials must be carried out in closed containers
placed in sealed safety cups, or in rotors that are loaded or unloaded in a
biological safety cabinet. The use of needles, syringes, and other sharp
objects should be strictly limited. Open wounds, cuts, scratches, and grazes
should be covered with waterproof dressings. Additional precautions should be
considered with work involving animals or large scale activities (31).
SECTION VIII -
HANDLING AND STORAGE
SPILLS: Allow aerosols to settle and, wearing protective clothing,
gently cover spill with paper towels and apply appropriate disinfectant,
starting at the perimeter and working towards the centre. Allow sufficient
contact time before clean up .
before disposal, steam sterilization, and incineration (31).
STORAGE: In sealed
containers that are appropriately labelled in a Containment Level 3 laboratory (31).
SECTION IX – REGULATORY
AND OTHER INFORMATION
REGULATORY INFORMATION: The import, transport, and use of pathogens in Canada is
regulated under many regulatory bodies, including the Public Health Agency of
Canada, Health Canada, Canadian Food Inspection Agency, Environment Canada, and
Transport Canada. Users are responsible for ensuring they are compliant with
all relevant acts, regulations, guidelines, and standards.
UPDATED: September 2010
PREPARED BY: Pathogen
Regulation Directorate, Public Health Agency of Canada.
Although the information,
opinions and recommendations contained in this Pathogen Safety Data Sheet are
compiled from sources believed to be reliable, we accept no responsibility for
the accuracy, sufficiency, or reliability or for any loss or injury resulting
from the use of the information. Newly discovered hazards are frequent and this
information may not be completely up to date.
Public Health Agency of Canada, 2010
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