1. RVF Ecology/Epidemiology

Report
Florida Department of Agriculture and Consumer Services
Charles H. Bronson, Commissioner
Rift Valley Fever - A Florida Animal
Health Perspective
Dr. Thomas J. Holt, State Veterinarian
FDACS, Division of Animal Industry
October 4, 2008
Rift Valley Fever (RVF)
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Epidemic hepatitis of ruminants
High mortality in neonates and abortion
RNA virus vectored by mosquitoes
Zoonotic with acute influenza-like illness with
some blindness, encephalitis and death
• Endemic to east Africa – Rift Valley region with
outbreaks in north Africa and Middle East
• Viewed as significant threat to the United States
1. RVF Ecology/Epidemiology
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Disease caused by virus in Family
Bunyaviridae, Genus Phebovirus
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First described in Kenya 1931 after epizootic
in sheep on a farm north of Lake Naivasha
Viral zoonosis that affects livestock and
humans in Africa
– affects primarily domestic livestock
– horses, pigs, poultry and wild birds nonsusceptible?
Human symptoms - a flu-like illness with fever,
weakness, back pain, dizziness, and weight
loss – leading to hemorrhage (severe
bleeding), encephalitis (inflammation of the
brain), or severe eye complications
Treatment – None, experimental use of
antiviral ribavirin
No U.S. licensed animal or human vaccine
Mortality – 1-25% in humans, 80-100% in
livestock
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Lake
Naivasha,
Kenya
Clinical RVF in Cattle
Feature
Characteristics
Incubation period
1-6 days
Clinical signs
Calves:
—Fever of 40°-42°C (104°-106°F)
—Depression
—Icterus
—Anorexia and weakness
—Listlessness
—Evident abdominal pain
Adults:
—Fever of 40°-42°C (104°-106°F)
—Excessive salivation
—Anorexia
—Weakness
—Near 100% abortion, fetid diarrhea
—Fall in milk yield
—Nasal discharge
Case-fatality rate
—Calves: 10%-70%
—Adults: <10% in indigenous breeds
Clinical features in Sheep
and Goats
Feature
Characteristics
Incubation period
Lambs: 12-36 hrs.
Adults: 1-6 days
Clinical signs
Lambs:
—Fever of 40°-42°C (104°-107°F)
—Anorexia and weakness
—Listlessness
—Evident abdominal pain
Adults:
—Fever of 40°-41°C (104°-106°F)
—Mucopurulent nasal discharge
—Vomiting
—Anorexia
—Listlessness
—Diarrhea
—Icterus
Complications
—Abortion rates can reach 100% (aborted fetus often autolysed)
—Peracute hepatic disease in lambs and kids <1 wk. of age
—Hepatitis
—Cerebral infections
—Ocular infections
Case-fatality rate
Lambs
—<1 wk. of age: as high as 100%
—>1 wk. of age: as high as 20%
Adults: 20%-30%
Short Duration Viremia
Examples: RVF, CHIK, CCHF
Fever
Virus/Ag
Nt/ELISA
Antibody
IgM Antibody
3-5 days
3-5 days
Time
Summary
Patterns of RVF Infection
• Incubation period for RVF is relatively short (3-5 days in
adult humans, 12 hours in young animals)
• Fever coincides with short viremia
• Viremia 3-10 days in humans
• Viremia 2-5 days in cattle
• Amplitude of viremia high (>108 PFU/ml))
• Long-lasting immune response
• Lifelong IgG and neutralization antibodies in humans
RVF Transmission
Biological – Mosquitoes
Mechanical – Flies, midges, other arthropods
Aerosol – Direct contact with infected tissues
Aedes mcintoshi infected with
RVF virus transovarially
Culex species - important secondary vectors
of RVF
Possible Sources of Introduction
Infected Vectors
Viremic Animals
Viremic People
Contaminated Viscera and Tissues
Contaminated Raw Milk
Potential Impacts of a
Zoonotic Disease Like RVF
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Direct and hidden costs
Costs due to potential loss
Effect on agricultural and public health industry
Effects on economy at large (livestock feed suppliers,
health care insurance, and food-service industry)
Loss of confidence in food source
BSE (1986) in UK cost EU > $100 billion
OIE imposes 4-year trade ban on country with RVF
OIE lifts ban after 6 months disease free
U.S. had $5.7 billion beef-related exports in 2003
Epidemiology Considerations in U.S.
• Zoonotic agent
• Wide variety of mammals (deer, rodents,
birds?)
• Mosquito species
• Vertical transmission in mosquitoes
• Few U.S. veterinarians have experience
with controlling vector-borne disease
Implications of RVF Outbreak
For U.S. and other Countries
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National – the U.S. is a major hub of global travel, a major hub of immigration
and commerce, large civilian and military presence all over the world and
specifically Horn Africa – govt., military, business, aid – so the disease could
impact U.S. national interests directly
Importation/introduction of RVF in the U.S. directly
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Risk not determined but even more serious than above
Decimation of the domestic beef cattle industry
No exports
Loss of confidence in the beef industry, also will happen with the sheep and goat
industries, affect dairy cattle because of safety concerns, abortions of pregnant
animals and death in young animals
Disease in people –
– There is no U.S. approved animal or human vaccine
– Only way to control it is through mosquito control
– Rivabirin – anti-viral drug – interferes with the replication of the virus genome, can
reduce human severity of the disease but is in short supply and may not be used on
a large scale
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Could be introduced into U.S. wildlife population
– Deer population and other wild ungulates at high risk
• Could become endemic in deer population in some or all regions of U.S./North America
• Could serve as a reservoir of the virus for humans and domestic animals
Implications of RVF Outbreak
For U.S. and other Countries (continued)
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Could be introduced into U.S. mosquitoes
– Various Culex and some Aedes species of mosquitoes are susceptible
to the virus and will transmit virus efficiently
– Transmission by mosquitoes would be widespread in all regions of
continental U.S.
– Virus might become established transovarially in Aedes mosquito
• Virus transmitted to eggs of mosquito and then passed from larvae,
pupae to adult
• Known to occur in Africa
• Virus would be virtually impossible to eradicate/eliminate
Potential Mechanisms of RVF
Introduction into the U.S.
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International travel by people
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Many people travel back and forth between U.S. and RVF endemic countries
Many FNs travel from endemic countries to the U.S.
Travelers/visitors on commercial flights from RVF endemic areas can reach
virtually any U.S. city in 36 hrs. (shorter than the incubation period of RVF)
Immigrants - many people immigrate to the U.S. from RVF endemic areas
Returning U.S. military forces previously deployed in RVF endemic areas
By mosquitoes
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On an airplane where there is a direct flight between an endemic region and the
U.S. – not common, but can happen – also by military flights
Maritime containers/ships:
Increased where you have plants-water with rodents
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may take weeks, but you have the life cycle going on, including virus transmission
there are maritime container ports near JKI - Kenya
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Example:
Containers are sealed and may contain mosquitoes:
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in a day or two, the container is put on a truck and driven to Mombasa
put on a ship
ship could go to multiple U.S. ports
e.g.. New Orleans, may be opened there or remain closed and be transported to
thousands of inland ports via truck rail or ship and open virtually at any city in the U.S.
Potential Mechanisms of RVF Introduction
into the U.S. (cont.)
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Movement of infected animals into the U.S.
– Rare from Africa but could enter easily via Mexico
Intentional introduction
– Somebody in EA knows an outbreak is going on
– Does not have to be sophisticated
– Could bring infected animal tissue
– If more sophisticated, could bring the virus in a container
– Infect domestic animal by inoculation
Rift Valley Fever
Tabletop Exercise
hosted by the:
Florida Department of Agriculture and Consumer
Services/Division of Animal Industry
prepared by the:
University of Florida/College of Veterinary Medicine
Dr. Paul Gibbs
State Emergency Operations
Center (SEOC)
November 18-20, 2008
Exercise Purpose
• The purpose of this exercise will be to
give participants an opportunity to
plan, initiate, and evaluate current
response concepts, and capabilities
in a simulated introduction and
outbreak of Rift Valley Fever in
Florida
Exercise Focus
• This exercise will focus on
multiagency coordination and the
critical decisions of key state
regulatory/emergency response
agencies in the first days of the
simulated disease outbreak
SEOC War Room
State Warning Point
Scheduled Participating Agencies
• Florida Division of Emergency Management
• Florida Department of Health
• Florida Fish and Wildlife Conservation
Commission
• FDACS/Office of Agricultural Law Enforcement
• FDACS/Agricultural Environmental Services
• FDACS/Division of Animal Industry
• FDACS/Division of Dairy
• FDACS/Commissioner’s Office
• USDA/APHIS
University of Florida,
College of Veterinary Medicine
The Florida
Veterinary Corps
(The Corps) has
been established to
enlist veterinarians
and veterinary
technicians who are
willing to volunteer
their services in
responding to animal
emergencies in the
state of Florida.
Role of Private Veterinarians in Emergency
Response
• Local Expert Consultations
• Disease Management for Specific Clients
coordinated with ICS
• Serve as ICS Responder – Paid or Unpaid
• Industry Outreach
• Planning/Operations

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