RVFV & EHDV Flashcards
What type of virus is RVFV? What Genus does it belong to?
- Bunyaviruses
- Phlebovirus
What are the characteristics of RVFV?
- Enveloped
- Single-stranded RNA (Group V)
- segmented genome:
- L (large) M (medium) S (small)
How is RVFV spread? How can the virus be inactivated?
- Arthropod-borne (mosquitos)
- Zoonotic
- Inactivated by lipid solvents, detergents, and low pH
How is RVFV spread? How can the virus be inactivated?
- Arthropod-borne (mosquitos)
- Zoonotic
- Inactivated by lipid solvents, detergents, and low pH
What is the genomic structure of RVFV?
- Segmented - 11.9kb
- Large: Viral polymerase
- Medium: Glycoproteins (Gn, Gc), NSm
- Small: Nucleoprotein (N), NSs
- Ambisense RNA segment
- Relatively low genetic diversity for RNA virus
What is the geographic spread of RFVF?
- Mosquito-borne zoonotic disease of domestic and wild ruminants:
- 1st reported in Kenya in early 1900s
- Endemic in tropical and subtropical regions of Africa, Madagascar, Arabian Peninsula
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What are the common results of epidemics/epizootics of RVFV?
- Acute febrile disease
- Abortion in livestock
- abortion storm
- death of young animals
- Major affected species:
- Sheep
- cattle
- goats
- influenza-like illness in humans
Why is RVFV important?
- Emerging transboundary viral disease
- Reportable FAD
When do outbreaks of RVFV occur?
- associated with abnormally heavy rainfalls or localized flooding
- Epidemics occur at 5-15y intervals in Africa - peaks in late rainy season, late summer
- Seasonal outbreaks in colder regions
Why are outbreaks of RVFV associated with heavy rainfall?
- Transovarial transmission in mosquitoes - dormant virus in eggs in soil
- Heavy rainfall ⇢ eggs hatch, infected mosquitoes emerge
- Virus can also subclinically cycle between mosquitoes and mammalian hosts between outbreaks
- Virus is spread by movement of viremic animals and wind-borne mosquitoes
What are the insect vectors of RVFV
- Mosquitoes:
- Aedes
- Anopheles
- Culex
- Other potential species including US mosquitoes
- Biting flies - mechanical vector
Can infected animals/humans infect mosquitos with RVFV?
- Infected livestock - sheep, cattle, goats
- High levels of viremia
- Sufficient to infect feeding mosquitoes
- Establishes disease in environment
- Leads to large epizootic/epidemics
- High levels of viremia
- Humans can have viremia levels high enough to infect mosquitos
What animals are the most susceptible to RVFV?
- Mortality 100%
- young animals (lambs, calves, kids, puppies, kittens, rodents)
- Severe illness abortion mortality
- Sheep, cattle, goats, humans
What animals are resistant to RVFV?
Horses and pigs
What is the mortality rate of RVFV in lambs/kids? Clinical signs?
- Very high mortality (90-100%)
- Incubation period 12-36 hours
- high fever (up to 108F)
- Listlessness
- Reluctance to move
- reduced appetite
- abdominal pain
- tachypnea
- Death within 12 hours to 3 days
What is the mortality rate of RVFV in sheep/goats? Clinical signs?
- Lower mortality (20-30%)
- Incubation period: 24-72h
- Fever
- lethargy
- diarrhea
- icterus
- hematemesis
- hematochezia
- mucopurulent nasal dishcarge
- Can be subclinical
What is the mortality rate of RVFV in calves? Clinical signs?
- Less susceptible than lambs (10-70% mortality)
- Clinical signs similar to lambs/kids:
- fever
- depression
- acute death
- Death within 2-8d after onset
What is the mortality rate of RVFV in cattle? Clinical signs?
- Lower mortality (5-10%)
- infections are often subclinical
- Fever
- weakness
- reduced appetite
- lacrimation
- salivation
- nasal discharge
- dysgalactia
- diarrhea
- hematochezia
- icterus
What are the clinical signs of RVFV in pregnant livestock?
- Abortion - may be only sign
- Abortion storm in affected herds
- Ewes/does: high rate (5-100%) seen, occurs at any stage of gestation
- Cattle: usually < 10%, can be up to 85% during outbreaks
- Aborted fetuses are usually autolyzed
Is there a vaccine for RVFV?
- Modified-live Smithburn vaccine
- Not available in US
- Side effects:
- early embryonic death
- congenital CNS abnormalities
- arthrogryposis
- Abortion / stillbirth
Who should perform the necropsy on animals with suspected RVFV?
trained personnel with appropriate PPE
What gross lesions are expected in an animal with RVFV?
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Hepatitis:
- Enlarged, soft, yellow, friable liver
- Irregular congested patches or petechial hemorrhages
- numerus grayish white necrotic foci
- Hemorrhage and edema of gallbladder wall and mucosa of abomasum
- Dark born intestinal contents
- Splenomegaly + lymphadenopathy with edema and petechiae
What microscopic lesions are expected in an animal with RVFV?
severe and extensive hepatic necrosis
When should RVFV be suspected?
When abnormally heavy rains and flooding are followed by widespread occurrence of abortions and mortality among newborn ruminants characterized by necrotic hepatitis, concurrent with influenza-like disease in people handling animals
How is RVFV diagnosed?
- Reportable FAD
-
PCR/VI
- tissue of aborted fetuses, liver, spleen
- blood of infected animals
-
Viral antigen detection
- ELISA, IHC, antigen staining of organ impression smears
-
Serological tests
- Acute and convalescent samples
- IgM ELISA - detects recent infection
How should RVFV be managed?
- Contact authorities:
- PPE - gloves, coveralls, boots, eyewear, respirator
- Avoid contact with infected tissues/blood
- Restrict animal movement, quarantine
- Do NOT slaughter sick animals - bury or burn
- Vaccination - NOT in US
- Vector control:
- insect repellents, environmental management (standing water breeds mosquitoes)
How do humans become infected with RVFV?
- Readily infects people via direct contact
- Slaughter or necropsy of infected animals
- Contact with infected tissues, body fluids, aborted fetuses
- High risk: veterinarians, farm laborers, abattoir workers, butchers
- NO person-to-person transmission reported
What are the human clinical signs of RVFV?
- Usually subclinical
- Incubation period 2-6 days
- flu-like illness - fever, malaise, myalgia, headache, nausea, vomiting, arthralgia
- Self-limiting - recovery in 4-7 days
-
Sever Disease 1-2% of cases
- Ocular disease (retinopathy), encephalitis, or severe hepatic lesions with hemorrhage
- Death in 10-20% of severe cases
- Overall mortality rate: ~1%
What family is Schmallenber virus (SBV) part of? Genus?
- Bunyaviruses
- Orthobunyavirus
What are the characteristics of SBV?
- Enveloped
- ssRNA viruses (Group V)
- Segmented genome
- Arthropod-borne (Culicoides sp)
- Domestic and wild ruminants only - not zoonotic
- Susceptible to common disinfectants
What is the history of SBV?
- Identified in 2011 - European cattle, sheep, goats, bison
- Affected dairy cow herds:
- fever, reduced appetite, reduced milk production, weight loss
- High herd morbidity (20-70%), recovery after a few days
- Sheep, goats, cattle:
- abortions and stillbirths with congenital malformations
- up to 20-50% aborted/deformed lambs in affected sheep flocks
- Affected dairy cow herds:
How is SBV transmitted?
- Biting flies (Culicoides sp)
- Vertical transmission by in utero infection
- Direct transmission between animals NOT reported - unlikely
What are the clinical signs of SBC in adult sheep/goats?
- Increased abortions and congenital malformations in offspring
- Otherwise generally subclinical
What are the clinical signs of SBV in adult cattle?
- Can be subclinical
- Transient fever, reduced appetite, malaise, reduced milk production, diarrhea, abortion - recovery within a few days
- Lower incidence of congenital malformations than sheep
What Congenital malformations can SBV cause in neonates and fetuses?
- Arthrogryposis/hydranencephaly syndrome (AHS)
- Specific signs reflect stage of gestation when infected
- Stillbirth, premature birth, mummified fetuses
- Arthrogryposis, hydranencephaly, ataxia, paralysis, muscle atrophy, joint malformations, torticollis, kyphosis, scoliosis, behavioral abnormalities, blindness
Why is SBV important?
- FAD - Reportable
- Chance of introduction to US
How is SBV diagnosed?
- PCR, VI, SN Ab test, ELISA, IFA
- fetus/neonate: brain, spleen, blood, placenta, amniotic fluid, meconium
- Dam/Adult: blood
How is SBV controlled?
- No specific treatment
- Vector control - house pregnant animals indoors at night during critical periods to reduce exposure
- breed outside the vector season
- Inactivated vaccines - available in some countriessss
