Transcript Flaviviridae - Webpages - Individual Webpages on Homepage

Flavi and Pestiviruses
October 12, 2010
BVD, Hog cholera, Border disease
Pestiviruses
Flaviviridae
Flaviviruses
Yellow fever
Japanese encephalitis
St. Louis encephalitis
Dengue
West Nile virus
(arthropods, biological vectors)
Hepacviruses
Hepatitis C virus
West Nile Outbreaks
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Israel - 1951-1954, 1957
South Africa - 1974
Romania – 1996
Italy – 1998, 2008
Russia - 1999 (human)
United States –1999-2009 (equine, human)
Canada - 2001-2009 (equine, human)
Israel – 1998, 2000 (human)
France (Rhine delta) - 2000 (equine)
return from south
late summer and
fall
spring
early summer
overwinter
or
eggs
dead-end hosts
amplification in birds
Saskatchewan mosquito species
shown to be capable of transmitting
WNV
• Aedes vexans (spring to fall)
• Ochlerotatus flavescens,
spencerii(July-August)
• Culex restuans*, tarsalis* (JulyAugust)
• Culiseta inornata*
• Coquillettidia perturbans
How does the virus overwinter
and spread?
• migratory birds?
• overwintering
mosquitos?
• bird to bird
transmission?
– Komar et al. EID March 2003
in the mosquito
3. virus leaks from
gut and infects
salivary glands
4. virus
released in
saliva during
feeding
1. virus
ingested
with
blood
meal
(sufficient amount
of virus must be
ingested - > 105
infectious units/ml)
2. virus multiplies in
gut epithelial cells
in mammals
virus transmitted in mosquito
saliva during probing
virus deposited in extra vascular tissue
replication in skin and lymph nodes
“flu” like
symptoms
amplification in extra-neural tissues
PCR
IgM,
viremia (secretion in milk)
viremia terminated by immune
response
crosses blood/brain barrier (repl’n in vascular
endothelium, exacerbated by concurrent infections)
inflammation perivascular infiltration
(plasma cells and macs), cerebral edema.
“neurological”
signs
viral damage to neurons and
glia or dysfunction
CSF IgM, pleocytosis,
PCR
equine cases of WNV
neurological disease
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Ataxia 86%
Depression 51%
Hind limb weakness 49%
Difficulty or inability to rise 46%
Muscle tremors 41%
Fever only 24%
• Differentials:
– rabies, EHV 1, EEE, WEE, botulism
• 10% to 50% of horses with neurological signs die
clinical signs in people
• most asymptomatic
• fever, “flu” like symptoms (fatigue, anorexia, nausea,
vomiting, arthralgia, rash, lymphadenopathy)
• encephalitis, meningoencephalitis - ataxia, painful
eyes, seizures, change in mental status (confusion)
case fatality rate in hospitalized patients - 10-12%
risk factor for severe disease (age 50-60 yr are 10 times and >80
yr are more than 40 times likely)
Petersen and Margin, WN virus: a primer for the clinician 2002. Ann Int med 137:173
unusual cases in USA
• infant infected through breast milk
• 2 people infected through blood
transfusion
• 2 laboratory workers while dissecting
infected animals
the Canadian experience
• 2000 - 2,288 birds examined, 185
tested - no positives
• 2001 - 2,807 bird carcasses from NF to
Sask tested
– 128 WNV infected birds from 12 health
dist. in Ontario
– no disease in horses or humans
human cases 2003-2005
May
June
July
Aug
Sept
Oct
http://www.phac-aspc.gc.ca/wnv-vwn/mon-hmnsurv-archive-eng.php
http://www.phac-aspc.gc.ca/wnv-vwn/mon-hmnsurv-eng.php
West Nile virus in domestic birds
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geese
ducks
chickens and turkeys
ostriches, emus
testing for WNV - serology
samples from 45 horses, Virden Manitoba (Aug-Sept, 2002)
strong + cont
weak + cont
IgM capture
ELISA
PDS immunol.
lab
vaccines
Fort Dodge
Intervet – PreveNile Live Flavivirus chimera
West Nile Virus – Common Client Questions
• Should we vaccinate our horse – is it safe and does it
work?
• Can I catch WNV from a horse?
• What signs might a horse show early on?
• Is there a treatment?
• What can we do to limit the risk to our horse?
• Can our other pets get it?
• When should we vaccinate our horses?
Pestiviruses
1940s
HCV
• Systemic haemorrhagic disease - pigs
(USA)
BVDV
• Enteric disease - calves (USA)
• Congenital, neurological “hairy-shakers”
(England/Wales)
BDV
Flaviviruses
Flaviviruses
Japanese
encephalitis
Louping ill
Murray Valley
Dengue
West Nile
St. Louis
encephalitis
Yellow fever
Pestiviruses
Hepatitis C
Pestiviruses of Artydactyla
bovine viral diarrhoea
border disease
(BVDV)
(BDV)
Wide host range (camelids, deer etc)
hog cholera
(HCV)
BVDV genome and gene
products
UTR
structural
nonstructural
gp53 p125
(p54+p80)
Regions that show the most variation
Biotypes of BVDV
Based on effect on cells in tissue-culture
NON-cytopathic
(natural state)
Cytopathic
(mutant)
CP vs NCP – genetic differences
UTR
structural
nonstructural
p125
(p54+p80)
Biotypes - implications
• Non-cytopathic
– Implications for vaccines and research
• Cytopathic
– Mucosal disease
BVDV “types” Not different
serotypes!!
• BVDV-1
• BVDV-2
Based on:
1. sequence differences
In non-translated region of genome
Does not imply differences in pathogenicity
2. Antigenic differences
UTR structural
nonstructural
Antigenic differences between
BVDV-1 and BVDV-2
Serum against
VN titre against
BVDV-1
BVDV-2
strains
strains
BVDV-1
strains
800->12,800
100->3,200
BVDV-2
strains
50->400
3,200->51,200
Pellerin et al.(1994) Virology 203:260-268
Pathogenesis - infection
• Intra-species
– PI carriers
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Inter species
Vaccine related?
Artificial breeding programs
Blood
Persistence in acutely infected animals
Pathogenesis
Pathogenesis - disease in
imm.competent, non-pregnant
animals
• Sub-clinical
• Mild fever, leukopenia, decreased milk
production
• Mild BVD - mild erosive lesions, ulcerative
stomatitis, diarrhoea, respiratory
• Severe disease - lesions mimic MD,
thrombocytopenia, haemorrhagic syndrome,
hyphemia
Pathogenesis - pregnant animals
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All syndromes described above
Embryonic death
Abortions
Birth defects
Persistently infected calves
Pathogenesis - PI animals
• Healthy, normal
• “poor-doers”
• Mucosal disease
Guess which one is persistently
infected?
Calves of the same age. From Lee et al. CVJ 38:29
consequences of having a PI
animal
• Loneragan et al. JAVMA, Feb 15, 2005
– PI animals more likely to be ill, require
treatment or die
– Incontact animals more likely to be sick,
require treatment
• Dieguez et al. Res Vet Sc, Aug 2009
• Correlation BVD status and respiratory
disorders, mortality
Mucosal disease
• NCP->CP (p80)
• Infection with antigenically related CP virus
(mutation, herd-mate, vaccination?)
• Low morbidity high mortality
• High fever, depression, anorexia, diarrhoea
• Ulcerative mucosal lesions
• Death 2 days -> 3 weeks
Mucosal Disease (by mutation)
MD
Mucosal Disease (by infection or
injection)
MD
No Mucosal Disease if CP virus
antigenically different
No MD
Immune response
Diagnostic procedures
• Virus isolation
– Small numbers ($31.50)
– Herd screening - microtitre ($10 -2->10, $6 >10)
• Antigen capture ELISA
– Herd screening
• Serology
– VN ($14)
– ELISA ($5/animal)
• PCR
– genotyping ($62)
– pooled samples ($30)
Diagnostic procedures
• PCR (BVDV-1 vs BVDV-2)
• Immunohistochemistry or IFA
BVDV-1a
– Abortions ($45)
– PI animals (approx. $6/animal)
BVDV-1b
BVDV-2
Immunohistochemistry - PI vs
acute
From Brad Njaa et al. 2000. J. Vet. Diag. Invest. 12:393-399.
Persistently infected calf:
Antigen in hair follicle
epithelium
Acutely infected calf:
Antigen in superficial layer
of epidermis (foci)
Diagnostic Parameters (acute
infection)
infection
5-7 days
incubation period
antibody
clinical disease
virus
infect. virus detectable in serum
antigens in biopsy
infect. virus detectable in
WBC
Virus det.
by PCR
Diagnostic parameters (abortion)
• Fetus
– Often no infectious virus
– Submit liver, kidney, spleen, thymus for IH
or IFA
– Fetal antibody if late term
Diagnostic parameters (PI)
• Large amounts of virus in blood, serum and
secretions (103-107 TCID50/ml)
• Maternal antibody interferes with isolation
• <3 months - submit blood
• >3 months - serum
• Repeat isolation in 3 months
• Immunohistochemistry - follicle epithelium
Herd screening
Management of BVD
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Test and remove PI animals
Test all new born calves for 9 months
For 9-12 months segregate age groups
Quarantine replacements
Vaccination with MLV BVDV
BVD infections may persist for some
time after removal of PI animals (Collins
et al. 2009)
Vaccines
• Inactivated or attenuated
• Most (all) contain CP BVDV
http://www.cattlenetwork.com/content.asp?contentid=119624
Interspecies transfer
• Sheep
• Wild ruminants
– Natural infections (caribou: 40-100%)
– Transfer (llamas, alpacas)