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Flavi and Pestiviruses. October 12, 2010. BVD , Hog cholera, Border disease. Pestiviruses. Flaviviridae. Flaviviruses. Hepacviruses Hepatitis C virus. Yellow fever Japanese encephalitis St. Louis encephalitis Dengue West Nile virus. (arthropods, biological vectors).

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flavi and pestiviruses

Flavi and Pestiviruses

October 12, 2010

slide2

BVD, Hog cholera, Border disease

Pestiviruses

Flaviviridae

Flaviviruses

Hepacviruses

Hepatitis C virus

Yellow fever

Japanese encephalitis

St. Louis encephalitis

Dengue

West Nile virus

(arthropods, biological vectors)

west nile outbreaks
West Nile Outbreaks
  • 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)
slide4

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
Saskatchewan mosquito species shown to be capable of transmitting WNV
  • Aedesvexans (spring to fall)
  • Ochlerotatusflavescens, spencerii(July-August)
  • Culexrestuans*, tarsalis*(July-August)
  • Culiseta inornata*
  • Coquillettidiaperturbans
how does the virus overwinter and spread
How does the virus overwinter and spread?
  • migratory birds?
  • overwintering mosquitos?
  • bird to bird transmission?
    • Komar et al. EID March 2003
in the mosquito
in the mosquito

3. virus leaks from gut and infects salivary glands

4. virus released in saliva during feeding

2. virus multiplies in gut epithelial cells

1. virus ingested with blood meal

(sufficient amount of virus must be ingested - > 105 infectious units/ml)

in mammals
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

viremia (secretion in milk)

PCR

viremia terminated by immune response

crosses blood/brain barrier (repl’n in vascular endothelium, exacerbated by concurrent infections)

IgM,

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
equine cases of WNV neurological disease
  • 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
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
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
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
human cases 2003-2005

May

June

July

Aug

Sept

Oct

slide14

http://www.phac-aspc.gc.ca/wnv-vwn/mon-hmnsurv-archive-eng.phphttp://www.phac-aspc.gc.ca/wnv-vwn/mon-hmnsurv-archive-eng.php

west nile virus in domestic birds
West Nile virus in domestic birds
  • geese
  • ducks
  • chickens and turkeys
  • ostriches, emus
testing for wnv serology
testing for WNV - serology

samples from 45 horses, Virden Manitoba (Aug-Sept, 2002)

strong + cont

weak + cont

IgM capture

ELISA

PDS immunol.

lab

vaccines
vaccines

Fort Dodge

Intervet – PreveNile Live Flavivirus chimera

west nile virus common client questions
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
Systemic haemorrhagic disease - pigs (USA)

Enteric disease - calves (USA)

Congenital, neurological “hairy-shakers” (England/Wales)

Pestiviruses

HCV

1940s

BVDV

BDV

flaviviruses
Flaviviruses

Flaviviruses

Japanese

encephalitis

Louping ill

Hepatitis C

Pestiviruses

St. Louis

encephalitis

Murray Valley

Dengue

Yellow fever

West Nile

Pestiviruses of Artydactyla

hog cholera

(HCV)

bovine viral diarrhoea

(BVDV)

border disease

(BDV)

Wide host range (camelids, deer etc)

bvdv genome and gene products
BVDV genome and gene products

nonstructural

structural

UTR

gp53

p125

(p54+p80)

Regions that show the most variation

biotypes of bvdv
Biotypes of BVDV

Based on effect on cells in tissue-culture

NON-cytopathic

(natural state)

Cytopathic

(mutant)

cp vs ncp genetic differences
CP vs NCP – genetic differences

nonstructural

structural

UTR

p125

(p54+p80)

biotypes implications
Non-cytopathic

Implications for vaccines and research

Cytopathic

Mucosal disease

Biotypes - implications
bvdv types not different serotypes
BVDV-1

BVDV-2

nonstructural

structural

UTR

BVDV “types” Not different serotypes!!

Based on:

1. sequence differences

In non-translated region of genome

Does not imply differences in pathogenicity

2. Antigenic differences

antigenic differences between bvdv 1 and bvdv 2
Antigenic differences between BVDV-1 and BVDV-2

VN titre against

BVDV-1

strains

BVDV-2

strains

Serum against

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

Inter species

Vaccine related?

Artificial breeding programs

Blood

Persistence in acutely infected animals

Pathogenesis - infection
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 - disease in imm.competent, non-pregnant animals
pathogenesis pregnant animals
All syndromes described above

Embryonic death

Abortions

Birth defects

Persistently infected calves

Pathogenesis - pregnant animals
pathogenesis pi animals
Healthy, normal

“poor-doers”

Mucosal disease

Pathogenesis - PI animals
guess which one is persistently infected
Guess which one is persistently infected?

Calves of the same age. From Lee et al. CVJ 38:29

consequences of having a pi animal
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
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
diagnostic procedures40
PCR (BVDV-1 vs BVDV-2)

Immunohistochemistry or IFA

Abortions ($45)

PI animals (approx. $6/animal)

BVDV-1a

BVDV-2

BVDV-1b

Diagnostic procedures
immunohistochemistry pi vs acute
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
Diagnostic Parameters (acute infection)

infection

incubation period

antibody

5-7 days

clinical disease

virus

infect. virus detectable in serum

infect. virus detectable in

WBC

Virus det.

by PCR

antigens in biopsy

diagnostic parameters abortion
Fetus

Often no infectious virus

Submit liver, kidney, spleen, thymus for IH or IFA

Fetal antibody if late term

Diagnostic parameters (abortion)
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

Diagnostic parameters (PI)
management of bvd
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)

Management of BVD
vaccines47
Inactivated or attenuated

Most (all) contain CP BVDV

Vaccines
interspecies transfer
Sheep

Wild ruminants

Natural infections (caribou: 40-100%)

Transfer (llamas, alpacas)

Interspecies transfer