Classical swine fever

David Paton

AETIOLOGY

• Family: Flaviviridae

• Genus: Pestivirus

• Single serotype, 3 major genotypes, 3-4 subgroups

• Generally low environmental persistence (days -weeks)

• Stable at pH 5 – 10

• Survives in animal products

GEOGRAPHIC DISTRIBUTION

OIE WAHID 6-monthly FMD incidence, Jul-Dec 2013

Eradicated from North America in 1976

REGIONAL CSF INCIDENCE2005-2014

Not reported since 2005 Reported since 2005 Last year of report

Aruba Brazil 2005

Belize Cuba 2014

Barbados Dominican Republic 2010

Cayman Islands Ecuador 2014

Costa Rica El Salvador 2008

French Guiana Guatemala 2013

Guyana Haiti 2014

Jamaica Honduras 2007

Suriname Mexico 2009

Trinidad and Tobago Nicaragua 2008

Peru 2014

Venezuela 2005

http://www.oie.int/wahis_2/public/wahid.php/Diseaseinformation/Diseasetimelines

PATHOGENESIS – VIRUS LIFE CYCLE

• Affects domestic pigs and wild boar

• Mild, virulent and chronic forms

• Age related susceptibility• Virus entry:

– Oronasal - tonsil as 1st target– Other mucosa or damaged skin– Transplacental

• Incubation period:– 2-14 days

• Virus shedding:– Can precede clinical signs and

continue until death– Most secretions and excretions

(saliva, nasal and ocular discharges, urine, faeces)

Primary replication in tonsil and regional

lymph nodes

Viraemia

Secondary replication(lymphoid tissues,

endothelia and parenchymatous

organs)

Delayed immune response

Virus shedding Clinical signs

Death, chronic disease or recovery

Incu

bation p

eriod

Late

nt

period

Exposure

PATHOLOGY

• Immunopathological disease

• Leukopenia and thrombocytopenia

• Tonsillitis, swollen lymph nodes, splenicinfarcts

• Haemorrhages – skin, epiglottis, bladder, lymph nodes, kidneys

• Button ulcers in caecum and colon

CLINICAL SIGNS• Depression, fever, anorexia

• Mild strains: rather non-specific signs

• Virulent strains: conjunctivitis, constipation, diarrhoea, inco-ordination, skin hyperaemia and haemorrhage, death in 5-25 days

• Chronic strains: initial improvement before relapse and death within 3 months

• Death after 10-20 days or up to 3 months in chronic cases

• Prenatal infection can lead to fetal death, fetalabnormalities and delayed onset signs after birth

CONJUNCTIVITIS

ERYTHEMA

Images from: http://www.afrivip.org/sites/default/files/CSF/diagnosis.html

Enlarged haemorrhagic lymph node Splenic infarcts

LYMPHOID LESIONS

Swine influenza

PDNS

PRRS

DIFFERENTIAL DIAGNOSIS

PMWS

ROUTES OF SPREAD

• Pig to pig horizontally

• Pig to pig vertically and via semen

• Pig meat eaten by pigs (swill)

• Indirect over long distances (lorries)

• Indirect over short distances (farmers, vets, animals, shared equipment, etc)

• Wild boar

19%

43%

11%

27%Purchase of infectedanimals

Transport vehicles

Human contacts

Neighbourhood infection(cases within 1km of asource caused by ??birds/flies)

ROUTES OF INFECTION BEFORE FIRST CASE CONFIRMED Netherlands 1997/8

17%

9%

13%11%

7%

1%

33%

9%

Purchase of infected animals

Transport vehicles

Human contacts

Rendering trucks

AI and infected semen

Slurry

Neighbourhood

Unknown

ROUTES OF INFECTION AFTER PROTECTION AND SURVEILLANCE ZONES IMPLEMENTED

Netherlands 1997/8

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

Live pigs frominf herd

Lorry on inffarm same

day

Person on inffarm same

day

AI from infcentre

500m vicinityfarm - 1wk

500-100mvicinity farm -

1wk

1000-2000mvicinity farm -

1wk

Probability of transmission

Probability of transmission

Rate of inter-herd transmission of classical swine fever virus by different types of contact during the 1997–8 epidemic in The Netherlands. Stegeman et al, 2002

CHALLENGES FOR EARLY DETECTION

• Low virulence of many virus strains

• Takes time before sufficient pigs affected

• Fevers difficult to measure

• If visit tracings too early do not recognise disease

• Random virological testing of all is impractical

• Serology - takes too long for antibodies to develop

• Value of individual clinical diagnoses and post mortems

• Clinical – Se 73%, Sp 53%

• PM – Se 72%, Sp 78%

• Elbers et al (2002, 2004)

The Herd Se of clinical diagnosis was 50% at 37 days after virus introduction and reached 90% at 47 days after virus introduction. The estimated herd specificity was 72%. Engel et al (2004)

DIAGNOSIS

• Virus detection (VI, RT-PCR, ELISA, FAT)• Blood and organs are usual samples (tonsil, LNs, spleen,

kidney, distal ileum)• RT-PCR is mainstay and DIVA PCR tests possible

• Serology• Several ELISA configurations – E2, Erns, NS• Some can differentiate antibodies induced by vaccines

and ruminant pestiviruses• VNT as gold standard

• Genetic typing• Helps determine outbreak source

VACCINES

• Cell mediated and/or humoral immunity can protect

• Modified live vaccine• Various attenuated strains, e.g. “C” strain• Highly effective and can be used in oral baits• Marker versions developed

• Subunit• E2 recombinant protein• Good DIVA capability

• Novel vaccines• Viral vectors – e.g. Adeno, pox, pseudorabies• Modified genomes – e.g. swaps with other pestiviruses• DNA• Peptide

CONTROL PRINCIPLES

• EU policy is stamping out

– Early detection of cases

– Movement restrictions to prevent spread

– Slaughter of affected herds

– Tracings of contacts

– Possible pre-emptive slaughter

– Emergency vaccination only

2/5/00 9/5/00

248 pigs 220 pigs

A B D F

SF

2000/2

SF2000/04

SF2000/01

N1

N2

N3

N4

SF2000/05

N5N6 N7

SF2000/03

16/5/00

225 pigs

23/5/00

271 pigs

30/5/00

287 pigs

11/7/00

236 pigs

18/7/00 25/7/00 1/8/00

210 pigs 226 pigs 258

pigsF1

F2

F3

F4

F5

F6

F7 F8 F9

F10 F11F11

G

20/6/00

222 pigs

TRACING FROM UK INDEX CASE, 2000

Infected Premises

supply farms

nursery farms

finisher farms

date pigs supplied

number of pigs supplied

11/7/00

232 pigs

27/6/00

244 pigs

20/6/00

222 pigs

13/6/00

279 pigs

6/6/00

245 pigs

CHALLENGES FOR CSF CONTROL

• High density pig keeping

• Animal movements

• Infection of wild boar

• Globalised trading

• Swill and scrap feeding

ACKNOWLEDGEMENTS

Photographs collated from multiple sources including:

• VLA-Weybridge archives

• UK 2000 CSF outbreaks

• Trevor Drew, AHPA, UK

• John Mackinnon, Stowe Vet Group, UK

http://www.afrivip.org/sites/default/files/CSF/diagnosis.html

Disease information from OIE WAHID:

EFSA Review 2009:

http://www.efsa.europa.eu/en/scdocs/doc/6e.pdf

http://www.oie.int/wahis_2/public/wahid.php/Diseaseinformation/Diseasetimelines