55. Classical swine fever (aetiology, epidemiology, pathogenesis, clinical signs, post mortem lesions).

Question 1

CSF INFO?

Answer 1

Classical swine fever (hog cholera) ʹ Notifiable disease! Flaviviridae, CSFV

• An acute, contagious disease of swine, characterised by general, febrile signs, haemorrhages & CNS disorders
• This was true in the last century ʹ but it is very variable nowadays
• The most atypical features of CSF: it is so atypical!

Question 2

Causative agent?

Answer 2

Causative agent:

• classical swine fever virus (Flaviviridae)

Ethiology

• Stenoxen: domesticated swine & wild boar
• Relatively resistant (enveloped virus)
• pH 3, 60oC ʹ30 80^oC 5 sensitive to high pH
• In meat, blood: 4oC ʹ 1 month, frozen ½ year survival
• In visceral organs longer survival
• Survives in marinade, smoked meat (1/2 year)
• Faeces, urine: 7 days, cadaver 1-2 days
• Serologically uniform, 3 genotypes
• Differentiation btwn CSFV wild-type & vaccine strains, & other pestiviruses by monoclonal
• Abs
• Gp55/E2 a neutralising antigen
• Differences in virulence: low virulence strains ʹ subclinical, foetopathogen

Question 3

Pathogenesis and course of the disease?

Answer 3

Pathogenesis

• Infection: PO, airborne, conjunctival, mating, transcutaneous (iatrogenic! ʹ fomites, boots, gloves,
• needles, syringes), transplacental
• oronasal -> tonsils-> head neck LNs->viraemia (from the 16-24th hour)
• >lymphatic tissue(Lns spleen Lymphoreticular cells) damage of the immune system(immunosuppression)
• secondary bacterial complications
• Damage of the BM stem cells-> thrombocytopenia, DIC, haemorrhages
• endothelial damage, hyaline dystrophy of the Bvs -> perivascular oedema-> circulation problems
• necrosis, haemorrhages (day 3-4)
• Generalised infection (day 5-6)
• Direct damage: lymphocytes, megacaryocytes
• Indirect damage: endothel damage, immunocomplexes

Course

TYPICAL:

Classical (w/out complications):

Peracute, acute, subacute, chronic

Complicated form:

Secondary bacterial infections

ATYPICAL: Necrotic pneumonia, diphteroid colitis

LOW VIRULENCE strain/VACCINE STRAIN infections

Question 4

Clinical signs?

Answer 4

Clinical signs

• Incubation: 8-22 days or longer
• Viraemia w/in 24h after infection ʹ fever!
• Virus shedding already in the incubation period
• PERACUTE: fever, sudden death
• ACUTE, SUBACUTE
• Permanent fever (40.5-40oC), loss of appetite, depression
• Suffusion, haemorrhages in the skin, oedema
• Weakness of the hind legs, ataxia, swaying, nystagmus
• Conjunctivitis, vision & orientation disturbances, blindness
• In the beginning obstipation, later bloody diarrhoea (rarely seen these days)
• Haematuria, bloody nasal discharge (rarely seen these days)
• High morbidity (90-100%)
• Death after 1-2 weeks illness
• 10-30% mortality
• red dots on the skin similar to the circiviridae and ASF(cant differentiate) differentiate!)
• CHRONIC
• Retarded growth, BW loss
• Diarrhoea, crustae on the skin
• PREGNANT SOW ʹ transplacental infection
• First half of the pregnancy: abortion, premature birth, weak, trembling piglets, splayleg,
• immunotolerant piglets!
• Third part of the first trimester ʹ when the BM, spleen & LNs are formed in the
• foetus so immunotolerance occurs always at this time
• Second half of pregnancy: less damaged, immunocompetent piglets
• WEAK VIRULENCE STRAINS/VACCINE strains
• Subclinical infection, serological response

Question 5

Pathology and histopathology?

Answer 5

Pathology & histopathology

• Peracute
• Macroscopically usually negative
• Brain lymphocytic infiltration! ʹ Leukoencephalitis (perivascular cuffing)
• +/- fine haemorrhage in the kidney cortex
• Acute
• Praesetais, stasis, haemorrhage, oedemas (paint brush)
• Skin haemorrhage, necrosis (ears, legs)
• Haemorrhages (also feature of ASF)
• On the mesenterium, on the serosal surfaces
• On the light kidneys, in the renal pelvis, on the mucosa of the urinary bladder
• In the gastric mucosa, in the regional LNs
• In the small & large intestine, colon, haemorrhagic enteritis
• In the larynx, lung, bones, muscles (by electric immobilisation too!)
• Rarely in the liver, gall bladder, retina, conjunctiva
• RBC infiltration of the LNs!
• Post-haemorrhagic anaemia, mild icterus
• Subacute
• Spleen: haemorrhagic or ischaemic infarcts at the edges, in uncomplicated cases normal size
• spleen (if bacterial complications then there is splenomegaly!)
• Stomach: gastritis, croupous pseudomembranes, buttons (in ~4% of the cases)
• LI: boutons (also in chronic form) ʹ origin of button = lymphoid follicle in MM wall ʹ
• pathognomic!
• Lung
• Lobular (lobar) haemorrhage, croupous pneumonia
• (normally viruses cause interstitial pneumonia)
• Enlarged interstitial tissue, oedematisation
• Pleural LNs are infiltrated with RBCs
• Tonsils: necrosis ʹ Characteristic(DD= AUJESZKYs disease)
• Brain: meninx, brain, spinal cord; 2-3 layer lymphoid cell cuffing, meningitis; poly- &
• leukoencephalitis
• Thymus: atrophy, lymphocyte numeric atrophy - immunosuppression
• Eyes: conjunctivitis, uveitis, retinitis, papillitis, neuritis
• Chronic
• Atypical lesions, complicated diagnosis
• Buttons are erased, no haemorrhages
• Thickened wall of the LI, necrotic mucosal surface, crustae
• Lung croupous-necrotic
• pneumonia, sequestra, adhesions, subacute-chronic pleuritic
• Post-inflammatory reparative processes in the brain
• 6-8 costal bone-cartilage developmental problems
• Intrauterine infections: foetal anasarca, edema, cerebellar hypoplasia
• Complicated cases, secondary infections
• Lymphoreticular tissue damage: immunosuppression
• Cl. septicum: gas gangrene in the stomach
• S. choleraesuis, L. monocytogenes
• High fever (~42oC), diarrhoea
• Hyperaemic or hyperplastic, acute, septic splenitis
• A. pleuropneumoniae: fever, pneumonia, dyspnoea
• P. multocida, A. equuli, E. rhusiopathiae, Ps. Aeruginosa, F. necrophorum
• Low virulence/vaccine strain infections: mild lesions

Question 6

Epizootiology?

Answer 6

Epizootiology

• Tranmission

• Live, infected swine ➝ transportation, trade
• Raw pork meat, raw pork products (also frozen) ➝ slaughterhouse, home-slaughtering, trade, tourism
• Raw pork wastage ➝ slaughterhouse, home-slaughtering, restaurants, tourism
• Fomites ➝ transportation, trade, tourism
• Humans ➝ technician, veterinarian, butcher, salesman

• Very contagious

• Quick spread in herd
• Virus shedding in discharge within 24 hours after infection
• Introduction with infected animal ➝ large-scale disease in second week
• Introduction with feed ➝ large-scale disease earlier

• Nowadays even virulent strains rarely cause high mortality

• Low virulence and vaccine strains

• Subclinical circulation in adult swine
• Or mild clinical signs
• Foetal damage
• Immunotolerant piglets
• Long-term carrier and shedder animals
• Seropositive animals in population

• Vaccinated herds

• Subclinical circulation of wild type virus
• Piglets show signs after clearance of maternal antibodies (6-12 weeks of age)