Hog Cholera Classical Swine Fever

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Hog Cholera(Classical Swine Fever)

• Sandra Axiak
• and
• Carolin Winter

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Definition of hog cholera

• highly contagious viral disease of swine
• can cause acute, chronic, or congenital disease
• considered a foreign animal disease

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Foreign animal disease (FAD)

• Definition
• a transmissible disease of livestock or poultry
• absent from the US and its territories
• has the potential for significant health or
  economic losses
• Examples of important FADs
• foot and mouth disease
• highly pathogenic avian influenza
• hog cholera

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Foreign animal disease

• Control of FADs usually means eradication.
• The U.S. spent 79 million during the final
  stages of hog cholera eradication (1971-1977)
• Hog cholera was officially eradicated from the
  U.S. in 1978

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Etiology

• Family Flaviviridae
• Genus Pestivirus
• Only one serotype of the virus
• Closely related to BVDV

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Epidemiology of HCV

• Hosts
• pigs and wild boar
• Incubation period
• usually 3-4 days, but can range from 2-14 days
• Distribution
• occurs in much of Asia, Central and South
  America, and parts of Europe and Africa
• disease has been eradicated from about 16
  countries, including Australia, Canada, and the
  United States (1978 - after a 16 year long effort)

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Epidemiology of HCV

• Transmission
• Blood, tissues, semen, secretions, and excretions
  of infected animals contain HCV
• transmission usually occurs via oral route
• can also occur via the conjunctiva, mucous
  membranes, skin abrasions, insemination, common
  needles, and contaminated instruments

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Epidemiolgy of HCV

• Transmission
• Feeding raw or insufficiently cooked waste food
  containing infected pork scraps can be a potent
  source of HCV
• Mechanical vectors can spread HCV
• farm visitors - on their person or their clothes
• vehicles
• insects and birds

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Epidemiology of HCV

• Transmission
• Transplacental infection with a lowly virulent
  strain of HCV can result in persistently infected
  piglets
• These piglets will persistently shed the virus
  for months before succumbing to the disease

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Forms of the disease

• Acute form
• Chronic form
• Congenital form

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Clinical signs of acute infection

• Fever of 106 to 108 degrees Fahrenheit
• may see huddling of pigs in warmest area of pen
• Lethargy and anorexia
• Intermittent vomiting of yellow fluid containing
  bile
• Transient constipation followed by diarrhea
• Conjunctivitis with encrustation around the eye
• Coughing and dyspnea

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Clinical signs of acute infection

• Terminal stages of infections
• Hemorrhagic lesions of the skin, especially on
  the abdomen and inner aspects of the thighs
• Cyanosis of the skin, especially the extremities
• ears, limbs, tail, snout
• Ataxia and paresis due to posterior weakness
• Convulsions may occur shortly before death
• Death usually occurs within 5 to 15 days of onset
• Mortality can approach 100 in young pigs

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Cyanosis of the skin (extremities)
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Gross lesions of acute infection

• Swollen, edematous, and hemorrhagic lymph nodes
• esp. submandibular and pharyngeal lymph nodes
• Splenic infarcts
• All serous and mucosal surfaces may have
  petechial or ecchymotic hemorrhages
• Peritonitis, pleuritis, and pericarditis
• straw-colored fluid

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Gross lesions of acute infection

• Petechial and ecchymotic hemorrhages on
• skin
• surface of the kidneys
• surface of the small and large intestine
• larynx
• heart
• epiglottis
• fascia lata of the back muscles

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Petechial hemorrhages - skin
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Petechial hemorrhages - kidney surface
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Petechial hemorrhages - abdominal viscera
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Petechial hemorrhages - larynx
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Other lesions of acute infection

• Leukopenia and thrombocytopenia
• Encephalomyelitis with microgliosis and
  perivascular cuffing is found in brains from
  about 75 of pigs acutely infected with HCV

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Clinical signs of chronic infection

• Prolonged and intermittent periods of
• anorexia
• fever
• dullness
• alternating diarrhea and constipation for up to a
  month
• alopecia

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Clinical signs of chronic infection

• May have a disproportionately large head relative
  to their small trunk
• Apparent recovery with eventual relapse
• All chronically infected pigs will die due to
  complications arising from HCV infection

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Gross lesions of chronic infection

• Lesions can be similar to those found in the
  acute form of infection, but are generally less
  severe.
• Button ulcers in the cecum and large intestine
  due to secondary bacterial infection are common
• Generalized depletion of lymphoid tissue
• Hemorrhagic lesions may not be present in
  chronically infected pigs

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Button ulcers
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Clinical signs of congenital infections

• Highly virulent strain
• abortion
• birth of diseased pigs that die shortly after
  birth
• Less virulent strain
• mummification
• stillbirth
• birth of weak, shaker pigs (congenital tremor)

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Clinical signs of congenital infections

• If infected with a lowly virulent strain during
  fetuss 1st trimester of life, piglets may
• not produce neutralizing antibody to the virus
• experience life-long viremia and persistently
  shed the virus
• have few clinical signs for the first few months
  of life, then develop anorexia, depression,
  diarrhea conjunctivitis, dermatitis, runting, and
  ataxia
• ultimately end up recumbent and die

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Gross lesions of congenital infections

• Cerebellar hypoplasia
• Microencephaly
• Pulmonary hypoplasia
• Central dysmyelinogenesis
• Thymus atrophy
• Deformities of the head and limbs
• Petechial hemorrhages of the skin and internal
  organs towards the end of the disease process

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Differential diagnosis

• African Swine Fever
• distinguished from hog cholera only via
  laboratory examination
• Erysipelas
• Salmonellosis
• Colisepticemia
• Thrombocytopenic purpura
• Acute pasteurellosis
• Infection with BVDV

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Diagnosis of hog cholera

• Specimens that should be collected and sent to
  the lab for virus isolation and antigen detection
  include
• tonsils (best)
• submandibular and mesenteric lymph nodes
• spleen, kidney, brain, and distal ileum
• For living cases, collect
• tonsil biopsies and blood in EDTA
• DO NOT freeze samples - interferes with some of
  the tests

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Laboratory diagnosis

• Direct IFA on cryostat sections of organs or
  impression smears of biopsy material
• ELISA - blood antibody test
• RT-PCR
• Virus isolation in cell culture
• detect virus by immunoperoxidase or
  immunofluorescence using labeled hog cholera
  antibody

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Typical response to an outbreak

• Slaughter all the pigs on affected farms
• Dispose of carcasses, bedding, manure, etc.
• Disinfect the premises thoroughly
• Designate a zone of infection and control the
  movement of pigs within that zone while
  maintaining careful surveillance of that zone and
  the surrounding area
• Detailed epidemiological investigation to
  determine the source of the infection and its
  possible spread

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Why prevent hog cholera?

• high death rates and severe illness cause
  significant production losses
• loss of productivity leads to an increase in the
  cost of food products obtained from swine
• lose economically important export markets until
  eradication is again achieved
• 1997 total value of exported U.S. pork products
  exceeded 1 billion
• Re-eradication can be very costly
• 1997 outbreak in the Netherlands cost 2 billion

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Prevention and control

• Affected pigs must be culled and the carcasses
  must be buried or burned
• Vaccination is used to reduce the number of
  outbreaks in countries where hog cholera is
  enzootic
• Vaccination is generally prohibited in countries
  which are free of disease or where eradication is
  in progress and nearing success

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Vaccination

• Modified live vaccines
• Lapinized Chinese strain
• Japanese guinea pigs cell culture-adapted strain
• French Thiverval strain
• All three are innocuous for pregnant sows and
  piglets over 2 weeks of age
• All three are considered equally effective

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Prevention and control

• Other prophylactic measures include
• quarantining incoming pigs before introducing
  them to the herd
• U.S. quaratines swine imported from affected
  countries for 90 days at a facility in Key West,
  FL
• keeping a good pig identification and recording
  system
• strict adherence to waste food cooking laws
• structured serological surveillance of breeding
  sows and boars to detect subclinical infections
• maintaining a strict import policy for live pigs,
  as well as fresh and cured pork

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Inactivating the virus

• Temperature
• partially resistant to temperatures up to 130
  degrees Fahrenheit
• pH
• inactivated by a pH less than 3 or greater than
  11
• Chemicals
• Susceptible to ether and chloroform

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Inactivating the virus

• Disinfectants
• 2 NaOH
• 1 formalin
• sodium carbonate

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Survival of the virus

• HCV can survive some forms of meat processing
• curing
• smoking
• It survives well in cold temperatures
• survives for months in refrigerated meat
• survives for years in frozen meat

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Recent outbreaks

• Haiti and the Dominican Republic eradicated hog
  cholera in the early 1980s
• Both, however, experienced outbreaks of the
  disease in 1997, causing pork producers to
  experience substantial economic losses
• Belgium and the Netherlands also experienced
  outbreaks of hog cholera in 1997

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Recent outbreaks

• Hog cholera was eradicated from Great Britain in
  1966
• Since then there have been a few sporadic cases
  in 1971 and 1986
• The disease returned to Great Britain in 2000,
  when a total of 16 cases were confirmed in East
  Anglia
• A total of 74,793 pigs, including those on
  in-contact farms, were slaughtered

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Hog cholera in Luxembourg

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Hog cholera in Luxembourg

• October 2001
• wild boar was found dead in Berbourg Forest in
  eastern Luxembourg
• boar tested positive for hog cholera
• November 2001
• four additional wild boars were found dead in the
  Berbourg area
• all four tested positive for hog cholera

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Hog cholera in Luxembourg

• January 2002
• an additional wild boar, which was found dead in
  Herborn (near Berbourg), tested positive for hog
  cholera
• February 2002
• 2 cases of hog cholera were diagnosed on a pig
  farm near Berbourg (breeding pigs)
• All 147 pigs on the farm were destroyed
• All pigs (178) within 1 km of the affected farm
  were also destroyed to prevent possible spread of
  the disease

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Hog cholera in Luxembourg

• March 2002
• Piglets that originated from the affected farm
  were traced to two farms, one in northern
  Luxembourg, one in southern Luxembourg
• These piglets, all other pigs on the two farms,
  and all pigs within 1 km of these two farms were
  destroyed for a total of 6,259 pigs
• Shows that drastic action is being to prevent a
  full-blown outbreak of hog cholera in Luxembourg
  in order to prevent the immense economic and
  production losses that could result form such an
  outbreak

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Sources

• The Gray Book - Classical Swine Fever
• http//www.oie.int/eng/en_index.htm
• http//aphis.usda.gov/oa/pubs/fscsf.html
• http//www.oie.int.eng/maladies/fiches/A_A130.htm
• http//www.defra.gov.uk/animalh/diseases/notifiabl
  e/disease/classicalsf.htm
• http//www.defra.gov.uk/animalh/diseases/notifiabl
  e/statistics/classicalsf.htm

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Thank you!

• Any Questions?