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Hog Cholera (Classical Swine Fever). Sandra Axiak and Carolin Winter. Definition of hog cholera:. highly contagious viral disease of swine can cause acute, chronic, or congenital disease considered a foreign animal disease. Foreign animal disease (FAD):. Definition:

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Hog cholera classical swine fever l.jpg

Hog Cholera(Classical Swine Fever)

Sandra Axiak

and

Carolin Winter


Definition of hog cholera l.jpg
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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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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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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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 fetus’s 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


Gross lesions of congenital infections l.jpg
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


Diagnosis of hog cholera l.jpg
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 1980’s

  • 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:

  • 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/notifiable/disease/classicalsf.htm

  • http://www.defra.gov.uk/animalh/diseases/notifiable/statistics/classicalsf.htm


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Thank you!

Any Questions?