Background

Classical Swine Fever (CSF) is a highly contagious acute or chronic hemorrhagic disease of RNA virus, affecting pigs. Disease progression depends on various factors like strain virulence, host factors, and secondary pathologies. The acute CSF shows symptoms like high fever, anorexia, weakness leading to neurological deterioration, haemorrhage and bluish discoloration of extremities. CSFV infection has a high morbidity and mortality rate. In chronic cases, subclinical symptoms like anorexia and intermittent fever can be seen; although not life-threatening, the morbidity is still high. As CSF has a worldwide distribution and a high impact on the economy, it is reportable to the World Organization for Animal Health (OIE). CSF outbreak in the Netherland between 1997 and 1998 has caused a substantial economic loss that led to the slaughter of around 12 million pigs costing over 2 billion euros. Southeast Asia and China are epidemic areas. Molecular epidemiology gives information on the interaction of genetic traits and environmental factors responsible for the disease. The CSFV is transmitted horizontally in both feral and domesticated pigs by direct contact of infected pigs with healthy animals. OIE and the United States Department of Agriculture (USDA) grouped the CSFV as Containment Group 4 organism. The structural glycoprotein E2 produces a neutralizing antibody response, as seen in pigs recovered from the disease and found to exhibit protection for future infection. Two strategies used in controlling CSF are (i) extensive culling and (ii) preventive immunization. For countries like the USA, Canada, Brazil, South Africa, Chile, and EU countries having no endemic CSF, culling is used to control CSF. Attenuated virus strain-based single dose modified live virus (MLV) vaccines are used to elicit a protective immune response in native pigs. MLV is commonly used to protect livestock and outbreaks in CSFV endemic areas. MLV vaccinated animals are immunologically indistinguishable from infected animals, so it has a significant impact on international trade. In India, pig farming is mostly primitive, and CSF was first reported in 1962. The most common and efficient method to control CSF in India is vaccination.

Cause

A viral disease caused by Pestivirus

Host Species

Pigs

• Source of infection is either an infected pig or its products.
• Clinically infected pigs shed a large quantity of the virus through nasal discharge, salivation, urine and feces.
• Pig's contract infection usually by ingestion but inhalation is also a possible portal of entry.
• It is a highly contagious disease. direct pig to pig contact is the most important route of spread.
• Aerosol transmission is possible when number of infected and healthy pigs are housed in the same airspace together.
• Infected boars also transmit the disease through semen either by natural service or by insemination.
• Beds and humans may also act as physical carriers of the virus.
• The transmission to new farms can occur in feeder pigs purchased for finishing, or indirectly by flies and mosquitoes, or on bedding, feed, boots, automobile tyres or transport vehicles.
• Farmers, veterinarians and vaccination teams can transmit the virus by contaminated instruments and medicines.
• Newly purchased pigs also transmit the diseases in to healthy herd.
• In disease free areas, the introduction of disease occurs usually by the importation of infected pigs or the feeding of garbage containing uncooked pork scraps.

Peracute form

• The young pigs die suddenly without showing any notable clinical signs.

Acute form

• This is the most common form.
• Affected pig's shows high rise of body temperature, dull, depressed, loss of appetite and stand in a drooped position with hanging of tail.
• They are not interested to move and show a swaying movement of the hindquarters and tend to lie down.
• Constipation followed by diarrhea and vomiting also occur.
• As disease progresses, a diffuse purplish discoloration of the abdominal skin occurs.
• Small areas of necrosis are sometimes seen on the edges of the ears, on the tail and lips of the vulva.

Chronic form

• The chronic disease occur's in field outbreaks.
• There is depression, low feed intake, persistent mild fever, unthriftiness, appearance of characteristic skin lesions including alopecia, dermatitis, blotching of the ears and a terminal, deep purple coloration of the abdominal skin.
• Sometimes, pigs apparently recover following a short period of illness but subsequently relapse and die if stressed.
• Pigs infected with the low virulent strains of the virus appear more susceptible to secondary bacterial diseases.
• The chronic form of the disease is suspected when there is an increased mortality from any apparent infectious cause that either does not respond, or responds only temporarily.

Nervous form

• Pigs lie down in lateral recumbency with varying degree of tetanic and clonic convulsion.
• The convulsion may be accompanied by loud squealing and followed by a period of terminal coma.
• In some cases convulsions do not occur but nervous involvement is manifested by coarse tremor of the body and limb muscles.
• Apparent blindness, stumbling and allotriophagia are also been observed.

Reproductive failure

• Reproductive failure can be a significant feature and may occur without other clinical evidence of disease within the herd.
• Infected sows usually show no clinical signs except a mild fever but it may be followed by a high incidence of abortion, low litter size, mummification, stillbirth and anomalies of piglets.
• Live born pigs are very weak or clinically normal and die within 2-10 months after birth.

Management

No specific treatment is there for classical swine fever. Only following supportive treatment will help.

• Good nursing is essential.
• Sick animals should be isolated and kept in clean, well ventilated pens and palatable food.
• Non-steroidal anti-inflammatory drug (NSAIDs) to control the fever.
• Anti-histaminic drug may be given.
• Antibiotic is prescribed to prevent secondary bacterial infections.
• Vitamin A containing multivitamins
• Injections of Cu-Zn combination

Preventive measures

• If culling is not possible, isolation of infected herds and sick animals for at least 45 days after recovery
• Strict implementation bio-security measures in swine farm is needed.
• Proper disposal of cadavers and products-burning or burial is often used.
• Stringent cleaning and disinfection of farms and equipment
• Quarantine of new animals before introduction into herds
• Control of animal & vehicle movement within infected areas
• Vaccination may be considered when the disease has spread more widely.

Control

• Vaccination is the only effective way to control the disease

Type of vaccines

Lapinized live attenuated classical swine fever vaccine

Vaccination schedule

The vaccination against classical swine fever is recommended to pig at the age of 3 months of age & yearly vaccination is practised.

Dose

1ml S/C route, deep I/M behind the ear area or following manufacturer's instructions

Note: Deworming is must at least 15 days before vaccination

Source/manufacturer of vaccine in India

Institute of Veterinary Biologicals, Lucknow (UP), Mhow (MP) and Kolkata (West Bengal)

Indian Immunologicals, Hyderabad - State Veterinary Vaccine Institute