Classical swine fever (hog cholera)
Swine fever, known as hog cholera or European Swine Fever is a highly infectious virus disease characterized by rapid spread and high morbidity and mortality rates. The virus belongs to the genus Pestivirus in the family Flaviviridae. The disease is prevalent worldwide.
Epidemiology: The virus affects only swine, both domestic and wild. The infection is usually acquired by ingestion, but inhalation is also a possible portal. All excretions, secretions and body tissues of the affected pig contain the virus. Garbage and kitchen scrap feeding has been an important mode of virus transmission between herds. Birds and human beings may also act as mechanical carriers of the virus.
Clinical signs: The incubation period varies from 3 to 8 days. Initial symptoms include fever, dullness or listlessness, anoerexia, constipation, diarrhoea, weakness in hindquarters, staggering in animals, vomiting, loss of appetite, body temperature 41o to 42oC and mucopurulent discharge from eyes. The disease takes a week or two to affect all individuals in a herd. Nervous symptoms occur quite commonly which may be manifested by grinding of the teeth, local paralysis, locomotor disturbances and occasionally lethargy and convulsions. Chronic cases may linger on for more than 30 days. Usually the recovered animals are permanently stunted.
Diagnosis: Clinical symptoms and post-mortem examination reveal pathognomonic lesion, viz. button type ulcer in the ileocecal junction that are indicative of hog cholera. The disease is diagnosed by high body temperature, leucopenia, high mortality and histopathological evidence of perivascular cuffing in the brain by inoculating suspected material in susceptible and immune pigs. The fluorescent antibody method is rapidly finding favour with diagnostic laboratories for the detection possible within a few hours. Field strains do not produce cytopathic effects in tissue culture, but viral activity can be detected by the fluorescent antibody technique. Virus isolation and neutralizing antibody assays are done in swine cell culture. Molecular methods of diagnosis using PCR and monoclonal antibody based ELISA is now-a-days commonly used.
Treatment, prevention and control: Test and slaughter policy is used in many countries to eradicate the disease. Animals recovered from an attack of swine fever have a long-lasting and durable immunity. A single immunological type of virus exists. At present most of the vaccinations are done by the use of modified live attenuated virus vaccines capable of producing lasting immunity without the risk of spreading infection to susceptible animals. Chemically treated vaccines do not confer a strong immunity. The use of vaccination and enforcement of garbage cooking regulations may reduce spread of this epidemic disease. Clinically normal 'carrier' animals pose the most serious problem.