Hog cholera: Description, Causes and Risk Factors:
Alternative Name: Classical swine fever (SWF).
Hog cholera is a contagious viral disease of pigs. The causative virus is a member of the genus Pestivirus of the family Flaviviridae
, and is closely related to the viruses of bovine viral diarrhea and Border disease. There is only one serotype of CSF virus (CSFV). The virus that causes it is often transmitted through direct contact between healthy swine and infected swine.
The incubation period can range from 2 to 15 days, depending on the virulence of the strain, the route of inoculation and the dose. Under field conditions, disease may not become evident in a herd for 2 to 4 weeks or longer.
There are three forms: acute, chronic, and mild.
Acute Hog Cholera: The acute form of hog cholera is highly virulent (severe), causing persistent fevers that can raise body temperatures to as high as 107°F. Other signs of the acute form include convulsions and lack of appetite. Affected pigs will pile or huddle up together. Signs of hog cholera may not be apparent for several days following infection. Death usually occurs within 5 to 14 days following the onset of infection.
Chronic Hog Cholera: The chronic form causes similar clinical signs in affected swine, but the signs are less severe than in the acute form. Discoloration of the abdominal skin and red splotches around the ears and extremities often occur. Pigs with chronic hog cholera can live for more than 100 days after the onset of infection.
Mild Hog Cholera: The mild, or clinically unapparent, form of hog cholera seldom results in noticeable clinical signs. Affected pigs suffer from short periods of illness, which are often followed by periods of recovery. Eventually, a terminal relapse occurs. The mild strain may cause small litter size, stillbirths, and other reproductive failures. High mortality during weaning may also indicate the presence of this mild strain of the disease.
The most common method of transmission is direct contact between healthy swine and those infected with hog cholera. The disease also can be transmitted through contact with body secretions and excrement (feces) from infected animals. Healthy pigs coming into contact with contaminated vehicles, pens, feed, or clothing may contract the disease as well. Birds, flies, and humans can physically carry the virus from infected swine to healthy swine. Swine owners can inadvertently spread hog cholera through feeding their herds untreated food wastes containing infected pork scraps.
Spread of disease in all age groups, accompanied by pyrexia, huddling, inappetance, dullness, weakness,conjunctivitis, constipation followed by diarrhea
, and an unsteady gait are the prevailing signs. Several days afterthe onset of clinical signs, the ears, abdomen
and inner thighs may show a purple discoloration. Animals withacute disease die within 1-3 weeks. Sudden death in the absence of clinical illness is not symptomatic of CSF.
Identification of the agent: The direct fluorescent antibody test (FAT) on cryostat sections oforgans from affected pigs can be used for the detection of CSF antigen. A panel of monoclonalantibodies (MAbs) is used to determine whether the fluorescence is due to CSF or non-CSFPestivirus antigens. For the detection of CSF genome, polymerase chain reaction (PCR) iscommonly used. The isolation of CSFV should be attempted in the pig kidney (PK-15) cell line, orother suitable cell lines. The cultures are examined for virus growth by immunofluorescence orimmunoperoxidase staining; positive isolates are further characterized by the use of MAbs and bypartial genetic sequencing. Polymerase chain reaction protocols for the identification of CSFVnucleic acid have now gained international acceptance and are being used in several laboratories,both for detection of the agent and differentiation from ruminant Pestivirus. Antigen-captureenzyme-linked immunosorbent assays (ELISAs) are also useful for herd screening, but should notbe used on a single animal basis.
Histopathological findings are not pathognomonic. Lesions may include parenchymatous degeneration oflymphatic tissue, cellular proliferation of vascular interstitial tissue, and a nonsuppurative meningoencephalomyelitis, with or without vascular cuffing.
There is no cure for Hog cholera. CSFV is moderately fragile in the environment. This virus is sensitive to drying and ultraviolet light. It is stable at pH 5-10, but is rapidly inactivated by pH 3 or less, or pH greater than 11. Sodium hypochlorite and phenolic compounds are effective disinfectants. Detergents, organic solvents, quaternary ammonium compounds, and aldehydes (formaldehyde, glutaraldehyde) are also reported to destroy this virus. CSFV can survive for several months in refrigerated meat and years in frozen meat. In this proteinaceous environment, the virus is not inactivated by smoking or salt curing. However, it can be destroyed by cooking. Techniques reported to be effective include heating the meat to 65.5ºC or greater for 30 minutes, or 71ºC for one minute. The virus can also be inactivated in swill by heat treatment. Many countries have completely banned the practice of feeding swill to pigs.
NOTE: The above information is educational purpose. The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition.
DISCLAIMER: This information should not substitute for seeking responsible, professional medical care.