Classical swine fever

Do not confuse with swine flu or African swine pest

Classical swine fever is a highly contagious and often fatal viral disease that affects both domestic and wild pigs. The first reports of this disease date back to the year 1830 in the Midwest region of the United States. The first description was made in 1810 in Tennessee, USA, and the second was made in 1833 in Ohio, USA, and appeared in Europe, England in 1860. This pathology is classified within the list of diseases of mandatory declaration by the World Organization for Animal Health (OIE) and affects only members of the Suidae family, to which domestic pigs, wild boars and wild pigs belong. It is currently considered one of the diseases that causes the most damage in the world. global pork industry, both from an economic and health point of view. Since 1990 in Europe, different outbreaks have occurred in several countries such as Holland, Belgium and the United Kingdom.

The disease is enzootic in areas of Central America and the Caribbean, South America (Argentina is free of CSF without vaccination since May 2005), Southeast Asia and Russia. Currently it constitutes an economic problem for the affected countries, influencing the deterioration of the economic and social situation of several developing nations. The European Union (EU) is considered free of the epizootic although it constitutes an area of high risk of re-emergence of the disease due to the high density of the pig population, the non-vaccination policy and its geographical proximity to the countries of Europe. This, where the disease remains enzootic. One of the problems that has been associated with the re-emergence of the disease in this region is the presence of wild boars and wild pigs with persistent infections. These re-emergencies have taken place despite the robust control programs implemented within the EU, which include the stamping out of the entire infected population and the restriction of trade in pigs from affected areas to areas free of the disease.

Etiology

The etiological agent of classical swine fever was identified at the beginning of the last century through the filtration of body fluids from sick pigs, and its name is generic for the disease caused by CSFv (classical swine). fever virus). It is an enveloped virus, with RNA as genetic material, with a diameter of 40 to 60 nm, and hexagonal symmetry.

CSFv, together with the bovine viral diarrhea virus (BVDv) and the sheep border disease virus BDv, make up the genus Pestivirus, formerly classified within the Togaviridae family. Currently, the homology between their sequences, the polarity and organization of their genome, and their replication strategy have led to their inclusion in the Flaviviridae family, along with the genera Flavivirus and Hepacivirus, whose only representative is the human Hepatitis C virus.

Diagnosis

Given the great variety of symptoms and the different forms of presentation, laboratory tests are essential for a correct diagnosis.

Samples of blood, tonsils, mesenteric lymph node, retropharyngeal lymph node, distal ileum, kidney and spleen should be sent to the laboratory for analysis.

The laboratory study may consist of direct isolation of the virus. Detection of viral nucleic acid by PCR test or detection of specific antibodies

Symptomology

The clinical presentation is very varied depending on the age of the animal, the immune situation and other factors. There are apparently healthy animals that carry the virus and are of great importance in the spread of the disease. 5 presentations have been described:

Hyperacute clinical form.

Affected animals die within a very short period (around 5 days) after infection. The symptoms are reduced to high fever.

Acute form.

High fever, decreased appetite and general depression, decrease in leukocytes and platelets in the blood (leukopenia and thrombopenia). Later, tremors and overcrowding of the animals appear in a state of freedom. In the terminal phase, the pigs have an undulating gait due to paralysis of the posterior third, which subsequently becomes generalized and the animals remain lying on their side and moving their limbs continuously as if they were rowing.

Subacute form.

Animals survive between 20 and 30 days after infection.

Chronic form.

Did you mean: La supervivencia es superior a los 30 días.

Did you mean:

Forma transplacentaria y congénita

It results in the birth of animals with congenital disease.

Vaccination

The first vaccines used against CSFv were inactivated vaccines with formalin or crystal violet, which were not effective in preventing the disease. In the 1940s, the first vaccination experiments were carried out with attenuated CSFv strains after serial passage in rabbits (lapinized strain). These studies led to a new generation of safer, live vaccines. These vaccines induced protection against highly virulent strains, and were protective in pregnant females.

Currently, live attenuated vaccines derived from CSFv are routinely used for the control of classical swine fever, especially in areas where the disease is enzootic. Five vaccines of this type have been developed called: lapinized Chinese “C” strain, attenuated “C” strain in culture of RK-13 cells, Japanese strain (GPE-) attenuated by passage in mouse cells, the French Thiverval strain and the PAV-250 strain, attenuated in PK-15 cells.

There is a strong controversy about the convenience of using this type of vaccines, given that it is not possible to differentiate vaccinated animals from sick and/or carriers because the antibodies induced by this type of vaccines are indistinguishable from those found in infected animals in the field. Furthermore, incorrect conservation and handling of these vaccines can cause failures in the protection they confer, favoring the appearance of animals carrying the virus that cannot be identified as such using current laboratory techniques.

To overcome the limitations presented by live attenuated vaccines, the so-called “marker” vaccine or recombinant vaccine (DIVA; differentiation of infected from vaccinated animals) has been developed. These vaccines must induce an effective protective response and also allow identification by serology between vaccinated and infected animals. Viral subunit vaccines have been developed, which use different sequences of the E2 glycoprotein, present in the CSFv membrane. The E2 sequence most used as an antigen is the one that lacks the C-terminal transmembrane segment, which is secreted into the supernatant of artificial cultures of insect cells, genetically transformed by the baculovirus system.

More recently, the E2 vaccine antigen has been produced in the milk of genetically modified goats that function as living reactors. In these cases the protein is secreted into the cell culture supernatant, the baculovirus is inactivated and the E2 protein contained in the medium is adjuvanted by oil emulsion or purified directly from milk and formulated in an oil adjuvant.

When applying these vaccines, immunized animals only develop antibodies against the antigenic protein E2, while infected animals also present antibodies against the rest of the viral proteins. The latter can be differentiated by enzyme-linked immunosorbent assay (ELISA), using a second glycoprotein specific to CSFv (Erns) that would be present in the infecting virus. This vaccination strategy allows the development of DIVA and could be introduced in areas where vaccination with attenuated viral strains is currently prohibited.

Public health

Classical swine fever should not be confused with swine influenza. Swine fever is a disease that affects pigs (and wild boars) and its transmission to humans has not been proven. Even so, it is recommended not to eat meat from animals suspected of suffering from the disease.