Classical Swine Fever-An Updated Review

Abstract

Classical swine fever (CSF) remains one of the most important transboundary viral diseases of swine worldwide. The causative agent is CSF virus, a small, enveloped RNA virus of the genus Pestivirus. Based on partial sequences, three genotypes can be distinguished that do not, however, directly correlate with virulence. Depending on both virus and host factors, a wide range of clinical syndromes can be observed and thus, laboratory confirmation is mandatory. To this means, both direct and indirect methods are utilized with an increasing degree of commercialization. Both infections in domestic pigs and wild boar are of great relevance; and wild boars are a reservoir host transmitting the virus sporadically also to pig farms. Control strategies for epidemic outbreaks in free countries are mainly based on classical intervention measures; i.e., quarantine and strict culling of affected herds. In these countries, vaccination is only an emergency option. However, live vaccines are used for controlling the disease in endemically infected regions in Asia, Eastern Europe, the Americas, and some African countries. Here, we will provide a concise, updated review on virus properties, clinical signs and pathology, epidemiology, pathogenesis and immune responses, diagnosis and vaccination possibilities.

Keywords: Pestivirus; classical swine fever; clinical signs; control; diagnosis; epidemiology; marker strategy; pathogenesis; porcine viruses; vaccination.

Figure 1

Global distribution of classical swine fever virus (CSFV) sub-genotypes (map based on Global Administrative Areas (GADM database 2.8; November 2015)).

Figure 2

Acute CSFV infection with moderately virulent strains. The incubation period in most cases is from 7 to 10 days. Atypical clinical signs range from one to two weeks. Typical clinical signs occur around 2 to 4 weeks. The convalescent period is from 3 to 4 weeks. Death can occur as late as five weeks post-infection. (a) Swine are huddling, 10–15 days post-infection; (b) swine are presenting with hunched back; (c) severe conjunctivitis; (d) severe cyanosis of the skin around the face, ears, and limbs; (e) neurological signs, swine was unable to stand; and (f) dead swine with classic cyanosis of the ears.

Figure 3

Chronic CSFV infection. The incubation period is the same as with the acute course. However, it may take up to a month until they are truly recognized. Atypical clinical signs can be present throughout and until death, occurring up to three months or even later after the infection. Antibodies can be detected at low levels after two weeks or later but do usually not persist. Viral shedding is observed from about four days post infection till the death of the animal. (a) Pigs are depressed, hunched over, and anorexic; (b) pig with petechial bleedings and ecchymosis in the anogenital region; (c) stunted and wasting pig beside a normally developed one of the same age; and (d) pig with diarrhea, shedding high viral loads until death.

Figure 4

CSF related lesions: (a) Diphtheroid-necrotizing enteritis; (b) hemorrhages on the epiglottis; (c) severe secondary infections of the lung (Actinobacillus pleuropneumoniae); (d) necrotic tonsillitis with an ulcer; (e) gallbladder edema; (f) hemorrhagic lymph node; (g) necrotizing ileocecal valve; and (h) splenic infarcts.