Investigation of congenital tremor associated with Classical swine fever virus genotype 2.2 in an organized pig farm in north-eastern India

Abstract

The present study describes an outbreak of Classical swine fever (CSF) in an organized pig farm followed by an episode of CSF virus (CSFV) associated congenital tremors in piglets. The outbreak was recorded in a newly procured herd of Hampshire pigs housed adjacent to the existing pigs of the farm. The recorded CSF outbreak caused a mortality of 100% in the newly procured and 54.28% in the existing herd. As the disease subsides, the clinically recovered boars were served naturally with Tamworth gilts. Though, the sows farrowed on usual gestation period, litters born to each sow showed congenital tremors and eventually died within 24 h of birth. Necropsy analysis of affected piglets was indicative of CSFV infection and was further confirmed using RT-PCR signifying a transplacental infection. The CSFV strains from the initial outbreak and post outbreak episode of congenital tremors were successfully isolated in PK-15 cells and detected in indirect FAT and RT-PCR. Phylogenetic analysis based on E2 gene and 5'NTR of CSFV grouped the isolates within the genotype 2.2 and revealed close resemblance with previously reported Indian isolates of CSFV genotype 2.2 origin. To the best of our knowledge, this is the first report of CSFV induced congenital form reported from India under natural conditions.

Keywords: Classical swine fever virus; Congenital tremor; Genotype 2.2; Phylogenetic characterization; Piglets; Transplacental infection.

Fig. 1

Piglets exhibiting congenital tremors with hind leg splays and dog-sit posture

Fig. 2

a A cryosection of kidney of CSFV affected Hampshire boar showing bright green cytoplasmic fluorescence. b No fluorescence was observed in cryosection of kidney of a healthy pig (400×)

Fig. 3

Gross pathological finding in a 24 h-old piglet died after exhibiting post-parturition tremors a Petechial haemorrhages in renal cortex b Splenic infarction

Fig. 4

Histopathological changes seen in piglets associated with congenital tremors, HE staining. a Kidney; interstitial nephritis and focal areas of acute glomerular nephritis characterized by swelling of the glomerular tuft, b spleen; focal to diffuse haemorrhages in the red pulp with a depletion of the lymphocyte in the splenic corpuscles, c lymph node; depletion of lymphocytes in the lymphoid follicle and necrosis with cellular debris and haemorrhages

Fig. 5

a Agarose gel electrophoresis showing amplification of E2 gene and 5′NTR (271 bp) regions of CSFV in tissue specimens of piglets died exhibiting congenital tremors; Lane 1: non template control; Lane 2: E2 gene positive control; Lane 3–7: amplification of E2 gene in tissue samples; Lane 8: 5′NTR positive control; Lane 9–15: amplification of 5′NTR in tissue samples; Lane 16: 100 bp plus DNA ladder (GeneRuler). b Immunofluorescence staining of isolation of CSFV in PK-15 cells at 72 h post infection (× 200) at passage 3

Fig. 6

Phylogenetic tree of nucleotide sequences of E2 gene of CSFV employing neighbour-joining algorithm using MEGA 6 software. The CSFV isolates of the present study, KJ885559 and KT852941 (indicated with blue diamonds) lies within the clade of Genotype 2.2

Fig. 7

Phylogenetic tree of nucleotide sequences of 5′ NTR of CSFV employing neighbour-joining algorithm using MEGA 6. The CSFV isolates of the present study, KJ645981 and KJ645982 (indicated with blue diamonds) lies within the clade of Genotype 2.2