Hematobiochemical and splenic pathological evaluation in slaughtered pigs

Introduction

The spleen is a major secondary lymphoid organ involved in blood filtration, removal of senescent erythrocytes, antigen processing and immune responses. Because of its close association with the circulating blood and mononuclear phagocyte system, splenic lesions frequently accompany systemic infectious and inflammatory diseases. In pigs, commonly recognized splenic abnormalities include enlargement, atrophy, haemorrhage, infarction, abscessation, parasitic lesions and lymphoid depletion. Slaughterhouse examination provides a practical opportunity to identify such lesions in animals that may have shown no obvious clinical abnormalities before slaughter (Khonde et al., 2026) [7] . It can therefore complement farm-level disease surveillance and provide information on the occurrence of infectious and other pathological conditions within the source population. Classical swine fever (CSF), caused by classical swine fever virus (CSFV), is an important transboundary disease of swine (Choudhury et al., 2025) [4] . Its pathological expression varies with viral virulence, host factors and immune status. Splenic enlargement, haemorrhage, infarction and lymphoid depletion are recognized pathological findings, although none is individually pathognomonic for CSF (Blome et al., 2017) [2] . Experimental studies have demonstrated marked depletion of splenic lymphoid tissue during CSFV infection, associated with lymphocyte apoptosis and macrophage activation (Sánchez-Cordón et al., 2005) [14] . Serological detection of CSFV antibodies is useful for assessing population exposure; however, antibody positivity may reflect either previous infection or vaccination. Consequently, seropositivity should not be equated with active infection in the absence of direct evidence of viral infection (Blome et al., 2017) [2] . Although splenic pathology, bacterial infection and CSFV serology have been studied individually in pigs, integrated assessment of naturally occurring splenic lesions together with hematobiochemical changes in slaughtered pigs is limited. Slaughterhouse inspection is an important component of animal disease surveillance and food safety (Ocepek et al.,) [10] . Systematic post-mortem examination of slaughtered animals provides an opportunity to identify gross and microscopic pathological lesions that may remain clinically undetected during life. Such surveillance can generate valuable information on the prevalence and distribution of infectious, parasitic and other pathological conditions and may contribute to reducing the risk of contaminated meat entering the food chain, including diseases of potential public health significance (Barbara et al., 2020; Quiroga-Robayo et al, 2026) [1,11] . The present study therefore aimed to characterize gross and histopathological splenic lesions in slaughtered pigs and evaluate their association with hematological and serum biochemical parameters, bacterial isolation and CSFV antibody status.

Materials and Methods

The investigation was conducted in the Department of Pathology, Bombay Veterinary College, Mumbai on 200 randomly selected nondescript pigs slaughtered at an organized slaughterhouse. The animals originated from different districts of Maharashtra and Gujarat. Blood was collected before slaughtering into EDTA-containing tubes for hematological examination and into plain tubes for serum separation. The spleen was examined grossly during postmortem examination and representative tissue was collected in 10% neutral buffered formalin for histopathology (Luna, 1968) [9] . Additional splenic tissue was collected aseptically for bacterial isolation. Hemoglobin, packed cell volume (PCV), total erythrocyte count (TEC) and total leukocyte count (TLC) were determined using an automated hematologyanalyzer (Abacus-Diatron). Differential leukocyte counts were performed manually on Leishman-stained blood smears and converted to absolute counts.Serum total protein and albumin were estimated using commercial reagent kits on a semi-automated analyzer. Globulin was calculated from total protein and albumin, and the albumin (A) ratio was determined.Formalin-fixed splenic tissues were routinely processed and stained with hematoxylin and eosin (H & E). Bacterial isolation was performed using enrichment and selective culture methods followed by standard identification and biochemical testing ( Sarma and Sarma, 1996) [15] . Serum samples were examined for antibodies against CSFV by indirect ELISA at the DBT Network Project Centre on Classical Swine Fever, Department of Pathology, Nagpur Veterinary College. Titres of ≥1:20 were considered positive according to the protocol used in the original study. For analysis of CSFV serological status, animals were categorized according to antibody titre as 1:20, 1:40, 1:80, >1:80 and negative( Sarma and Sarma, 1996) [15] . Data were analyzed using the completely randomized design following Snedecor and Cochran, 1994 [16].

Results

Splenic lesions were identified in 16/200 (8%) pigs. Nine animals (4.5%) had parasitic lesions (Fig. 1, a), two (1.0%) had splenomegaly, five (2.5%) had atrophy (Fig. 1,b), abscessation (Fig. 1,c) and/or nodular hyperplasia (Fig.

Discussion

The present study demonstrates that splenic lesions in slaughtered pigs are morphologically diverse and may reflect parasitic, bacterial, inflammatory and vascular processes. Although only 8% of the examined pigs had identifiable splenic lesions, the lesions were associated with discernible hematologicalchanges; particularly in animals with splenomegaly (Suardana et al., 2024) [17] . The parasitic lesions were characterized by organized inflammatory responses around cystic or larval structures (Krishna and Dayal, 2024) [8] . The comparatively higher eosinophil count in this groupwas compatible with a parasitic stimulus ( Poulsen et al., 2024) [12] . Splenomegaly represented the most distinctive clinicopathological group. The marked leukocytosis and neutrophilia, together with vasculitis, redpulp expansion and perivascular haemorrhage, suggested an active systemic inflammatory response. The isolation of Salmonella spp. from both animals strengthens this interpretation. Systemic salmonellosis in pigs is known to produce septicemic disease with involvement of lymphoid organs and can be associated with splenomegaly (Brown et al., 2006) [3] . Nevertheless, the small number of animals in this group warrants caution in attributing the lesion exclusively to Salmonella infection. The coexistence of infarction, haemosiderosis, fibrosis and abscessation in Group C suggests multiple pathological mechanisms. Pigment form of excess iron is frequently deposited in phagocytic cells of the reticuloendothelial system whenthere is iron excess, as in chronic hemolyticanemia or other pathological conditions (Brown et al., 2006) [3] . It also occurs in association with chronic passive congestion of the spleen, leading to hemolysisofexcessive numbers of erythrocytes ( Jones et al., 1992) [6] . Infarction reflects vascular compromise, whereas abscessation represents localized suppurative inflammation.

Splenic infarction is a recognized lesion in acute CSF but is not specific for the disease (Blome et al., 2017) [2] . Thus, infarction in a slaughter pig should be interpreted in conjunction with other pathological and laboratory findings rather than considered diagnostic of CSF. The lower globulin concentrations and increased A ratios observed in animals with splenomegaly and atrophy/abscess/infarction indicate altered serum protein balance. Spleen lesionsare heavily correlated with an altered albumin-to-globulin (A:G) ratio, typically manifesting as a low A:G ratio (<1.0). Because the spleen is a core lymphoid organ responsible for filtering blood, mounting immune responses, and housing B and T lymphocytes, pathology in this organ reflects major systemic disruptions that directly skew these blood proteins (Oh SI et al., 2022) [11] . These changes should not, however, be interpreted as direct evidence of immunosuppression because serum globulin comprises several protein fractions and was not individually characterized in the present study. An important finding was the high prevalence of CSFV antibodies, with 71% of animals testing positive. CSF is associated with lymphoid depletion and other splenic lesions during active infection 3& 4 . However, the absence of corresponding lesions in the seropositive-normal group emphasizes an important distinction between serological exposure and active disease. Indirect ELISA detects antibodies and therefore cannot by itself establish current viral replication. The 13% bacterial isolation rate from spleen samples also demonstrates the value of microbiological examination alongside histopathology. The concordance between Salmonella isolation and splenomegaly in both affected animals provides stronger pathological context. Salmonella infection is also relevant to food safety because pigs can serve as reservoirs of humanassociated Salmonella (Summerfield and Ruggli, 2015) [18] . Overall, the findings illustrate the value of integrating postmortem pathology with hematology, serum protein analysis, microbiology and serology. The study was conducted on a slaughterhouse population and therefore did not permit longitudinal assessment of disease progression. Individual vaccination histories were unavailable for most animals, limiting interpretation of CSFV antibody titres. Furthermore, no CSFV antigen detection, PCR or immunohistochemical confirmation was performed; hence, seropositivity cannot be interpreted as evidence of active CSFV infection. The relatively small number of pigs within individual splenic lesion categories also limits statistical inference.

Conclusion

Splenic lesions were detected in 8% of slaughtered pigs and included parasitic, inflammatory, suppurative and vascular alterations. Splenomegaly was associated with marked leukocytosis and neutrophilia and coincided with Salmonella isolation, whereas parasitic lesions showed a comparatively higher eosinophil response. Alterations in serum globulin and A ratio accompanied some splenic lesion groups. CSFV antibodies were detected in 71% of pigs, but the absence of significant splenic lesions in seropositive animals and the occurrence of high titres in vaccinated animals indicate that antibody positivity should be interpreted as evidence of exposure and/or vaccination rather than active CSF.

Acknowledgement

AcknowledgmentsThe authors are thankful to the Dean, Bombay Veterinary College for providing support and to Prof. Dr. Renuka Nehete, former Head, Department of Veterinary Pathology, Bombay Veterinary College and Dr. N. V. Kurkure, former Professor, Department of Veterinary Pathology, Nagpur Veterinary Collegefor their valuable guidance.

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