Correlations Between Lung Pneumonic Lesions and Serologic Status to Key Respiratory Pathogens in Slaughtered Pigs in Northern Uganda

Abstract Background: A cross-sectional study was conducted in three selected slaughter slabs in Lira district Uganda in 2019 to (i) determine prevalence and severity of pneumonia and (ii) establish associations between lung pneumonic lesions and serologic status to key respiratory pathogens in slaughter pigs. Blood samples were collected from pigs at antemortem from which sera were prepared. Using enzyme-linked immunosorbent (ELISA) assays, sera were screened for antibodies against Mycoplasma hyopneumoniae (M. hyo), Actinobacillus pleuropneumoniae (App), porcine reproductive and respiratory syndrome virus (PRRSv) and porcine circovirus type 2 (PCV2). At post-mortem, lungs were scored for possible pneumonic lesions and the type of pneumonia as previously described. Pneumonia types were grossly characterized as catarrhal purulent bronchopneumonia (CPBP), pleuropneumonia (PLP) and pleuritis as previously described. Metastrongylus spp infection was determined by examining lungs for gross presence or absence of helminths as previously described. T-tests were used to compute prevalence of pneumonia. Chi-square tests were used to compare the percentage of lungs positive or negative to CPBP, PLP and pleuritis. Ordinal logistic regression model was used to evaluate the odds of multiple pneumonia forms, with serostatus for different pathogens and Metastrongylus spp. infection as predictors. Results: One hundred and sixty seven (n=167) lungs were examined for pneumonic lesions. The prevalences of CPBP, PLP and pleuritis were 29.9% (95% CI 22.9-36.9), 74.2% (95% CI 67.5-80.9) and 17.3% (95% CI 22.4-36.3), respectively. The odds of multiple pneumonia forms increased in pigs with multiple pathogens and concurrent Metastrongylus spp. infestation (ORs 2.6, p=0.01 and 2.5, p=0.003, respectively), reaffirming synergistic effects of coinfections in the induction of lesions. Conclusions: This study revealed a high prevalence and severity of pneumonic lesions in slaughter pigs. It provides baseline information, undeniable evidence on the magnitude of pneumonia and justifies future studies on its potential economic impacts in Ugandan pigs.