BackgroundActinobacillus pleuropneumoniae (A.pp.) is the causative agent of porcine pleuropneumonia leading to high economic losses in the pig industry. Infrared thermography (IRT) of the thorax might offer a new method to select swine with lung alterations for further diagnostics.In this study 50 german landrace pigs were infected with A.pp. in an established model for respiratory tract disease, while 10 healthy pigs served as control animals. To avoid drift errors during IR measurements absolute skin temperatures and temperature differences between a thoracal and an abdominal region were assessed for its diagnostic validity.ResultsIRT findings during the course of experimental A.pp.-infection were verified by computed tomography (CT) before and on days 4 and 21 after infection. Significant correlations were found between clinical scores, CT score and lung lesion score. Ambient temperature, body temperature and abdominal surface temperature were factors influencing the skin surface temperature of the thorax. On day 4 but not on day 21 after infection the right thoracal temperature was significantly higher and the difference between a thoracal region in the height of the left 10th vertebra and an abdominal region was significantly lower in infected pigs than in control pigs. At a cut off of 28°C of right thoracal temperature the specificity of the method was 100% (CI 95%: 69-100%) and the sensitivity 66% (CI 95%: 51-79%).At a cut off of 2°C temperature difference between thoracal and abdominal region on the left body site the specificity of the method was 100% (CI 95%: 69-100%) and the sensitivity 32% (CI 95%: 19-47%) with all control pigs detected negative.Orientation for lung biopsy by IRT resulted in 100% specificity and sensitivity (CI 95%: 69-100%) of bacteriological examination of tissue samples during the acute stage of infection.ConclusionIRT might be a valuable tool for the detection of inflammatory lung alterations in pigs, especially during the acute stage of infection and if ambient temperatures are constant during individual measurements. External and internal factors interfere with this method, so that its application in the field might be restricted to a selection of pigs for further diagnostic with adequate specificity.

Background Actinobacillus (A.) pleuropneumoniae is the causative agent of porcine pleuropneumonia and causes significant losses in the pig industry worldwide. Early host immune response is crucial for further progression of the disease. A. pleuropneumoniae is either rapidly eliminated by the immune system or switches to a long-term persistent form. To gain insight into the host-pathogen interaction during the early stages of infection, pigs were inoculated intratracheally with A. pleuropneumoniae serotype 2 and humanely euthanized eight hours after infection. Gene expression studies of inflammatory cytokines and the acute phase proteins haptoglobin, serum amyloid A and C-reactive protein were carried out by RT-qPCR from the lung, liver, tonsils and salivary gland. In addition, the concentration of cytokines and acute phase proteins were measured by quantitative immunoassays in bronchoalveolar lavage fluid, serum and saliva. In parallel to the analyses of host response, the impact of the host on the bacterial pathogen was assessed on a metabolic level. For the latter, Fourier-Transform Infrared (FTIR-) spectroscopy was employed.ResultsSignificant cytokine and acute phase protein gene expression was detected in the lung and the salivary gland however this was not observed in the tonsils. In parallel to the analyses of host response, the impact of the host on the bacterial pathogen was assessed on a metabolic level. For the latter investigations, Fourier-Transform Infrared (FTIR-) spectroscopy was employed. The bacteria isolated from the upper and lower respiratory tract showed distinct IR spectral patterns reflecting the organ-specific acute phase response of the host.ConclusionsIn summary, this study implies a metabolic adaptation of A. pleuropneumoniae to the porcine upper respiratory tract already during early infection, which might indicate a first step towards the persistence of A. pleuropneumoniae. Not only in lung, but also in the salivary gland an increased inflammatory gene expression was detectable during the acute stage of infection.Electronic supplementary materialThe online version of this article (doi:10.1186/s12917-017-0979-6) contains supplementary material, which is available to authorized users.

This study was performed to characterise the response of iron (Fe), zinc (Zn), copper (Cu) and selenium (Se) in bacterial-induced porcine acute phase reaction (APR). Twenty piglets were challenged by aerosolic infection with Actinobacillus pleuropneumoniae (A.pp.) serotype 2, ten piglets serving as controls. Blood sampling was done initially and at day 4 and 21 after infection, collection of liver tissue was done at day 21 (autopsy). A.pp.-infection caused fever and respiratory symptoms. APR at day 4 after infection was marked by an increase in total white blood cells, granulocytes and monocytes in whole blood samples and an increase in globulin/albumin ratio (G/A), α2-globulins, C-reactive protein, haptoglobin, ceruloplasmin (Cp), Cu and Se in serum. Concurrently, there was a decrease in haemoglobin (Hb) and packed cell volume (PCV) in whole blood as well as a decrease in albumin, transferrin, total iron binding capacity and Fe in serum and Zn in plasma. The subacute stage at day 21 was characterised by progressively increased concentrations of G/A, β-globulins and γ-globulins reflecting the specific immune reaction. Hb and PCV showed further decreases, all other parameters returned to the initial concentrations. Glutathione peroxidase activity in plasma and liver tissue remained unaffected by A.pp.-infection. The liver concentration (day 21) of Zn was found to be higher, that of Se was lower in the A.pp.-group, whereas hepatic concentrations of Cu and Fe were not affected by A.pp.-infection. In summary, the acute and subacute stages of A.pp.-infection were accurately characterised by the APR-related parameters. Se was only marginally affected by the A.pp.-infection. The elevated plasma Cu concentration may be a side effect of the transient hepatic induction of Cp synthesis. Zn responded, being distinctly reduced in plasma and probably having been sequestered in the liver tissue. Reduction in serum Fe can be regarded as an unspecific defence mechanism in A.pp.-infection to withdraw Fe from bacterial acquisition systems.