Prevalence of porcine proliferative enteropathy associated to Lawsonia intracellularis in pigs slaughtered in Mato Grosso State, Brazil.

Background: Porcine proliferative enteropathy (PPE) is an infectious enteric disease that often affects pigs during the growing and finishing stages. Its etiological agent is the obligate intracellular bacterium Lawsonia intracellularis. This study evaluates PPE frequency and geographic distribution in Mato Grosso state, Brazil, based on PPE diagnosis and epidemiology data from pig herds. Materials, Methods & Results: An amount of 735 small intestine samples were collected from the ileum of finishing pigs and culling sows in three slaughterhouses that received animals from 14 breeding farms adopting very similar husbandry systems located in 11 municipalities in Mato Grosso state, Brazil, between August 2006 and July 2007. All samples were processed in the Laboratory of Veterinary Pathology, Federal University of Mato Grosso, according to standard laboratory routines for histological analyses. These samples were stained using the hematoxilin-eosin (HE) procedures. Those sections that presented at least one of the characteristic histopathological lesions of EPS were evaluated by HE, Alcian blue and Warthin-Starry combined stain (CST) to detect Lawsonia intracellularis-like structures, inside enterocytes and also by immunohistochemistry (IHC) based on a polyclonal antibody. Upon initial histological examination, 124 samples (16.87%) presented histopathological lesions that met the L. intracellularis infection criteria. These 124 samples were analyzed using the CST and IHC protocols, which revealed 2 and 3 positive results, respectively. PPE prevalence in Mato Grosso state was 0.41% in slaughtered pigs, based on the original number of 735 samples analyzed. Discussion: In Mato Grosso state, the geographic distance between farms does not favor the epidemiological conditions required for the dissemination of L. intracellularis. Another important epidemiological aspect is the low number of new acquisitions and turnover rates of animals in farms. The influence of these biosecurity variables may therefore explain the low PPE prevalence observed in the present study. The PPE prevalence measured using the IHC protocol in the present sample was similar to that observed in other studies with the same technique. On the other hand, PPE prevalence measured by IHC in this study differs significantly from that found by PCR in previous research, which have shown that, due to its high specificity, PCR is one of the most accurate methods to detect symptomatic as well as asymptomatic animals carrying L. intracellularis. IHC is not as sensitive as PCR, though it is the technique of choice in PPE diagnosis because it allows the identification of the pathogen in the lesion site, which increases reliability of results, instead of merely identifying the agent. The relevance of the results found in this epidemiologic study lies in the representative number of farms and municipalities listed for sample collection, which affords an insight on the number of pigs with L. intracellularis. Also, a geographic panorama of L. intracellularis prevalence is presented, providing elementary data on the animals' health condition and a useful tool for monitoring the spread of the disease in pig herds in Mato Grosso state, Brazil.