Molecular characterization of Mycoplasma hyopneumoniae in a multi-site endemic farm by MLVA

Multiple Locus Variable Tandem Repeat Analysis (MLVA) is a useful method to characterize bacterial strains and understand the transmission chains and sources of infection in order to implement more effective control measures. The present study is aimed to use MLVA technique to characterize M.hyopneumoniae (M.hyo) strains in pigs from wean to finish in the same herd.

The study was carried out in a three-site herd in the North of Italy with endemic M. hyo infection on both vaccinated and unvaccinated animals. Tracheobronchial swabs (TBS) were taken from each pig at the first week of life (T1) and once a month until 9 months old (T2-T10). During the slaughtering, lungs were inspected and the presence and severity of lesions were recorded. TBS and lung samples were analyzed by qPCR directed against the p102 gene of M. hyo. Based on qPCR results, 113 positive samples (74 TBS and 39 lungs) belonging to 18 different animals were characterized by MLVA. The method is based on the detection of the number of tandem repeats at four multiple variable number tandem repeat (VNTR) loci within the genome (Locus 1, Locus 2, p 97-1, p 97-2). The monitoring of M.hyo population in this specific herd was further deepened analyzing other 8 samples (7 nasal swabs and two lungs), collected at 1 and 2 years after the study.

Both in vaccinated and unvaccinated animals, M.hyo infection was detected by qPCR from T5 but a general decrease was observed at T10. Furthermore, most of the animals showed fluctuating level of M.hyo and only few animals were positive throughout the study until the 10th month. Out of 113 specimens 97 samples were completely characterized by MLVA. Two distinct strains (MLVAtype-1 and MLVAtype-2) were identified: MLVAtype-1 was detected in all the analyzed animals from T5 until the last time point and in the lungs; MLVAtype-2 was detected in five pigs. The second genotype was identified especially in the lungs (10) and in TBS collected from two animals at T9 or T10. Furthermore, in one animal a coinfection of two different strains in the same lung samples was observed. The 8 samples collected at 1 and 2 years after the study were characterized by MLVAtype-2.

At the beginning of the study a single M.hyo genotype was prevalent in the herd infecting all the examined animals. A second genotype, detected at the last time points and in the lungs, could indicate a second wave of infection This second strain seems to persist in the herd as observed during the following analysis. Moreover, the present study evidenced the presence of two different strains of M.hyo in the same herd and even in the same animal.

Disclosure of Interest: None Declared.