Lungworms (Metastrongylus Spp.) Demonstrated in Domestic Pigs with Respiratory Disease - What was the True Relevance of that?

BackgroundAn outdoor pig herd was affected by severe respiratory disease in one out of three pastures. At necropsy, Mycoplasma hyopneumoniae and Pasteurella multocida were detected in the lungs, as well as the lung worm Metastrongylus apri. The life cycle of Metastrongylus spp. includes earth worms as an intermediate host, and since domesticated pigs mainly are reared indoors lungworms has not been diagnosed in domestic pigs in Sweden for decades, not even in pigs reared outdoors. Therefore, this disease outbreak was scrutinised from the view of validating the impact of Metastrongylus spp..ResultsAt the time of the disease outbreak, neither eggs of Metastrongylus spp. nor Ascaris suum were detected in faeces of pigs aged ten weeks. In contrast, five-months-old pigs at the pasture with respiratory disease shed large amounts of eggs from Ascaris suum, whereas Ascaris suum not was demonstrated in healthy pigs aged six months at another pasture. Low numbers of eggs from Metastrongylus spp. were seen in faecal samples from both these age categories.At slaughter, seven weeks later, ten normal weighted pigs in the preceding healthy batch were compared with ten normal weighted and five small pigs from the affected batch. Healing Mycoplasma-like pneumonic lesions were seen in all groups. Small pigs had more white spot liver lesions, and all small pigs shed eggs of Ascaris suum in faeces, compared to around 50% of the pigs in the normally sized groups. Metastrongylus spp. were demonstrated in 13 of the 25 pigs (52%), %), representing all groups included.ConclusionAs Metastrongylus spp. were demonstrated regardless of health status, and in another healthy outdoor herd, the impact of Metastrongylus spp. on the outbreak of respiratory disease was depreciated. Instead, Metastrongylus spp. was suggested to be common in outdoor production, although rarely diagnosed. The reason for this is because they will escape detection at routine inspection at slaughterhouses, and that they appeared to generally not induce clinical signs of respiratory disease. Instead, a possible association with a high burden of Ascaris suum was suggested to have preceded the severe outbreak with respiratory disease.