Increased Production of Proinflammatory Cytokines following Infection with Porcine Reproductive and Respiratory Syndrome Virus and Mycoplasma hyopneumoniae. Roongroje Thanawongnuwech, Brad Thacker, Patrick Halbur, and Eileen L. Thacker. Clin Diagn Lab Immunol. Sep 2004; 11(5): 901–908. doi: 10.1128/CDLI.11.5.901-908.2004
What are they studying?
The interaction between PRRSV and M. hyopneumoniae in pigs.
How is it done?
70 piglets inoculated at 6 weeks of age with Sham, M.hyo, PRRS or M.hyo+PRRS. Clinical evaluation and necropsies were performen on days 10, 28 and 42. Bronchoalveolar lavage was performed to measure levels of proinflamatory cytokines. Also, in-vitro studies were performed with culture cells.
What are the results?
Pigs infected with both pathogens had a greater percentage of lung lesions, increased clinical disease, and slower viral clearance than pigs infected with either pathogen alone.
Mycoplasmal pneumonia was enhanced by PRRSv. Also, pigs with mycoplasmal pneumonia lesions had increased viral pneumonia compared to pigs only infected with PRRSv.
The levels of proinflammatory cytokines were higher when 2 pathogens were present (in vivo and in vitro) than with only one pathogen.
Graphic 1. Levels of proinflamatory cytokines and lung lesions in pigs infected with M. hyo and PRRSV vs. pigs infected with only PRRSV or M. hyo.
What implications does this paper have?
Both PRRSV and M.hyo pathogens have a great effect on inflammatory cytokine production, which may favour the induction of disease and the persistence of the microorganisms in the host.
The disease and lesions caused are higher than those induced by single infections.
The field view by Enric Marco
The aggressiveness of PRRS infections in the field varies widely. From outbreaks that go unnoticed to clinical pictures with difficult-to-control respiratory symptoms. This variation is usually explained by the existence of a wide number of strains and their different pathogenic capacity. However, this article focuses on the increase of pathogenicity experienced by the virus when PRRS occurs as part of a coinfection with such a frequent lung pathogen in our herds as M. hyopneumoniae. The combination does not only aggravate the pneumonia and therefore the clinical symptoms, but may even prolong viraemia and therefore, virus persistence.
Consequently, and since a vast majority of commercial farms are endemically infected with M. hyopneumoniae, the control measures applied against PRRS should include measures against M. hyo. These measures against a M. hyo must include a proper replacement gilt acclimation program in case the animals come from negative herds (SPF). The measures must include an adequate vaccination plan prior to contact with the animals in the recipient farm, as well as infection control throughout the production of piglets, since this is where recirculation of PRRSv occurs. Control measures in piglets can be based either on the use of medications or early vaccination. Medications have been used for many years with satisfactory results in the control of M. hyopneumoniae but with the advent of vaccines and the good results achieved with them, medications have shifted towards a more occasional use in acute infections or as an adjunct to vaccination in refractory cases. The most common vaccination plans include vaccination of piglets, either during lactation or around weaning, with one-dose or two-dose products.
Given that, as this paper demonstrates, the combined pathogen infection increases the production of certain inflammatory elements, the use of anti-inflammatory treatments associated with antibiotics at the time of clinical expression could be an interesting strategy. The anti-inflammatory medication would help to improve response to antibiotic treatment, reducing the severity of the clinical phase, and shortening its duration.