Mycoplasma hyopneumoniaePotentiation of Porcine Reproductive and Respiratory Syndrome Virus-Induced Pneumonia

Abstract

An experimental model that demonstrates a mycoplasma species acting to potentiate a viral pneumonia was developed. Mycoplasma hyopneumoniae, which produces a chronic, lymphohistiocytic bronchopneumonia in pigs, was found to potentiate the severity and the duration of a virus-induced pneumonia in pigs. Pigs were inoculated with M. hyopneumoniae 21 days prior to, simultaneously with, or 10 days after inoculation with porcine reproductive and respiratory syndrome virus (PRRSV), which induces an acute interstitial pneumonia in pigs. PRRSV-induced clinical respiratory disease and macroscopic and microscopic pneumonic lesions were more severe and persistent in M. hyopneumoniae-infected pigs. At 28 or 38 days after PRRSV inoculation, M. hyopneumoniae-infected pigs still exhibited lesions typical of PRRSV-induced pneumonia, whereas the lungs of pigs which had received only PRRSV were essentially normal. On the basis of macroscopic lung lesions, it appears that PRRSV infection did not influence the severity of M. hyopneumoniae infection, although microscopic lesions typical ofM. hyopneumoniae were more severe in PRRSV-infected pigs. These results indicate that M. hyopneumoniae infection potentiates PRRSV-induced disease and lesions. Most importantly,M. hyopneumoniae-infected pigs with minimal to nondetectable mycoplasmal pneumonia lesions manifested significantly increased PRRSV-induced pneumonia lesions compared to pigs infected with PRRSV only. This discovery is important with respect to the control of respiratory disease in pigs and has implications in elucidating the potential contribution of mycoplasmas in the pathogenesis of viral infections of other species, including humans.

Serological evidence of Mycoplasma cynos infection in canine infectious respiratory disease

“…In other cases, no obvious bacterial cause could be detected. Mycoplasmas have been known for some time to modulate host susceptibility to secondary infections (Kaklamanis and Pavlatos, 1972;Thacker et al, 1999). In view of this, the presence of other initiating agents could be suspected and mycoplasma agents could be involved.…”

“…Mycoplasmas are recognised agents of respiratory disease in a wide range of animal species including www.elsevier.com/locate/vetmic Veterinary Microbiology 120 (2007) 358-362 man. Generally, the disease is mild but has been shown to predispose the animal to more severe secondary infection and to exacerbate concurrent infections (Thacker et al, 1999). Mycoplasmas have been implicated as potential agents of canine respiratory disease (Greig, 1954;Rosendal, 1978).…”

The combination of PRRS virus and bacterial endotoxin as a model for multifactorial respiratory disease in pigs

“…Most important, many of these studies yielded conflicting results. Using the same PRRSV-bacterium combination no disease was reported by some researchers and severe disease by others (Albina et al, 1995;Cooper et al, 1995;Van Alstine et al, 1996;Thacker et al, 1999;Wills et al, 2000). In the latter case, it was not always clear whether the effects of the combined inoculation were additive or synergistic.…”

“…Few studies, however, have been able to reproduce clinical respiratory disease by experimental inoculation with PRRSV followed by a secondary virus or bacterium. Dual infections have been performed with PRRSV followed by various bacteria such as Actinobacillus pleuropneumoniae, Bordetella bronchiseptica, Haemophilus parasuis, Mycoplasma hyopneumoniae, Pasteurella multocida, Salmonella choleraesuis and Streptococcus suis (Galina et al, 1994;Albina et al, 1995;Cooper et al, 1995;Van Alstine et al, 1996;Carvalho et al, 1997;Pol et al, 1997;Solano et al, 1997;Segalés et al, 1999;Thacker et al, 1999;Brockmeier et al, 2000;Halbur et al, 2000;Thanawongnuwech et al, 2000;Wills et al, 2000;Brockmeier et al, 2001;Schmitt et al, 2001). The outcome of these combinations ranged from no interaction (H. parasuis and P. multocida) to increased lung colonization (B. bronchiseptica) or increased mortality (S. suis).…”

Control of Mycoplasma hyopneumoniae infections in pigs

“…The generation of IFN-g secreting cells in blood following vaccination might suggest that IFN-g may also play a role in protection against M. hyopneumoniae through the activation of macrophages (Thacker et al, 2000a). Increases in concentrations of pro-inflammatory cytokines such as TNF-a, are thought to be associated with lesion development and to be one possible mechanism for the potentiation of PRRSV-induced pneumonia by M. hyopneumoniae (Thacker et al, 1999). Vaccination against M. hyopneumoniae reduced the potentiation of PRRSV-induced pneumonia by M. hyopneumoniae (Thacker et al, 2000c).…”