ShapeShapeauthorShapechevroncrossShapeShapeShapeGrouphamburgerhomeGroupmagnifyShapeShapeShaperssShape

Factors affecting the efficacy of the <i>Mycoplasma Hyopneumoniae</i> vaccine

by 5m Editor
27 July 2001, at 12:00am

By E. Thacker and B. Thacker, Veterinary Medical Research Institute, Iowa State University. - Porcine respiratory disease complex (PRDC) causes significant economic losses to swine producers world wide. PRDC is characterized by slow growth, decreased feed efficiency, lethargy, anorexia, fever, cough and dyspnea. Porcine reproductive and respiratory syndrome virus (PRRSV) and Mycoplasma hyopneumoniae (M. hyo) are two of the most common pathogens isolated from pigs exhibiting signs of PRDC.

Introduction

Recent research in our laboratory found that M. hyo potentiated the pneumonia induced by PRRSV (1). M. hyo, the cause of mycoplasmal pneumonia, causes a mild chronic pneumonia commonly complicated by opportunistic infections. Vaccines against M. hyo are commonly used as aids for controlling swine respiratory disease.

Current M. hyo vaccines are bacterins administered either intramuscularly or subcutaneously. A previous study conducted in our laboratory demonstrated that M. hyo vaccines provide protection against experimental M. hyo challenge, although pneumonia was not completely eliminated and colonization was only slightly reduced (2). In spite of the experimental data that document M. hyo vaccine efficacy, vaccine failure under field conditions is commonly observed. Recent studies in our laboratory have suggested several possible explanations for the decreased efficacy (and potential failure) of M. hyo vaccines.

Materials and Methods

In two separate studies, the effect of maternal antibodies on vaccine induced serological response was evaluated (3).

In a recent study in our laboratory, pigs were vaccinated with a M. hyo bacterin at 3 and 5 weeks of age with or without PRRSV modified live virus (MLV) vaccine at 4 weeks of age (4). Pigs were challenged with M. hyo and/or PRRSV at 7 weeks of age (2 weeks after the 2nd M. hyo vaccination). Pigs were necropsied at 10 and 38 days following challenge and percentage of pneumonia evaluated.

In subsequent study, pigs were vaccinated with a MLV PRRSV vaccine at 3 weeks of age and vaccinated with a M. hyo bacterin at 4 and 6 weeks of age. At 8 weeks of age, the pigs were challenged with M. hyo. The pigs were necropsied 28 days later and the percentage of pneumonia was assessed.

Results

In studies investigating the effect maternal antibodies had on vaccination efficacy, it was found that the presence of maternal antibodies significantly decreased the antibody response induced by the M. hyo vaccine.

Pigs which received the PRRSV vaccine between the two M. hyo bacterins or were challenged with PRRSV at 7 weeks of age had equivalent percentages of mycoplasmal pneumonia as the non- vaccinated control group. The potentiation of PRRSV was significantly decreased in pigs receiving only M. hyo vaccine. If PRRSV vaccine was administered at 4 weeks of age, the decreased potentiation was eliminated and the PRRSV-induced pneumonia in dual infected pigs was equivalent to the positive control group.

In the study in which PRRSV vaccine was administered prior to M. hyo vaccination, no decrease in M. hyo vaccine efficacy was found.

Discussion

Efficacious vaccines produce long lasting immunity by stimulating production of both B and T lymphocytes. The efficacy and success of a vaccine in controlling infectious disease is dependent on numerous factors including the antigenicity of the vaccine, the age and passive immune and nutritional status of the host, the presence of other diseases and the environment in which the host is housed. The cause of vaccine failure within a herd is often unknown. Unfortunately, our understanding of the porcine immune system, whether humoral, cellular, systemic, local or mucosal is incomplete. Understanding the pathogenesis of the microbe, the immune response required for control and potential factors that interfere with an effective immune response is required to determine the optimal timing and use of a vaccine to avoid vaccine failure.

While immunization with most current M. hyo vaccines induces serum antibodies, there is no correlation between the serum antibody level and the level of protection achieved. In addition, there is minimal efficacy by the M. hyo vaccines against colonization by the M. hyo in the airways of the pig. Induction of serum antibodies by M. hyo vaccines tends to be slow, with seroconversion frequently occurring 2 weeks after the 2nd vaccination. Following that, antibody levels begin to decline in non-challenged pigs, often becoming seronegative 4-6 weeks following vaccination. Vaccinated pigs demonstrate an anamnestic response following challenge or infection with antibody levels becoming much higher compared to pigs receiving vaccination alone. In addition, recent research in our laboratory has ascertained that a M. hyo vaccine induces a local cellular and humoral immune response (5).

The research described here has suggested several possible explanations for the decreased efficacy (and potential failure) of M. hyo vaccines reported in the field. The presence of maternal antibodies appears to decrease the efficacy of the M. hyo vaccine. Thus, the antibody status of the sow herd may need to be assessed to determine optimal timing for M. hyo vaccination. Challenge studies to further investigate the effect of maternal antibodies on M. hyo vaccine efficacy are currently underway in our laboratory.

The interaction between PRRSV and M. hyo is complex. The first study reported here found that vaccination or infection with PRRSV during or closely following vaccination with M. hyo vaccines appeared to decrease the efficacy of the M. hyo vaccine. The mechanism by which PRRSV decreased the efficacy is unknown as M. hyo antibodies were present both systemically and in the epithelial lining fluid of the respiratory tract. In fact, pigs vaccinated with PRRSV vaccine had higher levels of systemic M. hyo antibodies than those receiving only the M. hyo vaccine. However, there was no decrease in the percentage of mycoplasmal pneumonia in pigs vaccinated with M. hyo bacterin when receiving PRRSV vaccine and/or challenge with PRRSV. Interestingly, M. hyo vaccination decreased the potentiation of PRRSV-induced pneumonia in the pigs infected with both pathogens. However that benefit was lost when pigs were vaccinated with PRRSV in addition to the M. hyo vaccine. In the second study, vaccination with PRRSV vaccine prior to M. hyo vaccination did not decrease M. hyo vaccine efficacy. These studies suggest that determination of PRRSV status and timing of seroconversion must be considered when formulating a herd's vaccination regimen.

In conclusion, these studies demonstrate how the interactions between pathogens and the immune system and status of the host can affect vaccine efficacy and should be considered when developing strategies for each herd.

Further Information

For further information on Mycoplasma Hyopneumoniae, PRDC and PRRSV
BROWSE or SEARCH our Pig Health Database

The following feature articles are also available on related topics:

Closed Herd Plan Helps Fight off PRRS

Embryo Transfer Preserves Genetics, Sidesteps PRRS

Managing Swine Respiratory Diseases

Health Management of the Growing Pig

Treating Pneumonia & managing respiratory disease for the long term

Timing Is Critical to Vaccine Effectiveness
References
1. Thacker, EL, Halbur, PG, Ross, RF, Thanawongnuwech, R, Thacker BJ. (1999) Mycoplasma hyopneumoniae potentiation of porcine reproductive and respiratory syndrome virus-induced pneumonia. J Clin Micro, 37:620-627.
2. Thacker, EL, Thacker, BJ, Boettcher, TB, Jayappa, H. (1998) Comparison of antibody production, lymphocyte stimulation and protection induced by four commercial Mycoplasma hyopneumoniae bacterins. SHAP 6:107-112.
3. Thacker , BJ, Boettcher, TB, Anderson, T, Thacker, EL, Young, TF. (1998) The influence of passive immunity on serological responses to Mycoplasma hyopneumoniae vaccination. Proc 15 th IPVS Congres, Birmingham, England, Vol 2, p. 155.
4. Thacker, EL, Thacker, BJ, Young TF, Halbur PG. (2000) Effect of vaccination on the potentiation of porcine reproductive and respiratory syndrome virus (PRRSV)-induced pneumonia by Mycoplasma hyopneumoniae. Vaccine 18:1244-1252.
5. Thacker EL, Thacker, BJ, Kuhn, M, Hawkins, PA, Waters, WR. (2000) Mucosal and systemic characteristics of protective activity of a Mycoplasma hyopneumoniae bacterin. AVJR. In press.

Article first presented at IPVS, 2000, Melbourne. Reproduced with permission