Single or double vaccination for Mycoplasma hyopneumonia control

Presented by Dr Pieter Grimbeek, a pig veterinarian at the PIC information day 2005 on behalf of Schering-Plough

The disease, Mycoplasma pneumoniae, probably needs little introduction to most producers, but for the sake of thoroughness the following aspects of the organism and disease profile could be accentuated.

• It is a contagious, widespread pulmonary disease of pigs characterised clinically by coughing, unthriftiness and very low mortality.

• One of the most common and economically important diseases.

• It forms complex interactions between other infections and seems to exarcebate and accentuate poor management and environment.

• Worldwide significance, most herds are infected.

• M. hyo the disease causes:

• Reduced ADG
• Reduced FE
• Increased medication costs and
• Increased variance

•  What sort of economic losses are experienced – decreased growth rate of up to 13% with similar results for feed efficiency are documented.  Lets take a normal South African piggery as an example. (See Table 1)

•  In monetary terms, with the pork price at R 10/kg and the feed price @ R 1500 /ton the loss in income experienced is about R 50 per pig.

• Economic effects are extremely variable between herds and are dependent on the costs of input, the price of pork, etc.  IT IS A MOVING TARGET.

• Growth inhibition studies on solid media have suggested antigenic differences between strains and isolates of M. hyo and the existence of different strains has been confirmed.

What factors affect the occurrence of the disease?

• Housing

• Continuous flow

• Variable temperatures

• Inconsistent feed and water supply

• Overstocking

• Dust

• Co-mingling

• Sow parity

 Some other facts:

• Mycoplasma are immunosuppressive

• It takes up to 4 weeks for lesions to develop.  Pigs are infected at about weaning time.

• It takes 10 to 14 weeks for lesions to heal, as the pigs own immunity / resistance develops

• The immunosuppresion affords other invaders such as APP, Haemophulus parasuis and Pasteurella the opportunity to gain easier access, leading to overwhelming infections, a real respiratory soup.

Control

•  In the past, improvements in husbandry and environment.

• The use of antimicrobials (with limitations)

If you medicate to early to prevent the infections in late weaner or early grower stage, breakdowns could occur in the finishing stage.

Depending on the drug used, protection only occurred for short periods and mycoplasmas were not completely eliminated and the pigs often deprived of developing an immunity.

This lead to the development of pulse medication or strategic medication programs to prolong the efficacy of the antibiotic used and or to target stress periods when the disease was likely to flare.

Many antibiotics are only effective for mycoplasma and not for secondary bacterial infections resulting in a variety of combinations being used where respiratory complexes are a problem.

Smaller producers pose a problem in that their grower facilities host multiaged pigs resulting in continual and over use of medication.

In the nineties, numerous mycoplasma vaccines were introduced to the market.  They were marketed as double dose vaccines and were effectively administered as a primer dose at 10 days of age and a booster dose at weaning, usually 2 to 3 weeks later.

The advent of vaccines afforded us an opportunity to relook at the disease mycoplasma and resulted in an improved understanding of the disease and its affect on swine economics.

• We know that it is generally accepted that the size of the lung lesions caused by Mycoplasma hyopneumoniae has a strong correlation with the amplitude of deleterious effect.

• Vaccines aim to reduce the level of lesions and thereby improve performance.  None of the vaccines prevent enzootic pneumonia 100% but generally they are effective in reducing lung lesions and permit the pigs to perform better.

 How do the vaccines work?

 The vaccines work at cellular level in lung tissue via a complex system of antibodies, enzyme inhibition and waterfall cascade effects.  There are cell mediated and circulating antibody responses.

Let me explain some interesting trials

Gnotobiotic pig trial:

We know that disease caused pathology, and that in the traumatic process caused by cellular necrosis certain enzymes and chemicals are released into the body or body fluids.

Disease free pigs were experimentally inoculated with an infective dose of M. hyo organisms and compared to an untreated, control group.  M. hyo caused the release of enzymes, chemicals and cellular debris, which were harvested by tracheal lavage and measured.  Similarly a group of pigs were then double vaccinated, experimentally infected with M. hyo, tracheally lavaged after six weeks and statistically significant reductions in clinical pathology was noted.  This proved that the vaccine had the ability to protect the animals against an artificial infection.

Since then numerous trials have been done on minimum immunogenicity dose, duration of immunity and field efficacy.  Coupled to this viscosity and injection force methods were studied.

The vaccine is effective

Field efficacy trials concentrated on:

• The reduction of lung lesion scores.

• Clinical disease.

• Body weight gain.

• Feed efficiencies.

How are farms assessed as candidates for vaccine usage?

Apart from clinical symptoms, production figures and mortality rates, abattoir surveys are probably the best way in determining the status of the disease.

Lungs are collected and examined from the abattoir line and using the Goodwin score, the level of M. hyo lesions are scored. 

A score out of 55 determines the seriousness of infection, and the age of the pigs is also taken into consideration.  The morbidity of the infection or percentage of pigs affected also plays a role.  If 20% of all pigs have lesions, and the lesion score is higher than 5/55, that farm is a candidate for vaccination.

As with all things there is an economic benefit that needs to be justified for the expense and in March of 2005 with the present cost of vaccine, price of pork, and feed prices, about 8 grams of growth per day in the grower period (30 kg – 90 kg) is needed to justify the vaccine expense.

The vaccine

We heard earlier that pigs are vaccinated twice, the primer and the booster.  The double dose had been marketed for about 5 years when an alternative product, a single dose product was offered.  The concept was in essence an American thing.

The single shot was administered to pigs that were 4 to 10 weeks old.  The volume of antigen was larger than the single dose regime and manufactures prided themselves on the solvents and diluants used in the vaccine to enhance the immune response.

These vaccines were used in South Africa with, on most farms, good results.  Then certain farms started having breakdowns, and had to revert to double dose vaccine again, but they never reached the complete effect achieved during the initial period of use.

Why would the vaccine fail?

Recommendations for use of the single dose are as follows:

• Use in relatively stable herds with low infection pressure from say PRRS and SIV

• Herds that practice all-in-all-out

• Vaccinate at the end of the weaner period

• Ensure high compliance to vaccination

In South Africa the PMWS epidemic started to play an important role in vaccination failure.  Producers were vaccinating piglets at 4 to 6 weeks of age and the immune response was inhibited by PCV-2 virus.

Another interesting reason is that some South African producers started weaning earlier, and because it is easy to vaccinate at weaning, pigs were injected at a time that maternally derived antibodies (MDA) were high.  This negated the effect of the vaccine.

MDA’s are the joker in the pack.  The sow herd is the asymptomatic carrier mechanism for M. hyo.  It has been suggested that younger sows excrete more M. hyo organisms than older sows, but recent work by Pijoan and Ruiz (Pigletter 2002) refutes this statement.

In a large production unit the dynamics of sow excretion, sow immunity, high and low levels of piglet immunity, age of weaning, prevalence of other disease, environmental deficiencies and other factors all influence the outcome and / or severity of the disease.

The vaccination of sows, as a practice, is frowned upon in continual flow units, purely because of the unpredictability of the results.  Just because a sow is vaccinated does not mean the M. hyo excretion is eliminated / reduced.  The high levels of MDA’s then also reduce the efficacy of the vaccine.

• M. hyo is a disease of growing pigs, not sows.

• M. hyo spreads laterally among grower pigs and vertical transmission reduction from vaccinated sows is not a given.

• The half-life of MDA’s is about 15 days

Once the piglet has absorbed the antibodies from the colostrum then the levels start to fall, and the half-life is about 15 days.  So a piglet with high initial antibody levels could still have significant levels, 60 days later, but one with low levels, be clean by 30 days of age, usually when the second double dose, or the only single dose is administered.  Hodgins and others looked at these responses in a Canadian trial.  They concluded that high MDA’s do not prevent challenge later in life, so sow vaccination can be considered to negatively impact on the protection of the piglet.

The following guidelines can be followed (see table 2).

• There is no real correct guideline for use.  Most herds are in a continual state of flux as far as herd composition and management systems are concerned.

• Regular monitoring, on farm assessments, abattoir surveys and results will accentuate the choice and future timing for which best program to follow.

I would like to thank Schering Plough for their support. Their product M-Pac® is one of the few products that still affords the producer the option to choose between single or double dose regimes.

References

1. Hawkins, P.A. (2001) In house training brochure, Pfizer.

2. Hodgins, D.C., Shewen, P.E. and Dewey, C.E. (2002)  Influence of age and maternal antibodies on antibody responses of neonatal piglets to Mycoplasma hyopneumoniae.  Proceedings of the International Pig Veterinary Society, Ames, Iowa, USA, 1, 255.

3. Miller, D.J.S. and Stipkovits, L. (1991)  Recent advances in the control of enzootic pneumonia in pigs.  Proceedings of the World Veterinary Congress, Rio de Janeiro, Brazil.

4. Yeske, P. (2001)  Experiences with mycoplasa vaccinations: what to do if vaccination doesn’t live up to expectations.  Proceedings of the Allen D. Leman Conference University of Minnesota, USA, pp 108 – 110.