By Dr. John Baker, Owner and Founder of Warrick Veterinary Clinic, Booneville, Indiana, USA
Mycoplasma hyopneumoniae is a common cause of respiratory disease throughout the world. Its impact in swine production is due to the reduced performance of infected pigs and the potentiation of other respiratory tract pathogens. The severity of clinical signs and resultant economic loss varies between pigs and herds. Introduction of Mycoplasma vaccination in the US in the 1980’s gave excellent control of Mycoplasma hyopneumoniae.
Mycoplasma infection has become a more important component of the Porcine Respiratory Disease Complex (PRDC) as respiratory viral agents such as PRRS virus, Porcine Circovirus type 2 (PCV2), and many recombinations of the Swine Influenza virus (SIV) have become common enzootic infections in the finishing barn.
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INTERACTION WITH PRRS VIRUS
Mycoplasma hyopneumoniae attacks the cells lining the airways of the lung called the mucocillary apparatus. This lining is the pig’s first line of defence against infection of the lung by any airborne pathogen. The organism not only causes the loss of the cells lining the airways, but also the cells that produce the mucus that traps airborne pathogens. These pathogens are then removed as the pig coughs them up and expels them from the lung.
The interactions between viral infections such as PRRS and Mycoplasma hyopneumoniae are many and both pathogens influence each other. In pigs infected with PRRS virus, or indeed other viruses such as PCV2, or SIV, the destruction of the body’s natural defence mechanisms can potentiate Mycoplasma infection and severely test the ability of a vaccine to control this disease.
When a herd is infected with PRRS virus, piglets are initially infected with virus at birth. As individual sows develop immunity to PRRS virus their pigs are no longer infected in the uterus and are negative to the virus at weaning. Since the primary challenge in PRRS control is getting all sows immune to the virus, there is a period at weaning when some litters are infected with PRRS virus while other litters are free of infection.
When these pigs are co-mingled in the nursery, within days the infection spreads to the PRRS free pigs. Many nurseries house pigs for 6 - 8 weeks. Since these buildings are not all in, all out, even when the majority or all of the pigs are weaned free of PRRS virus infection, post-weaning infection from older pigs is common without nursery depopulation. As discussed earlier, one potential problem with Mycoplasma vaccination is a reduced response of the pig’s immune system if the pig is viremic at the time of the Mycoplasma vaccination. For this reason Mycoplasma vaccination must be administered prior to this viremia to be effective during this period.
Research has shown that pigs can effectively be vaccinated as early as one day of age. Although high levels of maternally derived immunity have been shown to interfere with the pig’s ability to respond to Mycoplasma vaccination, highly antigenic vaccines have been shown to effectively overcome maternal interference.
Recent research by Dr Chae has demonstrated that pigs vaccinated with highly antigenic vaccines at seven days of age responded with stronger cellular immunity than pigs vaccinated with the same vaccine or other commercial vaccines at weaning.
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Pigs co-infected with PCV2 and Mycoplasma hyopneumoniae are much more likely to develop Post-weaning Multi-systemic Wasting Syndrome (PMWS) than pigs infected with the PCV2 virus alone. Initial reports indicated that Mycoplasma vaccination could also be a co-factor potentiating PCV2 and causing outbreaks of PMWS. However, clinical experience indicates that the benefits of Mycoplasma vaccination are far more important in reducing the incidence of PMWS in PCV2 and Mycoplasma co-infected pigs than the risk of causing PMWS. It has been shown that Mycoplasma vaccination should be administered prior to PCV2 viremia for the best control of PMWS.
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INTERACTION WITH SIV AND OTHER PATHOGENS
Mycoplasma hyopneumoniae infection of high health pigs in a good environment and under good management is often self-limiting. Pigs infected with Mycoplasma hyopneumoniae alone respond very rapidly to medication with Lincomycin administered by injection or in drinking water or feed. These pigs may have a little residual cough. Although different Mycoplasma hyopneumoniae isolates have been shown to vary in virulence in cell culture, at the farm level, this does not seem to make a difference.
Vaccination still provides acceptable control of respiratory disease. The severity of Mycoplasma hyopneumoniae is determined by the number and pathogenicity of co-infections invading a Mycoplasma infected lungs. As stated above, Mycoplasma hyopneumoniae destroys the mucocilliary apparatus of the respiratory tract. Swine influenza also attacks this vital protective mechanism in the lung. When infected with Swine Influenza, Mycoplasma positive pigs have increased morbidity and higher mortality than pigs free of this disease.
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MYCOPLASMA IN SOWS AND REPLACEMENT GILTS
In the US, several other factors have aggravated Mycoplasma hyopneumoniae problems. US replacement gilts purchased from breeding companies are commonly free of Mycoplasma infection, but most commercial swine farms in the US are Mycoplasma positive. Many of these animals are selected at market weight and added to the breeding herds. The animals are then exposed to and infected with Mycoplasma.
Research has shown that pigs can shed Mycoplasma organisms for up to 254 days. Therefore, these new gilts are still shedding Mycoplasma at farrowing and infecting their piglets. Studies have shown that the level of Mycoplasma infection at weaning strongly correlates to the severity of respiratory disease in the finisher. Herds that have a high culling or mortality rate tend to have more gilt shedding Mycoplasma organims to their pigs.
If pigs are found to have significant levels of Mycoplasma at weaning, an aggressive vaccination program of incoming replacement gilts should be instituted. Vaccination can reduce the level of infection that occurs as new gilts introduced into Mycoplasma positive breeding herds. This will reduce the duration of shedding that occurs from these gilts to their first litter. Another concern is that the addition of susceptible replacement animals to the breeding herd can result in destabilising the breeding herd.
This event is often identified by the development of varying levels of a dry non-productive cough in the sows. The sows may go on and off feed. If this has occurred, blanket vaccination of the breeding herd should be conducted at three month intervals until the cough is no longer heard. With effective replacement gilt vaccination this sow protocol will not need to be continued in most herds.
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HERD LEVEL ERADICATION OF MYCOPLASMA
Eradication the Mycoplasma hyopneumoniae from a herd, region or country would be the method of choice to control this disease. This was originally accomplished by delivering pigs by caesarian section into the sterile environment of a bubble attached to the surgical site. Pigs only breathed filtered air until they were removed from contact with the infected sow.
Pigs were then raised free from exposure to the organism in new, sanitised production facilities. Caesarian derived pigs that were raised and monitored in this program were called primary specific pathogen free (SPF) pigs. The progeny of these herds were then used to populate new or sanitised farms and were monitored in a similar fashion. The program was successful in creating populations of pigs free of clinical signs of Mycoplasma hyopneumoniae.
Segregated and Medicated Early Weaning (SEW and MEW) protocols were developed by Dr Hank Harris and others to eliminate the Mycoplasma hyopneumoniae organism from pig populations. The SEW protocol involved removing pigs from sows at six days of age and raising them in separate and sanitized farms. As part of the MEW protocol, sows were treated with antibiotics prior to farrowing to reduce or eliminate shedding of the organism to their pigs. This protocol allowed pigs to be weaned at older ages when they were easier to manage. Both protocols were successful in creating Mycoplasma hyopneumoniae free populations, as determined by the lack of clinical signs and the diagnostic testing available at that time.
In recent years other protocols have been developed to eliminate Mycoplasma hyopneumoniae from sow herds using combinations of herds’ closure and intensive, medication with antibacterials, including long acting injectables active against Mycoplasma hyopneumoniae such as Draxxin. These have also been successful.
With all these approaches, however, airborne spread of the Mycoplasma hyopneumoniae organism and other bio-security failures often resulted in reinfection of the pig populations and the reoccurrence of clinical signs of Mycoplasma hyopneumoniae, so the challenge has been keeping these farms from being re-infected. When the Mycoplasma hyopneumoniae organism is re-introduced into these naïve populations the resulting clinical disease and production loss has been severe.
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THE ROLE OF MYCOPLASMA VACCINATION
Commercial Mycoplasma vaccination was introduced in the US in the 1980’s. Vaccination was easy to implement and was highly effective at reducing the clinical signs and production losses associated with this disease. This resulted in a dramatic reduction in the amount of antibiotics used to control respiratory disease in grow finish pigs. Mycoplasma vaccination has been shown to reduce the clinical signs of respiratory disease caused by Mycoplasma. It also was shown to reduce gross and histological damage to the lung, while improving average daily gain and feed efficiency.
The significant expense of eradication programs and their common failure with reintroduction of the agent resulted in rapid acceptance and implementation of the new Mycoplasma vaccines. The common swine farm at that time in the US was a one site, continuous flow, farrow to finish farm. The replacement breeding animals were exposed to the Mycoplasma organism during their finishing phase or by airborne spread around the operation.
This meant that they entered the breeding herd with immunity to Mycoplasma. The initial commercial vaccine was a two dose product given to all pigs at 5 - 14 days in conjunction with processing and castration. It was boosted at least two weeks later usually at weaning at 4 - 6 weeks of age.
With changing production practices in the US, weaning ages were reduced to 13 - 16 days of age. This no longer allowed pigs to be vaccinated with two doses of vaccine at least two weeks apart prior to weaning. When the two vaccinations were given within 12 days of each other the efficacy was greatly reduced or eliminated. Therefore, Mycoplasma vaccination was moved to weaning and a booster given 2 - 3 weeks later.
The vaccine was still effective in controlling the clinical signs of Mycoplasma infection. However, the addition of vaccinating pigs after weaning was very unpopular. Compliance with the timing of the second vaccination or early exposure to Mycoplasma from the finisher resulted in breaks of Mycoplasmahyopneumoniae in finishing pig. This led to the development of one dose Mycoplasma vaccines. Acceptance was rapid and vaccination became commonly practiced at weaning. Control of Mycoplasma hyopneumoniae was still very good in most farms.
As stated, Mycoplasma vaccination cannot prevent the Mycoplasma organism from infecting the pig. Therefore, factors that damage the airways or reduce the natural resistance of the pig can reduce the performance of the Mycoplasma vaccine in controlling the damage caused by the infection. Over-crowding of pigs in pens increases the level of Mycoplasma exposure and reduces the pigs’ resistance to infection by increasing stress.
In a study conducted by Alex Hogg, Mycoplasma vaccinated pigs placed with unvaccinated pigs had a 6.82 lb (3.09 kg) improvement in slaughter weight gain. Similarly, groups of pigs that were vaccinated withMycoplasmavaccine and housed together without exposure to non-vaccinated pigs had a 20 lb (9.07 kg) slaughter weight gain over the control group.
This study demonstrates that as the overall challenge of Mycoplasma is reduced, vaccination response is increased. To fully realise the benefit of Mycoplasma vaccination, good management of the pigs and their environment is critical.
It must be understood that although vaccination will help control Mycoplasma hyopneumoniae in all situations, co-infections and co-factors, if left unaddressed, can result in unacceptable levels clinical respiratory disease and dissatisfaction with vaccination.
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Mycoplasma hyopneumoniae cannot be ignored. Vaccination provides immediate improvement in control of this costly disease. Correcting problems in environment and management that exacerbate Mycoplasma hyopneumoniae will increase the level of control provided by Mycoplasma vaccination. Working with your veterinarian to understand the health status of your herd will allow additional control programs to be created that will help reduce the compounding effects co-infections have on Mycoplasma hyopneumoniae. Understanding the PRRS status of your herd will also help position Mycoplasma vaccination for maximum benefit.
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- Incoming breeding stock is protected with Mycoplasma vaccination reducing shedding to their piglets.
- Breeding herds are stabilised for Mycoplasma infection to minimise shedding to piglets.
- Pigs are vaccinated at a young age, preferably within the first seven days of life to maximise protection against the development of clinical disease from Mycoplasma.
- Pigs are vaccinated prior to becoming viremic to PRRS virus.
- If exposure to Mycoplasma is early, it is minimised with the inclusion of an antibiotic such as Lincomycin in the feed to control the infection, until adequate immunity is allowed to develop.
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This article appeared in Asian Pork, October 2012.©Copyright 2012, All Rights Reserved.