Mycoplasma hyosynoviae is a swine pathogen causing arthritic diseases and severe economic losses. The authors report an outbreak of severe lameness in a pig farm in northern Italy in which approximately 35% of the growing herd showed clinical signs. Lameness was not associated with fever, change in appetite or stiffness in the limbs but was mostly related to swelling of the affected joint. M hyosynoviae was cultured from joints and identified by PCR; tests failed to detect the presence of other infectious causes of arthritic diseases. Antibiotic susceptibility tests were carried out on isolates of M hyosynoviae taken from the tissues in order to guide the choice of antibiotics for treatment. In consultation with the farm’s private veterinary surgeon, this was recommended to be a combination of spectinomycin and lincomycin. However the pigs frequently relapsed indicating the need for longer-term control such as vaccination which should also reduce antibiotic usage.
- joint diseases
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Lameness continues to be a major problem in pigs worldwide. Causes can be congenital, developmental, metabolic or infectious. Among the infectious agents, the most common causes are Haemophilus parasuis, Erysipelothrix rhusiopathiae, Streptococcus suis and some mycoplasmas, in particular, Mycoplasma hyosynoviae in growing pigs and Mycoplasma hyorhinis in nurseries.1 Consequently, rapid diagnosis is essential to enable the implementation of the most appropriate control or preventative measures. There is more awareness of arthritis caused by the fastidious M hyosynoviae today because of improved and more widely used diagnostic methods such as PCR. Like E rhusiopathiae, M hyosynoviae is more often seen in pigs that have been moved to grower/finisher areas. Infection can be exacerbated by many stress factors including mixing, management changes and/or overcrowding. Unlike E rhusiopathiae, however, M hyosynoviae infections do not respond to penicillin and affected pigs usually show low morbidity and mortality although up to 50% of animals may be affected.2 Treatment of the clinical signs of M hyosynoviae infections with antimicrobials can be successful if given early but this rarely eliminates the mycoplasma completely.2 Furthermore it is widely accepted that antimicrobials should not be used to mask poor husbandry or failing management systems but should only be used to complement good management, good nutrition, vaccination, biosecurity and farm hygiene.3
Outbreaks of lameness occurred in a farrow-to-finish pig farm of about 800 sows in an area of high intensity pig production near Treviso in the Veneto region of northern Italy.
Animals were finished about 9 months to achieve a target weight of 170 kgs. Gilts were vaccinated against Actinobacillus pleuropneumoniae, porcine reproductive and respiratory syndrome (PRRS) and swine parvovirus. Pregnant sows were vaccinated against PRRS and atrophic rhinitis. Additionally, primiparous sows were vaccinated against enterotoxic Escherichia coli and lactating sows received a booster dose against swine parvovirus. Growing animals received standard Italian vaccination protocols comprising the Aujeszky’s disease and Mycoplasma hyopneumoniae vaccines. Sporadic cases of lameness had been previously reported in animals of 80 kgs and 100 kgs but these had not been diagnosed in the laboratory.
Lameness was reported in the forelimbs and hindlimbs of approximately 35% of the growing herd mostly around the age of 80–100 days. No fever, change in appetite or signs of stiffness in the limbs was reported. The outbreak was mostly associated with swelling of the affected joint. There was no improvement in disease progression when stocking density in the pens was reduced.
Three swine carcases each weighing around 70 kgs were delivered from the farm to the Peripheral Diagnostic Unit of the Istituto Zooprofilattico Sperimentale delle Venezie,(Pordenone) for gross pathological and histopathological examinations of affected joints.
Pig 1: Examination revealed a fibrinous synovitis of the metacarpal and metatarsal regions. There was also haemorrhage of the coxofemoral joints with hyperaemia of the ligament of the head of femur (figure 1).
Pig 2: The carpal region had a swollen appearance associated with inflammation of the subcutaneous tissues (figure 2). Hyperaemia of the ligament of the head of femur was also evident.
Histopathological findings in the ligament of the head of femur, subcutaneous tissues of the tibia and coxofemoral joint revealed a fibrinous-purulent inflammation associated with haemorrhagic and lymphoplasmacellular infiltration.
Bacteriological investigations were carried out by conventional procedures. Samples were plated on eosin/methylene blue agar and blood agar and incubated in aerobic conditions for 24 hours at 37°C, and on blood agar with Staphylococcus aureus growth and incubated for 24 hours at 37°C in 10% CO2 enhanced atmosphere. Clinical samples included the synovial bursa from forelimbs and rear limbs from pig 1, ligaments from the head of the femur from pigs 1 and 2, joint from forelimb of pig 2 and joints of rear limbs from pig 3.
A specific PCR was carried for the detection of H parasuis,4 an occasional cause of arthritis in pigs.
In addition, the presence of mycoplasmas was specifically investigated by the in vitro culture of nine joint samples (joint fluid from forelimbs and rear limbs) collected from the three different carcases and submitted for mycoplasma isolation according to internal procedures.5 Briefly the samples for mycoplasma detection were placed directly into 2 ml of Mycoplasma Experience (ME) liquid medium (Reigate, UK). The cultures were checked daily in order to detect any change in colour or increased turbidity. Broths that showed any change were immediately inoculated onto a plate containing semisolid ME agar medium; the broths that did not show any change at 7 days, 15 days, 21 days or 28 days were inoculated onto agar medium. If no colonies were seen in these samples after 7 days, then they were considered negative. Detection and identification of any suspect mycoplasmas were carried out by a 16S rDNA PCR DGGE method which was performed using appropriate controls of porcine mycoplasmas.6
In order to evaluate the sensitivity of the mycoplasma isolates to commonly used antibiotics, a microdilution method was carried out to determine their minimum inhibitory concentrations (MIC.).7 8 Commercial MIC plates (Merlin Diagnostika) with a range of antibiotics were incubated aerobically at 37°C±1°C for at least 18 hours and then checked thrice daily to confirm the growth of the positive control well. Two different M hyosynoviae isolates were tested.
No pathogenic bacteria were isolated from any of the examined clinical samples by bacteriological methods and the specific H parasuis PCR was negative on the contents of the synovial bursa.
Mycoplasmas were detected in seven of nine clinical samples taken from the affected pigs and included synovial bursa, ligaments of the heads of the femur, and fore and rear joints. These isolates were all identified by PCR/DGGE as M hyosynoviae (figure 5).
The two M hyosynoviae isolates, selected for MIC determination, were considered sensitive in vitro to most of the selected antimicrobials, comprising tiamulin (≤0.008 µg/ml), lincomycin (≤0.5 µg/ml), spiramycin (≤0.5 µg/ml), fluorofenicol (≤0.5 µg/ml), tylosin (0.25 µg/ml), doxycycline (2 µg/ml), enrofloxacin (2 µg/ml) but not to oxytetracycline (4 µg/ml), tilmicosin (8 µg/ml) and erythromycin (>8 µg/ml). Although no breakpoints have yet been confirmed for animal mycoplasmas it has generally been accepted that MIC of less than 2 µg/ml for a given antibiotic may be effective in vivo.8 Consequently pigs were treated with a course of lincomycin plus spectinomycin on the recommendation of the veterinary surgeon (1 ml/10 kg corresponding to 5 mg/kg lincomycin and 10 mg/kg of spectinomycin every 24 hours for 3 days) which resulted in a temporary clinical recovery of animals. Relapses of disease were observed during the finishing period.
Outcome and follow-up
To date, the health situation in the pig unit is still characterised by sporadic outbreaks of lameness which appears to show a seasonal pattern with increased clinical cases seen during spring and autumn with frequent relapses. Clinical signs are contained with antibiotic treatment as described above but this does not offer a long-term solution. Plans are in place to develop an inactivated autogenous vaccine with isolates derived from the farm.
The authors report here a clinical case of pure M hyosynoviae infection producing widespread and costly disease in the fattening unit of a farrow-to-finish herd. It is highly likely that these outbreaks are under-reported worldwide because diagnosis requires specialist and expensive technology not found in all diagnostic laboratories. In the present case the choice of the best antimicrobials was identified rapidly, based on the MIC results, and veterinary expertise. However, while antibiotic treatment was effective in reducing clinical signs it did not eliminate infection, which continues sporadically to the present day. The most likely source of infection is the upper respiratory tract of sows and older pigs where the mycoplasma persists and resists treatment. Pigs are able to mount an immune response to mycoplasmas which has been shown to be protective in vaccination against enzootic pneumonia caused by M hyopneumoniae. Furthermore Lauritsen and others9 have shown that boosting colostral immunity to M hyosynoviae, which normally wanes after one month to two months, by maternal vaccination, extends protection over the early susceptible period of the piglet’s life. Thus the development of an autogenous vaccine may improve the control of mycoplasma arthritis and help reduce dependence on antibiotic usage for controlling infections.
Contributors MLM drafted the paper and carried out the laboratory work under the direct supervision of SC who led the investigation. MU and DV carried out the clinical and postmortem examinations and interpreted the results. SC and DV provided advice on treatment to the farmer. RAJN edited and completed the final version of the paper.
Competing interests None declared.
Provenance and peer review Not commissioned; externally peer reviewed.
Data sharing statement There are no additional data available for this paper.
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