Scientific Papers

Streptococcus equi subspecies zooepidemicus – a case report of sudden death in a German sow farm | Porcine Health Management


Farm description

The farrow-to-finishing farm in the North-Western part of Germany close to the Dutch border kept 320 sows in ten groups. It performed all-in-all-out in the farrowing, weaning and fattening stages, with two-week farrowing intervals and a suckling period of 21 days. In total the farm had six farrowing units and two gestating units – a larger for 100–130 sows, the other for 50–70 sows. The smaller unit was located in a separate building together with the breeding centre. Both compartments shared one ventilation-system, while the large gestating unit and the six farrowing units were all equipped with separate ventilation systems. All sows received a commercial diet and water ad libitum from a farm-owned well.

Sows were vaccinated routinely against influenza A Virus H3N2, H1N1 and H1N2 every four months. Vaccination against the Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) was performed in every reproduction cycle of a sow group on day 6 after farrowing and on day 60 of gestation (6/60 scheme) using a PRRSV-1 modified-live vaccine. Sows were vaccinated against porcine parvovirus and Erysipelothrix rhusiopathiae in the second week of lactation. Piglets were regularly vaccinated against Porcine Circovirus type 2 (PCV2), Mycoplasma hyopneumoniae and a PRRSV-1 modified-live vaccine within the first three weeks of life.

Gilts were purchased from a gilt rearing farm 50 km away from the case farm. The gilt rearing farm was under the care of the same veterinarian and had a high health status. Negative results for Actinobacillus (A.) pleuropneumoniae and PRRSV were recorded continuously during routine monitoring. Gilts were introduced to the herd after a six weeks quarantine period in a separate building with outdoor access between a horse holding site and the sow farm. The horse holding site with three horses was about 100 m away from the sow units.

Case history

The farmer reported fever, lethargy and lack of appetite in his sow herd. Within one day two sudden deaths in gestating sows and one abortion occurred in different compartments of the farm.

Blood samples were taken by the veterinarian from twenty sows showing fever and lethargy. Sows were tested negative for PRRSV and PCV2 by PCR in a routine diagnostic laboratory. Sows were positive for antibodies against influenza A virus in a haemagglutination inhibition assay (HIA), which was difficult to interpret because all sows had been vaccinated. Nasal swabs from suckling piglets and ten diseased sows were tested negative for influenza A virus by PCR. All sows were treated orally with metamizole (Metapyrin® oral 100%, Serumwerk Bernburg, Bernburg, Germany) for five days (50 mg metamizole per kg body weight) and all sows except those in the large gestating unit recovered. In the large gestating unit four sows died in day 102 to 114 of gestation four days after the first clinical signs had been recognized on the farm. Individual sows in this location showed dyspnoea, mucous nasal discharge and oedema of the ears, conjunctiva and nasal bridge. Sows were treated orally with doxycycline (Pulmodox®, Virbac, Bad Oldesloe, Germany) in a dosage of 40 mg/kg body weight for five days. Eight days after the first clinical signs had occurred, one sow died and several sows still showed signs of severe disease. The dead sow (sow 454) and one living sow showing signs of severe disease (sow 455) were brought to the Field Station for Epidemiology, Bakum, Germany, for necropsy and subsequent diagnostic measures. The stable climate was checked by a technician and drinking water pipes were sampled at five different locations for bacteriological examination resulting in detection of Staphylococcus spp. and yeasts. Six months before, drinking water quality had been checked by standard routine diagnostic procedures resulting in no abnormalities with respect to chemical and microbiological parameters. The inside surfaces of feed silos were checked for dirt and mould, without positive results.

No signs of disease occurred in suckling or nursery piglets, although they were located at the same site as the sows. Fattening pigs were kept 300 m away from the sow site and stayed also healthy. Slaughterhouse data remained constant during the course of the year. On average mild enzootic-pneumonia-like lung lesions in the cranial lobes in 20% of the pigs and mild pleuritis and pericarditis in 5% of the pigs were recorded.

Pathological findings

Post-mortem examination of the dead sow (454) resulted in a severe fibrinous and purulent polyserositis (pleurisy, pericarditis and peritonitis) with a diffuse, fibrinous to serosanguinous exudate in the body cavities and thickening of the serosa (Figs. 1, 2 and 3). Spleen and tracheobronchial lymph nodes were hyperplastic. The lung showed a severe, diffuse haemorrhagic congestion. Trachea and nasal cavities were filled with mucous exudate. Signs of inflammation (radiate, black stripes) were detected in the kidney cortex.

Fig. 1
figure 1

Fibrinous exudate on pleura and pericardium

Fig. 2
figure 2

Hyperaemia of the lung and pleuritis

Fig. 3
figure 3

Massive fibrinous exudate in the peritoneal cavity

Sow 455 was euthanized and showed a severe oedema of the ears, a severe congestion of the spleen (Fig. 4) and a severe purulent sinusitis.

Fig. 4
figure 4

Massive spleen hyperplasia

Haematological findings

An analysis of a blood sample from sow 455 resulted in leucocytosis with relative neutrophilia with an increase of juvenile neutrophils, relative lymphopenia and absolute erythropenia (Table 1) pointing to a bacterial infection.

Table 1 Blood cell counts

Histological findings

In sow 454 a subacute to acute, moderate to severe, fibrinous pleuropneumonia and pericarditis with pleural and broncho-alveolar exudate consisting of segmented neutrophils, macrophages and fibrin was diagnosed histologically. The pleural, interlobular and peribronchial lymphatic vessels were filled with oedema fluid, neutrophils, macrophages and coccoid bacteria. A severe alveolar and interstitial oedema and a marked hyperaemia of the lung tissue were recorded. The tracheobronchial lymph node was affected by a severe fibrinous-purulent inflammation. A diffuse, proliferative glomerulonephritis was diagnosed as well as a fibrinous serositis on the liver, spleen and uterus serosa surface characterized by neutrophils, fibrin and coccoid bacteria. In the gastric wall coccoid bacteria accompanied by fibrinous clots were found in the lymphatic vessels.

In sow 455 hyperaemia and accumulation of neutrophils in lung and spleen tissue, a glomerulonephritis and an acute, purulent hepatitis were recorded. In ear tissue samples a fibrinous-purulent lymphangitis with oedema fluid, fibrin, neutrophils and focal coccoid bacteria in lymphatic vessels and a perivascular dermatitis were diagnosed.

Microbiological findings

Microbiological examinations followed the routine standard cultivation protocols in the accredited labs of the Field Station for Epidemiology in Bakum. Selected bacterial colonies were further analysed with an analytical profile index test kit (api 20 Strep ®, Merial, Lyon, France). The api-code 4,463,607 identified S. zooepidemicus with an accuracy of 99.9%.

S. zooepidemicus was isolated in high yields from sow 454 (> 20 colony forming units (CFU) in a direct cultivation step) from nasal, bronchial, pericardial, thoracal cavity and urinary bladder swabs as well as from lung, spleen and kidney. S. zooepidemicus was isolated in low yields (< 10 CFU in a direct cultivation step) from a meningeal swab. The identification of the species was confirmed by MALDI-TOF MS (Matrix-assisted laser desorption time-of-flight) in an external veterinary diagnostic laboratory. The nasal swab and samples from the meningeal swab of sow 455 were also positive for S. zooepidemicus. No bacterial pathogens could be isolated from spleen, liver, kidney, lung and thoracal cavity swab of this animal.

A. pleuropneumoniae, Mycoplasma hyopneumoniae, influenza A virus and PRRSV-EU/-US were not detected by PCR in lung tissue of both animals. Testing for classical swine fever virus, african swine fever virus and porcine herpesvirus 1 by PCR performed in an authorized lab generated also negative results.

Bacteriological culturing of the various organ tissues followed standard procedures for clinical veterinary microbiology [19, 20]. Tissue samples and swabs were plated on four culture plates, as chocolate blood agar containing nicotinamide adenine dinucleotide (NAD, Blood Agar No. 2, Becton, Dickinson and company, Sparks, USA) for culture of Pasteurellaceae (e.g. Glaesserella parasuis) and Alcaligenaceae (e.g. Bordetella bronchiseptica), Columbia agar with 5% sheep blood (Becton, Dickinson and company, Sparks, USA), Gassner agar (OXOID, Hampshire, United Kingdom) and CNA blood agar (Becton, Dickinson and company, Sparks, USA) containing polymyxin E and nalidixinic acid for selective culture of Staphylococcus spp. and Streptococcus spp [21, 22]. Inoculated plates were incubated for 48 h at 37 °C under standard atmospheric conditions, while chocolate blood agar was incubated in an 8% CO2 atmosphere. Plates were inspected after 24 and 48 h. For further typing by their cultural and biochemical properties single bacterial colonies were subcultivated. Colonies resembling A. pleuropneumoniae were subcultivated on chocolate blood agar and tested biochemically for urease, catalase and the CAMP phenomena following routine diagnostic protocols [19].

Antimicrobial susceptibility testing of S. zooepidemicus in a microtiter plate assay followed routine diagnostic methods. Interpretation of growth inhibition followed the clinical breakpoints approved by the Clinical and Laboratory Standard Institute [23] and recommended for laboratories in veterinary medicine [24] (Table 2).

Table 2 Antibiotic sensitivity test of the isolated S. zooepidemicus by MIC (minimal inhibition concentration). S = sensitive, R = resistant

Geno- and phenotyping of the S. zooepidemicus isolate

Sequence type (ST) analysis, based on seven highly conserved housekeeping genes (arc, nrdE, proS, spi, tdk, tpi and yqiL) [25], revealed a new sequence type of the S. zooepidemicus isolate 21/455, namely 524 [26] (https://pubmlst.org/bigsdb?page=profileInfodb=pubmlst_szooepidemicus_seqdefscheme_id=1profile_id=524; access 20.06.2023). ST524 is a single locus variant to ST65.

At first, the isolate 21/455 showed a shiny, smooth colony phenotype typical for encapsulated strains. This phenotype was, however, lost during further passaging and reappeared after culturing in the presence of porcine serum. We investigated survival of S. zooepidemicus strain 21/455 in comparison to two other invasive S. zooepidemicus strains [16] in blood of weaning piglets (age: 8 weeks, n = 6) of a herd not affected by this pathogen. The isolate of this outbreak is characterized by a significantly higher proliferation rate in comparison to the other two S. zooepidemicus strains (Fig. 5).

Fig. 5
figure 5

Proliferation of S. zooepidemicus 21/455 isolated from a sow of the outbreak described in this case report in comparison to two other S. zooepidemicus strains (C2 and C33) characterized in a previous study [16]

Climate check

A climate check by an agrarian climate expert was focussed onto air flow and ventilation rates in the areas for gestating sows. Approximately 110 sows were kept in groups in one compartment of 10 m width and 26 m length. Three individual exhaust fans at the ceiling with a total power of 12 600 m3/h were equipped with gravity valves. The required total summer air exchange rate was calculated by 145 m3/h and sow, in total 16 000 m3/h and compartment. Temperature sensors were not optimally located at varying positions within the different compartments and ventilation rates were automatically adjusted due to target temperature.

Case outcome

The final diagnosis based on histopathological and microbiological findings was septicaemia caused by S. zooepidemicus. Two weeks after the onset of disease in the farm the veterinarian treated all sows intramusculary with 2 mg cefquinome (Cobactan®, MSD Animal Health GmbH, Haar, Germany) per kg body weight on three consecutive days.

No further sows developed fever and sows were no longer apathic. Mild oedemas at the head were still visible in individual sows. In summary, ten sows in late gestation phase died within 4 weeks.

Four weeks after first blood sampling sows were sampled again for paired testing of serum samples in the HIA for influenza A virus antibodies. Antibody titers had decreased, so that an infection with influenza A virus as the causative agent was considered to be unlikely.

Finally, in the short term the change in the antimicrobial treatment with respect to substance and route of administration led to termination of the disease. Neither in this farm nor in other farms in the responsibility of the veterinarian in charge of the stock S. zooepidemicus related disease has recurred so far. In the long term in our opinion an important measure on the case farm was a modification of the climate system in the large gestation unit, where the sows had been affected. Additional air supply ducts and air exhaust shafts with larger diameters were installed to increase the air exchange volume while maintaining the same air velocity.

The horse holding site was not modified, although the risk of inter-species transmission was discussed with the farmer.



Source link