Clinical case: Sudden increase in stillborn piglets and suckling pigs mortality

History

The owner of the herd reported an obvious increase in the suckling pigs mortality in the previous and recent farrowing batches. Apart from the previous farrowing batch the recent batch was also showing an increased number of stillborn piglets.

The production characteristics of the herd in Germany are:

• Number of sows: 250
• Number of weaned pigs per sow and year: 26.4 (suckling period: 24 days)
• Piglet producer, selling growing pigs at 10 weeks of age
• Sows and nursery pigs are housed in separate buildings in the same location
• Batch farrowing system (two-weeks interval)
• Farrowing and nursery units: all-in-all-out policy; the insemination centre and the units for the pregnant sows are re-stocked continuously.
• Replacement of gilts always with animals from the same multiplier; delivery of 25 gilts four times a year
• Gilt acclimatization in a separate building for eight weeks with a ten-day period of nose-to-nose contact with cull sows that will be slaughtered soon.
• Feed: two different standard feed compositions (lactating, non-lactating sows) from a large commercial supplier.
• Standard sow/gilt vaccination scheme during the last five years:
  • Vaccination of the entire sow herd against
    • Parvovirus and Erysipelas (killed vaccine) in month 4, 8, 12
    • Influenza (killed vaccine against subtypes H1N1, H1N2, H3N2) in month 3, 7, 11
    • PRRS (attenuated vaccine) in month 2, 6, 10
  • Gilts vaccinated during acclimatization period (8 weeks) against
    • Parvovirus and Erysipelas (killed vaccine) in week 2 and 6
    • Influenza (killed vaccine against subtypes H1N1, H1N2, H3N2) in week 3 and 7
    • PRRS (attenuated vaccine) in week 1
  • Pregnant sows are vaccinated against
    • E. coli (killed vaccine) 3 weeks before farrowing
  • Pregnant first litter sows are vaccinated against
    • E. coli (killed vaccine) 6 and 3 weeks before farrowing

Clinical signs and reproductive data

The sow herd was examined when all the sows of the current batch had farrowed. At that time the suckling pigs were between 2 and 6 days old. In this farrowing batch 3 out of 24 sows showed a purulent vaginal discharge and had already been treated with antimicrobials and analgesics because they had also shown fever (> 40.5°C) and their feed intake had been significantly reduced. The other sows in the farrowing unit and the rest of the sow herd showed no signs of disease. The farmer also reported not having noticed any symptoms during the previous weeks.

The litter size of the recent and the last farrowing batches was significantly reduced and the suckling pigs showed an obvious varying weight, condition and viability. Some litters of the recent batch were affected by diarrhoea (yellowish, watery faeces) which is usually not a problem in this herd. The evaluation of the reproductive data of the previous and recent farrowing batches revealed the following results:

* Mortality until the examination date, ** until weaning

The duration of the pregnancy was 114.8 days on average, with two abortions (at 45 and 60 days of pregnancy) during the last 2 months.

Laboratory diagnoses – first approach

In a first diagnostic approach cervical swabs from 2 of the 3 sows with purulent vaginal discharge, rectal swabs from 3 suckling pigs with diarrhoea, and blood samples from 8 sows with affected litters were collected.

E. coli was isolated from the cervical swabs with standard culture methods. E. coli was also found in the rectal swabs taken from the suckling pigs.

The blood samples (serum) were tested for various antibodies and by real time PCR for PRRSV and PCV2 genome fragments:

The interpretation of the diagnostic results revealed no evidences facilitating a proper diagnosis according to the clinical symptoms. Diseases like E. coli caused diarrhoea, as well as the Postpartum Dysgalactia Syndrome, which were seen only in some of the affected litters, and this can lead to an increased suckling pig mortality but does not explain the increased rate of stillborn pigs.

The detection of antibodies against PRRSV, SIV and Parvovirus was not to be interpreted, since the sow herd was regularly vaccinated against these agents. It is well-known that the vaccinations against these agents can cause the production of high levels of antibodies. Therefore, it remains something highly speculative whether the antibodies against PRRSV, SIV and Parvovirus had been induced by the vaccination or by a recent infection that could have caused the apparent disease.

Laboratory diagnoses – second approach

The herd veterinarian was not able to confirm a diagnosis on the basis of the clinical and laboratory findings. As the following batch of sows that had farrowed in the meantime was also affected by the same problem with an increase in the severity of the symptoms, he discussed the case with a colleague from the University. After this discussion it was concluded that the clinical signs were most indicative for PRRS while the other infections would be less likely. An impact of the SIV on the number of stillborn piglets and the suckling pig mortality is likely, since the sows had expressed the typical clinical signs, particularly fever. In the case of Parvovirus infections not only still- and weak-born piglets are seen, but also mummies of different sizes. Leptospira infections can possibly cause abortions, but a disease restricted to the symptoms that have been mentioned is not likely (as well as PCV2) as the cause of a herd problem.

The decision to put PRRS on the top of the list is based on the knowledge that a sudden and distinct increase in stillborn piglets and suckling pig mortality is highly indicative of a classical PRRS outbreak, while late-term abortions are not necessarily seen in every herd. Classical PRRS outbreaks are not only known to occur in naive herds, but can also sporadically occur in regularly vaccinated sow herds. Moreover, it is known that the duration of the viraemia in adult pigs (sows) is not as long as it is in younger pigs. In sows with a partial immunity viraemia could last only very few days, leading to a very limited chance to detect PRRSV by PCR in serum collected from these sows. Therefore, it is highly recommended to collect samples from newborn suckling pigs of up to 5 days of age for the diagnosis of the reproductive form of the PRRS. Since it is well known that the intrauterine PRRSV infection leads to a viraemia that lasts for several weeks in piglets, the blood serum from these animals is the material of choice. Taking into account that not all the piglets of the entire litter are necessarily infected with PRRSV, it is essential to take an adequate amount of samples. Consequently, the following diagnostic approach comprises blood samples from newborn suckling pigs. The sample size was comprised by blood sera collected from 18 piglets from 6 litters (3 piglets/litter). The sera of the piglets from a same litter were pooled to constitute a sample and these samples were tested by real time (RT) PCR:

* The isolate was identified by sequencing as EU wild type virus (86% identity with Lelystad virus)

Diagnosis

The clinical symptoms and the recent PCR results confirmed the diagnosis: “acute PRRS outbreak”.