Cristian Salogni et al. Infectious agents identified in aborted swine foetuses in a high-density breeding area: a three-year study. Journal of Veterinary Diagnostic Investigation, 28 (5), pp. 550-554
What are they studying?
The present study determined the presence of pathogens capable of causing abortions in a large number of aborted foetuses that were submitted from breeding herds in a high-density region in northern Italy.
How was it done?
The study examined 1,625 foetuses from 549 sows which were submitted to a Diagnostic lab in Northern Italy over a period of 3 years (2011 to 2013) for the investigation of reproductive failures in 140 conventional farms. All foetuses were tested for the presence of PCV2 and PRRSv by rtPCR, for PRV, PPV, PEVs, CSFV, and EMCV by virus isolation, and for presence of antibodies against PRV and PPV by competitive ELISA. Bacteria were isolated and identified from brain, lung, and liver tissues from all sampled foetuses in cultures on solid agar plates. Leptospira spp. were not surveyed because of extreme difficulty in achieving a reliable identification.
What are the results?
Samples from autumn (28.2 %) and winter (35.5 %) months were overrepresented in this survey without an association to any of the detected pathogens. Most samples (71 %) were derived from abortions which occurred during the second half of gestation. At least one aetiologic agent was detected in 323 out of the 549 investigated cases (58.8 %.) In 30 % of these cases, more than one pathogen was detected. The agents most often identified in the 323 positive cases were PCV2 and PRRSv: PCV2 138, PRRSv 108, E. coli 64, Strep sp. 63, PPV 20, PRV 6, Staphylococcus sp. 5, EMCV 3, Pasteurella sp. 3, Shigella sp. 1, and Yersinia sp. 1 time. CSFv and PEV were not detected.
What implications does this paper have?
Many infections are mixed infections, but they are restricted to a small number of pathogens. The fact that both PRRSv and PCV2 were found most commonly suggests that these two pathogens are widespread in these farms. Their presence may indicate either a poor control (PRRS) or an underestimation of their impact in the breeding herd (PCV2). Vaccination against PCV2 is rarely carried out in breeding herds in this region. Conversely, the low frequency of detection of both PPV and PRV is probably related to widespread and effective vaccination. The authors insist on the importance of a consistent collection and sampling protocol to ensure valuable data are available in cases of abortion and to investigate reproductive failure. Most of the submitted cases occurred during the second half of gestation. This might be related to the fact that foetuses which die during the first and second trimester of gestation are reabsorbed or small and therefore not visible or accessible for testing. Finally, health surveillance as described in this paper is useful to support decision on management measures to control reproductive failure.
The view from the field by Enric Marco
One of the most difficult problems to diagnose in swine clinic is abortion. In many cases the cause is no longer present when abortion happens, so diagnosis is impossible. Some studies estimate the proportion of undiagnosed abortions in more than 60% of the total.
This study can help us try to reduce their frequency or their impact. Extensive research provides interesting data. A majority of abortions occur during the cold months, regardless of their cause. The fact that they appear more frequently in the cold months is an indication that the facilities, as far as the gestations are concerned, possibly fail to sufficiently isolate the interior environment from the outside. Thermal stress can negatively affect the immune response of pigs by placing gestations in a state of greater vulnerability. Consequently, improving housing conditions should be a priority for farms with reproductive problems during the cold months. An increase in the amount of daily feed supplied would probably place pregnant sows in a more favourable situation, since it would allow them to reduce the negative impact of a cold environment.
The study also suggests that Porcine Circovirosis (PCV-2) and Porcine Respiratory and Reproductive Syndrome (PRRS) are among the most frequent infectious causes of abortion. These findings obviously suggest that a better control of both diseases in the breeding herd should be a priority in dense areas (such as the study area). As far as PCV2 is concerned, vaccination is widespread in piglets, but there are still few farms that vaccinate sows, and when they do so, it's never with a view to reducing reproductive problems, but to reducing the problems seen in growing piglets. A more frequent vaccination of sows against PCV2 might reduce the frequency of this aetiologic agent diagnosis in abortions. To reduce the frequency of PRRS virus diagnosis in cases of abortion, the measures to be taken are more complex since they should include immunisation of the breeding stock, improvements in the farm biosafety to avoid the introduction of new viral strains, and implementation of management measures aimed at reducing viral circulation in what we call "hot areas" (replacements and post-weaning areas.)