Thrombocytopenic purpura on an organic farm with pen mating: a case report on the re-emergence of an old disease

Abstract

Background: Thrombocytopenia is an immune-mediated disease, which affects suckling piglets. Piglets are pale and inactive, show multiple hemorrhages and often die within days. Pathological examination reveals severe haemorrhages and oedema in several organs. Severe thrombocytopenia and elongated bleeding time characterize the disease haematologically. The sow produces antibodies against the thrombocyte antigens of the boar, which are present in the blood of the piglets. These isoimmune antibodies attack the platelets and megakaryocytes of the piglets, causing thrombocytopenia in succeeding matings of the same boar and sow. There is no known therapy against this condition. In the last few decades, the disease has become rare due to the increase of artificial insemination. Case presentation: On an organic breeding farm in Switzerland with a high percentage of natural pen matings, piglets of three litters showed haemorrhages on the skin, prolonged bleeding time and were generally in a reduced general state. A pathological examination revealed multifocal haemorrhages in the stomach, kidneys, dermis, mesenterium and spinal cord. Haematology showed a massive thrombocytopenia and regenerative anaemia. Due to these findings the diagnosis of thrombocytopenic purpura was established. To avoid further matings of the same boar and sow and thus more affected piglets, out of three possible boars the responsible sire had to be determined. This was achieved through array genotyping and subsequent computation of identity by descent and calculation of Mendelian errors for parentage verification. Thereby the responsible boar was identified and as a consequence removed from the farm. Further preventive measures, that had been established, included the recording of all matings and regular exchange of boars. Conclusion: The decreased number of natural matings with the surge of artificial insemination has probably reduced the number of cases of thrombocytopenic purpura and thus the disease awareness of farmers and veterinarians. However, as consumers wish for better animal welfare and higher ecological standards we may see a rise in natural matings and thus a return of the disease. In case of affected litters, genetic testing was proven a valid method for investigation and prevention of more cases and may be used more in the future.

Clinical, histopathological, and hematological changes due to isoimmune thrombocytopenic purpura in piglets

“…Clinically, animals with ITP presented with dyspnea, weight loss, hyporexia, and apathy. Similar clinical findings have also been described by Stormorken et al (1963), Linklater et al (1973), Carrasco et al (2003), Hsu et al (2016) and Joller et al (2020), possibly associated with severe anemia presented by animals with EPTI. According to Thrall (2015c), anemia and/or intense blood loss result in decreased oxygen saturation, dyspnea, muscle weakness, decreased movement and hyporexia, which may explain the clinical signs observed in our study.…”

“…In a study carried out on breeding farms in Taiwan, the overall mortality rate of piglets due to ITP reached 2.4% (Hsu et al 2016), which is similar to our findings. However, the highest rate of mortality from PTI neonate piglets (50-70%) were observed by Joller et al (2020) when compared to our study. This difference may be related to the number of litters evaluated and the experience of workers to perform the rapid diagnosis and treatment of affected piglets.…”

“…Due to its acute nature, rapid diagnosis is difficult, and treatment is typically delayed. The litters affected, often have high rates of mortality (Joller et al 2020). The results of the current study indicate mortality rates of 20% in newborn piglets (EITP) and 60% in 13-14-day-old piglets (LITP), with overall rates of 0.9% and 1.6%, respectively.…”

“…The sow produces antibodies against the thrombocyte antigens of the boar, which are present in the blood of the piglets (Stormorken et al 1963, Nordstoga 1965, Dimmock et al 1982. After ingestion of colostrum with isoimmune antibodies, piglets develop severe thrombocytopenia, and consequently, massive hemorrhages (Galea et al 1981, Furukawa et al 2014, Valli et al 2015, Joller et al 2020) because isoimmune antibodies cause platelet agglutination and lysis of medullary precursors (megakaryocytes) in newborn piglets (Stormorken et al 1963, Nordstoga 1965, Saunders & Kinch 1968, Dimmock et al 1982, leading to clinical signs such as pallor, apathy, multifocal hemorrhaging, and death (Putsche & Kohn 2008). Separating piglets from their mother prior to colostrum consumption and being fostered by a different sow constitutes the main strategy for early treatment of the disease (Schmidt et al 1977).…”

“…In Brazil, ITP has been reported more frequently in swine farms that rear pure breeds, which are mainly produced by grandparents and great-grandparents breeding systems. Artificial insemination is a strategy for reducing the likelihood of ITP occurrence (Joller et al 2020); However, ITP is an emerging disease on commercial swine farms, and recurrent diagnoses occur in different producing regions of world causing mortality from piglets. In this context, the diagnosis of ITP must be rapid and accurate.…”