[Detection of Actinobacillus equuli ssp. equuli in piglets with purulent polyarthritis and tendovaginitis]. / Nachweis von Actinobacillus equuli ssp. equuli bei Saugferkeln mit eitriger Polyarthritis und Tendovaginitis.

Actinobacillus equuli ssp. equuli is an opportunistic pathogen in horses, mainly known to cause "sleepy foal disease". In comparison to horses, there are only few reports describing diseases in pigs associated with this gram-negative bacterium. This case report describes an outbreak of infection in a combined farrow-to-finish-farm. In September 2018, the following symptoms were noticed in one third of all newborn piglets from gilts and sows: 6-8 hours after birth piglets became weak and developed swollen joints with moderate to severe lameness. The piglets exhibited lethargy, a subset were non-ambulatory. An elevated piglet mortality within the first days within birth was noted. Seven piglets that succumbed to the disease (days 2-3 of life) were submitted for examination, 4 of which underwent pathological examination. The main findings were purulent polyarthritis and tendovaginitis. In addition, purulent inflammation was detected in the brain and kidneys of one animal. In the bacteriological examination A. equuli ssp. equuli was isolated in a total of 18 samples (brain, joints, suppurative structures of limbs), in a subset of cases as pure culture. For identification, cultural and biochemical characteristics were tested and a mass spectrometry analysis (MALDI-TOF MS) was performed. Further laboratory testing included 16 S rRNA-gene sequencing, a PCR in order to examine for special apx toxin genes as well as a PCR differentiating the two subspecies of A. equuli. It was not possible to identify the source of infection and routes of spread within the pig herd. The bacterial isolates were used for the production of an autogenous vaccine.

Serum antibody responses in horses and mice following immunization with Actinobacillus equuli outer membrane proteins and recombinant Aqx toxin.

The immune responsiveness of mice (without prior natural exposure) and mares (with naturally acquired antibodies) was determined following vaccination with Actinobacillus equuli outer membrane proteins (OMPs) and/or recombinant A. equuli toxin (rAqx). Mice were vaccinated subcutaneously on days 0 and 21 with one of three doses (5, 25 or 50µg) of A. equuli OMPs, rAqx or both, together with Freund's incomplete adjuvant (FIA). Antibodies against formalin-killed whole bacterial cells (WBCs), OMPs and Aqx were determined on days 0, 21 and 42. Mares were vaccinated subcutaneously on days 0 and 21 with 100µg OMPs, 100µg rAqx or a combination of 50µg of each antigen, together with FIA. Antibodies against WBCs, OMPs and Aqx were determined at 7day intervals for the first 42days, as well as on days 56, 70, 154 and 238. Vaccination of mice stimulated an apparent dose response to OMPs and Aqx. Antibodies against OMPs and Aqx were enhanced following vaccination of mares that had naturally acquired pre-existing antibodies. There was no evidence of interference with antibody responses to the individual antigens when OMPs and rAqx were combined prior to vaccination.

Serum antibodies in mares and foals to Actinobacillus equuli whole cells, outer membrane proteins, and Aqx toxin.

Actinobacillus equuli is carried in the alimentary tract of mares and can cause severe septicemia of neonatal foals. A hemolytic subspecies, A. equuli subsp. haemolyticus, and a non-hemolytic subspecies, A. equuli subsp. equuli, have been identified. Hemolytic strains produce the RTX toxin Aqx. The purpose of this study was to demonstrate sequentially in two sets of mare-foal pairs antibodies to A. equuli whole bacterial cells, outer membrane proteins, and recombinant Aqx and to compare the transfer of antibodies to these antigens between mares and their foals. Two mare/foal sets of sera were evaluated. Cohort A consisted of 18 mare-foal pairs obtained in the spring of 2005. Cohort B consisted of 10 mare-foal pairs obtained in the spring of 2006. For both sets, mare and foal sera were obtained immediately after foaling and prior to nursing (time 0) as well as at 12 and 24h and daily thereafter for 7 days. For Cohort B, sera were also obtained 30 days after birth. At parturition all mares had detectable antibodies to A. equuli whole cells and outer membranes; however, of those mares, two in Cohort A had undetectable antibodies to Aqx and their foals likewise had undetectable anti-Aqx antibodies. Antibodies against whole cells, outer membrane proteins, and Aqx were readily transferred from mares to foals. In most cases, there were significant correlations (p<0.05) between antibodies against whole cells, outer membrane proteins, and Aqx in mares' sera at the time of parturition and foal sera 24 after birth. Antibodies against the three antigen preparations had declined insignificantly (p>0.05) by day 30.

Antibodies to Aqx toxin of Actinobacillus equuli in horses and foals.

Actinobacillus equuli is found in the normal oral flora of horses, but has been associated with several diseases, and particularly with the usually fatal septicaemia in neonatal foals which is thought to be associated with a failure of the passive transfer of immunoglobulins via the colostrum. The Aqx protein of A equuli, belonging to the RTX family of pore-forming toxins, is also cytotoxic to horse lymphocytes. The presence of antibodies to Aqx was investigated in sera from individual horses from different regions; the sera from adult horses and foals 24 hours after birth reacted with Aqx, and sera from foals sampled shortly after an intake of colostrum also reacted with Aqx, but sera from foals taken before an intake of colostrum did not react with Aqx.