Primary infection protects pigs against re-infection with Lawsonia intracellularis in experimental challenge studies

Abstract

In two separate trials pigs were experimentally infected with Lawsonia intracellularis at 5-6 weeks of age followed by antibiotic treatment and resolution of the primary infection and then re-inoculated at 12-13 weeks of age. A treatment-control group of pigs received the primary infection and antibiotic treatment only, and served as control for the antibiotic treatment of the primary infection. A challenge-control group of pigs received the second inoculation dose only at 12-13 weeks of age to control infectivity of the challenge-dose and susceptibility of pigs to L. intracellularis at this age. Pigs were monitored for shedding of L. intracellularis in faeces by PCR, and for the development of antibodies and responses of acute phase proteins in serum. The presence of L. intracellularis antigen in the intestinal mucosa was examined in post mortem samples by immunohistochemistry. In both trials primary infected pigs were protected from infection after challenge inoculation as evidenced by absence of faecal shedding of L. intracellularis, lack of changes in acute phase protein concentrations after challenge and with low levels of bacterial antigen in the intestinal mucosa of re-inoculated pigs comparable to that of the treatment-control pigs. In contrast, challenge-control pigs shed L. intracellularis in faeces, had L. intracellularis antigen extensively present within all layers of the intestinal mucosa and developed a significant acute phase protein response in serum after the experimental infection. The acute phase protein response to L. intracellularis infection was detected as an increased rise in the serum concentrations of C-reactive protein and haptoglobin from day-6 post infection, and increased serum concentrations of haptoglobin were generally seen 2-3 weeks after inoculation both at 5-6 and 12-13 weeks of age. In conclusion substantial protection against L. intracellularis infection was found in the re-inoculated pigs in contrast to the development of infection in age-matched control pigs. The acute phase protein responses reflected both the observed protection against L. intracellularis infection upon secondary challenge and that increased resistance to the infection develops with age.

Cell-mediated and humoral immune responses in pigs following primary and challenge-exposure to Lawsonia intracellularis

“…We have previously demonstrated protection against re-infection in primary infected pigs compared to age matched challenge control pigs as evidenced by reduced colonisation and pathology of intestinal mucosa, absence of bacterial shedding and without increase in acute phase protein response [6]. Here we report detailed studies on humoral and CMI responses after both primary and secondary L. intracellularis infections in these pigs.…”

“…The experimental design has been described in detail in the previously published re-infection study, Experiment II [6]. Briefly, 22 piglets (age 5-6 weeks at day 0) were randomly assigned to three groups: the Re-infection (RE, N = 10) and Treatment control (TC, N = 5) groups received an oral primary L. intracellularis inoculation at day 0, while pigs in the Challenge control (CC, N = 7) group remained naive.…”

“…Faeces and blood samples were collected at the time-points indicated and the pigs were sacrificed at day 83 or 84. In a preceding Experiment I, similar groups of pigs in an almost identical study design [6] were used to isolate cells from intestinal tissues at necropsy on day 70 or 74 post primary inoculation (i.e. 3 weeks post challenge), but other immunological data of these pigs are not reported here.…”

“…In a preceding similar experiment (Experiment I [6]) intraepithelial (IEC) and lamina propria (LPC) cells were isolated from the intestine of pigs at experimental day 70 or 74. Approximately 15 cm of ileum were tied at one end, inverted, filled with HBSS and tied at the other end.…”

“…The manifestations of proliferative enteropathy are one of the most important diseases of modern pig production with decreased animal welfare, increased antibiotic usage and substantial economic losses. It has previously been shown that L. intracellularis infection and disease are reduced after vaccination [4] or re-infection [5,6], but the immunologic responses to infection with L. intracellularis have not been fully elucidated.…”