Protection of Piglets against Oedema Disease by Maternal Immunization with Stx2e Toxoid. Thi Kim Nguyen Oanh, Viet Khong Nguyen, Henri De Greve and Bruno Maria Goddeeris. Infection and Immunity. January 2012 Volume 80 Number 1 p. 469–473 doi:10.1128/IAI.05539-11
What are they studying?
Oedema Disease (OD) is a frequently fatal disease of piglets in the post weaning period caused by shiga toxin producing E. coli (STEC) most typically expressing the F18 fimbriae. Researchers investigated whether vaccination of dams with an experimental shiga toxoid vaccine could passively protect their piglets against an OD challenge after weaning.
How was it done?
An experimental vaccine was prepared with Stx2e toxoid derived from a genetically modified E.coli strain containing the operon responsible for synthesizing the toxin.
In all experiments, 2 doses of the vaccine were administered intramuscularly 2 weeks apart.
An Indirect ELISA was developed to detect Stx2e antibodies in the serum of vaccinated sows and piglets. This was used to monitor antibody titres in either active immunization or passive transfer.
Three separate experiments were carried out:
First, toxicity of Stx2e was tested in piglets after intravenous (IV) administration at 3 dose levels. An ideal challenge dose (50 ng/kg) that allows expression of typical OD clinical signs (eyelid oedema, ataxia, recumbency, paddling, dyspnea, paralysis and death) was determined for the challenge experiments.
Secondly, active immunization of piglets followed by experimental challenge and assessment of protection. Non-vaccinated controls were used for comparison.
Thirdly, the pre-farrowing sows were vaccinated with the same vaccine. Non-vaccinated control sows were included. Piglets from these sows were allowed to suckle colostrum and milk and then weaned at 26 days of age. Efficacy was tested by IV challenge with Stx2e toxin 5 days after weaning, at 31 days of age.
What are the results?
Piglet immunization resulted in high antibody responses with no negative effects on piglet weight gain. Following challenge 0/6 piglets in the vaccine group showed typical OD clinical signs and none showed typical gross post mortem lesions. In contrast, all the controls showed typical clinical signs, 1 died and one was euthanized within 2 days after challenge. Lesions consistent with OD were detected in all 3 controls.
Immunized sows developed an antibody response 10 times higher than the controls. Piglet serum showed high antibody titers that persisted up to 1 month after weaning (53 days of age), while those born from control sows had low Stxe2 antibody titers until termination of the study. Following challenge of offspring with Stx toxin 10 days after weaning, none of piglets from vaccinated sows showed OD clinical signs or died. In the control group, however, 6/6 piglets developed clinical signs and died 2 days after challenge.
What implications does this paper have?
The investigation demonstrated that the shiga (Stx2e) toxoid vaccine induced strong immune responses in sows as well as high levels of passive antibodies in piglets. Complete protection of these piglets from lethal doses of shiga toxin was demonstrated 5 days after weaning.
OD mainly occurs within the first 2 weeks postweaning and while active immunization has been demonstrated to provide clinical protection, the concern is the ability for young pigs to respond to vaccination ahead of field challenge. Also, passive immunity derived from high natural exposure to STEC in breeding herds could lead to interference of active immunization.
The view from the field by Enric Marco
Who has never heard of Oedema Disease?! The first time I had to face it as a veterinarian was on the evening of a December 31. It was dark and I was worried about not making it on time for New Year's Eve dinner. 30 years have gone by, and treatment is still the same: fasting plus antibiotic treatment. There's an apparent decline in prevalence when compared with the few previous years. Improvements in feed formulation and manufacture, housing and hygiene, and the reduction of genetic options, coupled with the work carried out with some of them to reduce the number of carriers of for F-18 receptors, are probably some of the reasons why this disease is less frequent today. However, when it appears in a farm, it tends to be an insidious process, easy to diagnose, but which treatment is still not very effective in reducing casualties, since it is always administered too late (the toxin is already circulating).
Really effective products to prevent the disease have only relatively recently been available. There are live vaccines against E. coli F-18 in the international market that have been successful in preventing oedema disease. There has been a vaccine available in Europe against this disease for a few years. The vaccine is a Stx2e toxoid that effectively protects piglets, very similar to the one described in the article. It has been the solution on farms where the disease was endemic and insidious. However, in early onset oedema disease it is always a challenge to find the right time to vaccinate and revaccinate piglets without risking an interference with maternal immunity. The article provides a very valuable alternative to the current vaccination programs that could be the solution for farms with early onset oedema disease, and it consists of vaccinating the dams at the end of gestation to achieve post-weaning piglets immunization. Furthermore, dam immunization would be a more economical alternative to vaccination and revaccination of all piglets in the litter. However, the article also raises questions, such as: Is dam vaccination and revaccination necessary at each farrowing? Would a revaccination from first farrowing be sufficient, similarly to what is done with other vaccines against E. coli? If we choose a traditional vaccination plan (revaccination after first farrowing), will colostral immunity in piglets from first parity sows last as long as that of piglets from subsequent farrowings? What is the actual duration of maternal immunity in the piglet, a month or more after weaning? Possibly only practice will give us the answer, over time.