A higher degree of intensification has contributed to the increased occurrence of ND, leading to significant economic losses (death and adverse effect on performance parameters) and overuse of antimicrobials. The frequency of ND cases has increased in EU countries in recent years, both on farms with conventional health status and on farms with high health status after restocking. Estimated costs for herds with ND with an estimated 10% mortality due to disease can be as much as €134 per sow per year (table 1† Together with swine dysentery, ND is one of the most expensive intestinal infections on pig farms.
Pathogens of the neonatal diarrhea complex
ND is by definition characterized by diarrhoea, usually accompanied by death, which develops during the first week of life of the piglets. The occurrence and severity of ND can be influenced by many factors and a number of pathogens have been implicated, including ETEC (Enterotoxigenic Escherichia coli) tribes from E coli and Clostridium perfringens types A and C. ETEC responsible for ND has adhesins, surface proteins called fimbriae, identified as F4, F5, F6 and, less commonly, F41. The fimbriae allow the microorganism to attach to specific receptors on the brush edges of the enterocytes of the small intestine. The most common ETEC with the fimbriae F4 colonizes the length of the jejunum and ileum and causes diarrhea.
C. perfringens type A (CpA) has been recognized in numerous studies as one of the major pathogens causing ND, therefore emphasis has been placed on its effective control. CpA is incorporated into the pig gut microbiota and well-equipped strains can cause intestinal disease. Infection of piglets is characterized by mild mucosal inflammation, sometimes with adherent necrotic material. Microscopic lesions may include superficial damage to epithelial ends of the villi of the small intestine during the first days of life. Other pathogens may play a role in cases of ND, along with contributing management factors.
Role of C. perfringens A and specific toxins
A recently published study using samples from a monitoring program in several European countries evaluated the occurrence of pathogens in the feces of piglets with neonatal diarrhea (ND) in 2020. In the bacteriological examination of the samples from 116 farms, the most isolated bacterial pathogens were E coli (48.6%), followed by C. perfringens (33.9%). Typing the C. perfringens isolates revealed that they all belonged to C. perfringens type A (CPA). 90.6% of them carried the coding genes for both the and 2 toxin, and therefore showed a high virulence potential. The analysis of their semi-quantitative detection showed that 79.4% of the E coli isolates occurred at moderate or high levels, and even 96.7% of C. perfringens isolates, suggesting their role in the pathogenesis of diarrhea. In piglets, CpA causes enteropathy after significant multiplication, sometimes associated with the adhesion of Clostridia to the intestinal mucosa. All strains of CpA produce the main toxin CPA (alpha toxin) in varying amounts. Beta2 toxin is another important toxin, often produced by strains of CpA that cause diarrhea in piglets. Many authors suggest that Beta2 toxin plays a role in causing the intestinal infection in pigs, as well as in other animal species. Gene detection and presence of the Beta2 toxin gene is used for diagnostics and characterization of strains causing diarrhea in piglets and has been proposed as a marker of pathogenicity
Role of Beta2 Toxin
Most isolates of CpA from clinical cases contain the beta2 toxin gene, suggesting a role in the pathogenesis of ND in piglets. In the author’s own study, where all isolates were collected from clinical cases of ND during the identification of vaccination candidates, 94.2% of the C. perfringens strains examined belonged to type A and 87.9% of the isolates were also positive for the 2 toxin gene (cpb2). Strains with low or medium toxin-forming capacity often showed significant formation of the 2-toxin in vitro† It is suggested that there is a synergistic effect of both toxins based on an enhancement of the uptake of the toxin by the 2 toxin with a negative effect on the intestinal mucosa and its integrity. At the same time, intoxication studies showed that vaccinated sows form antibodies against both toxins – and 2 – which are transmitted to their offspring via the colostrum and play a role in protection. This was demonstrated during the registration of the new vaccine against ND that contains seven different antigens, including both alpha and beta2 toxoids (Enteroporc Coli AC, Ceva Santé Animale, France).
Figure 1 – Dominant Role of CpA Positive for Beta2 . Isolates toxin from clinical cases of ND. Number and percentage of isolates with and without ß2 toxin gene from a total of 117 isolates by country of origin. Number of isolates per country in brackets.
Efficacy of vaccination against CpA under field conditions
The aim of the present study was to evaluate the efficacy of the C. perfringens type A (CpA) component of a licensed C. perfringens type A/C toxoid vaccine (Enteroporc AC) under field conditions. During the process (Figure 2), piglets from 16 vaccinated and 18 control gilts were followed up to 26 days of age. Vaccination under field conditions resulted in an increase of antibodies against alpha and beta2 toxins in the serum and colostrum of the gilts and resulted in a significant (p < 0.05) reduction in the incidence of diarrhea: a total of 38.7% of the piglets (84/217) from vaccinated gilts with diarrhea vs. 62.6% piglets (161/257) from control gilts. The efficacy and protection induced by the vaccine were demonstrated under field conditions in the case of CpA infection, uncomplicated by other pathogens involved in ND.
Figure 2 – Significant reduction in diarrhea in vaccinees piglets compared to control.
Conclusion
Cpb2-positive C. perfringens type A strains are commonly found in piglets suffering from diarrhea and play an important role in ND. Based on laboratory analysis aimed at quantifying the pathogen, 96.7% of C. perfringens type A isolates grow at a moderate or high rate, suggesting that they play a role in clinical cases submitted for diagnosis.
Using a commercial C. perfringens type A vaccine containing both toxoids led to the formation of antibodies against the and 2 toxins in the colostrum, which protected the piglets from the effects of the above-mentioned toxins and emphasizes the role of vaccination against the pathogen and the ND complex . Preventive medicine programs should aim to protect piglets before weaning, with pregnant sows vaccinated to induce passive transfer of antibodies and cellular immunity to the piglets via colostrum.
References are available on request.
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