As the global demand for pork increases, pig farming has become more intensive.
This means that farmers need to rely heavily on vaccines to control diseases and prevent major financial losses. However, sometimes, even with a perfect vaccination schedule, vaccines do not work as expected.
Understanding why these failures occur is critical for farmers who constantly face threats from swine diseases.
While many factors can affect a vaccine’s effectiveness, those that weaken a pig’s immune system are a major reason why an otherwise good vaccine might fail to protect the animal (Augustyniak & Pomorska-Mól, 2023)
A vaccine can fail for several reasons...
Sometimes, the issue lies with the vaccine itself—such as being stored at the wrong temperature or administered incorrectly. Other times, the problem is related to the pig, including factors like age, genetics, or diet.
However, a particularly serious concern arises when something actively suppresses the pig’s immune system, making it unable to build protection even with a wellformulated vaccine (Augustyniak & Pomorska-Mól, 2023)
One of the most common—and often overlooked—causes of this immune suppression is hidden in the animal’s daily feed: mycotoxins.
THE HIDDEN CHALLENGE: MYCOTOXINS
Mycotoxins are a natural defense mechanism produced by certain types of molds—such as Aspergillus, Fusarium and Penicillium, which are common in agricultural settings.
25%
Mold contamination is a global problem: the Food and Agriculture Organization (FAO) estimates that at least 25 % of the world’s crops are affected each year (Thapa et al., 2021; Bracarense et al., 2011).
These mycotoxins—including aflatoxins (AF), deoxynivalenol (DON), zearalenone (ZEN), fumonisins (FB), and ochratoxin A (OTA)- can develop on crops in the field or during feed storage (Bulgaru et al., 2021)
While consuming a large dose of mycotoxins can make a pig visibly sick, a more frequent and costly problem arises from the ingestion of low levels of these toxins over a prolonged period.
At such levels, mycotoxins weaken the immune system.
This immune impairment reduces pigs’ resistance to disease, slows their growth and productivity, and—most importantly—undermines the very health programs designed to protect them, such as vaccination (Pierron et al., 2016; Oswald et al., 2005).
HOW DO MYCOTOXINS WEAKEN THE IMMUNE SYSTEM?
A healthy immune system is a dynamic network of cells that are constantly working and replicating to protect the body.
This continuous activity makes it particularly vulnerable to toxins that interfere with fundamental cellular functions.
Mycotoxins exploit this vulnerability to disrupt the animal’s natural defenses (Pierron et al., 2016; Oswald et al., 2005).
General mechanisms of immune disruption
Mycotoxins impair the immune system through several interconnected pathways:
DIRECT EFFECTS ON IMMUNE CELLS
Many mycotoxins are cytotoxic to key immune cells, such as lymphocytes (T and B) and phagocytes (macrophages, neutrophils).
INTERFERENCE WITH CYTOKINE SIGNALING
Cytokines are essential signaling proteins that coordinate the immune response and mycotoxins can disrupt this communication
INDUCTION OF OXIDATIVE STRESS
An imbalance between reactive oxygen species (ROS) and the body’s antioxidant capacity leads to oxidative stress.
Fumonisin B1 (FB1) can induce apoptosis (programmed cell death) in swine macrophages, leading to a reduction in these essential defensive cells (Pierron et al., 2016; Oswald et al., 2005).
Aflatoxins (AF) may inhibit certain inflammatory cytokines, while deoxynivalenol (DON) can alter the expression of inflammatory genes, leading to a dysregulated and less effective immune response (Pierron et al., 2016; Oswald et al., 2005).
Mycotoxins such as zearalenone (ZEN) can promote ROS production, causing cellular damage that impairs immune cell function and hinders the development of protective immunity (Liu et al., 2020; Bulgaru et al., 2021).
Specific consequences for immune function
These mechanisms result in functional impairments across various components of the immune system.
IMPAIRED HUMORAL IMMUNITY
The B-lymphocyte-mediated arm of the immune system is responsible for producing antibodies, which are essential for vaccine efficacy.
COMPROMISED CELL-MEDIATED IMMUNITY
T-lymphocytes play an essential central role in cell-mediated immunity, being responsible for eliminating infected cells.
REDUCED PHAGOCYTIC ACTIVITY
Macrophages and neutrophils constitute the first line of innate immune defense.
DAMAGE TO LYMPHOID ORGANS
The thymus, bursa, and spleen are crucial for the maturation and activation of immune cells, and mycotoxins can cause direct damage to these vital organs
Fumonisin B1 (FB1) has been shown to reduce the specific antibody response to vaccination in pigs.
Co-exposure to deoxynivalenol (DON) and zearalenone (ZEN) can impair antibody production against Classical Swine Fever virus (Pierron et al., 2016; Oswald et al., 2005; Chen et al., 2008).
Aflatoxins particularly affect this component by suppressing delayed-type hypersensitivity responses.
Zearalenone (ZEN) has also been shown to the viability of T and B lymphocytes 2016; Oswald et al., 2005; Bulgaru et al., 2021).
Aflatoxin B1 (AFB1) inhibits their ability to engulf and eliminate pathogens.
Ochratoxin A (OTA) impairs neutrophil motility and phagocytic function.
Fumonisins (FB) reduce macrophage activity, increasing the animal’s susceptibility to infections (Pierron et al., 2016; Oswald et al., 2005).
Combined DON and ZEN may cause lymphocyte depletion in the spleen and lymph nodes, weakening the entire immune infrastructure (Chen et al., 2008).
WHEN PROTECTION IS DISRUPTED: THE LINK TO VACCINATION
When a pig’s immune system is weakened, it is no surprise that vaccines cannot perform their role effectively.
The purpose of vaccination is to train a healthy immune system to recognize a pathogen and remember how to fight it.
Mycotoxins interfere with this learning process at every stage (Augustyniak y Pomorska-Mól, 2023).
Why vaccinations may be less effective with mycotoxins
There is a wide array of mycotoxin-induced effects on the immune system can lead to vaccination failure.
INSUFFICIENT ANTIBODY TITERS
A key indicator of vaccine efficacy is the level of specific antibodies generated and animals consuming mycotoxincontaminated feed may fail to produce adequate antibody titers
POOR CELL-MEDIATED IMMUNE MEMORY
Long-term protection depends on the generation and maintenance of memory T cells.
INCREASED SUSCEPTIBILITY TO DISEASE
With a compromised immune system, the body is unable to mount a coordinated response to establish effective protection.
Fumonisin B1 (FB1), aflatoxin B1 (AFB1), and T-2 toxin have all been reported to lower postvaccination antibody levels in swine.
Exposure to deoxynivalenol (DON) can also reduce the effectiveness of PRRSV vaccination, with some animals showing no detectable antibody response (Augustyniak y Pomorska-Mól, 2023; Pierron et al., 2016; Oswald et al., 2005; Rückner et al., 2022).
Mycotoxins, particularly aflatoxins, can impair T-cell function and hinder the development of a robust memory response. As a result, protective immunity may not be sustained, leaving animals vulnerable to future challenges (Pierron et al., 2016; Oswald et al., 2005).
This can result in a breakdown of vaccineinduced immunity, leading to disease outbreaks and creating situations in which animals are vaccinated yet remain vulnerable (Pierron et al., 2016; Oswald et al., 2005).
Clinical signs of reduced vaccination efficacy
At the farm level, this issue may manifest as multiple production challenges:
OUTBREAKS OF PREVENTABLE DISEASES
The most direct sign is the occurrence of diseases against which the herd has been vaccinated (Pierron et al., 2016; Oswald et al., 2005).
SUBOPTIMAL GROWTH AND INCREASED HEALTH PROBLEMS
Immunosuppressed animals perform poorly, showing reduced growth rates along with higher morbidity and mortality.
SECONDARY INFECTIONS
A weakened immune system allows opportunistic pathogens to establish infection.
In one study, pigs exposed to deoxynivalenol (DON) displayed clinical signs as severe as those in unvaccinated animals after a challenge, indicating a failure of the vaccine to provide protection (Rückner et al., 2022).
An increased incidence of secondary infections may therefore indicate an underlying issue such as mycotoxin-induced immunosuppression (Pierron et al., 2016; Oswald et al., 2005).
STRATEGIES FOR RESTORING BALANCE AND ENHANCING PROTECTION
Protecting the investment in vaccination requires an integrated and proactive approach to mycotoxin risk management.
The goal is to minimize exposure to these toxins while supporting the animal’s natural resilience, thereby creating conditions in which vaccines can achieve their full effectiveness.
PREVENTION AND MONITORING
Prevention begins with Good Agricultural Practices (GAP) and proper drying and storage of grains to inhibit mold growth.
Regular testing of feed ingredients for mycotoxins is an essential management tool to identify potential risks and apply timely corrective actions (Pistol et al., 2013; Lafleur Larivière et al., 2022).
FEED MANAGEMENT AND SUPPORT
When mycotoxins are detected, proven feed additives, such as mycotoxin binders, can provide support, adsorbing certain toxins in the digestive tract, thereby limiting their absorption.
For other toxins, such as deoxynivalenol (DON), enzymatic deactivators that transform them into non-toxic compounds can be effective (Thapa et al., 2021; Lafleur Larivière et al., 2022).
NUTRITIONAL AND HOLISTIC HEALTH
A well-formulated diet can help counteract the effects of mycotoxins and supplementation with antioxidants (e.g., vitamin E, selenium) and other immunesupportive nutrients can protect immune cells.
This nutritional strategy should be part of a holistic health program that also includes robust biosecurity measures and veterinary consultation to ensure that vaccination protocols are optimized for the farm’s specific challenges, including potential mycotoxin risks (Burel et al., 2013).
In conclusion, the correlation between dietary mycotoxin contamination and vaccination failure is a critical concern for swine production.
Mycotoxins can weaken immunity and compromise the protection normally provided by vaccines.
By recognizing this risk and implementing a comprehensive management strategy, farmers can safeguard animal health and ensure that vaccination programs achieve their intended effectiveness.
References
Augustyniak, A., & Pomorska-Mól, M. (2023). Vaccination Failures in Pigs—The Impact of Chosen Factors on the Immunisation Efficacy.Vaccines. https://doi.org/10.3390/vaccines11020230
Bracarense, A.-P. F. L., Lucioli, J., Grenier, B., Pacheco, G. D., Moll, W.-D., Schatzmayr, G., & Oswald, I. P. (2011). Chronic ingestion of deoxynivalenol and fumonisin, alone or in interaction, induces morphological and immunological changes in the intestine of piglets.British Journal of Nutrition. https://doi.org/10.1017/ S0007114511004946
Bulgaru, C. V., Marin, D. E., Pistol, G. C., & Taranu, I. (2021). Zearalenone and the Immune Response.Toxins. https:// doi.org/10.3390/toxins13040248
Burel, C., Tanguy, M., Guerre, P., Boilletot, E., Cariolet, R., Queguiner, M., Postollec, G., Pinton, P., Salvat, G., Oswald, I. P., & Fravalo, P. (2013). Effect of Low Dose of Fumonisins on Pig Health: Immune Status, Intestinal Microbiota and Sensitivity to Salmonella.Toxins. https://doi.org/10.3390/toxins5040841
Chen, F., Ma, Y., Xue, C., Ma, J., Xie, Q., Wang, G., Bi, Y., & Cao, Y. (2008). The combination of deoxynivalenol and zearalenone at permitted feed concentrations causes serious physiological effects in young pigs.Journal of Veterinary Science.
Lafleur Larivière, É., Zhu, C., Sharma, A., Karrow, N. A., & Huber, L.-A. (2022). The effects of deoxynivalenol-contaminated corn in low-complexity diets supplemented with either an immune-modulating feed additive, or fish oil on nursery pig growth performance, immune response, small intestinal morphology, and component digestibility. Translational Animal Science. https://doi.org/10.1093/tas/txac068
Liu, X., Xu, C., Yang, Z., Yang, W., Huang, L., Wang, S., Liu, F., Liu, M., Wang, Y., & Jiang, S. (2020). Effects of Dietary Zearalenone Exposure on the Growth Performance, Small Intestine Disaccharidase, and Antioxidant Activities of Weaned Gilts.Animals. https://doi.org/10.3390/ani10112157
Oswald, I. P., Marin, D. E., Bouhet, S., Pinton, P., Taranu, I., & Accensi, F. (2005a). Immunotoxicological risk of mycotoxins for domestic animals.Food Additives and Contaminants. https://doi.org/10.1080/02652030500058320
Pierron, A., Alassane-Kpembi, I., & Oswald, I. P. (2016). Impact of mycotoxin on immune response and consequences for pig health.Animal Nutrition. https://doi.org/10.1016/j.aninu.2016.03.001
Pistol, G. C., Gras, M. A., Marin, D. E., Israel-Roming, F., Stancu, M., & Taranu, I. (2013). Natural feed contaminant zearalenone decreases the expressions of important pro- and anti-inflammatory mediators and mitogen-activated protein kinase/NF-kB signalling molecules in pigs.British Journal of Nutrition. https://doi.org/10.1017/ S0007114513002675
Rückner, A., Plagge, L., Heenemann, K., Harzer, M., Thaa, B., Winkler, J., Dänicke, S., Kauffold, J., & Vahlenkamp, T. W. (2022). The mycotoxin deoxynivalenol (DON) can deteriorate vaccination efficacy against porcine reproductive and respiratory syndrome virus (PRRSV) at subtoxic levels.Porcine Health Management. https://doi.org/10.1186/ s40813-022-00254-1
Thapa, A., Horgan, K. A., White, B., & Walls, D. (2021). Deoxynivalenol and Zearalenone - Synergistic or Antagonistic Agri-Food Chain Co-Contaminants?Toxins. https://doi.org/10.3390/toxins13080561
