Cereals are an excellent nutritive source for pigs and microorganisms. Some of the latter, the fungi, may grow on cereals and produce different molecules, including toxins called mycotoxins (myco- prefix denotes mushroom in Greek). One of these mycotoxins, the vomitoxin (chemical name: Deoxynivalenol or DON), is regularly found in pig feed. However, research data suggest that DON, beside its negative impact on animal weight gain, lowers the immune response of pigs infected with PRRS, the number one enemy of the swine industry. Consequently, these animals produce a weaker defense response against this virus.
In livestock management, it is common to vaccinate herds against PRRS. Current effective vaccine technologies use a live, attenuated, virus, which means that, through various methods, the virus was enfeebled to make it incapable of causing damage while keeping its capacity to stimulate the immune system so it can produce a protective response.
It is precisely this issue that worries Drs. Younès Chorfi and Carl A. Gagnon from the Faculty of Veterinary Medicine of the Université de Montréal. Indeed, if a mycotoxin can cancel the immune response against a normal virus, would it cause the same effect against an attenuated (enfeebled) virus? With the financial support of the Swine and Poultry Infectious Diseases Research Center (CRIPA), this team has enlisted the help of the postdoctoral fellow Dr. Christian Savard to test the immune response following the injection of Ingelvac PRRSV® (MLV) vaccine in pigs fed with food free of mycotoxins or with feed contaminated with natural exposition doses of the mycotoxin DON. The results corroborate the suspicions of Dr. Chorfi and Dr. Gagnon that DON lowers the vaccine efficiency against PRRS. More precisely, DON lowers the virus replication, which blocks the immune system from being sufficiently exposed to the vaccine enfeebled virus to stimulate its response.
Since the vaccination with attenuated virus is actually the best strategy available, it will be important to check the level of DON in food before and during the vaccination period against PRRS.
Finally, the effects of other mycotoxins, in addition to those of DON on other viruses or bacteria, are currently unknown and will be studied.
Source: Deoxynivalenol (DON) naturally contaminated feed impairs the immune response induced by porcine reproductive and respiratory syndrome virus (PRRSV) live attenuated vaccine.
Savard C, Gagnon CA, Chorfi Y. Vaccine, July 2015.