Timing and immune status shape the safety of ASFV-G-ΔI177L vaccination in pregnant sows
This study demonstrates that while pre-immunized sows tolerate ASFV-G-ΔI177L booster vaccination during pregnancy without adverse effects, first-time vaccination of naïve sows during gestation poses severe risks including maternal illness, reproductive failure, and potential vertical transmission.
Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer
African swine fever is a devastating disease that threatens pig farms and wild pig populations across the globe. It is so lethal that it can kill nearly every pig it infects, causing massive economic losses and disrupting food supplies. For decades, controlling the disease has relied on strict hygiene, moving animals less, and culling infected herds, because no safe, approved vaccine existed for widespread use. Recently, scientists developed a new type of vaccine made from a weakened version of the virus itself, designed to teach the pig's immune system to fight the real disease without causing illness. While this vaccine has shown promise in young pigs, a critical question remained: is it safe for pregnant mothers? In the world of animal health, a vaccine that works well in a young animal might behave very differently in a pregnant one, potentially harming the mother or the developing piglets inside her.
Researchers at the Friedrich-Loeffler-Institut in Germany set out to answer this question by testing the new vaccine, known as ASFV-G-ΔI177L, on pregnant sows. Their goal was to determine if the timing of the shot and the mother's prior exposure to the virus mattered. They divided the animals into groups to test two main scenarios. In the first scenario, the sows received the vaccine before they became pregnant, building up their defenses, and then received a second dose, or booster, while they were already carrying piglets. In the second scenario, the sows had never seen the vaccine before; they received their very first dose while they were already pregnant, either early in the pregnancy or late in the pregnancy. The researchers then watched closely to see how the mothers and their offspring fared, checking for signs of sickness, whether the virus spread through their bodies, and if the piglets survived.
The results painted a stark picture of two very different outcomes depending on the sow's immune history. The sows that had been vaccinated before pregnancy handled the booster dose with ease. Whether they received the extra shot on the 40th day or the 80th day of their pregnancy, these mothers remained healthy. They showed no serious signs of illness, their blood did not show high levels of the virus, and they gave birth to healthy litters. Their piglets were born strong, and the mothers passed on protective antibodies to them through their milk, ensuring the newborns had a head start against the disease. This group demonstrated that the vaccine is safe for breeding females, provided they are already immune before they conceive.
In sharp contrast, the sows that received their first vaccine dose while pregnant faced severe consequences. When these mothers were vaccinated for the first time during pregnancy, the weakened virus acted too aggressively for their unprepared immune systems. The animals developed high levels of the virus in their blood and suffered from severe clinical signs, including high fevers and widespread infection throughout their bodies. The outcome was tragic for many: several sows had to be humanely euthanized because they became too sick, while others suffered miscarriages or gave birth to stillborn piglets. The severity of the illness appeared to depend on when the shot was given. Sows vaccinated later in pregnancy, around the 80th day, all became critically ill and were euthanized before they could give birth. Those vaccinated earlier, around the 40th day, had a mixed fate; some survived to farrow, but their litters often included many stillborn or weak piglets that did not survive long after birth.
The study also looked closely at whether the vaccine virus could pass from the mother to the baby inside the womb. In the group of sows that were vaccinated for the first time while pregnant, the researchers found evidence that this transmission did happen, but only in specific cases. One mother, vaccinated early in her pregnancy, passed the virus to almost all of her piglets, who were found to have high levels of the virus in their organs at birth. However, another mother in the same group, who also received her first dose early in pregnancy, did not pass the virus to her offspring at all. This suggests that while vertical transmission is a real risk when vaccinating a pregnant animal for the first time, it is not guaranteed to happen in every single case. In the group of sows that were vaccinated before pregnancy, no transmission to the piglets was detected, confirming that pre-existing immunity blocks this dangerous pathway.
Ultimately, the study concludes that the safety of this vaccine depends entirely on when the animal is vaccinated. The vaccine is a viable option for breeding herds, but only if the sows are vaccinated before they become pregnant. This initial vaccination builds a shield that protects the mother and her future piglets, allowing for safe booster shots during pregnancy if needed. However, giving the vaccine for the first time to a pregnant sow is dangerous and should be avoided, as it poses a high risk of severe illness for the mother and death for the piglets. These findings provide the necessary safety data to move this vaccine closer to approval for use in European breeding farms, ensuring that the protection it offers does not come at the cost of the reproductive health of the herd.
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