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‘Immune-mediated protection’ key to managing Group C rotavirus

Rotavirus is not a new disease facing the swine industry, but it’s also not going away. There are various groups of rotaviruses that impact piglets differently. For example, Group C rotaviruses often cause neonatal and pre-weaning diarrhea and mortality, while Group A rotaviruses remain mostly a post-weaning enteric-disease challenge.

A common method to control rotavirus-associated disease in piglets is to boost the sow’s immunity, which she transfers to her piglets.  That protects them until they reach a less-susceptible age.

Commercial and autogenous vaccines have provided variable results for Group A rotavirus protection, noted Kyoung-Jin Yoon, DVM, Iowa State University researcher. But Group C is more of a challenge because it’s difficult to grow this rotavirus in the laboratory, which prevents vaccine production.

Planned exposure or “feedback” of farm-specific live-rotavirus isolates to sows 2 to 5 weeks before farrowing is an option to boost sow immunity and transfer to her piglets, but it produces mixed results. According to Yoon, there is a need to better understand the immune-mediated protection against Group C rotavirus in piglets.

Two experiments

This prompted him to conduct a Pork Checkoff-funded study to investigate whether maternal immunity protects piglets against Group C rotavirus-associated disease. Yoon also wanted to determine the antibody response to various vaccine forms in older pigs.¹ In the process, he conducted two experiments, with the findings summarized in the National Pork Board’s Research Review newsletter.

The first experiment involved passive transfer of rotavirus-specific concentrated immunoglobulin (IgG) to mimic maternal immunity in neonates and assess whether maternal-antibody levels correlate with protection against an oral rotavirus challenge.

Yoon fed concentrated Immunoglobulin G (IgG) and exposed a porcine-rotavirus-C isolate to Cesarean-derived, colostrum-deprived piglets immediately after birth. He then monitored the piglets for antibody decay and protection against challenge over time.

In the second experiment, Yoon looked at how the antibody responded in piglets after receiving cell-culture-derived live virus. He used ice cubes containing rotavirus-positive feces in an attempt to estimate the material antibody level that can passively transfer to piglets via colostrum.

What he found

According to Yoon, the study demonstrated the following:

• Naïve pigs could develop a serum-antibody response with neutralizing activity after receiving a low dose of live virus, orally or injected, with a recombinant viral protein.
• Virus-neutralizing antibody response appeared to be subtype-specific (i.e., G type).
• Orally fed, virus-specific IgG could reduce the severity of rotavirus-associated disease but not infection.

In conclusion, he added:

• IgG feeding can provide temporary relief of clinical symptoms of Group C rotavirus infection.
• Both killed and live vaccines provide control options, but their use depends on the farm’s rotavirus status. “More importantly, subtype matching should be considered when devising a vaccine for better efficacy,” he said.

The full report is available here.

¹ Yoon K-J. Iowa State University. Understanding and searching for immune protection against group C rotavirus in piglets. National Pork Board research #13-065.