Are pigs able to be infected with SARS-CoV-2? According to research at Kansas State University, pigs cannot be infected by or transmit coronavirus. Similar studies in Germany and China have concluded the same.
Previous work has shown that if cats are infected with SARS-CoV-2, and then mixed in with naïve sentinels a day or two later, the sentinels become infected, explains Juergen A. Richt, the Regents and University Distinguished Professor at Kansas State University.
“We know if the virus replicates in a susceptible animal like a cat, it is readily transmitted to sentinels,” Richt says.
Richt set out to determine if pigs would experience the same response to SARS-CoV-2 as cats. In the study, he infected nine 5- to 6-week-old pigs with SARS-CoV-2 intranasally, orally and intratracheally simultaneously, a very stringent challenge for a respiratory virus in pigs.
After inoculating these pigs with virus at a 10x higher dose than in previously done studies, his research team put the infected pigs into two pens and added two groups of three pigs (sentinel naïve animals that were not infected with the virus) to each pen to see if the virus would replicate in principal infected pigs and transmit to the sentinel animals.
Richt’s team discovered sporadic positives in nasal swabs early after infection. Because the RNA level was low and the researchers could not isolate the virus, they determined this was residual RNA from inoculation.
“Since animals were sporadically positive for low levels of viral RNA and negative for infectivity early after infection, we concluded that this was due to residual RNA from the virus inoculum,” he says. “Viral RNA seems to stay around for days in the nasal cavities after we inoculate the virus.”
“None of our animals were positive for SARS-COV-2,” Richt says. “However, the most interesting thing was if we put the virus in cell cultures derived from pigs – one was a swine testicle cell and one was a swine kidney cell – and we passaged the virus a couple times, those pig cells became infected with SARS-CoV-2.”
But is direct infection of testicles or kidneys a likely way pigs would be infected with SARS-COV-2? Richt says it is not.
“Yes, pig cells can be infected in vitro with SARS-CoV-2,” he adds. “But, pigs, inoculated by the most stringent way – intratracheal plus intranasal plus oral with a high dose of virus – could not be infected. In addition, the infected pigs did not transmit SARS-CoV-2 to sentinel animals. None of these animals did sero-convert (had neutralizing antibodies against SARS-CoV-2).”
That’s why Kansas State University researchers concluded, like the Germans and Chinese, that pigs are not susceptible by infection with the U.S. version of the SARS-CoV-2 virus through intratracheal-intranasal-oral challenge and are unlikely to be significant carriers of SARS-CoV-2.
“However, we have to be aware that this only applies to the rather young pigs, the commercial pig breed and the virus we have used for infection. It could be different in an old sow or boar, in a different pig breed or with a different virus,” Richt explains. We always have to be aware that if the virus changes – if the genome changes – the story could be different.”
Richt’s study has been peer-reviewed and is in the final stages of revision, he says. He plans to continue this research on additional animal models.
Farm Journal’s Pork | Jennifer Shike | September 18