Nasal vaccines deliver solid infection protection

The best offense is a good defence, particularly when trying to protect young calves, says a scientist with VIDO

Intranasal vaccines offer the best protection against respiratory infection in calves, particularly when administered at branding and again at weaning, studies have found.

Dr. Philip Griebel of the Vaccine and Infectious Disease Organization in Saskatoon said bovine respiratory disease remains difficult to treat because it is so complex. Multiple viral and bacterial pathogens, combined with the stress of weaning, can cause significant health problems in calves at feedlots, even though they are vaccinated there.

“It is really almost too late to be helping those calves in many situations,” he told the Saskatchewan Beef Industry Conference.

Despite the prevalence of vaccines and antibiotics, BRD continues to cost money.

“Statistically, what we’re seeing is that gradually the morbidity and the mortality rates are starting to creep up again,” he said.

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The problem is that calves have high levels of maternal antibodies, delivered in colostrum, that neutralize the virus delivered intramuscularly by a modified live virus vaccine. These antibodies can be present for months.

Some studies have found a bit of immune memory from that vaccine, Griebel said, but couldn’t say whether that actually offered disease protection.

A study at Guelph found that calves vaccinated with a killed bacterial vaccine, also delivered intramuscularly, developed no protective immunity.

Griebel said the question then is not the potency of the vaccine but the delivery method.

The maternal antibody IgA represents only about 10 percent of the antibodies that calves receive but it moves out of the bloodstream to the surface of the respiratory or intestinal tracts, Griebel said.

Nasal secretion tests showed that IgA disappeared within three to five days, leading researchers to consider nasal vaccines as a way to circumvent maternal antibodies.

Griebel said there are several immune induction sites at the back of the nose and throat that can accept the vaccine.

Studies examined the response to groups of calves that received no vaccine, a modified live virus vaccine delivered intramuscularly once at branding, a modified live virus vaccine at branding and weaning, a killed viral vaccine, and an intranasal modified live virus vaccine, all in the face of maternal antibodies.

Four months after the vaccinations, the non-vaccinated group had no maternal antibodies, and the groups with the intramuscular vaccinations had no antibodies and no evidence of an immune response.

“Those calves that got the intranasal vaccine, they had significantly higher antibody titres,” he said.

Then, 10 calves from each group were abruptly weaned and taken to Saskatoon for further study.

The calves that had never received the vaccine didn’t get any upon arrival, but the other groups were re-vaccinated in the same manner.

Four days later they were infected with a dose of respiratory virus that researchers knew would make them sick. They were monitored for clinical response, including how much virus was shed in the nasal secretions to determine how much they would infect other calves.

Not surprisingly, Griebel said they found high levels of more than one million in each millilitre of nasal secretion in the non-vaccinated calves.

They found no difference in the amount of shedding in the groups with intramuscular injections.

“Whether we gave just a single shot at branding or a second shot at weaning, it made no significant difference in the amount of virus shedding, so that intramuscular vaccination at branding is really providing no benefit, even when you booster it at weaning time,” he said.

This also applied to calves that received the killed viral vaccine.

“The only place we see a very significant and profound reduction in virus shedding is where we gave the intranasal vaccine at branding time and then boosted that at weaning,” Griebel said.

These calves rapidly cleared the virus within seven days of infection.

Griebel said this indicates the calves are producing their own antibodies sooner.

“We actually do have a strategy now that if we want to access those calves at branding time, if we do give an intranasal vaccine, we can actually induce sufficient immune memory that will last four to five months and then we can induce protective immunity at the time of weaning,” he said.

He added that producers who have a good vaccine program in place for the cows should consider the vaccine delivery method for their calves. Cows vaccinated one month before delivery and even pre-breeding can transfer high levels of maternal antibodies to the calves.

Intramuscular vaccines are still valuable, Griebel said, if they are given three weeks pre-weaning when maternal antibodies have waned.

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