Gram-negative vaccines need caution

Some cattle diseases are harder to control and require a solid understanding of vaccine science. | File photo

Veterinarians who look after cattle are shifting priorities to emphasize disease prevention over treatment, says Gordon Atkins of the University of Calgary’s veterinary school.

The change is occurring as greater focus falls on reducing antibiotics in livestock production. Overall management, nutrition practices and the need to gain a better understanding of the advantages of appropriate vaccination programs have vaulted to the forefront.

“To add a word of caution to the overwhelming positives gained from vaccines, a very small element of uncertainty exists in field vaccinations. Genetics and nutrition of the animal are a significant factor and producers should be vigilant for rare possibilities of unexpected reactions,” Atkins says.

He says viral and bacterial diseases challenge livestock health but can often be prevented or controlled with suitable vaccinations.

Many vaccine principles need to be understood and followed.

As well, it should be recognized that bacterial diseases comprise two basic classifications of bacteria: gram-positive and gram-negative.

Differences between the two are based on their response to a staining technique known as the gram stain. This procedure initiates a colour change in bacteria based on cell wall structure.

While most bacterial intestinal infections are caused by gram-negative bacteria, both negatives and positives may trigger infections in other areas of the body including the respiratory tract, reproductive tract and the mammary system.

Gram-negative bacteria causing disease in cattle include E. coli, klebsiella, histophilus, mannheimia, pasteurella, campylobacter, salmonella, and multiple strains of leptospira.

Gram-positive bacteria consist of staphylococcus, streptococcus, trueperella, anthrax and numerous strains of clostridia.

While gram-positives are normally controlled by penicillin-like antibiotics, gram-negatives have a complex cell wall protecting them from the action of these more common antibiotics, and their successful treatment often requires antibiotics used extensively in human medicine, such as aminoglycosides, fluoroquinolones and cephalosporins.

“Because of the risk of developing antibiotic-resistant bacteria problematic in human medicine, restricted use of many of these newer antibiotics is being advocated in cattle practice and our main focus is to prevent diseases by a combination of good management and nutrition practices, as well as suitable vaccination programs,” Atkins says.

But gram-negative vaccines are not as trouble-free as their positive relations due to the makeup of their protective cell wall.

“Since the outer cell membrane is comprised of a complex lipopolysaccharide layer whose ‘lipid A’ component can cause a toxic reaction when lysed (broken down) by immune cells, administration of multiple vaccines for gram-negative bacteria can be particularly problematic. Delivering more than two gram-negative bacterial vaccines at a single event results in the stacking of endotoxin and may lead to reactions.”

To counteract this issue, at a recent American Association of Bovine Practitioners conference, it was recommended no more than two gram-negatives be given in a single vaccination.

Atkins said he understands this is easier said than done at the ranch level because handling and logistics are not always easily combined. To minimize cattle handling, multiple vaccinations can be given at the same time, but some factors should be addressed.

From a reproductive perspective, caution must be exercised when vaccinating pregnant females with a commercially distributed vibrio and lepto combination. They should only be administered before breeding to avoid abortion issues. For some purebred breeds, risk of abortion can be enhanced if an injectable vitamin solution is given together with gram-negative vibrio and lepto vaccines.

“Although reactions to gram-negatives have been shown to be more prevalent with animals in a state of vitamin and mineral deficiency, supplementation with injectable vitamins must be viewed with caution since it will increase the risk of an endotoxic reaction. Using dry vitamin mix in feed does not create this problem and is a safer tactic to supplement vitamins.”

Age, stage of gestation, lactation, plus management and environmental conditions should be considered to gain the optimal immune response and avoid costly losses, stresses Atkins. Goals of vaccination primarily include the establishment of a protective immunity without harming the animal.

He notes sensitivity to an endotoxic reaction is also greater at high ambient temperatures and vaccination during heat stress ( above 30 C) should be avoided.

Beyond the dramatic impact of abortions, anaphylactic or hypersensitivity reactions can also occur. Epinephrine should always be close at hand for anaphylactic reactions while corticosteroids and fluid therapy might be required to counteract hypersensitivity issues because they are more systemic.

Atkins says a new type of gram-negative vaccine has been recently introduced, known as siderophore receptor and porin. It creates antibodies blocking the uptake of iron by the cell needed for bacterial growth. They have no endotoxin but contain a potent modulant to initiate their immune function.

Siderophore receptors are specialized porin proteins that transport iron-siderophore complexes through the cell wall and while they are effective for several gram-negative organisms including klebsiella and salmonella, there are also safety concerns with their use. It is recommended they be administered separate from other vaccines.

Atkins advised producers to consult their veterinarian when choosing vaccines.

“All of what we have found in studies and research, plus information at hand, comes from well researched recommendations, but individual vaccination programs should be designed by a veterinarian familiar with the history and whole management strategy of the herd.”

Bovine disease control priorities must continue to emphasize prevention rather than treatment, says Atkins. Because antibiotics to counteract gram-negative organisms can’t be used readily due to their use in human medicine, strict guidelines need to be kept front of mind when they are used.

“It doesn’t mean every time we use more than two gram-negatives at a single event, we’re going to have an issue, it just means we’re dramatically increasing the risk of a reaction if we’re using more than two,” Atkins says.

“Keep weather and climate in mind, monitor vibrio- and lepto-based vaccines, avoid adding a vitamin injection together with them, keep epinephrine on hand and consult a veterinarian to simplify the entire matter.”

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