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How vaccines can keep up with changing bacteria

Scott Smith for Progressive Dairy Published on 06 August 2021

Over the past several decades, much has changed in the dairy industry and how we manage cattle. As herds get bigger and more complex, we tend to manage groups of cows rather than individuals.

New technology has improved efficiencies, genetic progress and productivity.



As fast as the evolution of dairy herds has happened, so has the evolution of the pathogens that impact animal health. Bacteria have changed and adapted to their environment over time, which means the way we prevent, control and treat infections and other diseases that result from bacteria need to evolve as well. Fortunately, we’ve learned a lot about bacteria, including how they infect cattle and how they create the damage seen in diseases like pneumonia.

The leukotoxin-endotoxin effect

You can see how vaccines have advanced to match the evolution of bacteria by how we’ve addressed the control of Mannheimia haemolytica, the most common bacteria associated with bovine pneumonia, also referred to as bovine respiratory disease or BRD. While establishing the infection in the lung the M. haemolytica bacteria have a very effective defense system that can destroy the calf’s white blood cells or leukocytes (leuko- “white,” cyte- “cell”). Leukocytes travel through the bloodstream and wait to be called upon when there is a potential site of infection.

When M. haemolytica enters an animal’s lungs and begins multiplying, it triggers a leukocyte response. As the leukocytes arrive at the site of infection, the M. haemolytica release a toxin, known as leukotoxin, that attacks the cell wall of the leukocyte, causing those leukocytes to die and release their contents into the surrounding tissue. These cellular contents contain super-reactive granules, one of which is the equivalent of bleach, carried inside the cell which activate a larger immune response, resulting in significant inflammation and damage to the lungs. Thus, it is the consequences of the animal’s own immune response that result in much of the damage done during BRD associated with M. haemolytica. Severe disease can manifest itself in as little as 36 hours after initial infection and can result in death.

Calves are especially susceptible to pneumonia during periods of stress such as during hot or freezing temperatures, nutrition transitions, weaning and grouping. M. haemolytica is a normal inhabitant and often colonizes in the upper respiratory tract of healthy calves. These bacteria remain relatively inactive until the calf’s immune system is compromised during some type of stress event or infection with a virus.

The key in creating a vaccine to control M. haemolytica is including enough pure leukotoxoid in the vaccine to initiate a protective antibody response against the leukotoxin the bacteria produce. The antibodies created by the calf will bind to the leukotoxins and render them non-toxic. That way, when M. haemolytica invades the lungs, the leukotoxins it creates do not kill the white blood cells, allowing them to do their job attacking the invading pathogen: M. haemolytica. Generating protection against the M. haemolytica leukotoxin is an important aspect of creating effective immunity against this major pathogen. With this in mind, we need to immunize the calf against the negative effects of leukotoxin as much as we need to immunize against the bacteria itself.


Just as when leukotoxins break open white blood cells to release cellular contents and initiate infection and immune response, the contents of gram-negative bacteria found in the cell wall can release material called endotoxins that can cause significant illness. Gram-negative bacteria contain a thick outer capsule containing lipopolysaccharides (endotoxins) that, when released, can have a profound negative impact on animal health.

Because of the way some vaccines are manufactured, endotoxins can easily end up as part of the final product. Let’s use whole-cell bacterins as an example. Whole-cell bacterin vaccines are made by a fermentation process. During this process, the bacterial cells can be ruptured or broken open, resulting in the release of the endotoxin found in the cell wall of the bacteria.

Nearly every gram-negative bacterial vaccine contains endotoxins at some measurable level. Cattle become more susceptible to the effects of endotoxins when several gram-negative vaccines are used at once. This creates what is often referred to as “endotoxin stacking” and substantially increases the risk of an adverse reaction. These reactions can vary from shock-like symptoms to abortion, fever, anorexia, hypotension and even mortality. For this reason, it is widely recommended to not administer more than two vaccines that have endotoxin potential at the same time.

Vaccines can make the impact of endotoxins much less severe. Again, as with leukotoxin control, it matters what vaccine you use when it comes to avoiding the impacts of endotoxins. As mentioned, the vaccine production process can result in a heavy load of endotoxin when the fermentation process is going on. There are vaccines that go through a different manufacturing process which includes only a portion of the bacterial cell wall instead of the whole bacteria. The vaccine does need to stimulate the calf’s immune system to develop antibodies to the outside of the bacteria (cell wall and cell wall components) as well as the leukotoxin. In an ideal situation, we could have sufficient antibodies made against the cell wall and its components with minimal levels of endotoxin being produced.

The process in the manufacturing of certain vaccines (Nuplura PH and Nuplura PH+) does just that. Think of the bacteria as a basketball. Instead of using the whole outer shell of the basketball, just the dimples of the basketball are used to manufacture the vaccine. That means far fewer endotoxins are captured in the manufacturing process while at the same time stimulating good antibody production. Producers can use these products with other gram-negative vaccines with a potential of reduced risk of endotoxin shock because the endotoxin levels are vastly lower than many other gram-negative vaccines.

Vaccine handling

Sometimes the way producers handle vaccines can increase endotoxin levels. Here are a couple of tips for proper handling:


  • Don’t shake. Roll. Often, the first thing producers do when they get a vaccine or even an antibiotic is shake the bottle to mix the contents. In old-school products like penicillin, this was common practice to ensure contents of the bottle were mixed together. However, vigorous shaking can break open cell walls and release endotoxins. Instead, gently roll the bottle to combine ingredients if any precipitate is at the bottom of the bottle.

  • Don’t freeze. The same issue related to breaking cells open occurs when vaccines freeze. Ice crystals formed inside the cell have very sharp edges. During the freezing and thawing process, the ice crystals break open cells and can release endotoxins in the vaccine. It’s OK to cool the vaccine, but don’t let it freeze.

o Remember the environment where the refrigerator is located, especially in cold climates where refrigerators could be in unheated shops. When the temperature falls to well below freezing, the contents in the refrigerator will drop that low as well, increasing the risk of a refrigerated vaccine actually unintentionally freezing.

  • Have protection ready. To treat an allergic response, work with your veterinarian to develop a treatment plan in the case of vaccine-associated reactions. It is a good idea to have epinephrine or other products prescribed by your veterinarian readily available to administer should an animal have an adverse reaction.

The industry has learned a lot about how bacteria cause disease. The manufacturing process for vaccines has evolved alongside the bacterial changes to keep up with prevention mechanisms that help cattle avoid disease. In addition to beneficial manufacturing practices, the right vaccine handling and administration techniques can help as well. To discuss questions about leukotoxins and endotoxins, and vaccines to help avoid these negative impacts, consult with your herd veterinarian.  end mark

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Scott Smith
  • Scott Smith

  • Veterinarian
  • Elanco Animal Health
  • Email Scott Smith