Dr. James Evermann
Lecture 10: Basis for Immune Resistance in Livestock (Principles
of Vaccination)
The Purpose/Objective of Vaccination is to Stimulate a Protective Immune
Response for the Longest Period of Time
I emphasize protective immune response because anything you inoculate into an
animal’s body will elicit an immune response.
Successful Vaccination is Dependent Upon
Types of vaccines (Active Immunization)
Comparison
Between Modified Live and Killed Vaccines (See Table 1)
The modified-live products provide longer lasting and more immunity. Complete
immunity means simulation of both T cytotoxic cells and B cells. MLV
vaccines do not require multiple vaccinations to stimulate memory. Usually the administration
of one
modified-live vaccine, if given at the correct time, will stimulate memory cells.
MLV vaccines do not require revaccination or require fewer revaccinations during the life of
the animal.
Killed products result in short-lived systemic immunity, anywhere between one and two years or less. Killed vaccines only stimulate half of the immune response. Killed vaccines stimulate primarily B cells resulting in high levels of antibodies but not cellular immunity. Killed vaccines require multiple vaccinations for immunity. You give the first inoculation, then you wait a period of time, anywhere between two and six weeks, and then give a booster. Killed vaccines may require annual re vaccination for the rest of the animal’s life. Killed vaccines require revaccination to ensure immunologic memory. Killed vaccines may contain adjuvants to elicit a greater immune response. Adjuvants are usually aluminum derivatives and may cause adverse reactions. The intramuscular injection of a killed vaccine that contains an adjuvant may cause a granuloma to develop at the injection site. That is a vaccination site reaction. Killed vaccines are safer; they cannot cause disease, even in immunologically compromised animals. Normally where you will use killed vaccines is in pregnant animals. MLV vaccines might cause abortion. Recall that pregnant aniamls have a depressed immune response; primarily T-cell response is depressed. There are advantages and disadvantages of both MLV and killed vaccines.
How
to Determine What Type of Vaccines are Being Used in Your Animals--Review
the package inserts.
An example vaccine is Bovi-shield. It has IBR, BVD, BRS vaccine virus in it. It
also has Leptospira in it. The package insert tells you that the viruses are
modified-live, plus it tells you there is a liquid portion which is the
Leptospira bacterin. This is the killed portion. Whenever you see the word bacterin it means killed.
This is a vaccine that has a modified-live component and a killed component in the
same product. The animal will develop better immunity to the viruses
(MLV) than to Leptospira (killed).
Another type of immunization product is a toxoid. Clostridium type C and D and tetanus are toxoids. Toxoids are killed products. Toxoids are inactivated toxins from a bacteria. Inoculate toxoids into animals and they stimulate a B cell response resulting in high levels of antibodies. The CMI response is not a significant factor in Clostridial diseases. Don’t let me give you the impression that all killed products are bad. It depends on the agent. Killed vaccines against Leptospira are not very good vaccines. Clostridia perfringens toxoid is a very good vaccine.
There are also Clostridium perfringens type C and D antitoxins. Antitoxins are usually made in horses or sheep. The toxoids are given to horses and sheep who then make lots of antibodies which are the antitoxin. Antitoxin is pre-formed antibody so when you give antitoxin to an animal, you are giving them a form of passive immunization. It takes 10 to 14 days for an animal to develop an acquired immune response after receiving the toxoid but the response to antitoxin is immediate because it is pre-formed antibody. The antitoxin provides immediate protection. If you suspect an animal is developing toxemia, you can give an antitoxin immediately; subcutaneously or even intravenously to get immediate protection.
To clear up any confusion: toxoid acts as an antigen to stimulate acquired immunity with a 10 to 14 day delay. Antitoxin is pre-formed antibody created in another species that will provide immediate protection when administered.
It is important to read the labels. You’d be surprised how many people give antitoxin, thinking they are giving a toxoid or vice versa. The other important thing is that antitoxin is more expensive than toxoid.
Genecol is an antitoxin. Genecol is made with monoclonal antibodies. The antibody is specifically directed against a specific epitope on the surface of an E. coli bacteria. Genecol provides passive immunity as you are administering preformed antibodies for immediate protection.
Vaccination Failure – Some Reasons
Passive Immunization is the transfer of antibodies from a resistant (immune) animal to a susceptible (non-immune) animal
Advantages and Disadvantages of Passive Immunity
Advantages: provides for immediate protection against cell-free infections and toxins
Disadvantages of passive immunity
Questions to Ask Regarding Vaccines Prior to Use
1. Are they safe?
2. What is the duration of protection? 4 months? 1 year? 3 years?
Vaccine companies will have on their inserts to vaccinate twice a year or annually. They say that for everything. Frequently they say annual boosters are required. Now that is not completely true. That is why you have to ask questions. They are going to try to sell you products. Your business is to protect the animals with the product that they sell to you. An example of a short lived vaccine that requires boostering is Leptospirosis. A vaccine that you might have to administer annually is IBR in cattle, or equine Mito. A vaccine you have to give every 3 years is BVD virus if you use a modified-live vaccine. The frequency of vaccination is dependent upon the efficacy of the vaccine and upon stimulating the correct arm of the immune response.
3. What is the percent of protection from infections the animal will come in contact
with 50%? 75%? 90%.?
Remember: No vaccine is 100% effective
It is important to reduce the infectious agent in the environment as much as possible
Keep at-risk animals away from other animals as much as possible
Question: Is there a limit on memory?
Answer: No, once you have memory that population retains it. That is the beauty of the acquired immune response. That is probably why
as a child you can immunize once or twice and you have that memory for your whole life.
Question: What’s the duration of the lepto vaccine?
Answer: The duration of protection is only 4 months. The degree of protection is only 50%.
So why would you vaccinate? You are trying to protect as many animals as you have the
capability of protecting. It is not your problem that you don’t have a product out
there that you can use that will give you three years of protection. They are working on a
product. You just have to use what the vaccine companies make available. Some people would like to
stop vaccinating for lepto. I am not advocating that. What I am trying to advocate is that
you be sure you recognize that you are only getting marginal protection from some products
and you have to give them more frequently. Until biotechnology develops a new vaccine.
That is a question we get asked every day.
Why vaccinate if it is such a poor vaccine?
Figure 1. Comparison of the Advantages and Disadvantages of Modified-Live and Killed
(Inactivated) Vaccines (From
Larson and Bradley, 1996)