Vaccines contain antigens from viruses, bacteria, bacterial toxins, or parasites. They are given to pigs, usually by injection, to stimulate an immune response which will protect the pigs against later natural infection with the organism from which the vaccine was derived. Most stimulate both a humoral response and a cell-mediated response.

Vaccines can be live, containing living organisms which will multiply in the pig, or inactivated, containing only killed organisms which will not multiply in the pig.

In live vaccines the organisms has usually been attenuated (i.e. its virulence has been reduced) so that although it will multiply in the pig it will not normally cause any cause disease. Examples are the PRRS vaccine (although some may cause mild reactions), aujeszky's disease (pseudorabies) vaccines and classical swine fever vaccines. Live attenuated vaccines have the advantage that because they multiply in the pig they give a bigger antigenic stimulus resulting in stronger longer-lasting immunity. They have the disadvantage that they may die in wrong storage conditions (e.g. heat) or during dosing (e.g. by exposure to antiseptics or disinfectants) and are then useless. It is also important that they are stable and not able to return to full virulence.

Inactivated (dead) vaccines may contain whole organisms, antigenic parts of organisms or antigens which have been synthesised chemically. An example of a commonly used whole organism vaccine is the erysipelas vaccine. (In North America such vaccines are often called Bacterins).

For example : - Erysipelas vaccine

This is made by growing the erysipelas bacteria in a liquid nutrient broth (several strains may be used).

1. The bacteria are then killed.
2. A liquid or adjuvant is added to the bacterial suspension.
3. This produces the vaccine.
4. A predetermined number of bacteria are injected into the pig. The first dose (usually 2ml).
5. A 2nd dose is required to complete the immune response, usually given 14 to 24 days after the first.
6. 7 days after the second dose the pig is protected.

Synthesised antigen vaccines are still largely in the experimental stage.

The immunity produced by inactivated vaccines can be enhanced by adding substances or adjuvants such as aluminium hydroxide or certain types of oil. You should take care, however, if you use vaccines with oily adjuvants because they can cause serious local reactions if you accidentally inject yourself, e.g. your hand.

Inactivated vaccines may also contain toxins which have been modified so that they still stimulate an immune response but are no longer toxic to the animal. Toxins which have been modified in this way are called toxoids. The classic vaccine of this type is the tetanus toxoid which is used commonly in horses but rarely in pigs. In pigs, some of the E. coli vaccines against piglet diarrhoea and the clostridial vaccines against piglet dysentery also contain toxoids.

Live vaccines are usually ones where the gene for the actual production of disease is deleted (gene deleted vaccines). The vaccine response can be differentiated from the actual disease and thus carrier animals removed. An example would be Aujeszky's disease or Pseudorabies vaccines.

Autogenous vaccines

Autogenous vaccines are bacterial vaccines that are manufactured from the specific pathogenic bacteria isolated from the diseased pig. They are usually made under a licence for use only on that farm. You should consult with your veterinarian. These are available from Salus (QP) Ltd.. They can be useful when serious disease outbreaks occur and standard commercial vaccines are not available.

Such vaccines could be made from most bacteria including :-

• Actinobacillus pleuropneumoniae
• E. coli
• Haemophilus parasuis
• Pasteurella
• Salmonella
• Streptococcus suis
• Staphylococcus hyicus (Greasy pig disease)

One drawback to vaccinating a herd is that you cannot then use blood tests to check whether the organism is present in the herd or not. All the pigs will test positive which has obvious implications for an eradication programme based on blood tests, for example the eradication of swine fever or aujeszky's disease (pseudorabies). To get over this, gene-deleted vaccines have been developed. A part of the organism's gene which codes for an antigen has been removed so that when the organism multiplies in the pig it does not stimulate antibodies against that antigen. Special blood tests can then distinguish between the array of disease antibodies and those stimulated by the vaccine. A new generation of such gene manipulated vaccines, and possibly also synthetic polypeptide vaccines, can be anticipated.

Autogenous vaccines are those prepared with infectious pathogens from the herd which is to be vaccinated. The causal organisms has to be isolated, grown up, killed, and made into a safe vaccine form. Autogenous vaccines may be useful when serious disease outbreaks occur and standard commercial vaccines are not available.

Vaccine usage

Fig.3-5 lists the pig diseases for which vaccines are available. This list is not exhaustive and some vaccines will be available in some countries and not in others. However they are used in most countries both to protect against disease and to assist in eradication programmes. Some examples of commercial vaccines available are shown in chapter 4 these are but a few of the many available.

Vaccines commonly used on pig farms throughout the world include erysipelas, parvovirus infection (SMEDI syndrome), E. coli diarrhoea, clostridial dysentery of piglets, enzootic pneumonia caused by Mycoplasma hyopneumoniae, necrotic pleuropneumonia caused by Actinobacillus pleuropneumoniae and atrophic rhinitis caused by toxigenic Pasteurella multocida. In many countries, vaccines against diseases, such as, salmonellosis, PRRS and TGE are also used depending on commercial availability.

The effectiveness of vaccines

This varies, because of the need to stimulate mucosal immunity locally. As mentioned earlier, vaccines given by injection against respiratory and intestinal disease are generally not as effective as those against systemic or generalised diseases. An exception to this is the vaccine for enzootic pneumonia (M. hyopneumoniae) because it stimulates cell-mediated immunity. If, however, they are fed or sprayed into the upper respiratory tract they may produce a stronger local immunity. The vaccine against piglet dysentery is a toxoid and if given routinely to sows in adequate doses is usually reasonably effective in providing passive protection via the colostrum.

Sometimes vaccines do not work particularly well on a farm and in such cases the following possibilities need to be considered:

• The vaccine was contaminated.
• The vaccine was not capable of producing the required immunity.
• The pig was already incubating the disease when it was vaccinated.
• The vaccine had been incorrectly stored. High temperatures reduce the effectiveness. (Always keep vaccines in a refrigerator but do not freeze).
• The vaccine had been exposed to sunlight.
• The vaccine had gone out of date.
• The needle and syringe were dirty or faulty.
• Chemical sterilisation destroyed the vaccine.
• The animal had inadvertently missed being vaccinated. This is particularly common with parvovirus vaccination in the gilt.
• Vaccine response was poor because there was maternal antibody present.
• The vaccine was deposited in fat and was not absorbed. Faulty injection techniques

The management of vaccines

• Check the expiry date.
• Store in a fridge.
• Monitor the temperature daily with a max/min thermometer. Freezing destroys vaccines.
• Don't overstock the fridge.
• Don't store food in the fridge.
• Follow the instructions.
• Ideally use a fresh needle for each pig but change at least every 5 pigs.
• Do not mix vaccines or medicines.
• Dispose needles in a sharps box.
• Clean out syringes immediately after use.
• Only use vaccines licensed in your country.
• Clean bottle tops before and after use.