Vaccination of farm animals
What diseases can vaccination prevent?
Vaccination protects hundreds of millions of animals worldwide from disease and
possibly death.
Animals, just like humans, suffer from a range of infectious diseases. As veterinary
medicine has advanced, prevention of disease has become a priority as healthy food comes
from healthy animals. One of the best means of preventing disease is by creating immunity
in the animal. This is usually achieved by vaccination.
The principle of vaccination has been established for over 200 years. Since those early
days, enormous strides have been made in the development of vaccines, which have helped to
prevent and in some cases eliminate many diseases in humans, farm animals and the family
pet.
Animals which develop disease often require treatment with medicines so vaccination
helps reduce the amount of pharmaceuticals used in the treatment of animals. Vaccination
presents no hazard to consumers of produce from vaccinated animals.
Not all animals need every vaccine. Some, like clostridial disease prevention, are
basically routine, just like childhood vaccination programmes. The vaccination programme
chosen for farm animals depends on the management system, the location of the farm and the
history of the herd or flock (and whether or not a disease is likely to be encountered).
Most farm animals are young, and these animals (just like children) are often more
susceptible to infection. So, for example, calves often need to be protected by
vaccination against respiratory disease. Some of the diseases that can be prevented are
shown below.
SPECIES DISEASES CONTROLLED BY VACCINES IN THE UK
Cattle Blackleg, tetanus, 'husk' (lungworm disease), rotavirus,
infectious bovine rhinotracheictis (IBR), respiratory syncytial virus, pasteurellosis,
enteritis, leptospirosis, mastitis, ringworm, BVD, PI3, coronavirus, salmonella, E Coli.
Sheep (& goats)Clostridial diseases (8 different species
including tetanus), pasteurellosis, ovine abortion (chlamydiosis and toxoplasmosis),
louping ill, contagious pustular dermatitis (orf), footrot
Pigs Erysipelas, parvovirus, colibacillosis, clostridial disease,
atrophic rhinitis, enteritis, porcine pneumonia, PRRS
Poultry Avian coccidiosis, avian encephalomyelitis, avian infectious
bronchitis, avian infectious bursal disease, avian reovirus, chicken anaemia virus, duck
virus enteritis, egg drop syndrome 1976, erysipelas, infectious laryngotracheitis, Marek's
disease, Newcastle disease, pasteurellosis, post-natal colibacillosis, salmonellosis,
swollen head syndrome, turkey haemorrhagic enteritis, turkey rhinotracheitis
Fish Enteric redmouth disease, furunculosis, vibriosis (vibrio
anguillarum, vibrio salmonicida and Vibrio viscosus (now named moratella viscosus))
How do vaccines work?
Vaccines stimulate the body to produce its own defence against infection. Mimicking
what happens when an animal has been exposed to disease, the body and its defensive system
will "remember" the identity of the invading organisms. So, when the animal
comes into contact with a disease, its body is ready to fight it and the animal will not
fall ill and suffer. This protects the individual animal and because this animal will not
develop the disease and will not become infective, it will also help protect the
population from the disease - "herd immunity".
A vaccine may consist of live but attenuated viruses or bacteria, or killed
(inactivated) viruses or bacteria, or parts of them.
"Killed" or inactivated vaccines are prepared from killed
organisms or fractions of the organism incapable of causing disease. They
generally provide a relatively short period of immunity.
In attenuated vaccines, the immunising agent (antigen) is an organism such as a virus,
bacterium or parasite, which has been developed to stimulate the production of the
appropriate antibodies without causing the disease. Live vaccines are particularly
effective in providing long-term protection, because they are a more powerful stimulus to
the immune system. They are also more versatile in their route of administration.
Biotechnology can provide vaccines for diseases which cannot be controlled by
conventional vaccine technology and create more specific, better defined products with
even greater safety and efficacy.
Vaccination can be by a wide variety of routes: through water, baits, airspray, eye
inoculation, intranasally, orally or using the more classical injection.
Achieving initial immunity may require more than one injection. Once established, this
can be boosted by subsequent vaccination, as required. Modern vaccine research and
technology means that some vaccines can actively protect against a variety of diseases, in
a single product. These are called multivalent vaccines and using these reduces the number
of injections, broadens disease protection - and helps reduce costs to the farmer.
How are vaccines controlled?
In the early days vaccination was risky. Vaccines were crude, using cultures or
suspensions of diseased material treated to reduce infectivity. Some of the impurities in
the injection also produced unwanted side effects.
But now, through much development work by vaccine manufacturers, risk from the
immunising agent has been decreased while its efficiency has been increased. Present day
vaccines are safe and effective, having been designed specifically to avoid side effects
and any remaining ability to cause disease. The advent of biotechnology has opened new
doors to even more exciting developments.
Whether for disease prevention or treatment, the veterinarian, the animal owner and the
public all have a right to expect that the research, development and bringing to market of
animal medicines is reliably based on the triple standards of quality, safety and
efficacy. The extremely stringent requirements for product registration set down in
European law reflect this. If these requirements are not met, a vaccine will not be
allowed on the market. Careful monitoring and review of products and disease patterns
ensure that once on the market, vaccines remain safe and effective. There are very strict
quality control processes to guarantee the safety and efficacy of each dose of vaccine.
Today's vaccines are very effective and have a remarkably high safety record. Millions
of doses are used annually in the UK alone. The use of vaccines has brought significant
levels of control against diseases that farm animals previously suffered.
There is a constant quest for new preventive measures to meet the changing challenges
to animal health. Indeed the diseases threatening animals evolve themselves; just like
with human influenza, when the medical profession needs to be prepared with a vaccine to
counter the particular strain that is prevalent at the time.
So the work goes on, as animal medicine companies continue to look for new vaccines to
help farmers protect their animals. Vaccines, when available, provide a safe and effective
answer to many animal welfare problems and represent an important field of ongoing
research.
CASE STUDIES
Case Study 1: Clostridial disease in sheep and lambs
Clostridia are soil dwelling bacteria that can enter sheep even as they graze. They
pose a constant and serious threat to flock health: before the introduction of vaccines
they were causing losses of up to 50% of lambs. The potential for this remains. Onset is
sudden, death is rapid and there is often no opportunity for successful treatment - flock
vaccination provides the only method of control.
Clostridial vaccine manufacturers report that farmers who make mistakes in their
vaccination regime - or are prevented by organic production contracts from using the
vaccines routinely - can find that sudden and large-scale losses with clostridial diseases
such as pulpy kidney or braxy occur.
Luckily clostridial vaccines make this scenario much less common.
Case Study 2: Aujeszky's disease (pseudorabies)
A serious, frequently fatal, viral infection in pigs, Aujeszky's was a disease that
European vets and farmers were determined to eradicate. Pigs that do recover can still
carry infection, acting as a risk to others. Because they have had the disease, they bear
residual antibodies. Early vaccines contributed to a reduction in disease. However they
left vaccinated pigs with antibodies indistinguishable from those in an animal which had
recovered from the disease but remained a carrier. So it was impossible to distinguish a
vaccinated animal from an infected one.
One option to eradicate the disease involved removing all pigs with antibodies - this
was actually used in Great Britain. But the vaccine was redesigned to remove from the
vaccine virus the 'gene message' for a non-essential glycoprotein, which is found in all
known infective strains of the virus. In parallel, a serological test was developed to
accompany this. Now vaccinated animals could be differentiated from those naturally
infected. This meant that there was no longer a need to slaughter all pigs with
antibodies, and vaccination could play a role in the eradication schemes.
Case Study 3: Newcastle Disease
Newcastle disease is caused by a highly contagious virus that not only affects poultry
(chickens in particular) but also can exist in carrier state in wild birds. Although
endemic in many countries of the world, the UK has been free of the disease for some
years. There is no treatment, but the UK's disease free status is maintained by routine
vaccination, usually via the drinking water or by coarse spray, although sometimes
intranasal or intraocular vaccines are given.
Case Study 4: Leptospirosis
Leptospirosis occurs in 60% of UK dairy herds, is an important bacterial disease of
cattle and can lead to significant economic losses through symptoms as varied as abortion,
reproductive failure and loss of milk production. Leptospirosis can also be transmitted
from cows to humans where it can cause a flu-like syndrome. Vaccination against
leptospirosis will protect cattle from developing the disease and thus economic benefits
for the farmer. Vaccination also has human health benefits as it will prevent transmission
to farm workers.
Case Study 5: Bovine Respiratory Disease
Calf pneumonia remains one of the most important causes of economic loss to cattle
farmers as well as being a cause of suffering to the affected animals. The total cost to
farmers in the UK has been estimated to be over £80 million.
Calves suffering from pneumonia can stop eating, lose weight, suffer pain, and in some
cases may die. They also require extra nursing and treatment with antibiotics and some
cases anti-inflammatory medicines. Even after they recover affected calves are often slow
to put on weight and grow properly.
There are a number of triggers of calf pneumonia including management and other facts
but the actual causes are a variety of bacteria, viruses and mycoplasmas. Vaccines are now
available which will provide effective control of the most common bacterial and viral
causes of calf pneumonia. These vaccines are given before high-risk times such as housing
and the winter months. This means that there is an improvement in animal welfare as
pneumonia is an important cause of suffering in animals, as well as obvious economic
benefits for the farmer since the total cost of pneumonia can reach in the order of £80
per affected calf.
Case study 6: Trout Vaccination
Enteric Red Mouth caused by Yersinia ruckeri first entered British trout farming in
1982/3. From the first point of entry it spread rapidly around the country and became an
endemic problem causing up to 20 percent mortality even with regular treatments. Immersion
vaccination was introduced in 1983 and the severity of the disease was contained but
problems persisted particularly as the intensity of production increased. In recent years
an oral booster vaccine has been introduced which has enabled trout farmers to produce
their fish without significant antibiotic intervention.
Case Study 7: Salmon Vaccination
Furunculosis has been present in wild salmon since the 1800's. With the advent of
salmon farming the disease became a serious problem causing significant losses. In the
late 1980's the viability of the industry was threatened by this endemic disease problem.
The industry invested very heavily with government backing and developed a unique vaccine
based upon special antigens linked to the infection mechanisms of the bacteria causing the
disease. This vaccine was introduced in the early 1990's and in conjunction with good
husbandry measures resulted in a dramatic turn around. Mortalities to the disease are now
almost unknown and welfare of the farmed salmon is greatly enhanced.
September 2002 |
