REASONS FOR VACCINE FAILURE IN LIVESTOCKS

Vaccines are like a training course for the immune system. They prepare the body to fight disease without exposing it to disease symptoms.

When foreign invaders such as bacteria or viruses enter the body, immune cells called lymphocytes respond by producing antibodies, which are protein molecules. These antibodies fight the invader known as an antigen and protect against further infection. According to the Centers for Disease Control and Prevention (CDC), a healthy individual can produce millions of antibodies a day, fighting infection so efficiently that people never even know they were exposed to an antigen.

Unfortunately, the first time the body faces a particular invader, it can take several days to ramp up this antibody response. For really nasty antigens like the measles virus or whooping cough bacteria, a few days is too long. The infection can spread and kill the person before the immune system can fight back.

That’s where vaccines come in .vaccines are made of dead or weakened antigens. They can’t cause an infection, but the immune system still sees them as an enemy and produces antibodies in response. After the threat has passed, many of the antibodies will break down, but immune cells called memory cells remain in the body.

When the body encounters that antigen again, the memory cells produce antibodies fast and strike down the invader before it’s too late.

Vaccines also work on a community level. Some people/animal can’t be vaccinated, either because they are too young, or because their immune systems are too weak, according to the CDC. But if everyone around them is vaccinated, unvaccinated people/animal are protected by something called herd immunity. In other words, they’re unlikely to even come in contact with the disease, so they probably won’t get sick. When it comes to vaccines, sometimes it can pay to follow the crowd.

Today, there are five main types of vaccines. Live, attenuated vaccines fight viruses and contain a weakened version of the living virus (e.g., measles-mumps-rubella and varicella vaccine). Inactivated vaccines also fight viruses and contain the killed virus (e.g., polio vaccines). Toxoid vaccines prevent diseases caused by bacteria that produce toxins in the body and contain weakened toxins (e.g., diphtheria and tetanus vaccine). Subunit vaccines include only the essential antigens of the virus or bacteria (e.g. whooping cough vaccine). Conjugate vaccines fight a different type of bacteria which have antigens with an outer coating of sugar-like substances (polysaccharides) that “hide” the antigen from the child’s immature immune system; the vaccine connects (conjugates) the polysaccharides to antigens, so the immune system can react.

There are several variables in the vaccination equation: the people, the animals, and the vaccine. All these variables work together to create immunity to diseases in our livestock. With so many variables, things can sometimes go wrong and the animal fails to develop the desired immune response. Put another way; the animal can get sick even though it was vaccinated.

There are several reasons for vaccine failure. People are ultimately responsible for ensuring that all variables are correct, but here are some big mistakes we sometimes make:

• Giving the wrong sized dose – carefully read and follow all label instructions.

• Incorrect booster timing – schedule time to administer the initial vaccination only when you know you can booster it in a timely manner. Many vaccines require a booster 2-3 weeks after the initial dose. Be sure to read the label.

• Incorrect vaccine injection site on the animal – some vaccines are supposed to go in the muscle; some are supposed to go under the skin. Again read the label instructions and follow them.

The animal is very important to the equation as well. Animals that are thin, sick, or animals under stress can fail to develop the desired response to vaccines. Cattle that are lacking in nutrients or are diverting nutrients to other physical needs may not develop the desired immunity. Young animals that still have residual passive immunity acquired from the mother since its birth, also may not develop lasting immunity. Check with your local vet for a livestock vaccination schedule.

The vaccine itself is important too, of course. Vaccines should be stored at the proper temperature. Check your refrigerator that you store vaccines in to make sure it maintains a constant temperature of 35-45 degrees F. Vaccines are sensitive to heat and freezing temperatures. Don’t store excess or unused, vaccine. Use all vaccine immediately and discard any unused vaccine. Be sure to use vaccines before the expiration date. Expired vaccines may become ineffective causing the animal to fail to develop immunity.

The take home message is always read label instructions carefully! Store and administer vaccinations according to the label instructions and recommended schedules, and maintain a healthy herd by following recommended best management practices.

Points to be noted during vaccination

• Animals should be in good health at the time of vaccination.

• The cold chain of the vaccines wherever prescribed should be maintained till the time of administration to the animal.

• The manufacturers’ instruction on the route and dosage should be strictly followed.

• A minimum vaccination coverage of 80% of population is required for proper control of the disease.

• It is beneficial to deworm the animals 2-3 weeks before vaccination is carried out for better immune response.

• Vaccination should be carried out at least a month prior to the likely occurrence of the disease.

• Vaccination of animals in advanced pregnancy may be avoided even though in most cases nothing untoward may happen.

PRECAUTION FOR USE OF VACCINES:

1. Vaccination should not be done when the animals are in stress period particularly few days before or after the debeaking, transfer shifting and grading because negative Immuno-modulation occur in these conditions, which ends with low level of active immunity.

2. Vaccinating the animals during extreme weather is not wise, because heat stress on one end affect the bird and on other end affects the vaccine due to high environment temperature.

3. In poultry, Metal drinkers and containers are supposed to avoid for mixing of vaccines, as the metal ions and metals react with the vaccines to inactivate the live vaccines offered through the drinking water. Aluminum and brass containers are not recommended due to their maximum inactivation properties. It is recommended to use the PVC or Plastic containers.

4. Sterile diluents for reconstitution of injectable vaccines should be preferably of the same company as the different sources are not synchronized with the optimal requirements.

5. The vaccines should be used as soon as possible they are reconstituted. Delay to offer by the farmers or consumption by the birds/animals, leads to temporal decrease in the vaccine titers.

6. In poultry, In those areas where the salt concentration is too high preferably, the birds/animals should be vaccinated through injection or eye, nose or mouth dropping.

• In poultry, Addition of skim milk is recommended, as the particles of vaccines are distributed well in the water. In case milk with fat or fresh milk is used it make aggregates on or near the surface of the container (due to light weight fat) where the vaccine is mixed, leading to develop different concentration zones in the container

Common reasons for vaccination failure

• Lack of maintenance of cold chain from the time of manufacture till vaccination.

• Poor immune response in weak and improperly fed animals.

• Lack of herd immunity due to only a few animals being vaccinated.

• Poor quality of vaccine – Quality will deteriorate if repeatedly thawed and cooled.

• Low efficiency or ineffective vaccine – May occur in case of strain variation (eg. FMD).

Vaccine Failure in LIVESTOCKS: Factors to Consider

Vaccination involves the administration of antigen to stimulate the immune system to produce specific antibodies against viral, bacterial, and protozoan diseases. Antigens or vaccine or vaccination itself does not produce immunity rather it is the animal’s immune system in general and immune cells in particular that provoke the immune response and present the antigen to T lymphocytes and by macrophages and from there it is expressed to B lymphocyte where the immune response is initiated in terms of antibodies.The successful vaccination is denoted by higher and stronger immunity. Vaccination does not guarantee that animals are protected. There are number of factors which may furnish the success of a vaccine.

Vaccines are products containing minimally harmful viral or bacterial antigens(surface proteins and sugars) similar to those contained on the surfaces of wild-typeinfectious-disease-causing organisms which, when administered to an animal, are designed to induce a protectiveimmune system response against disease-causing organisms that might infect that animal.

Sometimes, however, despite our best efforts, a vaccinated animal will develop signs of the disease that we are trying to protect it from. This is termed vaccination failureor failure of immunization.

Generally, it occurs because of one of two reasons:

1) The clinical disease is being caused by the vaccine itself (live vaccines only) OR

2) The clinical disease is being caused by a wild-type, infectious disease organism that has infected the animal from its local environment.

Clinical disease caused by the vaccine:

Live vaccines are functional, replicating strains of the exact same viruses and bacteria that we are trying to protect our pets from. They only differ from the wild-type disease causing agents in that they been specially ‘bred’ and selected for their avirulent properties (e.g. they might not replicate as quickly as the wild viruses or they might not access the host’s cells as well). Consequently, when live vaccines are manufactured and used correctly, it is very unlikely that they should ever cause disease in a normal animal with a normal immune system (even a naive immune system which has not yet been exposed to the vaccine viruses, like that found in our puppies at first vaccination)

In some cases, however, live avirulent vaccines can cause the diseases they are trying to prevent. This happens for the following reasons:

1) There has been a failure of quality control at the manufacturer and a virulent strainof virus has made it into the vaccine.

The effect of injecting a virulent strain ofvirus (e.g. parvo, distemper) is the same as if you had just taken a small puppyand let it lick up the poo from a dog with parvo! The animal will develop diseasebecause its immune system is naive and not able to cope with the virulence of the virus strain.

2) The vaccine was given by the wrong route.

The most notable occasion when this happensis with the injectable cat-flu vaccines. Live, injectable cat-flu vaccines are oftenmoderately virulent strains of virus. The main reason they do not normally inducedisease is that they are inoculated at a site that they do not normally grow well in(under the skin). If, however, they are accidentally inhaled (this can occur when a vaccineis drawn up and aerosolized in the cat’s presence), they will get accessto the cells of the respiratory tract (which is their preferred site for replicatingand causing disease). Cat-flu will result with all of the sneezing, fever, eye dischargeand nasal discharge associated with the condition.

3) Mild clinical disease is a known side effect of the vaccine route.

Sometimes, mild signs of the disease are common and accepted side effects of the vaccine. This is particularly true of the intranasal vaccines (kennel cough and cat flu intranasal spray vaccines): animals will often get mild signs of coughing, sneezingand watery eye and nose discharges after these vaccines. It is also a known side effect of the feline calicivirus injectable (sometimes kittens will show lamenessand fever after vaccination, a condition sometimes seen in the calicivirus disease).Generally, these mild side effects are self-limiting and do not need medication.

4) Vaccination of the pregnant animal with a live virus vaccine.

Foetuses are unprotected against live vaccineviruses (their immune systems are very immature) and many of the organisms willpreferentially replicate in the rapidly-dividing cells of the foetus. Damage tofetal cells can result in stillbirths, abortion, fetal abnormalities or puppies andkittens born with clinical disease. Well known examples of this: fetal kittens whosemother received a live panleukopenia vaccine can be born showing signs of anunderdeveloped cerebellum (they will tremor whenever they move).

5) Vaccination of neonatal (newly born) puppies and kittens that did not get theircolostrum with a live vaccine.

Although live vaccines are fine for usein animals over 4 weeks old (which have a functional, though naive immune system) and newborn animalsprotected by their mother’s colostrum, newborn animals (termed neonates) unprotected by maternal antibodies have a greatly reduced immune response (not much better than the late-stage fetus) and live vaccines may produce disease in them.

6) Vaccination of animals with a poor immune system.

Although live vaccines arenot as virulent as wild-type vaccines, they do replicate in cells and damage them(it just takes them longer). By the time they grow numerous enough to do any real harm,the immune system has generally come along to kill them off, thereby preventing vaccine-associateddisease and acquiring the needed immunity. If, however, the immune system response fails to ‘show up’, the live vaccine viruses will continue to replicate as the wild-types doand they will eventually produce symptoms of disease.

Situations where animals might have a poor immune system:

– Animals born with a bad immune system.

Some purebred dogs and cats (and other species) have a genetic predisposition to immunodeficiency (they lack parts of their immune system).

An example of this is CID (Combined Immuno Deficiency) in Arabian horses. These foals areborn with non-functional T cells and, as a result,not only do their T cells not work, but their B cells also can not be activated to make antibodies (immature B cells initially need T cells to activate them). They suffer froma lack of both humoral and cell-mediated immunity (see How Vaccines Work page for details on what these terms mean). Live vaccines would induce disease in these animalsand they often die young from overwhelming infection – they essentially have no immune system.

– Animals that acquired a bad immune system.

There are many diseases and drugs whichdamage (permanently or transiently) the immune system, making it inadequate to fight off wild-type diseases and live vaccine organisms. These include:

A) Radiation therapy – can destroy the bone marrow which makes most of the white cells.

B) Bone-marrow-invasive disease – diseases such as leukemia (bone marrow cancer can invade and destroy the bone marrow so that white blood cells can’t be made.

C) Bone-marrow-suppressive drugs – some medications stop the bone marrow making white cells. These include most chemotherapy drugs (e.g. vincristine, azathioprine, cyclophosphamide),corticosteroids (e.g. prednisolone) and long-term estrogen products in dogs (normally used to treat incontinence).It is a reason we don’t vaccinate dogs on immune suppressive drugs such as prednisolone.

D) Auto-immune diseases that kill the white blood cells in the blood or the cells in the bone-marrow that make them.

E) Viral diseases – FIV in cats (feline AIDS) kills off many of the T cells. Felineleukemia virus can result in auto-immune diseases (point D) and leukemia (point B).Canine and feline parvoviruses also damage the bone marrow during clinical illness (note that a veterinarian would never vaccinate a dog or cat this unwell).

F) Bone marrow suppression can occur in undesexed female ferrets (they get estrogen poisoning).This is why vets recommend desexing female ferrets.

– There are also some situations where the condition of the animal may induce hormonaland chemical changes in its body that might result in a poor immune system response anda potential for vaccine-induced disease signs. These include:

A) Excessive stress (including pregnancy) – natural cortisols produced during times of excessive, prolonged stress (we are not talking about the otherwise well, shivering chihuahua sitting on the consult table) will suppress the immune response to vaccination.

B) Very old animals – over time and age, the immune system of most animals starts todeteriorate. This can result in a subnormal immune response.

C) Fever – certain elements of the immune system do not work as effectively duringtimes of high body temperature.

D) Subnormal temperatures – as with fever, some immune cells do not work as wellwhen body temperatures are very low. It would be rare for vets to vaccinate a cold animal,however, one situation in which this could occur is when vaccines are given to animalsthat are under anaesthesia.

E) Severely malnourished animals – animals need nutrition for immune cells to replicateand for antibodies to be made.

Unwell animals that are already relatively immunosuppressed because their immune systemis invested in fighting another disease process can potentially develop vaccine-associatedinfections with live vaccines. The fact is, there are not enough immune cells to go around! Vaccination of unwell animals can result in live vaccines causing disease (e.g. dogs infected with nasty, wild-type parvo virus that are then vaccinated against distemper have been known to develop clinical distemper from the vaccine!). It can alsoresult in the pre-existing disease becoming worse (white blood cells abandon the initial area of disease to ‘fight the vaccine’, resulting in the initial disease becoming more severe). It is for this reason that vets do not vaccinate sick animals.

CONCLUSION:

• Commercial vaccines are safe and efficacious, regulated by various regulatory authorities. Proper storage, handling, transportation and administration are critical to their success. It is crucial to periodically train and evaluate vaccination crews and to avoid the loss of properly trained personnel in charge of vaccine administration. If there is a breakdown in the biosecurity program and a disease outbreak occurs, the vaccination programs must be adequate and effective to limit resulting losses. A thorough understanding of vaccine failure helps prevent such losses in the future. An enormous growth of poultry industry requires precise vaccination schedule and the perfect efficacy of vaccines administered. Proper care in vaccination efficiency is thus important by finding out the culprits and consequences.

Reference-On Request