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What is a Vaccine?

By: Dr. Dawn Ruben

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Our world is full of many different forms of life. Some of the more potentially dangerous creatures for pets include parasites, bacteria and viruses. In response to the severe and devastating illnesses or even fatalities that these creatures can cause, researchers and scientists have been working to find ways to eliminate them. Medications were developed to treat many parasite infections. Antibiotics were discovered to treat bacterial infections but the effective treatment of viral infections still eludes us. So far, the best we have been able to do is prevent viral infections, as well as some bacterial and rickettsial infections, through the use of vaccinations.

Vaccinations are the introduction of vaccine into the body to produce immunity to a specific disease. The term vaccination comes from the Latin vacca or cow, and was coined when the first inoculations were given with organisms that caused the mild disease cowpox to produce immunity against smallpox.

For centuries, the smallpox virus caused serious, debilitating illness in people. Once someone became infected, there was nothing that could be done. In the late 1700s, Edward Jenner noticed that milkmaids who developed the mild and temporary cowpox virus did not become infected with smallpox. As an experiment, he intentionally infected people with the cowpox virus, also known as vaccinia. As with the milkmaids, these people did not get smallpox. The procedure of using a similar substance to prevent viral infection became known as vaccination, as homage to the vaccinia disease, which started it all.

Have you ever wondered why you get chicken pox once and are considered immune for life but you can get the influenza virus year after year? The reason for this is directly related to your immune system's ability to recognize, detect and destroy previous invaders. The chicken pox virus doesn't change, so your body can recognize it. The flu virus mutates nearly every year and each mutation is considered a new virus. This is the principle behind vaccinations.

A virus is a packet of genetic material, often DNA, surrounded by a viral envelope or membrane. This virus is quite fragile when outside the body but is very damaging when allowed to thrive inside a body. Once it enters a body, it attaches to certain cells and inserts its DNA into the cell. This DNA takes over the function of the cell and begins to rapidly reproduce itself. In a short time, the cell becomes so full of viral particles that it bursts and releases more viruses throughout the body. Each of these then repeats the process until the body is overwhelmed with virus and illness develops.

As the body undergoes this attack by the virus, the immune system begins to realize there is an invader present. Since the immune system has been basically ambushed and has never seen this invader before, the immune system is not prepared, although it makes a valiant attempt to destroy the virus. In time, the immune system often destroys the virus and the body recovers from the illness. Unfortunately, there are some viruses that never leave the body and ultimately cause death.

In the case of viral infections that result in recovery, the immune system is now prepared and memory cells circulate through the body, waiting for that virus to try to invade again. If and when this occurs, the immune system is ready and the virus is destroyed before it is ever allowed to get a foothold.

This is how vaccines work: A modified virus is injected into the body. This altered virus is unable to cause illness but it is recognized by the body as a viral invader. Sometimes, vaccines are made from mutated viruses, sometimes by killed viruses. Newer recombinant vaccines are being developed that work with the viral DNA.

Once the modified virus is injected into the body, the immune system responds and mounts an attack. Since the virus is unable to replicate and cause illness, the immune response quickly subsides, although memory cells continue to circulate. If the real live virus is encountered, the immune system is primed and ready for attack. The virus is destroyed before ever causing illness.

The effects of vaccines vary. Some last for years and others for just a few months. This is the reason that repeated vaccinations are needed. Vaccines are helpful in preventing some viral diseases but they are not foolproof. Some vaccines only provide partial immunity and some vaccines fail to elicit an immune response. For this reason, just because your pet was vaccinated does not guarantee complete protection from the virus.

Now that you know what a vaccine is and how it works, you can understand the importance, as well as the limitations, of this important part of preventative medicine. Due to the amazing courage and foresight of one man in 1798 who intentionally infected people with one virus to protect against another, many people and animals throughout the world have been protected and saved from certain viral, bacterial and even rickettsial infections.

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