proteins on the virus and its specific
receptors on the host cell. This is the first step of
If the virus does not attach, infection does not occur.
|Entry and Uncoating||Uncoating of the virus usually occurs in vesicles with then release the genome.|
usually replicate in
the cytoplasm and DNA virus replicate in the nucleas of the host
DNA viruses insert their genetic material right into the host cell’s DNA. The RNA virus must first make DNA from the
RNA using the host cell’s “machinery” before it can insert its DNA into the host cell’s. Once the DNA has been inserted it is ready to be replicated.1
and capsids (protein
coat) are synthesized and assembled.
The virus is released from the cell via lysis of the cell or budding
off of the cell. 3
1) Modified live virus vaccines (MLV) (Attenuated):
This type of vaccine contains living viral organisms that have gone through a process to render them less virulent in order to not cause disease in the vaccinated animal. The steps to making a MLV include collecting the virus from a diseased animal, grow that virus in a series of abnormal host cells so that it changes or attenuates. After several passages through the abnormal cells, the less virulent virus is administered back to an animal to see if it still has the potential to cause disease. If the virus does not cause disease, the vaccine manufacturer must check to see if it is still capable of causing an animal to create antibodies to it. If both of these criteria are met, then the vaccine should be successful pending clinical trials.4 It is this type of vaccine that requires reconstitution with an approved liquid, usually sterile saline, in order to administer it to the animal.15
2) Inactivated or killed vaccines
This type of vaccine is easier to develop because virulence after growth is not a problem as a virus is collected directly from an outbreak and inactivated so that it no longer has the capability to cause disease. It is inactivated by chemical physical methods, most commonly by using formalin and ultraviolet light respectively. The major concern when producing this type is that there may be a loss of epitopes. This loss may not allow the animal to mount the appropriate immune response and may be the reason behind the decreased efficacy compared to the MLV vaccine. 4 Adjuvant is frequently added to this type of vaccination to heighten the immune response and to hold the killed virus in the injection site.15
3) Genetically Altered vaccines
This type of vaccine is made by genetically altering the virus. This is usually accomplished through generating mutations to decrease virulence or viral growth characteristics. 4 A common method is to grow the virus at an ambient temperature that is outside of the normal body temperature range of the host. This causes the virus to mutate so that it grows best in that temperature, and not within the host’s body. 9 Therefore, the virus is still live, it is just modified. 4
4) Autogenous VaccinesThis type of vaccine is made privately for use by veterinarians and cattle owners. These vaccines do not fall under federal guidelines, therefore they can not be sold to other farms. The viruses for these vaccines are usually derived from specific cultures submitted from a particular farm in order to combat a pathogen that is not able to be controlled with conventional vaccinations. It is important to know that these vaccines are not tested for safety or efficacy like the ones mentioned above.