In the popular lexicon, gone viral means spreading really fast, and most commonly the phrase is used to refer to spread of a video. The last few months have seen both videos and disease spread rapidly and cause great pain and destruction around the world. Farmers hear quite a bit about viruses because of the variety of viral diseases animals can suffer from. But, just exactly what is a virus anyway, and are viruses actually alive?
    Viruses are an inert complex of molecules. They cannot replicate on their own. They require the cells of other organisms to make their progeny for them. So, by most common definitions, they are not really alive. Yet they are known to infect all living organisms, not just animals, and a broad variety contribute to animal and human disease. There are so many different viruses in nature that most of them do not even have names. While the structure of viruses varies between viral groups, all viruses have an outer coat, or capsid, and genetic material, or genome, inside. Capsids are mostly made up of proteins. Enveloped viruses have an outer layer made up mostly of fats; the components of that layer may come from host cells. Coronaviruses are enveloped viruses. The type of capsid may be important when choosing a disinfectant to inactivate the virus, because some disinfectants work better on different capsid types.
    The viral genome is made up of either DNA or RNA. DNA and RNA exist in all living cells. RNA is kind of a single-stranded photocopy of DNA. RNA serves as a messenger between the genetic information coded in cellular DNA and the various cellular machinery that will begin the processes of performing the tasks coded by the DNA. Viral DNA or RNA is relatively simple, and typically only has coding for replication of the physical structure of the virus. Everything else needed for replication comes from the host.
    The first phase of viral infection involves entry into a host cell. The virus needs to attach to and then penetrate the wall of the host cell. Once the viral genome is inside, the cell begins to synthesize proteins that will lead to assembly and release of new virus particles. Viral entry and attachment usually does not require energy on the part of the virus. Once new particles have been constructed, they are released from the cell.
    The simplicity of viruses explains, to some degree, the difficulty we have in controlling them. It is hard to kill something that is not alive. Destroying or inactivating an organism with complex machinery may only involve targeting one small part, but very simple organisms have fewer parts to target. We do not have broad spectrum antiviral drugs similar to broad spectrum antibacterial drugs readily available in human or veterinary medicine.
    Fortunately for us, effective vaccines exist for all sorts of human and animal diseases. Vaccines are especially important for viral diseases because we have so few ways to directly combat viruses once an animal is infected. The very first vaccine was developed by Edward Jenner in 1796. He used live cowpox virus to inoculate humans against smallpox. Later the virus was called vaccina virus. In Latin, vacca means cow and vacinnae means of, or relating to cows. So, every time we hear the words vaccine or vaccinate, we can remember that connection and thank our favorite animal, the cow, for this particular contribution to human health.
    The term herd immunity is used a lot in the media today in relation to the current human coronavirus pandemic. Of course, this, too, is borrowed from veterinary medicine. Effective herd immunity is unlikely to be achieved in the human population without widespread use of an effective vaccine. This is because effective herd immunity would require that a large percentage of humans in any given herd, perhaps 60%-70% according to Dr. Michael Osterholm from the University of Minnesota, have adequate levels of protective antibodies. Adequate levels of antibodies would also have to persist for a significant amount of time, likely years; otherwise previously infected individuals would be susceptible again. Coronavirus vaccines are nothing new in veterinary medicine, and include vaccines for TGE in swine, coronavirus diarrhea in cattle, feline infectious peritonitis in cats and canine coronavirus in dogs. We can all hope that an effective vaccine is developed soon for humans and is made available in sufficient quantity to vaccinate most of us as soon as possible.
    Yes, viruses are small. They are simple, but simple does not mean unimportant or of little consequence.
    Some of the information in this article comes from: Actor, J. Basic Virology: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7152364/.
    Bennett is one of four dairy veterinarians at Northern Valley Dairy Production Medicine Center in Plainview, Minn. He also consults on dairy farms in other states. He and his wife, Pam, have four children. Jim can be reached at bennettnvac@gmail.com with comments or questions.