By: Katie Jones, CVT
When you or your horse is diagnosed with a certain disease, the details of the disease are often explained as a bacterial or viral infection. These two terms are very commonly used to describe many diseases we are exposed to in our daily lives. There are many similarities and differences between a viral and bacterial infection.
The similarities between bacterial and viral infections create some difficulty in differentiating between the two. Both can be spread by coughing, sneezing, and contact made with infected individuals, contaminated surfaces, food and water, or contaminated carriers. In addition to how the disease is contracted, both viral and bacterial infections share similar symptoms; some of which are: fever, inflammation, vomiting, diarrhea, and coughing. In both bacterial and viral infections microbes are the cause; they can be acute (short-lived), chronic (long lasting), or latent infections that could take months to show symptoms. Though both viral and bacterial infections share many similar characteristics they are different in many other important ways. These differences are mainly caused by the organisms’ structural differences.
Bacteria are complex, single celled organisms with a rigid cell wall. Due to this structure, bacteria can survive extreme environmental conditions. They are also able to reproduce on their own. A microbiologist estimated roughly 5 million trillion trillion bacteria reside in the world. This is an incomprehensible number, but not all of them are harmful to the human or horse population; many of them aid in normal bodily function. Approximately less then 1% of bacteria cause diseases that are harmful to people.
Viruses are smaller organisms then bacteria. The virus’ structure is simply a protein coat and a core made of genetic material (either RNA or DNA). Unlike bacteria, viruses cannot live without a host. The virus will attach to a host cell, enter the cell, and release its DNA or RNA inside it. The virus’ genetic material then takes over the host cell which causes the cell to replicate the virus within itself. Typically the virus will only attach to a certain type of cell. Viruses are transmitted to a new host by swallowing, inhalation, or spread by insect and parasite bites.
The body has a number of defenses against viruses. The skin discourages easy entry into the body, the body has a natural immune defense which will attack and destroy many viruses, and in the process it will remember the attacking virus to allow an even quicker attack if the body becomes exposed again. Drugs designed to combat viral infections are called anti-viral drugs. These types of drugs work by interfering with the replication process of the virus. Remember, viruses are tiny organisms that replicate inside cells using the cells’ own metabolic functions; therefore, there are only certain ways anti-viral drugs can target the virus. This limited effectiveness causes the development of anti-viral drugs to be difficult and some can even be toxic to cells. In addition viruses can easily develop drug resistance, while other anti-viral drugs can strengthen the bodies’ natural immune response to the viral infections. Vaccines fall under this immune strengthening form of anti-viral drugs. Antibiotics are not effective against viral infections, but could be beneficial if there is a secondary bacterial infection due to the viral infection.
Bacterial and viral infections have similar characteristic which can lead to confusion when a diagnosis is determined; however, once the organism is identified as one or another, the diagnosing veterinarian has a more clear direction for a treatment plan.