Animal Health Matters: Understanding diseases in and out of the classroom
Teaching the Animal Diseases and Control course at SDSU allows me a great chance to interact with animal science and pre-vet students about interesting animal health issues. As most of you know, course delivery has changed greatly with campus COVID-19 restrictions. Overall, the students are doing a great job of navigating the changes.
While how we interact with each other is different, the course content hasn’t changed. My goal is to give the students a solid base for understanding diseases in general: attributes of different germs, transmission routes, practices that stop spread of germs between animals. We eventually discuss specific diseases, but as I learned from my vet school experience, only learning about current diseases doesn’t prepare them for all the yet-to-emerge diseases they’ll invariably encounter in their future careers.
Speaking of previously unknown diseases, how about COVID-19? It’s a great example of how we’ve all had to draw upon our general knowledge of diseases rather than a well-defined playbook from previous outbreaks.
In class, we study the general progression of infectious diseases, with the goal of understanding how to stop that progression at the different steps along the way. We use animal diseases as the basis for these discussions – but COVID-19 is providing a pertinent example as well.
Any infectious disease starts with an exposure. Exposure means the person or animal is close enough to a germ source for a long enough time for the germ to enter the body. For COVID-19, that means being within 6 feet of an infected person for at least 5-10 minutes – or where a doorknob or other surface harbors the virus.
In class, we brainstorm how to prevent each disease progression step – this is the essence of disease prevention. For COVID-19, social distancing and disinfection work to prevent exposure – therefore the disease.
Exposure doesn’t necessarily mean that the next step will take place. That step is the germ’s entry into the body. For COVID-19 the person has to breathe air from the close-by infected person, or wipe their mouth with the hand that touched the contaminated doorknob. If the exposed person wore an N95 mask or washed their hands after touching the doorknob, the virus can’t enter the necessary part of the body (nose or throat in this case).
If the germ successfully enters, the next disease step is possible: infection. Infection means the germ’s invaded body cells or tissues. Infection doesn’t necessarily mean the person or animal is sick, which is a common misuse of the term. At this stage, the germ can be detected by certain tests. For COVID-19 a nose or throat swab is tested for specific parts of the virus.
At the infection stage the immune system can recognize and respond to the invading germ. Immune cells recognize the invader and set off many different responses, one of which might be the production of antibodies. Here’s another way to diagnose the condition. Blood tests detecting antibodies (soon we’ll have one for the COVID-19 virus) indicate whether a person’s been infected and mounted an immune response, possibly protective against future infections. Antibody production lags a week or two behind infection, but can last long after the body has cleared the germ.
An infected person could expel germs before they feel sick, exposing others, referred to as pre-symptomatic spread. For COVID-19, people can apparently shed the virus for a couple days before they feel sick.
Vaccines are the intervention that stops disease progression in the infection stage. While vaccines exist against many diseases of people and animals, of course there’s no COVID-19 vaccine yet.
Vaccinated or not, the infected person’s immune system might stop disease progression at this stage. If it doesn’t, the next step is illness, which results from the germ multiplying, spreading, and damaging body cells. The COVID-19 virus attacks respiratory cells, with the resulting damage and inflammation causing fever, cough, and difficult breathing. As with other diseases, the effects can range from very mild to severe or even fatal.
When animal diseases occur, I tell my students it’s because we failed to prevent the progression of disease at any of these stages. The same can be said about COVID-19. We can stop its progression through social distancing (decreasing exposure), handwashing (decreasing entry), and maintaining good health in general (diminishing illness effects).
COVID-19 has changed the way my students are learning this semester, but its lessons will be with all of us when the next big disease issue hits us or our animals.