Animal Health Matters: Time is a critical factor with disease transmission
We’ve all become more educated on infectious disease dynamics these past few months. The onslaught of COVID-19 has brought disease transmission to our the front of our minds every day. You can all recite the recommendations by heart: Wash your hands. Stay home when you’re sick. Practice social distancing. Cover your face.
Have you ever wondered how these recommendations come into being? Somewhere, some very smart people have to take reams of scientific data about virus transmission and distill that information down into messages that everyone – kids, adults, non-English speakers – can understand.
I don’t consider myself an infectious disease expert, but as someone tasked with educating college students and the general public about such conditions, I can appreciate the challenge involved. Sometimes the scientific data that supports messages like my lessons in animal disease class or public health organizations’ prevention recommendations is very solid. Sometimes the data is all over the board. Most of the time, the science-based evidence is extremely convincing except for a handful of weird outliers that make you question things. A quote I reference often, “There are no absolutes in a biological system,” comes to mind. Mother Nature is good at serving up curveballs every now and then. Those weird outliers shouldn’t paralyze us from crafting solid disease prevention messages that cover the vast majority of situations, though.
Developing solid messaging can be challenging enough with known diseases, like human influenza or porcine epidemic diarrhea. When a totally new virus emerges and causes a pandemic, there’s no bank of information to fall back on, however. Disease information has to be translated on the fly. Sometimes messaging developed in the early stages of an outbreak has to be adjusted as more information is gained.
We recently saw a good example of this from the Centers for Disease Control and Prevention (CDC), regarding what constitutes an exposure to the virus causing COVID-19. In the early stages of the pandemic, the CDC called you “exposed” to COVID-19 if you spent 5-10 minutes within 6 feet of a COVID-positive person. Now the guideline has been adjusted to 15 minutes of exposure.
To their credit, the CDC looked at the information coming in and, rather than stubbornly sticking with their initial message, they adjusted it – a real example of science in action. There have been other examples of message-adjusting as this pandemic plays out before our eyes.
Their recognition that people have to spend more time with a COVID-infected individual than previously thought, brought home to me the importance of exposure time in the transmission of infectious diseases. Exposure time is something we teach in animal diseases class, too – limiting the time a vulnerable animal spends with an infected animal or in a contaminated environment is one of the three main methods I preach to prevent disease transmission.
Plenty of examples of minimizing contact time exist in animal health management. Consider early weaning of pigs. Certain disease issues such as Mycoplasma pneumonia become established in piglets from bacteria they pick up from their mother. Piglets don’t become infected if they spend less than 21 days nursing their mother. If they’re on the sow longer, enough exposure time has elapsed for the bacteria to take hold in the pigs’ lungs. Another example is the prevention of diarrhea diseases in dairy calves by their prompt removal from the calving pen after birth.
These examples illustrate that a germ needs to spend time with the vulnerable patient’s system in order for disease to occur – brief, chance encounters usually aren’t enough. This is why the most common COVID-19 transmission stories we hear are among family members or co-workers in close quarters, or people attending funeral services or choir practices. More time means more virus comes in contact with a person’s respiratory cells, and more of a chance the virus will infect enough cells to overwhelm a person’s natural defenses.
Sure, there are instances where long-term exposures aren’t apparent with some COVID-19 infections. So the other prevention measures still apply: distancing, hand washing, disinfecting surfaces, wearing masks. But keeping in mind the amount of time we spend in places and with people should also be on our mind as we seek ways to keep ourselves and our loved ones healthy during this outbreak.