Dr. Robert Tremblay
I have spent a large part of my veterinary career working on the treatment, control and prevention of infectious diseases. Although my focus has been on the infectious diseases of cattle, it is difficult for me not to pay attention to what is happening with infectious diseases in other species, too, including Homo sapiens. Our ability to manage infectious diseases in people and in animals is heavily influenced by human behaviour. In fact, human behaviour is often the biggest factor in dealing with infectious diseases of animals as well as in people.
How people managed COVID-19 is a reasonable illustration of the application of the principles of how to control infectious diseases and especially diseases caused by viruses. The early steps in control were mainly to prevent spread of infection and reduce the number of new cases by applying biosecurity measures. I had never imagined that people would be talking about ‘R’. R is used in the study of diseases as a measure of how rapidly or readily a disease spreads. When I was introduced to R in 1977, I was studying how molds spread on crops. By the time I was taught about it, the concept of R had been around for about a century.
In general, the lower the ‘R’, the fewer new cases will arise from each existing case. The objective is to keep R as low as possible. Back in 1977, I hardly imagined that the day would come when the importance of the concept of R would become widely reported in the daily news the way it did in relation to control of COVID.
One of the features of coping with epidemics is that it can be difficult to know exactly what you need to do to control a disease. If the disease is truly new, like COVID was, you are often making recommendations based on principles rather than actual knowledge about the disease itself. Inevitably, that means that errors will be made especially early in the outbreak.
It was hard to determine how much each of those biosecurity measures that were recommended to help lower R in 2020 ended up working to reduce the spread of the COVID virus during the first wave and lockdown. Many expressed concern that we were being asked to do things that had not been proven to be beneficial. That was always going to be the case because we knew so little about that specific COVID virus at the time. Even still, when we look back at the disease pattern in the first wave, most people would accept that the sacrifices we all made had a beneficial impact. If you still doubt that, look at the graphs of the number of COVID cases in the second wave compared to the first wave. Like the first wave, the second wave happened before we had access to vaccines. That ‘flat’ first wave curve was likely due to the fact that we were all a lot more conscientious about biosecurity in the first wave.
Another of the great challenges in controlling outbreaks of infectious diseases is that it is difficult to understand the situation as it exists today. When you track diseases by looking at who gets sick, then you always try to play catch up because you’re looking at where the virus has been not where it is today. That is because there is always a lag between when someone gets infected with the virus and when they actually get sick.
If it can take up to two weeks after infection to get sick, then measuring the number of people who are sick right now tells you what infections occurred two weeks ago, not what is happening today – so you often need to work hard to get ahead of the spread of the virus. That lag between infection and sickness also means that if you did something that completely stopped spread of the virus, it is likely you wouldn’t know whether what you did worked until days to weeks later.
It also means that you can’t expect experts to change the spread of disease quickly. Even if we do everything that experts recommend; we won’t see the benefits of a change for at least a week and likely longer.
There are a couple of good books describing epidemics of human disease – A Journal of the Plague Year about the last major outbreak of bubonic plague in England, and the Canadian book, Plague: A story of smallpox in Montreal. They contain a lot of discussion about human behaviour. Both books describe how people start to do things during epidemics that didn’t make much sense even at the time. Interestingly, when that smallpox epidemic occurred in Montreal, the smallpox vaccine had been available for years but there were lots of people in the city who refused to take it.
The current avoidance of vaccines and fascination with ivermectin might be just about the same behaviour in our own COVID pandemic. I don’t really want to discuss vaccines, but it is important to understand that even though the actual COVID vaccines are new, the technologies that are the basis of the vaccines used in Canada had been under development for decades. That is a big reason why companies could produce so many different vaccines so quickly.
The older evidence for the effectiveness of ivermectin against COVID has been largely discredited and it doesn’t look as if there is much new evidence to establish that ivermectin is useful against COVID. Safe to say that the treatment is unproven.
And yet, it appears that there is unusual interest in the veterinary forms of ivermectin. Most of the available veterinary products are designed to be used in cattle or horses. I can’t even begin to imagine that it would be a good idea for humans to consider using that stuff.
There is an approved human form of ivermectin in Canada. It is a prescription drug to treat parasitic infection.
Dr. Robert Tremblay is a veterinarian for Boehringer-Ingelheim and lives near Guelph.