April 20, 2021
It is hard to believe that it has been a year since I wrote my National Hog Farmer online article in April 2020 entitled “Approach to COVID-19 similar to battling swine pathogens: Herd immunity is a key concept for both swine and public health.” We live in a time where One Health—the concept that human and animal health are one in the same (i.e., what we learn from animal health can be applied to human health and what we learn from human health can be applied to be animal health)—is becoming more widely known. This article will explore lessons learned from the COVID-19 pandemic that have reinforced the need for and hopefully improved disease control practices used in the swine industry.
Using basic principles of biosecurity that include personal protective equipment (PPE) (e.g., masks), decreased density (i.e., social distancing- dilution is the solution), cleaning and disinfecting (e.g., hand washing) and isolation (e.g., virtual classrooms and office spaces) not only had an effect on COVID-19 pandemic and the target virus, severe acute respiratory virus 2 (SARS2) but on the spread of other airborne respiratory viruses. The effect on decreasing influenza virus infections in people was the most dramatic.
Let me begin with influenza numbers from my home state of South Dakota. Positive influenza cases in S.D. are historically in the 2,000-14,000/year (Figure 1) with an average ~6,000/year. In 2020-2021, we had 66 cases of influenza which was >200 times lower than the previous year and >9 times lower than the five-year average (Table 1). Hospitalizations in S.D. were 85 times lower compared to the five-year average, and deaths were approximately 20 times lower compared to the five-year average. For the U.S., 2020—2021 influenza hospitalizations rate was 0.7 per 100,000 population (CDC, 2021). This is much lower than the average for this point in the season and lower than rates for any season since routine influenza data collection began in 2005, including the low influenza season in 2011-2012. The current rate is one-eighth the rate at this time during the 2011-2012 season. There was one pediatric death in 2020-2021 in the U.S. compared to the average of 177/year over the last three years.
Vaccine coverage (the percentage of the total population that got influenza vaccine) in the 2019-2020 was approximately 50% in the U.S., up about 2-3% from 2018-2019. There is little preliminary influenza vaccine coverage data available for 2020-2021 season, but indications suggest that despite the increased influenza vaccine campaign, there was an increase of 3-5% in coverage. One small data set comparing vaccination coverage rates from 2019-2020 and 2020-2021 in pregnant women who are a high-risk group and good indicator of compliance was available (Table 2). The preliminary data vaccine coverage was up an average of 3% from the same time in the fall of 2019 compared to the fall of 2020.
The dramatic drop in influenza cases is probably more due to our “enhanced biosecurity” with a contribution from the increased vaccination. Biosecurity and PPE works both for the human herd as well as in swine enterprises.
International movement and disease spread
The disruption of international travel as a result of COVID-19 pandemic dramatically decreased measles cases in the U.S. Although we don’t think of the measles virus in terms of a “foreign human disease,” it is as infectious to the human population as foot and mouth disease virus (FMD), the foreign animal disease (FAD) feared most in the U.S. because of its high rate of spread among multiple livestock species (swine, cattle and sheep).
The high level of measles vaccine coverage—approximately 94% in kindergarten children—with an efficacy of 93% has resulted in historically low numbers of cases in the U.S. since the vaccine was introduced in 1963. Cases in the U.S. were in 100,000s/year in the 1960s prior to mass vaccination with the last “peak” being 28,000 cases in 1990. In the last 20 years, the U.S. has averaged <200 cases/year with four exceptions (Figure 2).
Vaccination has essentially eradicated local U.S. measle infections. In fact, almost all U.S. cases of measles now can be traced back to unvaccinated foreign travels visiting the U.S. from Europe, Asia, the Pacific, and Africa, where measles is common. In 2019, there were 1,282 cases, which was a dramatic increase over the prior years (Figure 2). The 2019 total of measles cases was more than the total for the last 25 years and was the most since 1992. In almost every U.S. case, the origin of the infection into a “susceptible human herd” (unvaccinated people) was the result of foreign travel and spread.
Due to COVID-19 related travel restrictions in the U.S., international travel was basically nil and there were only 13 cases of measles in the U.S. in 2020. This was despite a 10% decrease in measles vaccination rate from January 2020 to August 2020 due to lack of access to primary health care as a result of COVID-19 restrictions. If the infected human herd can’t move, neither can the disease.
Still, measles is also an airborne disease, so the importance of the measures discussed above also likely contributed to the decline. Reducing “the foreign human disease” measles reinforces the importance of our foreign testing and quarantine procedures that protect the U.S. swine herd against FAD like FMD and African swine fever (ASF).
Vaccine development improves
Probably one of the greatest positive outcomes of the COVID-19 pandemic has been the development of new and better vaccine technologies. By the time this article hits the internet, over 50% of the U.S. human herd over 16 years old may be fully vaccinated with highly efficacious COVID-19 vaccines.
Many of the lessons we have learned from human HIV (human immunodeficiency virus) vaccine trials have also resulted in improved animal vaccines. One can only hope that these COVID-19 approaches which had only been tested in the lab but are now proven in the field can be further developed to help in the development of efficacious PRRSV (porcine reproductive and respiratory syndrome virus) vaccines and to provide timely vaccine protection against ASF.
The cornerstones of any good swine herd health program depends on good on-farm biosecurity and diligence to prevent foreign disease introductions. The draconian measures we have had to live with over the past year to work our way through the COVID-19 pandemic further reinforce the importance of these same measures that protect the U.S. swine industry. Our experience with COVID-19 prevention measures and their positive effect on reducing influenza and measles cases in the human herd reinforces the importance of these measures being an essential part of our disease prevention toolbox. I, too, am tired of wearing a mask, but now I also ponder what “else” I prevent by wearing it. More importantly, I can further understand how these measures protect the U.S. swine herd.
Source: Chris Chase, DVM, PhD, Dipl ACVM, South Dakota State University, who is solely responsible for the information provided, and wholly owns the information. Informa Business Media and all its subsidiaries are not responsible for any of the content contained in this information asset. The opinions of this writer are not necessarily those of Farm Progress/Informa.
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