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Publications in the last 15 years have increasingly covered just eight pathogens, suggesting the pathogens may be emerging and have received increased research funding priority.

Pathogens: What we’ve been researching the last 50 years

Though African swine fever is currently grabbing headlines, the pathogen ranks 10th on the list of worldwide swine pathogen research over the last 50 years.

It’s hard to find an industry meeting this year without African swine fever on the agenda. It’s a pertinent concern for swine producers globally, as more cases continue to be reported in China and across Europe. So, it may be surprising to know ASF is currently 10th on the list for worldwide swine pathogen research over the last 50 years.

“We might expect this to change given the increased interest that is now being generated. When we look at publication trends regionally, we do see that ASF has been at the top of the list for sub-Saharan Africa,” says Kimberly VanderWaal, assistant professor, Department of Veterinary Population Medicine, University of Minnesota.

“That’s not surprising, since that is where it originated, but we are also see more historical interest in ASF in southern and northern Europe, and even more so in Eastern Europe and central Asia. These are areas that have experienced ASF outbreaks or are in close proximity to where ASF occurs.” she says.

57,000 publications checked
VanderWaal and her colleague, John Deen, a U-M professor also in the Department of Veterinary Population Medicine, recently dove into 57,000 publications to find the pathogens that have been researched the most in the global swine industry from 1966 through 2016.

“You would expect that if lots of articles have been published on a particular pathogen within a country, then that pathogen A) has a large impact on animal health or production, B) is important due to potential zoonotic risk, or C) may be currently absent [such as a foreign animal disease] but would have a large impact if it were introduced,” VanderWaal says.

VanderWaal says that it’s important to remember that her and Deen’s rankings, which were recently published in the Proceedings of the National Academy of Sciences, are not a metric of how common a pathogen is in a given country, but rather an indicator of priority.

Prioritization is pivotal
In order to establish rankings of the most researched swine pathogens, VanderWaal and Deen first assembled a list based on their publication counts in the world. Forty swine pathogens were identified.

After that, the different pathogens were classified by the three primary interests in research. Was it because it would affect production? Could the pathogen potentially be zoonotic? Or was it a reportable disease? They then observed how publication rates in these three classifications changed over time.

“We generally find a shift in the last 40 years, where we are increasingly prioritizing research related to zoonotic pathogens. But, you can also see patterns of increases in pathogens that affect production,” VanderWaal says.

Areas of growing interest
The researchers also used publication counts to categorize each pathogen as to whether there appeared to be accelerated interest, perhaps because it is an emerging pathogen, or the effects of that pathogen have been changing over time, or if there has been a decrease in interest because those pathogens were eradicated or controlled, or because certain pathogens may not be an issue now in more intensified pig production.

“Biosecurity that has been put in place around intensive production has reduced the importance of certain pathogens,” VanderWaal says.

For example, in the 1960s and 1970s, there were many more research efforts focused on reportable diseases, such as foot-and-mouth disease and classical swine fever as well as pseudorabies, since the latter was more of an issue in Europe and North America at that time.

Most researched pathogens
Salmonella, E. coli, influenza, pseudorabies and FMD rounded out the top five pathogens most researched, followed closely by porcine reproductive and respiratory syndrome, CSF and Actinobacillus pleuropneumonia.

The researchers also broke down the pathogens into whether they were viruses, bacteria, protozoans or helminths, and how research on each of these vary regionally.

“We generally find that regions of the world that have more intensified production have a greater portion of their publications focused on bacteria, viruses, and diseases impacting production and less on helminths and protozoa. This relationship was fairly linear when we used the proportion of the human population living in urban areas as a proxy for intensive pig production,” VanderWaal says.

In fact, more publications in the last 15 years have covered just eight pathogens, suggesting that the pathogens may be emerging and have received increased research funding priority.

“In general, it’s difficult to draw direct links between intensification and the emergence of certain disease, because intensification has occurred gradually over decades,” VanderWaal says.

While high density can promote rapid transmission on a farm, and moving more pigs around the world can accelerate the ability of new pathogens to spread, intensive swine production has also led to better control of other pathogens.

What other regions study
VanderWaal says it’s interesting to note what other regions are researching. For example, Eastern European research has been much more focused on helminths and protozoan parasites. In fact, Trichinella was one of the top five pathogens researched in the region; while the rest of Europe, which incorporates more intensified production, had Trichinella at a low research priority level.

Eastern Asia is another interesting example. 

“Although the economic profile of East Asia suggests that they would prioritize pathogens more similarly to other developing economies, their pathogen prioritization resembles highly intensive regions of the world such as North America and much of Europe. This highlights the rapid growth of intensive pig production in the region,” VanderWaal says.

PEDV research in eastern Asia
Eastern Asia’s main research efforts have been on PRRS, E. coli, influenza, CSF and porcine circovirus 2.

Through their publication count research, VanderWaal and Deen also saw an uptick in PEDV research being done in eastern Asia two years prior to the North American epidemic in 2013.

“This observation highlights that the U.S. industry needs to be globally aware of what is circulating in other regions of the world, especially areas in which we are more connected such as eastern Asia and China,” VanderWaal says. “Additionally, this work is being done alongside other new initiatives to better monitor what is going on globally.”

What’s next?
VanderWaal says it’s hard to project where research efforts will go next, as new pathogens could emerge, and the industry could achieve success in controlling other pathogens. She does see the trend of increasing research focus on diseases affecting production not going away, given that the intensification of the industry is unlikely to reverse.

While this paper is among the first comprehensive global reviews of swine pathogen research, the researchers do realize that there are limitations to their work — one being that they were not able to disentangle the different strains of pathogens. They also didn’t dive into the subject matter of the publications to divide up the research based on outbreaks, vaccine development, immunology, epidemiology, etc.

“This could be a valuable next step to better understand how research is being prioritized,” VanderWaal says.

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