NHF: What does livestock-associated MRSA mean for the neighborhood?

Our monthly collaboration with the National Hog Farmer continues; this month Dr Peter Davies from the University of Minnesota, College of Veterinary Medicine,  explains what is livestock-associated MRSA and if it affects people living near pig farms.

“Livestock-associated” MRSA first isolated in 2004

Methicillin Resistant Staphylococcus aureus (MRSA) Source: Wikimedia Commons

Most people are likely familiar with MRSA (methicillin resistant Staphylococcus aureus), a flagship “superbug” that is a major concern to human medicine. And just about everybody in the pig industry has heard that certain variants of MRSA are very common in some livestock populations (including pigs), and these are referred to as “livestock-associated” MRSA (LA-MRSA).

A novel variant of MRSA (labelled ST398 using a DNA typing method) was first found in pigs in the Netherlands in 2004. Subsequently, ST398 MRSA and several other types (e.g., ST9 in Asia, ST5 in North America) were reported in pigs in numerous countries, and often in their caretakers as well. The discovery that pigs may be a large MRSA reservoir created some justifiable panic and confusion, raising questions about the implications for human health, particularly for industry workers (e.g., farmers, veterinarians, processing plant workers), pork consumers and, last but not least, people living in the neighborhood of pig farms.

Generally, LA-MRSA  lack most of the key “virulence factors” that enable the bacteria to cause clinical infections in people.

Human clinical infections by “livestock-associated” MRSA are rare

Although workers on MRSA-positive farms often harbor LA-MRSA in their nose, significant clinical infections in healthy workers have been rare. Human clinical infections with LA-MRSA do occur, but most cases tend to be of relatively mild disease (such as skin infections), with more severe infections typically limited to elderly and medically compromised patients.

Remembering that about 2% of healthy U.S. citizens carry human adapted variants of MRSA, the relative clinical importance of LA-MRSA appears to be minimal in most countries. Globally since 2004, there have been around 10 fatal cases of LA-MRSA infections reported, compared with about 50 fatal MRSA cases per day (18,650 per year in 2005) in the United States alone.

2016 study of Iowa hospitals found probable livestock variants in only 0.24% of MRSA cases, and 1% of S. aureus infections. In North Carolina, another leading swine-producing state, there were no LA-MRSA variants among more than 1,200 MRSA isolated from human bloodstream infections between 1995 and 2015 (Dr. Vance Fowler, Duke University, personal communication).

Living next to pig farms does not increase the risk of exposure

Although MRSA can be isolated from meat products, there is little evidence to suggest cause for concern about food-borne transmission. In contrast, conclusions of studies looking at the neighborhood risk of exposure to LA-MRSA from pig farms are conflicting. We will focus on the findings of studies that have compared pig workers and neighbors directly, measured the distance from pig barns to residences directly; and used laboratory testing to confirm the presence of LA-MRSA in the study populations. 

Across three early studies in Europe, LA-MRSA prevalence (nasal carriage) was greater than 180 times higher in 352 pig industry workers (44%) than in 2,094 rural residents without farm exposure (0.24%).

  • A similar study in Holland in 2017 showed similar prevalence of nasal colonization (0.56%) in people without livestock contact, but also found the positive people on average lived closer to farms (of any type). Importantly, the authors noted that routes of transmission underlying this were not known.
  • A very detailed study of cases of MRSA infection in Denmark showed that overall MRSA risk did not differ between pig-dense regions versus other regions. However, the likelihood that a MRSA infection would be a LA-MRSA type was higher in the pig-dense regions, confirming some “spillover” from the industry to the community.
  • Notably, a follow-up study published in 2018 found that, within pig-dense areas, the patients with LA-MRSA infections did not live closer to pig farms than population controls. The authors conclude that direct environmental spread from neighboring pig farms was unlikely and suggested that community spread through contact with people working with livestock,  might be the predominant mechanism.

In summary, the overall impact of LA-MRSA relative to human variants remains very small in most countries including the United States. There is no evidence that residence in rural areas increases overall MRSA risk.

NHF: Unknowns remain about water quality impact on pig performance

Our monthly collaboration with the National Hog Farmer continues; this month Drs. Johnston, Shurston, Lozinski, and  Urriola from the College of Extension and the College of Food, Agricultural and Natural resources Sciences explain why there is much left to research on water quality.

Non-thriving pigs in the nursery are a concern among swine producers. Pigs are eating less, they get sick and do not perform well overall.

“Could bad water on the farm be a cause for reduced health and growth performance of these challenged nursery pigs?”

That depends on how bad the water is and how you define bad versus good water. Currently, there is no standard.

Aging literature references

In the scientific literature, the most widely quoted standards for quality of water fed to livestock comes from the U.S. National Research Council (1974) and the Canadian Council of Minister of the Environment (1987 and 2005).

Inconsistent findings in current research

McLeese et al. focused on the total dissolved solids (TDS) content in water. By increasing TDS 20-fold, they noticed that it had no impact on weaned pigs fed a medicated diet whereas it reduced significantly feed efficiency in non-medicated pigs. Several studies showed that pigs scours when drinking water with an increased concentration of sulfate, without necessarily affecting performances.

Another parameter to take into consideration is that some of the barns are getting older and so is the water distribution system. Water pipes and drinkers can impact water quality if they are not properly and regularly cleaned and maintained. However, despite the importance of water distribution systems in hog barns, scientifically-evaluated treatment and procedures are hard to find.

Conclusion

In 1992, McLeese et al. stated, “However, the current literature is neither conclusive nor thorough with respect to the impact of water quality on pig health, welfare and productivity.” It seems we are still in this position in 2018.

NHF: Developing targeted disease surveillance and control plans

Our monthly collaboration with the National Hog Farmer continues; this month Dr. Kim VanderWaal shares her research regarding swine disease surveillance.

The multi-site pig production structure of the U.S. swine industry requires frequent movement of swine, making swine populations vulnerable to disease spread. This scenario becomes even more relevant in highly dense regions that concentrate thousands of pigs.

Super spreader
Farm icon created by Ferran Brown for the Noun Project

By targeting sites that play an important “connectivity” role such as gilt producing sites, prevention and control strategies for disease containment can be developed together with targeted surveillance for early detection of disease.

Swine movement data in three large production systems in the United States were analyzed to measure how a specific farm could influence a potential disease spread. Several network metrics were measured including:

  • the number of other farms to which a specific farm sent or received pigs,
  • the Mean Infection Potential (MIP), which measures potential incoming and outgoing infection chains.

For example, if a nursery farm received pigs from several sow farms and then sent pigs to multiple finisher farms, that farm would likely have a high MIP and could be called a “super-spreader” :  a farm that could contribute to a high number of infections.

The study found that by directing disease interventions toward farms based on their MIP, the potential for infectious disease transmission in the production system can be substantially reduced. Interestingly, production type (sow, nursery, finishing, farrow-finish and wean-to-finish) did not seem to be a key determinant of the MIP.

When we really break it down, it’s all about incoming and outgoing contacts and the impact on risk. For more information about analysis of movement data, identifying super-spreaders farms and implications for disease control for farms in your system, contact Kim VanderWaal.

NHF: PRRS is also a summer disease

Our latest collaboration with the National Hog Farmer was written by the Morrison Swine Health Monitoring Program team regarding the incidence of PRRS in the summer.

Although our understanding of disease and control methods has improved in recent years, we continue to learn new features of PRRSV epidemiology in part thanks to the Morrison Swine Health Monitoring Project. One of the most recent questions that we have addressed based on enquires from MSHMP participants is whether PRRS incidence during the summer was higher in recent years (i.e. 2016-17) compared to previous years (i.e. 2009-15). We know that PRRSV outbreaks tend to have a seasonal pattern and that they are more frequent during the fall and winter, but we know little about the breaks that happen in the summer and spring.

In order to dig into this question, we analyzed MSHMP data from 2009 to 2017 which included 1,329 outbreaks. Of these, 66% of the breaks occurred during fall and winter and 14% and 20% of the breaks occurred during summer and spring, respectively. Although there were fewer breaks in the spring and summer, the number of breaks in warmer seasons was still significant which represents an on-going frustration to producers because the “PRRSV season” is supposed to be over.

As part of the analysis we learned that between 3% and 6% of the herds break yearly during the summer and spring seasons, respectively. This represents approximately 83 herds out of the 917 reporting in the MSHMP database. If we estimate that the average sow farm has 3,000 sows, then almost a quarter of a million sows break yearly during these two seasons.

Remember, although the risk of PRRSV introduction is lower during the spring and summer, PRRSV breaks still happen, so biosecurity efforts should not be decreased. PRRSV is a sneaky virus so keep your biosecurity up, even in the summer.

All of our collaborations with the National Hog Farmer can be found here.

NHF: Enteroids as in vitro model for ileitis

Our new contribution to the National Hog Farmer was written by Dr. Talita Resende, a PhD candidate at the University of Minnesota under the supervision of Dr. Connie Gebhart. Talita’s research focuses on swine ileitis and models to better understand its pathogen: Lawsonia intracellularis. Today, she explains how she uses enteroids.

The small intestine is largely responsible for nutrient digestion and absorption in the gastrointestinal tracts of pigs, but it is also an ideal colonization site for enteric pathogens. The investigation of the interactions between host and enteric pathogens can be conducted in vivo, or in vitro, with advantages and disadvantages for each of the models. Enteroids, small intestinal organoids, represent a new in vitro approach to investigate those interactions. But why are enteroids a new approach and what are their advantages in comparison to the current models?

Enteroids are three-dimensional structures originated from embryonic stem cells, induced pluripotent cells or adult stem cells from intestinal tissue. Therefore, they present all the cell types and a structural organization similar to crypts and villi found in the small intestine. This complex structure offers ideal conditions to investigate the mechanisms by which Lawsonia intracellularis causes proliferative enteropathy – also known as ileitis – in pigs.

Swine microbiome studies: Why, how and where are we going?

There is no Science Page this week; we will return to our normal schedule next week. In the meantime,  you may read our previous publications on our website.

Today, we will be talking about swine microbiome studies. Dr. Andres Gomez, expert in microbiome, who joined the University as part of the new AGREETT positions wrote an article for the National Hog Farmer about research on swine microbiome.

What does microbiome mean?

Microbiome refers to all of the microbes present in an area. For example, gut microbiome is the entire population of microorganisms (most of the time bacteria) present in the intestinal tract.

Microbes have been traditionally viewed through a lens of distrust, as pathogens affecting health. However, molecular and computational breakthroughs to study microbial diversity and function by sorting DNA sequences have presented a novel concept of an animal “flora” that acts as a friend as opposed to a foe.

Characterizing the microbiome to improve nutrition

Characterizing the specific microbes that increase or decrease in abundance upon pharmaceutical or dietary interventions is critical to determine precise dose-response relationships and to potentially reduce feed costs while achieving desired improvements in pig health and productivity.

Defining “healthy” microbiomes to identify poor-doing pigs

Regular “microbiome snapshots” along the most critical stages of pig growth (e.g., pre- and post-weaning), can be used to predict health and potential pathogen threats for disease by early identification of bacteria in slow-growing pigs or those that are at most risk of infection. This would allow producers to make early decisions on therapeutic or dietary interventions to enhance performance and health.

swine gut microbiome
 1) nutrients and feed additives modulate gut microbiomes to impact health and performance, 2) microbiomes across the pig anatomy are accurate biomarkers of stress such as diseases, early weaning, and heat, and 3) microbiomes in manure can be modulated to mitigate harmful gases.

Enhancing the protective microbiome

The microbiome in the gut or respiratory tract is a protective layer against infectious diseases. Thus, with microbiome research, we can determine how novel feed additives and management interventions work, by either enhancing the abundance of microbes that promote health and/or displacing those that cause disease.

Microbiome beyond pork production

For instance, specialized bacteria and fungi can degrade otherwise underutilized natural resources to maximize pig productivity, while decreasing the environmental footprint. Additionally, specialized microbial communities can also mitigate the production of dangerous gases  produced in manure pits.

NHF: Coping with shortage of vitamins A and E in swine diets

This month, the swine nutritionist team at the University of Minnesota share in the National Hog Farmer, how to cope with the shortage of vitamins A and E in swine diets.

Usually, vitamins A and E are added to swine diets at up to 4 times the recommendation made by the National Research council. This is due in part to the variability of requirements in swine. However, a system-wide approach could help the industry to cope with the increase in price and the limited supply.

A wide range of alternatives are proposed to make up for the shortage:

  • Rely on body reserves
  • Add ingredients with high levels of vitamins
  • Remove vitamins A and E from finishing diets 35 days before harvest (it has no effect on their performances)
  • Minimize storage time to avoid degradation
  • Avoid low-quality oils to increase vitamin E absorption by the liver
  • Polyphenols and carotinoids can be used as alternatives
  • Strategically use injectable form

In addition to those strategies, farm personnel needs to be vigilant and look for signs of deficiency like impaired reproductive performances and Mulberry Heart Disease.

Alternatives to vitamin A and E in swine diets.jpg