In this article written for the National Hog Farmer, PhD candidate April Estrada describes the high diversity of Streptococcus suis (S.suis) isolates.Continue reading “Distribution of pathogenic Streptococcus suis in the US”
An article from our colleagues in the College of Food, Agricultural and Natural Resource Sciences, and published in the National Hog Farmer explores how much space the sows really need. It is critical to find the right balance between the welfare of the animals and the productivity of the farm.Continue reading “How much floor space do group housed sows need?”
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
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.
A 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.
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.
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.
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.
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.