Reducing the likelihood of a piglet reservoir when dealing with influenza in swine herds

Drs. White, Torremorell and Craft from the University of Minnesota recently published an article in Preventative Veterinary Medicine regarding practices that can decrease the likelihood of creating an endemic piglet reservoir in the case of an infection by swine influenza. Indeed, a stochastic model was developed considering that the pigs were in one of the following categories: Susceptible, Exposed,  Infectious, Recovered, or Vaccinated. Loss of immunity over time and differences between naturally infected and vaccinated animals were taken into account. Several scenarios were evaluated regarding their impact on piglet prevalence: timing of gilt introductions, gilt separation, gilt vaccination upon arrival, early weaning, and sow vaccination strategies.

In this model, homologous mass vaccination and early weaning were the most efficacious interventions. By combining frequent homologous mass vaccination, early weaning, gilt separation, gilt vaccination and longer periods between gilt introductions reduced endemic prevalence overall by 51% relative to the null scenario and the endemic prevalence in piglets by 74%.

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Abstract: Recent modelling and empirical work on influenza A virus (IAV) suggests that piglets play an important role as an endemic reservoir. The objective of this study is to test intervention strategies aimed at reducing the incidence of IAV in piglets and ideally, preventing piglets from becoming exposed in the first place. These interventions include biosecurity measures, vaccination, and management options that swine producers may employ individually or jointly to control IAV in their herds. We have developed a stochastic Susceptible-Exposed-Infectious-Recovered-Vaccinated (SEIRV) model that reflects the spatial organization of a standard breeding herd and accounts for the different production classes of pigs therein. Notably, this model allows for loss of immunity for vaccinated and recovered animals, and for vaccinated animals to have different latency and infectious periods from unvaccinated animals as suggested by the literature. The interventions tested include: (1) varied timing of gilt introductions to the breeding herd, (2) gilt separation (no indirect transmission to or from the gilt development unit), (3) gilt vaccination upon arrival to the farm, (4) early weaning, and (5) vaccination strategies of sows with different timing (mass and pre-farrow) and efficacy (homologous vs. heterologous). We conducted a Latin Hypercube Sampling and Partial Rank Correlation Coefficient (LHS-PRCC) analysis combined with random forest analysis to assess the relative importance of each epidemiological parameter in determining epidemic outcomes. In concert, mass vaccination, early weaning of piglets (removal 0–7 days after birth), gilt separation, gilt vaccination, and longer periods between introductions of gilts (6 months) were the most effective at reducing prevalence. Endemic prevalence overall was reduced by 51% relative to the null case; endemic prevalence in piglets was reduced by 74%; and IAV was eliminated completely from the herd in 23% of all simulations. Importantly, elimination of IAV was most likely to occur within the first few days of an epidemic. The latency period, infectious period, duration of immunity, and transmission rate for piglets with maternal immunity had the highest correlation with three separate measures of IAV prevalence; therefore, these are parameters that warrant increased attention for obtaining empirical estimates. Our findings support other studies suggesting that piglets play a key role in maintaining IAV in breeding herds. We recommend biosecurity measures in combination with targeted homologous vaccination or vaccines that provide wider cross-protective immunity to prevent incursions of virus to the farm and subsequent establishment of an infected piglet reservoir.

Link to the full article

Advances in Mycoplasma hyopneumoniae elimination: a podcast series

This past month, the Morrison group invited Dr. Paul Yeske, swine practitioner at the Swine Vet Center (St. Peter, MN), Dr. Amanda Sponheim, PhD candidate at the University of Minnesota and Support Veterinarian at Boerhinger Ingelheim, and Dr. Maria Pieters from the University of Minnesota to discuss the latest progress made in successfully eliminating Mycoplasma hyopeumoniae from swine herds. Dr. Pieters is the head of the MycoLab at the College of Veterinary Medicine and focuses on diagnostics and epidemiology of swine mycoplasms to help veterinarians control associated diseases.

  1. History of Mycoplasma hyopneumoniae herd elimination and practices: podcast
  2. Sampling techniques and protocols to use during the process of elimination: podcast
  3. Starting the elimination: when is day zero? podcast

The podcasts in the press

Monitoring Salmonella resistance to antimicrobials in Minnesota during the past 9 years

The STEMMA laboratory at the University of Minnesota and more particularly Dr. Alvarez’s team is aiming at monitoring of antimicrobial resistance in animal and human bacteria. Therefore, the research they present in this article published this month, focused on Salmonella species both in swine and cattle. Records from the Veterinary Diagnostic Laboratory between 2006 and 2015 were compiled to study the evolution of the proportion of resistant strains of Salmonella in Minnesota.

Dr Hong, in collaboration with researchers from the U of MN, captured the number and the type of antimicrobials each strain was resistant to. He also monitored the evolution of the resistances over the nine-year period.

Evolution in antimicrobial resistant Salmonella isolates
recovered from swine at the MVDL in 2006–2015.

Explanation of the figure: Proportion of Salmonella isolates recovered from swine samples that were resistant to ampicillin (A), ceftiofur (C), enrofloxacin (E), florfenicol (F), gentamicin (G), neomycin (N), oxytetracycline (O), sulfadimethoxine (Sul), spectomycin (Sp) and trimethorpim/ sulfamethoxazole (Ts)

Abstract: Salmonellosis remains one of the leading causes of foodborne disease worldwide despite preventive efforts at various stages of the food production chain. The emergence of multi-drug resistant (MDR) non-typhoidal Salmonella enterica represents an additional challenge for public health authorities. Food animals are considered a major reservoir and potential source of foodborne salmonellosis; thus, monitoring of Salmonella strains in livestock may help to detect emergence of new serotypes/MDR phenotypes and to gain a better understanding of Salmonella epidemiology. For this reason, we analyzed trends over a nine-year period in serotypes, and antimicrobial resistance, of Salmonella isolates recovered at the Minnesota Veterinary Diagnostic Laboratory (MVDL) from swine (n = 2,537) and cattle (n = 1,028) samples. Prevalence of predominant serotypes changed over time; in swine, S. Typhimurium and S. Derby decreased and S. Agona and S. 4,5,12:i:- increased throughout the study period. In cattle, S. Dublin, S. Montevideo and S. Cerro increased and S. Muenster became less frequent. Median minimum inhibitory concentration (MIC) values and proportion of antibiotic resistant isolates were higher for those recovered from swine compared with cattle, and were particularly high for certain antibiotic-serotype combinations. The proportion of resistant swine isolates was also higher than observed in the NARMS data, probably due to the different cohort of animals represented in each dataset. Results provide insight into the dynamics of antimicrobial resistant Salmonella in livestock in Minnesota, and can help to monitor emerging trends in antimicrobial resistance.

Link to the full article

Happy Holidays from the swine group at the University of Minnesota!

2016 was a great year for the swine group at the University of Minnesota. The Food Centric Corridor Infectious Disease Research Laboratory was remodeled to create an open and luminous space to foster collaboration between researchers. The Leman conference and Leman China were tremendous successes, sharing research-based solutions to swine veterinarians and producers in Minnesota and around the world. The new animal isolation units construction has started and will be achieved next year, allowing our scientists to perform cutting edge research on infectious diseases. Our researchers have made great discoveries and shared them with the community.

Thanks to all of you who are supporting the swine group, 2016 was indeed a great year and we hope 2017 will be even better.

We wish you a very happy holiday season and all the very best for 2017!

The U of MN hosts the Minnesota Pork Board Research committee for a day of productive exchanges.

The University of Minnesota highly values its partnerships with the industry stakeholders. With the objective to continue a fruitful and mutually beneficial collaboration, the College of Veterinary Medicine (CVM) and the College of Food, Agricultural and Natural Resource Sciences (CFANS) at the University of Minnesota hosted the Minnesota Pork Board (MPB) Research Committee on December 15th, to exchange ideas and to discuss projects that would be the most beneficial for the swine industry in Minnesota.

After a review of the current and future swine projects happening at both Colleges, Dean Ames (CVM), and Dean Buhr (CFANS) gave an update on the new facilities being built on the St. Paul Campus including the new animal isolation units that will allow our scientists to perform cutting edge research on infectious diseases.

Lastly, the MPB research committee toured the newly remodeled Food Centric Corridor Infectious Disease Research Laboratory as well as the Veterinary Diagnostic Laboratory.

The U of MN would like to thank all the representatives from the Minnesota Pork Board who came to meet our researchers and made this day the great success it was.

Dr. Fernando Leite receives Lynn Jones Memorial Award for Best Oral presentation at CRWAD

Dr. Fernando Leite, a PhD student under the supervision of Dr. Richard Isaacson, won the Lynn Jones Memorial Award for the best oral presentation at the 97th Conference of Research Workers in Animal Diseases (CRWAD). His talk entitled “Lawsonia intracellularis vaccination decreases Salmonella enterica serovar Typhimurium shedding in co-infected pigs” presented the results of the work  he did in collaboration with Drs. Gebhart, Singer, and Isaacson at the University of Minnesota.

Please join us in congratulating Fernando for his award!

Abstract: Salmonella enterica serovar Typhimurium and Lawsonia intracellularis are two of the most prevalent intestinal pathogens of swine. S. Typhimurium causes diarrhea but also results in subclinical persistent colonization of pigs and can lead to food borne illnesses. S. enterica is responsible for over 1 million cases of food borne illness per year in the United States. L. intracellularis infection has been found as a risk factor for increased S. Typhimurium shedding in swine. The objective of this study was to investigate if vaccination against L. intracellularis could lead to decreased S. Typhimurium shedding. To test this hypothesis, groups of nine pigs were either challenged with S. Typhimurium, S. Typhimurium and L. intracellularis, S. Typhimurium and vaccinated against L. intracellularis, or S. Typhimurium L. intracellularis and vaccinated against L. intracellularis. A non-infected control group served as a negative control. Fecal shedding of S. Typhimurium was monitored using an enrichment most probable number method two days after infection and weekly thereafter until animals reached the age of 14 weeks. The co-challenged vaccinated group had a tendency of shedding the least S. Typhimurium and at one-week post infection is when the greatest differences among groups was observed and the vaccinated co-challenged group shed significantly less Salmonella (p>0.05) than the group co-infected without vaccination and the group challenged with Salmonella alone. These differences were of 1.63 and 2.12 Log10 organisms per gram of feces, respectively. The instestinal microbiome of these animals is being investigated to understand how it may have impacted Salmonella shedding levels in the different treatments. These results indicate that vaccination against L. intracellularis may aid in the control of S. Typhimurium in herds co-infected with L. intracellularis.

Defining parameters to develop epidemiological models of a Foot and Mouth Disease incursion: meta-analysis of the disease biology

kinsley-epidemiological-models-of-fmd-in-swine

Models are primordial to develop the best control and eradication measures as well as to decrease response time in the event of a Foot and Mouth Disease (FMD) incursion on US soil. However, to be as representative of real-life situation as possible, these models need the most accurate information on disease biology. This scientific article, written by a U of M team of epidemiologists: Drs. Kinsley, Patterson, VanderWaal, Craft, and Perez, is a meta-analysis of the peer-reviewed literature defining what the exact values for the duration of various disease periods such as: latency, incubation and sub-clinical phases are. The total duration of infection is also examined.

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Time course of a FMD infection in pigs infected through contact with an inoculated pig.

Abstract: In the event of a foot-and-mouth disease (FMD) incursion, response strategies are required to control, contain, and eradicate the pathogen as efficiently as possible. Infectious disease simulation models are widely used tools that mimic disease dispersion in a population and that can be useful in the design and support of prevention and mitigation activities. However, there are often gaps in evidence-based research to supply models with quantities that are necessary to accurately reflect the system of interest. The objective of this study was to quantify values associated with the duration of the stages of FMD infection (latent period, subclinical period, incubation period, and duration of infection), probability of transmission (within-herd and between-herd via spatial spread), and diagnosis of a vesicular disease within a herd using a meta-analysis of the peer-reviewed literature and expert opinion. The latent period ranged from 1 to 7 days and incubation period ranged from 1 to 9 days; both were influenced by strain. In contrast, the subclinical period ranged from 0 to 6 days and was influenced by sampling method only. The duration of infection ranged from 1 to 10 days. The probability of spatial spread between an infected and fully susceptible swine farm was estimated as greatest within 5 km of the infected farm, highlighting the importance of possible long-range transmission through the movement of infected animals. Finally, while most swine practitioners are confident in their ability to detect a vesicular disease in an average sized swine herd, a small proportion expect that up to half of the herd would need to show clinical signs before detection via passive surveillance would occur. The results of this study will be useful in within- and between-herd simulation models to develop efficient response strategies in the event an FMD in swine populations of disease-free countries or regions.

Link to the full article

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