Breed-to-wean farm factors associated with influenza A virus infection in piglets at weaning

A scientific article written by Dr. Fabian Chamba Pardo when he was doing his PhD in the Torremorell lab was recently published on the journal of Preventive Veterinary Medicine. The study presented aimed to look at the various factors influencing the influenza infection status of piglets at weaning.

Highlights

  • Sow vaccination decreased influenza infections in piglets at weaning.
  • Influenza positive gilts at entry were associated with positive piglets at weaning.
  • More work is needed to assess herd closure, gilt isolation and gilt vaccination.

83 farms from 2 different pig production companies and located in Iowa, Minnesota and South Dakota were enrolled in this study. Samples were collected at weaning on a monthly basic for a little less than 6 years as part of routine surveillance programs. The majority of farms submitted 4 oral fluid samples per month but some collected nasal swabs or oro-pharyngeal swabs.

23% of the samples tested positive for influenza allowing the collection of 173 hemagglutinin sequences. In the H1 hemagglutinin subtype, isolates were 93.8% to 99% similar between each other and 94.3% to 97.4% similar to the vaccine strains. The largest discrepancy was found in the delta 1 clade. In the H3 hemagglutinin subtype, isolates were 95.9 to 99.7% similar among each other and 997.3% to 97.5% similar to the vaccine strains.

influenza factors for piglet positive at weaning

The influenza status of the piglets at weaning was influenced by several factors.

Seasons and vaccination status of the sows against influenza influenced piglet infection status at weaning. Indeed, sow influenza vaccination was significantly associated  with a decreased probability of piglets testing influenza positive at weaning. Both whole-herd and pre-farrow vaccination protocols were better compared to no vaccination and there were no differences between both protocols. Additionally, having influenza positive gilts at entry increased the probability of detecting positive piglets at weaning.

Among all the factors evaluated, sow influenza vaccination and gilt influenza status at entry were the only factors associated with influenza in piglets at weaning in Midwestern breed-to-wean farms.

Abstract

Breed-to-wean pig farms play an important role in spreading influenza A virus (IAV) because suckling piglets maintain, diversify and transmit IAV at weaning to other farms. Understanding the nature and extent of which farm factors drive IAV infection in piglets is a prerequisite to reduce the burden of influenza in swine. We evaluated the association between IAV infection in piglets at weaning and farm factors including farm features, herd management practices and gilt- and piglet-specific management procedures performed at the farm. Voluntarily enrolled breed-to-wean farms (n = 83) agreed to share IAV diagnostic testing and farm data from July 2011 through March 2017 including data obtained via the administration of a survey. There were 23% IAV RT-PCR positive samples of the 12,814 samples submitted for IAV testing within 2989 diagnostic submissions with 30% positive submissions. Among all the factors evaluated (n = 24), and considering the season-adjusted multivariable analysis, only sow IAV vaccination and gilt IAV status at entry significantly reduced (p-value<0.05) IAV infections in piglets at weaning. Results from this study indicate that veterinarians and producers could manage these identified factors to reduce the burden of influenza in piglets prior to wean and perhaps, reduce the spread of IAV to other farms and people.

Read the entire publication on the journal website.

 

Science Page: Making epidemiological sense out of large datasets of PRRS sequences

This is our Friday rubric: every week a new Science Page from the Bob Morrison’s Swine Health Monitoring Project. The previous editions of the science page are available on our website.

This week, we are sharing an epidemiological report regarding a large PRRS sequence dataset from Dr. Igor Paploski in the VanderWaal research group.

Key points:

  • Occurrence of PRRS lineages is not equal in different years, systems or production types
  • Occurrence of specific PRRS lineages is associated with movement of animals
  • Continuous surveillance for PRRS occurrence is important in understanding its determinants and might be able to provide insights that can
    help on its prevention

By utilizing a dataset of 1901 PRRS sequences provided by the Morrison Swine Health Monitoring Project (MSHMP) participants over 3 recent years, the spatiotemporal patterns in the occurrence of different lineages of PRRSV was described and the extent to which the network of pig movement between farms determines the occurrence of PRRS from similar lineages was investigated.

PRRS lineages occurred at different frequencies across geographically overlapping production systems. Preliminary analysis showed that the relative frequency in which specific lineages occur increase while others are decrease over time. The rate at which these changes occur appears to be system-specific. Some lineages were also more common in farms of specific production types (i.e. sow farm or nurseries). As expected, farms that were connected via pig movements were more likely to share the same lineages than expected by chance across all years.

These findings suggest that system-specific characteristics partially drive PRRS occurrence over time and across farms of different production types. Our results also
indicate that animal movement between farms is a driver of PRRS occurrence, strengthening this hypothesis of viral transmission.

Additional research is needed to quantify risks and develop mitigation measures related to animal movement.

Large PRRS sequencing dataset

Science Page: Transmission and survivability of African swine fever virus

boar-3599160_1920
Wild boar  Source:pixabay.com

This is our Friday rubric: every week a new Science Page from the Bob Morrison’s Swine Health Monitoring Project. The previous editions of the science page are available on our website.

This week, we are sharing a literature review on ASF virus transmission and survivability created by Carles Vilalta. Other recent posts on African Swine Fever can be found on this blog.

Keypoints

  • New introductions of ASF to free areas of the disease are usually by uncooked pork fed to pigs.
  • Virus can be inactivated with temperature and low pH.
  • Survivor animals may play a role in the transmission and persistence of the disease.

Further outbreaks of African Swine Fever virus (ASFV) were reported last week in China several miles away from what is thought to be the first outbreak. This geographic dispersal leads us to think about dissemination mechanisms within the country and between countries.

EPIDEMIOLOGY

Infected animals will go through a viremic phase and can shed the virus through nasal secretions, feces and urine. Therefore, the main transmission route is oral-nasal, as pigs can be exposed to ASF positive secretions or tissues (i.e. pork products). Indirect transmission can also occur by exposure to contaminated fomites. This virus can also be transmitted by ticks. This vector-borne route becomes relevant when the wild boar
population is present and moves across regions and countries. The common introduction route into ASF free regions is usually through positive pigs transported into the area, or contaminated pork products that are fed to other pigs. ASFV has also been detected in air samples; however, airborne transmission is considered a secondary route of transmission due to the high virus load needed.

VIRUS SURVIVABILITY

Inactivation and persistence

Although ASFV is highly resistant, the virus can be inactivated at pH < 4 and pH >11. Survivability outside the host is heavily related to temperature. For instance, the infectious half-life in urine and feces can range from 3 to 15 days and 4 to 8 days at 37°C and 4°C, respectively. The virus may persist for several weeks or months in frozen, fresh, or uncooked pork, as well as in salted dried pork products. In contrast, ASFV is inactivated at high temperatures (i.e. 70°C cooked or canned hams) and in cured or processed products such as Spanish cured pork products after day 122–140 of curing. Pigs can become persistently infected and the virus can stay viable in their carcasses for up to six months. Therefore, infected carcasses represent a risk to other pigs. More recently, an investigation simulating a trans-Atlantic shipping of ASFV contaminated feed ingredients from Europe proved that viable virus can be recovered after 30 days.

The role of survivor pigs

ASFV recovered and sub-clinically infected pigs become a source of virus to other pigs. This plays an important role in disease transmission and persistence in endemic areas as well as becoming one of the most important routes of transmission into disease-free zones. In-vivo experiments have revealed an infectious period of moderately virulent virus isolates ranging from 20 to 40 days. In another in-vivo transmission study, pigs that had been exposed to ASFV 90 days prior were commingled with naive pigs and the virus was transmitted to naive pigs.

Serological field studies performed in positive regions of Brazil, the Iberian Peninsula, East Africa, Kenya and Uganda revealed that the there was a very low percentage of seropositive animals one year after the outbreak. It was hypothesized that those few seropositive pigs were still carriers and could have been responsible of some of the newer outbreaks.

CONCLUSION

ASF has a complex epidemiology with different routes of transmission that can involve animals and ticks as direct transmission, and contaminated clothes, tools, and surfaces as indirect transmission. Thus, early detection and intervention of the diseases are key to containing disease spread in absence of an effective vaccine.

Science Page: Effective disease surveillance and response strategies depend on detailed swine shipment data

This is our Friday rubric: every week a new Science Page from the Bob Morrison’s Swine Health Monitoring Project. The previous editions of the science page are available on our website.

This week,  we are sharing a report regarding the use of swine shipment data for effective disease surveillance by Drs. Amy Kinsley, Meggan Craft, Andres Perez, and Kim VanderWaal.

Key point:

  • A production system’s vulnerability to disease spread can be greatly reduced when selectively identifying a subset of farms as disease control targets.

What was done:

In this study, we used a network approach to describe annual movement patterns between swine farms in three multi-site production systems (1,063 farms) in the United States.

We measured:

  1. degree: number of farms to which a farm ships or receives pigs
  2. farm’s individual contribution to disease spread via its movements
  3. mean infection potential (MIP), which measures potential incoming and outgoing infection chains

What was found:

Removing farms based on their mean infection potential substantially reduced the potential for transmission of an infectious pathogen through the network when compared to removing farms at random, as shown by a reduction in the magnitude of R0 attributable to contact pattern.
The MIP was more efficient at identifying targets for disease control compared to degree and farm’s contribution to disease spread.

What does this mean?

By targeting disease interventions towards farms based on their mean infection potential, we can substantially reduce the potential for transmission of an infectious pathogen in the contact network, and performed consistently well across production systems.
Fine-scale temporal movement data is important and is necessary for in-depth understanding of the contact structure in developing more efficient disease

 

 

 

Science Page: Assessment of PRRS area spread for sow herd outbreaks in US swine dense regions

This is our Friday rubric: every week a new Science Page from the Bob Morrison’s Swine Health Monitoring Project. The previous editions of the science page are available on our website.

This week, we are sharing a project from Dr. Andreia Arruda in collaboration with the MSHMP team regarding Porcine Reproductive and Respiratory Syndrome virus (PRRSV) area spread for sow herd outbreaks in US swine dense regions.

Dr. Arruda has also been investigating PRRS seasonality in the US and how topography surrounding a farm influences outbreak risk.

Key points

  • Strong evidence of area spread was not found after evaluating three farm clusters located in two swine dense regions.
  • All barns of a nursery/finishing site should be sampled to define status.
  • Sick pen might not be the best target when sampling for PRRSV in grower pig sites

Background and Objectives

Area spread refers to the transmission of a pathogen (here PRRSV) through small particles in the air as well as through fomites on which the pathogen would have deposited on.

The objective of the study was to determine if the virus detected in a recently infected sow farm was similar to the one detected in neighboring farms (in other words: was local spread a likely source of infection?)

Methods and Results

35 farms were monitored for PRRSV. As soon as a farm broke, all of the neighboring farms were sampled for PRRSV independently of the type of production on site. If a sick pen was present on the farm, effort was made to include it in the sampling. Positive samples were then sequenced to compare to the original virus from the outbreak.

PRRS area spread arruda
Graphical representation of the results of one specific region.

For two of the three area spread assessments performed, no similar sequence to the one obtained from the farm under investigation was found. Also it was not always possible to detect PRRSV in sick pens of the growing pig sites sampled in our study.

Science Page: Stability of Porcine Epidemic Diarrhea Virus on Fomite Materials at Different Temperatures

This is our Friday rubric: every week a new Science Page from the Bob Morrison’s Swine Health Monitoring Project. The previous editions of the science page are available on our website.

This week, we are sharing the summary of Dr. Cheeran’s team study on the stability of PEDv on fomite materials at different temperatures.

Key points:

  • Type of material and temperature have an impact on PEDV stability.
  • Infectious PEDV was not recovered from any fomite material after 2 days at room temperature (25ºC / 77ºF).
  • PEDV showed higher stability on plastic, cloth, Tyvek® coveralls, aluminum foil, Styrofoam at 4ºC (39.2ºF).
  • Virus could be detected by qRT-PCR from contaminated fomites even when infectivity was not observed.

PEDV survival on fomites Cheeran et al

Click here for our full post on the subject.

Influenza epidemiology in breed-to-wean farms and infection dynamics in nursery pigs

Fabian Chamba portrait photoEarlier this year, Dr. Fabian Chamba Pardo successfully defended his PhD under the supervision of Drs. Montse Torremorell and Marie Culhane. The focus of his thesis is influenza epidemiology with an emphasis on sow farms and nurseries. We share with you today a summary of his work.

Motivation

Influenza is an economically important disease in pigs and a public health threat. Breed-to-wean (BTW) farms play a central role in influenza epidemiology and control because piglets maintain and disseminate influenza A virus (IAV) to other farms. Despite the importance of piglets in influenza epidemiology, there is limited information on IAV infection parameters in piglets, risk factors that impact IAV prevalence in piglets at weaning, and how strategies that are implemented in BTW farms affect IAV infections in weaned pigs.

Objectives

In this thesis, my goal was to address some of the questions that are central to the transmission and control of influenza in BTW farms, especially infection in piglets ready to wean. The questions addressed are also critical to guide control strategies to mitigate IAV infections in the post weaning period. More specifically, I aimed to: 1) estimate herd-level prevalence and seasonality of influenza in BTW farms, 2) evaluate farm factors associated with IAV infection in piglets at weaning, 3) assess transmission patterns and parameters of influenza in nursery pigs based on IAV prevalence at weaning, and 4) evaluate the impact of maternally-derived antibodies (MDA) at weaning on IAV infection parameters in nursery pigs.

Research Chapter 1

Influenza herd-level prevalence and seasonality in breed-to-wean pig farms in the Midwestern United States

Article published in Frontiers in Veterinary Science: https://www.frontiersin.org/articles/10.3389/fvets.2017.00167/full

Results showed that IAV herd-level prevalence in piglets at weaning from Midwestern BTW farms is seasonal with higher infection rates in winter (December) and spring (May) than those in summer and fall. Additionally, influenza seasonality was partially explained by the seasonal variations of outdoor air absolute humidity and temperature. Finally, there was significant genetic diversity of influenza strains circulating in those farms and that, co-circulation of more than one genetically distinct clade over time was very common in the studied farms. This is critical knowledge that may help to identify high risk periods where influenza control measures can be placed. It may also help to create research opportunities on absolute humidity and influenza transmission in pigs and finally, it supports other studies that have shown that genetic diversity and circulation is wide and common and that new vaccines and vaccination strategies should take that into consideration.

Chamba herd level influenza prevalence in the Midwest
Influenza A virus herd-level prevalence in Midwestern US breed-to-wean pig farms.

Research Chapter 2

Breed-to-wean farm factors associated with influenza A virus infection in piglets at weaning

In this chapter, there were 24 farm factors evaluated for their association with influenza at weaning and among those, only IAV sow vaccination and the IAV-negative status of replacement breeding females (gilts) at entry to the herd were significantly associated with less IAV infected piglets at weaning. This is critical information that veterinarians and producers may use to manage IAV levels at weaning. In addition, there was also a lack of significant association with factors such as air filtration and farm density which may be indicative that endemic influenza infections are more important than airborne lateral transmissions between farms. Finally, disease control strategies such as herd closure, early weaning, batch farrowing, gilt isolation and gilt influenza vaccination were not fully evaluated in this study. Hence, more work is needed to further understand how to use these strategies to decrease influenza infections in pigs.

sow vac protocol - Copy
Influenza A virus (IAV) positive mean predicted probabilities over time for breed-to-wean farms with different sow vaccination protocols.

 Research Chapter 3

Influenza A virus transmission patterns and parameters in growing pigs

Results indicate that groups of piglets with different prevalence at weaning had different transmission patterns and parameters after weaning and these patterns were characterized by 1, 2 or no peaks of infection after weaning. Piglets with low prevalence at weaning had less influenza infections in the nursery. This information may help producers and veterinarians to make informed decisions when it comes to use control strategies such as sow vaccination aimed to reduce influenza infections in the nursery.

Figure 1

Research Chapter 4

Effect of maternally-derived antibodies on influenza A virus infection in growing pigs

In my last chapter, I reported that if pigs had high levels of strain-specific maternally-derived antibodies at weaning, IAV infection occurred later and it was of shorter duration after weaning. Piglets with hemagglutination inhibition (HI) titers of 1:40 or higher were less likely to test IAV positive at weaning and during the nursery. These results indicate that strain-specific maternally-derived antibodies generated with sow vaccination pre-farrow significantly reduce influenza infections at weaning and in the nursery.

Figure 1 (1)

Conclusions

Knowledge of influenza seasonality and what factors are significantly associated with influenza in breed-to-wean farms can help producers and veterinarians to better use and allocate influenza control strategies such as sow vaccination. In addition, lower prevalence of influenza at weaning due to high strain-specific maternally-derived antibodies levels may help decrease influenza spread from wean-to-finish farms. Reducing the burden of influenza in growing pigs should decrease influenza-associated economic losses and the generation of novel strains, including strains with pandemic potential. More studies are needed to further elucidate control strategies to limit influenza infections and spread in pigs.