October 2018 – Swine in Minnesota

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.

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.

Use of processing fluids and serum samples to characterize PRRSv dynamics in 3 day-old pigs

This new publication in Veterinary Microbiology describes the best methodology to monitor 3-day-old piglets for PRRS, using both serum and processing fluid samples. The first author of the publication is Dr. Carles Vilalta, member of the Morrison Swine Health Monitoring Program (MSHMP) team.

Key points

Processing fluids (PF) constitute a useful sample to detect PRRSV infections at processing.
PRRSV can circulate in the farm at a low prevalence, increasing the chances of a re-break.
Young parity female litters should be targeted for PRRSV detection.
Current practice to bleed 30 pigs could be underestimating PRRSV prevalence in the herd.
The decrease in sensitivity at the litter level can be compensated by sampling more litters to detect PRRSV at the herd level.

Methods

The study was conducted in a 6,000 sow farm with a PRRS stable status. Every 3 weeks, serum samples and processing fluids were collected from all piglets in 10 randomly chosen litters. This process was then repeated 8 times, meaning that the farm was monitored for a total of 24 weeks. All samples were tested via PCR. 3 samples with the lowest Ct value were tested by virus isolation and sequencing of the ORF5 gene was performed.

Results

10.6% of the piglets tested positive for PRRSv via serum PCR, representing 29.8% of the litters. The same number of litters tested positive via processing fluid PCR testing.

The percentage of processing fluid positive samples was significantly higher is parity 1 and 2 sows compared to parity 3 and older sows. Additionally, a significant association between parity and probability of detecting a positive pig was observed.

A significant higher proportion of positive serum samples was observed in males compared to females. A similar trend was obtained when comparing positive Ct values by gender with values from males being lower (i.e., higher viral load) than those from females.

ct value processing fluids versus serum samples PRRS — Cycle threshold (Ct) positive (≤35) and suspect (between >35 and 40) value distribution for serum (S, triangle) and processing fluid (P, circle) samples overtime (2, 5, 8, 11, 14, 17, 20 and 23 weeks post outbreak). Horizontal black lines indicate the mean Ct values for each week and sample type

Using a Ct value of 37, processing fluid samples had a Se and Sp of 87% (95% CI: 66%–97%) and 94% (95% CI: 85%–99%), respectively when compared with litter RT-PCR results obtained from individual serum samples. The total agreement between both tests was 92.2% and the positive and negative predictive values were 87% (95% CI: 66%–97%) and 94% (95% CI: 85%–99%), respectively. False negative processing fluids were identified in litters having 2 or less PRRSV positive piglets

The agreement between the PF and serum results was kappa = 0.81 (95% CI: 0.59–1.00). The difference in the proportion of positive samples between both types of sample was not statistically significant (McNemar test, p = 1).

Abstract:

Collection of serum samples of pigs at weaning to monitor for porcine reproductive and respiratory syndrome virus (PRRSV) has become a common practice to determine PRRSV herd infection status. Diagnostic sensitivity of this practice is low in herds undergoing PRRSV elimination once prevalence of infection is near zero. Thus, the goal of this study was to characterize the dynamics of PRRSV infection in 3 day-old pigs overtime using serum and serosanguineous fluids obtained as part of castration and tail docking practices (processing fluids (PF)). Secondary goal was to estimate sensitivity and specificity of PF in the 3 day old population. A 6000 breed-to-wean sow herd was monitored every three weeks for 23 weeks after a PRRSV outbreak by collecting both PF and individual serum samples from all pigs in the selected litters. Out of the 77 litters tested, 23 (29.8%) were identified as positive using the PF and the serum samples, with a Cohen’s kappa statistic of 0.81 (95% CI: 0.59–1) between the results obtained in each sample type. The sensitivity and specificity of the PF relative to the results in serum was 87% (95% CI: 66%–97%) and 94% (95% CI: 85%–99%) respectively. The percentage of PRRSV positive litters decreased over time and litters from gilts were more likely to test positive than those from older sows. Overall, the study demonstrates that PF can be a convenient and reliable specimen to monitor PRRSV infection in breeding herds.

Follow the link to read the entire article.

Science Page: Quarterly review of MSHMP reported PRRSv Restriction Fragment Length Polymorphism (RFLP) patterns

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 from the MSHMP team regarding reported PRRS RFLP patterns.

Keypoints:

Recording PRRSv RFLP and sequences will provide better insights into the epidemiology of the disease at local, state and national level.
Building a RFLP database will allow us to assess which factors could be involved or related with the emergence of a new RFLP.
The predominant pattern RFLP in this quarterly review is the 1-7-4.

In the first quarter of the 2018/2019 incidence year, 20 breaks affecting 12 production systems were reported. Out of these, 4 occurred in July, 13 in August and 3 in September.

Of those 20 farms, three had a break while still being status 1, one was status 2 in the process of eliminating the disease (not using any immunization protocol at that point), 6 were using field virus as the acclimatization protocol (2fvi), 8 were using vaccine (2vx), one was provisionally negative (status 3) and one broke from a status 4 after being almost 4 years completely negative (see figure below).

The distribution of the breaks is wide and affects different states. Thus, we had 6, 1, 4, 1, 4, 2, 1 and 1 break in the states of IA, IN, MN, MO, NC, NE, OK and PA, respectively. The closest 2 farms that broke were 1.2 miles apart, belonged to the same company and had the break a week from each other (no sequences was provided).

Eight out of the 20 breaks reported were accompanied by the associated RFLP. The predominant (4 out of 8) RFLP pattern since July is 1-7-4. Iowa was the state with the highest number of 1-7-4 cases.

Swine Disease Global Surveillance Report: bi-monthly update

The new swine disease global surveillance report was released earlier this week. Coordinated by the University of Minnesota in collaboration with the Swine Health Information Center, the aim of these reports is to have a structure for near real-time identification of hazards. In this report, updates are focusing on African Swine Fever in China and Belgium, Classical Swine Fever in Brazil and Japan, Foot and Mouth Disease in Colombia.

African Swine Fever

CHINA

Since last August, 30 outbreaks of ASF have been reported in China spreading through nine provinces. So far in October, seven outbreaks occurred, five of them in the province of Liaoning in the northeast of the country where the first case was reported two months ago. This peak in the number of outbreaks suggests the situation still remains far from
under control.

BELGIUM

Belgium keeps investigating the presence of the disease in the wild boar population. Fences and gates were built aiming to isolate an area, but so far 84 animals were detected positive since the first detection of the disease in the country, on September 13. There are several theories regarding introduction of the virus in this region in Europe and the role people play in carrying swine by-products or even hunting materials into this region is being discussed and investigated.

Classical Swine Fever

BRAZIL

On October 8, Brazilian Ministry of Agriculture (MAPA) reported an outbreak of CSF in a backyard free-range farm located in the state of Ceará (Forquilha-CE). The outbreak was reported to the veterinary service, where high mortality rates and clinical signs (anorexia, fever, incoordination) were observed in sows and younger pigs. The fatality rate was 97 percent and the remaining animals were euthanized. The farm was then isolated followed by the euthanasia for the animals, sanitary destruction of carcasses, disinfection, a restriction of movements in the region, and an initiation of an investigation in surrounding farms.

JAPAN

One month after the identification of the outbreak of CSF in Japan, investigations were implemented in the region of Gifu Prefecture, along with 25 other Prefectures. Overall, 19 wild boars were found positive (15 percent) for CSF in Gifu, and no positive animals were identified elsewhere. Investigations are ongoing.

Foot and Mouth Disease

Currently, the following countries have reported the presence of FMD in swine: China, Colombia, South Korea, North Korea, and Russia.

COLOMBIA

On October 10, the Colombian Agricultural Institute (ICA, by its Spanish acronym) reported an outbreak of FMD in a swine farm, located in the Departamento de Cesar, north of the country and very close to the Venezuelan border. Ten days prior, another outbreak was identified in cattle, in a city located approximately 500 miles (800km) away, in Departamento de Boyaca. Both regions have vaccination coverage and were recognized as “free with vaccination” on December 2017.

The full report with maps and location of the various outbreaks is available to read here.