Epidemiology – Page 15 – Swine in Minnesota

Best of Leman 2017 series #2: P Yeske – A survival analysis of Mycoplasma hyopneumoniae elimination efforts

We launched a new series on the blog last month. Once a month, we are sharing with you a presentation given at the 2017 Allen D. Leman swine conference, on topics that the swine group found interesting, innovative or that lead to great discussions.

Our second presentation today is from Dr. Paul Yeske from Swine Vet Center, who is coming back on his experience with Mycoplasma hyopneumoniae elimination and giving us an update if the herds stayed negative.

To listen to this presentation, please click on the picture below:

Happy Thanksgiving to you and your loved ones!

Flu control: it’s all about the piglet

Our latest collaboration with the National Hog Farmer was written by Drs. Montse Torremorell and Marie Culhane from the University of Minnesota.

Flu never seems to go away in some herds and that is because there are groups of pigs, or subpopulations, that are able to maintain and spread the flu virus.

One of the most important subpopulations that have been identified as sources of virus on a farm is the piglets. Piglets may be infected, but may not show any signs of disease, and as a result, are silent spreaders of flu. Then, at weaning, a small, but significant, percentage of the piglets can be subclinically infected with flu, meaning they appear healthy but are shedding flu at the nursery or wean-to-finish site.

This causes a challenge for producers because even though piglets are born free of flu, they tend to be contaminated by the dam during their second week of like. The peak of flu-positive piglets occurs at weaning when piglets are moved to a nursery where they may be put in contact with naive piglets from another source and therefore become a major source of infection.

We need to understand how piglets become infected in the farrowing room in order to prevent it. Sow vaccination is a tool commonly used to protect piglets via the transmission of antibodies through the colostrum or maternal immunity. It has been shown to decrease the prevalence of flu-positive piglets at weaning but is insufficient to constantly wean negative animals.

“At the University of Minnesota, we have been measuring the impact of piglets on the spread of flu for years. We found, in a study by Allerson of 52 swine breeding herds in the United States, 23 herds (44%) tested IAV RT-PCR positive at least once during a six-month study period. Groups of piglets from those herds also tested positive for flu at weaning about 25% (75 of 305) of the time.

Along those same lines, Chamba and partnering sow farms reported that out of the 34 farms studied for more than five years, all sow farms tested positive for flu at one time or another and the level of flu infection in the groups of weaned pigs ranged from 7% to 57%. More importantly, in this study, approximately 28% (427 of 1,523) of groups of pigs tested positive at weaning. […]

Ultimately, the successful control of on-going flu infections in growing pigs will depend on the sow farm’s ability to wean a negative pig […]”

Click to read the entire article on the National Hog Farmer website.

Science Page: Natural and experimentally-induced Senecavirus A infections in boars

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 study from Dr. Matt Sturos from the University of Minnesota, Veterinary Diagnostic Laboratory regarding Senecavirus A in boars.

Key points

Naturally-infected boars have been documented to shed Senecavirus A (SVA) RNA in semen for up to three months after exhibiting vesicular disease.
Experimentally-infected boars shed SVA RNA in semen for up to three weeks post-inoculation.
The majority of experimentally-infected boars did not exhibit clinical signs or develop apparent lesions.

Senecavirus A in boars — Testis of boar naturally-infected with Senecavirus A. Bright red areas indicate positive signal for SVA by in-situ hybridization.

“This update shows that SVA RNA is shed in semen from both naturally-infected and experimentally-inoculated boars. The prolonged shedding of viral RNA in semen and the presence of SVA RNA in the testes and tonsils of the naturally-infected boars for up to three months are concerning findings and raises the possibility of persistent infection in boars. While the duration of shedding in semen for the experimentally-infected boars was considerably shorter than for the naturally-infected boars, the fact that all contemporary-strain boars had PCR-positive semen on at least one collection indicate that shedding in semen is a repeatable phenomenon and shedding occurred in some boars which did not exhibit clinical signs or develop vesicular lesions. It is currently unknown whether semen from infected boars can serve as a source of infection if used to inseminate susceptible females.”

Influenza Herd-Level Prevalence and Seasonality in Breed-to-Wean Pig Farms in the Midwestern United States

The Torremorell lab is continuing to explore swine influenza epidemiology in this recent publication from Dr. Fabian Chamba Pardo in Frontiers in Veterinary Science. After showing that multiple genome constellations of similar and distinct influenza viruses co-circulate in pigs, the group is now presenting new data about influenza herd-level prevalence in the Midwest, and how it is influenced by seasons. Click on the banner below to read the entire research article.

60 sow farms from a single Midwestern production system were enrolled in this study. Between one and seven oral fluid samples were collected at each farm weekly and meteorological data (air temperature and relative humidity) was compiled from stations located from the farms.

Swine herd level prevalence Chamba 2017 28% of submissions had at least one influenza positive result. All farms tested positive at least once during study period. Herd-level prevalence ranged from 7% to 57% as show in the figure above. Prevalence was low in summer, rose during fall, and peaked twice in both early winter (December) and late spring (May). August was the month with the lowest prevalence. Influenza herd-level prevalence was higher when both mean outdoor air temperature and air humidity were lower.

The most common clades identified were H1 delta 1, H1 gamma 1, and clusters H3 IV A and H3 IV B. Furthermore, 21% of the farms had 3 different influenza genetic clades circulating during the study period and 18% had 2.

Abstract

Influenza is a costly disease for pig producers and understanding its epidemiology is critical to control it. In this study, we aimed to estimate the herd-level prevalence and seasonality of influenza in breed-to-wean pig farms, evaluate the correlation between influenza herd-level prevalence and meteorological conditions, and characterize influenza genetic diversity over time. A cohort of 34 breed-to-wean farms with monthly influenza status obtained over a 5-year period in piglets prior to wean was selected. A farm was considered positive in a given month if at least one oral fluid tested influenza positive by reverse transcriptase polymerase chain reaction. Influenza seasonality was assessed combining autoregressive integrated moving average (ARIMA) models with trigonometric functions as covariates. Meteorological conditions were gathered from local land-based weather stations, monthly aggregated and correlated with influenza herd-level prevalence. Influenza herd-level prevalence had a median of 28% with a range from 7 to 57% and followed a cyclical pattern with levels increasing during fall, peaking in both early winter (December) and late spring (May), and decreasing in summer. Influenza herd-level prevalence was correlated with mean outdoor air absolute humidity (AH) and temperature. Influenza genetic diversity was substantial over time with influenza isolates belonging to 10 distinct clades from which H1 delta 1 and H1 gamma 1 were the most common. Twenty-one percent of farms had three different clades co-circulating over time, 18% of farms had two clades, and 41% of farms had one clade. In summary, our study showed that influenza had a cyclical pattern explained in part by air AH and temperature changes over time, and highlighted the importance of active surveillance to identify high-risk periods when strategic control measures for influenza could be implemented.

A constellation of strains co-circulate in pigs during influenza epidemics

This recent publication in Nature comes from the Torremorell’s lab and aims at answering the question of the number of strains circulating in pigs during an influenza outbreak and how genetically different they may be. The full article is available in open access, click on the banner below to access it.

To answer the question of multiple strains of influenza in pigs, the group followed a cohort of 132 pigs placed in a 2,200-head a wean-to-finish barn, endemic for influenza. All the pigs originated from the same sow farm . The history of past influenza episodes did not include any information regarding the strain of viruses circulating in the barn. Nasal swabs were collected for each individual pig and were tested in the laboratory by PCR.

Results from this study showed that:

Only 2 pigs out of 132 tested negative every week during the entire duration of the study.
Around 88% of the pigs tested positive for influenza more than once.
20.5% of pigs were positive for influenza at weaning.
Weekly influenza prevalence ranged between 0% and 65%.
3 different viral groups were identified VG1, VG2, and VG3.
Groups belonged to the swine H1-gamma, H1-beta and H3-cluster-IV influenza A respectively. (Here is a review of the H1 genetic clades and one of the H3 genotype patterns)

The figure below shows the genetic make up of the influenza strains isolated each week, the viral group each genetic segment belonged to and the number of times this specific combination was found.

For example, the second line can be interpreted as: during week one, one sample in which 10 sequences were recovered, had influenza virus with segments 1, 2, 3, 4, 5, and 7 belonging to the Viral Group 1 (H1 gamma) and segments 6 and 8 were from Viral groups 1 and 3.

Influenza constellation Torremorell

In conclusion, this study shows that influenza infections in pigs after weaning and under field conditions are complex. The influenza virus genome is diverse and changes rapidly. Prolonged persistence of influenza viruses in pigs could be the result of multiple influenza epidemic events that take place repeatedly over time or the re-infection with influenza viruses that are closely related to each other.

Abstract

Swine play a key role in the ecology and transmission of influenza A viruses (IAVs) between species. However, the epidemiology and diversity of swine IAVs is not completely understood. In this cohort study, we sampled on a weekly basis 132 3-week old pigs for 15 weeks. We found two overlapping epidemic events of infection in which most pigs (98.4%) tested PCR positive for IAVs. The prevalence rate of infection ranged between 0 and 86% per week and the incidence density ranged between 0 and 71 cases per 100 pigs-week. Three distinct influenza viral groups (VGs) replicating as a “swarm” of viruses were identified (swine H1-gamma, H1-beta, and H3-cluster-IV IAVs) and co-circulated at different proportions over time suggesting differential allele fitness. Furthermore, using deep genome sequencing 13 distinct viral genome constellations were differentiated. Moreover, 78% of the pigs had recurrent infections with IAVs closely related to each other or IAVs clearly distinct. Our results demonstrated the molecular complexity of swine IAVs during natural infection of pigs in which novel strains of IAVs with zoonotic and pandemic potential can emerge. These are key findings to design better health interventions to reduce the transmission of swine IAVs and minimize the public health risk.