This document summarizes a clinical case report of an outbreak of pandemic H1N1 influenza virus (H1N1pdm) in an Italian pig farm between July 2012 and March 2013. The farm experienced increased respiratory disease and mortality in post-weaned pigs, testing confirmed the presence of H1N1pdm virus. A vaccination program was implemented using an inactivated trivalent swine influenza vaccine. Following vaccination of sows and piglets, clinical signs reduced and virus detection decreased, controlling the H1N1pdm outbreak.

1. Abstract accepted for 6th Asian Pig Veterinary Society congress, Ho Chi Minh City, Vietnam, September 23-25, 2013
CLINICAL CASE REPORT OF PANDEMIC H1N1 IN ITALY
Alberto Castellan1, Emanuela Foni2, Andrea Luppi3, Giorgio Leotti4, Thaïs Vila5
1DVM, Vicenza, Italy; 2IZSLER, Parma, Italy; 3IZSLER, Reggio Emilia, Italy;
4MERIAL S.p.A. Italia, Milan, Italy;5MERIAL SAS, Lyon, France
giorgio.leotti@merial.com
Introduction
Swine influenza (SI) is an acute respiratory disease caused by Influenza A viruses. This case report describes clinical observations and isolation of pandemic H1N1 (H1N1pdm) virus from an outbreak of acute respiratory disease and mortality in an Italian farrow-to-feed operation. Moreover the vaccination strategy and subsequent results are reported.
Case Description
The operation is a 1000-sow farrow-to-feed farm operating one-week batch system and self-replacement of gilts, located in Po valley, Italy. Post-weaners are grown until 40 kg under a continuous flow production system. PRSSv is considered to be controlled by sow vaccination and piglet vaccination at three weeks of age with a MLV vaccine despite recirculation evidences are regularly observed at the end post-weaning stage. No vaccination program against SI is ongoing in the farm.
July-August 2012: Batches of pigs aged 45-70 days regularly displayed severe and chronic respiratory symptoms with 20%-to-30% prevalence. Routine antibiotherapy did not affect clinical signs occurence. A full serological screening conducted at the end of August evidenced serological titres against H1N1pdm.
Beginning of September 2012: Nasal swabs were collected in hyperthemic 45-day-old pigs. The nasal swabs were submitted to Real Time PCR for Gene M of influenza A virus1 and the samples positive were submitted to virus isolation. The isolates were characterized by serology using reference sera and by Multiplex RT-PCR2 as H1N1pdm.
October 2012: The herd experienced similar clinical observations first in the stock gilts at the beginning of the month. No similar abnormality was noticed until the end of the month during which post-weaners displayed symptoms with a steadily increasing severity over time. Clinical observations and laboratory analyses performed during October 2012 are reported in Table 1.
Table 1. Summary of investigations in October 2012.
02/10/2012
Diagnostic investigation results
10 affected gilts:
Positive H1N1pdm (serology)
5 asymptomatic gilts:
Negative H1N1pdm (serology)
Dead post-weaners
aged 40-70 days:
Interstitial pneumonia (gross lesions evaluation) SIV -; PRRSv +, Streptococcus type 2 +
Haemophilus parasuis + (PCRs and bacteriological results)
From 02/10/2012 to 23/10/2012
No clinical signs
23/10/2012
Diagnostic investigation results
Dead pigs:
Enzootic pneumonia like lesions (gross lesions evaluation)
Feverish 50-day-old post-weaners:
4/6 H1N1pdm positive nasal swabs (PCR and virus isolation)
31/10/2012
Diagnostic investigation results
Post weaners displaying severe clinical signs:
11 H1N1pdm positive nasal swabs (PCR and virus isolation)
Interstitial pneumonia (gross lesions )
As a consequence, mortality rate raised from a normal baseline of 4-5% to 18-20% during acute phase depending on the piglet batch. Fertility of the gilts and sows were nevertheless not affected during SIV outbreaks.
Vaccination program:
In the absence of a specific H1N1pdm vaccine, the following vaccination plan against SI was implemented in the farm with an inactivated adjuvanted vaccine containing the 3 SIV strains H1N1, H1N2 and H3N2 (GRIPOVAC ®3, MERIAL):
- Vaccination of the sows in October 2012
- Mass vaccination of the post-weaners end 10/2012,
- Implementation of a booster injection in sows before farrowing at the beginning of 12/2012.
Reduction of clinical symptoms and H1N1pdm circulation was observed following both vaccination of sows and mass vaccination in piglets (Table 2). Particularly, following the implementation of the full flu vaccination program in sows, the clinical situation of the post-weaners was stabilized to normal and the H1N1pdm virus was rarely found in diagnosed piglets.
Table 2. Summary of laboratory investigations following vaccination implementation. Nasal swabs were collected in feverish pigs; lungs investigations were performed in dead pigs.
05/12/2012
Lungs: 0/5 SIV positive ; 3/5 PRRSv positive
January 2013
Proportion of H1N1pdm positive nasal swabs decreased,
lungs were always flu negative
March 2013
1/15 H1N1pdm positive nasal swabs,
0/5 H1N1pdm positive lungs
Conclusion
A survey conducted in approximately two thousand 2008-2009 outbreaks of respiratory disease in Italian pig farms demonstrated an extremely low prevalence of H1N1pdm3 (1 positive isolation out of 216 Influenza A gene M PCR positives out of 1854 samples from outbreaks of respiratory disease). This case reports H1N1pdm recurrent findings over a 8-month period in 2012-2013 in an Italian herd. H1N1pdm circulation was detected in the whole herd. Other respiratory agents being satisfactorily controlled, the virus was associated with acute respiratory disease outbreaks and high mortality in post-weaners despite mild clinical signs are more often used to be reported4,5. The implementation of a swine influenza vaccination program helped to control H1N1pdm circulation and to reduced clinical symptoms.
Literature cited
1. Slomka et al. 2010. Influenza Other Respi Viruses. 4(5):277-93. doi:10.1111/j.1750-2659.2010.00149.x.
2. Chiapponi C. et al. 2012. J. Virol. Methods. 184, 117-20
3. Foni et al. 2010. 36th Annual Meeting of SIPAS, Montichiari, Italy
4. Howden KJ et al. 2009. Can Vet J, 50, 1153-1161
5. Holyoake PK et al. 2011. Australian Vet. J. Vol89, No 11, 427-431