VIROLOGIE

Classical Swine Fever
• Role of birds in transmission of classical swine fever virus.
• Principles of sound control strategy.
• Infection of porcine reproductive and respiratory syndrome virus suppresses the antibody response to classical swine fever virus vaccination.
PRRS
• Costs of PRRSV in commercial production.
• Homologous PRRSV challenge after vaccination with an inactivated PRRS vaccine: Progressis® Merial.
• Is there a “new” PRRS?
• Experiences with eradication of PRRS in Danish swine herds.
• L’EARL Gicquel, adepte de la vaccination SDRP (Gicquel: owner of a swine operation system and PRRSV vaccination enthousiast).
• Parameters of humoral and cellular immunity following vaccination of pigs with a European modified-live strain of porcine reproductive and respiratory syndrome virus (PRRSV).
• Use of PRRS virus sequence information within herds.
• New data on homologous protection.
• Immunological features of porcine reproductive and respiratory syndrome (PRRSV) against homologous and heterologous challenge in a population of breeding age female swine.
PMWS-CIRCOVIRUS-PDNS
• PCV2-associated diseases: research and diagnostic update.
• PMWS-Immunologic stimulation and clinical signs.
• New insights in the pathogenesis of PCV2 infections in fetuses.
• PMWS problems persist.
• Effect of vaccination with selective bacterins on conventional pigs infected with type 2 porcine circovirus.
• In vitro studies on the infection and replication of porcine circovirus type 2 in cells of the porcine immune system.
• Porcine circovirus 2-associated disease in Eurasian wild boar.
• Survey of veterinary practitioners on PMWS and PDNS in the UK.
• Risk factors for porcine postweaning multisystemic wasting syndrome (PMWS) in 149 French farrow-to-finish herds.
Swine influenza
• Swine Influenza in Italy.
• Protection against a European H1N2 swine influenza virus in pigs previously infected with H1N1 and/or H3N2 subtypes.
• Association of porcine circovirus 2 with porcine respiratory disease complex.

Role of birds in transmission of classical swine fever virus.
KADEN V, LANGE E, STEYER H, BRUER W, LANGNER CH
J. Vet. Med, 2003, Volume 50, 357-359
The aim of this study was to understand how transmission of classical swine fever virus (CSFV) could have occurred between infected wild boars and domestic pigs during CSF epidemics in wild boars in Germany and more particularly if carrion birds served as vectors for virus spread. Domestic pigs were either in contact with laying hens inoculated with CSFV or fed with feces from contaminated crows and ravens. In both case no active transmission of CSFV was demonstrated. The role of carrion birds in the spread of CSFV is thus unlikely.

Principles of sound control strategy.
TOO H, SENEQUE S
Asian Pork Magazine, 2003, October/November, 18-21
When standard prevention and control measures for classical swine fever (CSF) get slack, the consequences of resulting outbreaks are economically devastating. The occasional occurrence of CSF outbreaks in Europe and the endemic situation in Asian countries leads the authors of this paper to warn pig producers against their potential lack of commitment. Several points are to abided by. First of all, the prevention of the entry of CSF virus into the herd purchasing replacement breeders from known CSF-free herds and the prevention of the spread of infection through proper disinfection procedures are to be considered essential. Furthermore, a correct use of vaccines intending handling, storage and appropriate timing of the vaccination programs considering the epidemiological status of the herd and the maternally derived antibody levels, is absolutely necessary. We remind you that the handbook, “ Classical Swine Fever: handbook for swine practitioners”, published by the authors with the assistance of Merial is available for further information.

Infection of porcine reproductive and respiratory syndrome virus suppresses the antibody response to classical swine fever virus vaccination.
LI H, YANG H
Veterinary Microbiology, 2003, Volume 95, 295-301
This study included four groups of pigs: in one group, pigs were inoculated intranasally with PPRSV and then vaccinated with a CSF vaccine C-strain provided by China Institute of Veterinary Drug Control, the three other groups were used as control group and animals were either only vaccinated, only inoculated with PPRSV, or sham-inoculated. Pigs infected with PPRSV prior to vaccination had significantly lower antibody response when compared to that obtained in control animals.

Costs of PRRSV in commercial production.
MAIN RG
Proceedings of the ISU Swine Disease Conference for Swine Practitioners 2003: 172-173
This paper reports an example of analysis to estimate the impact of PRRSV on wean-to-finish performance in a multi-site production system in the American Midwest. Three types of status were attributed: status 0 to consistently weaning PRRSV-negative pigs, status 1 to consistently PRRSV-positive finishing pigs with minimal seroconversion to PRRSV evident in late nursery and status 2 to consistently PRRSV-positive nurseries. An increased margin per pig weaned of 2.12$ and 7.07$ was evaluated for status 0 pigs over status 1 and status pigs respectively.

Homologous PRRSV challenge after vaccination with an inactivated PRRS vaccine: Progressis® Merial.
REYNAUD G, CHARREYRE C, TEDESCHI L, BRUN A, JOISEL F, JEANNIN P
Proceedings of the 1st APVS Congress, Seoul, September 2003, 171-172
Six-week old piglets were vaccinated twice with PROGRESSIS® (Merial) inactivated adjuvanted vaccine with a 3-week interval while others were kept as non-vaccinated controls. All of them were challenged intranasally with the parental virulent strain of PRRSV 35 days later. Subsequently, vaccinated and control animals were kept either separated in PRRSV-free premises or all together in the same barn. The results of this study confirm that PROGRESSIS® significantly reduces the percentage of viremic piglets, both in PRRSV-free and PRRSV-contaminated environment.

Is there a “new” PRRS?
ANONYMOUS
http://www.vetsci.sdstate.edu/prrs/SAMS.htm
Atypical severe outbreaks of reproductive failure have recently occurred in the USA. The syndrome was characterized by high rates of abortion (>10%) in short period of time (2-4 weeks) with high sow/boar mortality (>5%). PRRSV was clearly demonstrated to be involved but further investigations are needed to understand the risk factors associated with herds affected with this syndrome.

Experiences with eradication of PRRS in Danish swine herds.
BØTNER A
Association Française de Médecine Vétérinaire Porcine, Maisons-Alfort, 4-5 December 2003
The tricky situation of PRRS in Denmark has arisen from the introduction, in 1996, of a modified live vaccine based on an American strain of PRRSV (Ingelvac® PRRSV MLV, Boehringer Ingelheim) which has resulted in outbreaks of reproductive failure (abortions and stillborn piglets, mortality in suckling piglets) and the spread of the American (US) type of the virus among the Danish pig population. Currently both the European (EU) and the US types of PRRSV are circulating in Denmark. Two serologic tests, i.e. immunoperoxydase monolayer assay (IPMA) and double-blocking ELISA, allow to differentiate between the EU and US strains of PRRSV, the latter being routinely used for large scale screening whereas the former is used for serologic herd profiles. On a herd level, the sampling should be carried out in 4-5 pigs in each of the different age groups. The eradication strategy consists in: partial depopulation, one-way flow of pigs in the production and introduction of only immune breeding animals in the herd. The first objective is to achieve the stabilization of the sow unit with no virus shedding in order to obtain PRRSV-free piglets. However the risk of re-infection is still quite high due to the widespread of the virus.

L’EARL Gicquel, adepte de la vaccination SDRP (Gicquel: owner of a swine operation system and PRRSV vaccination enthousiast).
GILOT C
Porc Magazine October 2003, n°370: 60-62
The paper reports the successful implementation of Progressis® vaccination program in a French herd previously experiencing reproductive failure due to PRRSV. MERIAL killed oil-adjuvanted vaccine is used in breeders only and consists in a first vaccination (two injections at a 3-4 week interval) followed by a booster 60-70 days before each gestation, with a cost of 6 Euro per sow per year. A gain of 1.35 weaned piglet per sow was observed. However, the vaccination program is all the more beneficial if associated with measures such as a longer quarantine period prior to the introduction of new gilts.

Parameters of humoral and cellular immunity following vaccination of pigs with a European modified-live strain of porcine reproductive and respiratory syndrome virus (PRRSV).
SIPOS W, DUVIGNEAU C, PIETSCHMANN P, HÖLLER K, HARTL R, WAHL K, STEINBORN R, GEMEINER M, WILLHEIM M, SCHMOLL F
Viral immunology, 2003, volume 16, N°3, 335-346
The in vivo immunological response induced by the European strain of PRRSV was investigated and compared with that obtained in vitro.

Use of PRRS virus sequence information within herds.
TORRISON J, ROSSOW K, YESKE P
Allen D. Leman Swine Conference 2003: 46-51
The control of porcine reproductive and respiratory syndrome virus (PRRSV) is still under investigation. The determination and interpretation of its genomic sequence represents a useful weapon to battle against it. The recommended sampling protocol during an outbreak includes serum samples from clinically infected pigs (10-15 piglets at 4-5 days of age and 10-15 sows). Then samples are amplified by PCR and the sequence of the virus is determined with a comprehensive cost of 195$ for each sample. The interpretation of the virus sequence is based on three diagnostic reports i.e. the sequence of the opening reading frame 5 region, the dendrogram (relationships among groups of viruses) and the homology chart (percent base similarities of virus sequences). In PRRSV-positive herds, in case of concurrent infection, it is possible to determine whether the virus originates from the indigenous virus by mutation or whether it results from outside sources.

New data on homologous protection.
Allen D. Leman Swine Conference 2003: 52-54
Homologous immunity should not be taken as granted and PRRSV clearly proves it: animals are not completely protected against further homologous virus challenge since it is followed by a brief viremia, suggesting that, under experimental conditions, homologous immunity, though significant, does not provide a unfailing shield. To what extent this incomplete homologous immunity may have repercussions under field conditions has yet to be determined.

Immunological features of porcine reproductive and respiratory syndrome (PRRSV) against homologous and heterologous challenge in a population of breeding age female swine.
BATISTA L, DEE S, OLIN M, MOLITOR T, XIAO Z, MURTAUGH MP, JOO HS, PIJOAN C
Allen D. Leman Swine Conference 2003: 55-59
Humoral and cellular immune responses were assessed in both naïve and previously PRRSV-challenged gilts when re-challenged with different strains of PRRSV. On day 0, all gilts were inoculated with a field isolate. On day 120 they were allocated into 6 different groups: in group 1 animals were not subjected to further challenge, in group 2 animals were re-challenged with the same isolate (homologous group), whereas in each of the other 4 groups animals were re-challenged with a different isolate presenting a sequence heterology of 3.4%, 5.4%, 16.5% and 11.3% respectively with the first isolate (heterologous groups). Heterologous groups showed viremia on day 3pi but not later on. Fever, anorexia and depression were present is all heterologous groups with exception of group 4 (5.4% heterology). Homologous immunity protected all animals of group 2 while heterologous immunity protected at least 66% of the animals of heterologous groups which showed viremia only on day 3. In all heterologous groups a rapid and high anamnesic antibody response was observed on day 14pi and no difference in the humoral response could be demonstrated between them.

PCV2-associated diseases: research and diagnostic update.
HALBUR PG, OPRIESSNIG T, HOOGLAND M, THACKER E, YU S, MENG XJ
Proceedings of the ISU Swine Disease Conference for Swine Practitioners 2003: 152-160
State-of-the-art and recommendations for control of PCV2-associated diseases.

PMWS-Immunologic stimulation and clinical signs.
CHARREYRE C
Proceedings of the ISU Swine Disease Conference for Swine Practitioners 2003: 161-169
To date our knowledge of the pathogenesis of PMWS is still incomplete. However several key points have been established and are reported in this paper. Virus properties are described as well as the clinical signs with reference to experimental reproductions of PMWS. The role of lymphoid organs in PCV2 infection is emphasized but nonlymphoid organs involvement (lung, gastro-intestinal tract and more specifically liver) is the true cause of death in PMWS affected pigs. Variable and mild peripheral lymphadenopathy, especially in the bronchial lymph nodes, is associated to subclinical PCV2-infection whereas multifocal to diffuse mixed angiocentric granulomatous inflammation is to be considered as diagnostic for clinical PMWS. Histiocytic, monocytic and lymphatic cells are target cells for PCV2 but they do not allow PCV2 replication. Thus, though probably including parenchymal cells, the primary site of replication of the virus is still unknown. As replication goes on, phagocytic cells accumulate the virus in their cytoplasm and could disseminate the virus throughout the pig body in this way. Early or inappropriate immune stimulation is an aggravating factor for PMWS and co-infection with porcine parvovirus (PPV), porcine reproductive and respiratory syndrome virus (PRRSV) or Mycoplasma are considered as triggering factors.

New insights in the pathogenesis of PCV2 infections in fetuses.
NAUWYNCK H, SANCHEZ R, MEERTS P, MATEUSEN B, PENSAERT M
Proceedings of the 1st APVS Congress, Seoul, September 2003, 3-6
Late abortion, mummification, stillbirth and prolonged gestation are the main reproductive symptoms associated with PCV2 infection. A summary of the research performed on PCV2-related reproductive failure is provided together with the main relative statements. PCV2 infection of fetuses is a rather rare event but seronegative gilts and sows are more at risk to be affected by reproductive failure than infection-immune sows. When dealing with possible routes of infection, there is yet no indication of transplacental transmission of the virus to fetuses whereas semen containing infectious virus was demonstrated to infect both seronegative dam and fetuses after insemination. Intrafetal inoculation of PCV2 at different stage of gestation showed that fetuses inoculated at 57 days of gestation were more susceptible to PCV2 infection compared to those inoculated at 75 or 92 days of gestation. Such increased susceptibility was associated with higher virus titers and higher number of infected cells and myocarditis whereas fetuses inoculated later showed no pathological lesions at day 21pi. The clinical and pathological outcome of these fetuses were also different since those inoculated at 57 days of gestation died, became mummified and transmitted PCV2 to the other fetuses of the litter, those inoculated at 75 days of gestation were stillborn at birth while those inoculated at 92 days of gestation did not show any pathology. Cardiomyocytes, hepatocytes and cells of the monocyte/macrpophage lineage were found to be the target cells of PCV2 in these fetuses.

PMWS problems persist.
ABBOTT R
Pig Progress, 2003, Volume 19, N°5, 22-23
The opinions of two protagonists of swine health and production on PMWS are reported: Derek Amstrong, veterinary scientist at the UK’s Meat and Livestock Commission and Robin Brice, Rattlerow Farms production director. Amstrong greatly emphasizes the need for a complete collaboration between researchers and scientists from EU pig-producing countries in order to fully understand PMWS, develop the proper medication and successively eradicate it. On the other hand, Brice addresses pig producers a “wake-up call” and advocates changes in pig management. Several measures based on his own knowledge and experience are pointed out as necessary to achieve PMWS control: to convert units to three-weekly flows, to improve nutrition, hygiene and to reduce stress wherever and whenever possible. Brice’s key way to tackle PMWS is to change management systems so as to please the pig, not the producer. A booklet, the “Clean Flow Health management”, has been published in order to introduce all these practical management methods to pig producers.

Effect of vaccination with selective bacterins on conventional pigs infected with type 2 porcine circovirus.
OPRIESSNIG T, YU S, GALLUP JM, EVANS RB, FENAUX M, PALLARES F, THACKER EL, BROCKUS CW, ACKERMANN MR, THOMAS P, MENG XJ, HALBUR PG
Vet. Pathol., 2003, Volume 40, 521-529
Vaccination against Actinobacillus pleuropneumoniae and Mycoplasma hyopneumoniae following the US protocol was shown to significantly prolong and increase viremia of PCV2, to widen tissue distribution of the virus and increase the severity of lymphoid depletion. Thus, vaccination protocols in PMWS-affected herds need to be designed considering these negative effects.

In vitro studies on the infection and replication of porcine circovirus type 2 in cells of the porcine immune system.
GILPIN DF, MC CULLOUGH K, MEEHAN BM, MC NEILLY F, MC NAIR I, STEVENSON LS, FOSTER JC, ELLIS JA, KRAKOWKA S, ADAIR BM, ALLAN GM
Veterinary Immunology and Immunopathology, 2003, Volume 94, 149-161
The detection of PCV2 nucleic acid and/or antigens in monocytes and macrophages of pigs affected with PMWS clearly shows that the virus interacts with monocytic cells. However, even if monocytic cells allow the persistence of PCV2, they do not support viral replication and seem to be involved only in the dissemination of the virus in the host. PCV2 is likely to bypass the immune system and remain silent until immunomodulatory signals trigger the expression of the disease.

Porcine circovirus 2-associated disease in Eurasian wild boar.
ELLIS J, SPINATO M, YONG C, WEST K, MC NEILLY F, MEEHAM B, KENNEDY S, CLARK E, KRAKOWKA S, ALLAN G
J. Vet. Diagn. Invest., 2003, Volume 15, 364-368
Several 6-week-old boar piglets from a Canadian farm of wild boars were investigated. The animals had clinical signs and lesions similar to those observed in PMWS-affected pigs and the presence of a circovirus with an opening reading frame 2 (ORF2) sharing 98.7% homology with the ORF2 of a reference PCV2 was demonstrated. These results show the ability of PCV2 to infect and cause disease in Sus scrofa subspecies other than domestic swine.

Survey of veterinary practitioners on PMWS and PDNS in the UK.
GRESHAM A, COOK AJC, THOMSON JR, KENNEDY S
Veterinary Record, 2003, Volume 153, 400-403
Data about the levels and duration of mortality in PMWS or PDNS-affected herds are reported. While the “French plan”, described by Madec and others (1999) and aiming at reducing the impact of PMWS through improvement of hygiene and health, significantly reduced the mortality before the outbreak, it had no significant beneficial effect on the level and duration of mortality associated with PMWS and PDNS. Even if this survey was conducted in a limited number of farms not selected at random, the results indicate that PMWS and PDNS are widespread in England.

Risk factors for porcine postweaning multisystemic wasting syndrome (PMWS) in 149 French farrow-to-finish herds.
ROSE N, LAROUR G, LE DIGUERHER G, EVENO E, JOLLY JP, BLANCHARD P, OGER A, LE DIMMA M, JESTIN A, MADEC F
Preventive Veterinary Medicine, 2003, Volume 61, 209-225
One hundred and forty-nine French farms were investigated in order to explore the potential risk factors for PMWS. Three groups were constituted according to the PMWS status of the farms: current and typical PMWS (case), PMWS-free (control#1) and recovered from PMWS (control#2). Both control groups were compared to the case group. The impact on the odds of PMWS of co-infections, vaccination, the origin of semen and the type of housing was assessed. Two factors were found to decrease the odds of PMWS: the existence of a self-replacement scheme for gilts and the vaccination of sows against E. coli. Conversely, the odds of PMWS were increased by: co-infection with porcine parvovirus (PPV) and porcine reproductive and respiratory syndrome virus (PRRSV), the use of farm semen versus semen from insemination center, large pens in weaning and farrowing facilities, regular treatment against external parasites, housing pregnant sows in collective pens versus individual pens, the use of a common pit for several adjacent fattening rooms versus separate pits and high level of cross-fostering.

Swine Influenza in Italy.
BARIGAZZI G, DONATELLI I
Veterinary Research Communications, 2003, Volume 27, Suppl. 1, 93-99
Several tables are included in this paper which reviews the situation of swine influenza in Italy since 1976 and reports the results of the tests carried out on lungs, nasal swabs and serum samples from swine with acute respiratory syndrome for the presence of influenza virus (H1N1, H3N2 and H1N2 subtypes), bacteria, Mycoplasma hyopneumoniae, PRRSV and PCV2 since that date. It is reminded that nasal mucous obtained by swabbing nasal cavities during acute illness is the best sample for virus isolation and that the antigenic variation of influenza virus requires an accurate work and monitoring for new subtypes, as it is currently the case with the new H1N2 subtype against which the available vaccines do not provide cross-protection.

Protection against a European H1N2 swine influenza virus in pigs previously infected with H1N1 and/or H3N2 subtypes.
VAN REETH K, GREGORY V, HAY A, PENSAERT M
Vaccine, 2003, Volume 21, 1375-1381
This study completes previous studies carried out by Kriestien Van Reeth et al. on the same subject (cf. bibliographical bulletin, issue n°16), i.e. the effects of infection with H1N1 and/or H3N2 and resulting immunity on the protection against the H1N2 subtype. Dually H1N1/H3N2 infected-immune pigs were shown to develop reliable immunity against H1N2 (disease and virus replication were absent) while Haemagglutinin (HA) are considered as probably not involved in the process of cross-protection whereas internal proteins, which are relatively conserved in the three different subtypes, are highly suspected to be so.

Association of porcine circovirus 2 with porcine respiratory disease complex.
KIM J, CHUNG HK, CHAE C
Veterinary Journal, 2003, Volume 166, 251-256
The presence of porcine circovirus 2 (PCV2), porcine reproductive and respiratory syndrome virus (PRRSV), swine influenza virus (SIV), porcine parvovirus (PPV), Pasteurella multocida, Mycoplasma hyopneumoniae, and Actinobacillus pleuropneumoniae was investigated in 105 epidemiologically unrelated Korean pigs with PRDC. PCV2 was detected in 85 pigs and the most frequent association was that of PCV2 with PRRSV (58 cases), followed by that with P. multocida (36 cases) and M. hyopneumoniae (38 cases). These results show that PCV2 is widely present in pigs with PRDC and that respiratory disease in most pigs with PRDC is caused by more than one pathogen. The involvement of PCV2 in PRDC should be further investigated.