VIROLOGIE

Classical Swine Fever
• Chapter 2:Aims of the study
• Chapter 3.1: Transmission routes of Classical Swine Fever Virus: A review of present knowledge
• Chapter 3.2:Airborne transmission of Classical Swine Fever under experimental conditions
• Chapter 4.1: The use of vaccination in the control of Classical Swine Fever, a historical review and recent developments
• Chapter 4.2: An experimental infection with Classical Swine Fever in E2 sub-unit marker vaccine in vaccinated and non-vaccinated pigs
• Chapter 4.3: An E2 sub-unit marker vaccine does not prevent horizontal or vertical transmission of Classical Swine Fever
• Chapter 4.4: A comparative study for emergency vaccination against Classical Swine Fever with an E2 sub-unit marker vaccine and a C-strain vaccine
• Chapter 4.5: General discussion
• Swine Fever: Classical Swine Fever and African Swine Fever
PRRS
• Serological profiles of PRRS-affected, post-weaning pigs from continuous flow farms
• Advantages and drawbacks of serological tests used in the epidemiology of PRRS
• Timeline of infection and detection of PRRSV in the boar
• Porcine Reproductive and Respiratory Syndrome (PRRS) diagnostics: Interpretation and limitations
PMWS/PDNS - Circovirus
• Post-Weaning Multisystemic Wasting Syndrome (PMWS) in France: serological profiles of affected versus non-affected herds and preliminary analytic epidemiology
• Passive transfer of maternal antibodies to PCV2 protects against development of Post-Weaning Multisystemic Wasting Syndrome (PMWS): experimental infections and a field study
• Post-Weaning Multisystemic Wasting Syndrome (PMWS)-field observations in Spanish herds
• Post-Weaning Multisystemic Wasting Syndrome (PMWS)-two points of interests
• PCV/PMWS: Field disease, experimental infections and immunity
• PMWS: Current knowledge and hypothesis on the pathophysiology of the disease
• Porcine circovirus type 2 (PCV-2) co-infections in US field cases of Post-Weaning Multisystemic Wasting Syndrome (PMWS)
• Experimental in utero inoculation of late-term swine fetuses with porcine circovirus type 2
• Case-control study on the association of porcine circovirus type 2 and other swine viral pathogens with Post-Weaning Multisystemic Wasting Syndrome
• Porcine Dermatitis and Nephropathy Syndrome. Clinical and pathological features of cases in the United Kingdom (1993-1998)

Chapter 2:Aims of the study
DEWULF J
In Epidemiology and Control of Classical Swine Fever: Experimental Assessment of Virus Transmission and Potential Benefits of Ermergency Vaccination 2002 :7-9
The study on Classical Swine Fever (CSF) will focus on two main points: the different routes of transmission of the virus which will help redefining control measures and the efficacy of emergency vaccination.

Chapter 3.1: Transmission routes of Classical Swine Fever Virus: A review of present knowledge
DEWULF J
In Epidemiology and Control of Classical Swine Fever: Experimental Assessment of Virus Transmission and Potential Benefits of Emergency Vaccination 2002 : 13-28
A review of the current knowledge of direct and indirect transmission of CSFV in within-herds or between-herds is necessary for a reassessment and improvement of the disease control measures.
-Direct transmission of CSFV
Direct animal contact through oronasal and lacrimal secretions, urine and feces is the most important route of infection in horizontal transmission. Another dangerous route of transmission is the persistance of viremia in contaminated piglets born of an infected sow (vertical transmission). However, it has been proved that preventing direct transmission only is not sufficient to control the disease. Different routes of indirect transmission are involved but some of them still remain doubtdul.

-Indirect transmission of CSFV:
Swill feeding has been prohibited by the EU (even after heat treatment) because waste food is a real potential source of infection. Similarly infected wild boar populations and artificial insemination have been confirmed as potential routes of indirect transmission to the domestic pigs. However, little or no evidence or experiments have supported the likeliness of indirect virus transmission by contaminated livestock trucks, liquid manure, arthropods, ruminants, pets, rats and birds or contaminated clothing and footwear. There is a potential risk of CSF spread by the use of infected instruments, equipment or drugs and airborne transmission of the virus has been verified experimentally but not under field conditions. More experimental and epidemiological research is needed to develop effective control strategies.

Chapter 3.2:Airborne transmission of Classical Swine Fever under experimental conditions
DEWULF J, LAEVENS H, KOENEN F, MINTIENS K, DE KRUIF A
In Epidemiology and Control of Classical Swine Fever: Experimental Assessment of Virus Transmission and Potential Benefits of Emergency Vaccination 2002 : 29-44
Vet. Record 2000, 147: 735-738
The experiment described in this chapter confirms previous evidence of a possible airborne transmission of CSFV in an isolation unit and the role of air currents in this transmission. The unit was divided in three compartments : A (pens 1-3) B (pen 4) and C (pen 5). Each compartment had its own ventilation system with air currents from compartment A to B but not C. One pig in pen 2 was experimentaly inoculated with CSFV. During the post-inoculation period, blood samples were taken and the health status of pigs was recorded. Pigs from pen 4 and 1 became viremic but infection was not observed in pen 5. The airborne spread of the virus was clearly demonstrated in this experiment but the value of this data is difficult to assess under natural conditions.

Chapter 4.1: The use of vaccination in the control of Classical Swine Fever, a historical review and recent developments
DEWULF J, LAEVENS H, KOENEN F, MINTIENS K, DE KRUIF A
In Epidemiology and Control of Classical Swine Fever: Experimental Assessment of Virus Transmission and Potential Benefits of Emergency Vaccination 2002 : 103-119
The different control policies implemented over 40 years in EU are reviewed in this paper. In order to eradicate CSF, inactivated vaccines were first developed. They were soon replaced by more efficient live vaccines in the 70ies, and each European country independently conducted its own vaccination programme. Emergency vaccination became more common until the 80ies when the member states of the EU decided on a non-vaccination policy and a restricted use of emergency vaccination after each country was declared free of CSF. This policy has been criticized ever since as several huge outbreaks of CSF were recorded in the 90ies. The situation has led to the development of new vaccines, sub-unit marker and live marker (recombinant vaccines and DNA vaccines) vaccines. The former has proved its efficacy experimentally and the latter is still being tested. Consequently, an effective global vaccination policy can only be determined if extensive knowledge on conventional and marker vaccines is available.

Chapter 4.2: An experimental infection with Classical Swine Fever in E2 sub-unit marker vaccine in vaccinated and non-vaccinated pigs
DEWULF J, LAEVENS H, KOENEN F, VANDERHALLEN K, MINTIENS K, DELUYKER H, DE KRUIF A
In Epidemiology and Control of Classical Swine Fever: Experimental Assessment of Virus Transmission and Potential Benefits of Emergency Vaccination 2002 : 121-139
Vaccine 2001 19: 475-482
An experimental CSF infection was conducted in an isolation unit of three compartments (one pen with vaccinated pigs and two others with non-vaccinated pigs) in order to check whether the double vaccination with a E2 sub-unit marker vaccine could provide protection both clinically and virologically. A strict protocol was enforced so that the only virus transmission route was airborne. The experimental infection of one pig in pen 2 resulted in viremia detected in all non-vaccinated pigs and also in nearly half of the vaccinated pigs (PCR detection). The clinical signs of CSF were observed only in non-vaccinated pigs. Hence, the use of a marker vaccine prevented the clinical course of the disease but not indirect contact infection. Moreover, it was noted that the serological response after vaccination was slow. Considering these results, it remains doubtful whether a marker vaccine can be used in case of an emergency vaccination.

Chapter 4.3: An E2 sub-unit marker vaccine does not prevent horizontal or vertical transmission of Classical Swine Fever
DEWULF J, LAEVENS H, KOENEN F, MINTIENS K, DE KRUIF A
In Epidemiology and Control of Classical Swine Fever: Experimental Assessment of Virus Transmission and Potential Benefits of Emergency Vaccination, 2002 : 141-157
Vaccine 2002 20: 86-91
The criteria set by the Scientific Veterinary Committee and determining the use of a marker vaccine in case of emergency vaccination (vaccination should confer protection against CSF and should prevent transplacental infection) were not met in this experiment: it turned out that nearly all vaccinated gilts were viremic after experimental inoculation of two non-vaccinated gilts housed in neighbouring boxes. Viremia was only detected by PCR. Additionally, transplacental infection was observed in 3 out of 8 vaccinated pregnant gilts. However, almost no clinical signs of CSF were recorded in vaccinated gilts compared to inoculated, non-vaccinated gilts.

Chapter 4.4: A comparative study for emergency vaccination against Classical Swine Fever with an E2 sub-unit marker vaccine and a C-strain vaccine
DEWULF J, LAEVENS H, KOENEN F, MINTIENS K, DE KRUIF A
In Epidemiology and Control of Classical Swine Fever: Experimental Assessment of Virus Transmission and Potential Benefits of Emergency Vaccination 2002 : 159-179
Two types of vaccine against CSF, an E2 marker sub-unit vaccine and a conventional modifed live vaccine (Pestiffa®, Merial), were tested in an emergency vaccination scenario to assess the reduction or prevention of virus transmission from infected to contact pigs. Thirty-two conventional weaner pigs were allocated to two compartments and were vaccinated with either of the two vaccines. Four pigs in each compartment were challenged with a CSF strain at 0, 7 and 14 days post vaccination (dpv). Pigs were clinically examined during the experiment and the effect of vaccination on virus transmission was recorded. Although no virus transmision was observed at 14 days post vaccination with the marker vaccine, the latter does not offer full protection against virus transmisison at 7 dpv and no protection at all at 0 dpv. Conversely, no detectable virus transmission was observed with a conventional vaccine at 0, 7 or 14 dpv. Consequently, the prevention of virus transmisison to neighbouring herds in case of an emergency vaccination is best achieved with a conventional vaccine as the interval between vaccination and onset of immunity is shorter for this vaccine.

Chapter 4.5: General discussion
DEWULF J, LAEVENS H, KOENEN F, MINTIENS K, DE KRUIF A
In Epidemiology and Control of Classical Swine Fever: Experimental Assessment of Virus Transmission and Potential Benefits of Emergency Vaccination 2002 : 181-193
In the light of the results from previous experiments conducted to test the efficacy of either an E2 sub-unit marker vaccine or a conventional vaccine, the alternative control strategies to the current eradication strategy adopted by the EU are reviewed. Market Authorisation Strategy (MAS) focuses on vaccination aiming at reducing the number of secondary outbreaks in the neighbourhood of an infected herd. Delayed Destruction Strategy (DDS) relies on eradication of the infected herd as well as the neighbouring herds and dangerous contact pigs after vaccination of the neighbouring herds. The only alternative strategy which is most likely to bring improvement to the current strategy is the DDS with a conventional vaccine.

Swine Fever: Classical Swine Fever and African Swine Fever
KLEIBOEKER SB
Vet Clin Food Anim 2002 18: 431-451
The author gives a detailed account of two viral infections caused by CSFV (Classical Swine Fever Virus) or ASFV (African Swine Fever Virus), two highly contagious viruses which are shed in great amounts and can spread rapidly causing heavy herd losses. Emphasis is put on the risk incurred by a probable incursion of these viruses into North America, a territrory free of foreign animal diseases. Based on previous CSF outbreaks in Europe, American health authorities are bound to be overwhelmed if any of the two diseases is diagnosed in North America. Consequently, the author calls for higher vigilance from all actors of the swine industry and larger enforcement of biosecurity measures.

Serological profiles of PRRS-affected, post-weaning pigs from continuous flow farms
CANDOTTI P, NODARI R, LAZZARINI C, CHARREYRE C, REYNAUD G, LEOTTI G, JOISEL F, LONGO S, MIELI L
AFMVP, Maisons-Alfort, 5-6 December 2002. Actualités en Production Porcine 2002 : 162-172
A serological and epidemiological survey was conducted in Italy in 19 continous flow farms with a history (or no history) of reproductive and/or respiratory problems. Blood samples were collected from 4 groups of pigs (3, 6, 9, 12 weeks) at T0 and T1 (21 days later). An ELISA kit was used to analyse them. The following relevant findings of the study were noted: the seroprevalence of PRRS in pigs increases as they grow older, especially in farms with a recent history of PRRS; even in farms with continous-flow post weaning, pigs at 6-9 weeks can be taken as sentinels for the circulation of the virus in the sows and 30% or more seropositive piglets at the end of the post weaning is most likely linked to PRRSV-induced reproductive disorders in the sows.

Advantages and drawbacks of serological tests used in the epidemiology of PRRS
MIELI L, CHARREYRE C, REYNAUD G, JOISEL F, HERIN JB, LAMANDA P, BAUDOUARD MA, LEBON E
AFMVP, Maisons-Alfort, 5-6 December 2002. Actualités en Production Porcine 2002: 154-160
The performances of four ELISA kits (A,B,C,D) with one IPMA-IgM test were assessed in three farrow-to-finish herds. The highest specificity, sensibility and reproductibility were achieved by the A kit although it detected maternal antibodies over a shorter period of time compared to the B kit. In one herd, the four kits were unable to determine the exact time of infection by PRRSV in piglets. In this case the IPMA IgM test was the only technique available to precisely determine the time of active seroconversion in piglets.

Timeline of infection and detection of PRRSV in the boar
CHRISTOPHER HENNINGS J
Allen D. Leman Swine Conference 2002 :60-63
PRRSV detection in boar semen is assessed in relation with the timeline of PRRSV infection in boars. PRRSV infection in boars can be divided into three stages: early (up to 9 days), middle (9 to 35 days) and late (35 days and over) infection. During the first stage, boars are viremic, PRRSV-negative, and shed virus in semen. During the middle stage, they become aviremic, PRRSV-positive and antibodies will be detected in semen. Boars shed PRRSV in semen around 35 days. During the late stage, neutralizing antibodies are observed, PRRSV gradually disappear in semen but may still be present in tissues. It is not known whether boars can still transmit the virus.

Porcine Reproductive and Respiratory Syndrome (PRRS) diagnostics: Interpretation and limitations
CHRISTOPHER HENNINGS J, FAABERG KS, MURTAUGH MP, NELSON EA, ROOF MB, VAUGHN EM, YOON KJ, ZIMMERMAN JJ
Journal of Swine Health and Production 2002 10: 213-218
A number of diagnostic tools (ELISA, IFA test, SVN test, RT-PCR, RFLP, Virus Sequencing, PRRSV phylogenic ananlysis) commonly used in the detection and control of PRRSV are evaluated in order to provide veterinarians with guidelines on the correct use of these assays depending on their benefits and limitations.

Post-Weaning Multisystemic Wasting Syndrome (PMWS) in France: serological profiles of affected versus non-affected herds and preliminary analytic epidemiology
ROSE N, BLANCHARD P, LAROUR G, LE DIGUERHER G, EVENO E, JOLLY JP, OGER A, LE DIMNA M, JESTIN A, MADEC F
Pig Journal 2002 50 : 124-134
The present study, which is part of a larger French epidemiological study on the risk factors related to PMWS, focuses on the role of PCV2 infection in PMWS-affected or non-affected farms in association with other pathogenic agents. Three groups of farms were selected for the study: a group composed of confirmed cases of PMWS and two control groups (no PMWS or a previous history of PMWS). Serological analyses were carried out on different categories of pigs (young and old sows, growing pigs) from each group. Blood samples were tested for PRRSV, PPV, Influenza virus, Lawsonia intracellularis antibodies. The results show a high seroprevalence for PCV2 in growing pigs from PMWS farms compared to the control farms, a higher number of positive old sows in PMWS farms and conversely a lower number of positive young sows in these affected farms compared to the control ones. Also, a correlation between other pathogenic agents (PRRSV, PPV) and the PMWS status of the farms has been pointed out. Other variables such as rearing, feeding practices need to be assessed in a following survey in order to understand what is precisely involved in the occurrence or exacerbation of the disease.

Passive transfer of maternal antibodies to PCV2 protects against development of Post-Weaning Multisystemic Wasting Syndrome (PMWS): experimental infections and a field study
ALLAN GM, MCNEILLY F, MCNAIR I, MEEHAN B, MARSHALL M, ELLIS J, LASAGNA C, BORIOSI G, KRAKOWKA S, REYNAUD G, BOEUF-TEDESCHI L, BUBLOT M, CHARREYRE C
Pig Journal 2002 50: 59-67
An experimental infection study and a field study bring further evidence of the protective role of passive transfer of antibodies to PCV2 from sows or gilts to piglets against the development of PMWS. In the first experiment, 10 CF (colostrums-fed) piglets derived from sows/gilts with high serum antibody levels to PCV2 did not develop the disease after challenge with a PCV2 isolate, had higher weight gain and had fewer clinical signs than the 10 other piglets derived from sows/gilts with a low serum antibody levels to PCV2 (two of which had PMWS). Similarly, the results of the field study carried out on a PMWS-affected farm indicate that piglets derived from sows/gilts with the highest PCV2 serum antibody levels (>1/1250) did not develop PMWS whereas the mothers showing low or moderate PCV2 serum antibody levels (<1/50, 1/250, 1/400) had PMWS-affected piglets in their litter.
Protection against PMWS is thus achieved through passive transfer of maternally-derived PCV2 antibodies and may play a significant role in the control of the disease on commercial farms.

Post-Weaning Multisystemic Wasting Syndrome (PMWS)-field observations in Spanish herds
MARCO E
Pig Journal 2002, 50: 135-142
A review of the occurrence of PMWS in Spain is presented. The author details the clinical signs and post-mortem findings recorded in PMWS-affected Spanish herds. He also suggests several control strategies and the currently most effective treatments. An interesting point is the observation of signs characteristic of Congestive Heart Failure in some of these PMWS–affected Spanish pigs. Similarly, myocarditis and cardiomegalia may be found in sick pigs.

Post-Weaning Multisystemic Wasting Syndrome (PMWS)-two points of interests
NASH WA
Pig Journal 2002 50 : 119-123
The PPV (Porcine Parvovirus) status of British herds and vaccination against PPV is considered in a first part. It is known that vaccination can prevent virus from crossing the placenta but cannot prevent infection in herds. Also, it is thought that a co-infection with PPV and PCV2 is unlikely in 6-12 week old piglets. In a second part, a case of PMWS in a unvaccinated herd (not vaccinated against Enzootic Pneumonia) is described, with the conclusion that the lung scores observed in sick pigs are due to PCV2 plus secondary infection and not by EP.

PCV/PMWS: Field disease, experimental infections and immunity
ALLAN GM, MCNEILLY F, MEEHAN B, KRAKOWKA S, ELLIS J, CHARREYE C, BØTNER A, NAUWYNK H, MCCULLOUGH K
AFMVP, Maisons-Alfort, 5-6 December 2002. Actualités en Production Porcine 2002 : 49-54
A international Research Consortium represented by the authors has been successfully conducting research studies into PCV2 and PCV2- related diseases for the past five years. The knowledge derived from these studies focuses on:
- The identification of PCV1 and PCV2, a newly discovered virus
- The description of gross and histological lesions of PMWS,
- The role of PCV2 as the causative agent of PMWS and as a potential infectious component in other diseases such as PDNS
- The consequences of a PCV2-infection on the immune status of the pig (leukopenia, lymphopenia)
- The diagnostic tools to be used for diagnosis of PCV2-related diseases.
Other questions such as the immunosuppressive effects of PMWS, the probable vertical transmission of the virus, the disease control methods, the potentiation of PCV2-replication need to be further investigated.

PMWS: Current knowledge and hypothesis on the pathophysiology of the disease
JESTIN A, MAHE D, BLANCHARD P, DE BOISSESON C, CARIOLET R, BEVEN V, OGER A, LOIZEL C, DORY D, ROSE N, MADEC F
AFMVP, Maisons-Alfort, 5-6 December 2002. Actualités en Production Porcine 2002 : 62-72
Thi paper considers all aspects of the wasting disease, known as “MAP” in French. A full description of the disease is given with an in-dept study of the genomic sequence analysis of PCV1 and PCV2. Other aspects such as the occurrence of the disease, the serological analyses used for the detection of PCV2, the role of adjuvants in immunity and other co-infectious agents in the clinical expression of PMWS. are reviewed in details and testify to the complexity of the disease.

Porcine circovirus type 2 (PCV-2) co-infections in US field cases of Post-Weaning Multisystemic Wasting Syndrome (PMWS)
PALLARES FJ, HALBUR PG, OPRIESSNIG T, SORDEN SD, VILLAR D, JANKE BH, YAEGER MJ, LARSON DJ, SCHWARTZ KJ, YOON KJ, HOFFMAN LJ
J Vet Diagn Invest 2002 14: 515-519
A retrospective survey (2000-2001) was conducted in order to examine which coinfecting agents were most prevalent in field cases of PMWS in North America. PMWS was diagnosed in 484 animals out of 4,688 animals submitted to the diagnostic laboratory in Iowa (presence of lymphoid lesions was a selective criteria). The most common combinations of PCV-2 + coinfecting pathogens were PCV-2+ PRRSV (52%), PCV-2 + M. hyopneumoniae (35.5%), PCV-2+ bacterial septicemia (14%) and bacterial pneumonia (7.6%). In only 1.9% of cases PCV-2 was found alone. Consequently, this study supports the hypothesis that coinfections with PCV-2 are probably necessary for the potentiation of PCV-2 replication and full development of PMWS.

Experimental in utero inoculation of late-term swine fetuses with porcine circovirus type 2
JOHNSON CS, HAN SJ, DIREKSIN K, YOON KJ, CHOI YK
J Vet Diagn Invest 2002 14: 507-512
An experimental in utero inoculation of fetuses with PCV-2 from 3 sows at 86, 92 and 93 days of gestation was performed in order to examine whether PCV-2 infection occurs in late-term fetuses. Fetuses were successfully infected as shown by the presence of PCV-2 antigen and antibodies in blood and tisssue samples. The birth of mummies, weakborn and stillborn piglets are indicative of reproductive failure caused by PCV-2.

Case-control study on the association of porcine circovirus type 2 and other swine viral pathogens with Post-Weaning Multisystemic Wasting Syndrome
POGRANICHNIY RM, YOON KJ, HARMS A, SORDEN SD, DANIELS M
J Vet Diagn Invest 2002 14: 449-456
Thirty one PMWS cases and 56 control pigs (PMWS-free) were selected for this study. Serum and tissue samples were collected from them and tested for PCV (1 and 2) as well as other common swine viral agents (PRRSV, PPV, SIV, porcine enterovirus, porcine respiratory coronarovirus, …) so as to examine which pathogen has the strongest association with the clinical disease. PCV-2 was detected in 29 out of 31 PMWS-affected pigs suggesting that this pathogen plays a significant role in the pathogenesis of PMWS. Interestingly, 63% of control pigs without clinical signs of PMWS were positive to PCV-2. The second most prevalent pathogen was PRRSV in PMWS (42%) and control animals (20%). The remaining infectious agents were present in varying proportions but no difference was noted between case and control pigs in terms of virus distribution. A concurrent infection of PCV-2 with PRRSV is likely to increase the risk of PMWS.

Porcine Dermatitis and Nephropathy Syndrome. Clinical and pathological features of cases in the United Kingdom (1993-1998)
THOMSON JR, HIGGINS RJ, SMITH WJ, DONE SH
Journal of Veterinary Medicine 2002 49: 430-437
A clinical and histopathological description of 69 cases of PDNS from Scottish and English farms was provided over five years. The herds were unaffected with PMWS. Characteristic clinical signs were skin lesions varying from multifocal, flat and discrete lesions to large coalescing lesions. Some of them were unusually located on the ventral abdomen, hind limbs and flanks. Severe kidney lesions were also observed and ranged from acute glomerulitis to chronic glomerular sclerosis, suggesting a progressive condition although all affected pigs died after a short clinical course. Deposits of IgM and IgC in glomeruli, Bowman’s capsules and dermis were detected by immunostaining. The etiology of this condition is unknown but it is thought to be an immune-complex disorder according to the pathological and immunological findings.