STUDY OF THE EFFICACY OF AN INACTIVATED VIRUS VACCINE AGAINST PORCINE PARVOVIRUS

Transcription

1 STUDY OF THE EFFICACY OF AN INACTIVATED VIRUS VACCINE AGAINST PORCINE PARVOVIRUS P. Vannier, A. Brun, G. Chappuis, G. Reynaud To cite this version: P. Vannier, A. Brun, G. Chappuis, G. Reynaud. STUDY OF THE EFFICACY OF AN INAC- TIVATED VIRUS VACCINE AGAINST PORCINE PARVOVIRUS. Annales de Recherches Vétérinaires, INRA Editions, 1986, 17 (4), pp <hal > HAL Id: hal Submitted on 1 Jan 1986 HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

2 STUDY OF THE EFFICACY OF AN INACTIVATED VIRUS VACCINE AGAINST PORCINE PARVOVIRUS P. VANNIER A. BRUN G. CHAPPUIS 2 G. REYNAUD 1: Ministère de lagriculture, Direction de la Qualité, Services Vétérinaires, Station de Pathologie Porcine, Ploufragan, France. 2: Rh6ne Mérieux, IFFA, 254 rue Marcel Mérieux, Lyon, France. Résumé ÉTUDE DE L EFFICACITÉ D UN VACCIN À VIRUS INACTIVÉ CONTRE LE PARVOVIRUS PORCIN. &horbar; L efficacité d un vaccin à virus inactivé contre la parvovirose porcine a été étudiée en immunisant quatre truies pendant la gestation. Une souche virulente de Parvovirus a été inoculée à ces truies en même temps qu à deux truies non vaccinées utilisées comme témoins, entre le 5Ù et le 57 1 jour de gestation. Dans les portées des truies vaccinées, 82! des porcelets étaient normaux et vivants; ni anticorps, ni antigène n ont pu être révélés chez les autres foetus mort-nés des quatre truies vaccinées. En revanche, seulement 9,5 % des porcelets nés de deux mères non vaccinées étaient vivants à la naissance bien que probablement infectés en cours de gestation. Au total, 86 % des foetus des deux portées étaient momifiés. Une étude réalisée en élevage a permis dp montrer que les anticorps induits par une double vaccination persistaient, à des titres constants, pendant au moins 13 mois. De plus, les performances de reproduction de 413 cochettes vaccinées avant la saillie ne sont pas modifiées par ce traitement. Porcine parvovirus (PPV) is now recognised worldwide as a major cause of infectious reproductive failure in pigs (Cartwright and Huck, 1967 ; Wrathall, 1975 ; Vannier and Tillon, The circumstances of the spread of the virus in one herd are relatively well known up to now. It was shown that in certain cases, after an acute phase of the disease with a high proportion of mummified fetuses, the spread of the virus stops and the herd becomes progressively fully receptive to a new infection as the oldest immune sows are regularly culled and are replaced by non immune gilts (Vannier et al., In such a case, the vaccination remains the alone method to protect before mating the non immune gilts. So, several porcine parvovirus vaccines have been developed and evaluated in pregnant sows (Sorensen and Askaa, 1981 ; VVrathall et al., 1984; Paul and Mengeling, Most of them were shown to be efficient in regard to the resistance of the pregnant sows and their litters to the challenge. Nevertheless, differences appeared between the antibodies titers induced by the vaccination (VVrathall et al., 1984; Paul and Mengeling, In France, an inactivated virus vaccine (Parvovax ND) has been developed and its efficacy tested on pregnant sows and on the field. Indeed, the rate of mortality was compared between the litters of the vaccinated sows and those of the

3 unvaccinated ones. The general immunity induced by the vaccination has been compared to the one obtained by other searchers. After measuring the efficacy of the vaccine in experimental conditions, we could verify that this vaccine was also efficient in natural conditions. Materials and Methods 1. Vaccine and vaccination protocol The strain of Parvovirus of which titer is 128 hemagglutinating unit for 2 ml is inactivated by ethylene-imine after multiplication on a fetal porcine cell line. Aliquots of the antigen suspension were tested before and after the inactivation treatment for PPV infectivity and hemagglutinating activity. Aqueous phase was combined with an oil phase and thoroughly blended together so as to form a stable emulsion vaccine. The vaccine produced by Rh8ne M rieux (Lyon) is injected twice, at 4 weeks interval, by the intramuscularly route to gilts. Booster vaccinations can be done on lactating sows, before each weaning, The volume of each dose is 2 ml. 2. Experimental model 2.1. Animals Six specific pathogen free sows have been used for testing the efficacy of the vaccine. The sows were born in an isolated unit of the research center of Ploufragan in which the first breeders have been obtained by hysterectomy (Cariolet and Tillon, The serum of the sows was free of PPV antibodies. Four sows (1-4) were vaccinated twice with the inactivated virus vaccine at 23 to 26 days of gestation and 19 days later. Each sow was given 1 dose (2 ml) of the vaccine by the intramusculary route. The two other sows (5-6) were used as controls. The sows were raised two by two in totally isolated rooms. Tight panels separated the rooms; the air was filtered through absolute filters and the staff showered before entering the rooms Challenge For challenge, strain NADL-8, a virulent strain of PPV in its 4th in vivo passage consisted of 50 % suspension of lungs, liver, spleen and brain from PPV infected fetuses. One sow at 40 days of gestation was given, intravenously, 5 ml of the 3rd in vivo passage of the NADL-8 strain. The origin of this sow was the same as the ones used for the experimental model. The serum of the sow was free of antibodies before inoculation. The pregnant sow was slaughtered 15 days later and PPV antigen was looked for on a part of the lung of all the fetuses by immunofluorescence. Lungs, liver, spleen and brain of the infected fetuses are ground; 50 9o suspensions of fetal tissue are prepared and pooled. After centrifugation, the supernatant of the pool is subdivided into 5 ml portions and freezed at &horbar; 70 C. Each portion represents a challenge virus dose of which the titer is hemagglutinating units per 50 pl. The challenge was done between 50 and 57 days of gestation i.e. 12 days after the second vaccination. The sows farrowed in the isolated rooms Observations At the birth, the length of the fetuses was measured; PPV antibodies were searched from the sera or liquids of the live-born or mummified piglets. PPV antigen was looked for from the lung of the mummified fetuses. During the experiment, blood samples were collected on all the sows once a week. 3. Field studies 3.1. Observations of the performances in 11 herds in which gilts had been vaccinated Most of the farms were breeding and fattening units of which the mean number of sows was between 60 and 300. In five herds, typical PPV clinical signs had been observed; in two of them, mummified fetuses regularly appeared but no etiology could be found; in the four remaining, no major sanitary problem has been observed. In these 11 herds, 7 to 100 gilts were vaccinated twice before mating. In all the herds, reproductive performances were recorded. The percentage of the culled vaccinated gilts between the mating and the farrowing was noted as the percentage of vaccinated gilts with at least one return in cestrus after the mating. The number of live born piglets as well as the number of stillborn or mummified fetuses per litter of the vaccinated primiparous was also recorded Serofogical study in another herd In one breeding and fattening herd of 120 sows, three groups of gilts individually identified were followed during 11 to 13 months. The different groups were composed of four gilts. Three were vaccinated twice with the PPV inactivated virus vaccine and one was not vaccinated and was used as control. Indeed, the four sows of each group were kept and covered together. There were belonging to the same batch of sows of which the oestrus is grouped. Each batch is composed of 16 to 20 sows and 3 weeks is the interval between each batch according to the physiological state. Blood samples were done on the gilts before the first vaccination and each month during 1 to 13 months. At the same time, blood samples were done on older sows of the herd to follow the evolution of the PPV antibodies in their sera for the same period. 4. Direct lmmunofluorescent test Cryostat-microtome sections of fetal lung were examined by direct immunofluorescence microscopy according to the method of Mengeling et al. (1975). 5. Haemagglutination inhibition test IHf Test) Serum samples to be tested for PPV antibodies were treated as previously described (Vannier et al., 1984) as well as the fetuses for the search of PPV antibodies. Serum titres are expressed as the value of the log 10 of the reciprocal of the highest dilution of serum inhibiting haemagglutination of virus. The positivity threshold is 2,2. Results 1. Experimental studies 1.1. Data on the litters Most of the piglets born from the vaccinated

4 dams were normal and alive (table 1 It can be noticed that the litter of the sows n 3 was composed of 9 living piglets with 4 stillborn and 1 mummified fetus. In the 2 control litters, most of the fetuses were mummified except that of the sow n 5 in which 2 living piglets have been observed. The sow n 6 aborted at 103 days of gestation 111 mummified fetuses which were included in their envelopes which appeared brown and opaque Serological and viral searches on the fetuses and piglets Neither PPV antigen nor PPV antibodies could be revealed in the stillborn, mummified fetuses issued from the vaccinated sows. PPV antibodies have been detected in the serum of one living piglet born from a vaccinated dam (titer ), High titers of PPV antibodies (3.41 ) were detected in the mummified or stillborn fetuses born from the sow n 5. But, positive results by the immunofluorescence test have been obtained from 3 samples of lungs on the 6 tested. At the contrary, in the other litter 6, no PPV antibody was detected in the exsudate of the 11 fetuses whereas a positive fluorescent picture was observed in the lung of 9 on the 10 tested fetuses. The last one gave a doubtful response difficult to interpret Serological study in the serum of the sows In vaccinated sows, after the booster vaccination, the antibodies titer rise roughly up to 3.41 except for the sow 2 of which titer of antibodies increased more slowly (fig. 11. In this group after the challenge the titer of the PPV was quite not modified. This titer was quite constant for the whole experiment. In the serum of control sows, the antibodies were detected 1 week after the challenge (fig. 1); their titer reached the maximum value between 5.01 to 5.31 five weeks after the challenge. A slight decrease of this titer could be notified 8 weeks after the challenge Serological studies in the serum of the piglets Blood samples had been collected from all the piglets born from the vaccinated sows 1 and 4 before the colostrum ingestion. No PPV antibody was detected in the sera. One week after the birth, the mean titer of the colostral antibodies varied between 3.41 to 3.71 in these litters (fig. 2!. In the litter 2, blood samples could be taken before the colostrum ingestion on only 2 piglets. No PPV antibody was detected in the sera of these animals whereas high titers could be demonstrated in the sera of the others after the colostrum suckling. In the last litter 3 the sera of piglets were taken 1 day after their birth and high titers of antibodies could be revealed. There after, the level diminished slowly to reach the level below the positivity threshold as soon as the 8th to 9th week in the litters 2, 3 and 4. PPV antibodies were detected until the 10th week in the sera of the piglets in litter 1. The titers of antibodies in the sera of the piglets inside a same litter did not differ more than a 2 dilutions interval. In the serum of the 2 live-born piglets of the unvaccinated sow n 5, high titer of antibodies were detected, but the samples had been realized after the colostrum ingestion. Nevertheless, this titer remains constant for the 10 weeks period of observation and they could have been induced by an active immunity.

5

6 2. Field studies 2.1. Observations of the performances in 11 herds in which gilts had been vaccinated As shown in table 2, the reproductive performances of the 413 vaccinated gilts did not seem to be affected by the vaccination Kinetics of antibodies in vaccinated sows of one herd In the groups 1 and 3, all the sera of the gilts were free of PPV antibodies before the vaccination (fig.3l; after the double vaccination, PPV antibodies titer increases more or less rapidly. This titer remained relatively constant for the 11 to

7 13 months of the observation period. The PPV antibodies titers remained low in the serum of the sow 605 and frequently below the positivity threshold for the 1 months of the observation period. For this period, the sera of the control sows remained free of PPV antibodies which means that a PPV infection did not occur in these groups of sows. Unfortunately, in the group 2, PPV antibodies were detected in the serum of 2 gilts before the vaccination (593, 591 So, it was not possible to measure the level of the active immunity induced by the vaccination of these 2 sows. On the third one, antibodies appeared after the second vaccination with a titer similar to the groups 1 and 3. As previously, the serum of the unvaccinated gilt was free of PPV for 6 months until the sow has been culled. High titers of PPV antibodies have been detected in the sera of 3 unvaccinated old sows. These titers were remarkably constant for, at least, 8 months. The serum of the last control old sow remained free of PPV antibodies for the same period. Discussion This oil emulsion, inactivated PPV vaccine proved to be efficient to protect the fetuses of a pregnant sow from the viral infection. After the double vaccination, high titers of HI antibodies have been obtained which were similar to those induced by the same type of vaccine in England (Wrathall et al., 1984). But, these titers are higher than those reported by others. For example, Sorensen and Askaa (1981 ) vaccinated seven gilts and these had HI titers of 64 to 128 after the double injection. Two reasons can explain these differences. First, most of the vaccines experimented previously were constituted of aluminium hydroxyde gel as an adjuvant (Sorensen and Askaa, 1981 ; Mengeling et a/., 1981) instead of this vaccine and the one described by Wrathall et al. (1984). If so it would tend to support the views of Anderson et al. (1971) that oil emulsion vaccines can provoke strong and long lasting immunity in pigs. Second, the sensitivity of the HI l technics seems not to be comparable. In most of the cases the red blood cells are not counted which could have an influence on the sensitivity of the test as a higher quantity of viral particles could be necessary to obtain a hemagglutination picture when the red blood cells are added in excess. In this experiment, it was shown that the antibodies titer did not vary very much after the challenge in the serum of the vaccinated sows. Those results are similar to those obtained by Wrathall (1984) who observed only a slight rise of the Hi titers after the challenge of sows given a double vaccination. A clear difference of the performances between the vaccinated sows and the unvaccinated ones was demonstrated. Nevertheless some stillborn fetuses were present among live born piglets from the vaccinated dams. But, no PPV antigen was found in fetuses as well as no PPV antibody could be revealed in their sera. Moreover, their size was quite similar to the one of the normal live born piglets which means that the death occurred several weeks after the challenge. Antibodies were detected in the serum of a live born piglets dead a few hours after the birth. But, in this case, the

8 blood sample was performed after the colostrum suckling and the antibodies detected in the serum were probably passively acquired. No infectious causes are probably responsible of this stillbirth (Wrathall, The cause of the mummification of one fetus in the litter 3 is not clear. But neither PPV antibody nor antigen could be detected in the fetus and the virus does not seem to be the cause of the fetal death. No PPV antibodies were detected in the sera of the live born piglets from the sows 1 to 4 before they suckle the colostrum, which is meaning they were not infected by the Parvovirus. Indeed, most of the time, an infection occurring at the end of the gestation period induces an immune response and generally no antigen can be detected at this stage of the pregnancy (Vannier and Tillon, Most of the fetuses of the 2 control sows were abnormal and mummified. In one litter, antibodies were detected whereas the PPV antigen was not systematically revealed by immunofluorescence. In the other litter, no PPV antibody was detected in the sera of the fetuses which were all infected by the virus. Similar results have been found previously (Vannier and Tillon, The PPV infection spreads inside the litter 6 probably more slowly than in the other litter in which the fetuses were not able to produce antibodies against PPV before the death. Moreover, in the litter 5, there was also an infected stillborn fetus which was probably infected after the mummified fetuses but before the live born piglets. Besides, in this litter, 2 piglets were born alive with probably actively acquired antibodies which confirms that these piglets were infected later than the others inside the litter. Indeed, the HI antibodies titers did not diminish after the birth at the opposite of the colostral antibodies of the piglets born from the vaccinated sows which disappear between the 7th to the 10th week after the birth. The field study showed that HI titers in the serum of the vaccinated sows last a long time and, at least, 13 months. It is not possible to evoke the occurrence of an infectious episod, as in each group, the serum of the unvaccinated sows remained free of PPV antibodies. Once again, these results are similar to those obtained by Wrathall et a/. ( 1984) who showed that there was no discernible fall in titers for seven months at least. At the opposite, these results were not obtained by Sorensen and Askaa (1981) and Mengeling et al. (1981) who observed slight falls in titers from about 8 to 10 weeks after the initial vaccination. In the 1 herds, the reproductive performances of the vaccinated gilts did not seem to be affected by the vaccination when they are compared with the national mean data (Dagorn, In conclusion, these experiments show that the vaccination induces a good active immune

9 response which protects the litters against a viral infection during pregnancy. The vaccination does not affect the reproductive performances of the vaccinated breeders and presents advantages to the traditional practice of the farmers to contaminate their gilts for the quarantine period with feces, fetuses or delivery of older sows. This practice was often unsuccessful especially when the PPV does not spread any more in a herd. Received, 29th July Accepted, 30th January Acknowledgements We thank Dr Brown from the National Disease Institute who kindly provided the NADL-8 PPV strain. The excellent technical assistance of Mr Delalande, Mrs Floch, Mr Cariolet, Mr Keranflec h and Mr Benevent is highly appreciated. Summary The efficacy of an inactivated virus vaccine against porcine parvovirus has been studied by immunizing 4 sows during pregnancy. A parvovirus virulent strain has been inoculated to these sows and to two other unvaccinated sows used as controls. The infection was performed between the 52nd and the 57th day of gestation. In the litters born from the vaccinated sows, 82 % of the piglets were alive and normal. Neither PPV antibodies nor antigen could be revealed in the stillborn fetuses born from the 4 vaccinated sows. Reversely, only 9.5 % of the piglets born from the 2 unvaccinated sows were alive at birth, although they were probably infected during pregnancy. In total, 86 % of fetuses in these 2 litters were mummified. A field study allowed to show that the double vaccination antibodies induced, persisted with constant titers for, at least, 13 months. Moreover, the reproductive performances of 413 gilts, vaccinated twice before mating, were not affected by this treatment. References ANDERSON E.C., MASTERS R.C., MOWAT G.N., Immune response of pigs to inactivated Foot and Mouth Diseases vaccines. Res. Vet. Sci., 12, CARIOLET R., TILLON J.P., La production de porcelets exempts d organismes pathog6nes spécifiques (EOPS) A la Station de Pathologie Porcine de Ploufragan. Sci. Tech. Anim. Lab., 3, CARTWRIGHT S., HUCK R.A., Viruses isolated in association with herd infertility, abortions and stillbirths in pigs. Vet. Rec., 80, DAGORN J., Les r6sultats technico-économiques de I ann6a Variation des marges et critbres explicatifs. Tech. Porc., 6, (2), MENGELING W.L., CUTLIP R.C., WILSON R.A., Fetal mummification associated with porcine Parvovirus infection. J. Am. Vet. Med Assoc., 166, MENGELING W.L., GUTEKUNST D.E., PIRTLE E.C., PAUL P.S., Immunogenicity of bivalent vaccine for reproductive failure of swine induced by pseudorabies virus and Porcine Parvovirus. Am. J. Vet. Res., 42, PAUL P.S., MENGELING W.L., Oronasal and intramuscular vaccination of swine with a modified live porcine parvovirus vaccine: multiplication and transmission of the vaccine virus. Am. J. Vet. Res., 45, SORENSEN K.J., ASKAA J., Vaccination against Porcine Parvovirus infection. Acta Vet. Scand., 22, VANNIER P., TILLON J.P., CARIOLET R., MADEC F., A Seroepizootiological study of Parvovirus in pig herds. Zentralbl. Veterinaermed., 31 B, VANNIER P., TILLON J.P., Diagnostic de certitude de I infection! Parvovirus dans les troubles de la reproduction de 1 espoce porcine. Recl Med. Vet., 155, WRATHALL A.E., WELLS D.E., CARTWRIGHT S.F., FRERICHS G., An inactivated, oil emulsion vaccine for the prevention of porcine parvovirus-induced reproductive failure. Res. Vet. Sci., 36, WRATHALL A.E., Reproductive disorders in pigs. 311 pp. Commonwealth Agricultural Bureaux, Farnham Royal.