Method for determining the optimum age for vaccinating piglets by measuring antibody levels in the colostrum of sows within a farm

Abstract

The invention relates to the use of an anti-PCV2 antibody titer taken from a biological sample of at least one sow in a pig farm to determine the optimum age for vaccination against porcine circovirus type 2 (PCV2) of at least one piglet born to said sow or born to a sow that farrowed in said pig farm. The invention is characterized in that the biological sample is a colostrum sample. [Fig 1]

Description

Title of the invention: Method for determining the optimum age for vaccination of piglets by measuring the antibody content in the colostrum of sows on a farm Technical field

[0001] The subject of the invention is a method for determining the optimum age for vaccination against PCV2 of piglets on a pig farm, by measuring the anti-PCV2 antibody content in the colostrum of at least some of the sows on said farm. Prior art

[0002] More particularly, the invention relates to the development of a method for predicting the optimal age for vaccinating piglets against porcine circovirus type 2 (PCV2) within a farm.

[0003] Porcine circovirus type 2 (PCV2) is a DNA virus associated with the syndrome called "Post Weaning Wasting Syndrome" (PWWS) or "Porcine Multisystemic Wasting Syndrome" (PMWS). Once it has entered the body, the PCV2 virus spreads to different organs where it causes lesions.

[0004] Symptoms of PCV2 are untypical: weight loss, coarse hair, weakness, lymphadenopathy, diarrhea, and shortness of breath. Fetuses can be infected transplacentally via the blood of the non-immune mother, which can lead to mummification or stillborn or weak piglets at birth.

[0005] Vaccination against this virus remains today the most effective solution to prevent piglets from developing pathologies associated with this virus but also the spread of the virus within a farm or between farms. The effectiveness of commercial vaccines against PCV2 has been widely demonstrated thanks to the drastic reduction in the incidence of diseases associated with PCV2 under field conditions. As a result, the widespread and continuous use of these vaccines has given rise, in most farms, to a scenario of subclinical infection by PCV2, possibly obtaining seronegative batches at slaughter age. In all cases, vaccination against PCV2 is economically profitable.

[0006] However, if piglets are vaccinated too early, maternal antibodies against PCV2 present in the piglets' blood may interfere with the PCV2 vaccine, reducing its effectiveness. This situation may arise: - when using vaccines at a lower dose than recommended, - when vaccinating sows and their piglets at the same time, - when we change the protection strategy by vaccinating piglets instead sows. Vaccinated sows transfer a higher antibody titer to piglets than unvaccinated ones.

[0007] It is possible to obtain an immune response in piglets more reliably by adapting the timing of vaccination to the actual needs of each farm.

[0008] Currently, the most commonly recommended age for vaccination of piglets against PCV2 is 3-4 weeks of age (around weaning). However, there is little information available on whether this is the age at which maximum performance from vaccination is achieved.

[0009] Also, despite the above recommendations, there is now a need to further refine the vaccination strategy of a farm in order to further optimize the vaccination of piglets on a farm.

[0010] At birth, piglets have no protection against PCV2 because maternal antibodies, also called MDA for "maternally derived antibodies", do not pass the placental barrier. Piglets will acquire immunity against PCV2 by ingesting the mother's colostrum during the first two days of their life, provided that the mother has developed immunity against this virus either by vaccination or because she has previously contracted the disease. After these two days, maternal antibodies no longer pass into the piglets' blood. The quantity of maternal antibodies (MDA) present in the piglets' blood is maximum 7 days after birth and then decreases over time.

[0011] Vaccination of piglets must therefore take place when maternal immunity is no longer sufficient to protect the piglets against PCV2 infection.

[0012] However, it has been shown that anti-PCV2 MDAs can prevent the piglet from developing its own immunity against PCV2. It is therefore preferable to wait until the MDAs have reached a sufficiently low level, called the interference threshold, for the piglet vaccination to be effective and for it to optimally develop its own immunity against the virus.

[0013] Administration of the vaccine at an age at which vaccination is effective, which results in seroconversion, therefore requires knowing the moment when the MDA will fall below the said interference threshold. When vaccination is carried out too early, the piglets do not develop their own immunity and are therefore not protected against PCV2 infection. It is then necessary to carry out a new vaccination, which has a significant cost for the farmer.

[0014] To determine the age at which vaccination is effective, the best method is to carry out serological profiles, which allow vaccination to be personalized by determining when to vaccinate the piglets. Ideally, it would therefore be necessary to take a sample from each piglet to determine when to administer the vaccine and avoid interference from MDA. This solution However, this is not economically viable because it is time-consuming and expensive due to the labor required and the cost of the test. An alternative solution could be to take the sow's blood immediately after farrowing. This solution is also time-consuming and expensive and potentially less reliable.

[0015] Furthermore, such invasive blood sampling can be particularly traumatic and not without risk. Indeed, the stress generated by a blood sample just after birth can lead the sow to trample her young or to refuse them the breastfeeding essential for birth. As for sampling a piglet, this is also traumatic and potentially a source of mortality, morbidity or reduced growth. Technical problem

[0016] Considering the above, there is now a need to further improve vaccination campaigns against PCV2 of piglets in a pig farm.

[0017] Such an improvement should advantageously make it possible to vaccinate said piglets from a farm at an optimum age for even more effective vaccination.

[0018] Furthermore, determining such an optimum age should not be traumatic or anxiety-provoking, either for the piglets or their mothers.

[0019] Thus, the determination process should ideally be able to respect animal welfare.

[0020] More particularly, such a method should make it possible to limit invasive steps as much as possible, and take care of the health and comfort of the animals. Such a method should spare the animals any avoidable suffering or stressful situation in order to ensure the protection and well-being of the animals.

[0021] Such a process should therefore comply with good practice guides and French, European and international regulations in the field of animal welfare. Technical solution

[0022] The solution of the invention to this technical problem posed relates to a method for determining the optimum age for vaccination of piglets from a pig farm against porcine circovirus type 2 (PCV2), with an immunogenic composition comprising at least one PCV2 antigen, said piglets being born from sows from said pig farm optionally vaccinated against porcine circovirus type 2 (PCV2), characterized in that it comprises the following steps: - determination of the average anti-PCV2 antibody titer in colostrum taken from a sample of sows statistically representative of the sow population of the pig farm, and - calculation of the optimum age for vaccination of piglets with the im composition munogenic comprising at least one PCV2 antigen from the following equation: Tvac = ô + (log(yx CT + z) - log(S)) / P in which: TVac corresponds to the optimum age of vaccination, in days, of said piglets; CT corresponds to the average anti-PCV2 antibody titer in the colostrum of the sample of sows representative of the sow population of the pig farm; y and z are constants determined by linear regression between the anti-PCV2 antibody titer of the colostrum of a group of reference sows and the serum antibody titer of piglets born from said reference sows; S corresponds to an interference threshold, corresponding to the serum titer of maternal antibodies (MDA) of the piglets below which the maternal antibodies no longer interfere with the immunogenic composition comprising at least one PCV2 antigen; P has the formula Logl0(2) / Ti / 2 where Ti / 2 is the half-life of maternal anti-PCV2 antibodies in piglet serum; and ô is the day on which the serum titer of maternal anti-PCV2 antibodies in the serum of reference piglets is determined, the day between the end of colostrum intake and approximately 10 days after the birth of reference piglets.

[0023] It relates more particularly to a method for determining the optimum age for vaccination of piglets from a pig farm against porcine circovirus type 2 (PCV2), with an immunogenic composition comprising at least one PCV2 antigen, said piglets being born from sows from said pig farm, optionally vaccinated against porcine circovirus type 2 (PCV2), characterized in that it comprises the following steps: collection of colostrum from a sample of sows statistically representative of the sow population of the pig farm; determination of the average anti-PCV2 antibody titer in the colostrum taken from said sample of sows, and calculation of the optimum age for vaccination of piglets with the immunogenic composition comprising at least one PCV2 antigen from the following equation: Tvac = ô + (log(yx CT + z) - log(S)) / P in which: TVac corresponds to the optimum age of vaccination, in days, of said piglets; CT corresponds to the average anti-PCV2 antibody titer in the colostrum of the sample of sows representative of the sow population of the farm porcine; - y and z are constants determined by linear regression between the anti-PCV2 antibody titer of the colostrum of a group of reference sows and the serum antibody titer of piglets born from said reference sows; - S corresponds to an interference threshold, corresponding to the serum titer of maternal antibodies (MDA) of the piglets below which the maternal antibodies no longer interfere with the immunogenic composition comprising at least one PCV2 antigen; - P responds to the formula Log 10(2) / T1 / 2 where T1 / 2 is the half-life of the antibodies maternal anti-PCV2 in piglet serum; and - ô is the day on which the serum titer of maternal anti-PCV2 antibodies in the serum of reference piglets is determined, the day between the end of colostrum intake and approximately 10 days after the birth of reference piglets.

[0024] The invention also relates to a kit comprising: a. at least one sample of colostrum from a sow that gave birth on a pig farm, b. a quantitative or semi-quantitative test for the detection of anti-PCV2 antibodies in the colostrum of at least one sow from a pig farm; c. a support for presenting the optimum day for vaccination against porcine circovirus type 2 (PCV2) with an immunogenic composition comprising at least one PCV2 antigen, characterized in that it comprises a correlation table indicating said optimum day for vaccination of at least one piglet from a pig farm with said immunogenic composition comprising at least one PCV2 antigen, as a function of the antibody titer measured in the colostrum of at least one sow from said pig farm measured with a quantitative or semi-quantitative test for detecting anti-PCV2 antibodies, preferably the mother of said piglet.

[0025] It also relates to the use of an anti-PCV2 antibody titer obtained from a biological sample taken from at least one sow from a pig farm to predict an optimum age for vaccination against porcine circovirus type 2 (PCV2) of piglets born to said at least one sow, characterized in that said biological sample is a colostrum sample.

[0026] It also relates to an immunogenic composition comprising at least one PCV2 antigen, for its use in the prevention of diseases associated with PCV2 in a piglet, characterized in that an optimum age for administration of said composition in at least one piglet is determined by the method according to the invention.

[0027] It also relates to an immunogenic composition comprising at least one PCV2 antigen, for use in a method for controlling PCV2 infection or disease caused by PCV2 in a pig farm, the method comprising administering the immunogenic composition to piglets at an age determined by the method according to the invention.

[0028] It also relates to an immunogenic composition comprising at least one PCV2 antigen, for use in the vaccination of piglets against infection by PCV2 or the disease caused by PCV2 in a pig farm, the vaccination comprising the administration of the immunogenic composition to the piglets at an age determined by the method according to the invention.

[0029] It also relates to an immunogenic composition comprising at least one PCV2 antigen, for its use in inducing protective immunity against PCV2 in piglets present in a farm, the protective immunity being obtained by a method comprising the administration of the immunogenic composition to the piglets at an age determined by the method according to the invention.

[0030] It also relates to an immunogenic composition comprising at least one PCV2 antigen, for its use in the prevention of diseases associated with PCV2 in a piglet, comprising: administering said immunogenic composition to sows, and administering the immunogenic composition to piglets at an age determined by the method according to the invention.

[0031] It also relates to an immunogenic composition comprising at least one PCV2 antigen, for its use in a method for controlling an infection by PCV2 or the disease caused by PCV2 in a pig farm, the method comprising: administering said immunogenic composition to sows, and administering the immunogenic composition to piglets at an age determined by the method according to the invention.

[0032] It also relates to an immunogenic composition comprising at least one PCV2 antigen, for its use in the vaccination of piglets against infection by PCV2 or the disease caused by the PCV2 virus in a farm, the vaccination comprising: administering the immunogenic composition to sows, and administering the immunogenic composition to piglets at an age determined by the method according to the invention.

[0033] It also relates to an immunogenic composition comprising at least one PCV2 antigen, for its use in inducing protective immunity against PCV2 in pigs present in a farm, the protective immunity being obtained by a method comprising: • administration of the immunogenic composition to sows, and • administration of the immunogenic composition to piglets at an age determined by the method according to the invention. Benefits provided

[0034] The Applicant has notably been able to develop a process which has several advantages such as in particular: i) it avoids generating stress in the sow or her young; ii) it is quick and simple to implement: the approach envisaged is to collect colostrum from a limited number of sows of different parities (primiparous or multiparous) in a farm of several hundred or even several thousand sows and to deduce an age at vaccination of the piglets according to a value of the antibody titre in the colostrum collected; iii) it is inexpensive because the number of sows taken is limited; iv) it allows an iterative process: each series of samples allows the data to be consolidated and a higher confidence interval to be obtained for each vaccination; v) it allows the age of vaccination to be adapted according to the history of the farm; for example, when an infectious episode of PCV2 has started shortly before farrowing, the colostrum of the sows will be richer in anti-PCV2 antibodies and the age of vaccination can therefore be determined more precisely.

[0035] Furthermore, the method developed makes it possible, by means of a statistical analysis based on the maternal anti-PCV2 antibody titer in the colostrum of the sows, to predict the closest date for carrying out effective vaccination of the piglets. Brief description of the drawings

[0036] The invention and the advantages resulting therefrom will be better understood upon reading the description and the non-limiting embodiments which follow, illustrated with reference to the appended drawings in which: Fig.l

[0037] [Fig.l] [Fig.l] illustrates the correlation of the S / P ratio between the colostrum of the sow at farrowing and the serum of the piglet at 7 days of age. Fig.2

[0038] [Fig.2] [Fig.2] illustrates the relationship between the difference in post-vaccination serum titer minus serum titer on the day of vaccination expressed as S / P ratio (ordinate) versus serum titer on the day of vaccination expressed as S / P ratio (abscissa). This gives the linear relationship between (TSPost - TSvac) versus TSvac Description of embodiments

[0039] The subject of the invention is a determination method, or a method of calculation or measurement of the optimum age for vaccination of piglets in a farm against PCV2. The measurement method is preferably an in vitro measurement method, i.e. it is implemented outside the organism, and / or outside its natural context and under defined and controlled conditions.

[0040] The optimum vaccination age is defined as the time closest to the birth of the piglets where maternal antibodies no longer interfere with an immunogenic composition comprising at least one PCV2 antigen.

[0041] Preferably, the piglets to be vaccinated are born from sows of said farm, themselves possibly vaccinated against PCV2.

[0042] Vaccination of said piglets is generally carried out using an immunogenic composition comprising at least one PCV2 antigen allowing immunization of the piglet.

[0043] Also, the immunogenic composition comprising at least one PCV2 antigen is advantageously a vaccine containing the inactivated PCV2 virus, the live attenuated PCV2 virus, a recombinant vaccine containing the inactivated PCV1 / 2 virus (i.e. for example a capsid of the PCV2 virus containing the hybrid genome ORF1 of PCV 1 / ORF2 of PCV2) or subunits of the capsid of PCV2, expressed by a baculovirus.

[0044] The following immunogenic compositions may be cited, for example: - The Suigen® vaccine marketed by the Applicant is a vaccine described in particular in application WO2012083837 which comprises as active substance an inactivated porcine circovirus 2d genotype. - The CIRCOVAC™ vaccine marketed by the company CEVA, which contains the inactivated PCV2 virus as its active substance; - The Ingelvac CircoFLEX™ vaccine marketed by BI, which contains the PCV2 ORF2 protein as active substance; - The Porcilis PCV™ vaccine marketed by the company Intervet, which contains as active substance the type 2 subunit antigen ORF2 of the porcine circovirus; - The Suvaxyn PCV™ vaccine marketed by Zoetis, which comprises as active substance an inactivated recombinant porcine circovirus type 1 expressing the protein encoded by ORF2 of porcine circovirus type 2;

[0045] Such immunogenic compositions are mainly used for the active immunization of piglets to prevent PMWS (Post-weaning multi-systemic wasting syndrome). Associated with the effect of circovirus in intensive pig farming, this disease manifests itself by respiratory difficulties, anemia, diarrhea and loss of appetite, and it produces significant mortality in piglets and diseases associated with PCV2, and for the prevention of reproductive disorders in gilts and sows. Vaccination of sows results in an increase in colostral antibodies, thus improving passive immunity.

[0046] The process or method according to the invention comprises several important steps.

[0047] The first step is a step of collecting colostrum from a sample of sows statistically representative of the sow population on the farm.

[0048] A statistically representative sample of a population is understood to mean a subset of a reference population composed according to the representative characteristics of its elements, similar to those of the entire population. Its study must provide a relatively faithful view of the entire population, while limiting the cost of collecting information. For example, in a farm where only 10% of sows are vaccinated against PCV2, a sample containing 10% of vaccinated sows will be chosen as a representative sample.

[0049] The principle is to measure the anti-PCV2 antibody titer in the colostrum of a number n of sows. Colostrum is a thick liquid rich in proteins and antibodies secreted by the mammary gland before and / or after the birth of the young animal, before milk secretion begins.

[0050] Advantageously, the colostrum is collected, in the same farm, from a group of primiparous and / or multiparous sows, preferably representative of the parity distribution of a pig farm. The collection of colostrum and the measurement of the anti-PCV2 antibody titer in the colostrum are carried out during farrowing, in particular between the birth of the first piglet and the birth of the last piglet of each litter.

[0051] According to a preferred embodiment of the invention, the colostrum is taken, in the same pig farm, from at least 1% of a set of sows possibly vaccinated against PCV2, preferably from at least 10% of a set of sows possibly vaccinated against PCV2 in gestation, from a pig farm.

[0052] The size of the representative sample of the sow population of the pig farm depends in particular on the number of sows on the farm. Generally speaking, the more sows there are on the farm, the smaller the sample can be in order to reduce costs. The sample can represent from 0.05% to 20% of the total number of sows on the farm, more preferably between 0.1% and 10% of the total number of sows on the farm.

[0053] The second step of the method comprises determining the antibody titer in each of the samples taken in order to calculate an average anti-PCV2 antibody titer in the colostrum taken from said sow sample. The anti-PCV2 antibody content is expressed by the S / P ratio, detailed below.

[0054] According to the invention, the average anti-PCV2 antibody titer of colostrum is represented by the mean, median, range or average of the smallest value and the largest value or a certain percentile (e.g. the 85th percentile, the 90th percentile or the 95th percentile), of the anti-PCV2 antibody titres measured in the colostrum of the sows in the sample representative of the sow population of the pig farm. The choice of the mean value can be made in particular by taking into account the distribution of anti-PCV2 antibody titres in the samples or the standard deviations between the samples.

[0055] The determination of the anti-PCV2 antibody titer can be carried out by any semi-quantitative or quantitative method known to those skilled in the art. Advantageously, the determination of the average anti-PCV2 antibody titer of the colostrum taken from the sample of sows representative of the sow population of the farm is carried out by a direct ELISA test or an indirect ELISA test.

[0056] Direct ELISA (Enzyme-linked ImmunoSorbent Assay) is based on the fixation of the viral antigen on microplates, then it is bound by an antibody specific to it and which is also conjugated to an enzyme or other molecule that allows detection. That said, most PCV2 ELISA tests are based on indirect ELISA, although there are other types on the market.

[0057] Indirect ELISA is based on the binding of viral antigen to the microtiter plates used to perform the test, followed by the addition of the serum sample to be tested. The reaction is usually revealed by the addition of an antibody specific to porcine IgG, linked to an enzyme. When a suitable substrate is added, if the antigen-antibody reaction has occurred and the enzyme is present, the solution will change color. In this type of ELISA, the color intensity developed by the substrate is proportional to the amount of antibody, allowing for semi-quantitative titration of colostrum. The antibody titer of the sample is usually represented by a unitless value S / P representing the relative intensity of the sample (S) compared to the intensity of a positive standard sample (P).The S / P ratio of a sample varies depending on the kit used to determine the antibody titer and therefore comparison of values ​​between different brands of kits cannot be made directly. However, a defined kit is usually calibrated and therefore it is possible, from the S / P value of a given kit, to determine the MDA titer in the colostrum sample.

[0058] The method according to the invention further comprises a step of calculating the optimum age of vaccination TVac, in days, of piglets against PCV2 with the immunogenic composition comprising at least one PCV2 antigen, from the following equation: Tvac = ô + (log(yx CT + z) - log(S)) / P

[0059] ô is the day on which the serum titer of maternal anti-PCV2 antibodies is determined in the reference piglet serum, day between the end of colostrum intake and approximately 10 days after the birth of reference piglets, ô is typically 5, 6, 7, 8, 9 or 10, preferably 7.

[0060] In the method according to the invention, blood samples from the reference piglets to determine the half-life of the antibodies can be taken from any time between the end of colostrum intake and approximately 10 days after birth.

[0061] The half-life of maternal antibodies is an average biological value which will be used in the formula for different farms and therefore, based on measurements carried out in the field, it is possible to establish a curve of decline of maternal antibodies in the piglet's blood. The half-life is defined according to the principles of pharmacokinetics as the time required for the serum antibody titer to decrease by half.

[0062] To obtain the maternal antibody decay curve, several successive blood samples will be taken from piglets, for example between 2 and 5 samples per piglet, preferably from day 6 after birth and until the piglets are vaccinated, for example 42 days after birth.

[0063] When ô = 7, which corresponds to where the quantity of maternal antibodies in the piglet's blood is at its highest, the optimum age of vaccination in days is calculated by the following equation: Tvac = 7 + (log(yx CT + z) - log(S)) / P

[0064] In this equation, TVac corresponds to the optimum vaccination age, in days, of the piglets.

[0065] CT corresponds to the average anti-PCV2 antibody titer in the colostrum of the sow sample representative of the sow population of the pig farm.

[0066] y and z are constants determined by linear regression between the anti-PCV2 antibody titer of the colostrum of a group of reference sows and the serum antibody titer of piglets born from said reference sows. Following the establishment of the correlation of the S / P ratio between the colostrum of the sow at farrowing and the serum of the piglet at 7 days, the antibody level in the serum of the piglets appears to be proportional to the antibody level in the colostrum. This is more particularly detailed in Example 1.

[0067] In the context of their work, the Inventors were able to establish that for sows and piglets, the values ​​of the constants are typically included in intervals of 0.8 and 0.9 for y and 0.2 and 0.3 for z. More preferably, the values ​​of the constants are included in intervals of 0.86 and 0.87 for y and 0.22 and 0.23 for z. Even more preferably, the values ​​of the constants are included in intervals of 0.864 and 0.865 for y and 0.221 and 0.222 for z.

[0068] S corresponds to an interference threshold, corresponding to the serum antibody titer maternal anti-PCV2 antibodies (MDA) of piglets below which maternal anti-PCV2 antibodies no longer interfere with the immunogenic composition comprising at least one PCV2 antigen. The interference threshold between MD A and a given vaccine is a value specific to each vaccine. It is therefore necessary to determine this interference threshold for the anti-PCV2 vaccine that will be administered to piglets according to the method described below.

[0069] According to the invention, the interference threshold S is determined by the following steps detailed below:

[0070] The first step is a step a) of determining the antibody titer called “TS vac” in the serum taken on the day of administration of the immunogenic composition comprising at least one PCV2 antigen in piglets, said administration having been carried out between approximately 21 and 63 days, in particular between 21 and 42 days after birth.

[0071] The second step is a step b) of determining the anti-PCV2 antibody titer, called TSpOSt, in the serum taken between 14 and 63 days, advantageously between 14 and 42 days, after the administration of the immunogenic composition comprising at least one PCV2 antigen to the reference piglets.

[0072] The third step is a step c) of determining the relationship between (TSpost - TSvac ) and TSvac making it possible to deduce the interference threshold S between the maternal anti-PCV2 antibodies and the immunogenic composition comprising at least one PCV2 antigen.

[0073] The number m of reference piglets used for determining the threshold must be sufficient to be statistically reliable, for example between 50 and 1000 piglets.

[0074] Thus, advantageously, the interference threshold S is determined by the following steps: a. determination of the anti-PCV2 TSvac antibody titer in the serum collected on the day of administration of the immunogenic composition comprising at least one PCV2 antigen in m piglets, said administration having been carried out between 21 and 63 days, in particular between 21 and 42 days after birth, b. determination of the TSpost anti-PCV2 antibody titer in the serum collected between 14 and 63 days, advantageously between 14 and 42 days, after administration of the immunogenic composition comprising at least one PCV2 antigen to the reference piglets, c. determination of the relationship between (TSpost - TSvac) and TSvac and deduction of the interference threshold S between maternal anti-PCV2 antibodies and the immunogenic composition comprising at least one PCV2 antigen.

[0075] The value P of the equation “Tvac = ô + (log(yx CT + z) - log(S)) / P” of the process according to the invention corresponds to the formula Logl0(2) / Ti / 2 where Ti / 2 is the half-life of maternal anti-PCV2 antibodies in the serum of piglets.

[0076] Thus, the data generated by the Applicant were generated for a given test (ELISA test marketed by the company Biochek) and a given vaccine (the SUIGEN PCV2 vaccine marketed by the company Virbac). However, the optimum age of vaccination can be determined for any PCV2 vaccine and any anti-PCV2 antibody diagnostic kit by applying the method described above and in the examples.

[0077] The method according to the invention thus makes it possible to avoid a newly born piglet the stress of being separated from its mother to undergo a blood test and the stress caused by the blood test itself. The method according to the present invention therefore makes it possible, on the one hand, to contribute to the well-being of the piglet, but also to reduce the risks of mortality, morbidity or reduced growth linked to this anxiety.

[0078] Also, the present invention relates to the use of the method as defined above for improving the welfare of a piglet and / or reducing the risks of mortality, morbidity or reduced growth in a piglet.

[0079] According to a preferred embodiment of the invention, the immunogenic composition of the method according to the invention comprising at least one PCV2 antigen for the vaccination of said piglet is a vaccine against porcine circovirus type 2 comprising the inactivated Genotype 2d of porcine circovirus (strain H) (SUIGEN® PCV2), and the equation allowing the determination of the optimum age of vaccination of said piglet is determined from the following equation: Tvac = ô + (log(0.8646 x CT + 0.221) - log(l, 1)) / 0.011953 with ô = 7, which corresponds to where the quantity of maternal antibodies in the piglet's blood is at its highest.

[0080] The invention also relates to a support for presenting the optimum day for vaccination against porcine circovirus type 2 (PCV2). Said support according to the invention comprises a correlation table indicating said optimum day for vaccination of at least one piglet from a pig farm, as a function of the antibody titer measured in the colostrum of at least one sow from said pig farm. This step is carried out with a quantitative or semi-quantitative test for detecting anti-PCV2 antibodies, originating from the mother of the piglet from a pig farm.

[0081] Typically in pig farms, there is a synchronization of the heats of sows in successive groups of the same farm for a synchronization of the farrowing of the sows. This will thus make it possible to determine a vaccination day for all the piglets from the same group of a farm.

[0082] The method according to the present invention therefore makes it possible, for a set of synchronized sows, to determine the exact age for administering the immunogenic composition comprising at least one PCV2 antigen to their piglets. For reasons

[0083]

[0084]

[0085]

[0086]

[0087]

[0088]

[0089] However, in practice, all piglets may be vaccinated at an age expressed in weeks corresponding to the number of weeks closest to the age expressed in days determined by the method. For example, when the optimum age for administering the vaccine is 26 days, vaccination will be carried out at 28 days, or 4 weeks of age. Furthermore, vaccination will not be carried out at a vaccination age lower than 21 days because the piglets are too young. The invention also relates to a kit comprising at least: - a presentation medium as described above on the one hand; and - a quantitative or semi-quantitative test for the detection of antibodies in the colostrum from at least one mother of a herd; and / or - an immunogenic composition or a vaccine comprising at least one antigen of the virus. According to a first embodiment, the kit according to the invention comprises a support and a test as described above. According to a second embodiment, the kit according to the invention comprises a support and a vaccine as described above. According to a third embodiment, the kit according to the invention comprises both a support, a test and a vaccine as described above. More preferably, the kit according to the invention comprises: - at least one sample of colostrum from a sow that gave birth on a pig farm, - a quantitative or semi-quantitative test for the detection of anti-PCV2 antibodies in the colostrum of at least one sow from a pig farm; - a support for presenting the optimum day for vaccination against porcine circovirus type 2 (PCV2) with an immunogenic composition comprising at least one PCV2 antigen, characterized in that it comprises a correlation table indicating said optimum day for vaccination of at least one piglet from a pig farm with said immunogenic composition comprising at least one PCV2 antigen, as a function of the antibody titer measured in the colostrum of at least one sow from said pig farm measured with a quantitative or semi-quantitative test for detecting anti-PCV2 antibodies, preferably the mother of said piglet. More particularly, the subject of the invention is the use of an anti-PCV2 antibody titer obtained from a biological sample taken from at least one sow from a pig farm to predict an optimum age for vaccination against porcine circovirus type 2 (PCV2) of piglets born to said at least one sow, characterized in that said biological sample is a colostrum sample. Preferably, the anti-PCV2 antibody titer of the colostrum of at least one sow is the average anti-PCV2 antibody titer in colostrum from a representative sample of the sow population of the pig farm.

[0090] More preferably, the representative sample of the population of sows from the pig farm comprises at least 1% of a set of sows vaccinated with an immunogenic composition comprising at least one PCV2 antigen, preferably at least 10% of a set of vaccinated sows, preferably pregnant, from a pig farm.

[0091] The invention also relates to an immunogenic composition comprising at least one PCV2 antigen, for its use in the prevention of diseases associated with PCV2 in a piglet, characterized in that an optimum age for administration of said composition in at least one piglet is determined by the method according to the invention.

[0092] It also relates to a PCV2 vaccine, in particular an inactivated PCV2 vaccine, for use in the vaccination of pigs against infection by PCV2 or disease caused by PCV2 in a pig farm, the vaccination comprising the administration of a dose of the vaccine to the piglets at an age determined by the method according to the invention.

[0093] It also relates to a PCV2 vaccine, in particular an inactivated PCV2 vaccine, for its use in inducing protective immunity against PCV2 in pigs present in a pig farm, the protective immunity being obtained by a method comprising the administration of a dose of the vaccine to the piglets at an age determined by the method according to the invention.

[0094] According to a first particular embodiment, the present invention also relates to an immunogenic composition comprising at least one PCV2 antigen, for its use in a method for controlling PCV2 infection or disease caused by PCV2 in a pig farm, the method comprising: • administering the immunogenic composition to sows, and • administration of the immunogenic composition to piglets at an age determined by the method according to the invention.

[0095] According to a second particular embodiment, the present invention also relates to an immunogenic composition comprising at least one PCV2 antigen, for its use in the vaccination of pigs against PCV2 infection or disease caused by PCV2 in a pig farm, the vaccination comprising: • administration of the immunogenic composition to sows, and • administration of the immunogenic composition to piglets at an age determined by the method according to the invention.

[0096] According to a third particular embodiment, the present invention relates to further an immunogenic composition comprising at least one PCV2 antigen for use in inducing protective immunity against PCV2 in pigs present in a pig farm, the protective immunity being obtained by a method comprising: • administration of the immunogenic composition to sows, and • administration of the immunogenic composition to piglets at an age determined by the method according to the invention.

[0097] The time indicated for vaccinating sows depends in particular on the nature of the vaccine.

[0098] When the immunogenic composition is an inactivated PCV2 vaccine of genotype 2d (whole H strain), for example the SUIGEN™ PCV2 vaccine marketed by the Applicant, two administrations to the sow at 6 and 3 weeks before farrowing are recommended for initial immunization. For subsequent pregnancies, a single administration 3 weeks before farrowing is recommended.

[0099] The time indicated for administering said immunogenic composition is therefore, depending on whether it is an initial or subsequent immunization, 3 and 6 weeks before giving birth or 3 weeks before giving birth.

[0100] The present invention therefore also relates to an inactivated PCV2 vaccine, for example an inactivated PCV2 vaccine of genotype 2d (whole H strain), for use in a method for controlling PCV2 infection or disease caused by PCV2 in a pig farm, the method comprising: • administering a dose of the vaccine to sows at 3 and 6 weeks before farrowing or 3 weeks before farrowing, and • administering a dose of the vaccine to piglets at an age determined by the method according to the invention.

[0101] It also relates to an inactivated PCV2 vaccine, for example an inactivated PCV2 vaccine of genotype 2d (whole H strain), for use in the vaccination of pigs against infection by PCV2 or disease caused by PCV2 in a pig farm, the vaccination comprising: • administration of a dose of the vaccine to sows at 3 and 6 weeks before farrowing or 3 weeks before farrowing, and • administering a dose of the vaccine to piglets at an age determined by the method according to the invention.

[0102] It also relates to an inactivated PCV2 vaccine, for example an inactivated PCV2 vaccine of genotype 2d (whole H strain), for its use in inducing protective immunity against PCV2 in pigs present in a pig farm, the protective immunity being obtained by a method comprising: • administration of a dose of the vaccine to sows at 3 and 6 weeks before giving birth or 3 weeks before giving birth, and • administering a dose of the vaccine to piglets at an age determined by the method according to the invention.

[0103] In one embodiment, the present invention also relates to an inactivated PCV2 vaccine, in particular an inactivated PCV2 vaccine of genotype 2d (whole H strain) such as the SUIGEN™ PCV2 vaccine, for use in a method for controlling PCV2 infection or disease caused by PCV2 in a pig farm; or in vaccinating pigs against PCV2 infection or disease caused by PCV2 in a pig farm; or to induce protective immunity against PCV2 in pigs present in a pig farm as defined above in which the administration of the vaccine to the piglets is carried out at an age of 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55 or 56 days.

[0104] The method according to the present invention may also be particularly useful in the context of determining the ideal time for weaning the piglet since it is practical to vaccinate the piglets while they are still under the mother. Indeed, at weaning, the piglets are moved to a post-weaning room and may be more difficult to handle. In this case, the optimum age of vaccination determined according to the method of the present invention conditions the weaning age of the piglets.

[0105] Thus, the present invention also relates to a PCV2 vaccine, in particular an inactivated PCV2 vaccine, for use in a method for controlling PCV2 infection or disease caused by PCV2 in a pig farm, the method comprising: • administering a dose of the vaccine to piglets under the mother, and • weaning the piglets at an age determined by the method according to the invention.

[0106] The invention described in the present description can be applied to other viruses and other animals, in particular farm animals, to determine the optimum age for vaccination against one or more viruses in said farm.

[0107] Thus, in a cattle farm, colostrum can be taken from a sample of cows representative of the cows on the cattle farm to determine the optimum age for vaccinating calves born to these cows. The method described in the invention can in particular be used to determine the optimum age for vaccinating calves against a respiratory virus, in particular chosen from the syncytial virus (RS or BRS in English for "Bovine Respiratory Syncytial"), the infectious bovine rhinotracheitis virus (IBR), the Parainfluenza virus type 3 (PI3) and the Bovine Viral Diarrhea virus (BVD).

[0108] In a sheep or goat farm, colostrum can be taken from a sample of ewes or goats representative of the ewes or goats in the sheep or goat farm to determine the optimum age for vaccination of lambs or kids born to these ewes or goats. The method described in the invention can in particular be used to determine the optimum age for vaccination of lambs or kids against a virus chosen from bluetongue virus (BTV or blue tongue disease), lumpy skin disease virus, sheeppox virus, goatpox virus, Rift Valley fever virus and peste des petits ruminants virus.

[0109] The present invention will now be illustrated by means of the following examples: Example 1: Correlation of the S / P ratio between the colostrum of a sow at farrowing and the serum of a piglet at 7 days of age:

[0110] The principle is first of all to measure the antibody titer in the colostrum of a number n of sows and the antibody titer in the serum of m piglets born to these sows from one or more pig farms.

[0111] Two studies were carried out with 141 pairs of values ​​(sows / piglets): 98 in a study in the Netherlands and 43 in a study in Taiwan.

[0112] The measurement of the antibody level in the piglets' serum was carried out 7 days after the birth of the piglets.

[0113] The anti-PCV2 antibody titer was measured with an indirect ELISA kit and the antibody titer is expressed as an S / P ratio.

[0114] The data obtained following the ELISA test made it possible to establish a linear regression line between the TSJ7 antibody titer in the serum of piglets on the seventh day after birth (D=7) and the CT colostrum of sows. This is represented in [Fig. 1].

[0115] Thus, the equation obtained is in the form: TSJ7= yx CT + z ;

[0116] where y and z are constants determined by linear regression.

[0117] The final equation obtained is therefore: TSJ7 = 0.8646 CT + 0.221 Example 2: Determination of the kinetics of depletion of the S / P ratio in the serum of piglets between 7 days of age and the day of vaccination:

[0118] In order to determine the depletion kinetics, a blood sample was taken from each piglet 7 days after birth and then at different times until the day of vaccination, carried out between 3 and 9 weeks, preferably between 3 and 6 weeks after birth.

[0119] Thus, data were obtained representing the antibody titer in the serum (TS) of the piglets as a function of time.

[0120] From these data, the linear regression curve of Logio(TS) was plotted as a function of time.

[0121] The transformation into decimal logarithm made it possible to deduce the half-life time (t 1 / 2) of maternal antibodies (MDA) according to the slope P of the linear regression: ti / 2= Log io(2) / P

[0122] The average slope P = 0.011953 j1 obtained was used from all groups of the different studies.

[0123] The ti / 2 of MDA in the serum of piglets was thus estimated at 25.2j. Example 3: Estimation of the interference threshold between MD A and seroconversion induced by vaccination with SUIGEN™ PCV2 in piglet serum.

[0124] The principle of the method for determining the interference threshold is described in the articles by Fraile et al. published in Vaccine 30 (2012) 1986-1992 (doi:10.1016 / j.vaccine.2012.01.008) and in Veterinary Microbiology 161 (2012) 229-234 (http: / / dx.doi.Org / 10.1016 / j.vetmic.2012.07.021)

[0125] For this estimation, the serum anti-PCV2 antibody titer was first determined in piglets on the day of vaccination and then at the earliest 3 weeks after vaccination.

[0126] Then, the relationship between the difference in post-vaccination serum titer minus serum titer on the day of vaccination as a function of the serum titer on the day of vaccination was established.

[0127] A point cloud was obtained from which the linear regression line was determined: (TSPost- TSvac) as a function of TSVac

[0128] The regression line thus obtained intersects the X axis at the value where seroconversion is zero. This is the value of the interference threshold S which is the MDA titer from which the MDAs interfere with the vaccine.

[0129] The interference threshold value is 1.1. (the interference threshold is specific to a given vaccine) Example 4: Calculation of the relationship between the S / P ratio in sow colostrum and the recommended age for vaccination

[0130] To calculate the age of vaccination Tvac as a function of the antibody titre in the colostrum, it is necessary to use the formula obtained in the first step which corresponds to the linear regression line between the antibody titre TSJ7 in the serum of the piglets at D=7 and the colostrum of the sows CT: TSJ7 = 0.8646 CT + 0.221

[0131] From the maternal antibody titer in colostrum and the data obtained using Virbac's data and vaccine (Virbac Suigen PCV2), the following formula is obtained: TVac = 7 + (log (0.8646 CT + 0.221) - log (1.1)) / 0.011953

[0132] Using this formula, where the only variable is the CT, we can calculate the optimum vaccination age of a piglet but also generate “vaccination grids”, such as in table 1 below:

[0133] Table 1: Colostrum S / P Ratio Exact Vaccination Age (days) Rounded Up Vaccination Age (days) 1.0 6.523095791 21 1.5 18.65420632 21 1.7 22.55872426 28 2.0 27.72387225 28 2.1 29.29382073 35 2.4 33.63223038 35 2.5 34.97001868 35 3.0 41.00457143 42 3.5 46.17524821 49 It is also possible, using the data generated using the equation, to establish a vaccination grid allowing, based on an interval of S / P values, to recommend an age for vaccination expressed in weeks (table 2): Table 2: S / P colostrum Vaccination age (weeks) <1.9 3 1.9-2.2 4 2.3-2.7 5 2.8-3.4 6 3.5-4.2 7 >4.2 8

Claims

Claims

1. Method for determining the optimum age for vaccination of piglets from a pig farm against porcine circovirus type 2 (PCV2), with an immunogenic composition comprising at least one PCV2 antigen, said piglets being born from sows from said pig farm, optionally vaccinated against porcine circovirus type 2 (PCV2), characterized in that it comprises the following steps: - collection of colostrum from a sample of sows statistically representative of the sow population of the pig farm; - determination of the average anti-PCV2 antibody titer in the colostrum taken from the said sow sample, and - calculation of the optimum age for vaccination of piglets with the immunogenic composition comprising at least one PCV2 antigen from the following equation: Tvac = ô + (log(yx CT + z) - log(S)) / P in which: - TVac corresponds to the optimum age of vaccination, in days, of said piglets; - CT corresponds to the average anti-PCV2 antibody titer in the colostrum of the sow sample representative of the sow population of the pig farm; - y and z are constants determined by linear regression between the anti-PCV2 antibody titer of the colostrum of a group of reference sows and the serum antibody titer of piglets born from said reference sows; - S corresponds to an interference threshold, corresponding to the serum titer of maternal antibodies (MDA) of the piglets below which the maternal antibodies no longer interfere with the immunogenic composition comprising at least one PCV2 antigen; - P corresponds to the formula Log 10(2) / T 1 / 2 where T1 / 2 is the half-life of maternal anti-PCV2 antibodies in the piglet serum; and - ô is the day on which the serum antibody titer is determined maternal anti-PCV2 in reference piglet serum, day between the end of colostrum intake and approximately 10 days after the birth of reference piglets.

2.

3.

4. The method of claim 1, wherein δ is 5, 6, 7, 8, 9 or 10, preferably 7. Method according to claim 1 or 2, characterized in that the interference threshold S is determined by the following steps: a. determination of the anti-PCV2 TSvac antibody titer in the serum collected on the day of administration of the immunogenic composition comprising at least one PCV2 antigen in m piglets, said administration having been carried out between 21 and 63 days, in particular between 21 and 42 days after birth, b. determination of the TSpost anti-PCV2 antibody titer in the serum collected between 14 and 63 days, advantageously between 14 and 42 days, after administration of the immunogenic composition comprising at least one PCV2 antigen to the reference piglets, c. determination of the relationship between (TSpost - TSvac) and TSvac and deduction of the interference threshold S between maternal anti-PCV2 antibodies and the immunogenic composition comprising at least one PCV2 antigen. Method according to one of the preceding claims, characterized in that the immunogenic composition comprising at least one PCV2 antigen for the vaccination of said piglet is a vaccine against porcine circovirus type 2 comprising the inactivated Genotype 2d of porcine circovirus (strain H) (SUIGEN® PCV2), and in that the equation allowing the determination of the optimum age for vaccination of said piglet is determined from the following equation: Tvac = 7 + (log(0,8646 x CT + 0,221) - log(l.l)) / 0,011953.

Images