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Contagious bovine pleuropneumonia is a major threat for cattle in Africa. Since 1956 the T1/44 strain has been used as a vaccine, and later on, T1sr, a streptomycin‐resistant variant that gives fewer post‐vaccinal reactions had been developed. These vaccines are known not to be very efficient but they normally should provide protection for about eight months. However, recent emergency vaccinations, performed in various countries in the southern part of the continent apparently met with failure, casting doubts on the identity as well as the protection afforded by the T1sr strain. A vaccine trial has been designed to reassess the real protection afforded by these vaccines in face of recently isolated pathogenic strains. Great care has been taken to test the original vaccinal strains at a dose corresponding to the minimum requirement by international standards. The test was performed in Cameroon, Kenya, and Namibia as to take into account the genetic diversity that exists among the pathogenic strains. In those conditions, the protection rate at three months varied from 33 to 67%, whatever the strain used, T1/44 or T1sr. These results call for additional research for vaccine development and careful planning of strategies in the fight against CBPP.

-Mycoplasma mycoides subsp. mycoides SC (MmmSC) is the etiological agent of contagious bovine pleuropneumonia (CBPP). Although eradicated in most developed countries, the disease reappeared in Europe in the 1990s. This reappearance may have been caused either by importation from sub-Saharan Africa, where CBPP is still endemic, or by the reemergence of virulent strains in Europe, as suggested by earlier studies. A multilocus sequence analysis scheme has been developed to address this issue and, most importantly, to be able to monitor new epidemics. The alignment of the full genome sequence of the reference strain PG1 and the partial genome sequence of a pathogenic strain allowed the identification of polymorphic sites. Nineteen initial loci were selected within housekeeping genes, genes of unknown function and non coding sequences. The suitability of these loci for genotyping MmmSC strains was first tested on six strains of diverse geographic origin. The analyses showed that the published PG1 sequence contained a number of specific polymorphisms that were therefore of no use for molecular typing. Among the eight informative polymorphic loci finally selected, only one (ftsY) was positioned within a housekeeping gene. Three main groups and 31 different allelic profiles were identified among 51 strains and strain variants examined. Cluster analysis confirmed that European strains from the 1990s did not originate from Africa. It also showed a genetic link between a European strain isolated in 1967 and those found in southern Africa and Australia. This was in agreement with historical data showing that CBPP was introduced in these regions during colonisation in the 19th century.Mycoplasma mycoides / contagious bovine pleuropneumonia / multilocus sequence analysis / molecular epidemiology

-A better understanding of protective immune memory against contagious bovine pleuropneumonia (CBPP) is needed in order to facilitate the development of safer vaccines based on selected components of the pathogen. For this purpose, cells collected from lymph nodes draining the lungs of Mycoplasma mycoides subsp. mycoides small colony biotype (MmmSC)-infected cattle were stimulated with the pathogen in vitro and evaluated concurrently for proliferation (CFSE based method), expression of activation, memory markers and cytokine production. Direct evidence is presented for a major contribution of CD4 + T cells to the vigorous proliferative and T1 biased cytokine recall responses observed in cattle that have recovered from infection but not in animals developing the acute form of the disease. Two different phenotypes of MmmSC-specific memory CD4 were observed based on CD62L expression and proliferative capacities. Furthermore, recall proliferation of B cells also occurred but was strictly dependent on the presence of CD4. The information provided in this study will facilitate the search for MmmSC antigens that have potential for the development of subunit vaccines against CBPP.contagious bovine pleuropneumonia / Mycoplasma mycoides subsp. mycoides SC / vaccine / memory / CD4

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La péripneumonie est une maladie infectieuse qui touche uniquement les bovidés et connaît actuellement une recrudescence en Afrique. Dans le passé de nombreux pays ont pu contrôler la maladie, voire l'éradiquer, grâce à une prophylaxie médicale basée sur l'utilisation de deux souches vaccinales : T1/44 et sa variante streptomycino-résistante T1sr. Des échecs récents ont pu jeter un doute sur l'identité et l'efficacité de la souche T1sr. Depuis, son identité a été confirmée. Il devenait indispensable de vérifier son efficacité dans des conditions contrôlées. Les deux souches ont été utilisées en primovaccination à la dose minimum recommandée, soit 107 mycoplasmes par dose vaccinale. La reproduction expérimentale de la maladie a été réalisée par intubation endobronchique de 40 zébus du Nord-Cameroun qui ont servi à infecter par contact des animaux vaccinés et des animaux témoins. Tous les animaux ont fait l'objet d'un suivi clinique et sérologique. La transmission de la maladie a pleinement réussi et près de 40 % des animaux témoins ont succombé à la péripneumonie. La mortalité a été inférieure chez les animaux vaccinés mais la différence est à la limite de la signification statistique (p = 0,054). Quelle que soit la souche, la protection conférée par la vaccination, calculée sur la réduction de la mortalité, avoisine 37 % seulement. Il est difficile de comparer ces résultats avec des essais anciens qui étaient pratiquement tous réalisés avec des doses vaccinales beaucoup plus élevées et qui utilisaient une souche d'épreuve isolée en Australie. Les résultats obtenus soulignent le caractère partiel de la protection conférée par la vaccination actuellement pratiquée. Ils appellent d'une part à une meilleure définition des stratégies actuelles de lutte contre la péripneumonie et d'autre part à la mise au point de vaccins plus efficaces.

A better understanding of how T1 vaccination confers immunity would facilitate the rational design of improved vaccines against contagious bovine pleuropneumonia (CBPP). We show here that mycoplasmas-induced recall proliferation and IFN-γ responses are detected in cattle that received multiple shots of T1 vaccines. These anamnestic responses were under the strict control of CD4+ T lymphocytes. Moreover, CD62L expression indicated that both CD4+ effector memory (Tem) and central memory (Tcm) T lymphocytes are elicited in these animals. Comparative analysis with data from cattle that completely recovered from CBPP infection revealed similar anamnestic T-cell responses albeit at a lower magnitude for T1-vaccinated animals, particularly in the Tcm compartment. In conclusion, we discuss how our current understanding of T-cell responses will contribute to ongoing efforts for the improvement of future CBPP vaccines.

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