Assessment of the duration of maternal antibodies specific to the homologous peste des petits ruminant vaccine “Nigeria 75/1" in Djallonké lambs

The duration of maternal immunity was determined from 112 lambs born from vaccinated ewes with the homologous PPR vaccine “Nigeria 75/1" at day 90 and day 120 of pregnancy. Serum samples were collected from lambs starting from day 15 to day 150 after birth and analyzedusing the PPR specific competitive ELISA. At day 75 and day 90 after birth, 70% and 95% of these lambs respectively became negative. So it is recommended to vaccinate lambs against PPR in the interval from 75 to 90 days after birth

Diagnosis and surveillance of rinderpest using reverse transcription - PCR

PCR technique was used as an alternative method to detect evidence of rinderpest virus for diagnosis and in epidemiological surveys. Viral RNA was purified in 20 to 30 min using a commercial kit (RNaid (BIO 101). Primers used mapped in the nucleocapsid protein gene of rinderpest virus and gave specific and sensitive amplification from pathological samples. The size of the amplified fragment was 297 bp and the result was confirmed using internal non-radioactive probe SB1. The specificity of the PCRproducts was also confirmed by cleavage using restriction enzyme RsaI to give a major band of 200 bp

Comparison of two competitive ELISAs for the detection of specific peste-des-petits-ruminant antibodies in sheep and cattle populations

Peste-des-petits-ruminant (PPR) continues to be a major problem of small ruminants in Africa, the Middle East and Asia. The closely related paramyxovirus causing rinderpest (RP) has been largely eradicated by a global vaccination campaign. However, PPR screening of large populations has lacked a sufficiently reliable, fast and cheap screening test. This study compares two commercially available PPR antibodies ELISA kits using serum collected from experimental sheep and cattle populations with four different vaccination histories for RP and PPR. The aim was to estimate the levels of cross-reaction between antibodies to the two diseases for each kit and their test parameters in the different populations. There was considerable variation between kits and between the different vaccination groups. There was a clear problem of cross-reaction in both PPR kits with RP positive sera. However, in areas where RP has been eradicated and vaccination stopped both tests could be useful for screening small ruminants for PPR

Development and validation of an epitope-blocking ELISA using an anti-haemagglutinin monoclonal antibody for specific detection of antibodies in sheep and goat sera directed against peste des petits ruminants virus

International audiencePeste des petits ruminants (PPR) is a contagious and economically important disease affecting production of small ruminants (i.e., sheep and goats). Taking into consideration the lessons learnt from the Global Rinderpest Eradication Programme (GREP), PPR is now targeted by the international veterinary community as the next animal disease to be eradicated. To support the African continental programme for the control of PPR, the Pan African Veterinary Vaccine Centre of the African Union (AU-PANVAC) is developing diagnostics tools. Here, we describe the development of a blocking enzyme-linked immunosorbent assay (bELISA) that allows testing of a large number of samples for specific detection of antibodies directed against PPR virus in sheep and goat sera. The PPR bELISA uses an anti-haemagglutinin (H) monoclonal antibody (MAb) as a competitor antibody, and tests results are interpreted using the percentage of inhibition (PI) of MAb binding generated by the serum sample. PI values below or equal to 18% (PI ae 18%) are negative, PI values greater than or equal to 25% (PI ae 25%) are positive, and PI values greater than 18% and below 25% are doubtful. The diagnostic specificity (DSp) and diagnostic sensitivity (DSe) were found to be 100% and 93.74%, respectively. The H-based PPR-bELISA showed good correlation with the virus neutralization test (VNT), the gold standard test, with a kappa value of 0.947. The H-based PPR-bELISA is more specific than the commercial kit ID ScreenA (R) PPR Competition (N-based PPR-cELISA) from IDvet (France), but the commercial kit is slightly more sensitive than the H-based PPR-bELISA. The validation process also indicated good repeatability and reproducibility of the H-based PPR-bELISA, making this new test a suitable tool for the surveillance and sero-monitoring of the vaccination campaign

Ex-ante assessment of different vaccination-based control schedules against the peste des petits ruminants virus in sub-Saharan Africa

International audienceBACKGROUND: Peste des petits ruminants (PPR) is a highly contagious and widespread viral infection of small ruminants (goats and sheep), causing heavy economic losses in many developing countries. Therefore, its progressive control and global eradication by 2030 was defined as a priority by international organizations addressing animal health. The control phase of the global strategy is based on mass vaccination of small ruminant populations in endemic regions or countries. It is estimated that a 70% post-vaccination immunity rate (PVIR) is needed in a given epidemiological unit to prevent PPR virus spread. However, implementing mass vaccination is difficult and costly in smallholder farming systems with scattered livestock and limited facilities. Regarding this, controlling PPR is a special challenge in sub-Saharan Africa. In this study, we focused on this region to assess the effect of several variables of PVIR in two contrasted smallholder farming systems. METHODS: Using a seasonal matrix population model of PVIR, we estimated its decay in goats reared in sub-humid areas, and sheep reared in semi-arid areas, over a 4-year vaccination program. Assuming immunologically naive and PPR-free epidemiological unit, we assessed the ability of different vaccination scenarios to reach the 70% PVIR throughout the program. The tested scenarios differed in i) their overall schedule, ii) their delivery month and iii) their vaccination coverage. RESULTS: In sheep reared in semi-arid areas, the vaccination month did affect the PVIR decay though it did not in goats in humid regions. In both cases, our study highlighted i) the importance of targeting the whole eligible population at least during the two first years of the vaccination program and ii) the importance of reaching a vaccination coverage as high as 80% of this population. This study confirmed the relevance of the vaccination schedules recommended by international organizations

Peste des Petits Ruminants

Heartwater (or cowdriosis) is a tick-borne disease caused by Ehrlichia ruminantium, an obligatory intracellular bacterium of the order Rickettsiales, transmitted by several ticks of the genus Amblyomma. The organism is genetically highly variable which prevented until now the development of efficient vaccines. The disease is enzootic in sub-Sahelian Africa and in some Caribbean islands. It affects domestic and wild ruminants, the susceptibility to cowdriosis varying greatly between breeds and species: African wildlife shows mainly asymptomatic infections; local cattle breeds are generally protected due to enzootic stability; and introduced cattle breeds and small ruminants, even in enzootic regions, are usually susceptible to heartwater and can suffer high mortality rates. Cowdriosis is characterized by a sudden and acute fever followed by nervous, respiratory, and gastrointestinal symptoms and by hydrothorax and hydropericardium during postmortem examination. In West Africa, the only vector is Amblyomma variegatum, present in areas where pluviometry is higher than 500 mm. Therefore, animals of a high proportion of the Sahelian region are usually not infested by the tick and not infected by the bacterium. They are thus susceptible when introduced in southern parts of the Sahel or in the subhumid neighboring areas of the West African countries, for example during transhumance. Tetracyclines are effective drugs to treat heartwater when administered before occurrence of the nervous symptoms. Various vaccines have been tested, and are still developed, but, up to now, none of them showed enough effectiveness against all the field strains of E. ruminantium to allow its marketing. Prevention is therefore mainly achieved by drastic vector control or, on the contrary, acquisition of enzootic stability following tick infestation combined with tetracycline treatment as soon as hyperthermia occurs