Large-Scale International Validation of an Indirect ELISA Based on Recombinant Nucleocapsid Protein of Rift Valley Fever Virus for the Detection of IgG Antibody in Domestic Ruminants

Diagnostic performance of an indirect enzyme-linked immunosorbent assay (I-ELISA) based on a recombinant nucleocapsid protein (rNP) of the Rift Valley fever virus (RVFV) was validated for the detection of the IgG antibody in sheep (n = 3367), goat (n = 2632), and cattle (n = 3819) sera. Validation data sets were dichotomized according to the results of a virus neutralization test in sera obtained from RVF-endemic (Burkina Faso, Democratic Republic of Congo, Mozambique, Senegal, Uganda, and Yemen) and RVF-free countries (France, Poland, and the USA). Cut-off values were defined using the two-graph receiver operating characteristic analysis. Estimates of the diagnostic specificity of the RVFV rNP I-ELISA in animals from RVF-endemic countries ranged from 98.6% (cattle) to 99.5% (sheep) while in those originating from RVF-free countries, they ranged from 97.7% (sheep) to 98.1% (goats). Estimates of the diagnostic sensitivity in ruminants from RVF-endemic countries ranged from 90.7% (cattle) to 100% (goats). The results of this large-scale international validation study demonstrate the high diagnostic accuracy of the RVFV rNP I-ELISA. Standard incubation and inactivation procedures evaluated did not have an adverse effect on the detectable levels of the anti-RVFV IgG in ruminant sera and thus, together with recombinant antigen-based I-ELISA, provide a simple, safe, and robust diagnostic platform that can be automated and carried out outside expensive bio-containment facilities. These advantages are particularly important for less-resourced countries where there is a need to accelerate and improve RVF surveillance and research on epidemiology as well as to advance disease control measures.

Detection and molecular characterization of Peste des Petits Ruminants virus from outbreaks in Burundi, December 2017-January 2018

In December 2017, Peste des Petits Ruminants (PPR) emerged in Burundi (East Africa) and rapidly spread to five provinces (Gitega, Kirundo, Mwaro, Muramvya and Karuzi) in the country, causing severe disease and killing more than 4,000 goats in the province of Gitega alone. An initial outbreak investigation was conducted in December 2017 by the Burundi Government Veterinary Services and samples were collected for laboratory confirmation. A competitive Enzyme Linked Immuno-Sorbent Assay (cELISA: Chinese Patent No. ZL201210278970.9) supplied by the Lanzhou Veterinary Research Institute was used to test 112 sera and results showed around 37.5% positive samples. This high level of PPR positive sera in an animal population where PPR infection and vaccination had not been previously reported indicated the exposure of the animals to PPRV. Subsequently in January 2018, the laboratory tests conducted at the African Union-Pan African Veterinary Vaccine Centre (AU-PANVAC) laboratories following a joint investigative mission by the African Union-Interafrican Bureau for Animal Resources (AU-IBAR), AU-PANVAC and the East African Community (EAC) confirmed the presence of PPR in Burundi. Samples tested by conventional RT-PCR indicated the presence of the PPR virus (PPRV). Confirmatory isolation of the virus was also performed. Phylogenetic analysis revealed that the virus belongs to lineage III and shows a close relationship with PPRV isolates from Kenya in 2011 and Uganda in 2012. A possible explanation for the outbreaks of PPR in Burundi between December 2017 and February 2018 is presented.

Differences in genetic structure assessed using Y-chromosome and mitochondrial DNA markers do not shape the contributions to diversity in African sires

Up to 173 African sires belonging to 11 different subpopulations representative of four cattle groups were analysed for six Y-specific microsatellite loci and a mitochondrial DNA fragment. Differences in Y-chromosome and mtDNA haplotype structuring were assessed. In addition, the effect of such structuring on contributions to total genetic diversity was assessed. Thirty-five Y-chromosome and 71 mtDNA haplotypes were identified. Most Y-chromosomes analysed (73.4%) were of zebu origin (11 haplotypes). Twenty-two Y-haplotypes (44 samples) belonged to the African taurine subfamily Y2a. All mtDNA haplotypes belonged to the "African" taurine T1 haplogroup with 16 samples and nine haplotypes belonging to a recently identified subhaplogroup (T1e). Median-joining networks showed that Y-chromosome phylogenies were highly reticulated with clear separation between zebu and taurine clusters. Mitochondrial haplotypes showed a clear star-like shape with small number of mutations separating haplotypes. Mitochondrial-based F_ST -statistics computed between cattle groups tended to be statistically non-significant (p > .05). Most F_ST values computed among groups and subpopulations using Y-chromosome markers were statistically significant. AMOVA confirmed that divergence between cattle groups was only significant for Y-chromosome markers (Φ_CT  = 0.209). At the mitochondrial level, African sires resembled an undifferentiated population with individuals explaining 94.3% of the total variance. Whatever the markers considered, the highest contributions to total Nei's gene diversity and allelic richness were found in West African cattle. Genetic structuring had no effect on patterns of contributions to diversity.

Risk factors for MERS coronavirus infection in dromedary camels in Burkina Faso, Ethiopia, and Morocco, 2015

Understanding Middle East respiratory syndrome coronavirus (MERS-CoV) transmission in dromedary camels is important, as they consitute a source of zoonotic infection to humans. To identify risk factors for MERS-CoV infection in camels bred in diverse conditions in Burkina Faso, Ethiopia and Morocco, blood samples and nasal swabs were sampled in February-March 2015. A relatively high MERS-CoV RNA rate was detected in Ethiopia (up to 15.7%; 95% confidence interval (CI): 8.2-28.0), followed by Burkina Faso (up to 12.2%; 95% CI: 7-20.4) and Morocco (up to 7.6%; 95% CI: 1.9-26.1). The RNA detection rate was higher in camels bred for milk or meat than in camels for transport (p = 0.01) as well as in younger camels (p = 0.06). High seropositivity rates (up to 100%; 95% CI: 100-100 and 99.4%; 95% CI: 95.4-99.9) were found in Morocco and Ethiopia, followed by Burkina Faso (up to 84.6%; 95% CI: 77.2-89.9). Seropositivity rates were higher in large/medium herds (≥51 camels) than small herds (p = 0.061), in camels raised for meat or milk than for transport (p = 0.01), and in nomadic or sedentary herds than in herds with a mix of these lifestyles (p < 0.005).

Prevalence of Rift Valley fever in domestic ruminants in the central and northern regions of Burkina Faso

The seroprevalence of Rift Valley fever was determined in cattle, sheep and goats in selected areas of northern and central Burkina Faso. A total of 520 serum samples were screened for anti-Rift Valley fever virus immunoglobulin G (IgG) antibodies using an inhibition enzyme-linked immunosorbent assay (ELISA). An average seroprevalence of 7.67% (range 5% to 20%) was found in ruminants in Seno and Soum provinces, and prevalences of 20% and 22.5% in cattle in Yatenga and Oubritenga provinces, respectively. The location, species and age of the animals were found to influence the seroprevalence. All the ELISA IgG-positive samples were tested for IgM in a competitive ELISA and were found negative, thus ruling out recent infections. The IgG-positive samples, including weak positives, were further tested in a serum neutralisation test for neutralising antibodies and 54.5% of these samples tested positive. The results show that the virus is in circulation in central and northern regions of Burkina Faso, suggesting the need for improved surveillance and control systems to prevent future outbreaks and the consequent economic impact of the disease in Burkina Faso livestock.

[Prevalence of tuberculosis and brucellosis in intra-urban and peri-urban dairy cattle farms in Ouagadougou, Burkina Faso]

A study of the prevalence of bovine tuberculosis and brucellosis was conducted in dairy cattle farms in and around the city of Ouagadougou, Burkina Faso. It reveals the potential economic and health impact of these two major zoonoses in the study area. Three farming systems were included in the study. A total of 1,420 cattle were tested for tuberculosis and 1,689 cattle were tested for brucellosis. The intradermal tuberculin test was used for tuberculosis, and the buffered antigen test and indirect enzyme-linked immunosorbent assay were used for brucellosis. The overall prevalence rate is estimated to be 6.05% for tuberculosis and 3.61% for brucellosis. The prevalence rates of tuberculosis and brucellosis in urban and peri-urban dairy cattle farms in Ouagadougou were found to be high. As these two production-linked diseases are zoonotic, they could pose a major risk to human health and contribute significantly to reducing animal production and productivity in the areas covered by the study. Animals should be checked systematically prior to introducing them into dairy herds, with the ultimate goal of eradicating these two zoonoses.