Renaud Lancelot

Development of a competitive ELISA for detecting antibodies to the peste des petits ruminants virus using a recombinant nucleoprotein.

A competitive ELISA based on the reaction between a monoclonal antibody (mAb) and a recombinant nucleoprotein of the peste des petits ruminants virus (PPRV) was developed. This protein was obtained in large quantities from insect cells infected with a PPR nucleoprotein recombinant baculovirus (N-B). The competitive ELISA was compared with the virus neutralisation test (VNT) for detecting specific antibodies to PPRV in sheep and goats. The time consuming VNT is the only prescribed test that is capable of distinguishing between PPRV and the cross-reactive rinderpest virus (RPV). The competitive ELISA involves the simultaneous addition of the mAb and antibodies present in a positive serum, leading to competition for a specific epitope on the N-B. Optimum conditions were obtained by using serum samples which had positive or negative neutralising activity against PPRV or RPV. A negative cut-off point was determined on PPRV-negative sera from RPV-vaccinated cattle. A threshold value of 48 per cent inhibition, calculated from the mean for this population plus 2.7 standard deviations, was used in routine testing. A total of 683 sera were analysed by the competitive ELISA and the VNT. A good correlation (r = 0.94) was observed between the titres obtained in the two tests, with 80 sera that were from laboratory sources. The agreement between the two tests was determined on 271 field sera (kappa = 0.825). Their relative sensitivity (94.5 per cent) and specificity (99.4 per cent) were assessed on the 148 laboratory sera plus the 271 sera used for the determination of kappa.(ABSTRACT TRUNCATED AT 250 WORDS)

Asian Lineage of Peste des Petits Ruminants Virus, Africa

Interest in peste des petits ruminants virus (PPRV) has been stimulated by recent changes in its host and geographic distribution. For this study, biological specimens were collected from camels, sheep, and goats clinically suspected of having PPRV infection in Sudan during 2000–2009 and from sheep soon after the first reported outbreaks in Morocco in 2008. Reverse transcription PCR analysis confirmed the wide distribution of PPRV throughout Sudan and spread of the virus in Morocco. Molecular typing of 32 samples positive for PPRV provided strong evidence of the introduction and broad spread of Asian lineage IV. This lineage was defined further by 2 subclusters; one consisted of camel and goat isolates and some of the sheep isolates, while the other contained only sheep isolates, a finding with suggests a genetic bias according to the host. This study provides evidence of the recent spread of PPRV lineage IV in Africa.

Assessment of vector/host contact: comparison of animal-baited traps and UV-light/suction trap for collecting Culicoides biting midges (Diptera: Ceratopogonidae), vectors of Orbiviruses

BackgroundThe emergence and massive spread of bluetongue in Western Europe during 2006-2008 had disastrous consequences for sheep and cattle production and confirmed the ability of Palaearctic Culicoides (Diptera: Ceratopogonidae) to transmit the virus. Some aspects of Culicoides ecology, especially host-seeking and feeding behaviors, remain insufficiently described due to the difficulty of collecting them directly on a bait animal, the most reliable method to evaluate biting rates.Our aim was to compare typical animal-baited traps (drop trap and direct aspiration) to both a new sticky cover trap and a UV-light/suction trap (the most commonly used method to collect Culicoides).Methods/resultsCollections were made from 1.45 hours before sunset to 1.45 hours after sunset in June/July 2009 at an experimental sheep farm (INRA, Nouzilly, Western France), with 3 replicates of a 4 sites × 4 traps randomized Latin square using one sheep per site. Collected Culicoides individuals were sorted morphologically to species, sex and physiological stages for females. Sibling species were identified using a molecular assay. A total of 534 Culicoides belonging to 17 species was collected. Abundance was maximal in the drop trap (232 females and 4 males from 10 species) whereas the diversity was the highest in the UV-light/suction trap (136 females and 5 males from 15 species). Significant between-trap differences abundance and parity rates were observed.ConclusionsOnly the direct aspiration collected exclusively host-seeking females, despite a concern that human manipulation may influence estimation of the biting rate. The sticky cover trap assessed accurately the biting rate of abundant species even if it might act as an interception trap. The drop trap collected the highest abundance of Culicoides and may have caught individuals not attracted by sheep but by its structure. Finally, abundances obtained using the UV-light/suction trap did not estimate accurately Culicoides biting rate.

Rift Valley fever in West Africa: the role of space in endemicity.

Rift Valley fever is an endemic vector‐borne disease in West Africa, which mainly affects domestic ruminants and occasionally humans. The aetiological mechanisms of its endemicity remain under debate. We used a simple spatially explicit model to assess the possibility of endemicity without wild animals providing a permanent virus reservoir. Our model takes into account the vertical transmission in some mosquito species, the rainfall‐driven emergence of their eggs and local and distant contacts because of herd migration. Endemicity without such a permanent virus reservoir would be impossible in a single site except when there is a strictly periodic rainfall pattern; but it would be possible when there are herd movements and sufficient inter‐site variability in rainfall, which drives mosquito emergence.

Peste des petits ruminants, the next eradicated animal disease?

Peste des Petits Ruminants (PPR) is a widespread viral disease caused by a Morbillivirus (Paramyxoviridae). There is a single serotype of PPR virus, but four distinct genetic lineages. Morbidity and mortality are high when occurring in naive sheep and goats populations. Cattle and African buffaloes (Syncerus caffer) are asymptomatically infected. Other wild ruminants and camels may express clinical signs and mortality. PPR has recently spread in southern and northern Africa, and in central and far-east Asia. More than one billion sheep and goats worldwide are at risk. PPR is also present in Europe through western Turkey. Because of its clinical incidence and the restrictions on animal movements, PPR is a disease of major economic importance. A live attenuated vaccine was developed in the 1980s, and has been widely used in sheep and goats. Current researches aim (i) to make it more thermotolerant for use in countries with limited cold chain, and (ii) to add a DIVA mark to shorten and reduce the cost of final eradication. Rinderpest virus-another Morbillivirus-was the first animal virus to be eradicated from Earth. PPRV has been proposed as the next candidate. Considering its wide distribution and its multiple target host species which have an intense mobility, it will be a long process that cannot exclusively rely on mass vaccination. PPR specific epidemiological features and socio-economic considerations will also have to be taken into account, and sustained international, coordinated, and funded strategy based on a regional approach of PPR control will be the guarantee toward success.

Rift Valley Fever in Small Ruminants, Senegal, 2003

Serologic incidence was estimated at 2.9%.

Using species distribution models to optimize vector control in the framework of the tsetse eradication campaign in Senegal.

Significance Tsetse flies transmit human and animal trypanosomoses in sub-Saharan Africa, respectively a major neglected disease and the most important constraint to cattle production in infested countries. They are the target of the Pan African Tsetse and Trypanosomiasis Eradication Campaign (PATTEC). Here we show how distribution models can be used to optimize a tsetse eradication campaign in Senegal. Our results allow a better understanding of the relationships between tsetse presence and various environmental parameters measured by remote sensing. Furthermore, we argue that the methodology developed should be integrated into future tsetse control efforts that are planned under the umbrella of the PATTEC initiative. The results have a generic value for vector and pest control campaigns, especially when eradication is contemplated. Tsetse flies are vectors of human and animal trypanosomoses in sub-Saharan Africa and are the target of the Pan African Tsetse and Trypanosomiasis Eradication Campaign (PATTEC). Glossina palpalis gambiensis (Diptera: Glossinidae) is a riverine species that is still present as an isolated metapopulation in the Niayes area of Senegal. It is targeted by a national eradication campaign combining a population reduction phase based on insecticide-treated targets (ITTs) and cattle and an eradication phase based on the sterile insect technique. In this study, we used species distribution models to optimize control operations. We compared the probability of the presence of G. p. gambiensis and habitat suitability using a regularized logistic regression and Maxent, respectively. Both models performed well, with an area under the curve of 0.89 and 0.92, respectively. Only the Maxent model predicted an expert-based classification of landscapes correctly. Maxent predictions were therefore used throughout the eradication campaign in the Niayes to make control operations more efficient in terms of deployment of ITTs, release density of sterile males, and location of monitoring traps used to assess program progress. We discuss how the models’ results informed about the particular ecology of tsetse in the target area. Maxent predictions allowed optimizing efficiency and cost within our project, and might be useful for other tsetse control campaigns in the framework of the PATTEC and, more generally, other vector or insect pest control programs.

Newcastle disease virus in Madagascar: identification of an original genotype possibly deriving from a died out ancestor of genotype IV.

In Madagascar, Newcastle disease (ND) has become enzootic after the first documented epizootics in 1946, with recurrent annual outbreaks causing mortality up to 40%. Four ND viruses recently isolated in Madagascar were genotypically and pathotypically characterised. By phylogenetic inference based on the F and HN genes, and also full-genome sequence analyses, the NDV Malagasy isolates form a cluster distant enough to constitute a new genotype hereby proposed as genotype XI. This new genotype is presumably deriving from an ancestor close to genotype IV introduced in the island probably more than 50 years ago. Our data show also that all the previously described neutralising epitopes are conserved between Malagasy and vaccine strains. However, the potential implication in vaccination failures of specific amino acid substitutions predominantly found on surface-exposed epitopes of F and HN proteins is discussed.

Learning influences host choice in tsetse

A learning capacity for feeding is described in many insect species including vectors of diseases, but has never been reported in tsetse flies (Diptera, Glossinidae), the cyclic vectors of human (sleeping sickness) and animal trypanosomoses in Africa. Repeated feeding on the same host species by a disease vector is likely to increase the within-species disease-transmission risk, but to decrease it between species. An experiment with cattle and reptiles in a stable provides evidence that the species of host selected for the second blood meal in tsetse flies depends on the host encountered for the first blood meal when the between-meal interval is 2 days. This preference disappears when the between-meal interval is extended to 3 days. The energetic advantages of this acquired preference and its importance in trypanosomoses epidemiology are discussed.

Host preferences of Palaearctic Culicoides biting midges: implications for transmission of orbiviruses

Feeding success depends on host availability, host defensive reactions and host preferences. Host choice is a critical determinant of the intensity at which pathogens are transmitted. The aim of the current study was to describe host preferences of Palaearctic Culicoides species (Diptera: Ceratopogonidae) Latreille using traps baited with the five different host species of poultry, horse, cattle, sheep and goat. Collections were carried out nightly in July and August 2009 in western France with three replicates of a 5 × 5 randomized Latin square (five sites, five hosts). Moreover, an ultraviolet (UV) light/suction trap was operated during host‐baited collections to correlate Culicoides biting rates and UV light/suction trap catches. A total of 660 Culicoides belonging to 12 species, but comprised mainly of Culicoides scoticus Downes and Kettle, Culicoides dewulfi Goetghebuer and Culicoides obsoletus Meigen, were collected on animal baits. Abundance was highest for the horse, which accounted for 95% of all Culicoides caught, representing 10 species. The horse, the largest bait, was the most attractive host, even when abundance data were corrected by weight, body surface or Kleibers scaling factor. Culicoides obsoletus was the only dominant species attracted by birds. Both C. scoticus and C. dewulfi were collected mainly from the upper body of the horse. Finally, the quantification of host preferences allows for discussion of implications for the transmission of Culicoides‐borne pathogens such as bluetongue virus.