C. Calvete

Gastrointestinal helminth parasites in stray cats from the mid-Ebro Valley, Spain

Gastrointestinal helminths were collected from 58 necropsied stray cats (Felis catus) in the mid-Ebro Valley, North-East Spain, from December 1989 to March 1992. The prevalence was 89.7%, with those of individual parasites being Toxocara cati 55.2%C, Ancylostoma tubaeforme 29.3% Joyeuxiella pasqualei 55.2%, Diplopylidium acanthotetra 20.7%, Dipylidium caninum 20.7%, Mesocestoides spp. 13.8%, Taenia taeniformis 8.6% and Diplopylidium nölleri 8.6%. In relation to sex, the differences were not significant. However, the season of the year significantly affected the prevalence of A. tubaeforme and D. acanthotetra.

Modelling the distributions and spatial coincidence of bluetongue vectors Culicoides imicola and the Culicoides obsoletus group throughout the Iberian peninsula.

Abstract Data obtained by a Spanish national surveillance programme in 2005 were used to develop climatic models for predictions of the distribution of the bluetongue virus (BTV) vectors Culicoides imicola Kieffer (Diptera: Ceratopogonidae) and the Culicoides obsoletus group Meigen throughout the Iberian peninsula. Models were generated using logistic regression to predict the probability of species occurrence at an 8‐km spatial resolution. Predictor variables included the annual mean values and seasonalities of a remotely sensed normalized difference vegetation index (NDVI), a sun index, interpolated precipitation and temperature. Using an information‐theoretic paradigm based on Akaike’s criterion, a set of best models accounting for 95% of model selection certainty were selected and used to generate an average predictive model for each vector. The predictive performances (i.e. the discrimination capacity and calibration) of the average models were evaluated by both internal and external validation. External validation was achieved by comparing average model predictions with surveillance programme data obtained in 2004 and 2006. The discriminatory capacity of both models was found to be reasonably high. The estimated areas under the receiver operating characteristic (ROC) curve (AUC) were 0.78 and 0.70 for the C. imicola and C. obsoletus group models, respectively, in external validation, and 0.81 and 0.75, respectively, in internal validation. The predictions of both models were in close agreement with the observed distribution patterns of both vectors. Both models, however, showed a systematic bias in their predicted probability of occurrence: observed occurrence was systematically overestimated for C. imicola and underestimated for the C. obsoletus group. Average models were used to determine the areas of spatial coincidence of the two vectors. Although their spatial distributions were highly complementary, areas of spatial coincidence were identified, mainly in Portugal and in the southwest of peninsular Spain. In a hypothetical scenario in which both Culicoides members had similar vectorial capacity for a BTV strain, these areas should be considered of special epidemiological concern because any epizootic event could be intensified by consecutive vector activity developed for both species during the year; consequently, the probability of BTV spreading to remaining areas occupied by both vectors might also be higher.

QUARANTINE LENGTH AND SURVIVAL OF TRANSLOCATED EUROPEAN WILD RABBITS

Abstract European wild rabbits (Oryctolagus cuniculus) are frequently translocated for hunting and conservation purposes. Quarantining these animals prior to release reduces the risk of releasing rabbits incubating field infections of myxomatosis or viral haemorrhagic disease (RHD), and it provides a way to vaccinate these animals against both diseases. However the optimal quarantine period needed to achieve these goals is not known. We therefore assessed the effects of quarantine lengths (2, 4, 6, 8 weeks) on rabbit biochemical parameters, immunity induced by vaccination against myxomatosis and RHD, and survival of translocated rabbits. We found that levels of total bilirubin, urea nitrogen, aspartate aminotransferase (AST), and alanine aminotransferase (ALT) enzymatic activities were significantly (P < 0.05) decreased during quarantine, independent of quarantine length, whereas hematocrit levels increased significantly. All pregnant female rabbits aborted or lost litters during quarantine. Seroconversion against myxomatosis and RHD following vaccination was not related to any biochemical parameter at vaccination time, but the proportion of seronegative rabbits that seroconverted was moderate. The heterophil/lymphocyte ratio, conjugated to unconjugated bilirubin ratio, and the serum AST and creatinine levels we measured after capture and transport were directly related to mortality through the quarantine period, whereas we found total serum protein level was negatively related to mortality. Mortality after release was positively related to urea nitrogen concentration and negatively related to hematocrit and the albumin/globulin ratio, but it was independent of quarantine length. Based on our findings, rabbit translocation programs that include a quarantine period could be improved by decreasing the acute stress induced by capture and handling prior to quarantine; facilitating a more rapid access to high quality feed during quarantine; and improving the vaccination protocol. In addition, the release from quarantine of rabbits should be determined by their physical condition, not merely by elapsed time in quarantine.

Effects of vaccination against viral haemorrhagic disease and myxomatosis on long-term mortality rates of European wild rabbits

The effects of vaccination against myxomatosis and viral haemorrhagic disease (VHD) on long-term mortality rates in European rabbits (Oryctolagus cuniculus) were studied from 1993 to 1996 by radiotracking a free-living population of wild rabbits. During the three months after immunisation, unvaccinated young rabbits weighing between 180 and 600 g were 13.6 times more likely to die than vaccinated young rabbits. In adult rabbits, vaccination did not significantly decrease mortality, mainly owing to the high proportion of rabbits which had previously been exposed to the antigens of both diseases. Compared with adult rabbits with natural antibodies to VHD, rabbits without these antibodies were 5.2 times more likely to die of VHD during annual outbreaks.

Protection of livestock against bluetongue virus vector Culicoides imicola using insecticide-treated netting in open areas.

The protection of livestock against Culicoides species (Diptera: Ceratopogonidae) using physical barriers or chemically treated barriers is difficult owing to the small size of these biting midges and animal welfare concerns associated with the reduction of air flow. Culicoides imicola Kieffer is the main bluetongue virus vector in the Mediterranean basin, including the southern Iberian peninsula, where livestock is mainly housed in open pens or sheds which offer no physical protection against C. imicola. In this study we assessed the efficacy of surrounding yearling ewe pens with a canvas barrier or a cypermethrin‐treated canvas barrier in reducing the entry of Culicoides spp. and C. imicola. Analyses were based on comparisons of Culicoides catches in traps in pens with and without barriers, and in traps located outside pens. Although there was no clear reduction in the abundance of Culicoides other than C. imicola in pens with either barrier, the C. imicola presence was markedly reduced by the insecticide‐treated barrier compared with the untreated barrier; the latter did not reduce the abundance of this species in pens. Estimates of the protection conferred against C. imicola by the treated barrier differed depending on whether catch comparisons were based on outside traps or on traps located inside no‐barrier pens. The results suggest that the use of insecticide‐treated barriers may reduce contact between livestock and C. imicola in open areas or sheds. More research is necessary to assess the degree of protection as a function of barrier height, C. imicola abundance, and the size of the area to be protected.

SHORT-TERM NEGATIVE EFFECTS OF VACCINATION CAMPAIGNS AGAINST MYXOMATOSIS AND VIRAL HEMORRHAGIC DISEASE (VHD) ON THE SURVIVAL OF EUROPEAN WILD RABBITS

Abstract The capture and handling of live European wild rabbits (Oryctolagus cuniculus) are unavoidable initial steps for immunization by vaccination against viral hemorrhagic disease (VHD) and myxomatosis as a management tool aimed at enhancing wild rabbit populations. We investigated the short-term effects of vaccination campaigns against VHD and myxomatosis on the survival of 206 European wild rabbits in a Spanish population. While no effect was observed on the survival of adult rabbits, young and subadult rabbits (P < 0.001) had higher mortality rates during the first week after handling than in the subsequent 3 weeks. The hazard rate of death from disease was inversely correlated with body condition (P < 0.001) during the first week. Vaccination increased the hazard rate of death due to disease during the first 7 days post-handling, although this detrimental effect was higher in young rabbits (P = 0.012) and modulated by body condition (P = 0.004). The hazard rate of dying from predation during the first week was higher for males than females (P = 0.023) and in subadults compared to young rabbits (P = 0.004). Body condition was inversely related to the predation hazard rate (P = 0.002). Our results suggest that vaccination campaigns had a short-term negative impact caused by the stress of handling in addition to the detrimental effects of vaccination against VHD and myxomatosis. Future studies should consider this negative impact to assess the true efficacy of vaccination campaigns in wild populations.

Absence reduction in entomological surveillance data to improve niche-based distribution models for Culicoides imicola.

Data-driven models for the prediction of bluetongue vector distributions are valuable tools for the identification of areas at risk for bluetongue outbreaks. Various models have been developed during the last decade, and the majority of them use linear discriminant analysis or logistic regression to infer vector-environment relationships. This study presents a performance assessment of two established models compared to a distribution model based on a promising ensemble learning technique called Random Forests. Additionally, the impact of false absences, i.e. data records of suitable vector habitat that are, for various reasons, incorrectly labelled as absent, on the model outcome was assessed using alternative calibration-validation schemes. Three reduction methods were applied to reduce the number of false absences in the calibration data, without loss of information on the environmental gradient of suitable vector habitat: random reduction and stratified reduction based on the distance between absence and presence records in geographical (Euclidean distance) or environmental space (Mahalanobis distance). The results indicated that the predicted vector distribution by the Random Forest model was significantly more accurate than the vector distributions predicted by the two established models (McNemar test, p<0.01) when the calibration data were not reduced with respect to false absences. The performance of the established models, however, increased considerably by application of stratified false absence reductions. Model validation revealed no significant difference between the performance of the three distinct Culicoides imicola distribution models for the majority of alternative stratified reduction schemes. The main conclusion of this study is that the application of Random Forests, or linear discriminant analysis and logistic regression on the condition that calibration data were first reduced on geographical or environmental information, potentially lead toward better vector distribution models.

Management and environmental factors related to benzimidazole resistance in sheep nematodes in Northeast Spain

A survey to determine the level of parasite resistance to benzimidazoles (BZ) under field conditions was performed on 107 commercial sheep farms located in the Aragon region of northeast Spain. Resistance was measured using the discriminant dose, a simplified form of the in vitro egg hatch assay (EHA). Taking into account the spatial structure of the data, a multivariate approach was applied to management and environmental variables as well as to their relationships with BZ resistance levels compiled from each flock. Results estimated that 11% of flocks had resistant parasite populations, although we suspected the presence of BZ-resistant parasite strains in 98% of the sample. Resistance levels were more similar among the nearest flocks, suggesting a contagious spatial distribution of resistance (i.e., resistance at neighbouring farms was not independent from one another). Management variables such as frequency of deworming, grazing in private pastures and underdosing were positively related to resistance levels, whereas only the use of BZ was negatively related to resistance levels, likely because BZ were replaced by other anthelmintics in flocks where reduced BZ efficacy was suspected. In addition to climatic conditions and seasonality, land use was an environmental variable associated with observed BZ resistance levels. Generally, resistance was highest in cooler and wetter areas but was lower in flocks sampled during January-March compared to flocks sampled in April-June or October-December. Variation partitioning procedures showed that the variation of resistance explained by the effect of environmental variables was higher than management variables. The effects of both variable groups, however, highly overlapped with the spatial structure of resistant levels, which suggests that a considerable amount of the effects attributable to both variable groups may be actually due to the spatial distribution of resistance. The resistance variation explained by the spatial component suggested that other uncontrolled factors acting at short spatial scale (e.g., common management and environmental variables; the importation of resistant strains and their posterior spread across neighbouring flocks; the selection history of the worms carried out by historical management events previous to this survey; and genetic, physiological or both types of parasite population variation) could yield this contagious spatial structure of BZ resistance. Although further research is needed, both seasonal variation and the dependence of resistance levels among neighbouring flocks should be taken into account in the design of future research or observational resistance programmes to minimise spatial and temporal pseudo-replication. Thus, research would avoid biased estimations of resistance prevalence or of its relationship with putative factors.

Collection of Culicoides spp. with four light trap models during different seasons in the Balearic Islands

Bluetongue (BT) is a viral disease that affects ruminants, being especially pathogenic in certain breeds of sheep. Its viral agent (bluetongue virus; BTV) is transmitted by several species of Culicoides biting midges (Diptera: Ceratopogonidae). Different models of suction light traps are being used in a number of countries for the collection of BTV vector species. To determine the relative effectiveness of different light traps under field conditions, four traps (Onderstepoort, Mini-CDC, Rieb and Pirbright) were compared. These traps were rotated between four sites on a cattle farm in Mallorca (Balearic Islands, Spain) for several non-consecutive nights. Results showed remarkable disparities in the efficacy of the traps for the collection of Culicoides midges. The highest number of midges collected in the Onderstepoort trap (x¯±SD=62±94.2) was not significantly different from that collected in the Mini-CDC (x¯±SD=58±139.2). The Rieb trap collected the lowest number of midges (x¯±SD=3±4.0). Significantly higher mean numbers of midges were collected in the Onderstepoort than in either the Pirbright (P=0.002) or Rieb traps (P=0.008). There were also differences in the Culicoides species composition as determine with the various traps. These results indicate that the Onderstepoort or Mini-CDC traps will be more effective than either the Rieb or Pirbright traps for the collection of large numbers of Culicoides midges.

Seasonal Abundance of Fleas (Siphonaptera: Pulicidae, Ceratophyllidae) on Wild Rabbits in a Semiarid Area of Northeastern Spain

Abstract This paper reports the annual dynamics of wild rabbit fleas in a study site located in the Middle Ebro Valley, northeastern Spain. Fleas collected directly from wild rabbits included the species Spilopsyllus cuniculi (Dale), Xenopsylla cunicularis (Smit), Echidnophaga iberica (Ribeiro, Lucientes, Osácar, and Calvete), Caenopsylla laptevi (Beaucournu, Gil-Collado and Gilot), and Pulex irritans (L.). Monthly collections of adult and larval fleas made from within the first meter of selected burrow entrances also yielded fleas belonging to the same five species. Larval specimens of X. cunicularis, E. iberica, and C. laptevi were also found. Spilopsyllus cuniculi, a winter species that can only breed during the rabbit breeding season, was common on hosts from November to April. Xenopsylla cunicularis and E. iberica were summer species, whereas C. laptevi was abundant during the autumn and winter. Xenopsylla cunicularis and E. iberica larvae were found in burrows only during April and May, whereas those of C. laptevi were collected from October to January. The data suggested that X. cunicularis and E. iberica might diapause during the egg stage whereas C. laptevi diapauses during the pupal stage.