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We study the kinetics of a search of a single fixed target by a large number of searchers performing an intermittent biased random walk in a homogeneous medium. Our searchers carry out their walks in one of two states between which they switch randomly. One of these states (search phase) is a nearest-neighbor walk characterized by the probability of stepping in a given direction (i.e. the walks in this state are not necessarily isotropic). The other (relocation phase) is characterized by the length of the jumps (i.e. when in this state a walker does not perform a nearest-neighbor walk). Within such a framework, we propose a model to describe the searchers' dynamics, generalizing results of our previous work. We have obtained, and numerically evaluated, analytic results for the mean number of distinct sites visited up to a maximum evolution time. We have studied the dependence of this quantity on both the transition probability between the states and the parameters that characterize each state. In addition to our theoretical approach, we have implemented Monte Carlo simulations, finding excellent agreement between the theoretical-numerical and simulations results. [ABSTRACT FROM AUTHOR]

Abstract  The objectives of this study are to find an appropriate ELISA technique to monitor IgA activity during infection byTeladorsagia circumcinctain sheep as well as to identify the degree of resistance to the infection. Previous studies have shown the relationship between IgA in infected sheep and the resistance to the infection. In this study, the titre of IgA in resistant and susceptible infected ewes was tested in blood, nasal secretions and saliva. ELISAs were carried out against somatic antigen from L4 and against a 203 amino acid fragment of a recombinant protein disulphide isomerase ofT. circumcincta(Tc-PDI). The results showed that, in general, the titres of IgA against a fragment of a Tc-PDI were lower than against the somatic antigen. These lower levels are clearly shown in blood samples and nasal secretions in contrast to saliva samples where the titre reached higher values testing the IgA against Tc-PDI. This could be due to the fact that, in the detection of IgA against Tc-PDI, the antibody–antigen reaction is more specific than against the whole somatic antigen. To differentiate between resistant and susceptible animals, the significant differences were more present with the somatic antigen. Nevertheless, the ELISA technique using the somatic antigen cannot be standardized, and the antigen–antibody reactions are more unspecific; therefore, the recombinant Tc-PDI could be a better option. [ABSTRACT FROM AUTHOR]

Abstract  The liver fluke Fasciola hepatica is a worldwide distributed trematode parasite of great veterinary importance. In Spain, the prevalence of the infection is up to 56% in sheep. Its control is mainly based on the use of anthelmitics, although some resistant populations have been described. Genetic studies of the genus Fasciola have been focused on the 28S ribosomal deoxyribonucleic acid (rDNA) gene, with no intraspecific variations and a few interspecific nucleotide differences. We have designed a specific polymerase chain reaction to amplify and sequence a 510-bp-long fragment of the gene to characterize several F. hepatica ovine isolates from the northwest of Spain. All the isolates rendered the expected results on the agarose gel, while sequencing revealed some differences in the 34 site. The anthelmintic-resistant specimens showed the same nucleotide differing of the sensitive ones. Comparing to other studies, our results conclude that there are some genetic variations in F. hepatica (at the level of the 28S rDNA), including heterozygous specimens. In conclusion, a genetic heterogeneity has been found in the F. hepatica populations of ovine origin in the northwest of Spain, using an assay that could be useful for further epidemiology and characterization studies. [ABSTRACT FROM AUTHOR]