Searching for antigen B genes and their adaptive sites in distinct strains and species of the helminth Echinococcus.

Twenty-seven PCR-derived antigen B (AgB) nucleotide sequences from four Echinococcus species (Echinococcus granulosus, Echinococcus multilocularis, Echinococcus oligarthrus and Echinococcus vogeli) were aligned with 78 already published sequences, to generate a maximum likelihood phylogeny of the AgB multigene family. The phylogenetic analysis confirms that the family is constituted by four groups of genes present in each one of the four species (AgB1, AgB2, AgB3 and AgB4), and suggests that it originated by ancient duplication events preceding speciation within the genus. AgB5 sequences, which had been formerly suggested to correspond to a putatively new AgB subunit, cluster with AgB3. Likelihood tests suggest that AgB gene evolution may have been driven by heterogeneous selection pressures acting on particular AgB1, AgB3 and AgB4 codons. No selection is detected in AgB2. We discuss implications of our findings in terms of AgB biology and its use as a diagnostic tool.

Screening for different genotypes of Echinococcus granulosus within China and Argentina by single-strand conformation polymorphism (SSCP) analysis.

Single-strand conformation polymorphism (SSCP) analysis was employed for the direct visual display of genetic variability in mitochondrial DNA (mtDNA) fragments within and among populations of Echinococcus granulosus from the People's Republic of China and from Argentina. Fragments of the NADH dehydrogenase I gene (NDI) and the cytochrome c oxidase subunit I (COI) were individually amplified from parasite DNA by polymerase chain reaction, denatured and subjected to SSCP analysis. Using NDI and COI fragments, samples representing different genotypes could be readily identified based on characteristic SSCP profiles. The results demonstrate the utility of SSCP for the direct visual display of nucleotide variation in mtDNA of E. granulosus prior to DNA sequence analysis. The approach compares favourably with existing genotyping procedures and provides a reliable and technically reproducible method for the routine laboratory identification of Echinococcus isolates.

Prevalence of antibodies to Neospora caninum in different canid populations.

A total of 1,554 dogs from 5 countries on 3 continents were tested for antibodies to Neospora caninum using an indirect fluorescent antibody test. In Australia, overall, 42/451 (9%, 95% confidence interval [CI] 6-12%) dogs were seropositive (Melbourne 11/207 [5%, 95% CI 2-9%]; Sydney 18/150 [12%, 95% CI 7-18%]; Perth 13/94 [14%, 95% CI 8-22%]). Antibodies to N. caninum were also detected in dogs in South America (Uruguay [20%, 95% CI 16-24%, n = 414]) and sub-Saharan Africa (Tanzania [22%, 95% CI 12-36%, n = 49]). In contrast, only 1 of 500 dogs tested from the Falkland Islands and none of 140 dogs from Kenya was seropositive. Of wild canids, 1/54 (2%, 95% CI 0-10%) British foxes and 15/169 (9%, 95% CI 5-14%) Australian dingoes had antibodies to N. caninum.

Diagnosis of canine echinococcosis: comparison of coproantigen and serum antibody tests with arecoline purgation in Uruguay.

Echinococcus granulosus is one of the most important and widespread of the helminth zoonoses. Diagnosis of E. granulosus infection in dogs currently relies on arecoline dosing and detailed examination of the purge for adult worms. Two immunodiagnostic tests (ELISA) based on genus specific coproantigen detection or serum antibody (IgG, IgA and IgE) detection were compared against arecoline purgation for the detection of Echinococcus in naturally infected dogs in Uruguay. The coproantigen ELISA had a sensitivity of 76.9% compared with 34.6% for the serum IgG ELISA when assessed against 26 purge positive dogs (purge worm count range 1-4331). Coproantigen reactivity was positively correlated (r = 0.65) to purge worm count, with a threshold at over 20 worms. There was no positive correlation of antibody levels with worm counts. In 26 matched Echinococcus positive dog samples, the overall sensitivity of serological detection increased to 69.2% when seroreactivity for IgA and IgE antibodies were included and to 96.2% for both coproantigen and antibody assays combined. The detection of current infection of individual dogs with E. granulosus by coproantigen ELISA has the potential to replace arecoline purgation, while specific serum antibody detection should be useful in assessing Echinococcus exposure in dog populations.

Immunological assessment of exposure to Echinococcus granulosus in a rural dog population in Uruguay.

An ELISA was used to screen a dog population in Uruguay (Sarandi Del Yi, Durazno District) for the prevalence of specific serum antibodies (IgG, IgA and IgE) to Echinococcus granulosus. The sensitivity (61%) and specificity (97%) of the ELISA were determined using well-defined serum groups. A total of 408 dogs from Sarandi del Yi and environs were screened serologically, and 29.7% (8.6-13.8% for each antibody class) of dogs had positive levels of antibody to E. granulosus. This antibody prevalence (exposure) was significantly higher than the percentage of dogs found to be positive for E. granulosus worms by arecoline purgation (7.6%). This level of exposure to E. granulosus determined by ELISA is considered unacceptable from a public health perspective. Measures will now focus on obtaining data on the true prevalence of current infection in this dog population and on determining the transmission patterns of the disease in this endemic region.

Serum antibodies in canine echinococcosis.

Specific IgG, IgA and IgE antibodies against E. granulosus protoscolex antigen were detected by enzyme-linked immunosorbent assay (ELISA) in sera from dogs experimentally or naturally infected with E. granulosus. The specificities of the IgG, IgA and IgE ELISAs were 100, 100 and 97.3%, respectively. Sera from 626 dogs of different categories and geographic regions in Australia, Uruguay and Kenya were tested. There were distinct differences in antibody responses in experimentally infected canids and in the number of naturally infected dogs found seropositive, depending on geographic region. The overall sensitivities of the ELISA (IgG, IgA and IgE) ranged between 73 and 84%, except for one geographic region where it was 54%. Genetic differences of the dogs and/or antigenic variations of the parasite appear to be responsible for the variations in specific antibody levels in infected dogs. In average, approximately one third of dogs from hyperendemic hydatid regions, without E. granulosus worms at autopsy or negative for E. granulosus infection by arecoline testing, were seropositive for anti-E. granulosus antibodies, suggesting previous infection with or exposure to the parasite. The results of this study demonstrate that, although the diagnosis of current intestinal E. granulosus infection on an individual dog basis is not always reliable by serology, serum antibody ELISA is useful as an epidemiological/educational tool for seroprevalence studies on canine echinococcosis.