Faecal examination and PCR to detect Strongyloides venezuelensis in experimentally infected Lewis rats

More sensitive methodologies are necessary to improve strongyloidiasis diagnosis. This study compared the sensitivities of the McMaster modified technique and polymerase chain reaction (PCR) assays, both performed in faecal samples. Lewis rats were subcutaneously infected with 4,000, 400 or 40 infective third-stage larvae, considered as high, moderate or low infection, respectively. Seven days later, they were euthanized to count adult nematodes recovered from the small intestine. Stool samples were used to count the number of eggs per gram (EPG) of faeces and to detect parasite DNA by PCR performed with a species and a genus primer pair. The sensitivity of these assays depended upon parasite burden and the primer specificity. All assays presented 100 percent sensitivity at the highest parasite load. In the moderate infection, EPG and PCR with the genus primer maintained 100 percent specificity, whereas PCR sensitivity with the species primer decreased to 77.7 percent. In low infection, the sensitivity was 60 percent for EPG, 0 percent for PCR with the species primer and 90 percent for PCR done with the genus primer. Together, these results suggest that PCR with a genus primer can be a very sensitive methodology to detect Strongyloides venezuelensisin faeces of Lewis rats infected with very low parasite burden.

Genetic basis of the resistance to Strongyloides venezuelensis (Nematoda, Rhabdiasidae) infection in mice (Mus musculus)

We investigated the resistance to Strongyloides venezuelensis primary infection of mice strains NIH (resistant) and C57BL/6 (susceptible) and the F1 and F2 offspring of crosses between these strains. The mice were infected with 2000 larvae and seven days later were sacrificed for parasite recovery and counting. There was no statistically significant (p > 0.05) sex effect on resistance. The F1 mice showed an intermediate mean number of parasites as compared to the parental NIH and C57BL6 strains. Out of 400 F2 mice, the 10 percent most resistant mice were infected with 21 to 97 parasites, while the 10 percent most susceptible mice were infected with 1027 to 1433 parasites. We also found that F2 mice with black fur (n = 72), the same color as the C57BL/6 susceptible parental strain, were more susceptible than white (n = 104) or gray furred (n = 224) mice. It is conceivable that some genes determining coat color are located on the same chromosome as where genes controlling helminth resistance.