Biomedical subjects

Annapaola Rizzoli

Publications and source records attributed to Annapaola Rizzoli.

4 recordsLinked to original sources

PubMed2006

Genospecies of Borrelia burgdorferi sensu lato in Ixodes ricinus ticks from the Autonomous Province of Trento, Italy.

Sequences of the variable intergenic spacer region 5S (rrfA) 23S (rrlB) rRNA were used to identify Borrelia genospecies present in Ixodes ricinus nymphs collected from the Lamar Lakes area of the Province of Trento, Italy (overall prevalence=6.3%). Four genospecies were identified, one for the first time in this Province (B. valaisiana), and three which have been noted previously (B. afzelii, B. garinii, and B. burgdorferi s.s.). In order to compare the genetic variability of these genospecies in Trento with that at a European level, our 21 sequences (15 new haplotypes) and all appropriate European Borrelia sequences registered in GenBank (up to the end of 2004) were subjected to a phylogenetic analysis (for a total of 73 sequences and 43 haplotypes). Clusters of sequences representing the five main European genospecies (afzelii, garinii, burgdorferi s.s., valaisiana, lusitaniae) are well-supported. At least two other groups of haplotypes (genospecies) are suggested by our analysis; moreover, divergent evolution may be occurring in several genospecies. The maximum uncorrected pairwise differences between sequences within genospecies ranges from 1.5% (B. burgdorferi s.s.), to 2.3% (B. garinii and B. valaisiana) to 4.7% (B. afzelii), and are not correlated with geographical distribution. Within the Province of Trento, these values for the same genospecies are 1.5%, 2.3%, 0.9%, 1.9%, respectively. These high mutation rates within genospecies suggest that the sequencing of haplotypes should continue if we are to fully understand and monitor the evolution and epidemiology of Borrelia.

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PubMed2003

Individual-based vs deterministic models for macroparasites: host cycles and extinction.

Our understanding of the qualitative dynamics of host-macroparasite systems is mainly based on deterministic models. We study here an individual-based stochastic model that incorporates the same assumptions as the classical deterministic model. Stochastic simulations, using parameter values based on some case studies, preserve many features of the deterministic model, like the average value of the variables and the approximate length of the cycles. An important difference is that, even when deterministic models yield damped oscillations, stochastic simulations yield apparently sustained oscillations. The amplitude of such oscillations may be so large to threaten parasites' persistence.With density-dependence in parasite demographic traits, persistence increases somewhat. Allowing instead for infections from an external parasite reservoir, we found that host extinction may easily occur. However, the extinction probability is almost independent of the level of external infection over a wide intermediate parameter region.

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PubMed2002

Geographical information systems and bootstrap aggregation (bagging) of tree-based classifiers for Lyme disease risk prediction in Trentino, Italian Alps.

The risk of exposure to Lyme disease in the province of Trento, Italian Alps, was predicted through the analysis of the distribution of Ixodes ricinus (L.) nymphs infected with Borrelia burgdorferi s.l. with a model based on bootstrap aggregation (bagging) of tree-based classifiers within a geographical information system (GIS). Data on L ricinus density assessed by dragging the vegetation in 438 sites during 1996 were cross-correlated with the digital cartography of a GIS, which included the variables altitude, exposure and slope, substratum, vegetation type and roe deer density. Ticks were more abundant at altitudes below 1,300 m a.s.l., in the presence of limestone and vegetation cover with thermophile deciduous forests and high densities of roe deer. A bootstrap aggregation procedure (bagging) was used to produce a model for the prediction of tick occurrence, the accuracy of which was tested on actual tick counts assessed by a further dragging campaign carried out during 1997 to determine infection prevalence and resulted in average 77%. Other tests of the model were made on additional and independent data sets. The prevalence of infection with Borrelia burgdorferi s.l, determined by polymerase chain reaction on 2,208 nymphs collected by random dragging in 245 transects selected within eight areas where the model predicted the occurrence of I. ricinus during 1997, was 17.5% and was positively correlated to tick abundance and roe deer density. These findings were used to relate the output of the bagged model (probability of tick occurrence) to the density of infected nymphs through a stepwise model selection procedure and thus to produce a GIS digital map of the probability distribution of infected nymphs in the Province of Trento at high resolution scale (50 by 50-m cell resolution). The application of the bagging procedure increased the accuracy of the prediction made by a single classification tree, a well-known classification method for the analysis of epidemiological data.

Animals↗

PubMed2002

First detection of spotted fever group rickettsiae in Ixodes ricinus from Italy.

Ixodes ricinus from Italy were examined for the first time to detect whether rickettsiae were present. Using molecular methods, we detected three different spotted fever group rickettsiae, including Rickettsia helvetica. Our results raise the possibility that bacteria other than R. conorii are involved in rickettsial diseases in Italy.

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