Pediculosis capitis risk factors in schoolchildren: hair thickness and hair length

The human head lice is a cosmopolitan ectoparasite that causes pediculosis. The main way of spreading lice is through direct head-to-head contact. It is popular knowledge that some individuals are more susceptible to contracting head lice than others. Reports of individuals who have never been affected by the disease are common, even living in the same environment and under the same conditions as people who regularly have lice infestations. Previous research has been carried out on the risk of this infection associated with different human factors like gender or age. However, studies on the influence of the individual hair characteristics are scarce. The objective of the study was to analyze the pediculosis risk using geographical location, gender, age and individual hair characteristics as variables. Pediculosis was diagnosed through the detection of living lice in the hair. This cross-sectional school-based epidemiological study was conducted in 310 schoolchildren aged 1 to 13 years of schools in 4 municipalities situated in the State of Paraná, Brazil. The prevalence of head louse infection in primary school students was 49.35 %. The Odds Ratio of presence of pediculosis (OR) was estimated using multivariate logistic regression analysis. The results obtained indicate that hair length and thickness increase the risk of infection. Furthermore, the inclusion of hair color, hair shape, kind of hair-scale as covariates increases the risk of pediculosis, indicating that these variables partly explain this susceptibility and that pediculosis is independent of gender. A smaller hair diameter may favor insect fixation to the hair in the nymphal phases. These results may explain why girls are a greater risk as they let their hair grow for cultural reasons, i.e., being of female gender is an agglutinating variable. The conclusions drawn may explain the discrepancies obtained in previous analyses.

RAPD analyses and rDNA intergenic-spacer sequences discriminate Brazilian populations ofTriatoma rubrovaria(Reduviidae: Triatominae)

Triatoma rubrovaria, a member of the 'infestans' subgroup, is a potential vector of Trypanosoma cruzi in southern Brazil. Surveillance data indicate a growing domiciliary and peridomiciliary invasion by Tri. rubrovaria in the rural areas of Rio Grande do Sul (RS). In fact, following effective control of Tri. infestans, Tri. rubrovaria, which seems to have pre-adaptative characteristics for anthropic ecotopes, has become the most frequent species of triatomine bug to be collected in these areas. To explore the intraspecific variability and domiciliation of Tri. rubrovaria, the ribosomal DNA (rDNA) of two RS populations of Tri. rubrovaria that were geographically separated by only 220 km was investigated. The RAPD profiles and nucleotide sequences of the intergenic region of the rDNA, including the internal transcribed spacers 1 and 2 (ITS-1 and ITS-2) and the 5.8S gene, were analysed. In the RAPD study, the use of three decameric primers revealed polymorphisms reflecting both genetic differences between the two populations and heterogeneity within each. A phenetic dendrogram of the Tri. rubrovaria specimens, based on the three-primer consensus and a simple-matching coefficient of similarity, showed two clusters, clearly differentiating the bugs from the two localities studied. The rDNA sequencing revealed four different nucleotide sequences, with two different genotypes in each locality. The level of intraspecific variability detected within ITS-1 and ITS-2 of the Tri. rubrovaria, which was remarkably high considering the physical closeness of the two populations sampled, may indicate that the two collection sites are separated by geographical barriers that ensure the reproductive isolation of each population. The ITS sequences, like the RAPD results, clearly distinguished the two populations while showing that there is heterogeneity within each of them. The present study appears to be the first to reveal ITS length differences between populations of the same triatomine species without any associated difference in the number of microsatellite repeats. These results are in agreement with those of earlier studies on iso-enzymes, chromatic patterns, the ecological effects of environmental modification by humans, and bloodmeal sources.

Origin and phylogeography of the Chagas disease main vector Triatoma infestans based on nuclear rDNA sequences and genome size

For about half of all Chagas disease cases T. infestans has been the responsible vector. Contributing to its genetic knowledge will increase our understanding of the capacity of geographic expansion and domiciliation of triatomines. Populations of all infestans subcomplex species, T. infestans, T. delpontei, T. platensis and T. melanosoma and the so-called T. infestans "dark morph", from many South American countries were studied. A total of 10 and 7 different ITS-2 and ITS-1 haplotypes, respectively, were found. The total intraspecific ITS-2 nucleotide variability detected in T. infestans is the highest hitherto known in triatomines. ITS-1 minisatellites, detected for the first time in triatomines, proved to be homologous and thus become useful markers. Calculations show that ITS-1 evolves 1.12-2.60 times faster than ITS-2. Despite all species analyzed presenting the same n=22 chromosome number, a large variation of the haploid DNA content was found, including a strikingly high DNA content difference between Andean and non-Andean specimens of T. infestans (mean reduction of 30%, with a maximum of up to 40%) and a correlation between presence/absence of minisatellites and larger/smaller genome size. Population genetics analysis of the eight composite haplotypes of T. infestans and net differences corroborate that there are clear differences between western and eastern populations (60%), and little genetic variation among populations (1.3%) and within populations (40%) within these two groups with migration rates larger than one individual per generation corresponding only to pairs of populations one from each of these groups. These values are indicative either of a large enough gene flow to prevent population differentiation by drift within each geographic area or a very recent spread, the latter hypothesis fitting available data better. Phylogenetic trees support a common ancestor for T. infestans and T. platensis, an origin of T. infestans in Bolivian highlands and two different dispersal lines, one throughout Andean regions of Bolivia and Peru and another in non-Andean lowlands of Chile, Paraguay, Argentina, Uruguay and Brazil.