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.

Prevalence of intestinal parasites, with emphasis on the molecular epidemiology of Giardia duodenalis and Blastocystis sp., in the Paranaguá Bay, Brazil: a community survey

Background

Intestinal protozoan parasites are major contributors to the global burden of gastrointestinal disease causing significant socioeconomic consequences. Children living in resource-poor settings with restricted access to water and sanitary services are particularly at risk of these infections.

Methods

A prospective, community-based, cross-sectional survey was conducted in Paraná (southern Brazil) between May 2015 and May 2016. A total of 766 stool samples were individually collected from volunteers (male/female ratio: 0.99; age range: 0–76 years) and used for investigating the presence of intestinal helminth and protozoan species by routine microscopic procedures including the Kato-Katz and modified Ritchie concentration methods and the Ziehl-Neelsen stain technique. Quantitative real-time PCR confirmed microscopy-positive samples for Giardia duodenalis and the assemblages and sub-assemblages determined by multilocus sequence-based genotyping of the glutamate dehydrogenase (gdh) and β-giardin (bg) genes of the parasite. Identification of Blastocystis subtypes was carried out by amplification and sequencing of a partial fragment of the small-subunit ribosomal RNA gene (SSU rDNA) of this heterokont microorganism.

Results

Overall, 46.1% (353/766) of the participants were infected/colonised by at least one intestinal parasite/commensal species. Protozoan and helminth species were detected in 42.7% and 10.1% of the surveyed population, respectively. Blastocystis sp. (28.2%), Endolimax nana (14.9%), and Giardia duodenalis (11.0%) were the most prevalent species found among protozoans and Ascaris lumbricoides (5.0%), Trichuris trichiura (4.6%) and hookworms (1.0%) among helminths. A total of 38 G. duodenalis-positive samples were genotyped at gdh and bg markers, revealing the presence of the sub-assemblages AII (47.4%), AII/AIII (2.6%), BIII (5.3%), BIV (26.3%) and BIII/BIV (13.1%). Two samples (5.3%) were only identified as assemblage B. AII was predominantly found in females aged 5–9 years and was associated with a higher likelihood of reporting gastrointestinal symptoms. A total of 102 Blastocystis-positive samples were successfully subtyped at the SSU rRNA gene revealing the presence of ST1 (36.3%), ST2 (15.7%), ST3 (41.2%), ST4 (2.9%), ST6 (1.0%) and ST8 (2.9%).

Conclusions

Data presented here indicate that enteric parasites still represent a pressing health concern in Paraná, Brazil, probably due to sub-optimal water, sanitation and hygiene conditions. A mostly anthroponotic origin is suspected for G. duodenalis and Blastocystis sp. infections.

Electronic supplementary material

The online version of this article (10.1186/s13071-018-3054-7) contains supplementary material, which is available to authorized users.

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.

Phylogeography and genetic variation of Triatoma dimidiata, the main Chagas disease vector in Central America, and its position within the genus Triatoma

Background

Among Chagas disease triatomine vectors, the largest genus, Triatoma, includes species of high public health interest. Triatoma dimidiata, the main vector throughout Central America and up to Ecuador, presents extensive phenotypic, genotypic, and behavioral diversity in sylvatic, peridomestic and domestic habitats, and non-domiciliated populations acting as reinfestation sources. DNA sequence analyses, phylogenetic reconstruction methods, and genetic variation approaches are combined to investigate the haplotype profiling, genetic polymorphism, phylogeography, and evolutionary trends of T. dimidiata and its closest relatives within Triatoma. This is the largest interpopulational analysis performed on a triatomine species so far.

Methodology and Findings

Triatomines from Mexico, Guatemala, Honduras, Nicaragua, Panama, Cuba, Colombia, Ecuador, and Brazil were used. Triatoma dimidiata populations follow different evolutionary divergences in which geographical isolation appears to have had an important influence. A southern Mexican–northern Guatemalan ancestral form gave rise to two main clades. One clade remained confined to the Yucatan peninsula and northern parts of Chiapas State, Guatemala, and Honduras, with extant descendants deserving specific status. Within the second clade, extant subspecies diversity was shaped by adaptive radiation derived from Guatemalan ancestral populations. Central American populations correspond to subspecies T. d. dimidiata. A southern spread into Panama and Colombia gave the T. d. capitata forms, and a northwestern spread rising from Guatemala into Mexico gave the T. d. maculipennis forms. Triatoma hegneri appears as a subspecific insular form.

Conclusions

The comparison with very numerous Triatoma species allows us to reach highly supported conclusions not only about T. dimidiata, but also on different, important Triatoma species groupings and their evolution. The very large intraspecific genetic variability found in T. dimidiata sensu lato has never been detected in a triatomine species before. The distinction between the five different taxa furnishes a new frame for future analyses of the different vector transmission capacities and epidemiological characteristics of Chagas disease. Results indicate that T. dimidiata will offer problems for control, although dwelling insecticide spraying might be successful against introduced populations in Ecuador.

Chagas disease is a serious parasitic disease of Latin America. Human contamination in poor rural or periurban areas is mainly attributed to haematophagous triatomine insects. Triatoma includes important vector species, as T. dimidiata in Central and Meso-America. DNA sequences, phylogenetic methods and genetic variation analyses are combined in a large interpopulational approach to investigate T. dimidiata and its closest relatives within Triatoma. The phylogeography of Triatoma indicates two colonization lineages northward and southward of the Panama isthmus during ancient periods, with T. dimidiata presenting a large genetic variability related to evolutionary divergences from a Mexican-Guatemalan origin. One clade remained confined to Yucatan, Chiapas, Guatemala and Honduras, with extant descendants deserving species status: T. sp. aff. dimidiata. The second clade gave rise to four subspecies: T. d. dimidiata in Guatemala and Mexico (Chiapas) up to Honduras, Nicaragua, Providencia island, and introduced into Ecuador; T. d. capitata in Panama and Colombia; T. d. maculipennis in Mexico and Guatemala; and T. d. hegneri in Cozumel island. This taxa distinction may facilitate the understanding of the diversity of vectors formerly included under T. dimidiata, their different transmission capacities and the disease epidemiology. Triatoma dimidiata will offer more problems for control than T. infestans in Uruguay, Chile and Brazil, although populations in Ecuador are appropriate targets for insecticide-spraying.

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.