Risk factors for treatment failure in scabies: a cohort study

BACKGROUND

Treatment failure, which occurs in about one-third of cases, is considered as a major factor in the increasing incidence of scabies in developed countries.

OBJECTIVES

To identify predictors of treatment failure of scabies in ambulatory populations.

METHODS

This multicentre study compared the clinical characteristics and treatment modalities between a group of patients with scabies treated successfully and another group who were not cured 3 months after antiscabies treatment.

RESULTS

In total 210 patients with a diagnosis of scabies were included, comprising 98 patients in the treatment success group and 112 in the treatment failure group. The main risk factors for treatment failure were (i) the use of only one type of treatment, topical benzyl benzoate (BB) or oral ivermectin, vs. the combination of both treatments [odds ratio (OR) 2·15, 95% confidence interval (CI) 1·22-3·77]; (ii) the use of a single intake (vs. two) of oral ivermectin (OR 10·2. 95% CI 4·49-23·2); (iii) intake of ivermectin during a meal vs. on an empty stomach (OR 4·31, 95% CI 1·89-9·84); (iv) absence of decontamination of furnishings (OR 8·72, 95% CI 3·50-21·8), in particular sofa and cushions (OR 5·90, 95% CI 2·34-14·9), mattresses (OR 4·16, 95% CI 1·35-12·8) or car seats (OR 6·57, 95% CI 3·27-13·2) and (v) absence of written documents explaining treatment modalities (OR 5·18, 95% CI 2·57-10·4). In multivariate analysis, treatment failure was mainly associated with (i) use of a single intake (vs. two) of ivermectin (OR 6·62, 95% CI 2·71-16·2); (ii) use of BB alone vs. two intakes of ivermectin (OR 3·51, 95% CI 1·55-7·95) and (iii) absence of decontamination of furniture with acaricides (OR 5·81, 95% CI 1·96-16·7).

CONCLUSIONS

Use of topical BB alone and a single intake (vs. two) of ivermectin are predictors of treatment failure.

Molecular and epigenetic regulations and functions of the LAFL transcriptional regulators that control seed development

The LAFL (i.e. LEC1, ABI3, FUS3, and LEC2) master transcriptional regulators interact to form different complexes that induce embryo development and maturation, and inhibit seed germination and vegetative growth in Arabidopsis. Orthologous genes involved in similar regulatory processes have been described in various angiosperms including important crop species. Consistent with a prominent role of the LAFL regulators in triggering and maintaining embryonic cell fate, their expression appears finely tuned in different tissues during seed development and tightly repressed in vegetative tissues by a surprisingly high number of genetic and epigenetic factors. Partial functional redundancies and intricate feedback regulations of the LAFL have hampered the elucidation of the underpinning molecular mechanisms. Nevertheless, genetic, genomic, cellular, molecular, and biochemical analyses implemented during the last years have greatly improved our knowledge of the LALF network. Here we summarize and discuss recent progress, together with current issues required to gain a comprehensive insight into the network, including the emerging function of LEC1 and possibly LEC2 as pioneer transcription factors.

LEC1 (NF-YB9) directly interacts with LEC2 to control gene expression in seed

The LAFL transcription factors LEC2, ABI3, FUS3 and LEC1 are master regulators of seed development. LEC2, ABI3 and FUS3 are closely related proteins that contain a B3-type DNA binding domain. We have previously shown that LEC1 (a NF-YB type protein) can increase LEC2 and ABI3 but not FUS3 activity. Interestingly, FUS3, LEC2 and ABI3 contain a B2 domain, the function of which remains elusive. We showed that LEC1 and LEC2 partially co-localised in the nucleus of developing embryos. By comparing protein sequences from various species, we identified within the B2 domains a set of highly conserved residues (i.e. TKxxARxxRxxAxxR). This domain directly interacts with LEC1 in yeast. Mutations of the conserved amino acids of the motif in the B2 domain abolished this interaction both in yeast and in moss protoplasts and did not alter the nuclear localisation of LEC2 in planta. Conversely, the mutations of key amino acids for the function of LEC1 in planta (D86K) prevented the interaction with LEC2. These results provide molecular evidences for the binding of LEC1 to B2-domain containing transcription factors, to form heteromers, involved in the control of gene expression.

Regulation and evolution of the interaction of the seed B3 transcription factors with NF-Y subunits

The LAFL genes (LEC2, ABI3, FUS3, LEC1) encode transcription factors that regulate different aspects of seed development, from early to late embryogenesis and accumulation of storage compounds. These transcription factors form a complex network, with members able to interact with various other players to control the switch between embryo development and seed maturation and, at a later stage in the plant life cycle, between the mature seed and germination. In this review, we first summarize our current understanding of the role of each member in the network in the light of recent advances regarding their regulation and structure/function relationships. In a second part, we discuss new insights concerning the evolution of the LAFL genes to address the more specific question of the conservation of LEAFY COTYLEDONS 2 in both dicots and monocots and the putative origin of the network. Last we examine the current major limitations to current knowledge and future prospects to improve our understanding of this regulatory network.