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Only recently have attempts been made to develop techniques for the early identification of scabies infections and to identify the genome of the mites. Most work with scabies employs rudimentary technology and requires skill for accurate diagnosis. Many countries still have no widely available dermatology service to deal with this infection and its sequelae.
Thaxtomin A is the main phytotoxin produced by Streptomyces scabies, a causal agent of potato scab. Thaxtomin A is a yellow compound composed of 4-nitroindol-3-yl-containing 2,5-dioxopiperazine. A collection of nonpathogenic streptomycetes isolated from potato tubers and microorganisms recovered from a thaxtomin A solution were examined for the ability to grow in the presence of thaxtomin A as a sole carbon or nitrogen source. Three bacterial isolates and two fungal isolates grew in thaxtomin A-containing media. Growth of these organisms resulted in decreases in the optical densities at 400 nm of culture supernatants and in 10% reductions in the thaxtomin A concentration. The fungal isolates were identified as a Penicillium sp. isolate and a Trichoderma sp. isolate. One bacterial isolate was associated with the species Ralstonia pickettii, and the two other bacterial isolates were identified as Streptomyces sp. strains. The sequences of the 16S rRNA genes were determined in order to compare thaxtomin A-utilizing actinomycetes to the pathogenic organism S. scabies and other Streptomyces species. The nucleotide sequences of the gamma variable regions of the 16S ribosomal DNA of both thaxtomin A-utilizing actinomycetes were identical to the sequence of Streptomyces mirabilis ATCC 27447. When inoculated onto potato tubers, the three thaxtomin A-utilizing bacteria protected growing plants against common scab, but the fungal isolates did not have any protective effect.
The regulatory effect of amino acids on the production of thaxtomin A, a phytotoxin produced by Streptomyces scabies, was investigated. Tryptophan had an important inhibitory effect on the toxin biosynthesis in all five strains of S. scabies tested. Two other aromatic amino acids (tyrosine and phenylalanine) also inhibited thaxtomin A biosynthesis, while aliphatic amino acids did not cause an important decline in thaxtomin A production. Methylation of tryptophan prevented or reduced the inhibitory effect on thaxtomin A biosynthesis. In spite of the inhibitory action of tryptophan and phenylalanine on thaxtomin A production, incorporation of these radiolabeled molecules into thaxtomin A confirmed that they are metabolic precursors for the biosynthesis of the phytotoxin.
Thirteen Rocky Mountain bighorn sheep (Ovis canadensis canadensis) with clinical signs of psoroptic scabies were captured in Wyoming. Signs included droopy ears, depilation on the head and neck, and exudate in the ears. Mites were identified as either Psoroptes cervinus or P. equi. Two ewes with scabies at the time of original capture had no clinical signs of mite infection 1 and 2 yr later.
Sarcoptes scabiei lives in the stratum corneum of its mammalian host. Keratinocytes and fibroblasts are among the first cells to encounter the burrowing mite and its products. The aim of this study was to determine if molecules in an extract of S. scabiei modulate the expression of cytokines by keratinocytes and fibroblasts. Human keratinocytes and fibroblasts were exposed to an extract of S. scabiei var. canis in the absence or presence of Escherichia coli lipopolysaccharide. Cytokine expression was measured by an enzyme-linked immunosorbent assay. Components in the S. scabiei extract induced marked increases in secretion of interleukin-6 (IL-6) and vascular endothelial growth factor (VEGF) and slight increases in production of granulocyte-colony-stimulating factor (G-CSF) by keratinocytes. The scabies extract down-regulated keratinocyte secretion of IL-1 receptor antagonist, but did not influence the production of IL-1alpha or IL-1beta. In comparison, components in the scabies extract induced marked increases in the elaboration of IL-6, IL-8, G-CSF, and VEGF by fibroblasts. Neither cell type produced eotaxin, stem cell factor, or tumor necrosis factor-alpha under any of the conditions tested. This study demonstrates that components in an extract of the mite S. scabiei are able to influence cytokine expression by human keratinocytes and fibroblasts.
Histological findings of the inflammatory lesions of scabies are distinctive enough to guide the pathologist in the direction of this diagnosis. It is characterized by a combination of an acute, vesicular, eczematous type of epidermal change and an erythema multiforme type of dermal reaction. When this combination is present, a search should be made to expose the organism in tissue sections or in scrapings of the cutaneous lesions.
Norwegian scabies is rare yet distinctive. The majority of reported cases have been in patients with relatively small group of diseases, including Down syndrome and lepromatous leprosy. A case occurred in a patient on long-term immunosuppressive therapy following a kidney transplant. Altered host factors appear to be the prime determinants in the pathogenesis of the disease.
A case of crusted (Norwegian) scabies is reported in a child who was a recipient of a bone marrow transplant. The infestation is presumed to have predated the bone marrow transplant and continued asymptomatically during chemotherapy and total body x-irradiation in preparation for transplant. The child was asymptomatic until 23 days after transplantation, when bone marrow engraftment was attained. The altered host-parasite relationship is emphasized by the observation that the onset of symptomatic pruritus coincided with successful engraftment.
Forty patients were treated for scabies with a 10% suspension of thiabendazole applied externally. Thirty-two patients (80%) had a satisfactory response to one course of therapy, while a second course was necessary in six (15%). Two patients (5%) required intralesional injections of triamcinolone diacetate because of persistent scabious nodules.
The sequential changes in the histology in scabietic lesions were investigated for hosts (rabbits) during sensitization and reinfestation with Sarcoptes scabiei. Experimentally infested naive hosts developed heavy scabies infestations but 65% of the hosts showed induced immunity (resistance) to reinfestation. All hosts (naive, immune, and susceptible) exhibited an initial cell infiltrate in scabietic lesions that consisted predominantly of neutrophils and a few macrophages. This was followed by a dense plasma cell infiltrate. Upon reinfestation the progression of neutrophil infiltration was faster and the response was greater in hosts who acquired immunity than those in the susceptible hosts.
Haematology and blood biochemistry were monitored during the development and regression of psoroptic scabies in sheep. There were rises in numbers of neutrophils and eosinophils and in the fibrinogen concentrations, with lowered haemoglobin concentrations any lymphocyte numbers. The only biochemical parameters that were affected were the estimated serum globulin concentration, which rose during the disease process, and the serum albumin concentration, which fell. All of these changes reverted to normal soon after treatment.
Two patients aged 50 and 84 years presented with generalized itching eczema that has been treated with external and internal steroids for months. Despite therapy, the condition worsened continuously. Examination of skin scrapings revealed numerous mites, so Norwegian scabies was diagnosed. General examinations excluded underlying diseases. Treatment with steroids over months most likely led via immunosuppression to the exacerbation of the disease.
An eighty-two year old patient had scabies and transient acantholytic dermatosis (TAD, Grover's disease) at the same time. Persistent itching papules after lindane therapy finally led us to the microscopic diagnosis of TAD. Different trigger mechanisms can apparently induce the typical acantholysis. In addition to solar radiation, tumors and tumor therapy-dependent conditions, cutaneous infections have been implicated reports (Demodex folliculorum, Malassezia furfur) as causes of TAD. This may be the first report about a relationship between TAD and mite infection with Sarcoptes scabiei.
Pseudoscabies, i.e. infestation of human skin with animal mites may occasionally occur and should be considered in the differential diagnosis of pruritic and papular skin disease. We report here on a 52-year-old woman with pseudoscabies or canine scabies (Sarcoptes scabiei var. canis), transmitted by indirect contact with a red fox in the urban area of Berlin. Red foxes may live in unhabited areas of metropolitan large cities, i.e. in garages, car wrecks and cellars. Full remission of the prolonged and pruritic rush was seen after topical administration of lindane together with systemic corticosteroids.
We describe a 20-year-old man with chronic graft-versus-host disease and progressive cutaneous changes. His skin became more lichenified despite therapy with azathioprine, prednisone, and cyclosporine. Although it was initially thought that lichenoid graft-versus-host disease had developed, it was subsequently discovered that the patient had crusted (Norwegian) scabies.
Parasitic agents determine some of the most common skin disorders. Although well known, they could present different manifestations or be modified by individual or external factors that make their diagnosis or treatment difficult. This review will discuss some of the most prevalent parasitic infections, scabies, and pediculosis and also mention reactions determined by contact with certain insects that, although rarely found, could induce important skin reactions.
Scabies and lice infestations are almost an everyday diagnosis in the dermatology clinics. Along with the unbearable itch, resistance to medication, secondary infection, and the high risk for spreading the parasite to their close contacts, the patients have also to battle with many myths, prejudice, and shames connected to those infestations.
Sarcoptes scabiei continues to cause major health and economic problems in a large range of animals and humans. Although the inflammatory response to the mite and its antigens is known to cause the main pathology, little work has been carried out on this response at the site of infection. This report presents an initial analysis of the proteins found in skin scrapings and their antigenic responsiveness in pigs. Skin scrapings and mite extracts were isolated from chronically infected sows while infected and uninfected sera were isolated from pigs with confirmed infections or mange-free pigs, respectively. Electrophoresis and sequencing confirmed the main components of both the skin and mite extracts to be serum proteins. Immunoblotting then suggested that transferrin was the major antigen recognised by pooled infected sera in the skin and the mite extracts. Immunoassays confirmed that a majority of infected pigs produced antibodies to transferrin while mange-free pigs did not. A pool of IgG from infected dogs was then used to isolate another antigen from pig skin scrapings which was shown to be haptoglobin. This was also found to induce high titres of antibody in infected pigs as compared with mange-free pigs. The use of albumin as a control antigen showed no reactivity in either group of sera. The finding of two iron-binding molecules as strong auto-antigens in pig scabies has implications for the importance of iron during this infection and may help to explain the persistence and magnitude of the host inflammatory response.