Larry G. Arlian

Prevalence of dust mites in the homes of people with asthma living in eight different geographic areas of the United States.

The density and species prevalence of dust mites were determined at various times over a 5-year-period in 252 homes of dust mite sensitive people with asthma who lived in eight geographic areas of the United States (Cincinnati, Ohio; New Orleans, La.; Memphis, Tenn.; Galveston, Texas; Greenville, N.C.; Delray Beach, Fla.; San Diego and Los Angeles, Calif.). The most common dust mites found in the homes were Dermatophagoides farinae (DF), D. pteronyssinus (DP), Euroglyphus maynei (EM), and Blomia tropicalis. All homes in all locations contained Dermatophagoides spp. mites, but few homes were populated exclusively by either DF or DP alone. Most homes (81.7%) were coinhabitated by both DF and DP. In coinhabited homes one species was predominant and usually made up at least 75% of the total mite population. Prevalence of the dominant or only species present varied between homes within a geographic area. EM occurred in significant numbers in 35.7% of homes in New Orleans, Memphis, Galveston, Delray Beach, and San Diego. Blomia tropicalis occurred in these same cities but in low densities. For all dust samples, only 13 homes of the 252 sampled had 100 or fewer mites/gm dust, which is considered to be the threshold for sensitivity. Most homes had average mite densities of 500 or more mites/gm dust. The results of the present study suggest a significant and widespread occurrence of both DF and DP. Therefore extracts of both mite species should be considered for diagnostic tests and immunotherapy. Significant levels of EM were present in some areas. Thus sensitivity to EM should be considered in these areas.

Water balance and humidity requirements of house dust mites

The house dust mites,Dermatophagoides farinae, D. pteronyssinus andEuroglyphus maynei, are prevalent in homes in humid geographical areas throughout the world. These mites thrive in humid environments in human dwellings where there is no liquid water to drink. However, their bodies contain 70–75% water by weight, which must be maintained in order to reproduce. Their primary source of water is water vapor which is actively extracted from unsaturated air. At relative humidities above 65–70%, adequate amounts of water can be extracted from unsaturated air to compensate for that lost by all avenues. Active uptake is associated with ingestion of a hyperosmotic solution which is secreted by the supracoxal glands. Active mites do not survive longer than 6–11 days at RHs ≤50%. They survive extended dry periods by forming a desiccation-resistant protonymphal stage which can survive for months at RHs below the critical humidity for active stages. Feeding rate and allergen production is directly influenced by RH. Mites feed, multiply, and produce more fecal matter at higher RHs than at lower ones.

Survival and infestivity of Sarcoptes scabiei var. canis and var. hominis

Sarcoptes scabiei var. canis served as a suitable model for the study of S. scabiei var. hominis survival. S. scabiei var. canis and var. hominis mites were found to survive off the host for 24 to 36 hours at room conditions (21 degrees C and 40% to 80% relative humidity [RH]), and the canine variety survived 19 days at 10 degrees C and 97% RH. Female mites survived decidedly longer than male mites at comparable conditions. Generally, higher RH values and lower temperatures favored survival, whereas higher temperature and lower RH led to early death. Most canine scabies mites that were held off the host for 36 hours at 75% RH and 22 degrees to 24 degrees C remained infective and penetrated when returned to the host. Live mites of the human variety that were recovered from bed linen slept on by infested patients would also penetrate a host after being held off a host for 96 hours in alternating 12-hour periods of room conditions and refrigeration. Penetration required less than 30 minutes for all life stages of both varieties, and it was accomplished by a mite secretion that dissolved the host tissue. Dislodged mites, particularly those in close proximity to the source, can be a likely source of infestation.

Allergenicity of the mite, Blomia tropicalis.

BACKGROUND Blomia tropicalis (BT) occurs in a significant percentage of homes in tropical and subtropical geographic regions of the United States and Europe and in countries in South America and Asia along with the pyroglyphid mites, Euroglyphus maynei (EM), Dermatophagoides pteronyssinus, and D. farinae. Blomia species may be major sources of allergens in house dust in addition to Dermatophagoides species and E. maynei. METHODS Crossed immunoelectrophoresis and crossed radioimmunoelectrophoresis were used to identify the antigens and allergens of BT and to determine the cross-reactivity between BT and the house dust mites, D. farinae, D. pteronyssinus, and the stored product mite, Tyrophagus putrescentiae. RESULTS Homologous crossed immunoelectrophoresis of BT resulted in 27 antigen-antibody complexes. Crossed radioimmunoelectrophoresis of these gels showed 21 different immunoglobulin E binding antigens when they were incubated in the sera from 14 patients with asthma whose radioallergosorbent test and skin test results were positive. Heterologous crossed immunoelectrophoresis reactions with BT and rabbit D. farinae body and feces, D. pteronyssinus body and feces, and T. putrescentiae body and feces antisera resulted in one to four precipitin lines. BT extract, reacted with rabbit antisera produced against the bodies of D. farinae, D. pteronyssinus, and T. putrescentiae, produced 3, 2, and 4 antigenic peaks, respectively; whereas crossed radioimmunoelectrophoresis of these gels with the sera of the 14 patients with asthma resulted in immunoglobulin E binding to 2, 2, and 4 peaks, respectively. CONCLUSIONS The results of this study indicated that BT contained multiple allergens of which most were species-specific. There was a limited amount of cross-reactivity between BT and the two common house dust mite species and the stored product mite. The amount of cross-reactivity appears to parallel the phylogenetic relatedness.

THE DEVELOPMENT OF PROTECTIVE IMMUNITY IN CANINE SCABIES

Seven of eight dogs that had been previously infested with Sarcoptes scabiei var. canis and then cured, expressed protective immunity when experimentally reinfested with scabies. All seven dogs that expressed resistance were spontaneously cleared of scabies by 64 days after they were experimentally reinfested. Five of the eight dogs were free of scabies by 24 days. The sequential changes in the inflammatory/immune cellular infiltrate in the scabietic lesions of each dog were determined during the sensitizing infestation, cure and the subsequent experimental reinfestation (challenge). During the initial infestation and in the subsequent challenge reinfestation, dogs developed mixed cellular infiltrates in their scabietic lesions that contained mononuclear cells, neutrophils, plasma cells and mast cells. Reinfestation induced more rapid increases in the densities of these cells than had occurred during the sensitizing infestation. Mononuclear and mast cells were the most numerous infiltrating cells during the sensitizing phase. During the challenge phase the most numerous infiltrating cells were mononuclear cells and neutrophils. The sensitizing and challenge infestations induced circulating scabies-specific antibody responses, but the response was more rapid during the reinfestation challenge. Both the cell-mediated response in the skin and the circulating antibody response waned in parallel with clearing of the mites following reinfestation.

Acaricidal Activity of Eugenol Based Compounds against Scabies Mites

Backgound Human scabies is a debilitating skin disease caused by the “itch mite” Sarcoptes scabiei. Ordinary scabies is commonly treated with topical creams such as permethrin, while crusted scabies is treated with topical creams in combination with oral ivermectin. Recent reports of acaricide tolerance in scabies endemic communities in Northern Australia have prompted efforts to better understand resistance mechanisms and to identify potential new acaricides. In this study, we screened three essential oils and four pure compounds based on eugenol for acaricidal properties. Methodology/Principal Findings Contact bioassays were performed using live permethrin-sensitive S. scabiei var suis mites harvested from pigs and permethrin-resistant S. scabiei var canis mites harvested from rabbits. Results of bioassays showed that clove oil was highly toxic against scabies mites. Nutmeg oil had moderate toxicity and ylang ylang oil was the least toxic. Eugenol, a major component of clove oil and its analogues –acetyleugenol and isoeugenol, demonstrated levels of toxicity comparable to benzyl benzoate, the positive control acaricide, killing mites within an hour of contact. Conclusions The acaricidal properties demonstrated by eugenol and its analogues show promise as leads for future development of alternative topical acaricides to treat scabies.

Biology, ecology, and prevalence of dust mites

The house dust mites D. farinae, D. pteronyssinus, and E. maynei are sources of multiple potent allergens in the indoor environment. They are common inhabitants in homes worldwide. Many biologically significant studies have revealed how well adapted these mites are to the microhabitats in homes. Ambient RH is a key factor in determining where these mites are found. Many aspects of the biology of house dust mites are not understood. A greater understanding of the biology of dust mites may reveal new strategies for controlling dust mites and their allergens in homes.

Reducing relative humidity to control the house dust mite Dermatophagoides farinae

BACKGROUND Indoor relative humidity (RH) is the key factor that determines the survival and population development of the house dust mite Dermatophagoides farinae. Maintaining RH below 50% is one recommendation in a comprehensive plan to reduce house dust mites and mite allergen levels in homes. Even when mean daily RH is reduced below 50%, RH may rise above 50% intermittently for brief periods because of activities in the home (eg, cooking, bathing, and ventilation). OBJECTIVE The purpose of this study was to determine how brief daily periods of moist air alternating with long spells of low ambient RH (0% or 35%) influence population survival and growth of D farinae. METHODS Population growth was determined for D farinae at daily RH regimens of 2, 4, 6, and 8 hours at 75% or 85% RH alternating with 22, 20, 18, and 16 hours at 0% or 35% RH. RESULTS D farinae populations declined at daily regimens of 2 hours at 75% or 85% RH alternating with 22 hours at 0% or 35% RH. Daily regimens of 4, 6, and 8 hours at 75% RH alternating with 20, 18, and 16 hours, respectively, at 35% RH provided sufficient moisture for small growths in population size. These growths after 10 weeks were reduced by 98.2%, 98.0%, and 97.3% for daily regimens of 4, 6, and 8 hours, respectively, at 75% RH (with the remainder of the day at 35% RH) compared with the growth of populations continuously exposed to 75% RH. Continuous exposure to 85% RH inhibited population growth, but alternating daily regimens of 16, 18, and 20 hours at 35% RH allowed small populations to develop, although they were reduced by 99.4%, 98.8%, and 99.1% compared with population growth at a continuous 75% RH. CONCLUSION This study indicates that maintaining mean daily RH below 50%, even when RH rises above 50% for 2 to 8 hours daily, effectively restricts population growth of these mites and thus the production of allergen. To completely prevent population growth of D farinae, RH must be maintained below 35% for at least 22 hours per day when the daily RH is 75% or 85% for the remainder of the day.

The effect of insecticide synergists on the response of scabies mites to pyrethroid acaricides.

Background Permethrin is the active component of topical creams widely used to treat human scabies. Recent evidence has demonstrated that scabies mites are becoming increasingly tolerant to topical permethrin and oral ivermectin. An effective approach to manage pesticide resistance is the addition of synergists to counteract metabolic resistance. Synergists are also useful for laboratory investigation of resistance mechanisms through their ability to inhibit specific metabolic pathways. Methodology/Principal Findings To determine the role of metabolic degradation as a mechanism for acaricide resistance in scabies mites, PBO (piperonyl butoxide), DEF (S,S,S-tributyl phosphorotrithioate) and DEM (diethyl maleate) were first tested for synergistic activity with permethrin in a bioassay of mite killing. Then, to investigate the relative role of specific metabolic pathways inhibited by these synergists, enzyme assays were developed to measure esterase, glutathione S-transferase (GST) and cytochrome P450 monooxygenase (cytochrome P450) activity in mite extracts. A statistically significant difference in median survival time of permethrin-resistant Sarcoptes scabiei variety canis was noted when any of the three synergists were used in combination with permethrin compared to median survival time of mites exposed to permethrin alone (p<0.0001). Incubation of mite homogenates with DEF showed inhibition of esterase activity (37%); inhibition of GST activity (73%) with DEM and inhibition of cytochrome P450 monooxygenase activity (81%) with PBO. A 7-fold increase in esterase activity, a 4-fold increase in GST activity and a 2-fold increase in cytochrome P450 monooxygenase activity were observed in resistant mites compared to sensitive mites. Conclusions These findings indicate the potential utility of synergists in reversing resistance to pyrethroid-based acaricides and suggest a significant role of metabolic mechanisms in mediating pyrethroid resistance in scabies mites.

Serum antibody to Sarcoptes scabiei and house dust mite prior to and during infestation with S. scabiei.

In this study, serum antibodies to Sarcoptes scabiei var. canis (SS), Dermatophagoides farinae (DF), and D. pteronyssinus (DP) were determined in 19 healthy, random-source dogs prior to infestation with scabies then again during a primary infestation, cure and challenge infestation with scabies. Prior to scabies infestation, serum of 11 dogs contained faintly detectable amounts of IgE and/or IgG to proteins in SS extract, probably resulting from sensitization to dust mites that share cross-reactive antigenic epitopes with SS. After becoming infested with scabies, the response to SS antigens became stronger with antibodies appearing to more antigens as the scabies infestation progressed. Three of the newly recognized proteins were 170, 155 and 142/133kD and could be used in a diagnostic test since antibodies to them appeared during the primary infestation. In addition, during the primary infestation, 14 of 15 dogs developed IgE to 1-11 new SS proteins in addition to an increase in IgE binding to those proteins recognized prior to infestation. Overall, the strongest antibody responses (IgE and IgG) were exhibited during cure of the first infestation, when dead mites were still present in the stratum corneum. As expected, the antibody response was strong and rapid during challenge when the infestation self-cured. The immunogenic SS proteins identified by serum antibody binding during challenge, when the hosts self-cured, are candidates for inclusion in a vaccine. These candidate proteins are 200, 185, 170, 155, 142/133, 112, 97, 74, 57, 45/42, 32 and 22kD. Some of the proteins in SS that exhibited new or increased antibody binding during the experiment also had IgE and IgG binding to proteins with similar molecular weights in DF and DP extracts. These results illustrate the difficulties involved in understanding and interpreting serum antibody for developing a serological test for the diagnosis of scabies, isolating relevant SS antigens that could be included in a vaccine for prevention of scabies, and for understanding the immune response mechanism to scabies.