The parasitism of the itch mite Sarcoptes scabiei (Acariformes: Sarcoptidae)]

The life cycle of the itch mite Sarcoptes scabiei (L.), an intracutaneous parasite of man and animals, has been studied. The paper concerns morphological adaptations, embryonal and postembryonal development, life cycle pattern, scabious passage as a reproductive formation, invasive stages, feeding, reproduction and topical relationships with the host, distribution and survival in the environment.     

Genetic epidemiology of Sarcoptes scabiei (Acari: Sarcoptidae) in northern Australia

Utilising three hypervariable microsatellite markers we have previously shown that scabies mites on people are genetically distinct from those on dogs in sympatric populations in northern Australia. This had important ramifications on the formulation of public health control policies. In contrast phylogenetic analyses using mitochondrial markers on scabies mites infecting multiple animal hosts elsewhere in the world could not differentiate any genetic variation between mite haplotype and host species. Here we further analyse the intra-specific relationship of Sarcoptes scabiei var. hominis with S. scabiei var. canis by using both mitochondrial DNA and an expanded nuclear microsatellite marker system. Phylogenetic studies using sequences from the mitochondrial genes coding for 16S rRNA and Cytochrome Oxidase subunit I demonstrated significant relationships between S. scabiei MtDNA haplotypes, host species and geographical location. Multi-locus genotyping using 15 microsatellite markers substantiated previous data that gene flow between scabies mite populations on human and dog hosts is extremely rare in northern Australia. These data clearly support our previous contention that control programs for human scabies in endemic areas with sympatric S. scabiei var. hominis and var. canis populations must focus on human-to-human transmission. The genetic division of dog and human derived scabies mites also has important implications in vaccine and diagnostic test development as well as the emergence and monitoring of drug resistance in S. scabiei in northern Australia.     

Identification of auto-antigens in skin scrapings from scabies-infected pigs

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.     

Functional analysis and localisation of a delta-class glutathione S-transferase from Sarcoptes scabiei

The mite Sarcoptes scabiei causes sarcoptic mange, or scabies, a disease that affects both animals and humans worldwide. Our interest in S. scabiei led us to further characterise a glutathione S-transferase. This multifunctional enzyme is a target for vaccine and drug development in several parasitic diseases. The S. scabiei glutathione S-transferase open reading frame reported here is 684 nucleotides long and yields a protein with a predicted molecular mass of 26 kDa. Through phylogenetic analysis the enzyme was classified as a delta-class glutathione S-transferase, and our paper is the first to report that delta-class glutathione S-transferases occur in organisms other than insects. The recombinant S. scabiei glutathione S-transferase was expressed in Escherichia coli via three different constructs and purified for biochemical analysis. The S. scabiei glutathione S-transferase was active towards the substrate 1-chloro-2,4-dinitrobenzene, though the positioning of fusion partners influenced the kinetic activity of the enzyme. Polyclonal antibodies raised against S. scabiei glutathione S-transferase specifically localised the enzyme to the integument of the epidermis and cavities surrounding internal organs in adult parasites. However, some minor staining of parasite intestines was observed. No staining was seen in host tissues, nor could we detect any antibody response against S. scabiei glutathione S-transferase in sera from naturally S. scabiei infected dogs or pigs. Additionally, the polyclonal sera raised against recombinant S. scabiei glutathione S-transferase readily detected a protein from mites, corresponding to the predicted size of native glutathione S-transferase.     

Analysis of Sarcoptes scabiei finds no evidence of infection with Wolbachia

The endosymbiont Wolbachia has been detected in a range of filarial nematodes and parasitic mites and is known to affect host reproductive compatibility and potentially evolutionary processes. PCR of Wolbachia surface protein (wsp), ftsZ and 16SrRNA genes from individual Sarcoptes scabiei mites obtained from a series of individual hosts, and database searches of an S. scabiei var. hominis EST library failed to detect Wolbachia genes. Therefore, Wolbachia appears not to be involved in the genetic subdivision observed between varieties of host-associated S. scabiei or, involved in the inflammatory disease pathogenesis of scabies unlike its activity in filarial infection.     

Distribution of deformed wing virus within honey bee (Apis mellifera) brood cells infested with the ectoparasitic mite Varroa destructor

The distribution of deformed wing virus (DWV) in adult female Varroa destructor and in their progeny in relation to the pupal host bee was investigated to evaluate acquisition and transfer of DWV by the mites. The results clearly show that adult female mites regularly act as competent vectors of DWV, however, they do not acquire or transfer virus on all possible occasions. Mother mites may contain DWV while the pupal host remains free from overt infection and both mother mites and mite progeny may not acquire detectable amounts of DWV from an infected host bee. However, a majority of mites feeding on pupae that emerge with deformed wings will contain DWV. The data also demonstrates that both adult and immature mite progeny most likely acquire DWV from DWV-infected host bees and not from their mother mites. Possible explanations for the obtained results are discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Interpopulation variation in the prevalence and intensity of parasitic mite infection in the land snail Arianta arbustorum

Abstract. The parasitic mite Riccardoella limacum sucks blood in the lung of its host, the land snail Arianta arbustorum . The infection of various host populations was examined in Switzerland. In a lowland snail population, prevalence of infection did not vary among seasons. However, intensity of mite infection in dissected individuals of A. arbustorum was high in autumn, but low in winter and spring when ≤100 mite eggs were found attached to the lung epithelium. A novel, non-invasive parasite screening method was used to estimate the number of mites on living host snails. An analysis of repeatability revealed that 92.9% of the snails were correctly classified as infected or non-infected with this non-invasive method. Prevalence of mite infection was examined in 997 adults of A. arbustorum from 11 natural populations distributed over an altitudinal gradient ranging 335–2360 m. No infected snails were found in 7 populations, while in the remaining 4 populations the prevalence of mite infection ranged 45.8–77.8%. Intensity of infection also differed among the 4 host populations. No geographic pattern in prevalence of infection was found. However, parasitic mites did not occur in snail populations situated at elevations of 1290 m or higher. A possible explanation for this finding could be that the host's hibernation period may be too long at high elevations for mites and their eggs to survive. At low elevations, other factors may affect the presence of R. limacum in the lung of A. arbustorum .     

Treatment of scabies infestations

Scabies is an intensely pruritic disorder induced by an immune allergic response to infestation of the skin by the mite Sarcoptes scabiei. The biology of the mite, the clinical aspects and diagnosis of scabies infestations as well as the treatment of choice with 5% permethrin dermal cream and the use of scabicides based on other chemical substances are reviewed.     

The role of host phenology in determining the incidence of an insect sexually transmitted infection

Changes in the timing of life history events within the year alter the degree to which the activity patterns of different species coincide, making the dynamics of interspecific interactions sensitive to the phenology of the interacting parties. For parasites, the availability of suitable hosts to infect represents a crucial determinant of dynamics, and changes in the host (and parasite) phenology may thus alter disease epidemiology and the conditions for disease maintenance. We tested the hypothesis that the incidence of a sexually transmitted mite infection, Coccipolipus hippodamiae, in Adalia bipunctata ladybird beetles in Sweden was determined by host phenology, namely presence/absence of sexual contact between cohorts of the host. We observed that the pattern of mite presence/absence across Swedish A. bipunctata populations was highly reproducible between years, implying a persistent biological/ecological basis underlying the incidence. Further, ladybirds from populations where the mite was absent were able to acquire mites during copulation, develop a mite infection, and transmit infection onward, indicating an ecological (rather than biological) driver of mite incidence. Observations of ladybird phenology in natural populations provided evidence of sexual contact between overwintered and new cohort adults in populations where the mite was present. In contrast, new cohort ladybirds in the two northern Swedish populations where the mite was not present had not had sexual contact with the overwintered generation, creating a ‘hard stop’ to mite transmission. We conclude that variation in host phenology may be an important driver of the incidence of sexually transmitted infections (STIs) by determining the presence/absence of sexual contact between generations. More generally, we hypothesize that sensitivity to variation in host phenology will be highest for parasites like STIs that infect one host species, one host life stage and are directly transmitted on contact between host individuals.     

Scabies in animals and humans: history, evolutionary perspectives, and modern clinical management

Scabies, a mite infestation frequently sexually transmitted, dates back to antiquity but remains a challenging parasite for study in clinical practice and community settings. Its history is one of centuries of slow progress to recognize the mite and to finally establish its nexus to the clinical syndrome of pruritis with several protean manifestations and different epidemiological patterns. Contemporary methods of management are briefly reviewed, with the future promise of improved evolutionary knowledge associated with the advent of molecular and genetic technology. Current information indicates that humans and earlier protohumans were most likely the source of animal scabies, first of dogs, and later of other species with subsequent spread to wildlife. Morphologically identical variants of Sarcoptes scabiei are nonetheless host specific, as determined by recent DNA studies, and invite future investigations into the dynamics of this troublesome sexually transmissible agent, with the goal of improved recognition and control.     

Scaling up tests on virulence of the cassava green mite fungal pathogen <Emphasis Type="Italic">Neozygites tanajoae</Emphasis> (Entomophthorales: Neozygitaceae) under controlled conditions: first observations at the population level

Virulence of entomopathogens is often measured at the individual level using a single host individual or a group of host individuals. To what extent these virulence assessments reflect the impact of an entomopathogen on their host in the field remains largely untested, however. A methodology was developed to induce epizootics of the cassava green mite fungal pathogen Neozygites tanajoae under controlled conditions to evaluate population-level virulence of two (one Beninese and one Brazilian) isolates of the entomopathogen—which had shown similar individual-level virulence but different field impacts. In unrepeated separate experiments we inoculated mite-infested potted cassava plants with either 50 or 25 live mites (high and low inoculum) previously exposed to spores of N. tanajoae and monitored the development of fungal infections for each isolate under the same conditions. Both isolates caused mite infections and an associated decline in host mite populations relative to the control (without fungus) in all experiments, but prevalence of the fungus varied with isolate and increased with inoculum density. Peak infection levels were 90% for the Beninese isolate and 36% for the Brazilian isolate at high inoculum density, and respectively 17% and 25% at low inoculum density. We also measured dispersal from inoculated plants and found that spore dispersal increased with host infection levels, independent of host densities, whereas mite dispersal varied between isolates. These results demonstrate that epizootiology of N. tanajoae can be studied under controlled conditions and suggest that virulence tests at the population level may help to better predict performance of fungal isolates than individual-level tests.     

Divergent host acceptance behavior suggests host specialization in populations of the polyphagous mite Abacarus hystrix (Acari: Prostigmata: Eriophyidae)

For phytophagous arthropods, host acceptance behavior is a key character responsible for host plant specialization. The grain rust mite, Abacarus hystrix (Nalepa), is an obligately phytophagous, polyphagous eriophyid mite recorded from at least 70 grass species. In this study, the hypothesis that two host populations of this mite (one collected from quackgrass and the other from ryegrass) are highly host-specific was tested using behavioral data. For this purpose, female behavior when exposed to familiar and novel host plants was observed in no-choice cross experiments. Altogether, 13 variables were used to describe mite behavior. Data were subjected to principal component analysis, and host acceptance behavior was subsequently tested with generalized estimating equations (GEE). Distinct variation in female behavior between familiar and novel hosts was observed. Females from neither population accepted novel hosts. This was recorded as significant differences in the occupation of and overall activity on particular plant parts. On their familiar host, females were not active and showed little tendency to move. On novel hosts females were more active and mobile, spending more time walking, running, and climbing on the whole plant surface and showing a tendency to disperse. Other differences in behavior between studied populations were also observed. Thus, the results suggest that mites of these two studied populations (1) differ in their behaviors during plant exploitation and (2) can quickly distinguish between their familiar host and an unfamiliar host used by a conspecific. These findings support the hypothesis of narrow host specialization of ryegrass and quackgrass populations of this highly polyphagous species.     

Horizontal transfer of the plant virulence gene, nec1, and flanking sequences among genetically distinct Streptomyces strains in the Diastatochromogenes cluster

Evidence for the horizontal transfer of a pathogenicity island (PAI) carrying the virulence gene nec1 and flanking sequences among Streptomyces strains in the Diastatochromogenes cluster is presented. Plant-pathogenic, thaxtomin-producing Streptomyces strains, previously classified as S. scabiei based on the conventionally used phenotypic characteristics, were found to be genetically distinct from the type strain of S. scabiei based on DNA relatedness and 16S rDNA sequence analysis. Pairwise DNA-DNA hybridizations between some of these strains and the S. scabiei type strain were as low as 36%, a value much below what is conventionally accepted for species identity (70%). The sequence of the nec1 gene, however, was identical in all the S. scabiei and S. scabiei-like strains tested, irrespective of their DNA relatedness to the type strain of S. scabiei, their geographic origin, or the isolation host. Furthermore, a 26-kb DNA fragment including and flanking nec1 was also conserved among these strains based on restriction and Southern analyses. These data indicate that the etiology of potato scab is more complex than previously recognized; this result has important implications for potato scab management strategies. Previous research has suggested that horizontal transfer of a PAI was the mechanism for evolution of pathogenicity in S. acidiscabies and S. turgidiscabies, species that lie outside of the Diastatochromogenes cluster. Data presented here support this model and indicate that PAI transfer also has occurred frequently in species closely related to S. scabiei.     

Prevalence, risk factors and economic importance of infestations with Sarcoptes scabiei and Haematopinus suis in sows of pig breeding farms in Hesse, Germany

A cross-sectional survey was performed in 110 randomly selected pig-breeding farms of southern Hesse, Germany to estimate the prevalence of ectoparasite infestations and to find possible risk factors. Ear scrapings of, if available, 10 sows per farm were examined for Sarcoptes scabiei var. suis (De Geer) (Acaridida: Sarcoptidae) by the potassium hydroxide digestion method, and a total of 2754 sows was inspected for skin lesions and infestations with Haematopinus suis (L.) (Anoplurida: Haematopinidae). Data on farm profiles and sows were collected by a questionnaire. In total, 19.1% and 2.5% of the sows were found to be infested with S. scabiei or H. suis, respectively. The percentage of mite or louse infestation was significantly higher in sows showing pruritus than in those without skin lesions. Both ectoparasite infestations were related neither to the age of sows nor their reproduction status, nor to the time interval to last ectoparasite treatment. Using farms as the unit of analysis, the estimated prevalence of mange mite and louse infestations was 45.4% and 14.5%, respectively. There was no significant association between the presence of S. scabiei and H. suis in the farms. Risk factors for S. scabiei infestation were mixed housing of dry and nursing sows in the same unit (vs. separate housing) and straw bedding (vs. strawless). For louse infestation, only mechanical cleaning of stable units (vs. additional use of disinfection methods) and pasturing of gilts and dry sows were identified as risk factors. The economic loss by S. scabiei infestation in the study population was assessed at euro 4200 per affected farm and year on average.     

Elimination of Sarcoptes scabiei in Pig Herds by Single or Double Administrations of an Avermectin

Attempts to eliminate Sarcoptes scabiei var. suis were made in 2 piglet producing herds by intramuscular injections with doramectin (Dectomax™, Pfizer inc., New York, USA). No hygienic measures of the environments were undertaken. In herd A, all animals were treated twice at a 14-day interval. Theoretically it should be possible to eliminate the mite with a single injection and therefore the animals in herd B were treated only once. The results were measured by attempts to demonstrate S. scabiei by skin scrapings, by recording skin lesions, by establishing rubbing indexes, and by measuring serum antibodies to S. scabiei. All adult animals greater than 8 months of age and 15 weaned piglets 8–16 weeks of age per herd were investigated prior to treatments and every fourth month for a total of 20 months following administration of the treatments. Live S. scabiei were demonstrated prior to treatments in both herds, but no further. Skin lesion scores, rubbing indexes and serum antibody levels remained low throughout the study. It is possible to eliminate S. scabiei from a herd with one single injection of doramectin. Precautions must be taken to ensure that all animals get a correct dose and that the drug is properly administered.     

Cellular response in the dermis of common wombats (Vombatus ursinus) infected with Sarcoptes scabiei var. wombati

The cellular response in the dermis of common wombats (Vombatus ursinus) with sarcoptic mange exhibited some typical aspects of an immune response to Sarcoptes scabiei. There was an induction phase for wombats experimentally infected with S. scabiei represented by absence of a dermal inflammatory infiltrate for at least 12 days after infection. T lymphocytes, plasma cells, mast cells, and neutrophils then entered the dermis, consistent with a type IV (delayed) hypersensitivity response. In free-living wombats with severe parakeratotic sarcoptic mange eosinophils were also present in the dermis suggesting that a type I (immediate) hypersensitivity response may develop after a type IV hypersensitivity response. Absence of plasma cells and B lymphocytes in free-living wombats with severe parakeratotic sarcoptic mange compared with their presence in wombats experimentally infected with S. scabiei suggested that some immune tolerance may develop with severe infections. A large proportion of cells in the dermal response were not identified but were possibly cells of connective tissue. The thickness of the epidermis increased within 4 days in response to S. scabiei infection. Some antibodies raised against human leucocyte antigens CD3, CD5, HLA-DP, DQ, DR, and CD79b cross-reacted with leucocyte antigens of common wombats and were used to identify cell types in inflammatory infiltrates using immunohistochemistry.     

High-resolution melt analysis for the detection of a mutation associated with permethrin resistance in a population of scabies mites

Permethrin as a topical acaricide cream is widely used to treat scabies. The neuronal voltage-sensitive sodium channel (Vssc), necessary for the generation of action potentials in excitable cells, is the target of pyrethroid acaricides such as permethrin. Pyrethroid resistance has been linked to specific mutations in the Vssc gene. Following the partial sequencing of the Vssc gene in the scabies mite Sarcoptes scabiei (L.) (Astigmata: Sarcoptidae), we compared Vssc gene sequences from permethrin-sensitive and -tolerant S. scabiei var. canis Gerlach mites, and identified a G to A single nucleotide polymorphism (SNP) in permethrin-tolerant mites resulting in an amino acid change from glycine to aspartic acid in domain III S6. The mutation is in a region of the gene where mutations have been identified in a range of pyrethroid-resistant arthropods. Results of in vitro permethrin exposure assays showed that survival rates for mites bearing the mutation were similar to those previously reported for mites from human subjects where clinical tolerance to permethrin had been observed. A real-time polymerase chain reaction-high-resolution melt (PCR-HRM) assay was developed to detect this SNP. This assay provides a useful methodology for screening for this and other mutations associated with permethrin resistance in scabies mite populations and thus facilitates surveillance for acaricide resistance.     

Specificity of attachment sites of larval water mites (Hydrachnidia, Acari) on their insect hosts (Chironomidae, Diptera)--evidence from some stream-living species

This study concerns the parasite-host associations of water mite larvae and their chironomid hosts in a small stream on the North German Plain. The different feeding sites on the host were tested as to whether they represented a strategy of the parasites regarding host partitioning. The attachment sites of nine ectoparasitic water mite species were observed in detail: Aturus fontinalis, Atractides nodipalpis, Feltria rouxi, Hygrobates nigromaculatus, Protzia eximia, Sperchonopsis verrucosa, Sperchon clupeifer, S. setiger and Lebertia inaequalis. Aturus fontinalis, A. nodipalpis, F. rouxi and H. nigromaculatus distinctly preferred sites on the abdomen of the host, whereas the other species preferred feeding sites on the thorax. The four species that preferentially attached to the abdomen of the host showed a distinct specificity for selected segmental and/or intersegmental regions. All species differed in their sites along the length of the abdomen. The order of attachment on the abdominal segments was, from anterior to posterior: H. nigromaculatus, F. rouxi, A. fontinalis and A. nodipalpis. The sites were analysed with regard to segmental and intersegmental attachment, the proportion of dorsal and ventral sites and the differences between attachment to different host species. Larvae attached to their hosts as single individuals showed only slight differences from the sites of mites on hosts that carried many mite larvae. The finding that less than 10% of the chironomids were parasitized by more than one water mite species suggested that, at least in the zoocoenosis of the studied collecting site, the interspecific competition for attachment sites was not strong. However, the specificity of attachment sites clearly had the potential of diminishing competition between water mite species by host partitioning. Intra- and interspecific competition for preferred sites and preparasitic constraints are discussed.     

Odonates,gregarines and water mites: why are the same host species infected by both parasites?

1. Damselflies and dragonflies are widely parasitised insects and numerous studies have tried to understand this host–parasite relationship. However, most of these studies have concentrated on a single host species, neglecting the larger pattern within the Odonata order. 2. The aim of this paper was to examine different damselfly and dragonfly species for common endo‐ and ectoparasites and whether a general infection pattern can be found. Additionally, the goal was to investigate whether the phylogeny of the host species could explain these possible infection patterns. To this end, a dataset from the existing literature was compiled and the prevalence of endoparasitic gregarines and ectoparasitic water mites was analysed for 46 different odonate species. 3. Three distinct patterns were found: (i) most of the odonate host species had both gregarines and water mites, rather than only either one or neither; (ii) there appears to be a positive association between gregarine and water mite prevalences across host species; (iii) a weak phylogenetic signal was detected in gregarine prevalence and a strong one in water mite prevalence. 4. It is hypothesised that, due to the infection and transmission mechanisms by which water mites and gregarines infect different odonate host species, parasitism is aggregated to common, high‐density species. However, much research is needed in order to fully understand this relationship between odonates and their parasites, especially within the same host populations and host species assemblages.     

Ectoparasite‐induced increase in Drosophila host metabolic rate

Parasites exert numerous effects upon their hosts, including physiological and metabolic changes that can in turn influence various aspects of host life history. Using flow‐through respirometry, we investigated how infection intensity of an ectoparasitic mite (Macrocheles subbadius) affects the respiratory rate (CO₂ production) of its host Drosophila nigrospiracula. Mean fly respiratory rate increased with infection intensity with the strongest effect, a 40% increase relative to uninfected controls, occurring with three mites attached. We also verified the causal relationship between elevated respiration rate and mite attachment by examining changes in host respiration before and after mite exposure. We found that the rate of CO₂ production increased by 11% for individual flies following parasite attachment. Fly locomotor activity was not significantly different between infected and uninfected individuals. Metabolic rate of hosts increased as a result of infection in an intensity dependent manner and was not simply due to changes in host activity. These results demonstrate that parasites can have a significant influence on the energy requirements of their host, which may account for the parasite‐mediated loss in host fitness.