The Biology of the Demodicids of Man. Clifford Edward Desch University of Massachusetts Amherst
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University of Massachusetts Amherst ScholarWorks@UMass Amherst Doctoral Dissertations 1896 - February 2014 1-1-1973 The biology of the demodicids of man. Clifford Edward Desch University of Massachusetts Amherst Follow this and additional works at: https://scholarworks.umass.edu/dissertations_1 Recommended Citation Desch, Clifford Edward, "The biology of the demodicids of man." (1973). Doctoral Dissertations 1896 - February 2014. 4117. https://scholarworks.umass.edu/dissertations_1/4117 This Open Access Dissertation is brought to you for free and open access by ScholarWorks@UMass Amherst. It has been accepted for inclusion in Doctoral Dissertations 1896 - February 2014 by an authorized administrator of ScholarWorks@UMass Amherst. For more information, please contact [email protected]. s Q) Clifford Edward Desch, Jr. All Rights Reserved THE BIOLOGY Of THE DEMODICIDS OF MAN A Dissertation Presented by Clifford Edward Desch, Jr* Submitted to the Graduate School of the University of Massachusetts in partial fulfillment of the requirements for the degree of Doctor of Philosophy February, 1973 Major Subjects Zoology THE BIOLOGY OF THE DEWOOICIOS Of WAN * Dissertation Presanted by Clifford Edward Desch, Jr, Approved as to style and content byi Dates abstract An expanded and corrected definition of the genus Demodax Owen (1843) is presented taking into account all life stages. Meristic and non-meristic characters are discussed in light of their taxonomic im¬ portance. Gemndfla. falliculoruai has often been noted as a polymorphic species. With reference to the redefinition of the genus, and the meristic and non-meristic characters, two distinct species of Demodex from man are recognized and redescribed: D. folliculorum (Simon) and and D. brevis Akbulatova. much confusion concerning species identification of demodicids is due to incomplete original descriptions and failure to recognize key taxonomic features, as evidenced by numerous references in the literature to varieties or subspecies of Demodex folliculorum and reports of inter¬ specific host transfer. Based on the above mentioned taxonomic characters demodicids of various domestic mammals are redescribed as distinct species D. bovis, D. Etiylloides, D. caprae and D. canis (meristic data only). A key is provided for the demodicids of man and common domestic mammals. The external and internal morphology of Demodex folliculnrnm is described with the aid of information obtained using light and electron microscopes. Functional aspects of each system or structure are con¬ sidered: all are compared with D. caprae and 0. antechini. Externally, the gnathosoma, the leg*v> and the cuticle are described. Contrary to previous reports the chelicerae lack fixed digits: the cuticle lacks pore canals. Internally, four systems are described: in adult D. folli¬ culorum and immature D. cap_rae the nervous, digestive and reproductive, and musculature in adult and immature 0. canis. Muscles are discussed as functional units: gnathosoma!, walking appendages, body muscles and sexually dimorphic musculature associated with reproduction. The large synganglion, located in the idiosoma, is described for the first time. The digestive system consists of a sclerotized pharynx, long narrow esophagus passing through the synganglion and gut cells of two types which nearly fill the opisthosoma. Type I cells engulf digested material from the esophagus and store waste products in a crystalline form; Type II cells contain large numbers of lipid droplets. A hind gut is absent} a sclerotized, finger-like pouch, believed to be the procto¬ deum, is present in the female. Large salivary glands connect with the preoral cavity} digestion is probably preoral. The reproductive system of both sexes is unpaired. The testis, seminal vesicle and aedeagus of the male, and the vagina, sperm storage area, uterus and ovary of the female are described* The centrolecithal ovum of Demodex caprae undergoes superficial cleavage. Subsequent to blastoderm formation cell proliferation produces a thickened germ band on the ventral and anterior surface. Segmentation of the germ band cuts off blocks of cells which form chelicerae, palps and legs. Vitellophages develop among the blastoderm cells. Development of the synganglion and digestive system are briefly described. Histological sections of human skin reveal that Demodex follintHn.-n, and D. brevis utilize different niches, the former reside in the simple hair follicles and the latter in the sebaceous glands of vellus hairs. Other than simple cell destruction, no pathogenic effects have been dis¬ covered. It is suggested that all host-parasite data obtained since Simon (1842) should be reworked in view of the fact that these two species are found on the same host species, and even the same host individual. The proctodeum, a key taxonomic character, is surveyed in 96 species of Demodex from 66 host species in 11 mammalian orders* One inter- ordinal and six intraordinal patterns are described. TABLE Of CONTENTS Page ACKNOWLEDGMENT — i I. INTRODUCTION 1 II. MATERIALS AND METHODS A. Taxonomy and external morphology -__ 5 B. Internal anatomy---^ C. Habitat and pathogenesis of Demodex folliculorum and D, brevis __________ ^ D. Karotype analysis -„- y III. REDEFINITION OF THE GENUS DEMODEX _ 8 IV. CHARACTERS OF TAXONOMIC IMPORTANCE _ n A. Non-meristic characters 11 B. Meristic data-” V. REDESCRIPTION OF DEMODICIDS OF MAN AND DOMESTIC MAMMALS— 15 A. Demodicids of man - 15 1. Demodex folliculorum -- 15 2. Demodex brevis ——___ 19 B# Demodicids of domestic mammals -—-___ 24 1. Demodex bovis__ 24 2• Demodex phylloides --______ 26 3 • Demodex caprae —-----____ 28 4. -Demodex canis -----____ 30 5. Demodex cati, Demodex ovis. Demodex equi. Demodex sp. erroneously described as Demodex folliculorum var. equi-—— -_„_ 33 6. Key to demodicids of man and domestic mammals — 35 VI. MORPHOLOGY OF ADULTS AND IMMATURES A. External morphology —« 37 1. Exoskeleton -- 38 2. Gnathosoma —-- 40 3• Walking appendages 47 B. Internal morphology — 51 1. Musculature --—- 51 2. Nervous system - 62 3. Digestive system — 66 4. Proctodeum - 73 5. Reproductive system 75 VII. DEVELOPMENT 89 Page VIII. POPULATIONS - 92 IX. KARYOTYPE, SEXOETERMINATION AND SEX RATIOS — 93 / .S X, HABITATS - 96 XI. PATHOLOGY -- 97 XII. PHYLOGENETIC PATTERNS OF PROCTODEAL STRUCTURE 98 XIII. SUMMARY--- 104 XIV. BIBLIOGRAPHY - 110 e V ACKNOWLEDGMENT Although I am indebted to a number of people for their helpful assistance which allowed me to complete this dissertation, I am most deeply appreciative of the encouragement and the thoughtful guidance given by my advisor and friend, Dr. William B. Nutting. Many thanks also go to: Mrs. Margaret Nutting for her excellent technical assistance; Dr. Herbert E. Potswald for helping to make the electron micrographs possible; Dr. Lawrence M. Bartlett for donating Demodex brevis from his private collection; Dr. Fritz S. Lukoschus for collecting the numerous South American bats and their mites; and Robert R. Lebel for the pleasant discussions on Demodex. -% Special thanks go to my wife, Marie, for her moral support during this study and for her typing of the rough drafts of this dissertation. I am grateful for the financial aid given to me by the University of Massachusetts as a Teaching Assistant, and by the Public Health Service Grant 5T0I AI-226 as a Research Trainee and Research Assistant. I. INTRODUCTION Despite the fact that the hair follicle mite of man. Demode* loniculorum, has been known for 130 years, many questions remain un¬ answered concerning the life cycle and the apparent polymorphism of this parasite. In the first published account of 0. folliculorum. Simon (1842) listed four developmental stages: the first with three leg pairs and a long posterior, the second a long form with four leg pairs, and two subsequent stages, also with eight legs, possessing shorter, pointed posteriors. He felt the adults would lack any posterior elong¬ ation, Although Simon observed over 100 specimens, he concluded that he had not found the adult stage, Wilson (1844) reported on the morphology and development of this organism in which he observed two varieties of the mite. Although he did not feel the two forms warranted specific status, he designated them as the long form and the short form. He also noted the differences between the developmental stages of the two forms, stating as a possible ‘ ‘ > • reason "some unknown modification of the elements of nutrition," Hirst (1919) concurred with Wilson*s observations concerning the morphology of Demodex folliculorum. In addition, he reported two individuals of the short form without sexual organs and, therefore, concluded that they represented a sub-adult stage of males of the long form. Hirst did not observe any immature .stages of the short form. He figured the legs of two hexapod stages of the long form but referred to these hexapods as small and large larvae. Fuss (1933) noted the variety of forms of Demodex folliculorum and suggested there may be subgroups within the population. Later, she postulated that these forms represented different stages in the life cycle of the mite (Fuss, 1935). In her view, mature mites of reproduc¬ tive age (the long form) produced round eggs which became oval and then cordiform; and short adult mites represented senescent individuals* Fuss (1937) modified her explanation of the life cycle by proposing that the mite possessed two modes of reproductions oviparity, yielding an oval egg, and viviparity, yielding an apodus, "cordiform"