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The Adherent Cylindrical Nit Structure and Its Chemical Denaturation In Vitro: An Assessment With Therapeutic Implications for Head Lice

The Adherent Cylindrical Nit Structure and Its Chemical Denaturation In Vitro: An Assessment With... Pediculus humanus capitis is the insect responsible for head lice. During the female louse's 30-day lifespan, she lays approximately 10 eggs per day and attaches each of them with a gluelike, waterproof substance to human hair, 1 mm from the scalp. Larvae emerge 8 to 10 days later from these nits, or eggs, which remain firmly attached to hair. No topical agent has been shown to be 100% ovicidal.1 The existence of any nits, a major aspect of lice infestations, signifies the potential that this contagious malady may still be present. Many schools, therefore, adhere to a "no-nit" policy before children can reenter the classroom after infestation, thereby imposing prolonged absenteeism. Insecticides fail to kill all nits and larvae because they act on the insects' central nervous systems, which are not fully developed in the first 4 days of the insects' existence. Several products, namely, Clear lice egg remover gel (Care Technologies, Greenwich, Conn), Step 2 (Genderm, Lincolnshire, Ill), and a 50/50 mixture of vinegar and water, have been suggested as beneficial in nit removal. However, no clinical benefit has been documented in the medical literature.2 The purpose of our investigation was to examine attachment of nits to the hair shaft and to test several substances for their effectiveness in facilitating nit removal from hair. Samples of adult lice and hairs with nits attached were obtained from affected patients. No attempt was made to designate specific nits or lice from any particular person. Our first assessment was microscopic examination of the appearance of the nit structure. With hairs intact, nits were noted to be firmly attached to the hair shaft by a cylindrical adherent material, the nit itself being part of the distal portion of the sheath (Figure 1). Lengths of cylindrical bands varied slightly. As nits were freed from hair, the cylindrical bands remained intact (Figure 2). Figure 1. View LargeDownload The louse nit with its adherent cylindrical sheath cemented to the hair shaft. The free, distal end of the nit would be directed toward the hair tip. The egg has a domed operculum (arrow) that embodies air holes, allowing the maturing larvae to breathe. The sheath length varies. Figure 2. View LargeDownload The cylindrical nit after sliding off the hair shaft remains intact with no discernible alteration in anatomical structure. The following agents were investigated as to whether they facilitate sliding of nit casts from the hair shaft: WD-40 (WD-40 Co, San Diego, Calif), vinegar, Detachol (Ferndale Laboratories Inc, Ferndale, Mich), acetone, Step 2, Clear topical lice egg remover gel, bleach, vodka, bug and tar remover (for cars), all-purpose degreaser and cleaner (for kitchen use), Royale with actein ("no-fungus shampoo," Straight Arrow, Leigh Valley, Pa), Osler Tangle Remover for dogs (Osler Professional Products, McMinnville, Tenn), petrolatum, dental plaque remover solution, 20% potassium hydroxide in dimethyl sulfoxide, and liquid nitrogen. No agent proved therapeutically efficacious. Products that seemed to assist mildly in nit removal included bleach, vodka, dental plaque remover solution, and vinegar, both at room temperature and heated. Interestingly, 20% potassium hydroxide in dimethyl sulfoxide dissolved the hair shaft without any discernible effect on the cylindrical nit cast. Live adult lice were placed in petrolatum and 2 pomades (Proclaim Conditioning Hair Dress [Brentwood Beauty Laboratories, Hillside, Ill] and Soft Sheen Sportin' Waves [Soft Sheen Products, Chicago, Ill]). Pomades are medicated ointments for hair used most commonly by African Americans. With all 3 substances, lice were unable to continue movement of appendages and died within 15 minutes. Nits were tested for assessment of chemical constituents and denaturation by acids or proteases under the microscope. In 6-mol/L hydrochloric acid, the sheath assumed a more bulky configuration within seconds. In 12-mol/L hydrochloric acid, the sheath lost its structural integrity, expanding its surface area 3-fold, while maintaining only a semblance of attachment to the nit. The louse egg itself remained unaffected in both solutions. Iodine test for carbohydrates was applied to the nit sheath both before and after denaturation with 6-mol/L hydrochloric acid. In both instances, iodine stained the cylindrical nit structure, suggesting the sheath is a complex carbohydrate. The cylindrical portion of nit structure does not disintegrate or fracture off with combing, liquid nitrogen, insecticides, or washing. None of the common substances used in this study had any visible effect. Once the firm bond between the nit sheath and hair is loosened, both structures retain their structural integrity under light microscopic examination. Thus, in terms of removal of nits, the structure presently has to be slid off the hair shaft. This should help patients and parents understand why fine combing and manual removal is necessary to eradicate this problem. Petrolatum has been used in the treatment of adult lice,3 but has no effect on egg viability. It is most difficult to remove from hair even after repeated washings, causing dust and other particles to adhere to the resultant greasy hair. Pomades are more readily washed out of hair. With several patients, we have verified that a thick application of pomade overnight is equally therapeutic to petrolatum for eradication of adult lice. Cosmetically, these are the obvious choice over petrolatum for those patients who refuse insecticides. Inasmuch as pomades do not kill nits, this therapy should be repeated weekly for 4 weeks to smother newly hatched lice. From our studies, it seems that agents that damage the hair shaft or allow shrinkage of keratin have minimal effect on nit removal. An alternative method in nit removal would be dissolution, or weakening of the nit cylindrical structure itself. The nit sheath seems to be a complex carbohydrate, as supported by iodine staining. Amino acid analysis from the University of Michigan Protein and Carbohydrate Structure Facility, Ann Arbor, revealed the nit sheath to be devoid of any proteinous constituent. Our studies do indeed reveal that the nit cylindrical structure is denatured with acids in vitro, and chemical nit removal may be in the future. Complex carbohydrates can often be hydrolyzed with catalases and/or by acid hydrolysis.4,5 The importance of our study is the verification that chemical nit removal is a possibility; in fact, we can now do it in vitro. This investigation was sponsored by grant 98-181 from the F. M. Douglass Foundation, Toledo, Ohio, and by St Vincent Mercy Medical Center, Toledo. References 1. Burkhart CGBurkhart CN An assessment of the topical and oral, prescription and over-the-counter treatments for head lice. J Am Acad Dermatol. In pressGoogle Scholar 2. Meinking TTaplin D Infestations. Schachner LHansen RCeds. Pediatric Dermatology. New York, NY Churchill Livingstone1995;1347- 1367Google Scholar 3. Bates B Petrolatum smothers "head lice from hell." Skin Allergy News. 1997;1932Google Scholar 4. Fan LTGharpuray MMLee YH Cellulose Hydrolysis. Berlin, Germany Springer-Verlag1987;1- 76 5. Kennedy JF Carbohydrate Chemistry. Oxford, England Clarendon Press1988;303- 341632 http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Archives of Pediatrics & Adolescent Medicine American Medical Association

The Adherent Cylindrical Nit Structure and Its Chemical Denaturation In Vitro: An Assessment With Therapeutic Implications for Head Lice

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Publisher
American Medical Association
Copyright
Copyright © 1998 American Medical Association. All Rights Reserved.
ISSN
1072-4710
eISSN
1538-3628
DOI
10.1001/archpedi.152.7.711
Publisher site
See Article on Publisher Site

Abstract

Pediculus humanus capitis is the insect responsible for head lice. During the female louse's 30-day lifespan, she lays approximately 10 eggs per day and attaches each of them with a gluelike, waterproof substance to human hair, 1 mm from the scalp. Larvae emerge 8 to 10 days later from these nits, or eggs, which remain firmly attached to hair. No topical agent has been shown to be 100% ovicidal.1 The existence of any nits, a major aspect of lice infestations, signifies the potential that this contagious malady may still be present. Many schools, therefore, adhere to a "no-nit" policy before children can reenter the classroom after infestation, thereby imposing prolonged absenteeism. Insecticides fail to kill all nits and larvae because they act on the insects' central nervous systems, which are not fully developed in the first 4 days of the insects' existence. Several products, namely, Clear lice egg remover gel (Care Technologies, Greenwich, Conn), Step 2 (Genderm, Lincolnshire, Ill), and a 50/50 mixture of vinegar and water, have been suggested as beneficial in nit removal. However, no clinical benefit has been documented in the medical literature.2 The purpose of our investigation was to examine attachment of nits to the hair shaft and to test several substances for their effectiveness in facilitating nit removal from hair. Samples of adult lice and hairs with nits attached were obtained from affected patients. No attempt was made to designate specific nits or lice from any particular person. Our first assessment was microscopic examination of the appearance of the nit structure. With hairs intact, nits were noted to be firmly attached to the hair shaft by a cylindrical adherent material, the nit itself being part of the distal portion of the sheath (Figure 1). Lengths of cylindrical bands varied slightly. As nits were freed from hair, the cylindrical bands remained intact (Figure 2). Figure 1. View LargeDownload The louse nit with its adherent cylindrical sheath cemented to the hair shaft. The free, distal end of the nit would be directed toward the hair tip. The egg has a domed operculum (arrow) that embodies air holes, allowing the maturing larvae to breathe. The sheath length varies. Figure 2. View LargeDownload The cylindrical nit after sliding off the hair shaft remains intact with no discernible alteration in anatomical structure. The following agents were investigated as to whether they facilitate sliding of nit casts from the hair shaft: WD-40 (WD-40 Co, San Diego, Calif), vinegar, Detachol (Ferndale Laboratories Inc, Ferndale, Mich), acetone, Step 2, Clear topical lice egg remover gel, bleach, vodka, bug and tar remover (for cars), all-purpose degreaser and cleaner (for kitchen use), Royale with actein ("no-fungus shampoo," Straight Arrow, Leigh Valley, Pa), Osler Tangle Remover for dogs (Osler Professional Products, McMinnville, Tenn), petrolatum, dental plaque remover solution, 20% potassium hydroxide in dimethyl sulfoxide, and liquid nitrogen. No agent proved therapeutically efficacious. Products that seemed to assist mildly in nit removal included bleach, vodka, dental plaque remover solution, and vinegar, both at room temperature and heated. Interestingly, 20% potassium hydroxide in dimethyl sulfoxide dissolved the hair shaft without any discernible effect on the cylindrical nit cast. Live adult lice were placed in petrolatum and 2 pomades (Proclaim Conditioning Hair Dress [Brentwood Beauty Laboratories, Hillside, Ill] and Soft Sheen Sportin' Waves [Soft Sheen Products, Chicago, Ill]). Pomades are medicated ointments for hair used most commonly by African Americans. With all 3 substances, lice were unable to continue movement of appendages and died within 15 minutes. Nits were tested for assessment of chemical constituents and denaturation by acids or proteases under the microscope. In 6-mol/L hydrochloric acid, the sheath assumed a more bulky configuration within seconds. In 12-mol/L hydrochloric acid, the sheath lost its structural integrity, expanding its surface area 3-fold, while maintaining only a semblance of attachment to the nit. The louse egg itself remained unaffected in both solutions. Iodine test for carbohydrates was applied to the nit sheath both before and after denaturation with 6-mol/L hydrochloric acid. In both instances, iodine stained the cylindrical nit structure, suggesting the sheath is a complex carbohydrate. The cylindrical portion of nit structure does not disintegrate or fracture off with combing, liquid nitrogen, insecticides, or washing. None of the common substances used in this study had any visible effect. Once the firm bond between the nit sheath and hair is loosened, both structures retain their structural integrity under light microscopic examination. Thus, in terms of removal of nits, the structure presently has to be slid off the hair shaft. This should help patients and parents understand why fine combing and manual removal is necessary to eradicate this problem. Petrolatum has been used in the treatment of adult lice,3 but has no effect on egg viability. It is most difficult to remove from hair even after repeated washings, causing dust and other particles to adhere to the resultant greasy hair. Pomades are more readily washed out of hair. With several patients, we have verified that a thick application of pomade overnight is equally therapeutic to petrolatum for eradication of adult lice. Cosmetically, these are the obvious choice over petrolatum for those patients who refuse insecticides. Inasmuch as pomades do not kill nits, this therapy should be repeated weekly for 4 weeks to smother newly hatched lice. From our studies, it seems that agents that damage the hair shaft or allow shrinkage of keratin have minimal effect on nit removal. An alternative method in nit removal would be dissolution, or weakening of the nit cylindrical structure itself. The nit sheath seems to be a complex carbohydrate, as supported by iodine staining. Amino acid analysis from the University of Michigan Protein and Carbohydrate Structure Facility, Ann Arbor, revealed the nit sheath to be devoid of any proteinous constituent. Our studies do indeed reveal that the nit cylindrical structure is denatured with acids in vitro, and chemical nit removal may be in the future. Complex carbohydrates can often be hydrolyzed with catalases and/or by acid hydrolysis.4,5 The importance of our study is the verification that chemical nit removal is a possibility; in fact, we can now do it in vitro. This investigation was sponsored by grant 98-181 from the F. M. Douglass Foundation, Toledo, Ohio, and by St Vincent Mercy Medical Center, Toledo. References 1. Burkhart CGBurkhart CN An assessment of the topical and oral, prescription and over-the-counter treatments for head lice. J Am Acad Dermatol. In pressGoogle Scholar 2. Meinking TTaplin D Infestations. Schachner LHansen RCeds. Pediatric Dermatology. New York, NY Churchill Livingstone1995;1347- 1367Google Scholar 3. Bates B Petrolatum smothers "head lice from hell." Skin Allergy News. 1997;1932Google Scholar 4. Fan LTGharpuray MMLee YH Cellulose Hydrolysis. Berlin, Germany Springer-Verlag1987;1- 76 5. Kennedy JF Carbohydrate Chemistry. Oxford, England Clarendon Press1988;303- 341632

Journal

Archives of Pediatrics & Adolescent MedicineAmerican Medical Association

Published: Jul 1, 1998

Keywords: head lice

References