IADVL
Indexed with PubMed and Science Citation Index (E) 
 
Users online: 5135 
     Home | Feedback | Login 
About Current Issue Archive Ahead of print Search Instructions Online Submission Subscribe What's New Contact  
  Navigate here 
  Search
 
  
 Resource links
   Similar in PUBMED
    Search Pubmed for
    Search in Google Scholar for
   Article in PDF (750 KB)
   Citation Manager
   Access Statistics
   Reader Comments
   Email Alert *
   Add to My List *
* Registration required (free)  

 
  In this article
   References
   Article Figures

 Article Access Statistics
    Viewed192    
    Printed2    
    Emailed0    
    PDF Downloaded15    
    Comments [Add]    

Recommend this journal

 


 
 Table of Contents    
LETTER TO THE EDITOR - STUDY LETTER
Year : 2019  |  Volume : 85  |  Issue : 6  |  Page : 647-649

Scabicidal effect of heat on the in vitro survival of scabies mites and their eggs: Optimal temperature and exposure time


Department of Dermatology, Faculty of Medicine, Siriraj Hospital, Mahidol University, Bangkok, Thailand

Date of Web Publication11-Oct-2019

Correspondence Address:
Dr. Sumanas Bunyaratavej
Department of Dermatology, Faculty of Medicine, Siriraj Hospital, Mahidol University, 2 Wanglang Road, Bangkoknoi, Bangkok 10700
Thailand
Login to access the Email id

Source of Support: None, Conflict of Interest: None


DOI: 10.4103/ijdvl.IJDVL_198_19

Rights and Permissions



How to cite this article:
Leeyaphan C, Pluetrattanabha N, Limphoka P, Bunyaratavej S. Scabicidal effect of heat on the in vitro survival of scabies mites and their eggs: Optimal temperature and exposure time. Indian J Dermatol Venereol Leprol 2019;85:647-9

How to cite this URL:
Leeyaphan C, Pluetrattanabha N, Limphoka P, Bunyaratavej S. Scabicidal effect of heat on the in vitro survival of scabies mites and their eggs: Optimal temperature and exposure time. Indian J Dermatol Venereol Leprol [serial online] 2019 [cited 2019 Nov 14];85:647-9. Available from: http://www.ijdvl.com/text.asp?2019/85/6/647/267723




Sir,

Scabies, caused by Sarcoptes scabiei var. hominis, is a common, highly contagious skin disease which spreads through direct skin contact.[1] Classical scabies is not readily transmitted via fomites but patients with crusted scabies who harbour millions of mites may transmit them through their apparels.[1],[2] Outside the human body the mites can survive for 24 to 36 hours at normal room temperature of 21°C and 40 to 80% relative humidity.[3]

This experimental study, conducted at Siriraj Hospital, Thailand, aimed to identify the optimal heat and exposure time needed to destroy scabies mites and their eggs. Because this study did not involve human subjects, certificate of approval from the Institutional Review Board was not required. Skin scrapings obtained from one patientwith untreated severe crusted scabies were promptly put on  Petri dish More Detailses and divided into two groups- control and experimental groups (in total of 12 specimens). The control group was again divided into two groups. One of them was incubated at room temperature (25°C) and the other at external body temperature (35°C) while the experimental group was kept at 50°C in the incubator.[4] Mite survival score was assessed once in every 5 minutes for a duration of 35 minutes using stereoscopy and microscopy. The survival score ranged from 0 to 4 (0 meant no movement and no gut peristalsis; 4 meant actively gross linear movement).[5] Similarly for egg viability analysis, different group of specimens were incubated at 25°C for 35 minutes, 35°C for 35 minutes and 50°C for 30 and 35 minutes. Then all of them were brought back to 25°C. After that, the cumulative number of eggs that have hatched were counted once in two days. Statistical analysis was performed using Chi-square to compare survival score at a specific time and to evaluate the different number of hatched eggs between each specimen.P value < 0.05 indicated statistical significance.

Initially, the mean number of mites in the control group was 14.5 mites per dish while that of the experimental group was 12.5 mites per dish. In the beginning, the control group had 277.5 eggs per dish while the experimental group had 254.7 eggs per dish. There was statistically significant difference in the survival score between the experimental and control groups after incubating for over 15 minutes [P < 0.001; [Figure 1]. All mites in the experimental group were found dead (survival score was 0) after incubating at 50°C for at least 30 minutes which was statistically different from the control group [P < 0.001; [Figure 1]. Regarding egg viability, none of the eggs in the experimental group hatched after incubating at 50°C for 35 minutes while seven eggs were hatching after incubating at 50°C for 30 minutes. Conversely, eggs continued to hatch in the control group [25°C and 35°C incubator; P< 0.001; [Figure 2].
Figure 1: Curve showing the relationship between the mean Sarcoptes scabiei mite survival score and heat exposure time after incubating at 25°C, 35°C and 50°C

Click here to view
Figure 2: Curve showing the number of viable eggs after incubating at 25°C for 35 minutes, at 35°C for 35 minutes and at 50°C for 30 minutes and 35 minutes

Click here to view


Studies on optimal time and temperature affecting the survival of scabies mite and egg have shown wide-ranging results. The experiment from Arlian et al. found that all scabies mites were dead after being incubated at 45°C for 4 to 20 hours.[6] Another previous study demonstrated that all scabies mites were found dead after incubating at 50°C for 10 minutes to 2 hours when incubating at 50°C.[5] However, this study demonstrated that almost all mites were still alive after incubating at 50°C for 10 min. Therefore, at 50°C, the shortest time that all mites were dead was 30 minutes which should be the optimal time for a scabicidal effect of heat.

Studies on the viability of eggs are limited. Our study found out that all scabies mites were destroyed and eggs became non-viable after incubating at 50°C for 35 minutes. This can be utilised to give practical advice to patients on the use of hot water and cloth dryers to disinfest their apparels suitably.[7]

Our study did not take into consideration the differential effect of heat on male and female adult mites and the effect of relative humidity on the survival of mites. In conclusion, our study highlights that a temperature of at least 50°C for 35 minutes is sufficient to destroy the itch mites and their eggs.

Acknowledgement

We would like to thank Assist. Prof. Chulaluk Komoltri, Dr. PH (Biostatistics), Mr. Chanai Muanprasert, BEd and Miss Rungsima Kiratiwongwan, MD for invaluable support.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
  References Top

1.
Tarbox M, Walker K, Tan M. Scabies. JAMA 2018;320:612.  Back to cited text no. 1
    
2.
Chang AY, Fuller LC. Scabies – An ancient disease with unanswered questions in modern times. JAMA Dermatol 2018;154:999-1000.  Back to cited text no. 2
    
3.
Walton SF, Currie BJ. Problems in diagnosing scabies, a global disease in human and animal populations. Clin Micro Rev 2007;20:268–79.  Back to cited text no. 3
    
4.
Centers for Disease Control. Scabies Frequently Asked Questions. Available at: https://www.cdc.gov/parasites/scabies/gen_info/faqs.html. Accessed August 29, 2018.  Back to cited text no. 4
    
5.
Arlian LG, Runyan RA, Achar S, Estes SA. Survival and infectivity of Sarcoptes scabiei var. canis and var. hominis. J Am Acad Dermatol 1984;11:210-5.  Back to cited text no. 5
    
6.
Arlian LG, Vyszenski-Moher DL, Pole MJ. Survival of adults and development stages of Sarcoptes scabiei var. canis when off the host. Exp Appl Acarol 1989;6:181-7.  Back to cited text no. 6
    
7.
Peck M, Brewer AC, Pressman M, Blank E, Mickalide A. Hot tap water legislation in the United States. J Burn Care Res 2010;31:918-25.  Back to cited text no. 7
    


    Figures

  [Figure 1], [Figure 2]



 

Top
Print this article  Email this article

    

Online since 15th March '04
Published by Wolters Kluwer - Medknow