- SCABIES - FIRST CASES OF IVERMECTIN RESISTANCE IN ABORIGINAL COMMUNITIES
northern Australia. Some of the inhabitants have been treated with over 50 oral
doses of ivermectin over the last 5 years [6]. Clinical and in vitro evidence of ivermectin resistance
has developed in two individuals [6]. No ivermectin-resistant arthropod has previously been reported
to cause human infestation, however, such resistance has been induced in the
laboratory under intense drug exposure with the horn fly [7], fruit fly [8], and a species of tick [9].
From their experience in this endemic population, Currie et al.
now recommend a weekly dosing interval for ivermectin rather than their
previous use of a fortnight between treatments [6]. Additionally, they note that higher doses have been suggested
by some authors [1].
Summary of available treatments for scabies
The standard treatment of scabies has been the application of a
prescription scabicide overnight to the entire body surface. The scalp is
normally excluded with adults, but treatment of this body region is important
in infants. Inasmuch as the mite prefers warm, moist areas, the finger and toe
creases, intergluteal cleft, umbilicus, and skin beneath finger and toe nails
must be treated thoroughly. To reduce the incidence of reinfestation and fomite
transmission, clothing, linens, and towels used within the previous week should
be washed in hot water and dried on high heat. All family members and close
contacts must be treated simultaneously, even if they have not developed
pruritus or other clinical signs of scabies. The relatively common occurrence
of asymptomatic mite carriers is greatly underappreciated.
The antiparasitic agent, ivermectin, has been used for 10 years in
humans for this disease and is slowly gaining prominence because of its high
efficacy, ease of treatment, and low risk of side effects. A summary of the
standard topical therapies with comments are listed in Table 1.
References
1. Burkhart CG, Burkhart CN. An epidemiologic and therapeutic
reassessment of scabies. Cutis 2000;65:233-40. PubMed
2. Arlian LG, Morgan MS, Paul CC. Evidence that scabies mites
(Acari: Sarcoptidae) influence production of interleukin-10 and function of
T-regulatory cells (Tr1) in humans. J Med Entomol 2006:43:283-7. PubMed
3. Arlian LG, Vyszenski-Moher DL, Rapp M, Hull BE. Production of
IL-1α and IL-1β by human skin equivalents parasitized by Sarcoptes scabiei. J
Parasitol 1996;82:719-23. PubMed
4. Arlian LG, Morgan MS, Neal JS. Modulation of cytokine
expression in human keratinocytes and fibroblasts by extracts of scabies mites.
AM J Trop Med Hyg 2003;69:652-6. PubMed
5. Arlian LG, Morgan MS, Neal JS. Extracts of scabies mites
(Sarcoptidae: Sarcoptes scabiei) modulate cytokine expression by human
peripheral blood mononuclear cells and dendritic cells. J Med Entomol
2004;41:69-73. PubMed
6. Currie BJ, Harumal P, McKinnon M, Walton SF. First
documentation of in vivo and in vitro ivermectin resistance in Sarcoptes
scabiei. Clin Infect Dis 2004:39:e8-e12. PubMed
7. Byford RL, Craig ME, DeRouen SM. Influence of permethrin,
diazinon, and ivermectin treatments on insecticide resistance in the horn fly
(Diptera: Muscidae). Int J Parasitol 1999;29:125-35. PubMed
8. Kane NS, Hirschberg B, Qian S. Drug-resistant Drosophila
indicate glutamate-gated chloride channels are targets for the antiparasitics
nodulisporic acid and ivermectin. Proc Natl Acad Sci USA 2000;97:13949-54. PubMed
9. Benavides E, Romero A. Preliminary results of a larval
resistance test to ivermectins using Boophilus microplus reference strains. Ann
NY Acad Sci 2000;916:610-2. PubMed
10. Rapp CM, Morgan MS, Arlian LG. Presence of host
immunoglobulin in the gut of Sarcoptes scabiei (Acari: Sarcoptidae). J Med
Entomol 2006;43:539-42. PubMed
