Safety and Efficacy of Topical Lime Sulfur in Mice Infested with Myocoptes musculinus

Abstract

Current treatment options for murine fur mites have limitations in safety and efficacy. This study evaluated whether topical lime sulfur (LS) is an adjunct or alternative to traditional treatment options for Myocoptes musculinus. To evaluate the safety of topical LS, mice were dipped in a 3% LS solution at 34 and 41 d of age. Mice were observed daily for side effects and mortality, with blood work and necropsy at 42 d of age to evaluate for pathologic changes. To determine the efficacy of topical LS, postweanling mice infested with M. musculinus were treated with LS once weekly for 2 wk and then housed with uninfested sentinel mice for 4 wk. Weekly tape tests and postmortem tape tests and skin scrapings were performed on all mice. Treated postweanling mice had significantly lower Hgb levels and higher BUN levels than did control animals. In mite-infested mice, the number of positive cages at euthanasia was the same between treated and control animals. Although topical LS did not cause gross or microscopic changes to organ systems, it may cause clinicopathologic changes, and topical LS is not effective as a sole treatment for M. musculinus infestation of postweanling mice.

Numerous treatment protocols have been described for murine fur mites, with drugs in the avermectin family (ivermectin, selamectin) and the related compound moxidectin being used commonly.^{2-4,8,9,13,19,29,34,37,40,51} The avermectins and related drugs, although effective and safe for use in many mice, can be toxic to neonatal mice and adults of some strains.^{24,25,38,42,43} CF1 mice, which are naturally deficient in P-glycoprotein, are susceptible to ivermectin toxicity, and the Mdr1a genetic mutation has been reported to affect as much as 25% of a random CF1 population.²⁴ Ivermectin must be used cautiously in transgenic mice, because serum levels of the drug can vary among strains, and mutations causing increased blood–brain barrier permeability or P-glycoprotein deficiency can lead to toxicity in valuable transgenic mice.^13,42 Ivermectin has been reported to cause toxicity to suckling mice of various strains, likely due to the incomplete formation of the blood–brain barrier in young pups; moxidectin was shown to be toxic in strains of senescence-accelerated mice.^25,38,43 In addition, ivermectin may affect behavior and immune function.^7,15 Topical products that can be applied directly to the animal or distributed in the bedding, such as organophosphates and permethrins, may not be as successful mitocides as are avermectins; these topical products can have harmful side effects, and exposure may be dangerous to animal care personnel.^12,20,52 A safer treatment protocol is needed for mice in which avermectin use is associated with lethal consequences and for investigators who are concerned about the effects of avermectins on research outcomes.

Lime sulfur (LS) is an antiparasitic that has been used safely in many species and therefore might offer a safer treatment option in ivermectin-sensitive mouse strains. LS has a long history of use in agriculture for the control of fungi and insects, and LS dips have been used in companion animals to treat mites and fungal infection.^{5,11,17,30,32,33,41,44,49} LS is a mixture of calcium and sulfur that can be applied topically as a rinse or dip. As an antiparasitic, the exact mechanism of action of LS is unknown. Its use has been described in dogs, cats, guinea pigs, horses, and tigers for treatment of dermatitis caused by demodicosis, ringworm, and sarcoptic mange.^{27,31,33,35,45,49} In one report, topical application of LS weekly for 6 wk was successful at eliminating the guinea pig sarcoptid mite, Trixacarus caviae.²⁷ Adverse effects in animals have not been reported with as-labeled use of LS, but it potentially can cause skin and eye irritation and inhalational injury, as well as gastrointestinal irritation if ingestion occurs.⁴⁷ Intentional ingestion in humans has resulted in severe toxicity; case reports from the United States and Japan describe metabolic acidosis and caustic injury to the gastrointestinal tract, including chemical burns, mucosal bleeding, and gastric perforation.^18,23 To our knowledge, the safety of LS has not previously been evaluated in mice.

Myocoptes musculinus is one of the most common murine fur mite species reported in contemporary rodent research facilities.^1,10,36 M. musculinus is a surface-dwelling, ambulatory mite that tends to infest the caudal half of the body, but mites can be found on the head and neck of its host. Eggs are laid distally on the hair shaft, hatching on day 5 onto the hair coat and completing a full life cycle in 14 d. The parasite spreads rapidly with direct close contact and can be present on neonates as young as 4 to 5 d of age.^1,36 Clinical signs can include alopecia, pruritus, dermatitis, erythema, weight loss, and cutaneous allergy manifestations.^1,22,31,36

The goal of the current study was to evaluate whether LS is safe when applied topically to mice and whether this treatment is effective in eliminating M. musculinus from postweanling mice. Postweanling mice were treated twice with LS and evaluated for acute toxicity by using blood work and necropsy. The efficacy study was designed according to the life cycle of M. musculinus. Because LS appears to be adulticidal only and because M. musculinus eggs hatch after 5 d, mice received 2 applications 1 wk apart. Mite remnants and egg casings can remain on a mouse even after effective treatment; with many diagnostic techniques, this situation complicates determining whether an animal is truly negative. Treated postweanling mice were housed with sentinel mice after treatment to evaluate for active infestations, which should be transmissible to the sentinels, and to mimic a ‘real world’ situation in which mice would be treated and returned to group housing. We hypothesized that LS would be a safe and effective treatment for M. musculinus in mice. To our knowledge, no previous prospective, controlled studies have evaluated LS use in mice.

Materials and Methods

Humane care and use of animals.

All mice were housed at Emory University, which is an AAALAC-accredited animal research program. All animal procedures were reviewed and approved by the IACUC at Emory University.

Mice and husbandry.

C57BL/6J mice were obtained from the breeding colony at Emory University for use in the safety study. The breeding colony has been maintained at Emory since 2001. Quarterly sentinel testing from the rooms that yielded the study animals were seronegative for ectromelia virus, mouse encephalomyelitis virus, K virus, lymphocytic choriomeningitis virus, mouse minute virus, mouse adenovirus, mouse cytomegalovirus, mouse hepatitis virus, mouse parvovirus, pneumonia virus of mice, NS1, polyoma virus, reovirus type 3, Sendai virus, mouse rotavirus, and Mycoplasma pulmonis, and endo- and ectoparasites; mice were seropositive for mouse norovirus. Mice used for the hematologic and serum chemistry safety evaluation only and as sentinel mice for the efficacy study were C57BL/6NCrl (Charles River Laboratories, Wilmington, MA) and, according to vendor health reports, came from housing where mice were free of all of the previously listed agents, including mouse norovirus. Mice that were infested with M. musculinus and used for the efficacy study were obtained from various colonies within Emory University and were all 34-d-old female wildtype C57BL/6J mice.

Mice were transferred from the breeding colony to a cubicle room that only housed the animals used in this study. This housing room was divided into multiple cubicles, with a full-panel glass door separating each cubicle from the anteroom. The mice were housed in polysulfone cages with microisolator tops and corncob bedding (Bed-o'Cobs, The Andersons, Maumee, OH) in cubicles with a 12:12-h light:dark cycle. Mice were fed autoclaved rodent chow (Rodent Diet 5001, Purina Mills Test Diet, Richmond, VA) and provided with reverse-osmosis–filtered water ad libitum. All mice received nesting pads (Ancare, Bellemore, NY) and shelters (Shepherd Shacks, Shepherd Specialty Papers, Animal Specialties and Provisions, Quakertown, PA) for enrichment. All cages were opened only in a class IIA biologic safety cabinet, which was cleaned (Virkon-S, DuPont Animal Health Solutions, Wilmington, DE) between cages and after use. Mice infested with M. musculinus were housed in the same room as but in a separate cubicle from the noninfested mice. Mite-positive mice were handled last for all husbandry and experimental procedures. If infested mice were handled, the biologic safety cabinet was sprayed with 0.25% fipronil solution (Frontline spray, Merial, Duluth, GA) after disinfection. There is anecdotal evidence that fipronil alone applied topically is effective against murine fur mites, and it has been used as part of a multimodal approach to fur mite eradication in some studies in mice; it also is commonly used to treat other canine and feline ectoparasites.^6,8,14,16,50 Although mite transmission should require animal-to-animal contact, the fipronil spray was used strictly as an additional environmental precautionary measure, because the disinfectant used is not labeled as an antiparasitic. Fipronil spray was never applied to the mice directly.

Safety study.

The safety of topical LS was assessed by using histology, CBC, and serum chemistries. For histology, 16 C57BL/6J mice (age, 4 to 5 wk) were randomly assigned into an experimental or control group, resulting in 8 mice total (4 male and 4 female) in each group. Treated mice were dipped in lime sulfur on days 0 and 7 and then euthanized on day 8; the remaining mice served as controls and had no treatment but were euthanized at the same time point as treated mice. All of these 16 mice were submitted for necropsy and microscopic evaluation.

We then randomly assigned 8-wk-old C57BL/6NCrl female mice to experimental and control groups to evaluate clinicopathologic effects of topical LS treatment. We treated 8 mice on days 0 and 7 and euthanized them on day 8, with blood collected immediately postmortem via cardiac puncture for complete blood count and serum chemistry analysis; the 8 control mice underwent no LS treatment but were euthanized with blood collection as for the experimental mice. Cardiocentesis was performed by inserting a 1-mL syringe with 25-gauge needle percutaneously through the diaphragm and into the heart, immediately after euthanasia. Blood for the CBC was placed into a collection tube containing EDTA anticoagulant prior to analysis. Hematology data analyzed included total WBC count, Hgb, Hct, and platelet count; serum chemistry data included ALT, ALP, total bilirubin, total protein, BUN, creatinine, glucose, and potassium.

Efficacy study.

Female 34-d-old C57BL/6J mice confirmed by tape test to be positive for M. musculinus were divided into 2 groups of 5 mice each. Experimental mice were dipped in LS on days 0 and 7, and mice were single-housed during this time. Mice were placed into a new, clean cage after treatment on day 0. Cages were not sterile but were cleaned by an automatic cage washing machine prior to use (STERIS, Mentor, OH). Immediately after the second treatment, these mice were placed into a new cage with 3 C57BL/6NCrl female contact-sentinel mice (Charles River Laboratories) with vendor reports indicating that they were from housing areas free of endo- and ectoparasites. On arrival at our institution, these mice were housed in trios in a separate cubicle to prevent fur mite infestation, until the start of the study. The remaining group of 5 mice served as controls, and mice were dipped in tap water (from the same source used to dilute the LS concentrate) on days 0 and 7; these mice were single housed during this 7-d period. Immediately after the second water dip, these mice were each placed into a new cage with 3 C57BL/6NCrl contact-sentinel mice. The experimental and control mice were housed with the sentinels for 4 wk, with tape testing occurring weekly. The sentinel mice also were tape tested weekly so that we could better determine whether the study mice had active mite infestation, in the event that a study mouse had a tape test that was positive for mite pieces or egg casings only. At the end of the 4-wk contact period, all mice were euthanized via CO₂ asphyxiation followed by cervical dislocation and were submitted for postmortem tape testing, skin scraping, and necropsy.

Diagnostic methods.

Tape testing was performed by placing a piece of clear cellophane tape (2 × 0.5 in.) onto the animal's hair coat, removing it, affixing it to a slide, and then examining the exfoliated hair shafts at 40× magnification for evidence of mites or mite eggs. Each mouse was tape tested on the back of the neck, back, tail base, abdomen, and inguinal regions.^9,19 Skin scraping was performed by using a no. 10 scalpel blade to scrape the pelage along the neck, back, tail base, abdomen, and inguinal areas. Exfoliated hairs were placed in mineral oil on a glass slide and examined at 40× magnification for evidence of fur mites.^9,39 A positive result on both tape test and skin scrape was defined as the presence of juvenile stage or adult mites with or without viable eggs attached to the hair shafts.

Administration of topical LS.

Lime sulfur (97.8% concentrate dip; Vet Solutions Lime Sulfur Dip, Vetoquinol USA, Fort Worth, TX) was diluted with tap water according to package instructions to make a final 3% solution for topical application. Fresh solution was prepared before each application session and discarded after use. Mice were restrained manually at the tail base; the ventrum was dipped in the solution and approximately 12 mL LS was poured on the dorsum, so that the entire hair coat from nose to tail base was treated. The same method was used to dip the control mice in the efficacy study in tap water. After application, the mice were returned to the cage, and the solution was allowed to air dry on the animals’ skin and hair coat. Mice were observed daily for any adverse effects, including signs of LS toxicity, mortality, and (for the efficacy study) clinical signs of acariasis, including pruritus, alopecia, and ulcerative dermatitis for the duration of the study.

Postmortem examination.

Mice were euthanized for necropsy via CO₂ asphyxiation followed by cervical dislocation. After euthanasia, a necropsy was performed on all mice in the safety study. The lungs and gastrointestinal tract were infused with 10% neutral buffered formalin by injection into the trachea or along the gastrointestinal tract by using a 25-gauge needle attached to a 3-mL syringe. All major organs were removed, and the entire mouse was placed in 10% neutral buffered formalin for at least 24 h prior to being processed for histology. After fixation, sections were collected from the tongue, salivary gland, trachea, larynx, thymus, esophagus, lungs, heart, spleen, pancreas, liver, kidneys, stomach, duodenum, jejunum, ileum, cecum, colon, and rectum, along with skin sections from the neck, back, and inguinal region. The sections were embedded in paraffin, sectioned at 5-µm, and stained with hematoxylin and eosin. A veterinary pathologist who was blinded to the study groups evaluated all slides for any abnormalities.

Mice in the efficacy study underwent full gross necropsy as described, but tissues were not submitted for microscopic evaluation. Samples were collected for tape testing and skin scraping to evaluate response to LS treatment.

Statistical analysis.

Statistical analysis was performed by using SPSS Statistics, version 19 (IBM, New York, NY). Hematology values and serum chemistry values from the safety study were evaluated for outliers and normal distribution by examination of box plots and Shapiro–Wilk test, respectively. Any variables that that had outliers or for which data were not normally distributed was evaluated by using the Mann–Whitney U nonparametric test (platelets, Hct, Hgb, ALP, ALT, glucose), whereas independent t tests were run on all other variables (WBC count, BUN, total bilirubin, total protein). Outliers were included in analysis in all cases, because they did not differ by more than 3 SD from the mean. One treated mouse in the safety study yielded insufficient volume for a CBC and so was excluded from analysis. Samples were excluded from final analysis of serum chemistries when they were hemolyzed or when there was insufficient volume; this exclusion resulted in the smaller group sizes reported in the Results section.

No statistical analysis was performed on the data from the efficacy study because the results were the same for both experimental groups, as presented in the Results section.

Results

Safety study.

All mice survived until the study endpoint, with no clinical signs noted. No significant gross or microscopic lesions were found in the skin, respiratory tract, gastrointestinal tract, or major thoracic and abdominal organs of any treated or control mice. In addition, the experimental and control groups did not differ significantly in WBC count, platelet count, or Hct (Table 1). However, Hgb differed significantly (U = 10.0, Z = −2.087, P = 0.037) between treated and control mice, with treated mice having a lower mean Hgb (Table 1).

Table 1.

Results (mean ± SEM) of hematology and clinical chemistry analysis during safety study.

Parameter		LS-treated	Control
(reference range)	Units	mice	mice
WBC (5.1–11.6)	x 103/μL	5.18 ± 0.71 (n = 7)	4.63 ± 0.52 (n = 8)
Platelets (100–1000)	x 103/μL	728 ± 86 (n = 7)	861 ± 35 (n = 8)
Hct (50–56)	%	54.1 ± 1.0 (n = 7)	57.3 ± 0.8 (n = 8)
Hgb (12.2–16.2)a	g/dL	16.1 ± 0.3 (n = 7)	17.2 ± 0.2 (n = 8)
BUN (8–33)a	g/dL	24.8 ± 1.1 (n = 5)	19.0 ± 0.6 (n = 6)
Total protein (3.5–7.2)	g/dL	5.74 ± 0.09 (n = 5)	6.08 ± 0.29 (n = 6)
Total bilirubin	mg/dL	0.3 ± 0.0	0.3 ± 0.0
(0.15–0.85)		(n = 5)	(n = 6)
ALP (35–96)	U/L	132.2 ± 3.9 (n = 5)	104.3 ± 18.7 (n = 6)
ALT (17–77)	U/L	86.0 ± 4.2 (n = 5)	111.8 ± 33.0 (n = 6)
Glucose (62–175)	mg/dL	253.4 ± 28.1 (n = 5)	265.0 ± 23.7 (n = 6)

^aSignificant (P < 0.05) difference between LS-treated and control groups.

Among serum chemistry values that were analyzed, BUN differed significantly (P = 0.001) between groups, with treated mice having a higher mean BUN (Table 1). Experimental and control groups did not differ in regard to total protein, total bilirubin, ALP, ALT, and glucose. None of the treated or control mice had a creatinine value that exceeded 0.4 mg/dL, which is still well within the normal range for mice (reference range, 0.2 to 0.9 mg/dL). Notably, all of the mice (treated and control) had elevated potassium values (that is, greater than 8.4 mEq/L; reference range, 5.0 to 7.5 mEq/L). These results were not analyzed further because discrete values were not obtained for samples that were beyond the range of the chemistry analyzer.

Efficacy study.

Treated mite-infested mice were dipped in LS once weekly for 2 wk and then housed with sentinel mice for 4 wk. Control mite-infested mice were dipped in tap water once weekly for 2 wk and then housed with sentinel mice for 4 wk. All mice in every cage (including sentinels) were tape tested weekly. At necropsy, mice were again tape tested, and a skin scrape was performed. At 4 wk after the completion of the LS treatment, 3 of the 5 treated mice were positive for M. musculinus and had at least one infested sentinel within the cage. All animals in the other 2 cages of treated and sentinel mice had negative tape tests every week for 4 wk after the second application of LS and had negative skin scrapes at 4 wk after treatment. The same results were seen among the control mice: 3 of the 5 water-dipped animals were positive on skin scrape and tape test at 4 wk after treatment and had at least one infected sentinel mouse in the cage, whereas the other 2 cages of control and sentinel mice had negative results throughout the study.

Discussion

Mice dipped in LS had no evidence of gross lesions or microscopic pathologic changes at necropsy. Treated mice had lower mean Hgb levels and higher mean BUN levels than did control animals. In addition, the difference in Hct between groups, with treated animals having a lower mean value than that of controls, approached significance. Despite the statistical significance of these differences, it is unlikely these changes in lab values would have a clinically significant effect on the mice. All individual Hgb and Hct levels for LS-treated mice were within the reference range for this species (12.2 to 16.2 g/dL and 50% to 56%, respectively), and none of the individual mice had values that would be expected to cause clinical signs or require veterinary intervention or supportive care. The same is true for the BUN values; the values for all individual mice were within the reference range of 8 to 33 mg/dL. In addition, no LS-treated mouse had an individual creatinine level above 0.2 mg/dL, indicating that the renal function of the treated mice was unaffected despite the high-normal BUN level. Furthermore, all of the mice in both groups had potassium levels outside of the normal reference range of 7 to 8.5mEq/L. This hyperkalemia was most likely secondary to the respiratory acidosis as a result of euthanasia by CO ₂ asphyxiation in these animals; therefore this value was not included in analysis of clinicopathologic changes caused by LS treatment.⁴⁶ Mice in this arm of our study were only treated twice with LS, because that frequency should be sufficient given the life cycle of the M. musculinus fur mite. Evaluating the longer-term safety of LS or its safety when used more than twice for treatment requires additional investigation.

LS dip was not an effective treatment for M. musculinus in postweanling mice in our study. LS had the same efficacy rate as tap water, as measured by tape test and skin scrape. A positive result was one where viable, unhatched eggs or adult stages of M. musculinus were identified either on tape test or skin scrape. There are many potential reasons for the treatment failure in this study. The exact mechanism of action of LS and the length of time it takes to actually kill a mite are unknown. LS-treated mice were placed into a cage with sentinel mice immediately after the second LS treatment; keeping treated mice separate for a longer period of time and increasing contact time between the treated host and the mites may have resulted in a higher efficacy rate. Along those lines, we noted that the day after treatment, the mice were completely dry, and there was no distinguishable difference between treated and control mice. It is unclear how long it takes a mouse to groom LS off the hair coat, but perhaps the treatment was unsuccessful because the mice were simply grooming it off themselves (or each other) too quickly to allow adequate contact time for LS to kill the fur mites. It is possible that treating mice twice was inadequate for elimination of M. musculinus. Because LS is thought to be an adulticidal agent and given the life cycle of M. musculinus, 2 treatments should be sufficient to clear the mites, but perhaps more than 2 treatments are required for maximum efficacy.

The apparent effectiveness of both the treatment and controls for 40% of the mice is likely due to false negative results, particularly for the water controls. The decision to dip control mice in tap water was made to ensure that any treatment success was the result of the LS and not something in the water itself. Our diagnostic tests may not have been sensitive enough to detect a mouse infested with low levels of M. musculinus. Diagnostic methods of detection include microscopic evaluation of postmortem and antemortem tape tests, fur plucks, skin scrapings, direct pelage examination, and PCR analysis.^{1,9,21,28,39,48} Sentinels exposed to dirty bedding of colony mice and subsequently evaluated with the aforementioned techniques have also been described.²⁶ Despite the variety of diagnostic techniques, there is no clear consensus on which method is the most reliable. In many institutions, the postmortem tape test may be used most frequently. Although this diagnostic test has recently been reported to be 100% sensitive in the detection of M. musculinus, other sources report skin scrapings or direct postmortem pelt examination to be a more accurate means of detection.^9,28,36,39 Direct examination of the pelt and the postmortem tape test require that the animals be held after death for at least 1 h and 6 to 12 h, respectively, prior to examination, making these diagnostics lengthy and inefficient.^21,28,36 Skin scraping is commonly used but may not be superior to other methods.^9,21,28,39

Antemortem testing methods do not offer more reliable results than does postmortem testing. The antemortem tape test is a common method that has the advantage of being faster than are most of the postmortem tests and does not require a dead or anesthetized rodent. The sensitivity of this test has been reported to be around 84%.¹⁹ Most of these diagnostics can be greatly affected by the mite burden, housing density, immune status, age, sampling sites, and skill of personnel.^9,19,28,39 We chose these 2 tests because they would have a low rate of false positives, particularly when the sentinels are used because an infested sentinel means that the study animal has an active infestation. The antemortem tape test allows serial sample collection without the risk of false positives from environmental contamination. Both tape testing and skin scrapings are essentially variations of the fur pluck method and can obtain M. musculinus from mouse pelage. The development of PCR testing for fur mites provides a more sensitive diagnosis method than tape testing and skin scraping but has the risk of false-positive results in treated animals. PCR testing involves swabbing a mouse or the caging to collect mite DNA. Although this method allows for the identification of very small amounts of genetic material, it is impossible to know from the presence of this DNA alone whether there is active infestation with live mites or merely the remnants of tissue or feces from dead mites. Because it can take as long as 8 mo for a mouse to shed its entire hair coat, PCR testing potentially could be positive for quite a long time after treatment ceases.³⁹ Although a positive PCR result does not necessarily indicate active infestation, it would prompt supplemental testing with another diagnostic method such as tape testing or skin scraping to confirm whether treatment was truly successful. A recent study compared PCR with tape testing and discovered that in some mice, PCR was negative despite visual positive identification of mites on tape test.⁴⁸ This inconsistency may be related to the ability of the test swab to collect DNA. In addition, all treated and untreated mice in our study were housed with 3 uninfested sentinel mice, which was done to safeguard against false negative results. Mice can transmit M. musculinus quite quickly with direct contact.²¹ If treated mice were negative on tape tests and skin scrapings but other mice from the same cage had positive results, then we could presume the treated mouse was not truly mite-free when it was placed in the cage after 2 LS treatments. PCR testing might have been useful in this study to evaluate those cages of mice where treatment appeared to be effective, as it could have provided a more sensitive means of identifying M. musculinus infestations. However, because LS treatment clearly was ineffective according to the testing we did use, we decided not to perform any follow-up PCR testing. All mice were further evaluated at necropsy by an additional tape test and skin scraping. The use of an additional negative control that received no treatment or incorporating other diagnostic techniques might have clarified the factors underlying our results.

The results of our current study suggest that LS treatment could lead to clinicopathologic changes in postweanling mice, and topical LS is ineffective against M. musculinus. The clinicopathologic changes seen in postweanling mice are unlikely to lead to clinical disease, but these changes may be important to investigators, depending on the nature of the research. This treatment modality was not effective against M. musculinus and is unlikely to be put into practice, given these results combined with the foul odor of LS and time-consuming process of applying it. The goal of this project was to expose mice to LS and evaluate them for any clinical adverse effects, clinicopathologic changes, anatomic or microscopic lesions. We did not attempt to characterize any immunologic or behavioral changes, so we are uncertain whether LS introduces variables to research projects relying on immunologic or behavioral parameters. We chose to use C57BL/6 mice because these mice are a commonly used background strain; perhaps LS causes adverse effects in other strains or transgenic mice. Although our treatment was not effective, we still feel it is important to report these results, so that other investigators can use this knowledge when developing treatment plans for fur mite outbreaks in their research colonies. Considering our results, we conclude that LS is not a suitable alternative to avermectins for eradicating murine fur mites.