Soiled Bedding Sentinels for the Detection of Fur Mites in Mice
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Journal of the American Association for Laboratory Animal Science Vol 50, No 1 Copyright 2011 January 2011 by the American Association for Laboratory Animal Science Pages 54–60 Soiled Bedding Sentinels for the Detection of Fur Mites in Mice Krista E Lindstrom,* Larry G Carbone, Danielle E Kellar, Melinda S Mayorga, and James D Wilkerson Identification and eradication of murine fur mite infestations are ongoing challenges faced by many research institutions. Infestations with Myobia musculi and Myocoptes musculinus can lead to animal health problems and may impose unwanted research variables by affecting the immune and physiologic functions of mice. The purpose of this study was to evaluate the utility and efficacy of soiled bedding sentinels in the detection of fur mite infestations in colony mice. Female young-adult CRL:CD1(ICR) mice (n = 140) were exposed over a 12-wk period to various volume percentages of soiled bedding (11%, 20%, 50%, and 100%) from fur-mite–infested animals. Mice were tested every 2 wk with the cellophane tape test to identify the presence of fur mite adults and eggs. At the end of 12 wk, all mice exposed to 11%, 20%, and 50% soiled bedding tested nega- tive for fur mites. One of the 35 mice (3%) receiving 100% soiled bedding tested positive for fur mites at the end of the 12-wk follow-up period. These findings suggest that the use of soiled bedding sentinels for the detection of fur mite infestations in colony mice is unreliable. Ectoparasite infestations present an ongoing threat to bar- potential research complications associated with murine acaria- rier facilities. Murine acariasis in laboratory mice frequently is sis.10,15,18-20,22,26,31,42,44 Mite infestations have been shown to cause caused by Myobia musculi, Myocoptes musculinus, and Radfordia elevations in IgE, IgG, and IgA levels; mast cell degranulation; affinis.1,13,17,40,41 These infestations can be challenging to iden- increased levels of inflammatory cytokines; and lymphocyto- tify and control and often lead to animal health problems and penia.18-20,22,26,31,44 The changes in the immunologic function of research complications. For this reason, many institutions strive affected mice can persist even after mite eradication.18 to exclude these parasites from their barrier facilities.1,17,18,41 Multiple chemical treatment modalities have been Infestations can further compromise ongoing research by dis- proposed for the eradication of fur mites in infested ani- rupting collaboration with institutions affected by sporadic or mals.2,3,5,8,12,14,17,25,29,30,32,36,43 Conflicting information exists endemic mite infestations in their facilities.18 regarding the success of many of these treatment regimes. Myocoptes musculinus is the most common fur mite identified In addition, several of the proposed treatments have been among laboratory mice, although mixed infections with Myobia associated with toxicity, adverse health effects in mice, and musculi are common.17 The life cycles of Myocoptes and Myobia alterations in the physiologic or immune function of the ani- are 14 and 23 d, respectively.2,17 Myobia mites most frequently are mals.2,3,5,8,12,14,17,25,29,30,32,36,43 The complications associated with found to inhabit the head and neck of mice, whereas Myocoptes identifying an effective treatment for murine acariasis while are reported to have a predilection for the back, ventral abdo- minimizing toxicity and the introduction of unknown research men, and inguinal regions.2,17 Mite infestations in live animals variables highlight the importance of rapid and effective detec- are often diagnosed by using cellophane tape tests.5,14,25 A clear tion of mite infestations in barrier facilities. piece of cellophane tape is pressed against the fur of the mouse, Many institutions rely on soiled bedding sentinels for their affixed to a slide, and examined microscopically for the pres- primary source of information on colony health status.9,21,33,35 ence of eggs or adult mites. Pelage collection and examination Several studies have demonstrated the efficacy of soiled bed- and skin scraping are 2 other common diagnostic methods. ding sentinels to detect common murine pathogens such as These tests have been shown to have increased sensitivity when mouse hepatitis virus, mouse norovirus, Helicobacter spp., compared with the tape test, but they have the disadvantage of and pinworms.4,7,24,28,37,38 However, not all pathogens are eas- requiring an anesthetized or recently euthanized animal.2,5,17 ily transmitted through soiled bedding exposure. Agents that Fur mites feed on the superficial skin tissues and secretions are not routinely identified through soiled bedding sentinels of the animals they infest.1,2,17 Mite infestations in mice have include those that are shed in low numbers, are susceptible to been associated with numerous health problems. Common environmental factors, or are not easily transmitted through clinical manifestations of acariasis include alopecia, pruritis, the fecal–oral route.6,21,33 Examples of pathogens that are not and scruffiness.1,2,10,15,17-20,22,26,31,42,44 Severe health problems easily transmitted or detected through soiled bedding exposure including ulcerative dermatitis, hypersensitivity dermatitis, include mouse Sendai virus, Pasteurella pneumotropica, lym- and pyoderma can develop also.1,2,10,17,41 Infested mice may phocytic choriomeningitis virus, and cilia-associated respiratory also be prone to secondary infections, reduced life span, and bacillus.7,9,11,16,35 In addition, the sensitivity of soiled bedding decreased body weight.2,17,42 Several studies have analyzed the sentinel programs varies with the number of animals affected within the colony.27,38 In 2008, our institution faced a fur-mite outbreak that affected Received: 16 Jun 2010. Revision requested: 14 Jul 2010. Accepted: 20 Jul 2010. Laboratory Animal Resource Center, University of California, San Francisco, more than 25 rooms in a single barrier facility. Animals positive California. for Myobia musculi, Myocoptes musculinus, or both were identified *Corresponding author. Email: [email protected] 54 Soiled-bedding sentinels and fur-mite detection through either health check requests for itching and scratch- periment and were confirmed to be negative for ectoparasites ing animals and by testing of animals scheduled for export to by 2 experienced slide readers. In addition, 10% of the slides other institutions. Despite the extent of this outbreak, the soiled collected from this group were sent to an outside comparative bedding sentinels in all mite-positive rooms consistently tested pathology laboratory at the University of California–Davis for negative on cellophane tape tests for fur mites. confirmatory testing. All slides submitted to the laboratory were To our knowledge, only one study has specifically examined confirmed to be negative for fur-mite adults and eggs. the efficacy of soiled bedding sentinels in the detection of fur Facilities. The Laboratory Animal Resource Center at the Uni- mites in mice.34 A separate study, examining the transmission versity of California–San Francisco is an AAALAC-accredited of mouse hepatitis virus to soiled bedding sentinels,38 dem- animal care and use program. All animal care and experimental onstrated that 75% of cages (3 of 4) exposed to soiled bedding procedures were in accordance with federal policies and guide- from colony animals tested positive for fur mites after 19 wk lines governing the use of animals and were approved by the of exposure. That previous study used 8 cages of 12 mice each; University of California–San Francisco Institutional Animal 4 cages received soiled bedding from colony animals, whereas Care and Use Committee. All animals in both groups were kept the other 4 cages received clean nonsoiled bedding. In that on paper chip bedding (Shepard Specialty Papers, Watertown, study,38 56.3% of colony mice were known to be mite-positive. TN) with continuous access to food (Purina PicoLab 5053 irradi- Other literature suggests that spread of mites to naïve animals ated, Purina Mills, St Louis, MO) and tap water. The housing requires direct contact and that soiled bedding does not serve room was maintained at 66 to 74 °F (18.9 to 23.3 °C) and with as an effective mechanism for transmission.1,17,23,39 However, an average humidity between 33% and 52% under a 12:12-h we were unable to identify any research or experiments that light:dark cycle. All racks were maintained in a quarantined substantiated these conclusions. room in an isolated facility and were kept separate from any The purpose of the present study was to evaluate whether investigators’ animals to prevent the possible transmission of CRL:CD1(ICR) mice housed in static microisolation caging on mites to other research animals. soiled bedding from mice with Myobia and Myocoptes infesta- Experimental design. Cage changing. All cages were changed tions can be used as sentinels for the detection of fur mites and once every week in a class II type A/B3 safety cabinet (NuAire, to determine how the efficacy of these soiled bedding sentinels Plymouth, MN). Fur-mite samples from the experimental colony for fur-mite detection varies with the prevalence of fur-mite were collected every 2 wk at the time of cage change. Two bio- infestation among colony animals. logical safety cabinets were available in the housing room. One safety cabinet was used exclusively to change all cages from the Materials and Methods fur-mite–infested colony. The second safety cabinet was used Subjects. History of fur-mite–infested colony. Mite-infested exclusively to change cages of experimental colony mice. Staff mice of several strains from multiple research groups were changing cages wore scrubs, gowns, head covers, shoe covers, collected and housed in static microisolation caging in a con- and gloves.