Bio

Academic Appointments


Administrative Appointments


  • Chair, Department of Comparative Medicine (2009 - Present)
  • Director, Veterinary Service Center (2009 - Present)
  • Editorial Review Board, Comparative Medicine (2005 - 2011)
  • Chair, Scientific Advisory Committee, AALAS (2005 - 2006)
  • Chair, Scientific Review Committee, ACVIM Foundation (2004 - 2006)

Honors & Awards


  • Distinguished Alumni, LSU School of Veterinary Medicine (2011)

Professional Education


  • Diplomate, American College of Veterinary Medicine, Large Animal Internal Medicine
  • PhD, UC-Davis, Neurobiology
  • DVM, LSU, Veterinary Medicine

Research & Scholarship

Current Research and Scholarly Interests


Xenopus are a major, non-mammalian laboratory animal model. They are a hardy, long-lived and fully aquatic amphibian species. Under laboratory conditions, they can lay eggs year around, thus providing researchers with a steady supply of biological material. Xenopus are used to study vertebrate embryology, cellular biology, biomedical-physiology, toxicology and biochemistry. My research focuses on the biology, health and disease of laboratory Xenopus. Stanford undergraduates and veterinary residents participate in Xenopus research projects on topics ranging from infectious disease, parasitology, husbandry and housing, to animal welfare and behavior.

Teaching

2013-14 Courses


Postdoctoral Advisees


Graduate and Fellowship Programs


Publications

Journal Articles


  • Prevalence of Batrachochytrium dendrobatidis in 120 Archived Specimens of Lithobates catesbeianus (American Bullfrog) Collected in California, 1924-2007. EcoHealth Huss, M., Huntley, L., Vredenburg, V., Johns, J., Green, S. 2013; 10 (4): 339-343

    Abstract

    The chytrid fungus, Batrachochytrium dendrobatidis (Bd), has been identified as a major cause of the recent worldwide amphibian decline. Numerous species in North America alone are under threat or have succumbed to Bd-driven population extinctions. The American bullfrog (Lithobates catesbeianus) has been reported as a tolerant carrier of Bd. In this report, we used a qPCR assay to test 120 archived American bullfrog specimens collected between 1924 and 2007 in California, USA and Baja California, Mexico. The overall prevalence of Bd infection in this archived population of L. catesbeianus was 19.2%. The earliest positive specimen was collected in Sacramento County, California, USA in 1928 and is to date the earliest positive archived Bd specimen reported globally. These data demonstrate that Bd-infected wild amphibians have been present in California longer than previously known.

    View details for DOI 10.1007/s10393-013-0895-6

    View details for PubMedID 24419668

  • Tissue Distribution of Enrofloxacin in African Clawed Frogs (Xenopus laevis) after Intramuscular and Subcutaneous Administration JOURNAL OF THE AMERICAN ASSOCIATION FOR LABORATORY ANIMAL SCIENCE Felt, S., Papich, M. G., Howard, A., Long, T., McKeon, G., Torreilles, S., Green, S. 2013; 52 (2): 186-188

    Abstract

    As part of an enrofloxacin pharmacokinetic study, concentrations of enrofloxacin and ciprofloxacin (metabolite) were measured in various tissues (brain, heart, kidney, liver, lung, and spleen) collected from treated (subcutaneous delivery, n = 3; intramuscular delivery, n = 3; untreated controls, n = 2) adult female Xenopus laevis by using HPLC. Enrofloxacin was rapidly absorbed after administration by either route and readily diffused into all sampled tissues. Enrofloxacin and ciprofloxacin were present in the tissue samples collected at 8 h. The highest average tissue concentrations for enrofloxacin were found in kidney, with the lowest concentrations in liver. Ciprofloxacin tissue concentrations paralleled but were always lower than those of enrofloxacin for all time points and tissues except brain and kidney. These results, together with previously published pharmacokinetic data and known minimal inhibitory concentrations of common pathogenic bacteria, provide a strong evidence-based rationale for choosing enrofloxacin to treat infectious diseases in X. laevis.

    View details for Web of Science ID 000316159700010

    View details for PubMedID 23562103

  • Prevalence of Batrachochytrium dendrobatidis in Xenopus Collected in Africa (1871-2000) and in California (2001-2010). PloS one Vredenburg, V. T., Felt, S. A., Morgan, E. C., McNally, S. V., Wilson, S., Green, S. L. 2013; 8 (5)

    Abstract

    International trade of the invasive South African clawed frog (Xenopus laevis), a subclinical carrier of the fungal pathogen Batrachochytrium dendrobatis (Bd) has been proposed as a major means of introduction of Bd into nave, susceptible amphibian populations. The historical presence of Bd in the indigenous African population of Xenopus is well documented. However, there are no reports documenting the presence of Bd in wild Xenopus populations in the US, particularly in California where introduced populations are well-established after intentional or accidental release. In this report, a survey was conducted on 178 archived specimens of 6 species of Xenopus collected in Africa from 1871-2000 and on 23 archived specimens (all wild-caught Xenopus laevis) collected in California, USA between 2001 and 2010. The overall prevalence rate of Bd in the tested Xenopus was 2.8%. The earliest positive specimen was X. borealis collected in Kenya in 1934. The overall prevalence of Bd in the X. laevis collected in California was 13% with 2 positive specimens from 2001 and one positive specimen from 2003. The positive Xenopus (3/23) collected in California were collected in 2001 (2/3) and 2003 (1/3). These data document the presence of Bd-infected wild Xenopus laevis in California. The findings reported here support the prevailing hypothesis that Bd was present as a stable, endemic infection in Xenopus populations in Africa prior to their worldwide distribution likely via international live-amphibian trade.

    View details for DOI 10.1371/journal.pone.0063791

    View details for PubMedID 23691097

  • Biology, behavior, and environmental enrichment for the captive African clawed frog (Xenopus spp) APPLIED ANIMAL BEHAVIOUR SCIENCE Chum, H., Felt, S., Garner, J., Green, S. 2013; 143 (2-4): 150-156
  • Mortality and Morbidity in African Clawed Frogs (Xenopus laevis) Associated with Construction Noise and Vibrations JOURNAL OF THE AMERICAN ASSOCIATION FOR LABORATORY ANIMAL SCIENCE Felt, S. A., Cowan, A. M., Luong, R., Green, S. L. 2012; 51 (2): 253-256

    Abstract

    In Spring 2008, 175 adult female Xenopus laevis were exposed to construction-related vibrations that caused overt water rippling in the frog tanks. The 3 affected tanks were custom-built static, 300-gal 'pond-style' tanks that sat on the floor of the housing room. The water in the tank developed visible ripples as a result of the vibrations transmitted through the floor during jack-hammering in an adjacent room that was approximately 10 ftaway. All frogs in the tanks displayed buoyancy problems, excessive air gulping, and skin sloughing; ultimately 7 frogs died. In addition, these 7 animals were bloated, and 5 of these 7 had regurgitated and everted their stomach and distal esophagus into the oral cavity, resulting in airway obstruction and death. Gross pathologic findings included regurgitation and eversion of the stomach of the distal portion of the esophagus into the oral cavity, obstruction of the airway, and lung overinflation. No significant histologic lesions were observed. Construction vibrations transmitted through the water appeared to have disrupted the mechanoreceptive function of the lateral line system, resulting in overstimulation of the noxious feeding response, regurgitation, and eversion of the stomach and distal esophagus into the oral cavity and subsequent suffocation due to airway obstruction. After immediate cessation of the jack-hammering and relocation of the remaining frogs, no additional morbidities or mortalities occurred.

    View details for Web of Science ID 000306772200016

    View details for PubMedID 22776127

  • Ongoing invasions of the African clawed frog, Xenopus laevis: a global review Biological Invasions Measey GJ, Rodder D, Green SL, Kobayashi R, Lillo F, Lobos G, Rebelo R, Thirion J-M 2012; 10.1007 (s10530-012)
  • Serum Clinical Biochemical and Hematologic Reference Ranges of Laboratory-Reared and Wild-Caught Xenopus laevis JOURNAL OF THE AMERICAN ASSOCIATION FOR LABORATORY ANIMAL SCIENCE Wilson, S., Felt, S., Torreilles, S., Howard, A., Behan, C., Moorhead, R., Green, S. 2011; 50 (5): 635-640

    Abstract

    The South African clawed frogs Xenopus laevis and X. tropicalis are fully aquatic amphibians and well-established animal models. Because genetically engineered laboratory Xenopus are now being produced, the establishment of normal reference ranges for serum biochemical and hematologic parameters is essential for phenotyping and as a diagnostic aide. We determined normal reference ranges for hematologic values from 3 populations of X. laevis: wild-caught frogs (n = 43) and frogs from 2 commercial sources (A, n = 166; B, n = 109). For serum biochemistry, we determined normal reference ranges for frogs from source A and wild-caught frogs divided by sex and season. Significant differences across populations were found in WBC and RBC counts, hemoglobin concentration, hematocrit, mean corpuscular hemoglobin concentration, and mean corpuscular volume. Among serum biochemical analytes, significant differences were found for albumin:globulin ratio, anion gap, and concentrations of albumin, globulin, total protein, lipase, alanine transaminase, ?-glutamyl transpeptidase; creatine phosphokinase; indirect, direct, and total bilirubin; cholesterol, low-density lipoprotein lipase, carbon dioxide, glucose, lactacte dehydrogenase, calcium, chloride, and sodium. We hypothesize that these differences can be attributed to differences in water quality, habitat, ambient temperature, diet, sex, recent transport or shipment, and genetic background. However, testing that hypothesis is beyond the scope of the current study. In addition, clinical chemistry and hematologic reference range values Xenopus laevis are quite distinct from those for other species and are most consistent with the only values published for another fully aquatic amphibian, the Eastern hellbender (Cryptobranchus alleganiensis).

    View details for Web of Science ID 000296070000004

    View details for PubMedID 22330708

  • The Pharmacokinetics of Enrofloxacin in Adult African Clawed Frogs (Xenopus laevis) JOURNAL OF THE AMERICAN ASSOCIATION FOR LABORATORY ANIMAL SCIENCE Howard, A. M., Papich, M. G., Felt, S. A., Long, C. T., McKeon, G. P., Bond, E. S., Torreilles, S. L., Luong, R. H., Green, S. L. 2010; 49 (6): 800-804

    Abstract

    Pharmacokinetics of enrofloxacin, a fluoroquinolone antibiotic, was determined in adult female Xenopus laevis after single-dose administration (10 mg/kg) by intramuscular or subcutaneous injection. Frogs were evaluated at various time points until 8 h after injection. Plasma was analyzed for antibiotic concentration levels by HPLC. We computed pharmacokinetic parameters by using noncompartmental analysis of the pooled concentrations (naive pooled samples). After intramuscular administration of enrofloxacin, the half-life was 5.32 h, concentration maximum was 10.85 ?g/mL, distribution volume was 841.96 mL/kg, and area under the time-concentration curve was 57.59 ?gh/mL; after subcutaneous administration these parameters were 4.08 h, 9.76 ?g/mL, 915.85 mL/kg, and 47.42 ?gh/mL, respectively. According to plasma pharmacokinetics, Xenopus seem to metabolize enrofloxacin in a manner similar to mammals: low levels of the enrofloxacin metabolite, ciprofloxacin, were detected in the frogs' habitat water and plasma. At necropsy, there were no gross or histologic signs of toxicity after single-dose administration; toxicity was not evaluated for repeated dosing. The plasma concentrations reached levels considered effective against common aquatic pathogens and suggest that a single, once-daily dose would be a reasonable regimen to consider when treating sick frogs. The treatment of sick frogs should be based on specific microbiologic identification of the pathogen and on antibiotic susceptibility testing.

    View details for Web of Science ID 000284791700002

    View details for PubMedID 21205443

  • Evaluation and Refinement of Euthanasia Methods for Xenopus laevis JOURNAL OF THE AMERICAN ASSOCIATION FOR LABORATORY ANIMAL SCIENCE Torreilles, S. L., McClure, D. E., Green, S. L. 2009; 48 (5): 512-516

    Abstract

    The most common method of euthanasia for Xenopus species is by immersion in tricaine methane sulfonate solution (MS222). A wide range of doses of MS222 (0.5 to 5 g/L) have been recommended, but few reports describe dose-response testing, the time to loss of consciousness, or the reliability of euthanasia. The objective of this study is to evaluate the efficacy of immersing individual and groups of frogs in MS222 at concentrations ranging from 1 to 5 g/L for euthanasia and of 3 less-common methods: intracoelomic injection of MS222, intracoelomic injection of sodium pentobarbital with phenytoin, and ventral cutaneous application of benzocaine gel. Our results indicate that immersion for at least 1 h in a 5-g/L buffered solution of MS222, intracoelomic injection of 1100 mg/kg sodium pentobarbital with sodium phenytoin (equivalent to 0.3 mL solution per frog), or ventral cutaneous application of 182 mg/kg benzocaine (equivalent to a 2 cm x 1 mm of 20% benzocaine gel) is necessary to euthanize adult X. laevis and ensure complete cessation of the heartbeat without recovery. These doses are considerably higher than those previously recommended for this species.

    View details for Web of Science ID 000270480000008

    View details for PubMedID 19807972

  • The Laboratory Xenopus sp. CRC Press, Taylor & Francis Group, Boca Raton, FL Green SL 2009
  • Assessment of the utility of using intra- and intervertebral minimum sagittal diameter ratios in the diagnosis of cervical vertebral malformation in horses VETERINARY RADIOLOGY & ULTRASOUND Hahn, C. N., Handel, I., Green, S. L., Bronsvoort, M. B., Mayhew, I. G. 2008; 49 (1): 1-6

    Abstract

    Cervical vertebral malformation is one of the most common causes of ataxia in horses. The most important factor in the diagnosis of cervical vertebral malformation is the identification of cervical vertebral canal stenosis, but published data for minimum sagittal diameter ratios in adult horses are only available for C4-C7 intravertebral sites. Intra- and intervertebral sagittal diameter ratios at C2-C7 were evaluated in 26 ataxic horses, for which a complete clinical and neuropathological evaluation was undertaken. Eight of these horses were diagnosed with cervical vertebral malformation. In these horses the majority of compressive lesions were intervertebral. The mean sagittal diameter ratios of horses with cervical vertebral malformation were significantly smaller than those of horses without cervical vertebral malformation, and for an individual horse in our study, the site with the smallest intervertebral sagittal diameter ratio was always the site at which the spinal cord was compressed. Mean sagittal diameter ratio intravertebral site measurements of horses with cervical vertebral malformation were smaller than those of horses without cervical vertebral malformation; however, the site of compression could not be predicted from the data. For our dataset, horses with a sagittal diameter ratio of < or = 0.485 at any inter- or intravertebral site could be correctly classified as having cervical vertebral malformation, and sagittal diameter ratio measurements were an effective tool to identify at least one site of compression in an individual case.

    View details for DOI 10.1111/j.1740-8261.2007.00308.x

    View details for Web of Science ID 000252331800001

    View details for PubMedID 18251286

  • Refuge cover decreases the incidence of bite wounds in laboratory South African clawed frogs (Xenopus laevis) JOURNAL OF THE AMERICAN ASSOCIATION FOR LABORATORY ANIMAL SCIENCE Torreilles, S. L., Green, S. L. 2007; 46 (5): 33-36

    Abstract

    The Guide for the Care and Use of Laboratory Animals recommends environmental enrichment for all laboratory animals, including amphibians. In this study, we evaluated the effect of adding environmental enrichment in the form of acrylonitrile- butadiene-styrene (ABS) pipes as covered refuge for laboratory Xenopus laevis housed in 2 pond-style tanks (capacity, 300 l; stocking density, approximately 150 frogs/tank; dimensions, 1.3 x 1.8 x 1.3 m). Medical records from animals housed in these 2 ponds between 1 January 2001 to 31 December 2003 revealed the incidence of bite wounds to be 5.0%, 4.0%, and 5.0% annually, respectively, and indicated 2 episodes of cannibalism (in 2003). In January 2004, we added ABS pipes as refuge housing to these tanks and continued to monitor the number of bite wounds and cannibalism. Over the following 24 mo (1 January 2004 to 1 January 2006), the incidence of bite wounds declined to 0.3% and 0.7% annually, respectively; no episodes of cannibalism were reported. The results of this investigation indicate that environmental enrichment in the form of ABS pipes for refuge cover has a quantifiable beneficial effect on the physical and social wellbeing of laboratory Xenopus laevis.

    View details for Web of Science ID 000252862500005

    View details for PubMedID 17877325

  • Ovarian hyperstimulation syndrome in gonadotropin-treated laboratory South African clawed frogs (Xenopus laevis) JOURNAL OF THE AMERICAN ASSOCIATION FOR LABORATORY ANIMAL SCIENCE Green, S. L., Parker, J., Davis, C., Bouley, D. M. 2007; 46 (3): 64-67

    Abstract

    Ovarian hyperstimulation syndrome (OHS) is a rare but sometimes fatal iatrogenic complication of ovarian stimulation associated with the administration of exogenous gonadotropins to women undergoing treatment for infertility. Laboratory Xenopus spp are commonly treated with human chorionic gonadotropin (hCG) to stimulate ovulation and optimize the number of oocytes harvested for use in biomedical research. Here we report cases of OHS in 2 gonadotropin-treated laboratory Xenopus laevis. After receiving hCG, the frogs developed severe subcutaneous accumulation of fluid, coelomic distention, and whole-body edema and were unable to dive, although they continued to eat and swim. At postmortem examination, extensive subcutaneous edema was present; ascites and massive numbers of free-floating eggs were found in the coelomic cavity and in aberrant locations: around the heart-sac and adhered to the liver capsule. Whole-body edema, gross enlargement of the ovaries, ascites, and abdominal distention are findings comparable to those observed in women with OHS. The pathophysiology of OHS is thought to be related to hormonally induced disturbances of vasoactive mediators, one of which may be vascular endothelial growth factor secreted by theca and granulosa cells. We know of no other report describing OHSlike symptoms in gonadotropin-treated frogs, and the cases described here are 2 of the 3 we have observed at our respective institutions over the last 6 y. According to these results, OHS appears to be rare in gonadotropin-treated laboratory Xenopus. However, the condition should be included in the differential diagnosis for the bloated frog.

    View details for Web of Science ID 000246535200013

    View details for PubMedID 17487957

  • Postoperative analgesics in South African clawed frogs (Xenopus laevis) after surgical harvest of oocytes COMPARATIVE MEDICINE GREEN, S. L. 2003; 53 (3): 244-247

    Abstract

    Heightened awareness for the welfare of earlier-evolved laboratory species has prompted increasing inquiries by institutional animal care committees, investigators, and laboratory animal veterinarians regarding the need for post-surgical analgesics in laboratory Xenopus. Basic research into the mechanisms and regulation of pain in Rana pipiens has demonstrated the clinical potential of opioid, alpha2-adrenergic, and non-opioid analgesic agents in amphibians. However, clinical studies using objectively established indices of amphibian pain, or pharmacological studies in either Rana pipiens or laboratory Xenopus have not been conducted. As discussed above, comparison of limited lethality data suggests that the safety index for these agents is quite narrow in Rana pipiens. Analgesic use in laboratory Xenopus has the added risk of drowning due to over sedation. Drug doses extrapolated from such studies and intended to provide pain relief in Xenopus should therefore be considered very carefully. An additional concern for laboratory Xenopus is that the effects of these agents on amphibian oogenesis, oocyte quality, and embryogenesis are unknown. As the numbers of laboratory Xenopus used in basic and biomedical research continues to increase, clinical studies that address all of these issues cannot come too soon.

    View details for Web of Science ID 000183932400003

    View details for PubMedID 12868565

  • Thermal shock in a colony of South African clawed frogs (Xenopus laevis) VETERINARY RECORD GREEN, S. L., Moorhead, R. C., Bouley, D. M. 2003; 152 (11): 336-?

    View details for Web of Science ID 000182199900015

    View details for PubMedID 12665149

  • Cryptosporidiosis associated with emaciation and proliferative gastritis in a laboratory-reared South African clawed frog (Xenopus laevis) COMPARATIVE MEDICINE GREEN, S. L., Bouley, D. M., Josling, C. A., Fayer, R. 2003; 53 (1): 81-84

    Abstract

    A 2-year-old emaciated female South African clawed frog (Xenopus laevis) was euthanized because of chronic weight loss. At necropsy, there was no evidence of bacterial, fungal or viral disease; however, the histopathologic findings indicated a proliferative gastritis and the presence of numerous cryptosporidial stages throughout the intestinal tract. Crytosporidial oocysts were present in the water taken from the aquarium housing the infected frog and were likely shed by the sick frog; however, the exact source of the oocysts could not be identified. Water samples from other frog aquaria in the facility did not contain cryptosporidial oocysts. Some Cryptosporidium species are important zoonotic pathogens and, to our knowledge, this is the first report of disease associated with Cryptosporidium infection in a laboratory Xenopus laevis.

    View details for Web of Science ID 000181240800011

    View details for PubMedID 12625511

  • Factors affecting oogenesis in the South African Clawed frog (Xenopus laevis) COMPARATIVE MEDICINE GREEN, S. L. 2002; 52 (4): 307-312

    Abstract

    Xenopus laevis, commonly known as the South African Clawed frog, is a hardy adaptable species that is relatively easy to maintain as a laboratory animal. Gametogenesis in wild Xenopus laevis is continuous and under ideal conditions, reproduction can occur year round. This unique aspect of amphibian reproduction offers an advantage over mammalian model systems: the eggs and oocytes collected from laboratory maintained Xenopus laevis provide an abundant and readily obtainable supply of material for cellular and biological research. However, many investigators report that laboratory Xenopus laevis go through periods of unexplained inefficient or complete failure of oocyte production or the production of poor quality oocytes. This results in experimental delays, inability to reproduce data, and ultimately the use of more animals. There is a lack of evidenced based information regarding the housing conditions that are necessary to optimize the health and fecundity of this species in captivity, but studies of wild Xenopus laevis have shown that temperature, age of the female, and nutrition are of key importance. The objective of this report is to review oogenesis with a special emphasis on these factors as they pertain to laboratory Xenopus laevis maintained for the purpose of providing a steady supply of eggs and oocytes. Harvesting methods and other experimental techniques that affect the quality of eggs and oocytes are also discussed.

    View details for Web of Science ID 000177674000005

    View details for PubMedID 12211272

  • Disease attributed to Mycobacterium chelonae in South African clawed frogs (Xenopus laevis) COMPARATIVE MEDICINE GREEN, S. L., Lifland, B. D., Bouley, D. M., Brown, B. A., Wallace, R. J., Ferrell, J. E. 2000; 50 (6): 675-679

    Abstract

    The fast-growing nontuberculous mycobacterial species Mycobacterium chelonae was isolated from six captive South African clawed frogs (Xenopus laevis) with chronic weight loss and nonhealing ulcerative skin lesions. Three of the M. chelonae isolates were evaluated to confirm the species identification using polymerase chain reaction restriction analysis. Disease associated with M. chelonae is reported mainly in people and in fish. To our knowledge, this is the first report of disease associated with M. chelonae in a colony of captive Xenopus sp.

    View details for Web of Science ID 000166363600020

    View details for PubMedID 11200577

Conference Proceedings


  • Identification and management of an outbreak of Flavobacterium meningosepticum infection in a colony of South African clawed frogs (Xenopus laevis) GREEN, S. L., Bouley, D. M., Tolwani, R. J., Waggie, K. S., Lifland, B. D., Otto, G. M., Ferrell, J. E. AMER VETERINARY MEDICAL ASSOC. 1999: 1833-?

    Abstract

    During the summer of 1996, an outbreak of Flavobacterium meningosepticum infection developed in a colony of South African clawed frogs (Xenopus laevis). Clinical signs were consistent with septicemia: ascites, anasarca, dyspnea, extreme lethargy, congestion of web vessels, petechial hemorrhages, and sudden death. Mortality rate reached 35%, and all infections were fatal. The organism was resistant to most antibiotics but was susceptible to enrofloxacin, chloramphenicol, and trimethoprim-sulfadiazine. Treatment with trimethoprim-sulfadiazine was unsuccessful. Although the point source of the infection was not determined, several environmental reservoirs were identified, including a communal water barrel and various pieces of equipment. Molecular strain typing by pulsed-field gel electrophoresis and biochemical analyses revealed that frogs were infected with a single strain of F meningosepticum. Sanitation and management procedures were effective in controlling the outbreak.

    View details for Web of Science ID 000080933900027

    View details for PubMedID 10382028

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