Fenbendazole resistance in Heterakis gallinarum, the vector of Histomonas meleagridis, on a broiler breeder farm in South Carolina.

Parasites are highly prevalent in poultry; thus, the management of parasites is a key component in the profitable production of poultry. The most common nematode parasite of poultry, Heterakis gallinarum, typically causes no direct pathology but is the vector of Histomonas meleagridis, a highly pathogenic protozoan parasite that causes blackhead disease. There are no approved treatments for H. meleagridis, making control reliant on controlling the helminth vector. In the United States, the benzimidazole anthelmintic fenbendazole (FBZ) is the only approved treatment for H. gallinarum. We were contacted by an industry veterinarian regarding clinical problems with histomoniasis despite frequent anthelmintic treatments. Given that we had recently diagnosed FBZ resistance in the closely related parasite Ascaridia dissimilis, we were interested to determine if H. gallinarum had also evolved resistance. An initial on-farm pilot study using 20 birds suggested that FBZ was poorly effective, therefore a larger controlled study was initiated. Heterakis gallinarum eggs were isolated from litter at the farm and used to infect 118 chicks. Treatment groups included a non-treated control, a label-, and a 2×-label dose of FBZ, with 36 birds per group divided into two replicates of 18 birds. Three weeks post-hatch, birds were infected with 150 embryonated eggs. Two weeks post-infection treated birds were administered either a label- or 2× label-dose of FBZ in water for five days (SafeGuard® Aquasol, 1 mg/kg BW). To increase the likelihood that all birds consumed the full intended dose, the dosage was calculated using 1.25 times the average body weight. One-week post-treatment, birds were euthanized, and parasites enumerated. There were no significant differences in worm numbers recovered from any of the three groups (p-value = 0.3426), indicating that both dosages of FBZ failed to provide the expected levels of efficacy. These data provide strong evidence that H. gallinarum has developed resistance to FBZ on this farm. Consequently, on this farm, or any farm with FBZ-resistant H. gallinarum, H. meleagridis will continue to cycle in an unrestricted manner despite administration of anthelmintic treatments. Given recent evidence of increasing problems with histomoniasis, and the fact that resistance was documented on the first farm we investigated, further investigations are needed to determine the prevalence of resistance in H. gallinarum on poultry farms. These data, when viewed together with our recent findings of FBZ resistance in A. dissimilis on multiple farms, suggest that drug resistance in ascarid nematodes may be an emerging problem in the US poultry industry.

Impact of fenbendazole resistance in Ascaridia dissimilis on the economics of production in turkeys.

Feed conversion efficiency is among the most important factors affecting profitable production of poultry.Infections with parasitic nematodes can decrease efficiency of production, making parasite control through the use of anthelmintics an important component of health management. In ruminants and horses, anthelmintic resistance is highly prevalent in many of the most important nematode species, which greatly impacts their control. Recently, we identified resistance to fenbendazole in an isolate of Ascaridia dissimilis, the most common intestinal helminth of turkeys. Using this drug-resistant isolate, we investigated the impact that failure to control infections has on weight gain and feed conversion in growing turkeys. Birds were infected on D 0 with either a fenbendazole-susceptible or -resistant isolate, and then half were treated with fenbendazole (SafeGuard Aquasol) at 4- and 8-wk postinfection. Feed intake and bird weight were measured for each pen weekly throughout the study, and feed conversion rate was calculated. Necropsy was performed on birds from each treatment group to assess worm burdens at wk 7 and 9 postinfection. In the birds infected with the susceptible isolate, fenbendazole-treated groups had significantly better feed conversion as compared to untreated groups. In contrast, there were no significant differences in feed conversion between the fenbendazole-treated and untreated groups in the birds infected with the resistant isolate. At both wk 7 and 9, worm burdens were significantly different between the treated and untreated birds infected with the drug-susceptible isolate, but not in the birds infected with the drug-resistant isolate. These significant effects on feed conversion were seen despite having a rather low worm establishment in the birds. Overall, these data indicate that A. dissimilis can produce significant reductions in feed conversion, and that failure of treatment due to the presence of fenbendazole-resistant worms can have a significant economic impact on turkey production. Furthermore, given the low worm burdens and an abbreviated grow out period of this study, the levels of production loss we measured may be an underestimate of the true impact that fenbendazole-resistant worms may have on a commercial operation.

Rare Event Analysis for Minimum Hellinger Distance Estimators via Large Deviation Theory.

Hellinger distance has been widely used to derive objective functions that are alternatives to maximum likelihood methods. While the asymptotic distributions of these estimators have been well investigated, the probabilities of rare events induced by them are largely unknown. In this article, we analyze these rare event probabilities using large deviation theory under a potential model misspecification, in both one and higher dimensions. We show that these probabilities decay exponentially, characterizing their decay via a "rate function" which is expressed as a convex conjugate of a limiting cumulant generating function. In the analysis of the lower bound, in particular, certain geometric considerations arise that facilitate an explicit representation, also in the case when the limiting generating function is nondifferentiable. Our analysis involves the modulus of continuity properties of the affinity, which may be of independent interest.

Resistance to fenbendazole in Ascaridia dissimilis, an important nematode parasite of turkeys.

An important factor in efficient production of poultry is management of parasites. Ascaridia dissimilis is the most prevalent small intestinal nematode parasite of turkeys with up to 100% of flocks infected. High worm burdens can cause necrotic enteritis leading to high mortality in flocks. Recently, we were made aware of multiple cases where high burdens were seen at slaughter despite the administration of anthelmintics at frequent intervals, suggesting that resistance may have evolved in A. dissimilis. To address this issue, we obtained eggs of A. dissimilis from 4 commercial turkey farms and performed controlled efficacy tests to determine if fenbendazole resistance was present. Three farms had histories of frequent use of fenbendazole and worms found at slaughter, suggesting they may have resistance, and one was an organic farm where we had no additional history other than the farm had transitioned to organic production a few years earlier. For each worm isolate there were 2 treated and 2 untreated groups containing 9 birds each, with all groups being replicated in 2 separate rooms. Birds were infected with approximately 200 infective eggs, and treated groups received fenbendazole in the water (SafeGuard Aquasol, 1 mg/kg) for 5 consecutive days starting on day 24 post-infection. One week after the last treatment birds were necropsied, intestinal contents were collected and worms enumerated. Three of the four isolates demonstrated greater than 99% efficacy, indicating they were fully susceptible to fenbendazole. However, the fourth isolate demonstrated a significantly reduced efficacy of 63.89%, indicating the presence of resistance. Interestingly, this was the organic farm, whereas the 3 farms with "suspected" resistance all turned out to be fully susceptible. Given that 1 randomly acquired isolate of A. dissimilis, out of 4 tested, demonstrated resistance in this study, fenbendazole resistance may be a much larger problem on turkey farms than is currently recognized. Additional studies are needed to determine the prevalence of resistance, as well as the economic impact that resistant A. dissimilis have on turkey production.

Robust Inference after Random Projections via Hellinger Distance for Location-Scale Family.

Big data and streaming data are encountered in a variety of contemporary applications in business and industry. In such cases, it is common to use random projections to reduce the dimension of the data yielding compressed data. These data however possess various anomalies such as heterogeneity, outliers, and round-off errors which are hard to detect due to volume and processing challenges. This paper describes a new robust and efficient methodology, using Hellinger distance, to analyze the compressed data. Using large sample methods and numerical experiments, it is demonstrated that a routine use of robust estimation procedure is feasible. The role of double limits in understanding the efficiency and robustness is brought out, which is of independent interest.

Comparison of fecal egg counting methods in four livestock species.

Gastrointestinal nematode parasites are important pathogens of all domesticated livestock species. Fecal egg counts (FEC) are routinely used for evaluating anthelmintic efficacy and for making targeted anthelmintic treatment decisions. Numerous FEC techniques exist and vary in precision and accuracy. These performance characteristics are especially important when performing fecal egg count reduction tests (FECRT). The objective of this study was to compare the accuracy and precision of three commonly used FEC methods and determine if differences existed among livestock species. In this study, we evaluated the modified-Wisconsin, 3-chamber (high-sensitivity) McMaster, and Mini-FLOTAC methods in cattle, sheep, horses, and llamas in three phases. In the first phase, we performed an egg-spiking study to assess the egg recovery rate and accuracy of the different FEC methods. In the second phase, we examined clinical samples from four different livestock species and completed multiple replicate FEC using each method. In the last phase, we assessed the cheesecloth straining step as a potential source of egg loss. In the egg-spiking study, the Mini-FLOTAC recovered 70.9% of the eggs, which was significantly higher than either the McMaster (P = 0.002) or Wisconsin (P = 0.002). In the clinical samples from ruminants, Mini-FLOTAC consistently yielded the highest EPG, revealing a significantly higher level of egg recovery (P < 0.0001). For horses and llamas, both McMaster and Mini-FLOTAC yielded significantly higher EPG than Wisconsin (P < 0.0001, P < 0.0001, P < 0.001, and P = 0.024). Mini-FLOTAC was the most accurate method and was the most precise test for both species of ruminants. The Wisconsin method was the most precise for horses and McMaster was more precise for llama samples. We compared the Wisconsin and Mini-FLOTAC methods using a modified technique where both methods were performed using either the Mini-FLOTAC sieve or cheesecloth. The differences in the estimated mean EPG on log scale between the Wisconsin and mini-FLOTAC methods when cheesecloth was used (P < 0.0001) and when cheesecloth was excluded (P < 0.0001) were significant, providing strong evidence that the straining step is an important source of error. The high accuracy and precision demonstrated in this study for the Mini-FLOTAC, suggest that this method can be recommended for routine use in all host species. The benefits of Mini-FLOTAC will be especially relevant when high accuracy is important, such as when performing FECRT.

A statistical approach for evaluating the effectiveness of heartworm preventive drugs: what does 100% efficacy really mean?

BACKGROUND: Initial studies of heartworm preventive drugs all yielded an observed efficacy of 100% with a single dose, and based on these data the US Food and Drug Administration (FDA) required all products to meet this standard for approval. Those initial studies, however, were based on just a few strains of parasites, and therefore were not representative of the full assortment of circulating biotypes. This issue has come to light in recent years, where it has become common for studies to yield less than 100% efficacy. This has changed the landscape for the testing of new products because heartworm efficacy studies lack the statistical power to conclude that finding zero worms is different from finding a few worms. METHODS: To address this issue, we developed a novel statistical model, based on a hierarchical modeling and parametric bootstrap approach that provides new insights to assess multiple sources of variability encountered in heartworm drug efficacy studies. Using the newly established metrics we performed both data simulations and analyzed actual experimental data. RESULTS: Our results suggest that an important source of modeling variability arises from variability in the parasite establishment rate between dogs; not accounting for this can overestimate the efficacy in more than 40% of cases. We provide strong evidence that ZoeMo-2012 and JYD-34, which both were established from the same source dog, have differing levels of susceptibility to moxidectin. In addition, we provide strong evidence that the differences in efficacy seen in two published studies using the MP3 strain were not due to randomness, and thus must be biological in nature. CONCLUSION: Our results demonstrate how statistical modeling can improve the interpretation of data from heartworm efficacy studies by providing a means to identify the true efficacy range based on the observed data. Importantly, these new insights should help to inform regulators on how to move forward in establishing new statistically and scientifically valid requirements for efficacy in the registration of new heartworm preventative products. Furthermore, our results provide strong evidence that heartworm 'strains' can change their susceptibility phenotype over short periods of time, providing further evidence that a wide diversity of susceptibility phenotypes exists among naturally circulating biotypes of D. immitis.

Validation of the FAMACHA© system in South American camelids.

Haemonchus contortus resistant to multiple anthelmintics threaten the viability of the small ruminant industry in areas where this parasite is prevalent. In response to this situation, the FAMACHA© system was developed and validated for use with small ruminants as a way to detect clinical anemia associated with haemonchosis. Given that H. contortus and multiple anthelmintic resistance is a similar problem in camelids, the FAMACHA© system might also provide the same benefits. To address this need, a validation study of the FAMACHA© system was conducted on 21 alpaca and llama farms over a 2-year period. H. contortus was the predominant nematode parasite on 17 of the 21 farms (10 alpaca and 7 llama farms) enrolled in the study, based on fecal culture results. The FAMACHA© card was used to score the color of the lower palpebral (lower eye lid) conjunctiva on a 1-5 scale. Packed cell volume (PCV) values were measured and compared to FAMACHA© scores using FAMACHA© score cutoffs of ≥3 or ≥4 and with anemia defined as a PCV ≤15%, ≤17%, or≤20%. PCV was significantly associated with FAMACHA© score, fecal egg count (FEC), and body condition score (BCS), regardless of the FAMACHA© cutoff score or the PCV% chosen to define clinical anemia (p<0.01 in all cases). The use of FAMACHA© scores ≥3 and PCV ≥ 15% indicating anemia provided the best sensitivity (96.4% vs 92.9% for FAMACHA© ≥4), whereas FAMACHA scores ≥ 4 and PCV ≤20% provided the best specificity (94.2% vs 69.1% for FAMACHA© ≥3). The data from this study support the FAMACHA© system as a useful tool for detecting clinical anemia in camelids suffering from haemonchosis. Parameters for making treatment decisions based on FAMACHA© score in camelids should mirror those established for small ruminants.

Serum Strongylus vulgaris-specific antibody responses to anthelmintic treatment in naturally infected horses.

Strongylus vulgaris is the most pathogenic helminth parasite of horses, causing verminous endarteritis with thromboembolism and infarction. A serum enzyme-linked immunosorbent assay (ELISA) has been validated for detection of antibodies to an antigen produced by migrating larvae of this parasite. The aim was to evaluate ELISA responses to anthelmintic treatment in cohorts of naturally infected horses. Fifteen healthy horses harboring patent S. vulgaris infections were turned out for communal grazing in May 2013 (day 0). On day 55, horses were ranked according to ELISA titers and randomly allocated to the following three groups: no treatment followed by placebo pellets daily; ivermectin on day 60 followed by placebo pellets daily; or ivermectin on day 60 followed by daily pyrantel tartrate. Fecal and serum samples were collected at ∼28-day intervals until study termination on day 231. Increased ELISA values were observed for the first 53 days following ivermectin treatment. Titers were significantly reduced 80 days after ivermectin treatment. Horses receiving daily pyrantel tartrate maintained lower ELISA values from 137 days post ivermectin treatment until trial termination. These results illustrate that a positive ELISA result is indicative of either current or prior exposure to larval S. vulgaris infection within the previous 5 months.

Assessing genome-wide statistical significance for large p small n problems.

Assessing genome-wide statistical significance is an important issue in genetic studies. We describe a new resampling approach for determining the appropriate thresholds for statistical significance. Our simulation results demonstrate that the proposed approach accurately controls the genome-wide type I error rate even under the large p small n situations.

An inconvenient truth: global worming and anthelmintic resistance.

Over the past 10-15 years, we have witnessed a rapid increase in both the prevalence and magnitude of anthelmintic resistance, and this increase appears to be a worldwide phenomenon. Reports of anthelmintic resistance to multiple drugs in individual parasite species, and in multiple parasite species across virtually all livestock hosts, are increasingly common. In addition, since the introduction of ivermectin in 1981, no novel anthelmintic classes were developed and introduced for use in livestock until recently with the launch of monepantel in New Zealand. Thus, livestock producers are often left with few options for effective treatment against many important parasite species. While new anthelmintic classes with novel mechanisms of action could potentially solve this problem, new drugs are extremely expensive to develop, and can be expected to be more expensive than older drugs. Thus, it seems clear that the "Global Worming" approach that has taken hold over the past 40-50 years must change, and livestock producers must develop a new vision for parasite control and sustainability of production. Furthermore, parasitologists must improve methods for study design and data analysis that are used for diagnosing anthelmintic resistance, especially for the fecal egg count reduction test (FECRT). Currently, standards for diagnosis of anthelmintic resistance using FECRT exist only for sheep. Lack of standards in horses and cattle and arbitrarily defined cutoffs for defining resistance, combined with inadequate analysis of the data, mean that errors in assigning resistance status are common. Similarly, the lack of standards makes it difficult to compare data among different studies. This problem needs to be addressed, because as new drugs are introduced now and in the future, the lack of alternative treatments will make early and accurate diagnosis of anthelmintic resistance increasingly important.

Effects of topical 2% dorzolamide hydrochloride alone and in combination with 0.5% timolol maleate on intraocular pressure in normal feline eyes.

OBJECTIVE: To evaluate the effect of topical 2% dorzolamide alone, and in combination with topical 0.5% timolol, on intraocular pressure (IOP) in normal cats. ANIMALS: Twenty-four healthy Domestic Short-haired cats. PROCEDURE: Baseline values of IOP were established at 7 am, 10 am, 1 pm, 5 pm and 9 pm during pretreatment phase (days 1-2). During treatment phase (days 3-10) cats received 2% dorzolamide HCl q 12 h in group A (n = 6), q 8 h in group B (n = 6), and combined with 0.5% timolol maleate q 12 h in group C (n = 6). Cats in control group D (n = 6) received artificial tears q 8 h. During treatment phase IOP measurements were continued at the same time-points as in the pretreatment phase. RESULTS: Mean pretreatment IOP in all cats was 18.46 +/- 2.99 mmHg. Mean IOP decreased significantly (P < 0.0086) in all treatment groups compared to pretreatment values (group A: 16.40 +/- 0.49 mmHg, group B: 16.04 +/- 0.49 mmHg, group C: 17.76 +/- 0.49 mmHg). IOP did not decrease in control group D (18.55 +/- 0.49 mmHg). The difference in IOP between treatment groups (A, B, C) was not statistically significant, but comparison of IOP between each treatment group and the control group was statistically significant (A-D; P = 0.0057; B-D, P = 0.0012; C-D, P = 0.0212). CONCLUSION: Topical 2% dorzolamide significantly lowers IOP in normal cats but the effect is mild. Concomitant application of 2% dorzolamide and 0.5% timolol does significantly decrease IOP, but the effect is not significantly greater than q 8 h administration of dorzolamide alone.

Quality of different in-clinic test systems for feline immunodeficiency virus and feline leukaemia virus infection.

Many new diagnostic in-house tests for identification of feline immunodeficiency virus (FIV) and feline leukaemia virus (FeLV) infection have been licensed for use in veterinary practice, and the question of the relative merits of these kits has prompted comparative studies. This study was designed to define the strengths and weaknesses of seven FIV and eight FeLV tests that are commercially available. In this study, 536 serum samples from randomly selected cats were tested. Those samples reacting FIV-positive in at least one of the tests were confirmed by Western blot, and those reacting FeLV-positive were confirmed by virus isolation. In addition, a random selection of samples testing negative in all test systems was re-tested by Western blot (100 samples) and by virus isolation (81 samples). Specificity, sensitivity, positive and negative predictive values of each test and the quality of the results were compared.

Evaluation of three different histamine concentrations in intradermal testing of normal cats and attempted determination of 'irritant' threshold concentrations for 48 allergens.

The purpose of this study was to determine the optimal histamine concentration and 'irritant' allergen threshold concentrations in intradermal testing (IDT) in normal cats. Thirty healthy cats were tested with three different histamine concentrations and four different concentrations of each allergen. The optimal histamine concentration was determined to be 1: 50,000 w/v (0.05 mg mL(-1)). Using this histamine concentration, the 'irritant' threshold concentration for most allergens was above the highest concentrations tested (4,000 PNU mL(-1) for 41 allergens and 700 PNU mL(-1) for human dander). The 'irritant' threshold concentration for flea antigen was determined to be 1:750 w/v. More than 10% of the tested cats showed positive reactions to Dermatophagoides farinae, Dermatophagoides pteronyssinus, housefly, mosquito and moth at every allergen concentration, which suggests that the 'irritant' threshold concentration for these allergens is below 1,000 PNU mL(-1), the lowest allergen concentration tested. Our results confirm previous studies in indicating that allergen and histamine concentrations used in feline IDT may need to be revised.

Renal evaluation in the healthy green iguana (Iguana iguana): assessment of plasma biochemistry, glomerular filtration rate, and endoscopic biopsy.

Plasma biochemistry, iohexol clearance, endoscopic renal evaluation, and biopsy were performed in 23 clinically healthy 2-yr-old green iguanas (Iguana iguana). Mean (+/- SD) values for packed cell volume (30 +/- 3%), total protein (62 +/- 7 g/L, 6.2 +/- 0.7 g/dl), albumin (25 +/- 2 g/L, 2.5 +/- 0.2 g/dl), globulin (37 +/- 6 g/L, 3.7 +/- 0.6 g/ dl), total calcium (3.0 +/- 0.2 mmol/L, 12.0 +/- 0.7 mg/dl), ionized calcium (1.38 +/- 0.1 mmol/L), phosphorus (1.32 +/- 0.28 mmol/L, 4.1 +/- 0.9 mg/dl), uric acid (222 +/- 100 micromol/L, 3.8 +/- 1.7 mg/dl), sodium (148 +/- 3 mmol/L or mEq/ L), and potassium (2.6 +/- 0.4 mmol/L or mEq/L) were considered within normal limits. Values for urea were low (< 1.4 mmol/L, < 4 mg/dl) with 70% of samples below the detectable analyzer range. After the i.v. injection of 75 mg/ kg iohexol into the caudal (ventral coccygeal or tail) vein, serial blood collections were performed over 32 hr. Iohexol assays by high-performance liquid chromatography produced plasma iohexol clearance graphs for each lizard. A three-compartment model was used to fit area under the curve values and to obtain the glomerular filtration rate (GFR) using regression analysis. The mean GFR (SD) was 16.56 +/- 3.90 ml/kg/hr, with a 95% confidence interval of 14.78-18.34 ml/kg/hr. Bilateral endoscopic renal evaluation and biopsy provided tissue samples of excellent diagnostic quality, which correlated with tissue harvested at necropsy and evaluated histologically. None of the 23 animals demonstrated any adverse effects of iohexol clearance or endoscopy. Recommended diagnostics for the evaluation of renal function and disease in the green iguana include plasma biochemical profiles, iohexol clearance, endoscopic examination, and renal biopsy.

Prevalence of anthelmintic resistant cyathostomes on horse farms.

OBJECTIVE: To determine prevalence of anthelmintic resistance in cyathostome nematodes of horses in the southern United States. DESIGN: Cross-sectional study. ANIMALS: 786 horses on 44 farms and stables in Georgia, South Carolina, Florida, Kentucky, and Louisiana. PROCEDURE: Fecal egg count (FEC) reduction tests were performed on 44 large farms and stables. Horses on each farm were treated with an oral paste formulation of fenbendazole, oxibendazole, pyrantel pamoate, or ivermectin at recommended label dosages. A mixed linear model was fitted to the percentage reduction in FEC, accounting for differences among farms, states, ages, treatments, and treatment by state interactions. RESULTS: By use of a conservative measure of resistance (< 80% reduction), the percentage of farms with anthelmintic-resistant cyathostomes was 97.7%, 0%, 53.5%, and 40.5% for fenbendazole, ivermectin, oxibendazole, and pyrantel pamoate, respectively. Mean percentage reductions in FEC for all farms were 24.8%, 99.9%, 73.8%, and 78.6% for fenbendazole, ivermectin, oxibendazole, and pyrantel pamoate, respectively. Pairwise contrasts between states for each treatment revealed that in almost all instances, there were no significant differences in results between states. CONCLUSIONS AND CLINICAL RELEVANCE: The prevalence of resistance found in this study was higher than that reported previously, suggesting that anthelmintic resistance in equine cyathostomes is becoming a major problem. Furthermore, data from these 5 southern states, which are geographically and physiographically distinct, were remarkably similar. This suggests that drug resistance in cyathostomes is highly prevalent throughout the entire southern United States and probably nationwide.

Determination of threshold concentrations of allergens and evaluation of two different histamine concentrations in canine intradermal testing.

The purpose of this study was to determine the optimal histamine concentration and allergen threshold concentrations for canine intradermal testing. Thirty healthy dogs were tested using two different concentrations of histamine and four different concentrations of each allergen. The optimal histamine concentration was determined to be 1:10 000 w/v. The threshold concentration was at least 1750 PNU/mL for all tested grasses, weeds, trees, moulds and insects, except for fleas which was as least 1:500 w/v. For Dermatophagoides pteronyssinus, the optimal threshold concentration was 250 PNU/mL, whereas for Dermatophagoides farinae and Tyrophagus putrescentiae, it was 100 PNU/mL. Threshold concentration for all epidermals except human dander was at least 1250 PNU/mL. The optimal threshold concentration for human dander was 300 PNU/mL. Our results suggest that the currently used 1:100 000 w/v concentration of histamine and the 1000 PNU/mL concentration for most grasses, weeds, trees, moulds, epidermals and insects may not be appropriate for canine intradermal testing.

Effects of treatment with and without adjuvant radiation therapy on recurrence of ocular and adnexal squamous cell carcinoma in horses: 157 cases (1985-2002).

OBJECTIVE: To determine the effects of treatment with and without adjuvant radiation therapy on recurrence of ocular and adnexal squamous cell carcinoma (SCC) at specific anatomic locations in horses. DESIGN: Retrospective study. ANIMALS: 91 horses. PROCEDURES: Medical records of horses with histologically confirmed ocular and adnexal SCC evaluated from 1985 to 2002 were reviewed. Sex, breed, age, type of treatment, location, and recurrence of SCC were recorded. Two treatment groups determined by recurrence of SCCs treated with and without adjuvant radiation therapy were established. RESULTS: The anatomic site with the highest recurrence rate was the limbus (junction of the cornea and sclera) or bulbar conjunctiva (477%), independent of treatment group. There was a significant difference in recurrence rates of ocular and adnexal SCCs between the 2 treatment groups, independent of anatomic location. Recurrence rates of SCCs treated with and without adjuvant radiation therapy were 11.9% and 44.1%, respectively. Recurrence rates for SCCs of the eyelid, limbus or bulbar conjunctiva, and cornea treated with adjuvant radiation therapy were significantly different from those for SCCs treated without adjuvant radiation therapy. The most frequently represented anatomic site for ocular and adnexal SCCs was the eyelid (28.7%). Coat color, breed, and the interaction of age and breed had a significant effect on tumor recurrence regardless of treatment type and anatomic location. CONCLUSIONS AND CLINICAL RELEVANCE: Results indicated that ocular and adnexal SCCs treated with adjuvant radiation therapy had a significantly lower recurrence rate, compared with SCCs treated without adjuvant radiation therapy, independent of anatomic location.

Effects of transcorneal iridal photocoagulation on the canine corneal endothelium using a diode laser.

OBJECTIVE: To investigate the potential damage to the canine corneal endothelium following transcorneal iridal laser photocoagulation using a semiconductor diode laser. ANIMALS STUDIED: Sixteen young mongrel dogs. PROCEDURES: Baseline corneal endothelial cell counts and corneal thickness were measured in the central and temporal quadrants using a noncontact specular microscope under general anesthesia. Transcorneal iridal photocoagulation was applied using a semiconductor diode laser in a continuous mode with the use of an operating microscope. Fifteen dogs were treated, and the sixteenth dog served as a control. Fifteen different treatment combinations were randomly assigned to the 30 eyes; the fellow eye was treated differently. Three treatment factors were investigated: (1) laser energy intensity, (2) target tissue to endothelial distance, and (3) laser application duration. After 3 weeks the dogs were euthanized, specular microscopy was repeated, and the cornea was examined by scanning electron microscopy. RESULTS: Dyscoria and focal iris darkening were noted in all eyes immediately following laser treatment. Focal corneal edema (n = 2) and an incipient anterior capsular cataract (n = 1) were also noted. Baseline mean corneal endothelial cell densities were 2530 cells/mm2 centrally and 2607 cells/mm2 temporally. Postlaser corneal endothelial cell densities were 2499 cells/mm2 centrally and 2523 cells/mm2 temporally. Mean prelaser corneal thickness measurements were 0.555 mm centrally and 0.549 mm temporally. Postlaser corneal thickness measurements were 0.580 mm centrally and 0.554 mm temporally. Statistical analyzes revealed no significant changes in endothelial cell densities (P > 0.05) or corneal thickness (P > 0.05) induced by any treatment combination. Aside from tissue handling and processing artifacts, scanning electron microscopy revealed no endothelial cell damage. CONCLUSIONS: Our study demonstrated by specular and scanning electron microscopy that diode laser iridal photocoagulation had no significant effect on the canine corneal endothelium within the parameters described. However, one must take into consideration the young age of the dogs and the potential for corneal endothelial cell regeneration in young dogs, and the relatively short period of postoperative study.