Transfection of non-susceptible cells with Ovis aries recombinant lymphocyte function-associated antigen 1 renders susceptibility to Mannheimia haemolytica leukotoxin

Mannheimia haemolytica is an important etiological agent of pneumonia in domestic sheep (DS, Ovis aries). Leukotoxin (Lkt) produced by this organism is the principal virulence factor responsible for the acute inflammation and lung injury characteristic of M. haemolytica caused disease. Previously, we have shown that the leukocyte-specific integrins, beta(2) integrins, serve as the receptor for Lkt. Although it is certain that CD18, the beta subunit of beta(2) integrins, mediates Lkt-induced cytolysis of leukocytes, it is not clear whether CD18 of all three beta(2) integrins, LFA-1, Mac-1 and CR4, mediates Lkt-induced cytolysis of DS leukocytes. Since polymorphonuclear leukocytes, which express all three beta(2) integrins, are the leukocyte subset that is most susceptible to Lkt, we hypothesized that all three beta(2) integrins serve as the receptor for Lkt. The objective of this study was to determine whether DS LFA-1 serves as a receptor for M. haemolytica Lkt. We cloned the cDNA for DS CD11a, the alpha subunit of LFA-1, and co-transfected it along with the previously cloned cDNA for DS CD18, into a Lkt-non-suceptible cell line. Transfectants stably expressing DS LFA-1 were bound by Lkt. More importantly, Lkt lysed the DS LFA-1 transfectants in a concentration-dependent manner. Pre-incubation of Lkt with a Lkt-neutralizing monoclonal antibody (MAb), or pre-incubation of transfectants with MAbs specific for DS CD11a or CD18, inhibited Lkt-induced cytolysis of the transfectants. Exposure of LFA-1 transfectants to low concentrations of Lkt resulted in elevation of intracellular [Ca(2+)](i). Taken together, these results indicate that DS LFA-1 serves as a receptor for M. haemolytica Lkt.     

Safety of an attenuated West Nile virus vaccine, live Flavivirus chimera in horses

REASON FOR PERFORMING STUDY: West Nile virus (WNV) infection is endemic and able to cause disease in naive hosts. It is necessary therefore to evaluate the safety of new vaccines. OBJECTIVES: To establish: 1) the safety of a modified live Flavivirus/West Nile virus (WN-FV) chimera by administration of an overdose and testing for shed of vaccine virus and spread to uninoculated sentinel horses; 2) that this vaccine did not become pathogenic once passaged in horses; and 3) vaccine safety under field conditions. METHODS: There were 3 protocols: 1) In the overdose/shed and spread study, horses were vaccinated with a 100x immunogenicity overdose of WN-FV chimera vaccine and housed with sentinel horses. 2) A reversion to virulence study, where horses were vaccinated with a 20x immunogenicity overdose of WN-FV chimera vaccine. Horses in both studies were evaluated for abnormal health conditions and samples obtained to detect virus, seroconversion and dissemination into tissues. 3) In a field safety test 919 healthy horses of various ages, breeds and sex were used. RESULTS: Vaccination did not result in site or systemic reactions in either experimental or field-injected horses. There was no shed of vaccine virus, no detection of vaccine virus into tissue and no reversion to virulence with passage. CONCLUSIONS: WN-FV chimera vaccine is safe to use in horses with no evidence of ill effects from very high doses of vaccine. There was no evidence of reversion to virulence. In addition, administration of this vaccine to several hundred horses that may have been previously exposed to WNV or WNV vaccine resulted in no untoward reactions. POTENTIAL RELEVANCE: These studies establish that this live attenuated Flavivirus chimera is safe to use for immunoprophylaxis against WNV disease in horses.     

Interpretation of serum antibody response to Anoplocephala perfoliata in relation to parasite burden and faecal egg count

REASON FOR PERFORMING STUDY: Increased knowledge is needed to assist in the interpretation of presently available diagnostic techniques for infection by the tapeworm Anoplocephala perfoliata in horses. HYPOTHESIS: The suggested cut-off level of an A. perfoliata specific ELISA may not adequately reflect the actual infection level. Hence, faecal egg counts may be a more useful diagnostic test for individual horses than previously reported. METHODS: Eighty-four horses admitted for slaughter at a Danish abattoir were examined for the presence of A. perfoliata. The number of tapeworms, their stage of development and gross pathological mucosal lesions were recorded and compared with serum antibody responses and faecal egg counts. Faecal egg counts were determined in samples from A. perfoliata infected horses using a semi quantitative centrifugation/flotation technique. Blood samples collected at slaughter were analysed by ELISA to determine serum antibody levels against A. perfoliata 12/13 kDa excretory/secretory antigens. RESULTS: Macroscopically visible tapeworms were detected in 24 (29%) of the horses. The overall sensitivity of the faecal egg count was found to be 0.46; however, if the detection limit was increased to above 20 tapeworms, sensitivity increased to 0.89. There was a correlation of 0.71 between worm burden and egg count. The antibody levels correlated significantly with infection intensity despite a wide variation among horses with similar levels of infection. The optimal cut-off value was determined using receiver operating characteristic analysis. If cut-off was chosen at optical density (OD) = 0.7, sensitivity was 0.68 and specificity 0.71. CONCLUSIONS: Both diagnostic methods were capable of revealing potentially pathogenic infections, with the faecal egg count being more applicable on the individual horse level. POTENTIAL RELEVANCE: In the population of Danish horses investigated the serum ELISA test should be interpreted such that horses in need of anti-Anoplocephala treatment have an OD = 0.7 or above.     

The efficacy of a single chain recombinant equine luteinizing hormone (reLH) in mares: induction of ovulation, hormone profiles, and inter-ovulatory intervals

The objectives of this study were to determine the efficacy of recombinant equine luteinizing hormone (reLH) in shortening the time to ovulation in cycling mares and to determine the effects of treatment on endogenous hormones and inter-ovulatory intervals. In study 1, mares of light horse breeds (3–20 years) were treated with either a vehicle, various doses of reLH, or human chorionic gonadotropin (hCG). Cycling mares were examined by palpation and ultrasound per rectum daily or every 12 h from the time of treatment to ovulation. In studies 2 and 3, jugular blood samples were collected daily or every 12 h from the time of treatment to ovulation for analysis of LH, follicle stimulating hormone (FSH), estradiol-17β (E₂), and progesterone (P₄) by radioimmunoassays (RIA). Increasing doses of reLH (0.3, 0.6, 0.75, and 0.9 mg) showed increasing effectiveness at inducing ovulation within 48 h of treatment. Treatments with the 0.75 and 0.9 mg doses of reLH resulted in 90% and 80% ovulation rates, which were similar to hCG treatment (85.7%). Except for the early rise in LH after treatment with 0.5, 0.65, and 1.0 mg of reLH, hormone profiles appeared to be similar between control and treated cycles. Inter-ovulatory intervals were similar between control and treatment cycles. In conclusion, reLH is a reliable and effective ovulatory agent that does not significantly alter endogenous hormone profiles or affect inter-ovulatory intervals.     

Bacteraemia in neonatal foals: clinicopathological differences between Gram-positive and Gram-negative infections, and single organism and mixed infections

REASONS FOR PERFORMING STUDY: Treatment for bacteraemia in foals must be started before the identity of the causative organism is known. Information aiding selection of effective antimicrobials should improve outcome. OBJECTIVES: To describe differences in clinical and clinicopathological data and outcome in foals with bacteraemia due to different classes of bacteria. METHODS: Records of foals with a positive blood culture, age < 10 days and presenting to a university hospital 1995-2004, were reviewed. Bacterial culture results, subject details, historical information, physical examination findings at admission and clinicopathological data generated during the first 48 h of hospitalisation were analysed. Results from foals with Gram-positive or Gram-negative organisms, single or mixed organism bacteraemias, and with bacteraemia due to 3 commonly isolated organisms were compared. RESULTS: Eighty-five foals met the inclusion criteria. Gram-negative organisms (n = 59) Gram-positive organisms (n = 13) or multiple organisms (n = 19) were cultured from individual foals. Foals with Gram-negative bacteraemia had lower total white blood cell and lymphocyte counts at admission than did those from which only Gram-positive bacteria were cultured. Mixed organism bacteraemia was associated with tachycardia, increased serum concentrations of sodium, chloride and urea nitrogen, acidosis, respiratory distress, recumbency on admission and nonsurvival. Actinobacillus spp. infections were associated with leucopenia, neutropenia, lymphopenia and depression on hospital admission. CONCLUSIONS AND POTENTIAL RELEVANCE: Recognising particular patterns of clinical and clinicopathological findings associated with infection with specific groups of bacteria may, in the future, aid antimicrobial selection and influence prognosis in bacteraemic foals.     

Mesenchymal stem cell therapy in equine musculoskeletal disease: scientific fact or clinical fiction?

The goal in the therapeutic use of mesenchymal stem cells (MSCs) in musculoskeletal disease is to harness the regenerative nature of these cells focussing on their potential to grow new tissues and organs to replace damaged or diseased tissue. Laboratory isolation of MSCs is now well established and has recently been demonstrated for equine MSCs. Stem cell science has attracted considerable interest in both the scientific and clinical communities because of its potential to regenerate tissues. Research into the use of MSCs in tissue regeneration in general reflects human medical needs, however, the nature, prevalence and prognosis of superficial digital flexor tendonitis has put equine veterinary science at the forefront of tendon regeneration research. Much has been investigated and learnt but it must be appreciated that in spite of this, the field is still relatively young and both communities must prepare themselves for considerable time and effort to develop the technology into a highly efficient treatments. The promise of functional tissue engineering to replace old parts with new fully justifies the interest. At present, however, it is important to balance the understanding of our current limitations with a desire to progress the technology.     

Thyroid imaging in the dog: current status and future directions

This review describes the advantages and disadvantages of radiography, ultrasonography, and nuclear medicine in the 2 most frequent thyroid pathologies of the dog: acquired primary hypothyroidism and thyroid neoplasia. Ultrasonography and scintigraphy remain the 2 most indicated imaging modalities for these thyroid abnormalities. However, as in human medicine, computed tomography and magnetic resonance imaging also have potential indications. This is especially the case in the evaluation of the extent, local invasiveness, and local or distant metastases of thyroid neoplasia. Based on experience with different imaging modalities in people, we suggest future directions in the imaging of the canine thyroid gland.     

Clinical, histopathological and therapeutic considerations in a flock of sheep with facial staphylococcal-associated dermatitis

In a flock of 290 sheep, a total of 20 ewes (6.9%) with an age range of 1.5-4 years, developed a nonpruritic dermatitis characterized by alopecia/hypotrichosis, erythema, hyperpigmentation, crusting, superficial ulcers, exudation and thickening of the skin that was localized mainly to the peri-ocular area. Frequent and massive feeding of swarming sucking flies on the lesional sites was witnessed. In every instance (n = 6), Staphylococcus aureus was cultured from the exudate and the aseptically obtained skin biopsy samples from both recurrent and new cases. The main predisposing factor was the presence of small troughs, which forced the sheep to compete for food. Intramuscular administration of cefalexin for 7 days resulted in the resolution of lesions over a 2-week period. No further cases or recurrences were seen over the 16-month follow-up period. The main histopathological feature of this skin disease was a superficial and deep, perivascular to interstitial eosinophilic and mononuclear dermatitis.     

Efficacy of topical eprinomectin in the treatment of Chorioptes sp. infestation in alpacas and llamas

Chorioptes sp. mite infestation is increasingly recognized as a cause of skin disease in New World camelids and there is a need for an effective treatment protocol to eliminate herd infestation. In this field trial, eprinomectin applied topically at the rate of 0.5 mg kg(-1) weekly for 10 weeks was found to be ineffective in a herd of 12 llamas and 16 alpacas.