Viral interference with MHC class I antigen presentation pathway: the battle continues

CD8+ cytotoxic T lymphocytes (CTLs) play a critical role in the defense against viral infections. In general, CD8+ CTLs recognize antigenic peptides in the context of the major histocompatibility complex (MHC) class I molecule. The MHC class I molecules are expressed on almost all the nucleated cells in the body. The trimolecular complex consisting of the class I heavy chain, beta2-microglobulin and the peptide are generated by the MHC class I antigen presentation pathway. This pathway is designed to sample the intracellular milieu and present the information to the CTLs trafficking the area. This rigorous sampling of intracellular environment enables the CTLs to quickly identify and eliminate the cells that synthesize non-self proteins as a result of a viral infection. Many viruses, including several viruses of veterinary importance, have evolved astounding strategies to interfere with the MHC class I antigen presentation pathway, as a means of evading the CTL response of the host. This review focuses on the diverse mechanisms of viral evasion of the MHC class I antigen presentation pathway with particular emphasis on viruses of veterinary importance.     

Characterization of renal defects in dogs with a syndrome similar to the Fanconi syndrome in man.

Ten adult dogs with multiple spontaneous defects of renal tubular reabsorption were studied. Clinical signs included polydipsia, polyuria, and glycosuria for 2 to 12 months. Eight of the dogs were Basenjis. Urinalyses revealed hyposthenuria, glycosuria, and amino aciduria in most dogs. Renal function was normal in 5 dogs and slightly reduced in the remainder. Moderate metabolic acidosis had developed in 3 dogs. Renal clearance studies revealed reduced tubular reabsorption of glucose, phosphate, sodium, potassium, and uric acid. Abnormal glucose tubular maximal curves were found. Results of oral glucose tolerance tests were normal. Two patterns of abnormal amino aciduria were evident: generalized amino aciduria and a pattern similar to that of cystinuria in dogs. Radiography of long bones and bone densitometry did not reveal any skeletal abnormalities. Five of the dogs died within 90 days of diagnosis; death was due to acute renal failure associated with profound dehydration, acidosis, and papillary necrosis. The other dogs remained stable without treatment after 18 months. Histopathology of kidneys did not reveal uniform abnormalities; some dogs had variable and nonspecific changes and others were normal. Electron microscopy did not reveal ultrastructural abnormalities in renal tubular cells. It was concluded that the syndrome in these dogs represents a new entity of renal disease in dogs, similar to idiopathic Fanconi syndrome in man.     

Enhancement of bromophenol levels in aquacultured silver seabream (Sparus sarba)

The effect of the addition of marine algae in fish feed on the levels of bromophenols in fish flesh was studied. These bromophenols include 2-bromophenol, 4-bromophenol, 2,4-dibromophenol, 2,6-dibromophenol, and 2,4,6-tribromophenol. Two types of algae-containing fish feeds with 30% Padina arborescens and 30% Sargassum siliquastrum were developed. The total bromophenol contents of these feeds were 132 and 340 ng/g respectively, which were significantly higher than that of the control feed (8.9 ng/g) (ANOVA, p < 0.05). Silver seabream was used as the model fish for the feeding experiment. Bromophenol contents of both fish gut and flesh were monitored at 2-week intervals throughout the 8-week period. Two-way ANOVA showed that only the 30% S. siliquastrum-containing feed significantly (p < 0.05) increased the total bromophenol content in the fish flesh with time. This also produced sensorial differences in the fish flesh.     

Community-associated methicillin-resistant Staphylococcus aureus in horses and humans who work with horses

OBJECTIVE: To evaluate the prevalence of nasal colonization with methicillin-resistant Staphylococcus aureus (MRSA) in horses and horse personnel. DESIGN: Prospective prevalence study. SAMPLE POPULATION: 972 horses and 107 personnel from equine farms in Ontario, Canada and New York state. PROCEDURE: Nasal swab specimens were collected from horses and humans on farms with (targeted surveillance) and without (nontargeted surveillance) a history of MRSA colonization or infection in horses during the preceding year. Selective culture for MRSA was performed. Isolates were typed via pulsed-field gel electrophoresis, and antibiograms were determined. RESULTS: MRSA was isolated from 46 of 972 (4.7%) horses (0/581 via nontargeted surveillance and 46/391 [12%] via targeted surveillance). Similarly, MRSA was isolated from 14 of 107 (13%) humans (2/41 [5%] from nontargeted surveillance and 12/66 [18%] from targeted surveillance). All isolates were subtypes of Canadian epidemic MRSA-5, an uncommon strain in humans. All isolates were resistant to at least 1 antimicrobial class in addition to beta-lactams. On all farms with colonized horses, at least 1 human was colonized with an indistinguishable subtype. For horses, residing on a farm that housed > 20 horses was the only factor significantly associated with MRSA colonization. For humans, regular contact with > 20 horses was the only identified risk factor. CONCLUSIONS AND CLINICAL RELEVANCE: Results confirm a reservoir of colonized horses on a variety of farms in Ontario and New York and provide evidence that 1 MRSA strain is predominantly involved in MRSA colonization in horses and humans that work with horses.     

Mycobacterium avium infection in a farmed deer herd

Tuberculous lesions were identified over a 2-year period in 36 clinically normal red deer from a single herd. The lesions were only present in the retropharyngeal lymph nodes and lymph nodes draining the intestinal tract, indicating infection by the oral route. Mycobacterium avium was isolated from 27 of 29 lesions examined by bacterial culture. Grossly and histologically, the lesions were indistinguishable from those caused by Mycobacterium bovis. DNA restriction endonuclease analysis revealed that all the 26 M. avium isolates available for examination had identical cleavage patterns. These patterns were identical to a New Zealand M. avium serotype 2 isolate from a pig and were very similar to a reference strain of M. avium serotype 2. The DNA examinations indicated that the deer were infected from a common source that was not identified.     

Actinomycin D as rescue therapy in dogs with relapsed or resistant lymphoma: 49 cases (1999--2006)

OBJECTIVE: To evaluate response rate and disease-free interval in dogs with relapsed or resistant lymphoma treated with actinomycin D, determine hematologic toxicoses, and identify prognostic factors associated with response to treatment. DESIGN: Retrospective case series. ANIMALS: 49 dogs with relapsed or resistant lymphoma. PROCEDURES: Medical records were reviewed for information regarding signalment, physical examination findings, results of diagnostic testing, substage, previous chemotherapy, previous treatment with prednisone, actinomycin D dosage, number of doses administered, response, disease-free interval, and results of CBCs performed after treatment. RESULTS: Actinomycin D was administered at a median dosage of 0.68 mg/m2 (range, 0.46 to 0.72 mg/m2), IV, every 3 weeks for 5 treatments or until disease progression. Twenty-six (53%) dogs received prednisone concurrently. Twenty (41%) dogs had a complete remission, and median disease-free interval in these dogs was 129 days. Thrombocytopenia was the most common hematologic toxicosis (n = 22 [45%]). Concurrent prednisone administration, a shorter duration of first remission, and an increased number of previous chemotherapy agents were significantly associated with a lower likelihood of responding to actinomycin D treatment. Concurrent prednisone administration and an increased number of previous chemotherapy agents were significantly associated with a shorter disease-free interval. CONCLUSION AND CLINICAL RELEVANCE: Results suggested that administration of actinomycin D as a single agent was effective for rescue chemotherapy of dogs with relapsed or resistant lymphoma and that treatment was well tolerated, although mild thrombocytopenia developed commonly.     

Salmonella,Campylobacter, Clostridium difficile,and anti‐microbial resistant Escherichia coli in the faeces of sympatric meso‐mammals in southern Ontario,Canada

The role of free‐ranging wildlife in the epidemiology of enteropathogens causing clinical illness in humans and domestic animals is unclear. Salmonella enterica and anti‐microbial resistant bacteria have been detected in the faeces of raccoons (Procyon lotor), but little is known about the carriage of these bacteria in other sympatric meso‐mammals. Our objectives were to: (a) report the prevalence of Salmonella and associated anti‐microbial resistance, Campylobacter spp, Clostridium difficile, and anti‐microbial resistant Escherichia coli in the faeces of striped skunks (Mephitis mephitis) and Virginia opossums (Didelphis virginiana) in southern Ontario; and (b) compare the prevalence of these bacteria in the faeces of these meso‐mammal hosts with raccoons from a previously reported study. Faecal swabs were collected from striped skunks and Virginia opossums on five swine farms and five conservation areas from 2011 to 2013. Salmonella was detected in 41% (9/22) and 5% (5/95) of faecal swabs from Virginia opossums and striped skunks, respectively. None of the Salmonella serovars carried resistance to anti‐microbials. The prevalence of Campylobacter spp., C. difficile, and anti‐microbial resistant E. coli ranged from 6% to 22% in striped skunk and Virginia opossums. Using exact logistic regression, Salmonella was significantly more likely to be detected in faecal swabs of Virginia opossums than skunks and significantly less likely in faecal swabs from skunks than raccoons from a previously reported study. In addition, Campylobacter spp. was significantly more likely to be detected in raccoons than opossums. Salmonella Give was detected in 8/9 (89%) of Salmonella‐positive Virginia opossum faecal swabs. Our results suggest that striped skunks and Virginia opossums have the potential to carry pathogenic enteric bacteria in their faeces. The high prevalence of Salmonella Give in Virginia opossum faecal swabs in this study as well as its common occurrence in other Virginia opossum studies throughout North America suggests Virginia opossums may be reservoirs of this serovar.