Effect of rice growth stages and silicon on sheath blight development

ABSTRACT The objective of this study was to determine the effect of silicon (Si) and rice growth stages on tissue susceptibility to sheath blight (Rhizoctonia solani Kühn) under controlled conditions. Rice plants (cv. Rio Formoso) were grown in pots containing low-Si soil amended with Si at 0, 0.48, 0.96, 1.44, and 1.92 g pot(-1) and inoculated with R. solani at the following days after emergence: 45 (four-leaf stage), 65 (eight-leaf stage), 85 (tillering), 117 (booting), and 130 (panicle exsertion). For plants inoculated with R. solani at all growth stages, Si concentration in straw increased as rate of Si increased from 0 to 1.92 g pot(-1). Concentration of calcium in the straw did not differ among plant growth stages. Although incubation period was not affected by the amount of Si added to the soil, this variable was shorter at booting and panicle exsertion stages. As the rates of Si increased in the soil, the total number of sheath blight lesions on sheaths and total area under the relative lesion extension curve decreased at all plant growth stages. The severity of sheath blight was lower at booting and panicle exsertion stages as the rates of Si increased in the soil. In general, plants grown in Si-nonamended pots and inoculated with R. solani were more vulnerable to infection at all growth stages, but especially at 45 days after emergence. Plant dry weights for inoculated plants increased as the Si rates increased from 0 to 1.92 g pot(-1). The greatest dry weight increases occurred for plants inoculated at booting and panicle exsertion stages. Si fertilization is a promising method for controlling sheath blight in areas where soil is Si deficient and when cultivars that exhibit an acceptable level of resistance to sheath blight are not available for commercial use.     

Babesia odocoilei infection in elk

Two male North American elk from a commercial herd were evaluated because of a sudden onset of lethargy, anorexia, and voiding of red urine. These 2 elk were kept in the same pen as 4 other male elk that had died during the preceding 2 months. Laboratory analyses revealed anemia and intraerythrocytic parasites, later confirmed as Babesia odocoilei (a protozoal hemoparasite of cervids). Of the 240 elk remaining in the herd, 59 were screened for B odocoilei by microscopic evaluation of blood smears, protozoal culture of blood, and immunofluorescent antibody testing of serum. Of those 59 elk, 34 (58%) were infected with B odocoilei. Babesia odocoilei infection in elk can be fatal and should be considered in cases of sudden death or acute hemolytic anemia. Familiarity with the disease in elk is essential for practitioners because of the increasing popularity of commercial elk farming.     

Real-time polymerase chain reaction testing for the detection of Mycobacterium genavense and Mycobacterium avium complex species in avian samples

Diagnosis of avian mycobacteriosis, caused by Mycobacterium genavense or species belonging to the Mycobacterium avium complex (MAC), is problematic. Polymerase chain reaction (PCR) offers rapid and sensitive detection of minute quantities of DNA, and conventional protocols have been used for evaluating avian specimens. The recent development of real-time PCR offers several advantages over conventional PCR. In attempts to improve diagnosing avian mycobacteriosis, a real-time TaqMan PCR assay was developed targeting the 65-kD heat shock protein gene of M. genavense and MAC spp. Nineteen reference isolates, 16 clinical isolates, and 32 avian tissue samples were used to evaluate the assay. When sufficient amplicons were produced, the species of mycobacteria was determined by standard sequencing of TaqMan PCR products and compared with results from commercial mycobacteriology laboratories and/or standard sequencing of conventional PCR products. The TaqMan PCR detected DNA from reference isolates of M. genavense, MAC spp., and Mycobacterium tuberculosis complex spp. Of the clinical isolates, the TaqMan PCR detected DNA from 10 of 12 Mycobacterium avium avium isolates and two of three Mycobacterium avium intracellulare isolates. For the tissue samples, the TaqMan PCR amplified DNA in six of nine samples that were identified by sequencing of conventional PCR products and/or by commercial mycobacteriology laboratories as being MAC spp. positive and three of four samples that were positive for M. genavense. There was some disagreement between speciation results from the TaqMan PCR and those from commercial mycobacteriology laboratories or conventional PCR or both. This disagreement was suspected to be because of relatively small numbers of base pairs in the TaqMan PCR products. The TaqMan PCR may provide a useful tool for evaluating clinical samples for DNA from mycobacteria species that most commonly infect birds; however, further refinement is needed in order to improve sensitivity and provide more accurate speciation.     

An adenovirus linked to mortality and disease in long-tailed ducks (Clangula hyemalis) in Alaska

An adenovirus was isolated from intestinal samples of two long-tailed ducks (Clangula hyemalis) collected during a die-off in the Beaufort Sea off the north coast of Alaska in 2000. The virus was not neutralized by reference antiserum against known group I, II, or III avian adenoviruses and may represent a new serotype. The prevalence of the virus was determined in live-trapped long-tailed ducks at the mortality site and at a reference site 100 km away where no mortality was observed. Prevalence of adenovirus antibodies in serum samples at the mortality site was 86% compared to 10% at the reference site. Furthermore, 50% of cloacal swabs collected at the mortality site and only 7% of swabs from the reference site were positive for adenoviruses. In 2001, no mortality was observed at either of the study areas, and virus prevalence in both serum and cloacal samples was low, providing further evidence that the adenovirus was linked to the mortality event in 2000. The virus was used to infect long-tailed ducks under experimental conditions and resulted in lesions previously described for avian adenovirus infections and similar to those observed in long-tailed duck carcasses from the Beaufort Sea. The status of long-tailed ducks has recently become a concern in Alaska due to precipitous declines in breeding populations there since the mid-1970s. Our findings suggest that the newly isolated adenovirus is a disease agent and source of mortality in long-tailed ducks, and thus could be a contributing factor in population declines.     

Evaluation of a single dose versus a divided dose regimen of danofloxacin in treatment of Actinobacillus pleuropneumoniae infection in pigs

A single versus a divided dose regimen of danofloxacin was evaluated in treatment of porcine Actinobacillus pleuropneumoniae infection using clinical observations combined with biochemical infection markers: C-reactive protein, zinc and ascorbic acid. Twenty hours after experimental infection, the 18 pigs received danofloxacin intravenously as a single dose of 2.5mg/kg or four doses of 0.6 mg/kg administered at 24h intervals. These dosage regimens resulted in similar AUCs of the plasma danofloxacin vs time curve. The maximum concentration was 3.5-fold higher using the single dose regimen, while the time with concentrations above the MIC was 2.5-fold longer using the fractionated regimen. Using the single dose regimen, temperature was normalised 32 h post-infection. In contrast, normalisation was delayed until 44 h post-infection using four low doses and a relapse with elevated temperatures at 52 and 68 h was observed. No other significant differences between the treatments were found, neither regarding clinical, haematological nor biochemical observations. The use of the more convenient single dose regimen was appropriate, as it was at least equivalent to the fractionated regimen.     

16alpha-Bromo-epiandrosterone therapy modulates experimental feline immunodeficiency virus viremia: initial enhancement leading to long-term suppression

16alpha-Bromo-epiandrosterone (epiBr), a synthetic derivative of the natural hormone dehyroepiandrosterone (DHEA), was evaluated for its effects on feline immunodeficiency virus (FIV) infection in experimental cats. The rationale for this study was based on the ability of DHEA to significantly reduce the mortality to viral infections in mice. DHEA and epiBr also have demonstrable in vitro anti-viral activity for both HIV-1 and FIV. Preliminary pharmacokinetic studies in cats demonstrated that subcutaneously injected epiBr was rapidly absorbed, completely metabolized, and nontoxic. Metabolites were excreted in both urine and feces, with the latter having the most complex pattern of breakdown products. Cats were then divided into four groups; two groups were infected with FIV and two uninfected. Two groups, one infected and one uninfected were treated on 5 consecutive days of weeks 0, 4, 8, 12 and 16 with epiBr. The remaining two groups were mock treated with the drug vehicle alone. Treatment started 1 week prior to infection and extended for 4 weeks after infection. Cats were observed for 20 weeks post-FIV infection. Infected cats had identical decreases in blood neutrophil and lymphocyte counts following, regardless of whether they were treated with epiBr or vehicle alone. The CD4/CD8 T-cell ratio was decreased following FIV exposure, but was significantly more decreased for the epiBr treated animals from week 2 post-infection onward. CD4+ T cells were decreased in FIV-infected cats treated with epiBr compared to their untreated cohort, while CD8+ T cells tended to be higher in treated animals. FIV infected cats that were treated with epiBr had over one-log higher virus loads at week 2 post-infection than non-epiBr treated cohorts. In spite of this enhanced initial viremia, the subsequent levels of virus in the blood were significantly lower in epiBr treated versus untreated animals. EpiBr treated cats had significantly higher FIV-p24 antibody responses than control cats receiving vehicle alone, although primary and secondary antibody responses to a T-cell dependent non-FIV antigen, keyhole limpet hemocyanin (KLH), were unaffected. EpiBr treatment significantly decreased the expected FIV-induced suppression of IL-12 p40 mRNA levels in peripheral blood mononuclear cells (PBMCs) observed at weeks 4, 5, 8, 9 and 16 post-infection, but had no influence on FIV-induced changes in IL-4, IL-6, IL-10, IFN-gamma, MIP-1alpha and RANTES.     

Benefits of prophylactic gastropexy for dogs at risk of gastric dilatation-volvulus

The lifetime probability of death from gastric dilation–volvulus (GDV) for five dog breeds was estimated based on published breed-specific longevity and GDV incidence. These breeds were Great Dane, Irish Setter, Rottweiler, Standard Poodle and Weimaraner. Lifetime risk (95% CI) of GDV in these breeds ranged from 3.9% (0–11.2%) for Rottweiler to 36.7% (25.2–44.6%) for Great Dane.

A decision-tree analysis for prophylactic gastropexy—using lifetime probability of death from GDV and expected cost savings for veterinary services as outcome measures—was undertaken to determine the preferred course of action in several dog breeds. Prophylactic gastropexy was the preferred choice of action for all breeds examined, with the reduction in mortality (versus no gastropexy) ranging from 2.2-fold (Rottweiler) to 29.6-fold (Great Dane). Assuming a prophylactic gastropexy costs US$ 400, the procedure was cost-effective when the lifetime risk of GDV was ≥34%. The maximum and minimum estimated breakeven costs for the gastopexy procedure ranged from US$ 20 (Rottweiler) to US$ 435 (Great Dane). The cost-effectiveness of prophylactic gastropexy was most sensitive to the cost of treating GDV (US$ 1500). Prophylactic gastropexy raises ethical issues that need to be considered by veterinarians and dog breeders.     

Controlling Echinococcus multilocularis-ecological implications of field trials

Two field trials to reduce the prevalence of Echinococcus multilocularis in foxes have been conducted in recent years. Although both trials reduced prevalence considerably, they failed to eradicate the parasite in the study region. Following the control trial in northern Germany, prevalence recovered unexpectedly and rapidly, reaching pre-control levels five quarters (15 months) after the end of control. To understand the internal dynamics of the parasite-host system's reaction to control, we developed a spatially explicit simulation model, Echi. The simulation model incorporates the information available concerning fox tapeworm population dynamics.Using epidemiological parameters to adjust pre-control prevalence, the model predicts the temporal evolution of the prevalence of E. multilocularis in controlled foxes without departing from the range of uncertainty of the field data. However, the model does not predict the rapid pre-control recovery observed in the field trial.The deviation of the model's prediction from field data indicates the involvement of processes not yet taken into account. We modified the model step by step to mimic processes with the potential to cause the rapid post-control recovery of the prevalence of E. multilocularis in foxes.Neither the longevity of tapeworm eggs nor the migratory behaviour of foxes showed any influence on the post-control reaction of the parasite-host system. However, landscape structures leading to a heterogeneous distribution of infected foxes have the potential to alter the system's reaction to control. If infected foxes are concentrated in multiple clusters in the landscape, the model prediction tallied with the range of uncertainty of the field data. Such spatial distribution of infected foxes may be caused by differential abiotic conditions influencing the survival of tapeworm eggs.The model was found to comply best with field data if the foxes acquire partial immunity by being exposed to the fox tapeworm.Both hypotheses explaining the rapid post-control recovery of the prevalence of E. multilocularis observed in the fox population were supported by field data.Both hypotheses have far-reaching consequences for future control trials. The spatial aggregation of infected foxes would enable control efforts to be concentrated on these highly infected areas. However, the acquisition of immunity acts as a buffer to control, necessitating intensified control measures.     

Isolation and identification of Mycobacterium kansasii from pleural fluid of a dog with persistent pleural effusion

A 3-year-old spayed female Whippet was examined for cough and respiratory distress. Lung lobe torsion with pleural effusion was diagnosed, and lung lobectomy was performed. Pleural effusion recurred during the following 27 months; conventional bacteriologic cultures of pleural effusion did not result in bacterial growth. A second lung lobectomy, pleuroperitoneal shunt placement. and pericardectomy were subsequently performed. Mycobacterium kansasii was eventually isolated from pleural fluid and identified by polymerase chain reaction amplification and DNA sequencing. The dog was euthanatized before therapeutic response could be evaluated. To our knowledge, this is the first report of M. kansasii infection in a dog. Additionally, this is the first report of mycobacterial isolation from pleural fluid, and one of few reports of antemortem mycobacterial isolation from a body fluid, as opposed to identification in specimens during histologic examination. Routine bacteriologic culture methods are insufficient to isolate mycobacterial agents, and special methods are indicated in dogs with persistent pleural effusion.