Evaluation of PetrifilmsTM as a diagnostic test to detect bovine mastitis organisms in Kenya

The study purpose was to validate Petrifilms^TM (3M Microbiology, 2005) against standard culture methods in the diagnosis of bovine mastitis organisms in Kenya. On 128 smallholder dairy cattle farms in Kenya, between June 21, 2010 and August 31, 2010, milk samples from 269 cows that were positive on California Mastitis Test (CMT) were cultured using standard laboratory culture methods and Petrifilms^TM (Aerobic Count and Coliform Count –3M Microbiology, 2005), and results were compared. Staphylococcus aureus was the most common bacterium isolated (73 % of samples). Clinical mastitis was found in only three cows, and there were only two Gram-negative isolates, making it impossible to examine the agreement between the two tests for Gram-negative- or clinical mastitis samples. The observed agreement between the standard culture and Petrifilm^TM (3M Microbiology, 2005) results for Gram-positive isolates was 85 %, and there was fair agreement beyond that expected due to chance alone, with a kappa (κ) of 0.38. Using culture results as a gold standard, the Petrifilms^TM had a sensitivity of 90 % for Gram-positive samples and specificity of 51 %. With 87 % of CMT-positive samples resulting in Gram-positive pathogens cultured, there was a positive predictive value of 93 % and a negative predictive value of 43 %. Petrifilms^TM should be considered for culture of mastitis organisms in developing countries, especially when Gram-positive bacteria are expected.     

PCR as a diagnostic tool for brucellosis

Numerous PCR-based assays have been developed for the identification of Brucella to improve diagnostic capabilities. Collectively, the repertoire of assays addresses several aspects of the diagnostic process. For some purposes, the simple identification of Brucella is adequate (e.g. diagnosis of human brucellosis or contamination of food products). In these cases, a genus-specific PCR assay is sufficient. Genus-specific assays tend to be simple, robust, and somewhat permissive of environmental influences. The main genetic targets utilized for these applications are the Brucella BCSP31 gene and the 16S–23S rRNA operon.

Other instances require identification of the Brucella species involved. For example, most government-sponsored brucellosis eradication programs include regulations that stipulate a species-specific response. For epidemiological trace back, strain-specific identification is helpful. Typically, differential PCR-based assays tend to be more complex and consequently more difficult to perform. Several strategies have been explored to differentiate among Brucella species and strains, including locus specific multiplexing (e.g. AMOS-PCR based on IS711), PCR-RFLP (e.g. the omp2 locus), arbitrary-primed PCR, and ERIC-PCR to name a few. This paper reviews some of the major advancements in molecular diagnostics for Brucella including the development of procedures designed for the direct analysis of a variety of clinical samples. While the progress to date is impressive, there is still room for improvement.     

Evaluation of the indirect fluorescent antibody test as a diagnostic tool for East Coast fever in eastern Zambia

Serological surveys using the schizont indirect fluorescence antibody test (IFAt) are routinely carried out to monitor the Theileria parva infection prevalence. The present study evaluates the diagnostic accuracy of the IFAt in eastern Zambia, where the transmission of T. parva is highly seasonal. The data set resulted from a sentinel herd (n = 105 animals) study carried out between 1995 and 2000 and was split into an epidemic period, during which the majority of the cattle became infected, and an endemic period with seasonal disease incidence in calves. In the epidemic period the T. parva seroprevalence followed closely the build up of the herd immunity. In the endemic period the seroprevalence fluctuates considerably although most of the animals had been infected. Overall, the diagnostic sensitivity of the IFA test was 55% at cut-off titre 1:40 and 28% at cut-off 1:160. The specificity of the test was 86 and 95%, respectively. A logistic regression model demonstrates that the sensitivity is significantly lower when the T. parva transmission is low (p < 0.01). The analysis of receiver operator characteristic curves classifies the test as moderately accurate (area under the curve, AUC = 0.79) during the epidemic period and less accurate in the endemic period (AUC = 0.63). Neonatal serology surveys yield a better estimate of the infection prevalence. The sensitivity of the neonatal test was 73% at cut-off titre 1:40 and 24% at cut-off 1:160.     

A field study evaluation of Petrifilm™ plates as a 24-h rapid diagnostic test for clinical mastitis on a dairy farm

Clinical mastitis is one of the most common and expensive diseases of dairy cattle. To make an informed treatment decision, it is important to know the causative pathogen. However, no detection of bacterial growth can be made in approximately 30% of all clinical cases of mastitis. Before selecting the treatment regimen, it is important to know whether the mastitis-causing pathogen (MCP) is Gram-positive or Gram-negative. The aim of this field study was to investigate whether using two 3M Petrifilm™ products on-farm (which conveys a higher degree of sample freshness but also bears a higher risk for contamination than working in a lab) as 24-h rapid diagnostic of clinical mastitis achieved results that were comparable to the conventional microbiological diagnostic method.     

Telomerase: a potential diagnostic and therapeutic tool in canine oncology

In recent years there has been considerable interest in telomerase as a target for therapeutic intervention in oncology. This largely stems from the vast number of studies that have demonstrated expression and activity of the enzyme telomerase in the majority of human cancer tissues with little or no activity detectable in normal somatic tissues. These studies have led to an interest in the role of telomerase in cancers associated with domesticated species, in particular tumors that affect dogs. This article reviews the biology of telomerase and the biological significance of telomerase activity in canine tumors and discusses the clinical implications of telomerase expression in canine cancers with regard to therapeutics and diagnostics.     

Urinary alkaloid excretion as a diagnostic tool for fescue toxicosis in cattle.

Fescue toxicosis research studies have often included serum prolactin as a physiologic index of the disorder. Serum prolactin has not been used as a clinical measure of fescue toxicosis because of variation associated with sex and physiologic condition of the animal and climatic and seasonal factors. The primary excretory route of the alkaloids responsible for this toxicosis is the urine. Three pasture experiments were conducted to examine serum prolactin and urinary ergot alkaloid variability among steers continuously grazing endophyte-infected (E+) or endophyte-free (E-) tall fescue and among steers that were switched from one pasture form to the other. A fourth grazing experiment was used to examine how to best to manage the steers prior to sampling for urinary ergot alkaloid excretion. Coefficients of variability for urinary alkaloid excretion were consistently lower (46-65%) than serum prolactin (64-142%). Urinary alkaloid excretion patterns changed within 12 hours following switching steers from E+ to E- pasture or vice versa, but serum prolactin was recalcitrant to change. Because it is less variable and more dynamic than serum prolactin, urinary alkaloid excretion can be used for health assessment of steers grazing E+ and E- pastures. Regression analysis established a quadratic relationship between alkaloid excretion and average daily weight gain, with a regression coefficient of 0.86. Urinary alkaloid analysis was useful in determining whether cattle were consuming toxic tall fescue.     

Encephalitic listeriosis in ruminants: immunohistochemistry as a diagnostic tool

A retrospective analysis of 42 ruminants (sheep, goats and cattle) with suspected meningo-encephalitis was performed. The clinical findings and the post-mortem results of the animals have been specified. Bacteriological culture, Gram's stain and Listeria-specific immunohistochemistry were performed in order to confirm the diagnosis of these cases. The results of the different methods were evaluated for the detection of listerial antigens. Bacteriological culture was positive in 28.5% of the cases. In 47.6% of the cases, Gram-positive bacteria were found and 80.9% of the cases were immunohistochemically positive for the listerial antigen. The most important conclusion from this investigation is that the traditionally used Gram's stain and the bacteriological culture techniques are insufficient compared with immunohistochemistry for the confirmation of a Listeria monocytogenes infection.     

N-acetyl-beta-D-glucosaminidase test for screening milk samples for subclinical mastitis.

The use of the N-acetyl-beta-D-glucosaminidase (NAGase) test for detecting subclinical mastitis was investigated in surveys of milk samples from 20 farms. A milk sample was considered to be mastitic if it had a milk cell count above 400,000 cells/ml, and the NAGase test results were graded accordingly. The test gave an average of 16.6 per cent false positives and 2.0 per cent false negatives per herd. It was concluded that the NAGase test could be used as a rapid screening method for selecting suspect samples for further analysis by standard methods.     

Bacteriologic examination of equine fecal flora as a diagnostic tool for equine intestinal clostridiosis

The fecal flora of 56 clinically healthy and 23 sick horses were examined bacteriologically for counts of Clostridium perfringens, molds, coliforms, alpha- and beta-hemolytic streptococci, and microbes belonging to genus Bacillus, as well as for the presence of Salmonella spp. Of the healthy horses, 85.7% had a C perfringens count less than 10(1) colony-forming units/g of feces. Of the healthy horses, lowest counts were found in race-horses. Of the sick horses, equine intestinal clostridiosis was diagnosed in 2 horses with large C perfringens counts (10(4) to 10(7) colony-forming units/g) and with acute diarrhea. The 7 isolates of C perfringens were identified as serotype A. Salmonella spp were not detected from any of the horses. The study indicated that diagnosing equine intestinal clostridiosis based on the determination of the fecal C perfringens count was suitable.     

Evaluation of nasotracheal aspiration as a diagnostic tool for Rhodococcus equi pneumonia in foals

The reliability of preparing bacteriological cultures from nasotracheal aspirates of foals routinely in order to diagnose R. equi pneumonia in foals was studied by isolating Rhodococcus equi from specimens obtained from 96 foals by nasotracheal aspiration with a silicon catheter. Results were compared with specimens obtained from 21 foals by transtracheal aspiration (percutaneous tracheal puncture). These 117 foals showed clinical signs of respiratory tract infection at sampling. R. equi was isolated from 14 of 21 (66.7%) specimens by transtracheal aspiration and from 59 of 96 (61.4%) specimens by nasotracheal aspiration, 649 of 655 isolates (99.1%) from the 73 positive specimens were virulent R. equi, and the culture-positive foals were diagnosed as having R. equi pneumonia. To assess the contamination of aspirates by organisms from the nasopharynx, the results of R. equi isolation from nasal swabs obtained from 56 of the 96 foals were compared to those obtained by nasotracheal aspiration from the same foals. R. equi was isolated from 2 of the 56 nasal swabs: one from a tracheal aspirate was positive, and the other was not. These results suggest that the nasotracheal aspiration technique, which is noninvasive and not associated with complications, could be used as an alternative to the transtracheal aspiration method, especially for the diagnosis of R. equi pneumonia in foals.     

Telomerase enzyme activity as a diagnostic tool to distinguish effusions of malignant and benign origin

Telomerase enzyme activity is high in populations of cells that are dividing, and is low or undetectable in quiescent cell populations. Activation of telomerase in tissues that normally lack the capacity for self-renewal is strongly correlated with neoplasia. Telomerase activity can be detected in samples containing very small numbers of cells and studies of human patients suggest that measurement of telomerase activity may be useful for the evaluation of samples that can be obtained in a minimally invasive manner. This study compares the presence or absence of telomerase activity with cytologic evaluation of body cavity effusions, to determine if neoplasia is the underlying cause for the effusion in dogs and cats. Detection of telomerase in effusions was no more sensitive than cytologic evaluation for the identification of underlying neoplasia, and was less specific (telomerase assay: sensitivity = 50%, specificity = 83%; cytology: sensitivity = 50%, specificity = 100%). We conclude that although the telomerase assay may constitute a useful adjunctive test for the diagnosis of neoplasia in some dogs and cats with body cavity effusions, the results of this assay are not sufficiently reliable to be used as a sole diagnostic test.     

Current and future uses of breath analysis as a diagnostic tool

The analysis of exhaled breath is a potentially useful method for application in veterinary diagnostics. Breath samples can be easily collected from animals by means of a face mask or collection chamber with minimal disturbance to the animal. After the administration of a 13C-labelled compound the recovery of 13C in breath can be used to investigate gastrointestinal and digestive functions. Exhaled hydrogen can be used to assess orocaecal transit time and malabsorption, and exhaled nitric oxide, carbon monoxide and pentane can be used to assess oxidative stress and inflammation. The analysis of compounds dissolved in the aqueous phase of breath (the exhaled breath condensate) can be used to assess airway inflammation. This review summarises the current status of breath analysis in veterinary medicine, and analyses its potential for assessing animal health and disease.     

Use of high-resolution ultrasound as a diagnostic tool in veterinary ophthalmology

The recent development of a 20-MHz, high-frequency ultrasound probe has allowed tissue to be visualized at resolutions of 20 to 80 microm, which is similar to a low-power histologic view. This high degree of resolution, however, limits tissue penetration to 5 to 10 mm, which is ideal for examination of the anterior segment of the eye. The detail provided by high-resolution ultrasound readily permits the clinician to distinguish between various anterior segment entities that may appear similar but are treated quite differently, such as anterior uveal tumors, iridociliary cysts, and iris bombé. High-frequency ultrasound is also a valuable aid in creating a surgical plan for treatment of ocular disorders in which the cornea is opaque, such as feline corneal sequestrum and tumor invasion into the cornea. Other applications of this technology include elucidation of the pathogenesis of glaucoma in veterinary patients and evaluation of regions of the lens that are difficult to examine directly.