Comparison of ELISA and CFT assays for Chlamydophila abortus antibodies in ovine sera

OBJECTIVE

To compare the sensitivity and specificity of Chlamydophila abortus antibody assays, to find a suitable serological assay for testing sheep for export.

DESIGN

Comparison of results from known positive and negative sheep populations.

PROCEDURE

Fifty-five positive and fifty negative sera were analysed by four enzyme linked immunosorbent assays (ELISA), three using recombinant antigens based on the chlamydial polymorphic outer membrane proteins (POMP90-3, POMP90-4, POMP80-90) and one using a synthetic peptide based on chlamydial major outer membrane proteins (MOMP-P). They were also analysed by complement fixation tests (CFT) using crude antigens from chlamydia isolated from an Australian sheep, a Californian parakeet and a Texan turkey. Assay sensitivity and specificity were expressed as point estimates and 95% confidence intervals. Results were compared using McNemar's test for paired samples.

RESULTS

ELISA sensitivity ranged from 70 to 98% and complement fixation test sensitivity from 60 to 96%; with POMP90-3 > POMP90-4 > CFT (parakeet) > CFT (turkey) > POMP80-90 > MOMP-P > CFT (sheep). There was no significant difference from POMP90-3 to POMP80-90 (P > 0.05). ELISA specificity ranged from 88 to 100% and CFT specificity was 100% for all three antigens; with CFT and POMP90-4 > MOMP-P > POMP80-90 > POMP90-3. There was no significant difference from CFT to POMP80-90 (P > 0.05). Changing the CFT cut-off from 1:32 to 1:4 substantially reduced the specificity with little improvement in sensitivity.

CONCLUSION

Assays using POMP90-4, POMP80-90, CFT (parakeet) and CFT (turkey) had equivalent sensitivity and specificity; none of the ELISAs were more specific than any CFT. The POMP80-90 ELISA is recommended as an alternative to CFT (parakeet) but as its specificity is not ideal the search for a more specific assay should continue.

A long-term bacteriological and immunological study in Holstein-Friesian cattle experimentally infected with Mycobacterium avium subsp. paratuberculosis and necropsy culture results for Holstein-Friesian cattle, Merino sheep and Angora goats

The aims were to longitudinally evaluate the interferon-gamma (IFN-gamma) test in comparison to faecal culture and the absorbed ELISA in a cattle infection model for Johne's disease and to determine the adult infection status, by necropsy and tissue culture, of sheep, goats and cattle infected as young animals. Clinical disease, faecal culture results and immunological responses for Merino sheep [Stewart, D.J., Vaughan, J.A., Stiles, P.L., Noske, P.J., Tizard, M.L.V., Prowse, S.J., Michalski, W.P., Butler, K.L., Jones, S.L., 2004. A long-term study in Merino sheep experimentally infected with Mycobacterium avium subsp. paratuberculosis: clinical disease, faecal culture and immunological studies. Vet. Microbiol. 104, 165-178] and Angora goats [Stewart, D.J., Vaughan, J.A., Stiles, P.L., Noske, P.J., Tizard, M.L.V., Prowse, S.J., Michalski, W.P., Butler, K.L., Jones, S.L., 2006. A long-term study in Angora goats experimentally infected with Mycobacterium avium subsp. paratuberculosis: clinical disease, faecal culture and immunological studies. Vet. Microbiol. 113, 13-24], in the same experiments as the Holstein-Friesian cattle, have been described. Two longitudinal experiments involving Holstein-Friesian cattle challenged with either bovine or ovine strains of Mycobacterium avium subsp. paratuberculosis (Map) have been conducted over a period of 54 and 35 months, respectively. Blood samples for the IFN-gamma test and the absorbed ELISA and faecal samples for bacteriological culture were taken pre-challenge and monthly post-challenge. Cell-mediated (CMI) responses were substantially higher for the bovine Map strain during the 42-month period following dosing but then declined in the remaining 12 months. However, for the ovine Map challenge and control groups, CMI responses were not significantly different from each other. None of the cattle developed clinical disease and only one of the cattle in the bovine Map gut mucosal tissue challenged group was a persistent faecal shedder and also an ELISA antibody responder which developed after shedding commenced. Culture of tissues, following necropsy at the completion of the experiments, showed no evidence of infection in any of the challenged cattle and sheep for either the bovine or ovine Map strain in contrast to positive cultures for challenged goats in the same experiments. The tissues from the control cattle, sheep and goats were culture negative. The cattle were less susceptible to the bovine and ovine Map strains than goats and sheep with the goats being the least naturally resistant.

Genotype and age effects on sheep meat production. 4. Carcass composition predicted by dual energy X-ray absorptiometry

This study compares the carcass composition of different genotypes of Australian sheep slaughtered at four ages (110, 236, 412 and 662 days of age, or 4, 8, 14 and 22 months of age). The genotypes used were Poll Dorsetgrowth × Border Leicester Merino (PDg × BLM), Poll Dorsetgrowth × Merino (PDg × M), Poll Dorsetmuscling × Merino (PDm × M), Merino × Merino (M × M) and Border Leicester × Merino (BL × M). Approximately 150 mixed sex animals were slaughtered at each age and the right sides (half carcass) were scanned by dual energy X-ray absorptiometry (DXA) for chemical lean, fat and bone mineral percentages of the carcass. Carcass lean percentage decreased (P < 0.001) across sire groups from Merino to Poll Dorset to Border Leicester at each age, while fatness increased (P < 0.001) in the opposite direction. With age, the magnitude of difference between genotypes for fatness became greater. There was a marked increase (P < 0.01) in ash mineral percentages in M × M and PDg × M genotypes relative to other genotypes in the 14- and 22-month groups. There were no differences (P > 0.1) between PDg × M and PDm × M in either chemical lean or fat percentages at any age but ash mineral percentage was higher in the PDg × M genotype at older ages (P < 0.05). This in turn led to differences in chemical lean : ash mineral content at later ages between PDg × M and PDm × M. Wethers had higher chemical lean (P < 0.05) and lower fat (P < 0.05) percentages in the carcass than ewes at all ages but ash mineral and chemical lean : ash mineral content did not differ between sexes. It was clear that the level of chemical lean or fat or ash mineral composition reached by some genotypes at one age was equivalent to that reached by other genotypes at the next measurement age. Those genotypes that reach a specification at younger ages will be more productive for meat production. Purebred Merino genetics will always be less productive in terms of carcass weight and muscle related productive traits (loin weight, semitendinosus muscle weight, eye muscle area) than BL and PD genetics, but the relative productivity of PD and BL genetics will depend on the traits used in the specification [see also Ponnampalam EN, Hopkins DL, Butler KL, Dunshea FR, Warner RD (2007) Genotype and age effects on sheep meat production. 2. Carcass quality traits. Australian Journal of Experimental Agriculure 47, 1147–1154]. The results suggest that selection for muscling had a greater impact on reducing ash mineral content associated with bone mineral mass than on increasing lean mass in the carcass.

Genotype and age effects on sheep meat production. 2. Carcass quality traits

The present study examines carcass quality traits in different genotypes of Australian sheep slaughtered at 4, 8, 14 and 22 months of age. Poll Dorsetgrowth × Border Leicester Merino (PDg × BLM), Poll Dorsetgrowth × Merino (PDg × M), Poll Dorsetmuscling × Merino (PDm × M), Merino × Merino (M × M) and Border Leicester × Merino (BL × M) genotypes were compared. Sires were selected on the basis of growth (PDg, M and BL) and muscle (PDm) using estimated breeding values (EBVs). Approximately 150 mixed sex animals were slaughtered at each age (595 in total for the four slaughters) and carcass quality traits, including hot carcass weight, loin and semitendinosus (ST) muscle weights, GR fat, fat C, rump fat depth and eye muscle area (EMA), were determined at 45 min to 3 days postslaughter. With age, all carcass quality traits increased in magnitude. Merinos produced the lightest and leanest carcasses (P < 0.01) with lowest values in nearly all the carcass quality traits. At 4 and 8 months of age carcass and loin weights, EMA and GR fat measures were greater (P < 0.01) in second-cross PDg × BLM sheep than all other genotypes. However, traits related to muscle content were similar between first- and second-cross Poll Dorset genotypes at 14 and 22 months of age. The BL × M genotype had lower values than the PD × M genotypes for these traits, at all ages. Traits related to carcass fatness showed that sheep with Border Leicester genetics tend to deposit more fat (P < 0.001) in the carcass than those with Merino or Poll Dorset genetics from 14 months of age onwards. Most carcass quality traits did not differ (P > 0.05) between first-cross Poll Dorset genotypes selected for growth or muscling (PDg × M v. PDm × M). Sires with high muscling EBVs are associated more with shorter carcass length than low muscling EBVs. From ~8 months of age, wethers had greater values (P < 0.05) than ewes of the same age for most carcass quality traits related to size and muscle development, but no effect was present for carcass quality traits that were related to fat deposition. It was clear that the carcass weight of M × M at 8 and 14 months were similar to that observed in PDg × BLM at 4 and 8 months, respectively. Loin weights of M × M and BL × M at 13 and 8 months were similar to that weights observed in PDg × BLM at 8 and 4 months of age, respectively. Animals slaughtered to a muscle weight specification will reach the target at a younger age when they have more Poll Dorset than Border Leicester background genetics. Alternatively animals slaughtered at a specified fat score (using fat C or rump fat depth) will reach the specification at a younger age when they have more Border Leicester than Poll Dorset genetics.

Factors affecting the concentration of short branched-chain fatty acids in sheep fat

The concentration of short branched-chain fatty acids, specifically 4-methyloctanoic acid (MOA) and 4-methylnonanoic acid (MNA), in subcutaneous fat were determined in five genotypes (Poll Dorset × Border Leicester Merino, Poll Dorset × Merino, Poll Dorsetmuscling × Merino, Merino × Merino, Border Leicester × Merino) of Australian sheep. In total, 264 ewes and wethers, either 8 or 22 months of age, were selected for genotype, age and gender. These animals were sired by 16 rams that were selected for growth based on estimated breeding values (EBVs), except for one group (Poll Dorsetmuscling × Merino), which was selected for muscling based on EBVs. There was a strong relationship between the concentration of MOA and MNA at 8 and 22 months of age. There were no differences between lambs sired by Poll Dorset rams selected for muscling or growth. The 8- and 22-month-old Poll Dorset × Merino sheep had higher levels of MOA and MNA compared with the other genotypes (P < 0.001). At 8 months of age, the wethers had higher levels of MOA and MNA (P < 0.001) than the ewes of the same genotype. There was a strong relationship (P < 0.001) between MOA and MNA and the fat and lean percentage for 22-month-old ewes. Effects of sire, dam and slaughter day (at the same slaughter age) on MOA and MNA were also found. The results suggest that there is good feasibility for selection against animals at risk of possessing higher levels of short branched-chain fatty acids.

A long-term study in Angora goats experimentally infected with Mycobacterium avium subsp. paratuberculosis: Clinical disease, faecal culture and immunological studies

Two longitudinal experiments involving Angora goats challenged with either bovine or ovine strains of Mycobacterium avium subspecies paratuberculosis (Map) have been conducted over a period of 54 and 35 months, respectively. Blood samples for the interferon-gamma (IFN-gamma) test and the absorbed ELISA and faecal samples for bacteriological culture were taken pre-challenge and monthly post-challenge. Persistent shedding, IFN-gamma production, seroconversion and clinical disease occurred earlier with the bovine Map gut mucosal tissue challenge inoculum than with cultured bacteria. The IFN-gamma responses of the gut mucosal tissue and bacterial challenge groups were substantially and consistently higher than those of the control group. The in vivo and cultured cattle strains were much more pathogenic for goats than the sheep strains with persistent faecal shedding, seroconversion and clinical disease occurring in the majority of bovine Map challenged goats. With the ovine Map, 3 goats developed persistent antibody responses but only one of these goats developed persistent faecal shedding and clinical disease. However, there was no significant difference between the IFN-gamma responses of the tissue challenged, bacterial challenged and control groups. Compared with sheep, the ELISA appeared to have higher sensitivity and the IFN-gamma test lower specificity.

Longitudinal DXA measurements demonstrate lifetime differences in lean and fat tissue deposition between boars and barrows under individual and group-penned systems

Thirty-two Large White × Landrace male pigs were used to determine the relationships between the rates of tissue deposition and age, in boars and barrows under 2 housing systems. A 2 × 2 factorial design was used, with the respective treatments being sex (boar or barrow) and housing condition (individually penned system or group-penned system). Surgical castration was performed at 7 days of age. Individually housed pigs were used to provide an estimate of potential growth and were weaned at 10 days into individual cages and provided with supplemental fermented skim milk for 2 weeks. Group-housed pigs were weaned at 24 days of age and reared in group pens of boars and castrates typical for commercial production. Conventional weaner, grower, and finisher diets were provided ad libitum to all pigs from weaning onwards. A Hologic QDR4500A dual-energy X-ray absorptiometer (DXA) was used to determine lean, fat, and bone composition at 4-weekly intervals from 10 until 150 days of age. Over the 20 weeks of the study, boars deposited less fat than barrows (136 v. 179 g/day, s.e.d. = 6.49, P < 0.001). Over the same time frame, boars deposited more lean tissue than barrows when individually penned (490 v. 444 g/day, s.e.d. = 14.4, P < 0.05) but there was no difference in group-penned pigs (464 v. 443 g/day, s.e.d. = 14.4, P > 0.1). This was more pronounced in the final 4 weeks of growth when individually penned boars deposited 200 g/day more lean than barrows (P < 0.001), with no increase in group-penned animals. However, during this growth phase, group penning further increased the fat deposition margin between boars and barrows where boars deposited 90 g/day less fat when individually penned (P < 0.001), but 140 g/day less fat (P < 0.001) when group penned. The results show that the advantages of boars in terms of growth and lean tissue composition are substantially reduced in group-penned situations. However, because of fat deposition, boars retain some advantage over barrows in group-penned systems at liveweights over about 50 kg. These data may aid in the accurate prediction of the nutrient requirements and optimum slaughter weight for barrows.

A long-term study in Merino sheep experimentally infected with Mycobacterium avium subsp. paratuberculosis: clinical disease, faecal culture and immunological studies

Two longitudinal experiments involving Merino sheep challenged with either bovine or ovine strains of Mycobacterium avium subsp. paratuberculosis (Map) have been conducted over a period of 54 and 35 months, respectively. Blood samples for the interferon-gamma test, the absorbed ELISA and faecal samples for bacteriological culture were taken pre-challenge and monthly post-challenge. Infections were induced with either a bovine or ovine strain of Map in separate experiments with infections being more easily established, in terms of faecal bacterial shedding and clinical disease when the challenge inoculum was prepared from gut mucosal tissue than cultured bacteria. The patterns of response for shedding and clinical disease were similar. Cell-mediated immune responses were proportionally elevated by at least an order of magnitude in all sheep dosed with either a bovine or ovine strain of Map. Conversely, antibody responses were only elevated in a relatively small proportion of infected sheep. Neither of the clinically affected tissue challenged sheep developed an antibody response despite the presence of persistent shedding and the development and decline in cell-mediated immunity. The results indicated that for sheep the interferon-gamma test may be useful for determining if a flock has been exposed to ovine Johne's disease.

The influence of dietary energy intake on growth performance and tissue deposition in pigs between 80 and 120 kg liveweight

Eighty crossbred pigs of a composite genotype were allocated at 80 kg liveweight to a 2 × 5 factorial experiment involving 2 sexes (boars and gilts) and 5 levels of dietary energy intake ranging from about 55% estimated ad libitum up to 100% ad libitum intake. The diet was formulated to be protein-adequate and contained 14.4 MJ DE/kg and 0.55 g available lysine/MJ DE and the pigs were slaughtered at approximately 120 kg liveweight. Growth rate and food conversion efficiency increased linearly, in response to increasing digestible energy (DE) intake, with boars consistently out-performing gilts at each level of DE intake. Protein deposition rate in the whole empty body of pigs was consistently higher in boars than in gilts and linearly related to DE intake in both sexes, with no evidence of a plateau at high energy intakes, suggesting no intrinsic limit to protein deposition in these pigs up to 120 kg liveweight. When pigs were offered the protein-adequate diet ad libitum between 80 and 120 kg liveweight, boars and gilts consumed 47.7 and 40.9 MJ DE/day, respectively, and protein deposition rates in the whole empty body of pigs reached 247 and 182 g/day, respectively. Maintenance energy requirements were estimated to be 351 kJ DE/kg0.75.day for both boars and gilts [maximal model; including nominal DE level (treated as a 5-level factor), actual DE intake (treated as a continuous variable), and sex (treated as a 2-level factor)] or 506 and 566 kJ DE/kg0.75.day for boars and gilts, respectively [reduced model; including actual DE intake (treated as a continuous variable) and sex (treated as a 2-level factor)]. Statistical analyses show that the maximal model reflects the data more closely than the minimal model, suggesting that the lower maintenance estimate of 351 kJ DE/kg0.75.day could reflect reality better. In conclusion, genetically improved boars, and to a lesser extent gilts, have a high capacity for lean growth, and their upper limit to protein retention might not be reached below about 120 kg liveweight.

Sources of variation in fibre diameter attributes of Australian alpacas and implications for fleece evaluation and animal selection

Sources of variation in fibre diameter attributes of Australian alpacas and implications for fleece evaluation and animal selection were investigated using data collected in the years 1994–97, from 6 properties in southern Australia. Data were analysed using REML (multiple regression analysis) to determine the effect on mean fibre diameter (MFD) and coefficient of variation of MFD (CV(FD)) of age, origin (property), sex (entire male, female), breed (Huacaya, Suri), liveweight, fibre colour, individual, and interactions of these effects. The mean (n = 100) age (range) was 4.2 years (0.1–11.9), liveweight 72.0 kg (12.0–134 kg), MFD 29.1 μm (17.7–46.6 μm), CV(FD) 24.33% (15.0–36.7%). A number of variables affected MFD and CV(FD). MFD increased to 7.5 years of age, and correlations between MFD at 1.5 and 2 years of age with the MFD at older ages were much higher than correlations at younger ages. Fibre diameter 'blowout' (increase with age) was positively correlated with the actual MFD at ages 2 years and older. There were important effects of farm, and these effects differed with year and shearing age. Suris were coarser than Huacayas with the effect reducing with increased liveweight; there was no effect of sex. Fleeces of light shade were 1 μm finer than dark fleeces. CV(FD) declined rapidly between birth and 2 years of age, reaching a minimum at about 4 years of age and then increasing; however, CV(FD) measurements on young animals were very poor predictors of CV(FD) at older ages, and the response of CV(FD) to age differed with farm and year. Suris had a higher CV(FD) than Huacayas on most properties, and MFD, liveweight, and sex did not affect CV(FD). Fleeces of dark shade had higher CV(FD) than fleeces of light shade in 2 of the years. It is concluded that there are large opportunities to improve the MFD and CV(FD) of alpaca fibre through selection and breeding. The potential benefit is greatest from reducing the MFD and CV(FD) of fibre from older alpacas, through reducing the between-animal variation in MFD and CV(FD). Sampling alpacas at ages <2 years is likely to substantially decrease selection efficiency for lifetime fibre diameter attributes.

Sources of sampling variation in saliva cortisol in dogs

The main advantage of collecting saliva cortisol as opposed to plasma cortisol is that it is non-invasive and therefore it is now widely used in stress measurement studies on farm animals and dogs. Although a plasma cortisol response to handling associated with blood collection generally occurs at 3 min from the commencement of handling, there is no information in the literature on the time course of the response of salivary cortisol concentration to handling. The aims of these experiments were to (1). determine if there is a response to up to 4 min handling that affects cortisol concentration in saliva and (2). determine the main causes of variation in saliva cortisol in dogs over time. In experiment 1, saliva was collected from six Kelpies at 0 min then 2, 3 or 4 min after the commencement of restraint. There was no handling effect found in up to 4 min sampling time. In experiment 2, saliva was collected from six Labrador Retrievers five times in 2 h (14:00-16:00), three days a week for four weeks. Some of the sources of variation in saliva cortisol over time included between dog variation that varied over a period of days and variation between occasions that affected the group of dogs as a whole.

Efficacy of a competitive enzyme-linked immunosorbent assay (cELISA) for estimating prevalence of immunity to rabbit haemorrhagic disease virus (RHDV) in populations of Australian wild rabbits (Oryctolagus cuniculus)

This study examines the efficacy of a cELISA in estimating the prevalence of immunity to rabbit haemorrhagic disease virus (RHDV) in wild rabbits in Australia. Rabbits (n = 343) captured from six locations in Victoria and Queensland were experimentally challenged with a lethal oral dose (1500 50%-lethal doses, LD50) of RHDV. Death or survival to challenge was used to determine the performance characteristics of the test. The diagnostic specificity, sensitivity and accuracy were highly variable between sites, making it difficult to select a representative cut-off value for all sites that achieved a reasonable level of accuracy for the prediction of surviving and non-surviving rabbits. Estimates of prevalence of immunity were biased owing to effects of site of capture (time of capture) and age structure of the population. Using predictive equations, the best estimates of survival were ±10% but these results came from a limited range of sites, all of which had survival in the range 49–70%. The cELISA will determine whether the RHDV is present in rabbit populations but it should be used with caution when estimating the prevalence of immunity to RHDV. The cELISA may thus be limited in its application for examining the epidemiology of RHDV in Australian rabbit populations.

Tuberculous lesions in free-ranging white-tailed deer in Michigan

Descriptions of the anatomical distribution of Mycobacterium bovis gross lesions in large samples of white-tailed deer (Odocoileus virginianus) are lacking in the scientific literature. This report describes the distribution of gross lesions in the 58 white-tailed deer that cultured positive for M. bovis among the 19,500 submitted for tuberculosis testing in Michigan (USA) in 1999. For the vast majority (19,348) of those tested, only the head was submitted; for others, only extracranial tissues (33) or both the head and extracranial tissues (119) were available. Among those deer that cultured positive, cranial gross lesions were noted most frequently in the medial retropharyngeal lymph nodes, although solitary, unilateral parotid lymph node lesions also were found. Extracranial lesions occurred most commonly in the thorax. The distribution of lesions largely agreed with the few existing case reports of the M. bovis in white-tailed deer, although gross lesions were also found in sites apparently not previously reported in this species (liver, spleen, rumen, mammary gland). Some practical issues that may assist future surveillance and public education efforts are also discussed.

Experimental inoculation of European starlings (Sturnus vulgaris) and American crows (Corvus brachyrhynchos) with Mycobacterium bovis

The purpose of this series of pilot studies was to determine whether the passerine species studied are susceptible to infection with Mycobacterium bovis. Separate experiments were conducted on wild-caught starlings (Sturnus vulgaris) and American crows (Corvus brachyrhynchos). In each experiment, four birds were challenged intraperitoneally and four were challenged orally with microorganisms. Challenge dose was 1 x 10(5) colony-forming units of M. bovis cultured from a white-tailed deer (Odocoileus virginianus) case in Michigan. Birds were euthanatized at 1 and 2 mo postinoculation. Histologic lesions suggestive of mycobacteriosis, without the presence of acid-fast bacilli, were noted in all experimental groups. Mycobacterial cultures performed on pooled tissue samples were positive for M. bovis in only some of the intraperitoneal inoculates of each species.

Bovine tuberculosis in free-ranging carnivores from Michigan

During a survey of carnivores and omnivores for bovine tuberculosis conducted in Michigan (USA) since 1996, Mycobacterium bovis was cultured from lymph nodes pooled from six coyotes (Canis latrans) (four adult female, two adult male), two adult male raccoons (Procyon lotor), one adult male red fox (Vulpes vulpes), and one 1.5-yr-old male black bear (Ursus americanus). One adult, male bobcat (Felis rufus) with histologic lesions suggestive of tuberculosis was negative on culture but positive for organisms belonging to the Mycobacterium tuberculosis complex when tested by polymerase chain reaction. All the tuberculous animals were taken from three adjoining counties where M. bovis is known to be endemic in the free-ranging white-tailed deer (Odocoileus virginianus) population. There were two coyotes, one raccoon, one red fox, and one bobcat infected in Alpena county. Montmorency County had two coyotes and one raccoon with M. bovis. Two coyotes and a bear were infected from Alcona County. These free-ranging carnivores/omnivores probably became infected with M. bovis through consumption of tuberculous deer. Other species included in the survey were opossum (Didelphis virginiana), gray fox (Urocyon cinereoargenteus), and badger (Taxidea taxus); these were negative for M. bovis.

Comparison of postmortem techniques for the detection of Mycobacterium bovis in white-tailed deer (Odocoileus virginianus)

A retrospective study of various diagnostic postmortem techniques used in a 4-year surveillance program for detection of Mycobacterium bovis infection in wild white-tailed deer (Odocoileus virginianus) was conducted. The tests evaluated were routine histopathology, acid-fast staining, detection of acid-fast bacilli in culture, and an M. tuberculosis group-specific genetic probe applied to pure cultures. Each of these techniques were compared with a reference or "gold standard" of mycobacterial culture and identification. Histopathology, the most rapid form of testing for M. bovis infection in white-tailed deer samples, had a sensitivity of 98% and a specificity of 87%, resulting in a positive predictive value of 94%. The detection of acid-fast bacilli by staining was less sensitive than histopathology (90%), but its higher specificity (97%) resulted in a positive predictive value of 99%. The detection of acid-fast bacilli on culture was both highly specific (93%) and sensitive (100%). The group-specific genetic probe had the highest sensitivity and specificity and produced results in complete agreement with those of mycobacterial culture, suggesting that this technique could be used as the new "gold standard" for this particular wildlife tuberculosis surveillance program.

AT1-receptor blockade enhances ischemic preconditioning in hypertrophied rat myocardium

The purpose of this study was to determine whether ischemic preconditioning protects contractile function in hypertrophied rat myocardium from ischemia-reperfusion (I/R) injury. Male salt-sensitive rats were fed a high-salt diet for 2 wk to induce myocardial hypertrophy. Nonhypertrophied hearts were obtained from age-matched Sprague-Dawley (SD) rats fed a regular diet. Heart weight-to-body weight ratios were higher in salt-sensitive rats than in SD rats (6.9 +/- 0.2 vs. 4.7 +/- 0.2 g/kg, P < 0.01). A second group of salt-sensitive and SD rats was administered losartan (10 mg. kg(-1). day(-1)), an AT(1)-receptor blocker, for 1 wk before the study. Isolated hearts were preconditioned with transient ischemia before global I/R. After I/R, preconditioned hypertrophied hearts exhibited greater recovery of left ventricular developed pressure compared with that of preconditioned normal hearts (73 +/- 8 vs. 18 +/- 8%, P < 0.01). Left ventricular developed pressure was further enhanced by losartan in both hypertrophied and normal myocardium (99 +/- 5 vs. 73 +/- 8%, P < 0.05 and 97 +/- 15 vs. 18 +/- 8%, P < 0.01). Hypertrophied rat myocardium can be protected from I/R-induced contractile dysfunction by ischemic preconditioning. Losartan improves the ischemic tolerance of normal and hypertrophied myocardium.

The chest radiograph in critically ill surgical patients is inaccurate in predicting ventilator-associated pneumonia

Chest radiographs (CXRs) are frequently obtained in surgical intensive care unit (SICU) patients when a diagnosis of ventilator-associated pneumonia (VAP) is suspected. The purpose of this study was to determine if the interpretation of the CXR correlated with a diagnosis of VAP in SICU patients. Prospective evaluation of 20 SICU patients clinically suspected of VAP was performed from July 1997 through December 1998. All patients required mechanical ventilation for at least 48 hours, and antibiotic use was discontinued 24 hours before entry into the study. Bronchoscopy with protected specimen brush (PSB) sampling of secretions from the right and left lung was performed. A positive PSB was present if quantitative analysis yielded > or = 10(4) colony-forming units/mL of bacteria. VAP was diagnosed if either the right or left PSB was positive and ruled-out if both the right and left PSB yielded < 10(4) colony-forming units/mL. Twelve of 20 patients (60%) were diagnosed to have VAP by PSB criteria. Eight of 20 patients (40%) had CXRs interpreted as negative for infiltrates; four patients had VAP by PSB criteria. There were four patients with focal infiltrates; two patients had VAP. The remaining eight patients had radiographs interpreted as bilateral infiltrates (one) or pulmonary edema (seven); of these, six patients (75%) had VAP. The sensitivity of the CXR in determining the presence of VAP was 25 per cent, the specificity was 75 per cent, and the accuracy was 0.45. The CXR does not improve the clinician's ability to diagnose VAP: a normal CXR does not exclude the presence of VAP and the finding of a focal infiltrate does not confirm the diagnosis of VAP.