Reduced spillover transmission of Mycobacterium bovis to feral pigs (Sus scofa) following population control of brushtail possums (Trichosurus vulpecula).

In New Zealand, bovine tuberculosis (bTB) is present in domestic cattle and deer herds primarily as the result of on-going disease transmission from the primary wildlife host, the brushtail possum (Trichosurus vulpecula). However, bTB is also present in other introduced free-ranging mammalian species. Between 1996 and 2007, we conducted a series of studies to determine whether poison control of possum populations would have any effect on the prevalence of Mycobacterium bovis infection in sympatric feral pigs (Sus scrofa). We compared trends in the prevalence of bTB infection in feral pigs in six study areas: possum numbers were reduced in three areas, but not in the other three, effectively providing a thrice-replicated before-after-control-intervention design. Before possum control, the overall prevalence of culture-confirmed M. bovis infection in feral pigs was 16.7-94.4%, depending on area. Infection prevalence varied little between genders but did vary with age, increasing during the first 2-3 years of life but then declining in older pigs. In the areas in which possum control was applied, M. bovis prevalence in feral pigs fell to near zero within 2-3 years, provided control was applied successfully at the whole-landscape scale. In contrast, prevalence changed much less or not at all in the areas with no possum control. We conclude that feral pigs in New Zealand acquire M. bovis infection mainly by inter-species transmission from possums, but then rarely pass the disease on to other pigs and are end hosts. This is in contrast to the purported role of pigs as bTB maintenance hosts in other countries, and we suggest the difference in host status may reflect differences in the relative importance of the oral route of infection in different environments. Despite harbouring M. bovis infection for a number of years, pigs in New Zealand do not sustain bTB independently, but are good sentinels for disease prevalence in possum populations.

Prevalence of ballooning of the severed carotid arteries at slaughter in cattle, calves and sheep.

Previous work in calves indicated that ballooning of the severed arteries is a potential concern in animals receiving a reversible stun before slaughter, and in animals not stunned before slaughter, as it could extend the duration of brain function before the animals die. This study determined the prevalence of ballooning of the carotid arteries in a total of 987 cattle, calves and lambs at slaughter. The severed ends of the carotid arteries were examined by palpation. The prevalence of ballooning that was 3cm or more in diameter, was 16%, 25% and 0% for cattle, calves and lambs, respectively. Artery sections were taken from a sample of large cattle and examined histologically. In ballooned arteries there was coagulated blood between the outer surface of the artery and the inner aspect of the connective tissue sheath surrounding the artery, suggesting the formation of a false aneurysm in the ballooning phenomenon.

Serotonin reuptake is less efficient in taste aversion resistant than in taste aversion-prone rats.

We have previously reported the development of rat lines bred selectively for differences in taste aversion conditionability. Earlier studies demonstrated that the taste aversion resistant (TAR) animals exhibited lower concentrations of brain serotonin and consumed greater amounts of ethanol than their taste aversion prone (TAP) counterparts. In the present study, TAR rats demonstrated significantly less efficient brain serotonin transport compared to TAP rats, but the rat lines demonstrated similar levels of serotonin transporter or V(max) and similar whole brain paroxetine (a specific serotonin reuptake inhibitor) binding (B(max)). These results suggest that the rat lines differ in the mechanisms that transport serotonin into nerve endings, but do not differ in the binding of serotonin to the transporter or in the number of serotonin transport sites. The data support the hypothesis that genetically determined differences in the serotonin system contribute to individual differences in taste aversion conditionability. The findings further suggest that differences in serotonin transport may influence the propensity to self-administer ethanol.

Left ventricular function in uremia: echocardiographic and radionuclide assessment in patients on maintenance hemodialysis.

Echocardiography and radionuclide ventriculography were performed in 37 uremic patients on maintenance hemodialysis with no apparent coronary artery disease, pericardial effusion, valvular heart disease or heart failure. These non-invasive studies were performed during the interdialytic period (about 18 hours after a dialysis). Sixty-two percent of our patients had abnormal left ventricular function with one or more abnormal echocardiographic parameters. The significant abnormalities were enlargement of the left ventricular cavity, a reduction of myocardial contractility, and thickening of the left ventricular posterior wall. Similar findings were found in 10 undialyzed uremic patients. Measurement of cardiac index and ejection fraction were found to be inadequate for a full assessment of left ventricular function and other parameters such as the mean velocity of circumferential fiber shortening and mean normalized posterior wall velocity should be included. There is a significant number of hemodialysis patients (7/37) with congestive cardiomyopathic features on the echocardiogram. Their clinical features are no different from the other patients in this study, except they have a significantly higher prevalence of uremic hyperparathyroidism. Our findings support that the existence of a specific uremic cardiomyopathy and uremic hyperparathyroidism may play an important role in the pathogenesis.

Aspects of myocardial ischaemia: sudden death.

The majority of patients who die suddenly have significant coronary artery disease, and it seems likely that myocardial ischaemia, in consequence of these diseased arteries, plays an aetiological role in causation of sudden death.

Longevity of Mycobacterium bovis in brushtail possum (Trichosurus vulpecula) carcasses, and contact rates between possums and carcasses.

AIM: To determine, for a variety of environmental conditions, how long Mycobacterium bovis might remain viable inside the carcass of a brushtail possum (Trichosurus vulpecula) that died of bovine tuberculosis (Tb), and to measure the rate of contact between free-ranging possums and possum carcasses. METHODS: Lesions of M. bovis were simulated by inoculating excised spleens weighing 0.5-1 g with 0.2 mL liquid culture containing approximately 5 x 10(7) cfu M. bovis/mL. Simulated lesions were inserted into possum carcasses (n=48) at the peripheral lymph nodes. Carcasses were placed in the field at two sites (a tussock grassland and a podocarp-broadleaved forest site) and in two seasons (summer and winter) for up to 62 days. Survival rates of M. bovis were estimated by sampling the simulated lesions over time, and culturing the recovered lesion to determine if any viable M. bovis bacteria were present. The time taken for a free-ranging possum to first encounter a dead possum in its home range was estimated by live-trapping possums and fitting them with proximity loggers (n=13). A 'contact' was recorded if these possums came within 40-50 cm of proximity loggers fitted to possum carcasses. RESULTS: There were strong seasonal and site effects in the survival rate of M. bovis in possum carcasses. In the grassland habitat, no viable bacilli were cultured from any carcass after 3 days in summer, whereas in winter all samples were culture-positive for the first 20 days, and some were still positive after 27 days. The survival rates for forest habitat were intermediate between the results for grassland, and there were no culture-positive carcasses after 9 days in summer or 27 days in winter. In summer, infected carcasses (n=6) were first encountered by possums a mean 1.9 (range 0.4-6.7) days after placement. CONCLUSIONS: Possum carcasses were contacted by free-ranging possums within the period that viable M. bovis were shown to survive in a carcass. The risk of such infection is likely to be most significant in winter or in areas with microhabitats where the survival of M. bovis is high. However, the generally low survival rate of M. bovis in possum carcasses and the low frequency of possum-to-carcass contacts indicate this route of transmission alone could not maintain Tb in a possum population.

Primary tuberculosis of the conjunctiva.

A five-year-old boy developed primary tuberculosis of the conjunctiva which spread to the preauricular and cervical lymph nodes, producing caseous lymphadenitis. Because conjunctival tuberculosis is rare, the correct diagnosis may be easily missed. When unilateral conjunctivitis is accompanied by lymph node enlargement and persists or progresses, tuberculosis should be suspected.

The prevalence of ST-segment depression on ambulatory electrocardiographic monitoring during daily life in high-risk asymptomatic police officers.

BACKGROUND: In individuals with no known ischaemic heart disease, the prevalence and significance of ST-segment depression on ambulatory electrocardiographic monitoring is unclear. We therefore determined the prevalence of ST-segment depression among middle-aged male police officers, an occupational group in whom an increased risk of ischaemic heart disease has been reported, who also had multiple individual coronary risk factors but no known ischaemic heart disease. METHODS: Full-time male police offices aged 45 years or more with at least two coronary risk factors but no known ischaemic heart disease performed a 24h ambulatory electrocardiographic monitor, timed to include a shift of work. The number and duration of episodes of ST-segment depression were determined. In those in whom ST-segment depression was detected, exercise thallium scintigraphy and repeat 24h ambulatory electrocardiographic monitoring were performed. RESULTS: The prevalence of ST-segment depression on 24h ambulatory electrocardiographic monitoring, including an 8h period of normal work, was 3.4% (95% confidence interval 1.3-8.3%). Exercise thallium scintigraphy was carried out in those in whom ST-segment depression had been detected. Despite two participants developing ST-segment depression during exercise, no evidence of myocardial ischaemia was observed on the perfusion scan. Therefore, the prevalence of ST-segment depression on ambulatory electrocardiographic monitoring in this asymptomatic but high-risk population was low and, when it did occur, no exercise-induced myocardial ischaemia was observed. CONCLUSION: These results suggest that ST-segment depression on ambulatory electrocardiographic monitoring in asymptomatic subjects may not represent myocardial ischaemia. The use of this parameter to screen asymptomatic populations for ischaemic heart disease is therefore highly questionable.

The effect of a selective beta adrenergic blocking agent on ventricular arrhythmias in the first year following myocardial infarction.

Fifty-five patients with recent acute myocardial infarction entered a single-blind cross-over trial to assess the effect of oral practolol 200 mg twice daily on the incidence and nature of ventricular arrhythmias in the first year following myocardial infarction. Patients had 24-hour Holter electrocardiogram tape monitoring at two weeks following infarction and at three-monthly intervals for one year. Twenty-six patients completed the full year of the trial with 12% of tape recordings technically unsatisfactory. A total of 46 periods of comparison of the action of practolol versus placebo therapy were available in thirty patients. Whilst receiving the selective beta adrenergic blocking agent, practolol, there was a significant reduction in the percentage of studied hours during which salvos of ventricular premature beats occurred (P < 0.025), however the percentage of patients in whom salvos were recorded was unchanged. The incidence of all other ventricular arrhythmias was not reduced in the practolol group. When the effect of practolol was related to the site of infarction, anterior or inferior, there was no significant reduction in the incidence of ventricular arrhythmias.

The diastolic murmur of renal failure.

A characteristic and transient early diastolic precordial murmur is commonly heard in patients with renal failure. On the basis of its clinical characteristics, this murmur has previously been attributed to functional aortic incompetence. We undertook a formal cardiac investigation, including aortography, in six of eight patients with renal failure in whom such a bruit developed. Aortic regurgitation was detected in only one of the six. Echocardiography revealed no abnormality of aortic-valve function but did indicate the presence of a small pericardial effusion in each of the five patients examined. We conclude that the early diastolic murmur associated with renal failure does not usually arise from functional aortic incompetence but may be a sound of pericardial origin.

Nickel gas chromatographic columns: an alternative to glass for biological samples.

Nickel tubing may be substituted for glass in the fabrication of gas chromatographic columns for use with samples of biological interest. Comparisons of separations of mixtures of steroids, narcotic alkaloids, phenothiazines, and amphetamines on stainless stell, glass, and nickel packed columns showed little or no observable sample decomposition on glass or nickel as contrasted to complete loss of certain compounds on stainless steel. The nickel columns are easily prepared, durable, economical, and not subject to breakage.