The effect of fertility control on the transmission of bovine tuberculosis in wild brushtail possums

AIM: To determine the effect of fertility control on the rate of transmission of bovine tuberculosis (Tb), caused by Mycobacterium bovis, in brushtail possums (Trichosurus vulpecula).

METHODS: At two study sites with a history of Tb infection in the resident possum population, a sample of adult male and female possums (n=50), determined by palpation to be Tb-free, was surgically sterilised by gonadectomy. A sample of untreated Tb-free male and female possums (n=54) served as controls. Each study site was trapped every 2 months over a 3-year period, and the Tb status of the individuals in the trial assessed. At the conclusion of the trial, all remaining experimental individuals were killed, necropsied and examined for characteristic lesions typical of Tb. The rate of transmission of Tb infection was estimated using the incidence of tuberculous cases in the experimental animals and comparing it between sites, sex and sterilisation treatment.

RESULTS: Sterilisation by gonadectomy resulted in a reduction in the rate of transmission of Tb in male possums by 53%, but a corresponding increase in sterilised females for reasons that are still unclear. However, this interaction was statistically weak (p=0.10). When the sexes were combined, there was no overall effect of sterilisation on the rate of transmission of Tb (p=0.43). Sterility treatment notwithstanding, there was a highly significant difference in the rate of transmission between the sexes (p=0.01), being almost one order of magnitude higher in untreated males compared with untreated females.

CONCLUSIONS: Although lacking strong statistical support, these results suggest that fertility control that targets endocrine control of fertility may provide some additional benefits for disease control over that achieved by reductions in population density, by reducing the rate of transmission of M. bovis in male possums. However, additional studies are needed to confirm the validity of these results. The large difference in the rate of transmission of M. bovis in untreated males compared with untreated females suggests that transmission of Tb among males may be an important driver of the dynamics of Tb infection in possums.     

The effect of transportation on the immune status of Bos indicus steers

This study investigated the effect of 72 h of road transport on the immune status of Bos indicus steers (n = 10; age = 15 to 18 mo). Total and differential leukocyte numbers and lymphocyte function were determined at 2 d before transport (-48 h), immediately after 72 h of transport (72 h), and 6 d after transport (216 h). Phytohemagglutinin (PHA)-stimulated lymphocyte proliferation, interferon-gamma production, and tetanus-toxoid specific antibody levels were determined. Total leukocyte and eosinophil numbers showed a transient decrease at 72 h (immediately after transport; P < 0.05) and returned to baseline values by 6 d after transport. Lymphocyte numbers and antibody titers were unaffected by transportation. The PHA-stimulated lymphocyte proliferation decreased (P < 0.05) at 72 h and returned to baseline levels 6 d after transport. This study demonstrated that transportation of mature Bos indicus steers caused transient decreases in leukocyte numbers and lymphocyte function, although all measures recovered by 6 d after transport. Therefore, Bos indicus cattle may be vulnerable to infection during this period.     

The use of computed tomography in the diagnosis of an ectopic ureter in a Quarter Horse filly

This report describes a 4‐month‐old Quarter Horse filly with an ectopic ureter. The filly presented with signs of urinary incontinence, which had been present since birth. Computed tomography (CT) examination and cystoscopy confirmed a diagnosis of a unilateral ectopic ureter. A nephrectomy of the left kidney was performed and renal function was closely monitored post operatively. The filly was treated for abdominal chylous effusion as a post operative complication. The filly survived to discharge from the hospital, and maintained normal urinary function at 12 months post operatively.     

Dye-sensitized photoinactivation of the lactic dehydrogenase and acetylcholinesterase from the boll weevil,Anthonomous grandis

The lactic dehydrogenase and acetylcholinesterase enzymes of the boll weevil, Anthonomous grandis, have been shown to be inactivated by dye-sensitized photooxidation mediated by substituted xanthenes. The efficiency of the photooxidation reaction was correlated with the degree of halogenation of the dye molecule, the efficiency of the dye in singlet oxygen formation, and the strength of binding to lactic dehydrogenase. Changes in the in vivo levels of these enzymes due to ingestion of rose bengal by adult weevils are not further modified in the presence of light.     

A comparison of predictions made by three simulation models of foot-and-mouth disease

AIMS: To describe results of a relative validation exercise using the three simulation models of foot-and-mouth disease (FMD) in use by the quadrilateral countries (QUADS; Australia, Canada, New Zealand, and United States of America; USA).

METHODS: A hypothetical population of farms was constructed and, following the introduction of an FMD-like disease into a single farm, spread of disease was simulated using each of the three FMD simulation models used by the QUADS countries. A series of 11 scenarios was developed to systematically evaluate the key processes of disease transmission and control used by each of the three models. The predicted number of infected units and the size of predicted outbreak areas for each scenario and each model were compared using the Kruskal-Wallis test. Agreement among the three models in terms of geographical areas predicted to become infected were quantified using Fleiss' Kappa statistic.

RESULTS: Although there were statistically significant differences in model outputs in terms of the numbers of units predicted to become infected, the temporal onset of infection throughout the simulation period, and the spatial distribution of infected units, these differences were generally small and would have resulted in the same (or similar) management decisions being adopted in each case.

CONCLUSIONS: Agreement among the three models in terms of the numbers of premises predicted to become infected, the temporal onset of infection throughout the simulation period, and the spatial distribution of infected premises provides evidence that each of the model developers are consistent in their approach to simulating the spread of disease throughout a population of susceptible individuals. This consistency implies that the assumptions taken by each development team are appropriate, which in turn serves to increase end-user confidence in model predictions.

CLINICAL RELEVANCE: Relative validation is one of a number of steps that can be undertaken to increase end-user confidence in predictions made by infectious disease models.