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Biomedical subjects

C E O'Connor

Publications and source records attributed to C E O'Connor.

7 recordsLinked to original sources
PubMed1998

Transmission of Leptospira interrogans serovar Balcanica infection among socially housed brushtail possums in New Zealand.

Leptospira interrogans serovar balcanica is a potential vector being investigated for spreading a biological control agent among introduced brushtail possums (Trichosurus vulpecula) in New Zealand. As previous studies have shown that possums are unlikely to contract leptospirosis through a contaminated environment alone, the objective was to determine whether L. interrogans serovar balcanica could be transmitted between sexually mature, socially housed possums. Possums were infected experimentally with L. interrogans serovar balcanica and housed in pairs or groups with uninfected possums for either 70 or 140 days, during the breeding or non-breeding seasons. No transmission occurred between any infected and uninfected possums during the non-breeding season. However, transmission occurred between females that had been socially housed in pairs or groups in the breeding season. Mixed sex transmission also occurred in pairs and groups, both from males to females and from females to males. Mixed sex transmission usually occurred rapidly (< 44 days) and was not associated with the production of offspring. No transmission occurred between males during the breeding or the non-breeding seasons. Transmission probably occurs as a result of affiliative or sexual behaviour, but is unlikely to occur through fighting. The social transmission pathways determined in this study suggest that L. interrogans serovar balcanica may have the transmission attributes desired in a vector for biological control.

Animals↗
PubMed1997

Duration of cyanide-induced conditioned food aversions in possums.

Learned aversions developed following sublethal ingestion of poisons are reported to be long-lived in many pest species. This study aimed to identify the duration of bait aversions following poisoning with a common poison (cyanide) used for possum control in New Zealand. Groups of possums with bait aversions (following cyanide poisoning) were reexposed to the bait (flavoured food) in a 2-choice test, at intervals of 1, 3, 6, 12, or 24 months. The relative intakes of the bait (used as the measure of bait aversion) did not differ between treatments (0.21, 0.21, 0.27, 0.32, and 0.20) for the 5 groups, respectively. The effect of repeated reexposures to the bait was also tested. The proportion of flavoured food eaten was 0.11, 0.19, 0.23, 0.33, and 0.36 for 1 to 5 reexposures, respectively. There was a significant increase in intake with repeated exposure. Thus, cyanide-induced aversions were strong and lasted for at least 24 months. The aversions weakened over several reexposures to the bait, but only for those individuals that had weaker initial aversions.

Animals↗
PubMed1997

Leptospirosis in brushtail possums: is Leptospira interrogans serovar balcanica environmentally transmitted?

In New Zealand, the biological control of introduced brushtail possums (Trichosurus vulpecula) may be the only affordable option for achieving a significant long term reduction in pest numbers on a national scale. Leptospira interrogans serovar balcanica is among the potential biocontrol agents and vectors currently being investigated for this purpose. As the transmission pathways of L. interrogans serovar balcanica between possums are poorly understood, the objective of the study was to determine whether infection could result from exposure to contaminated environments. Sixteen individually housed, uninfected possums, in three groups, were regularly exposed over a period of 32 days to contaminated cages or grass enclosures of 16 other experimentally infected possums all shedding leptospires in their urine. None of the 16 challenged possums developed serological evidence of L. interrogans serovar balcancia infection. These results suggest that this organism is unlikely to be transmitted environmentally, supporting previous circumstantial evidence that social contact may be required for transmission of L. interrogans serovar balcanica between possums.

Animals↗
PubMed1995

The influence of local tumor ulceration on the effectiveness of endocavitary radiation for patients with early rectal carcinoma.

BACKGROUND: Endocavitary radiation therapy is an alternative to surgical therapy for some early rectal carcinomas. Careful patient selection is necessary to ensure good results. The purpose of this study was to examine the authors' experience with endocavitary radiation at their institution from 1984 to 1991 to determine which factors were associated with treatment failure to provide for better future patient selection. METHODS: Thirty-two patients with carcinoma of the rectum, not apparently involving the muscle wall, underwent 75-120 Gy of endocavitary radiation as potentially curative therapy. Treatment was given as a series of 2-4 doses of 30 Gy at three weekly intervals. Twenty-two patients had polypoid tumors, 5 sessile, and 5 ulcerated. RESULTS: After a mean follow-up of 43 months (range, 6-103 months), 4 of 5 patients (80%) with ulcerated tumors developed local recurrences, compared with only 4 of 27 (15%) with sessile or polypoid lesions. Not only was the incidence of local recurrence greater for patients with ulcerated tumors (P = 0.009), but the time to recurrence was shorter also (P = 0.0001). Tumor size, anterior or posterior location, and dose of radiation received did not affect the rate of recurrence. CONCLUSIONS: These results indicate that superficial polypoid and sessile rectal tumors can be managed successfully with endocavitary radiation. Ulcerating tumors are likely to recur locally within a short time and therefore should be considered for surgical treatment initially.

Aged↗
PubMed1995

Cyanide induced aversions in the possum (Trichosurus vulpecula): effect of route of administration, dose, and formulation.

Possums (Trichosurus vulpecula) are New Zealand's main vertebrate pest. Control practices using poisons are likely to remain the most cost effective methods for the immediate future but poisons may be avoided in the field. A series of experiments were conducted to determine whether cyanide bait avoidance involved conditioned food aversions (CFA) induced by sublethal cyanide ingestion. Food aversions were conditioned in three experiments using intraperitoneal or oral routes of administration with three different cyanide formulations over a range of doses. Across all experiments there was a direct relationship between dose and the proportion of animals developing CFAs. When administered orally, doses greater than 5 mg/kg resulted in more than 50% of surviving animals developing aversions. Route of administration or formulation appeared to have no differential effect on development of CFA. Although there was considerable variation between individuals in the degree of aversion shown this may be one mechanism that could account for poor possum kill rates in some poisoning operations.

Administration, Oral↗