Prevalence and co-infection of Toxoplasma gondii and Neospora caninum in Apodemus sylvaticus in an area relatively free of cats.

The protozoan parasite Toxoplasma gondii is prevalent worldwide and can infect a remarkably wide range of hosts despite felids being the only definitive host. As cats play a major role in transmission to secondary mammalian hosts, the interaction between cats and these hosts should be a major factor determining final prevalence in the secondary host. This study investigates the prevalence of T. gondii in a natural population of Apodemus sylvaticus collected from an area with low cat density (<2·5 cats/km2). A surprisingly high prevalence of 40·78% (95% CI: 34·07%-47·79%) was observed despite this. A comparable level of prevalence was observed in a previously published study using the same approaches where a prevalence of 59% (95% CI: 50·13%-67·87%) was observed in a natural population of Mus domesticus from an area with high cat density (>500 cats/km2). Detection of infected foetuses from pregnant dams in both populations suggests that congenital transmission may enable persistence of infection in the absence of cats. The prevalences of the related parasite, Neospora caninum were found to be low in both populations (A. sylvaticus: 3·39% (95% CI: 0·12%-6·66%); M. domesticus: 3·08% (95% CI: 0·11%-6·05%)). These results suggest that cat density may have a lower than expected effect on final prevalence in these ecosystems.

Altered sympathoadrenal response to dynamic exercise in cardiac transplant recipients.

The cardiac denervation produced by heart transplantation modifies the physiological response to exercise. The cardiorespiratory and sympathoadrenal response of seven "healthy" orthotopic heart transplant recipients was compared to seven age matched normal subjects during progressive dynamic exercise. The initial venous noradrenaline concentration tended to be higher in the transplant group, at 3.6 (SEM 0.6) v 2.9(0.2) nmol-litre-1 (NS). Noradrenaline concentrations were significantly higher in the transplant group during exercise (p less than 0.05, by analysis of variance). The transplant recipients reached a lower maximum workload than the normal subjects, at 102(8) v 170(10) watts (p less than 0.01) and the peak noradrenaline concentrations were similar in the two groups. The fall in noradrenaline concentrations after exercise was similar in the two groups. This showed that noradrenaline clearance was normal in the transplant recipients and the higher noradrenaline level reflected increased sympathetic activity. Despite the normal peak noradrenaline concentration, the transplant recipients achieved lower maximum heart rates than the normal subjects, at 142(3) v 181(5) beats min-1 (p less than 0.01). Adrenaline concentrations were similar in the two groups during submaximal exercise and tended to be lower in the transplant recipients at maximal exercise. The increased sympathetic activity may be a response to altered cardiac performance because of efferent cardiac denervation or to loss of tonic inhibition of sympathetic activity by cardiac receptors due to afferent denervation. Both circulating noradrenaline and adrenaline appear to play a significant role in the heart rate response to exercise after cardiac transplantation.