Prevalence and transmission of Toxoplasma gondii in wild brown rats, Rattus norvegicus.

Prevalence of Toxoplasma gondii within 6 UK farmstead wild rat populations, and 1 population maintained within a captive cat-free environment for 2.5 years, was examined. The mean prevalence found was 35% (n = 235), which is more than 3 times as high as all other wild rat prevalence levels previously reported in the UK. There were no significant age, sex or site differences in prevalence between or within populations irrespective of habitat type or presence of cats. Toxoplasma was also maintained within the captive rat population in the absence of cats at a prevalence, intensity, age and sex distribution similar to that of the farmstead rat populations. These results suggest, firstly, that Toxoplasma can be perpetuated within wild rat populations without the sympatric presence of cats and secondly, that the congenital route is the predominant route of transmission in wild rats. This study concludes that wild rats represent a significant and persistent wildlife intermediate host reservoir for toxoplasmosis.