Transmission of Salmonella between wildlife and meat-production animals in Denmark.

AIMS: To investigate the transmission of Salmonella spp. between production animals (pigs and cattle) and wildlife on production animal farms in Denmark. METHODS AND RESULTS: In the winter and summer of 2001 and 2002, 3622 samples were collected from Salmonella-infected and noninfected herds of pigs and cattle and surrounding wildlife. Salmonella was detected in wildlife on farms carrying Salmonella-positive production animals and only during the periods when Salmonella was detected in the production animals. The presence of Salmonella Typhimurium in wild birds significantly correlated to their migration pattern and food preference. CONCLUSIONS: Salmonella was transmitted from infected herds of production animals (cattle and pigs) to wildlife that lived amongst or in close proximity to them. SIGNIFICANCE AND IMPACT OF THE STUDY: Salmonella in animal food products is associated with the occurrence of Salmonella in primary animal production. Strategies to control the introduction and spread of infection should include wildlife management, as the nearby wildlife may act as reservoirs for Salmonella spp. and/or may be passive carriers of the bacteria.

Prevalence of Pneumocystis carinii Delanoë & Delanoë, 1912 in rodents in Denmark.

Pneumocystis carinii has been found in 17 of 90 (19%) wild living trapped brown rats (Rattus norvegicus). The positive brown rats originated from about 25% of the trapping localities examined. Among brown rats of two breeding stocks, H and S, pneumocysts were found in 43.5% of the H rats, but in none of the S rats. By keeping brown H rats on a low protein diet for 8 weeks, it was possible to augment the prevalence to 53.8%. Pneumocystis carinii has furthermore been found in one of eight (12.5%) wild living long-tailed field mice (Apodemus sylvaticus), in one of 16 (6.3%) wild living house mice (Mus musculus), and in one of ten roof rats (Rattus rattus) of the Danish Pest Infestation Laboratory's breeding stock. Other rodent species, yellow-necked field mouse (Apodemus flavicollis), water vole (Arvicola terrestris), bank vole (Clethrionomys glareolus), field vole (Microtus agrestis), and an insectivor species, the common shrew (Sorex araneus) were all examined in small numbers, and were all negative for pneumocysts. Among rodents in Denmark. Rattus norvegicus seems to be the most important reservoir host for Pneumocystis carinii.

Palatability and toxicity of fipronil as a systemic insecticide in a bromadiolone rodenticide bait for rat and flea control.

Vector control in plague-infested areas requires a simultaneous killing of rodents and their fleas. We investigated the efficacy of a combination of a systemic insecticide, fipronil, in a rodenticide bait formulation under laboratory conditions. Four different concentrations of fipronil (0.05%, 0.005%, 0.0005% with acetone as a solvent, and 0.05% with propylene glycol as a solvent) and two controls (solvents only) were combined with the rodenticide bait (crushed organically grown wheat with 0.005% bromadiolone). Each concentration was offered together with an untreated non-poisonous challenge bait to 10 singly caged Rattus rattus L., each with 100 rat fleas Xenopsylla cheopis Rothschild (Siphonaptera: Pulicidae) in the nest. Treated bait consumption was relatively low and an unsatisfactory rat mortality of around 50% only was obtained in all tests. The palatability of the bait, however, was not affected by the fipronil concentration. Even at the lowest fipronil concentration, average flea mortality was still above 95%, and doses of more than I mg fipronil per kg rat body weight gave a nearly complete kill of fleas. Fipronil can be highly effective as a systemic insecticide to for flea control, provided that a more attractive bait base for roof rats is used.

Population structure of rat-derived Pneumocystis carinii in Danish wild rats.

The rat model of Pneumocystis carinii pneumonia is frequently used to study human P. carinii infection, but there are many differences between the rat and human infections. We studied naturally acquired P. carinii in wild rats to examine the relevance of the rat model for human infection. P. carinii DNA was detected in 47 of 51 wild rats and in 10 of 12 nonimmunosuppressed laboratory rats. Evidence for three novel formae speciales of rat-derived P. carinii was found, and these were provisionally named Pneumocystis carinii f. sp. rattus-secundi, Pneumocystis carinii f. sp. rattus-tertii, and Pneumocystis carinii f. sp. rattus-quarti. Our data suggest that low-level carriage of P. carinii in wild rats and nonimmunosuppressed laboratory rats is common and that wild rats are frequently coinfected with more than one forma specialis of P. carinii. We also examined the diversity in the internally transcribed spacer (ITS) regions of the nuclear rRNA operon of Pneumocystis carinii f. sp. carinii by using samples from wild rats and laboratory rats and spore trap samples. We report a lack of variation in the ITS1 and ITS2 regions that is consistent with an evolutionary bottleneck in the P. carinii f. sp. carinii population. This study shows that human- and rat-derived P. carinii organisms are very different, not only in genetic composition but also in population structure and natural history.