Fipronil and (S)-methoprene can lessen the risk of transmission of Bartonella clarridgeiae among cats with exposure to Ctenocephalides felis.

OBJECTIVE: To cohouse cats experimentally infected with Bartonella clarridgeiae (Bc) with naive cats in a flea-free environment or with Ctenocephalides felis, Bartonella henselae (Bh), Mycoplasma haemofelis, and Candidatus Mycoplasma haemominutum to determine which flea could be a vector and to assess whether transmission of the infectious agents could be blocked by fipronil and (S)-methoprene. ANIMALS: Specific pathogen-free cats (n = 34). METHODS: In experiment 1, Bc was inoculated in 1 cat that was housed with 9 naive cats without C felis. In experiment 2, the 2 cats inoculated with Bc were housed with 6 other cats (2 inoculated with Bh, 2 inoculated with M haemofelis, and 2 inoculated with Candidatus M haemominutum) in the center (enclosure 2) of 3 housing enclosures separated by mesh walls that allow passage of fleas but precludes fighting. C felis were placed only on cats in enclosure 2 (5 times). Cats in enclosures 1 (n = 8) and 2 (8) were untreated, and cats in enclosure 3 (8) were administered fipronil and (S)-methoprene. Blood was collected from all cats for PCR assays for the pathogens. RESULTS: None of the cats housed with the cat inoculated with Bc became PCR positive in the absence of C felis. All cats in enclosure 2 became Bc DNA positive. While 2 of 8 cats in enclosure 1 became Bc PCR positive, none of the treated cats in enclosure 3 became infected. CLINICAL RELEVANCE: The study demonstrated that C felis can be a vector for Bc. The results support the recommendation that flea control products can reduce the risk of transmission of flea-borne pathogens.

Total thyroxine and thyroid-stimulating hormone responses of healthy cats to different doses of thyrotropin-releasing hormone.

Thyrotropin-releasing hormone (TRH) stimulation can be used as a test of thyroid function and pituitary thyrotropin (thyroid-stimulating hormone, TSH) reserve, but optimal stimulation testing protocols in cats are unreported. We randomly divided 6 healthy young adult cats into 3 groups of 2 and administered 3 different intravenous doses of TRH (0.01, 0.05, 0.1 mg/kg) at weekly intervals in our crossover study. Serum TSH and thyroxine (T4) concentrations were measured using chemiluminescent immunoassay before, and at 30 and 60 min after, TRH administration. All cats were monitored for 4 h post-TRH administration for side effects. All 3 TRH doses induced significant TSH (0.01 mg/kg, p = 0.001; 0.05 mg/kg, p = 0.002; 0.1 mg/kg, p = 0.006) and total T4 (0.01 mg/kg, p = 0.008; 0.05 mg/kg, p = 0.006; 0.1 mg/kg, p = 0.001) responses. Lower TRH doses (0.01 and 0.05 mg/kg) caused fewer side effects (1 of 6 cats) than did the highest dose (3 of 6 cats), and may be safer in cats than the previously reported higher dose (0.1 mg/kg) of TRH. Our results do not support the use of maropitant to prevent side effects of a TRH stimulation test in cats.

Environmentally relevant concentrations of herbicides impact non-target species at multiple sublethal endpoints.

There is concern over herbicide exposure effects on aquatic primary production and zooplankton as herbicides are found in aquatic ecosystems at concentrations potentially toxic to phytoplankton. We first aimed to determine the effect concentrations (growth inhibition) and mixture interactions of the herbicides diuron (0.5 to 50µg/L) and hexazinone (0.5 to 40µg/L) on the green algae Pseudokirchneriella subcapitata. Secondly, we evaluated chronic effects on Daphnia magna that were periodically fed on P. subcapitata that had been exposed to low, medium, and high concentrations. We hypothesized that based on the mode of action of the herbicides we would observe additive growth inhibition in algae, and sublethal effects on D. magna. Growth inhibition in P. subcapitata following mixture exposure was most consistent with the concentration addition (CA) concept; while the independent action (IA) model underestimated the combined effect. The lowest observed effect concentrations (LOEC) were 1.50µg/L hexazinone, 1.18µg/L diuron, and 0.125 TU (0.30µg/L diuron×0.12µg/L hexazinone) in the single and binary mixture exposures, respectively. High hexazinone exposure decreased D. magna survival (80% vs. 55.6%). Neonate number was reduced by 13.9% in high mixture and 23.5% in high hexazinone treatments. Gravid body length was reduced by 9.5% following exposure to the high mixture. Herbicide exposure decreased neonate size, especially in later broods. Herbicides decreased the phototaxic responses of neonates in most treatments. Herbicide exposure effects were detected at environmentally relevant concentrations, levels considered to be safe according to current USEPA aquatic life benchmarks, suggesting that these benchmarks need to be updated to improve ecological risk assessment. As herbicides are some of the most applied pesticides worldwide, sublethal endpoints can serve as sensitive early warning tools to indicate their presence and can support regulatory assessments and monitoring to protect aquatic life.