Bluetongue virus infection in naïve cattle: Identification of circulating serotypes and associated Culicoides biting midge species in Trinidad.

To better understand risks associated with trading cattle, it is important to know which serotypes of Bluetongue virus (BTV) are circulating within the exporting and importing country. Hence, this study was conducted to identify the circulating serotypes of BTV in Trinidad. Blood samples were collected monthly from sixty BTV- naïve imported cattle over a six month period after their arrival in the country. Virological (PCR and virus isolation) and serological (ELISA) analyses were carried out on the samples and CDC light traps were placed near the cattle enclosure to trap and identify the species of Culicoides biting midges that were present. All of the cattle seroconverted for BTV antibodies within three months of their arrival in the country and real-time reverse transcription PCR (rRT-PCR) detected BTV-RNA in the samples throughout the remainder of the study. The patterns of infection observed in the cattle indicated serial infections with multiple serotypes. A combination of BTV serotype-specific rRT-PCR on the original blood samples and virus isolation followed by serotype-specific rRT-PCR on selected samples, confirmed the presence of BTV serotypes 1, 2, 3, 5, 12 and 17. This is the first report of BTV-2 and BTV-5 in Trinidad. Light-suction traps placed in close proximity to the cattle predominantly trapped Culicoides insignis Lutz 1913 species (96%), with a further six Culicoides species making up the remaining 4% of trapped samples. The circulation of multiple BTV serotypes in Trinidad underlines the need for regular surveillance, which will contribute to the development of risk assessments for trade in livestock.

Comparison of UV light-suction, incandescent light-suction, semiochemical /CO2-baited and sweepnet traps considering the Culicoides specimen yield, species diversity and crepuscular activity in South Oropouche, Trinidad, W I

Current Culicoides biting midge trapping studies in Trinidad, West Indies, using miniature CDC lightsuction traps have been yielding relatively low numbers of specimens and different species when compared to studies done over 20 years ago that primarily used similar incandescent light-suction traps (Mo et al., 1994). To determine whether this new data is a fair representation of the current status of midges in Trinidad, we compared three different trap types (UV light-suction, incandescent light-suction and 1- Octen-3-ol/CO2-baited), placed in three different set positions (3x3 randomized Latin square design) in a small dairy goat farm located in South Oropouche, Siparia, Trinidad. In a separate exercise at the same farm, we also investigated whether certain Culicoides species showed peak activity in the earlier evening (diurnal species) or later evening (nocturnal species). The farm was sweep-net every 15 minutes for the last two hours of daylight over four days. For both exercises, midges were sorted out and placed in 70% ethanol until speciated via morphology using established biological keys (Aitken et al., 1975). The trap-comparison exercise (total number = 30,702) indicated the semiochemical-baited and UV-light traps gave significantly better specimen yield and species diversity than the incandescent light traps; an apparent gender bias was also noted dependent on the type of trap used. The sweep-net exercise (total number = 975) indicated Culicoides species diversity was fairly constant with C. furens and C. pusillus present at all of the time intervals; however, the highest species diversity was observed between 18:00 and 18:15. Interestingly, C. aitkeni consistently appeared from 17:30 onwards.