Host preferences of tabanid flies based on identification of blood meals by ELISA
Introduction
Trypanosona evansi is a protozoan parasite which causes the animal disease surra. The disease affects livestock as well as wild life. In susceptible animals surra is manifested by pyrexia directly associated with parasitaemia, together with progressive anaemia, loss of condition and lassitude (OIE, 2004). It is endemic throughout southeast Asia and much of the Indonesian archipelago (Reid et al., 1999). The disease does not occur in Australia, but there is a risk of it entering the country from the north (Reid and Copeman, 2003, Van Hennekeler et al., 2008). Trypanosoma evansi is mainly spread mechanically on the mouthparts of blood-feeding tabanids (Herrera et al., 2005, Desquesnes et al., 2008). There are many species of tabanids in Australia (Mackerras, 1971), but very little is known about their feeding habits and host range. With vector-borne diseases, knowledge of the main hosts is a key element in understanding the potential importance of the vector and epidemiology of the disease (Van den Bossche and Staak, 1997).
Blood meal analysis has been used to determine main hosts, host preferences and feeding patterns in many biting insects; for example Anopheles mosquitoes (Mukabana et al., 2002, Mwangangi et al., 2003, Parida et al., 2006), Culex mosquitoes (Mboera and Takken, 1999, Lee et al., 2002, Zinser et al., 2004), Aedes mosquitoes (Ponlawat and Harrington, 2005, Richards et al., 2006), savannah tsetse flies (Snow et al., 1988, Clausen et al., 1998), rain-forest tsetse flies (Spath, 2000, Njioku et al., 2004), Lutzomyia sand flies (Marassa et al., 2006), Phlebotomus sand flies (Bongiorno et al., 2003, Svobodova et al., 2003), Simulium blackflies (Hunter and Bayly, 1991, Boakye et al., 1999) and biting midges, Culicoides sp. (Tempelis and Nelson, 1971, Blackwell et al., 1994). Tabanid flies remain among the least studied vectors, and analysis of feeding patterns by blood-meal identification have only been conducted in Louisiana (USA) (Wilson and Richardson, 1969), Connecticut (USA) (Magnarelli and Anderson, 1980) and Congo (Gouteux et al., 1989). The study in Congo only focused on two anthropophilic species of Chrysops which are known vectors of Loa loa among humans. No work has been done on host preferences of tabanid flies in Australia, although many species have been observed feeding on various animals (Mackerras, 1971, Muzari et al., 2010), and general observations indicated that humans were not preferred hosts but several species fed on domestic stock (Mackerras, 1971). This lack of knowledge remains a critical gap in our ability to evaluate the likely impact of tabanid-transmitted diseases like surra.
This study investigated the feeding patterns and host preferences of different tabanid species by identifying and comparing prevalence of blood meals from different host types among field-caught tabanids in Queensland, north-eastern Australia.
Section snippets
Study area and tabanid trapping
Tabanid flies were captured from their natural habitat in the Townsville area of Queensland using Nzi traps (Mihok, 2002) baited with octenol. Most of the area consisted of savanna vegetation dominated by Eucalyptus trees, with sections of open grassland generally used for grazing. Nine traps were deployed at permanent positions in February - March 2007 and insects were collected from them three times per week. Tabanids were identified to species based on the keys of (Mackerras, 1959,
Prevalence of host blood meals among different tabanid species
After optimisation, all the assays for identification of blood meals were sensitive enough to detect a minimum of 0.001 μl of blood residue in tabanid abdomen, and there were no cross-reactions among any tested hosts at the optimal reagent concentrations. When fully engorged, a medium-sized tabanid such as T. pallipennis contains ∼40 μl of blood (Muzari et al., 2010).
A total of 1597 tabanids belonging to ten species were captured over a five-week trapping period, and 1498 specimens from six most
Prevalence of host blood meals among different tabanid species and locations
The tabanid specimens analysed in this study were all captured using odour-baited traps, which generally catch flies that are in search of a blood-meal (Odulaja and Madubunyi, 1997, Muzari and Hargrove, 2005), and this represents only a subset of the blood-fed tabanid population. This consequently underestimates the prevalence of tabanid attacks on each host type, but more so on the less defensive hosts and in relation to tabanid species that are more persistent at trying to complete the
Conflict of interest statement
All authors declare that there are no financial or personal relationships with other people that could inappropriately influence their work.
Role of funding source
The authors further declare that the study sponsors had no involvement in the study design, in the collection, analysis and interpretation of data; in the writing of the manuscript and in the decision to submit the manuscript for publication.
Acknowledgements
The authors are grateful to Oonoonba Veterinary Research Institute, Heleen Downs Estates, Jaymie and Alex Raines, Wayne Krowe's family and Lee Berger for availing their properties for tabanid trapping as well as taking great care of the traps during the study. We also thank Dr Jan Smith and Dr Andrew van den Hurk for valuable advice on ELISA techniques and Dr Stephen Garland for helpful comments on earlier drafts of the manuscript. Research funding received from the Australian Biosecurity CRC
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