Aspects of the ecology of tabanid flies (Family Tabinidae) in North Queensland and their potential to transmit Trypanosoma evansi

van Hennekeler, Kirsty (2007) Aspects of the ecology of tabanid flies (Family Tabinidae) in North Queensland and their potential to transmit Trypanosoma evansi. PhD thesis, James Cook University.

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Abstract

Surra, the disease caused by the protozoal parasite, Trypanosoma evansi, is characterised by weight loss, anaemia, dependent oedema and death in susceptible animals. It affects all mammalian species tested, and is known to cause acute disease with high mortalities in wallabies and kangaroos (Reid et al., 2001). There is no evidence of presence of T. evansi in Australia, however it is considered a high biosecurity risk as it has the potential to cause significant economic loss due to livestock death and weight loss, as well as a possibly devastating effect on native wildlife (Reid, 2002; AFFA, 2003).

Tabanid flies (also called march flies or horse flies), especially the genus Tabanus, are considered the primary vectors of surra (Nieshulz, reviewed by Krinsky 1979). The distribution, abundance and population dynamics of insect vectors all influence the risk of T. evansi transmission. The risk of incursion is considered to be greatest in the northern-most parts of Queensland, Australia (Reid, 2002; Thompson et al., 2003a). Disease surveillance is expensive and logistically difficult in this region due to the low population density and remote location. Little historical information was available on the ecology of tabanid flies in Australia, so the main aim of this study was to seek ecological data on tabanids that would promote understanding of the times and places that tabanid abundance occurred in northern Queensland. This information would then be extrapolated over the northern Australian region and used in the production of risk maps for surra in Australia.

In this study, data on tabanid flies was collected in north Queensland over 21 months, and the weather and other environmental factors that were significantly related to their abundance was determined. This information was then applied to a GIS and the annual and spatial abundance of likely vector species was mapped. These maps will be used in conjunction with additional data on host animal density and distribution and disease spread between animals to provide risk maps that will help focus disease surveillance activities in areas of highest risk.

The yearly abundance of Tabanus spp. was greatest in the most northern part of Cape York Peninsula, and was related to average annual minimum temperature and solar radiation values. This area of northern Queensland corresponds to a high geographical risk of surra incursion associated with the proximity to West Irian (Indonesia) and Papua New Guinea, which is thought to be the likely route of entry for surra into Australia. In addition, species of Tabanus are present for an average of 11 months of the year in this region, as a result of a wide variety of species present in this area, including the presence of T. ceylonicus, which is active during the dry season. This indicates that there is a confluence of risk factors in the most northern part of Cape York, which increases the risk of incursion and establishment of surra in this region.

Other aspects of tabanid behaviour and ecology were also studied. It was established that the Nzi trap was the most efficient means of trapping tabanids in Australia, and that attractants greatly improved capture rates. Also the times of greatest daily activity, and activity between days, differed among various tabanid species and this was related to variation in response to meteorological variables.

This study has established relationships among tabanid numbers and weather and environmental factors. This has elucidated the annual temporal and spatial abundance patterns of tabanids in the north Queensland region. This information will provide the basis for further studies that further establish the links between vector intensity and disease incidence in surra endemic countries, which will in turn allow a greater understanding of the epidemiology of this disease.

Item ID: 4826
Item Type: Thesis (PhD)
Keywords: tabanid flies, North Queensland, trypanosoma evansi, bioecurity, surra, vectors, march flies, horse flies, disease transmission, epidemiology, Townsville, Cape York,parasite disease, abundance, fly traps
Date Deposited: 06 Sep 2009 23:59
FoR Codes: 07 AGRICULTURAL AND VETERINARY SCIENCES > 0707 Veterinary Sciences > 070708 Veterinary Parasitology @ 34%
06 BIOLOGICAL SCIENCES > 0608 Zoology > 060801 Animal Behaviour @ 33%
06 BIOLOGICAL SCIENCES > 0602 Ecology > 060201 Behavioural Ecology @ 33%
SEO Codes: 96 ENVIRONMENT > 9604 Control of Pests, Diseases and Exotic Species > 960403 Control of Animal Pests, Diseases and Exotic Species in Farmland, Arable Cropland and Permanent Cropland @ 100%
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