Research paperDingoes (Canis dingo Meyer, 1793) continue to be an important reservoir host of Dirofilaria immitis in low density housing areas in Australia
Introduction
Very little is known about the epidemiology of heartworm (HW) disease caused by the filarial nematode, Dirofilaria immitis, within wild and rural domestic dog (or human) populations. Concerns have been raised that wild canids constitute an important on-going reservoir for HW and other parasitic diseases that may be transmissible to domestic dogs and humans (Polley, 2005). Reports of canids that act as reservoirs for HW infection include jackals, foxes and wolves in Serbia (Penezić et al., 2014) coyotes in California (Sacks, 1998), the red fox in Australia (Marks and Bloomfield, 1998, Mulley and Starr, 1984) and the dingo in the dry tropics of northern Australia (Brown and Copeman, 2003, Starr and Mulley, 1988).
D. immitis is a serious and potentially life-threatening parasite of canines and felines. It is responsible for canine cardiopulmonary dirofilariasis, otherwise known as HW disease, in both tropical and temperate regions throughout the world. D. immitis infections are widespread in those regions of Australia where the climate is suitable for mosquito vectors of the genera Aedes, Culex and Anopheles (Welch et al., 1979).
Human infections are also possible. Many reported cases are asymptomatic but pulmonary infection may cause radiological coin lesions of the lung (Rena et al., 2002, Ro et al., 1989, Theis, 2005). This can result in radiological misdiagnosis of a primary or metastatic lung tumour, leading to invasive procedures to achieve a definitive diagnosis (Lee et al., 2010, Theis, 2005). Ocular dirofilariasis caused by D. immitis has also been reported in Australia (Moorhouse, 1978).
Historically, the presence of this nematode in domestic dogs and dingoes (or wild dogs) is well documented in Australia (Brown and Copeman, 2003, Carlisle and Atwell, 1984, Coman, 1972, Dunsmore and Shaw, 1990, Kelly, 1977, Starr and Mulley, 1988). However, there is a marked lack of recent literature on current distribution and prevalence, with most surveys dating back to the 1970s and 1980s. Previously, the prevalence of HW was reported to have been as high as 77% in domestic dogs from Townsville, a growing city of several hundred thousand people located in the dry tropics region of north Queensland (Aubrey and Copeman, 1972), but this decreased to about 15% in adult pound dogs in 2001 (Brown and Copeman, 2003). This decline is thought to have been due to the widespread use of effective prophylaxis in domestic dogs with macrocyclic lactones first used in Australia in 1994 (Brown and Copeman, 2003, Holm-Martin and Atwell, 2004). However, a subsequent high prevalence of 75% in Townsville in 2003 contradicts this explanation (Brown and Copeman, 2003) and highlights the need for a greater understanding of the epidemiology of HW.
Very high prevalences of D. immitis infections have been reported in domestic dogs from far north Queensland Aboriginal communities on the western side of Cape York Peninsula, with 88% and 90% in Kowanyama and Aurukun, respectively (Welch et al., 1979). A correspondingly high prevalence of anti-D. immitis antibodies and relatively elevated antibody titres were seen in the human population (Welch and Dobson, 1974). These communities have limited or no access to veterinary care and minimal management of domestic dog health.
Little is known about the transmission of HW from dingoes to domestic dogs and potentially humans. The availability of standing water used by mosqutio vectors is thought to be the most important risk factor and is influenced by temperature and rainfall (Carlisle, 1969). Previous studies have found that heartworm infection is most common in domestic dogs living in areas close to permanent bodies of water, where mosquito populations are high (Welch et al., 1979). However, the abundance of a pathogen in a reservoir host is known to vary with population-specific factors such as demography and behaviour (Carlisle, 1969).
Canine HW infection can be effectively prevented by chemoprophylactic treatment of animals (Boreham and Atwell, 1983). Over the past two decades successful programs have been available to domestic dogs resulting in reduced reports of infection. A recent study on HW infection in dog shelters across South Australia, New South Wales and Queensland reported prevalences ranging from 0 to 2.2% (Mitchell, 2012).
Therefore, in order to better predict the current and potential on-going threat of HW infection it is important to understand its epidemiology in wild canids. The first step in assessing the potential HW threat posed by dingoes to both domestic dogs and humans is to establish prevalence in wild populations under a range of ecological conditions. This study presents the results of the first survey for D. immitis in dingoes in the Wet Tropics of Far North Queensland, Australia; a potential high-risk region where the combination of high rainfall, humidity and temperature are favourable to increased mosquito populations. These results are compared with those found for other dingo populations previously surveyed in locations in northern Queensland.
Section snippets
Materials and methods
Australia's largest land predator, the dingo (Canis dingo Meyer, 1793) is distributed widely in all states of Australia with the exception of Tasmania. European settlement has led to hybridisation of dingoes and domestic dogs and this has resulted in fewer genetically pure bred wild dingoes in many areas (Ritchie et al., 2012, Woodall et al., 1996). We have chosen to use the term dingo for all animals referred to in this study as all resembled dingoes morphologically, including features such as
Results
Twenty-eight dingoes were sampled from three areas within the Wet Tropics, Cairns urban fringe (n = 12), adjacent natural forest areas surrounding Cairns (n = 11) and Atherton Tablelands, approximately 100 km distant to Cairns (n = 5). Overall, 10 of 28 dingoes were infected with HW (36%, 21–54% Wilson C.I.) from the Cairns and Atherton regions. All 5 dingoes killed in Atherton were negative for adult HW. They consisted of two males and one female under two years of age and one male and one female
Discussion
Overall, the prevalence of HW disease in dingoes of the Far North Queensland Wet Tropics coastal region is moderate. In dingoes caught outside of urban areas it is equivalent to the highest levels seen in wild dogs in Australia. Our result of 72.7% HW prevalence in wild trapped dingoes from Cairns region is similar to that reported in a previous study on wild dogs undertaken near Townsville, ∼350 km south of the current study area (prevalence of 75%) (Brown and Copeman, 2003). Townsville is
Conflict of interest
The authors have no financial or personal relationship with other people or organisations that could have inappropriately influenced their work.
Acknowledgments
The authors would like to thank CSIRO Atherton, Cassowary Coast Regional Council, Yarrabah Aboriginal Shire Council, Cairns Regional Council animal control officers, Matt Birch and Peter Box, Damian Morrant, Dr. Sarah Gill, Alfred Gray Jnr, Stephen Canendo, Shanna Mossman and Herman Sexton for assistance with sample collection and dingo trapping. Partial financial support was also provided by the Australian Research Council, Skyrail Rainforest Foundation, Terrain NRM and Australian Rainforest
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