Heterogeneous distribution of the reported prevalence of Dirofilaria immitis infections in Australian canids - A systematic review and meta-analysis.

Reports of Dirofilaria immitis infection vary by location in the USA and Europe, with an occurrence gradient increasing towards the equator and warmer climates. In Australia, heartworm preventative guidelines are not climate specific, implying homogenous risk of infection across the continent. We systematically reviewed the published literature to assess if the distribution of D. immitis infection varies in Australia. We sourced 41 relevant publications by searching multiple bibliographic databases and the citations of key articles. From those, we extracted the data from a total of 106 individual surveys of variable size and quality. The reported prevalences ranged from 0.0 % to 100.0 % and we meta-analysed the observed heterogeneity using survey location's latitude, climate zone or temperature/humidity zone. Crude heterogeneity between surveys was partly explained (approximately 30 %) by temperature/humidity zone, and the quality of the surveys did not affect the proportional explanation of heterogeneity. There was significantly higher pooled prevalence in humid summer zones (18.7 %, 95 %CI: 10.9-30.1 %) compared to cool winter zones (2.1 %, 95 %CI: 1.0-4.3 %). Historical reports of D. immitis infection in Australia concur with the strong association to warmer climates observed in other continents. The current blanket recommendation for dirofilariosis preventative usage does not reflect the important variability of infection risk to canids across locations of Australia.