Historical and projected impact of global climate change on the extrinsic incubation of Dirofilaria immitis

Canine heartworm disease is caused by a mosquito-transmitted filarial nematode, Dirofilaria immitis, and the observed heterogenous global distribution of D. immitis cannot be fully explained by the distribution of its vectors. Transmission of D. immitis requires maturation of larvae within the mosquito, requiring a sustained ambient temperature above 14˚C. Lower temperatures may limit transmissibility, with areas experiencing either year-round or seasonal Temperature Limited Transmissibility (TLT) reporting lower, apparently restricted, prevalence compared to areas never experiencing TLT, having the potential to become hyperendemic in the dog population and resulting in a zoonotic risk. We used weather records to investigate the effect of climate change on global D. immitis transmissibility since 1980 and investigated three different carbon emissions scenarios to assess the future impact of projected climate changes in the years 2040, 2070 and 2100. Since 1980, climate change has had a limited impacted on the epidemiology of D. immitis. Areas with hyperendemic potential (never experiencing TLT) increased in land area coverage by 10.7% but had no significant increase to human population coverage, although the portion of the globe experiencing year-round TLT has reduced significantly in land area coverage by 30.2% and human population coverage by 68.8%. Projected climate change is likely to have an impact on the epidemiology of D. immitis by extending the parts of the globe with hyperendemic potential into densely populated areas, impacting both dog and human populations. These changes are independent to changes in mosquito range changes and may approximate changes of other infectious diseases with similar extrinsic incubation.