Validating alternative models to cats and dogs for heartworm drug testing

Heartworm, caused by the filarial parasites Dirofilaria immitis and D. repens, is a disease of veterinary importance in cats and dogs. Left untreated it can cause life-threatening morbidities including congestive heart failure and cardiopulmonary embolism. The annual heart worm market is estimated to be in excess of US$150 million. New heartworm antiinfectives are being developed by animal health companies due to the emergence of resistance to current prophylactics and poor treatment outcomes with available adulticides. Currently there is no alternative to testing novel compounds in experimentally infected cats or dogs.

In this project we will develop in vitro and in vivo alternatives to cats and dogs to propogate D. immitis larval development. We will subsequently validate their utility as heartworm anti-infective screens using reference larvicides (ivermectin) or growth inhibitors targeting the endosymbiont, Wolbachia (doxycycline). Our approach exploits recent advances in mammalian cell co-culture systems supporting filarial larval development and the establishment of new models of human filariasis in compound immunodeficient mice. Proof-of-concept data has been generated that D. immitis infectious larvae can be generated by membrane feeding Aedes aegypti mosquitoes in our laboratory with D. immitis microfilariae shipped from veterinary sources in the USA. Further we have been able to isolate viable L4 larvae from subcutaneous tissues after inoculation of infectious larvae in a severe combined immunodeficient gamma chain knockout mouse strain.

Validation and future adoption of these alternative models will reduce overall numbers of animals used in heartworm translational research. Adoption of a mouse preclinical model will also refine animal use by substituting the majority of procedures causing chronic infection, pathology, severe pain and distress in cats or dogs with less severe, short term infections in mice which avoid pathology.