Validating alternative models to cats and dogs for heartworm drug testing

Heartworm is a parasitic worm disease in cats and dogs in many areas of the world. More infections are being identified in Northern Europe and cases have been identified in the UK. Left untreated, heartworm is potentially lethal. Current drugs used to prevent heartworm from infecting the heart are not working as well because of the development of drug resistant parasites. Drugs used to treat heartworms cause side effects which can be lethal. New heartworm drugs are being developed by animal healthcare companies. Currently, we don't have any alternative way of testing new drugs other than to experiment on cats or dogs. Sometimes cats or dogs will become very ill as a result of being infected with heartworm for the purposes of testing drugs.
In this project we will develop cell culture and mouse alternatives to cats and dogs to support the early larval growth of heartworm. We will select the best cultures and mouse strain and check to see whether two different types of drug can give the expected effects in these new models.
When we get to this point in the project we will advocate the adoption of these alternatives to a range of important potential end-users including testing laboratories and animal health care companies.
We calculate that these alternative models will reduce overall numbers of animals used in heartworm drug testing. We also estimate that using mice instead of cats or dogs in drug testing will refine testing by avoiding long duration infections that can induce severe pain and suffering.

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 anti-infectives 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.