Feline Heartworm – The Tip of the Iceberg?

Feline Heartworm – The Tip of the Iceberg?

Dr Richard L’Estrange (view profile)

Since 2014, Australia has seen a resurgence of Dirofilaria immitis (canine heartworm) infection in dogs. The Zoetis Heartworm Surveillance Program now has over 1360 cases diagnosed and recorded on the www.vetsaustralia.com.au/heartworm website.1 Many of these dogs either reside in or originate from the North Queensland coastal city of Mackay. Most of these dogs were asymptomatic and many had reportedly been on some form of prevention.1

While the profile of dogs infected with D. immitis is on the rise, the current prevalence in Australian cats is unknown, with testing rates in veterinary practice for cats lagging well behind that of dogs. One of the factors which may inhibit a veterinarian’s degree of suspicion of infection in cats is the differing clinical presentation of cats compared to dogs. Unlike dogs, the feline immune system reacts vigorously to the presence of heartworm larvae which results in a clinical syndrome termed “Heartworm-Associated Respiratory Disease (HARD)”.2

Zoetis manufactures both canine and feline heartworm preventatives and therefore has a major interest in heartworm in Australia. In addition to establishing the website previously mentioned for the recording of diagnosed cases, Zoetis has initiated a cross-sectional serological survey of cats in the Mackay region to assess the prevalence of exposure to, and infection with Dirofilaria immitis. The immune response initiated by cats when exposed to heartworm creates both challenges and opportunities for diagnosis, therefore a combination of antigen testing, antibody testing and the application of “heat treatment” prior to antigen testing of selected samples may offer improved overall sensitivity in the quest to determine the prevalence of D.immitis in cats.2,3

This presentation will briefly review heartworm disease in cats, explain Heartworm Associated Respiratory Disease and provide insight as to the early results of the serological study of the cats of Mackay.

  1. Zoetis data on file: Heartworm surveillance project data accessed 15th August 2018.
  2. Dillon and Weinberg 2007 “Pfizer Animal Health Technical Bulletin: Pulmonary Effects of Abbreviated Heartworm Infection in Cats: A New Perspective”
  3. Little et al. Prime detection of Dirofilaria immitis: understanding the influence of blocked antigen on heartworm test performance. Parasites & Vectors (2018) 11:186 https://doi.org/10.1186/s13071-018-2736-5