Publications
Feline Heartworm Diseaseand Other Factors of Emerging Heartworm Disease
Emerging Heartworm Disease: Part 4
This publication will review feline heartworm
disease and the influence it has on
the emergence of heartworm disease. It
will also look at other factors that may
be of future significance, such as the
French heartworm, and the movement of
a zoonotic microfilaria.
Feline Heartworm Disease
Feline heartworm disease is referred to
as Heartworm Associated Respiratory
Disease (HARD). The number of cats
diagnosed with heartworm disease has
increased. Litster and Atwell proposed
that the increase reflected an improvement
in veterinary and owner awareness
or surveillance of cats. True prevalence
data may be difficult to assess because of
the cat’s ability to independently eradicate
the parasite or die from the undiagnosed
infection.
The life cycle of heartworms in cats is very similar to that of heartworms in dogs, although cats are considered more resistant to infection than dogs. Prevalence of infection mimics that of canine heartworm disease and is reported to be 5–10 percent of that in dogs in any given area (Litster and Atwell 2008).
It is suspected that cats develop a strong immune response to heartworms and are able to spontaneously clear the infection. Feline heartworm infections are characterized by having fewer and smaller worms than heartworm infections in dogs. The life span of heartworms in cats is typically 2–3 years, which is shorter than in dogs, in which the lifespan is 5–7 years. Feline heartworm infections are typically a single-sex infection and may involve few heartworms (Nelson, et al. 2007).
Similar to dogs, all cats (both indoor and outdoor) are susceptible to heartworm infection because of the large population of mosquitoes that serve as vectors. Clinical signs are rarely seen in feline heartworm infections. When they are observable, symptoms may mimic asthma symptoms. They may even include vomiting. Once the infection reaches the pulmonary phase, live heartworms may suppress immune function. As mature worms begin to die, pulmonary inflammation and thromboembolism can result in fatal lung injury for the cat (Nelson, et al. 2007).
Because no approved adulticide is available at this time for cats, and canine treatments cause severe adverse reactions in cats, therapy is symptomatic care along with a heartworm preventive to avoid additional infection. Due to the low worm numbers with infection, ante-mortem diagnosis can be frustrating. Thoracic radiography and echocardiography may be helpful. Antigen or antibody serology testing is meaningful when positive.
Other Considerations
The French heartworm, Angiostrongylus vasorum,
was recently introduced into new areas and became a
source of new infections in Newfoundland and
Canada (Jefferies, et al. 2010). It is reported in all five
continents and considered endemic in France,
England, Ireland, Denmark, and Canada. The definitive
host is domestic dogs and foxes. Foxes may serve
as the primary wildlife reservoir host for the disease
(Koch and Willesen 2007). This heartworm is found in
areas with cooler climates. There is concern about the
spread of this heartworm to the United States.
Other aspects that can change the future distribution of heartworm disease include the movement of a filarial nematode seen in Europe. This parasite is more commonly associated with zoonosis than D. immitis. Dirofilaria repens affects dogs and is mainly located in Europe, Africa, and Asia. It can cause subcutaneous nodules in humans. In 2009, a German tourist who had recently traveled through India was diagnosed with skin nodules encysted with D. repens (Poppert, et al. 2009).
Conclusion
The emergence of heartworm disease may be related
to lack of compliance, potential resistance to preventives,
and feline heartworm disease. It may be difficult
to control changes in vectors, reservoir movement, and
climactic conditions, but the veterinary community
can help. Veterinarians must educate their clients
about proper compliance and potential resistance to
preventives, as well as the importance of heartworm
preventives for cats.
Pet owners and veterinary professionals should stay updated on the latest heartworm information available. Client education materials are available at heartwormsociety.org and knowheartworms.org.
The information given here is for educational purposes only. References to commercial products, trade names, or suppliers are made with the understanding that no endorsement is implied and that no discrimination against other products or suppliers is intended.
Copyright 2011 by Mississippi State University. All rights reserved. This publication may be copied and distributed without alteration for nonprofit educational purposes provided that credit is given to the Mississippi State University Extension Service.
By Dr. Jody Ray, Assistant Chief of Community Veterinary Services, College of Veterinary Medicine Animal Health Center.
Discrimination based upon race, color, religion, sex, national origin, age, disability, or veteran’s status is a violation of federal and state law and MSU policy and will not be tolerated. Discrimination based upon sexual orientation or group affiliation is a violation of MSU policy and will not be tolerated.
Publication 2646
Extension Service of Mississippi State University, cooperating with U.S. Department of Agriculture.
Published in furtherance of Acts of Congress, May 8 and June 30, 1914. GARY B. JACKSON, Director
(POD-01-11)