Diagnostic, treatment, and prevention protocols for feline heartworm infection in animal sheltering agencies
Introduction
Although cats are naturally resistant to Dirofilaria immitis, feline infection is likely to occur anywhere the parasite is found in dogs. The lack of highly reliable serological testing for cats makes it difficult to know the true risk of feline heartworm infection or what proportion of infected cats becomes symptomatic (Berdoulay et al., 2004, Snyder et al., 2000). In a national serosurvey in pet cats, heartworm antigen prevalence (0.9%) was similar to that of feline immunodeficiency virus (FIV) antibodies (1%) and feline leukemia virus (FeLV) antigen (1.9%) (Lorentzen and Caola, 2008). Cats in animal shelters may be more likely than pet cats to have heartworm infection because they have been roaming free as strays or were unwanted or neglected pets. When both cats and dogs are necropsied at animal shelters, worms are usually found in cats at approximately 5–15% the rate found in dogs in the same location (Levy et al., 2003). Shelter cats in northern Florida were found to harbor adult heartworms (4.9%) as commonly as they were infected with FeLV (4.7%) and FIV (6.1%) (Levy et al., 2003). Even more cats (17%) had heartworm antibodies, indicating at least transient dirofilariasis. Although diagnosis of retroviral infection is not usually as challenging as that of feline heartworm infection, all three infections have in common limited treatment options and the potential for substantial morbidity and mortality. Of the three infections, preventive strategies are most effective against dirofilariasis.
In December of 2008, a test for heartworm antigen was added to a commonly used point-of-care screening test for FeLV antigen and FIV antibodies (SNAP Feline Triple, IDEXX Laboratories, Inc., Westbrook, ME). The new test is likely to identify heartworm-infected cats during routine retroviral testing, which will raise awareness of feline heartworm infection in animal sheltering agencies throughout the country. Unexpected positive heartworm test results pose a challenge to shelter managers in terms of subsequent treatment, which is ill-defined in cats, and in terms of preparing cats and prospective cat owners for adoption.
The American Heartworm Society (AHS) guidelines for the diagnosis, treatment, and prevention of heartworm infection in cats call for the administration of preventive medications for all cats and outline diagnostic and therapeutic procedures for cats suspected to be infected (Nelson et al., 2005). However, the procedures in these guidelines are often unaffordable and impractical for implementation in animal shelters that lack adequate financial and staff resources. Although guidelines tailored for vaccination (Richards et al., 2006) and retroviral testing (Levy et al., 2008) of cats in shelters have been developed, similar guidelines regarding heartworm management have not. As a result, shelters are left to create their own protocols, often without the input of veterinarians. This results in an inconsistent approach to care for the 3 million to 4 million cats that are admitted to shelters each year.
The purpose of this study was to determine feline heartworm protocols currently used by sheltering agencies located in a heartworm-endemic region.
Section snippets
Sample population
Animal sheltering agencies, including traditional shelters with central animal housing facilities, sanctuaries, pet foster programs, and adoption programs based in veterinary clinics, operate as independent agencies in the United States. No registries exist that systematically catalog agencies in a central directory. A list of animal sheltering agencies in Alabama, Florida, Georgia, and Mississippi was created by consolidating existing directories from national animal welfare organizations,
Survey response
Of the 558 agencies that responded, 400 admitted cats in 2008 (Table 1). Of those that admitted cats, 282 (71%) were non-profit organizations, 225 (56%) had limited admission policies, and 278 (70%) used a central shelter facility for housing at least some of their cats. Although the majority of agencies (235; 59%) were small organizations that admitted fewer than 500 cats in 2008, the fewer larger agencies together admitted at least three times as many cats as the small agencies combined. Of
Discussion
A majority of agencies did not test cats for heartworm infection or provide heartworm preventive medications despite operating in a heartworm-endemic region. The most common reasons for not testing and providing preventive medications were expense and lack of testing for infection first. Failure to recognize heartworm infection in shelter cats can lead to disease progression or to the inadvertent adoption of infected cats to the public. Housing of unprotected cats near heartworm-infected dogs
Conclusions
The vast majority of animal sheltering agencies in a heartworm-endemic region failed to provide diagnostic testing (78%) or chemoprophylaxis (69%) for cats in their care. The most common reason cited was expense, although misunderstanding practical aspects of feline heartworm management and the local risk of transmission also appeared to play a role. Guidelines developed for management of heartworm infection in pet cats are not feasible for many sheltering agencies. Practical heartworm
Conflicts of interest
The authors declare no conflicts of interest regarding the content of this paper.
Acknowledgements
The study was made possible with funding by Maddie's Fund® and IDEXX Laboratories.
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