Resumen de Seroprevalence of heartworm infection, risk factors for seropositivity, and frequency of prescribing heartworm preventives for cats in the United States and Canada
Julie K. Levy, Amie N. Burling, Michael M. Crandall, Sylvia J. Tucker, Erin G. Wood, Jessie D. Foster
OBJECTIVE To determine the seroprevalence of heartworm infection, risk factors for seropositivity, and frequency of prescribing heartworm preventives for cats.
DESIGN Prospective cross-sectional study.
ANIMALS 34,975 cats from 1,353 veterinary clinics (n = 26,707) and 125 animal shelters (8,268) in the United States and Canada.
PROCEDURES Blood samples were collected from all cats and tested with a point-of-care ELISA for Dirofilaria immitis antigen, FeLV antigen, and FIV antibody. Results were compared among geographic regions and various cat groupings.
RESULTS Seropositivity for heartworm antigen in cats was identified in 35 states but not in Canada; overall seroprevalence in the United States was 0.4%. Seroprevalence of heartworm infection was highest in the southern United States. A 3-fold increase in the proportion of seropositive cats was identified for those with (vs without) outdoor access, and a 2.5-fold increase was identified for cats that were unhealthy (vs healthy) when tested. Seroprevalence was 0.3% in healthy cats, 0.7% in cats with oral disease, 0.9% in cats with abscesses or bite wounds, and 1.0% in cats with respiratory disease. Coinfection with a retrovirus increased the risk of heartworm infection. Heartworm preventives were prescribed for only 12.6% of cats at testing, and prescribing was more common in regions with a higher seroprevalence.
CONCLUSIONS AND CLINICAL RELEVANCE At an estimated prevalence of 0.4%, hundreds of thousands of cats in the United States are likely infected with heartworms. Given the difficulty in diagnosing infection at all clinically relevant parasite stages and lack of curative treatment options, efforts should be increased to ensure all cats receive heartworm preventives.
Cats are at risk for infection with the agent of heartworm disease, Dirofilaria immitis, wherever infected dogs exist.1 Most cats are capable of eliminating heartworms before the parasites reach the mature adult stage detectable by antigen tests; however, they are still susceptible to chronic heartworm-associated respiratory disease induced by immature heartworms. Such cats may have positive results of heartworm antibody testing or may escape detection altogether.
The most common clinical signs of infection in cats involve the respiratory system, with coughing, tachypnea, dyspnea, and increased bronchovesicular sounds similar to those in cats with asthma.1 Infected cats may have vomiting or neurologic signs. In some situations, sudden death is the first indication of infection. In contrast to dogs, curative treatment is not safe or practical for cats, so treatment is aimed at palliation of clinical signs. Whereas diagnosis and treatment of heartworm infection in cats can be challenging, heartworm preventives are safe and highly effective.
A suggested method for estimating the local prevalence of heartworm infection in cats when feline-specific data are unavailable is to calculate 5% to 20% of the regional heartworm infection rate for unprotected dogs.2–4 Over the past 27 years, necropsy studies3,5–10 involving a total of 2,360 southeastern US shelter cats have collectively led to the identification of adult heartworms in 115 cats, for an overall prevalence of 4.9%, but less information is available regarding the prevalence of infection in owned cats, particularly in those with no clinical signs. The purpose of the study reported here was to estimate the seroprevalence of and risk factors for heartworm infection in owned cats in the United States and Canada and to determine the frequency with which heartworm preventives were prescribed for cats.
