Performance of serologic tests used to detect heartworm infection in cats

OBJECTIVE: To compare heartworm serum antibody (Ab) and antigen (Ag) test results, using commercial laboratories and in-house heartworm test kits, with necropsy findings in a population of shelter cats. DESIGN: Prospective study. ANIMALS: 330 cats at an animal shelter. PROCEDURE: Between March and June 1998, 30 ml of blood was collected from the cranial and caudal venae cavae of 330 cats that were euthanatized at a local animal shelter. Results of heartworm Ab and Ag serologic tests for heartworm infection were compared with necropsy findings in this population of cats, using commercial laboratories and in-house test kits to measure serum Ab and Ag concentrations. RESULTS: On necropsy, adult Dirofilaria immitis were found in 19 of 330 (5.8%) cats. Combining results from serum Ab and Ag tests achieved higher sensitivities than using serum Ab and Ag test results alone (i.e., maximum sensitivities of 100% vs 89.5%, respectively, whereas use of serum Ag and Ab test results alone achieved higher specificities compared with the use of a combination of serum Ab and Ag results (i.e., maximum specificities of 99.4% vs 92.9%, respectively). CONCLUSIONS AND CLINICAL RELEVANCE: On the basis of our findings, if a cat has clinical signs that suggest heartworm disease despite a negative heartworm serum Ab test result, an alternative heartworm Ab test, a heartworm Ag test, thoracic radiography, or two-dimensional echocardiography should be performed.     

Adaptation of domestic cats to confinement

Although most cat owners believe that cats have a need to roam outdoors and that this activity benefits their welfare, roaming also carries welfare risks for the cat. On the other hand, most cats have not been selectively bred to be “house cats” that live indoors 24 hours a day. Until recently, most domestic cats were allowed to roam freely, and they contributed to the large population of stray and feral cats. In turn many pet cats come from the stray and shelter population. A large proportion of domestic cats have not been selected for easy adaptation to live in confinement and in close contact with people, and socialization to people may also not have been complete in these cats. However, cats are adaptable to a wide range of environments and are generally not known to show clear behavioral signs of problems, such as stereotypic behavior. Problem behaviors of cats are often not abnormal behaviors per se but natural behaviors that need to be redirected to appropriate substrates. The most frequent behavior problems cited by cat owners are: inappropriate elimination, scratching, aggression, anxiety, eating problems, vocalizations, and excessive activity. Despite the frequent reporting of these behaviors, most cats will generally adapt to indoor housing provided there is sufficient space and that they are accustomed to these conditions from an early age. The Five Freedoms, developed to assess the welfare of farm animals in intensive systems, can be modified to assess the welfare of cats housed in confinement. Specific features of the environment that can enhance the welfare of cats in confinement are discussed.     

Geographical information systems as a tool in the control of heartworm infections in dogs and cats

Geospatial tools (e.g., geographical information systems, remote sensing, global positioning systems, and virtual globes) are very useful for the simultaneous visualization of health data with environmental data, which holds promise to understand environmental-health linkages and to generate new hypotheses to be tested in future research. Current epidemiological studies clearly show that the distribution patterns of vector-borne infections are changing; for example, in Europe, heartworm infection and subcutaneous dirofilariosis are spreading throughout areas that previously had little to no incidence of heartworm. In view of the changes of the distribution patterns of Dirofilaria immitis and Dirofilaria repens, geospatial tools are now more useful for mapping (including territorial sampling), monitoring, ecological analysis, risk assessment, forecasting (including the choose of the timing of treatment), early warning, and surveillance of both heartworm and subcutaneous dirofilariosis. All these issues have control of these infections as the ultimate goal.     

Clinical evolution and radiographic findings of feline heartworm infection in asymptomatic cats

Clinical manifestations of heartworm disease in cats are variable; most cats seem to tolerate the infection well for extended periods. Heartworm-infected cats may undergo spontaneous self-cure due to the natural death of parasites without any symptomatology, or they may suddenly show dramatic and acute symptoms. Sudden death in apparently healthy cats is not a rare event. Thoracic radiographs are important tool for the diagnosis of cardiopulmonary disease. However, thoracic abnormalities are often absent or transient and highly variable in heartworm-infected cats. Findings, such as enlargement of the peripheral branches of the pulmonary arteries, with a varying degree of pulmonary parenchymal disease and hyperinflation, are the most typical features consistent with infection. A field study was performed for cats referred to the Veterinary Hospital Città di Pavia from January 1998 to December 2001 for routine health examinations and procedures to evaluate the clinical evolution and radiographic findings of feline heartworm infection. Thirty-four asymptomatic cats diagnosed with feline heartworm infection by antibody and antigen tests together with an echocardiogram that allowed worm visualization were included in the follow-up study. Cats were routinely examined every 3 months from the time of heartworm diagnosis until the outcome (self-cure or death). Self-cure was defined as no positive serology for heartworm antigens and no visualization of worms by echocardiography. A final examination for antibodies was carried after 12 months as a final confirmation of self-cure. Twenty-eight cats (82.4%) self-cured; including 21 that showed no clinical signs of infection throughout the study. Six cats died. The most common clinical features observed were acute respiratory symptoms and sudden death. Infection lasted over 3 years in the majority of the cats enrolled in the study. Thoracic radiograph appearance was variable, and the most commonly observed findings were focal and diffuse pulmonary parenchymal abnormalities.     

Prevalence of heartworm infection in healthy cats in the lower peninsula of Michigan

OBJECTIVE: To determine prevalence of heartworm infection among healthy, client-owned cats in the lower peninsula of Michigan. DESIGN: Cross-sectional prevalence study. ANIMALS: 1,348 healthy cats examined at private veterinary practices throughout the lower peninsula of Michigan. PROCEDURE: Sera were tested by use of an ELISA-based antigen test kit to determine infection and 2 commercially available antibody detection kits to determine exposure. A questionnaire was used to collect data to assess risk factors associated with infection. RESULTS: 25 cats had positive results for heartworm antigen, yielding an observed prevalence of 1.9%. Neither antibody test was reliable or provided reproducible results, and neither yielded positive results for more than 20% of the antigen-positive heartworm-infected cats. Multivariate regression indicated that cats from southeastern Michigan and cats > or = 2 years old had a higher risk of infection. CONCLUSIONS AND CLINICAL RELEVANCE: Results indicated that most (80%) heartworm-infected cats in the lower peninsula of Michigan were from the southeastern part of the state, a pattern that closely paralleled the prevalence of heartworm infection in dogs. Therefore, knowledge of the regional prevalence of heartworm infection in dogs may be useful in assessing the risk of infection in cats. Results also suggested that currently available in-clinic heartworm antibody detection kits have limited utility in the diagnosis of heartworm infection in cats.     

Prevalence and risk factors for heartworm infection in cats from northern Florida

Necropsies were performed on 630 adult cats in northern Florida to determine the prevalence and risk factors for heartworm infection in cats of this region. Heartworms were identified in 4.9% of cats, and serological evidence of heartworm exposure was present in 17% of cats. Not all cats from which heartworms were recovered were seropositive for heartworm antigen or antibody. There was no association between heartworm infection and co-infection with feline leukemia virus (FeLV) or feline immunodeficiency virus (FIV). Male cats were at higher risk of infection with heartworm, FeLV, or FIV than were females. Because even a single heartworm can cause clinical disease or death in cats, the authors conclude that cats in this region should receive heartworm prophylaxis to prevent heartworm infection.     

Comparison of serological tests for the detection of natural heartworm infection in cats

Serological tests were performed on 380 cats with necropsy-confirmed heartworm disease to compare the performance of currently available commercial laboratory and point-of-care heart-worm serological tests in a heartworm-endemic area. Overall, antigen tests detected 79.3% to 86.2% of heartworm infections and were highly specific. Most cats with false-negative antigen tests had a single male worm. Antibody tests detected 62.1% to 72.4% of heartworm infections and had a wider range of false-positive results (1.4% to 19.1%) than antigen tests (0.3% to 2.0%). Serological tests for feline heartworm infection varied in diagnostic performance. Combining results from antigen and antibody tests achieved greater sensitivity than using either test alone.     

The Arthus reaction in domestic cats

A classic Arthus reaction was elicited in normal domestic cats using chicken red blood cells as antigen. The response was quantitated grossly by measuring the area of the resulting skin bleb at several set time intervals and by microscopic examination of biopsies taken at the conclusion of each of the trials. This method produced an intense Arthus reaction in each of the cats tested.     

Effects of dietary lysine supplementation in cats with enzootic upper respiratory disease

To determine the effectiveness of dietary lysine supplementation in cats with enzootic upper respiratory disease (URD), 50 cats were fed a ration containing 11 or 51 g lysine/kg diet for 52 days. Food intake, body weight, clinical signs, plasma amino acid concentrations and presence of Chlamydophila felis or feline herpesvirus (FHV)-1 DNA within the conjunctival fornix were assessed. Food and lysine intake of both dietary groups decreased between days 17 and 22, coinciding with peak disease and viral presence. Mean disease score for cats fed the supplemented ration (0.94) was higher than for those fed the basal diet (0.21); however, this could be attributed to a small subset of male cats which demonstrated fighting behavior that may have contributed to stress within that cage. FHV-1 DNA was detected on 12 occasions in six cats receiving the supplemented diet and on one occasion in one cat fed the basal diet. C felis DNA was never detected. Mean plasma arginine concentration was lower and plasma lysine concentration was higher in supplemented cats. Mean plasma arginine concentration declined throughout the study in both dietary groups. Data from the present study raise important questions but do not permit a definitive conclusion regarding the efficacy of dietary lysine supplementation in cats with enzootic URD.     

Feline heartworm infection: serological survey of asymptomatic cats living in northern Italy.

Heartworm infection is now recognized as a potential cause of serious disease in cats. Epidemiological studies indicate that in locations where the infection is endemic in the dog, cats are at risk. The aim of this work was to carry out a serological survey for the presence of anti-Dirofilaria immitis antibodies in privately owned, predominantly asymptomatic cats living in different areas of northern Italy in order to determine the distribution of the parasite and the risk of infection in this species. Serum samples from 1045 cats were evaluated using a commercial antibody (Ab) detection kit (Heska Solo Step Filariosi Felina, Heska Corporation) and results were analyzed together with information obtained by questionnaire. Results showed that 16% of all tested cats were positive for anti-D. immitis antibodies, with values ranging from 9 to 27%, depending on location. Male cats and outdoor cats appeared to be at greater risk, with a significantly higher number of positive antibody tests. The results of this study suggest that the risk of exposure with D. immitis in cats is high in northern Italy and suggest that the use of preventive drugs would be advisable in this area endemic for canine heartworm disease.     

Survey of predation by domestic cats

Objectives To calculate the proportion of house cats which were observed by their owners to have caught prey and to describe the characteristics of these cats.
Design and procedure A telephone questionnaire was administered to a randomly selected population of 458 cat owners in metropolitan Perth. Specific questions were asked about demographic characteristics, habits and diets of the cats, and whether the owners had observed their cats catch prey in the 12 month period preceding the survey.
Results The owners of 36% of 644 cats had observed their cats with prey in the 12 month period preceding the survey. Cats which spent more time outside, were neutered, cross-bred, originated from households with only one or two cats or were not fed meat were significantly more likely to be observed to predate. The body condition and diet (other than feeding meat) of cats did not influence the reported frequency of predation.
Conclusion Although cats are only one factor involved in the reduction in the numbers and diversity of Australian wildlife, restriction of the outside activities of cats is likely to diminish predation, particularly in areas close to native vegetation.