Evaluation of a new in-clinic method for the detection of canine heartworm antigen

Canine heartworm is endemic in many parts of the world, and veterinarians rely on rapid in-clinic antigen tests to screen for this infection. Recently, an in-clinic, instrument-based rotor employing a colloidal gold agglutination immunoassay was launched in the marketplace (VetScan VS2(?) Canine Heartworm (HW) Antigen Test Kit; Abaxis, Inc.). Because of the widespread use of heartworm prevention and possible false negative test results in dogs with low heartworm burdens, the performance of the VetScan VS2(?) HW test and a commercially available in-clinic, membrane-based ELISA test (SNAP(?) Heartworm RT Test; IDEXX Laboratories) was compared using samples from dogs with low heartworm burdens and/or low levels of circulating antigen. Ninety serum samples were evaluated using the two methods. Testing was performed according to the manufacturer's product insert by personnel blinded to sample status. The samples were derived from two populations: dogs with necropsy-confirmed heartworm status (40 with 1-4 female worms, 30 with no worms), and field dogs (20) confirmed positive for antigen by microtiter plate ELISA (PetChek(?) Heartworm PF Antigen Test; IDEXX Laboratories). All 40 dogs with heartworms on necropsy were also confirmed to have circulating antigen by the PetChek HW ELISA. In necropsy-negative dogs (n=30), neither the VetScan VS2 HW nor SNAP HW tests detected heartworm antigen. Of the samples testing positive for antigen by PetChek HW (n=60), the VetScan VS2 HW and SNAP HW tests detected antigen in 15 and 56 samples, respectively. Percent agreement (plus 95% confidence interval) for each test relative to the PetChek HW qualitative result was 50% (40-60%) for VetScan VS2 HW and 96% (89-98%) for SNAP HW. Relative to the presence or absence of female worms at necropsy, agreement was 61% (50-72%) for VetScan VS2 HW and 99% (92-99.6%) for SNAP HW tests. It is clinically important that dogs with low heartworm burdens and/or low levels of circulating heartworm antigen be correctly identified by veterinarians in order to ensure prompt treatment, and the VetScan(?) VS2 HW test does not appear to be as accurate as the SNAP HW or PetChek HW tests when performed on this subset of patients.     

The validity of some haematological and elisa methods for the diagnosis of canine heartworm disease

Examinations for heartworm (Dirofilaria immitis) were performed on 175 impounded dogs from a hyperendemic area of the Po Valley (Italy). Each blood sample was used wiht five haematological diagnostic methods (filtration, direct smear, modified Knott, clotted blood and capillary tube) and three commercial ELISA kits (PetChek, Diasystems, Uni-Tec). The results were compared with the true infection status obtained from post-mortem examination of the heart, pulmonary arteries, thoracic venae cavae and lungs. The prevalence of the infection by adult worms at necropsy was 63%. The sensitivity of the tests ranged from 60% (capillary tube) to 81% (Diasystems) and the specificity from 88% (filtration) to 98% (PetChek). The results of all the tests differed significantly (p<0.01) from those obtained at necropsy. The sensitivity of the tests was also assessed with respect to the differing numbers of worms in the hosts. A positive correlation between the worm burden and the sensitivity was observed in all the tests. It is apparent that the ELISA methods were better able to detect cases with a low number of worms than the haematological tests.Abbreviations AC accuracy - CB clotted blood - CT capillary tube - DI Diasystems - DS direct smear - ELISA enzyme-linked immunosorbent assay - FI filtration - MK modified Knott - NPV negative predictive value - PE PetChek - PPV positive predictive value - SE sensitivity - SP specificity - UN Uni-Tec     

Incidence of positive heartworm antibody and antigen tests at IDEXX Laboratories: trends and potential impact on feline heartworm awareness and prevention

Data from the IDEXX Laboratories Reference Laboratory Network were retrospectively examined for feline heartworm testing trends in testing frequency, geographic bias, and prevalence for the years 2000--2006. Examination of the data supports the commonly held view that veterinarians do not embrace heartworm disease testing or prevention in cats to the same degree they do in dogs. Despite significant awareness and adoption of heartworm testing and prevention in dogs, we hypothesized that heartworm testing rates are lower for cats than for dogs despite a significant prevalence of feline infection. This is important because a perceived low rate of infection in cats is likely to manifest in a low adoption of testing and prevention. In reality, the overall feline heartworm antigen-positive rate is significant--on average 0.9% over the period studied--and in some regions was estimated to be as high as 4.6%. This compares with an average canine heartworm prevalence rate of 1.2%, a feline leukemia virus prevalence of 1.9%, and a feline immunodeficiency prevalence of 1.0%. Based on the low rate of testing and these prevalence rates, practitioners are routinely missing cases of adult feline heartworm infections and the recently defined heartworm-associated respiratory disease (H.A.R.D). Increased antigen testing would result in detection of a significant number of positive cases. In addition, this population of infected cats would represent the "tip of the iceberg" relative to the greater number of cats that have early infection or are at risk for infection.     

Comparison of results of three commercial heartworm antigen test kits in dogs with low heartworm burdens

OBJECTIVE: To compare results of 3 commercial heartworm antigen test kits performed on serum samples from dogs infected with low numbers of adult female heartworms. DESIGN: Blinded laboratory evaluation. Sample Population-Serum samples from dogs (n = 208) proven at necropsy to be infected with 1 to 4 adult female heartworms and from dogs (32) without heartworms. PROCEDURE: Samples were sequentially tested with each test kit, following the manufacturers' instructions, by licensed veterinary technicians in private practice who were not aware of infection status of the dogs. The order of test kit evaluations was randomly chosen. For each test kit, sensitivity, specificity, accuracy, positive predictive value, and negative predictive value were evaluated. RESULTS: All tests yielded some false-negative results, and there were significant differences among tests in regard to ability to detect low heartworm burdens. Sensitivity of the test kits ranged from 78 to 84%. For all test kits, sensitivity increased as number of female heartworms increased. All 3 test kits had high specificity (97%). CONCLUSIONS AND CLINICAL RELEVANCE: Results indicated that sensitivity of the 3 commercially available heartworm antigen test kits ranged from 78 to 84% when used to test serum samples from dogs with low heartworm burdens, and that sensitivity varied among test kits. For all 3 test kits, specificity was 97%. All 3 test kits yielded false-positive and false-negative results for some dogs with low heartworm burdens.     

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.     

Evaluation of heartworm immunodiagnostic tests

In this report, the use of appropriate statistical methods for the evaluation of heartworm immunodiagnostic tests is discussed. The evaluation of these tests is complicated by factors causing variation in sensitivity, specificity, accuracy, and predictive values of positive and negative test results. The primary sources of inconsistency are variation in the prevalence of heartworm infection among populations of dogs and the sensitivity of immunodiagnostic tests to various categories of heartworm infections (ie, patent, immune-mediated occult, unisex occult, and immature occult). Sample size (ie, number of dogs tested) affects the confidence limit values of sensitivity and specificity. At least 100 dogs should be used in each testing group (infected and uninfected) to generate values of sensitivity or specificity within reasonably narrow confidence limits. Use of more than 200 dogs in each testing group contributes little to further narrowing of confidence limits. The selection of appropriate statistical tests for comparison of tests or comparison of the sensitivity or specificity of a single diagnostic test to various categories of heartworm infections is critical. The McNemar paired chi 2 test is appropriate for comparison of diagnostic tests, but it must be done by use of duplicate sera from each animal. A chi 2 test of independence, or, in the case of a small sample size, the Fisher exact test, is appropriate for comparing the sensitivity or specificity of a single diagnostic test to various categories of 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.     

Understanding feline heartworm infection: disease, diagnosis, and treatment

Feline heartworm disease is a very different clinical entity from canine heartworm disease. In cats, the arrival and death of immature heartworms in the pulmonary arteries can cause coughing and dyspnea as early as 3 months postinfection. Adult heartworms suppress the function of pulmonary intravascular macrophages and thus reduce clinical disease in chronic feline heartworm infection. Approximately 80% of asymptomatic cats self-cure. Median survival time for symptomatic cats is 1.5 years, or 4 years if only cats living beyond the day of presentation are considered. Aberrant worm migration is more frequent than it is in dogs, and sudden death can occur with no prior clinical signs. The bacterial endosymbiont Wolbachia likely contributes to the inflammatory pathology of heartworm disease, but its role is not yet fully clear. Unfortunately, the diagnosis, treatment, and management of feline heartworm disease are far from simple. Antemortem diagnosis is hampered by low worm burdens, the frequency of all-male infections, and nonspecific radiographic lesions. It is up to the veterinarian to determine the correct index of suspicion and choose the right combination of diagnostic tests to achieve an answer. Treatment is symptomatic because adulticide therapy is risky and does not increase survival time. Despite the dangers of feline heartworm disease, less than 5% of cats in the United States are on chemoprophylaxis. It is important for veterinarians to take a proactive preventive stance because heartworm infection in cats is a multisystemic disease that has no easy cure.     

Are antigen test kits efficient for detecting heartworm-infected dogs at the southern distribution limit of the parasite in South America? Preliminary results

The aim of this study was to evaluate the performance of commercial heartworm antigen tests in dogs harbouring Dirofilaria immitis microfilariae near its distribution limit in South America. A total of 4934 blood samples of adult dogs from Southern Greater Buenos Aires were examined to detect circulating microfilariae in the buffy coat interface between December 2005 and April 2006. Microfilariae were detected in 88 (1.8%) blood samples and all the microfilariae observed were identified as D. immitis by acid phosphatase stain technique. In a first trial, 69 (78.4%) out of the 88 serum were positive by Speed((R)) Diro. Then, a new test was performed over 25 microfilariae-positive serum samples randomly selected among the 88 previously tested samples and using simultaneously Speed((R)) Diro, Witness((R)) Dirofilaria and Snap((R)) 3dx. This second trial showed identical results for the three different tests, in which 19 (76%) samples were positive. Therefore, more than 20% of microfilaremic dogs were antigen negative. The main hypothesis that could explain our finding is a low worm burden in the study area. According to our preliminary results, it is highly recommendable the complementary use of antigen tests and other procedures to obtain an accurate diagnostic near the distribution limit of the parasite.     

Comparative Evaluation of 2 In-Clinic Assays for Vector-Borne Disease Testing in Dogs

Vector-borne agents comprise medically important infections affecting dogs throughout much of the world. Sensitive detection of antibodies directed at tick-borne disease-causing organisms in dogs is diagnostically important for veterinarians, pets and their owners, and epidemiologically important for public health surveillance. The SNAP 4Dx Plus Test (IDEXX Laboratories, Inc., Westbrook, ME) identifies antibodies to or infection with multiple tick-borne pathogens and canine heartworm antigen in a single assay. Recently, VetScan FLEX4 Rapid Test (Abaxis, Inc., Union City, CA) was launched as a new assay to detect tick-borne pathogen antibodies and heartworm antigen. In the present study, we evaluated the comparative performance of SNAP 4Dx Plus (SNAP) and FLEX4 Rapid Test (FLEX4) using samples selected based on geographic distributions for canine vector borne diseases, including Borrelia burgdorferi (n = 105), Anaplasma phagocytophilum (160), Anaplasma platys (115), Ehrlichia canis (154), Ehrlichia ewingii (163), Ehrlichia chaffeensis (151) and Dirofilaria immitis (105). Canine vector borne diseases infection status was established for each sample by a combination of reference methods that included necropsy (D. immitis, heartworm disease), Western immunoblotting (B. burgdorferi), immunofluorescence assays (A. phagocytophilum and E. canis) and species-specific ELISAs (A. platys, E. canis, E. ewingii and E. chaffeensis). For comparisons among the 2 assays, samples were evaluated per the manufacturers’ instructions for each test kit.By testing each same sample set compared to the defined reference results, sensitivities differed substantially between SNAP and FLEX4, at 95.5 vs. 40.9%, respectively for B. burgdorferi, 97.1% vs. 61.4% for E. canis, 98.2% vs. 59.3% for E. ewingii, 64.3% vs. 35.7% for E. chaffeensis, 84.5% vs. 12.7% for A. phagocytophilum, 83.3% vs. 33.3% for A. platys, and 94.1% vs. 88.2% for D. immitis. Specificities for both rapid assay tests ranged from 98% to 100%.Based upon the comparative results derived from this study, the SNAP test was more sensitive than the FLEX4 test for detection of antibodies to all tick-borne pathogens and heartworm disease (Dirofilaria immitis) antigen in dogs.     

Comparison of serologic tests for detection of antigen in canine heartworm infections

In 30 random-source dogs, we determined sensitivity and specificity of 5 serologic tests for detection of canine heartworm antigens. Seventeen of the dogs were infected naturally with adult Dirofilaria immitis, and 4 of the infected dogs were amicrofilaremic. The ability of the serologic tests to predict whether a dog was infected or uninfected (overall test accuracy) ranged from 73 to 97%. Sensitivity was not affected by circulating D immitis microfilariae, but was markedly influenced by the number of adult D immitis present. False-positive reactions were rare and were not associated with intestinal parasites or Dipetalonema reconditum microfilariae. Modifications of some of the test procedures were necessary to maximize test accuracy and reproducibility. These modifications and other technical details might limit the usefulness of some of the tests in a veterinary practice.     

Comparison of canine heartworm removal rates using flexible alligator forceps guided by transesophageal echocardiography and fluoroscopy

Fluoroscopy (FS)- or transesophageal echocardiography (TEE)-guided heartworm removal was carried out using flexible alligator forceps to compare the rate of worm removal. As a result, the worm removal rates were similar between the two procedures. However, the TEE-guided procedure does not involve radiation exposure, and facilitates observation of worms in the cardiac chamber and pulmonary artery. Therefore, the TEE-guided procedure is thought to be more useful than the FS-guided procedure in clinical setting.     

Dirofilaria immitis: worm burden and pulmonary artery proliferation in dogs from Michigan (United States)

Despite the ability to prevent heartworm disease, infection with Dirofilaria immitis continues to be a major problem for domestic dogs. To determine worm burden in heartworm-positive dogs from three county animal shelters in the state of Michigan in the United States and to assess the relationship between gross intimal proliferation and worm burden, necropsy was done on 176 heartworm-positive dogs. Adult heartworms were found in the heart and pulmonary artery of 170 of the 176 (96.6%) dogs examined. Mean worm burden was 14 +/- 13 (range 0-85). Fifty-nine percent of dogs had < or =10 heartworms. In contrast, 52% of dogs in a published report from the southern US (Florida) had worm burdens >10 [C.H. Courtney, Q.Y. Zeng, The structure of heartworm populations in dogs and cats in Florida, in: Proceedings of the American Heartworm Symposium, 1989]. These data suggest that mean worm burden in northern areas may be < or = that in warmer areas. Also, since diagnostic tests are less sensitive with lower worm burdens, diagnosis of heartworm infection in Michigan and other surrounding more northern states may be a greater challenge than in areas with higher worm burdens.     

Use of echocardiography for the diagnosis of heartworm disease in cats: 43 cases (1985-1997)

OBJECTIVE: To determine the usefulness of echocardiography in the diagnosis of heartworm disease in cats and to compare this modality with other tests. DESIGN: Retrospective study. ANIMALS: 43 cats with heartworm infection that had echocardiographic examinations at 2 veterinary teaching hospitals between 1985 and 1997. Twenty-two of these 43 cats also underwent radiography of the thorax and heartworm antibody and heartworm antigen testing. PROCEDURE: Cats were determined to be infected with Dirofilaria immitis infection on the basis of 1 or more of the following findings: positive modified Knott or antigen test result, echocardiographic evidence of heartworm disease, or confirmation of the disease on postmortem examination. The percentage of echocardiographs in which heartworms were evident was compared with the percentage of radiographs in which pulmonary artery enlargement was evident and results of antigen or antibody tests in cats in which all tests were performed. RESULTS: Overall, heartworms were detectable by use of echocardiography in 17 of 43 cats, most often in the pulmonary arteries. In the 22 cats in which all tests were performed, antibody test results were positive in 18, antigen test results were positive in 12, and pulmonary artery enlargement was evident radiographically and heartworms were identifiable echocardiographically in 14. Heartworm infection was diagnosed exclusively by use of echocardiography in 5 cats in which the antigen test result was negative. CONCLUSIONS AND CLINICAL RELEVANCE: Although echocardiography was less sensitive than antigen testing, it was a useful adjunctive test in cats that had negative antigen test results in which there was a suspicion of heartworm disease. The pulmonary arteries should be evaluated carefully to increase the likelihood of detection of heartworms echocardiographically.     

Comparative efficacy of four commercially available heartworm preventive products against the MP3 laboratory strain of Dirofilaria immitis

A controlled laboratory study was conducted to evaluate the efficacy of four commercial products administered as a single treatment for the prevention of heartworm disease caused by Dirofilaria immitis in dogs. Forty-four commercially sourced Beagle dogs, 6-7 months of age, were received at the test site (Auburn University, Department of Pathobiology) on Study Day (SD) -72 to begin acclimation. On SD -30, each dog was inoculated subcutaneously with 100 infective, third-stage D. immitis larvae (MP3 strain, TRS Laboratories, Inc., Athens, GA). On SD -1, 40 dogs weighing 18.2-25.3 lbs were ranked by decreasing body weight and randomized to five groups of eight dogs each. On SD 0, the dogs assigned to Group 1 were treated orally with ivermectin/pyrantel pamoate chewable tablets, Group 2 dogs were treated orally with milbemycin oxime flavored tablets, Group 3 dogs were treated with selamectin topical solution, and Group 4 dogs were treated with imidacloprid/moxidectin topical solution. Group 5 dogs remained nontreated. Dosages for dogs in Groups 1-4 were based on the individual body weight of each dog and current labeled dose banding for each commercial product. All dogs were fasted overnight prior to treatment. Food was returned four hours after treatment. Animals were observed for abnormal clinical signs involving eyes, feces, respiration, behavioral attitude, locomotion/musculature, or skin conditions at prescribed intervals immediately after treatment and at twice daily intervals thereafter. On SD 90, whole blood was collected and tested for adult heartworm antigen. On SDs 119/120, the dogs were euthanized and subjected to necropsy examination for recovery of adult D. immitis and/or worm fragments. At necropsy, all 8 dogs in the nontreated group were infected with adult D. immitis (34-70 worms/dog, geometric mean (GM)=51.6 worms/dog). One or more adult D. immitis and/or worm fragments were recovered from 7 of 8 of the dogs each in Groups 1-3 (87.5% were heartworm positive). The respective GM worm burdens/dog for Groups 1-3 was 2.3, 2.4, and 2.3 which resulted in 95.6, 95.4 and 95.5% efficacy, respectively. No worms were recovered from any of the 8 dogs in Group 4 resulting in 100% efficacy.     

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.     

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.     

Comparison of three enzyme-linked immunosorbant assays with the indirect immunofluorescent antibody test for the diagnosis of canine infection with Ehrlichia canis

The aim of this study was to compare three different enzyme-linked immunosorbant assays (recombinant major antigenic protein 2 (rMAP2)-ELISA, the Immunocomb (Biogal, Israel) and the Snap 3Dx assay (IDEXX Laboratories Inc., USA)) with the indirect immunofluorescent antibody test in detecting anti-Ehrlichia canis immunoglobulin-G (IgG) antibodies. Samples tested were collected from dogs suspected to be naturally infected with E. canis and from experimentally infected dogs.When qualitative results (positive/negative) were compared, there was an overall agreement of 81% (54/67) between the indirect immunofluorescence antibody (IFA) test and the rMAP2-ELISA. An overall agreement of 94% (63/67) was found between the IFA test and the Immunocomb, and an overall agreement of 91% (61/67) was found between the IFA test and the Snap 3Dx assay. In 50 of 67 (74.6%) samples tested, complete agreement in the qualitative results was found in all four tests. Sixteen of 17 samples with disagreement in the qualitative results were found to have IFA titers of 1:320 or less. The sensitivities and specificities of the tests were found to be 0.71 and 0.85 for the rMAP2-ELISA, 0.86 and 0.98 for the Immunocomb, and 0.71 and 1.00 for the Snap 3Dx assay.The tests performed in this study were found to be highly specific in detecting E. canis antibodies. Their sensitivity was found to be low with sera having IFA titers of < or =1:320, while high with sera having titers greater than 1:320. Repeating the serological tests 1-2 weeks after the first antibody assay may overcome the sensitivity problem with titers of < or =1:320.     

An investigation of the role of immunologic factors in anemia associated with canine heartworm disease

Direct Coombs' antiglobulin tests were performed on 80 dogs with patent Dirofilaria immitis infection and 170 dogs negative for microfilaria of D. immitis. Presence or absence of anemia was determined by hematocrit in 55 of the heartworm negative dogs and 68 of the dogs with heartworm disease. Heartworm infected dogs showed a higher incidence (37%) of anemia than noninfected dogs (14.5%). Anemia was most prevalent in two groups of dogs with heartworm infection, one group showing vena caval syndrome (91%) and the other occult dirofilariasis (62.5%). These latter two groups of dogs also showed a significantly higher number of positive Coombs' reactions at 37 degrees C than other dogs with heartworm disease and the noninfected dogs. The number of positive Coombs' reactions at 4 degrees C among the total of 80 dogs with heartworm infection was significantly higher than that for dogs without heartworm disease. However, there was no positive correlation between anemia and the outcome of the Coombs' test at either temperature. These findings do not suggest that immunologic factors play a major role in the pathogenesis of anemia in dogs with heartworm disease.     

Diagnostic, treatment, and prevention protocols for feline heartworm infection in animal sheltering agencies

Cats are at risk for heartworm infection (Dirofilaria immitis) wherever the disease is endemic in dogs. Diagnosis is more difficult in cats, and little information is available regarding effective palliative and curative treatments for infected cats. In contrast to the challenges of diagnosis and treatment, chemoprophylaxis is highly effective, and current guidelines call for preventive medications to be administered to all cats in endemic areas. The purpose of this study was to survey feline heartworm management protocols used by 400 animal shelters and foster programs in the endemic states of Alabama, Florida, Georgia, and Mississippi. Only 23% of shelters performed feline heartworm testing. The most common reasons for not testing were expense (36%), lack of treatment options for infected cats (18%), and because the agency considers heartworm infections in cats to be less important than in dogs (12%). Most agencies (69%) did not provide preventive medication to cats. Reasons included because testing was not performed (36%), expense (35%), and the perception that local heartworm risk was low (10%). When preventive was provided, feline-labeled broad-spectrum products were used more commonly (81%) than livestock products (14%). The survey also indicated that many policy decisions were based on inaccurate knowledge of feline heartworm prevalence and pathogenesis. Issues of cost, feasibility, and education prevent most Southeastern sheltering agencies from adequately protecting cats against heartworm disease. Practical guidelines tailored to the needs of these agencies should be developed. Subsidized testing and preventive products may facilitate implementation of feline heartworm management protocols in sheltering agencies.