Performance of serologic tests used to detect heartworm infection in cats

Evaluation of feline heartworm disease based on gross necropsy, serology, pulmonary histopathology, and radiographic evidence in adult shelter cats in northeastern Alabama

BACKGROUND

Veterinary knowledge regarding feline heartworm has been increasing significantly over the past two decades. Necropsy surveys of shelter cats have shown feline adult heartworm infection prevalence to be 5-20% of the rate in unprotected dogs; however, other studies have shown feline heartworm antibody prevalence up to 33%, reflecting higher exposure rates and potential immature adult infections. Thus, the true prevalence of feline heartworm infection is likely underestimated due to the limitations of current diagnostic techniques, inadequate testing protocols, and the high likelihood of cats exhibiting transient clinical signs or dying without confirmation of infection. Diagnosing Feline Heartworm Disease (FHWD), also referred to as Heartworm Associated Respiratory Disease (HARD), is one of the conundrums of veterinary medicine. The purpose of this study was to evaluate and characterize the occurrence of Heartworm Associated Respiratory Disease [HARD] in shelter cats, naturally-infected with D.immitis.

METHODS

Fifty shelter cats slated for euthanasia between December 2009 and June 2010 were investigated by gross necropsy, radiography, serology, and lung histopathology using techniques that have been established in experimental models of cat heartworm infection. The relationship between pulmonary vascular disease and serological markers for heartworm was also examined using correlations and statistical modeling. Serology included standard heartworm antigen test and a commonly used heartworm antibody test. Also included were heat-treated heartworm antigen test and two additional heartworm antibody tests previously evaluated on experimentally-infected cats.

RESULTS

None of the cats were heartworm antibody (HW Ab) positive on a commonly used HW Ab test used by many reference laboratories even though 20% of the study cats were heartworm antigen (HW Ag) positive on heat-treated samples. Two additional HW Ab test were positive on 26% and 22% of the study cats. The combination of heat-treated HW Ag, HW Ab tests, and histopathology indicated 34% of the study cats had HARD.

CONCLUSIONS

Utilizing both, the above tests, and thoracic radiographs, enhanced the ability to predict vascular disease, possibly caused by infection with immature and adult heartworms and supported the premise that cats develop heartworm disease at the same rate as dogs.

Occurrence of Dirofilaria immitis infection in shelter cats in the lower Rio Grande Valley region in South Texas, United States, using integrated diagnostic approaches

Dirofilaria immitis is a mosquito-borne filarioid nematode that affects dogs and cats. Although heartworm infections in cats can be fatal, it is commonly neglected by cat owners and veterinarians. Moreover, diagnosing heartworm infection in cats can be challenging, requiring the integration of multiple laboratorial tests and clinical examination. The objective of this study was to estimate the occurrence of D. immitis infection in shelter cats in the Lower Rio Grande Valley (RGV) region of Texas using a combination of immunodiagnostic and molecular methods. The RGV has a large population of stray animals with limited access to veterinary care. One hundred and twenty-two paired samples of serum and DNA extracted from the blood clots of cats from 14 towns in this region were analyzed. Serum samples were used for heartworm antibody detection (Heska® Solo Step®), and heartworm antigen detection using a commercial ELISA kit (DiroCHEK®) pre- and post-immune-complex dissociation (ICD) via heat treatment. A species-specific probe-based qPCR assay targeting a fragment of the cytochrome oxidase c subunit 1 of the mitochondrial DNA was utilized to detect the presence of parasite DNA. Twenty-two cats (18%) were positive in at least one diagnostic test. Antibody testing detected most cases (19/122; 15.6%); pre- and post-ICD antigen testing detected 6 cases (6/122; 4.9%); and qPCR detected the fewest cases (4/122; 3.3%), with 2 cats positive on all three diagnostic tests. Veterinarians should encourage local cat owners to utilize year-round heartworm prevention.

Molecular prevalence of Dirofilaria immitis and Wolbachia infections in pet and semi-domesticated cats in Bangkok, Thailand

Background and Aim:

Although cats are not natural hosts for heartworm infections (Dirofilaria immitis), evidence suggests that feline heartworm disease can be detrimental because of a severe inflammatory response. Recent studies have found that infection with bacteria of the genus Wolbachia is the principal cause of acute inflammatory filaria disease; nonetheless, the prevalence of cats naturally infected with heartworms and Wolbachia remains unclear. This study aimed to estimate the prevalence and current distribution of feline heartworm disease and its association with Wolbachia infection in pet and semi-domesticated cats in Bangkok, Thailand.

Materials and Methods:

A total of 260 cats (130 pet cats and 130 semi-domesticated cats) were enrolled in this study. Blood samples were placed into ethylenediaminetetraacetic acid tubes for hematological analysis and DNA extraction. A polymerase chain reaction (PCR) was performed to analyze samples for the presence of D. immitis and Wolbachia infections.

Results:

The prevalence (95% confidence interval [CI]) of D. immitis infection in pet, semi-domesticated, and all cats were 3.9% (1.3-8.8%), 27.7% (20.2-36.2%), and 19.6% (15.0-25.0%), respectively. The prevalence (95% CI) of Wolbachia infection in pet, semi-domesticated, and all cats were 18.5% (12.2-26.2%), 31.5% (23.7-40.3%), and 25.0% (19.9-30.7%), respectively. The prevalence of D. immitis and Wolbachia infections in semi-domesticated cats was significantly higher than in pet cats (p=0.002 and p=0.022, respectively). There was a significant association between D. immitis and Wolbachia infections (p<0.001). There was also a significant association between D. immitis infection and the presence of eosinophilia (p<0.045).

Conclusion:

From the PCR analysis, it can be concluded that semi-domesticated cats were at higher risk for D. immitis infection than pet cats. There was a significant association between positive D. immitis infection and positive Wolbachia infection. Combinations of anthelmintic and antimicrobial therapy should be considered in heartworm-positive cats.

Optimizing heartworm diagnosis in dogs using multiple test combinations

Background

Various heartworm (HW) diagnostic testing modalities detect products of, or reactions to, different life cycle stages of Dirofilaria immitis. Microfilariae (Mf) can be directly visualized in blood, antigen (Ag) from immature and adult heartworms may be detected on commercial assays, and antibody (Ab) tests detect the host immune response to larval stages. Ag and Mf tests are commonly used in dogs, which frequently carry adult HW infections, but Ab tests have only been validated for use in cats. In some HW-infected dogs, Ag is blocked by immune complexing leading to false-negative results. Heat-treatment (HT) to disrupt these complexes can increase the sensitivity of HW Ag tests. The aim of this study was to compare different methods for diagnosing HW infection in dogs at high risk using individual and paired diagnostic tests, including an exploration of using Ab tests designed for cats to test canine samples.

Methods

One hundred stray adult (≥ 2-year-old) dogs in Florida shelters were tested using Mf, HW Ag, and HW Ab tests (feline HW Ab tests currently not commercially validated/approved for use in dogs); two versions of each test platform were used.

Results

Fourteen dogs tested positive using point-of-care (POC) Ag tests; an additional 2 dogs tested positive with microtiter well assay, and an additional 12 dogs tested positive using HT Ag testing. For individual tests, Ag test sensitivity/specificity compared to HT Ag was 50–57%/100%, and Ab tests were 46–64%/82–94%. Sensitivity estimates for individual tests were higher when comparing to non-HT Ag. Pairing POC Ag tests with Mf tests improved sensitivity without loss of specificity, while pairing POC Ag and Ab tests modestly increased sensitivity at the expense of specificity.

Conclusions

Screening dogs for HW infection using both POC Ag and Mf detection, which is recommended by the American Heartworm Society, improved diagnostic performance in this study compared to single Ag test use, but may have missed more than one in four infected dogs. The need to improve access to highly accurate, rapid, and inexpensive large-scale HW testing for dogs in animal shelters remains largely unmet by current testing availability. The development of practical and validated protocols that incorporate heat or chemical treatment to disrupt Ag-Ab complexes in POC testing or decreasing the cost and time required for such testing in reference laboratories might provide solutions to this unmet need. Similar studies performed in countries where the prevalence of parasites such as D. repens or A. vasorum is different to the USA could potentially yield very different positive predictive values for both HT and non-HT Ag tests.

Graphic abstract

Efficacy of a novel topical combination of esafoxolaner, eprinomectin and praziquantel for the prevention of heartworm disease in cats

NexGard® Combo is a novel topical endectoparasiticide formulation for cats combining the insecticide/acaricide esafoxolaner, the nematodicide eprinomectin and the cestodicide praziquantel. The efficacy of this novel formulation for the prevention of heartworm disease in cats was tested in two experimental studies using an induced infection model and a randomized, blinded, placebo-controlled study design, and two USA isolates of Dirofilaria immitis. In each study, 20 naïve cats were each inoculated sub-cutaneously with 100 third-stage larvae of D. immitis 30 days before treatment. Following randomization to two treatment groups of ten cats, each cat was treated topically once, either with the minimum recommended dose of the novel formulation, or with an identical volume of placebo. Five months after treatment (6 months after infections), the cats were humanely euthanized for parasite recovery and count. Efficacy was calculated by comparison of the numbers of adult D. immitis recovered in the control and in the novel formulation groups. In the control groups of each study, D. immitis were recovered in seven and nine cats (respective worm counts ranges 1-7 and 1-16, respective geometric means 1.6 and 5.1). In both studies, none of the treated cats harbored any D. immitis at necropsy and the calculated efficacy of the novel formulation was 100%. There were no adverse reactions related to treatment with the novel formulation. The results of these two studies demonstrate that a topical NexGard® Combo application at the minimum label dose is well-tolerated and efficacious in preventing heartworm disease in cats.

Clinical Case of Life-threatening Co-infection Due to Dirofilaria Immitis and Aelurostrongylus Abstrusus in a Cat: First Report of Feline Heartworm Disease in Bulgaria

The present report describes the first clinically manifested and serologically proven case of Dirofilaria immitis infection in a cat in Bulgaria. A 10-year-old intact male cat was referred to the Small Animal Clinic, Trakia University with a history of anorexia, weight loss, intermittent coughing and itching skin lesions on the head and neck. Physical examination revealed abnormal heart sounds and respiration, cyanosis of the mucous membranes, and generalized enlargement of the lymph nodes. Mild infestation with hard ticks and fleas was also detected during the initial skin inspection. In addition, adult Otodectes cynotis mites were observed in the skin lesions. The fecal sample was positive for larvae of Aelurostrongylus abstrusus and eggs of Toxocara cati. Blood serology revealed antigens of D. immitis as well as antibodies against both feline immunodeficiency virus and D. immitis. Thoracic radiographic findings included a pronounced generalized reticular interstitial pattern; alveolar and bronchial shades with multiple nodular thickenings throughout the lungs. Electrocardiography demonstrated a sinus tachycardia, a peaked P-wave (P-pulmonale) and an abnormally low ST-segment. The clinical signs disappeared after treatment with selamectin, doxycycline and corticosteroids. Despite the improvement in general health condition, the cat suddenly died several months later.

Heartworm prevalence in dogs versus cats: Multiple diagnostic modalities provide new insights

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Prevalence of adult heartworm (HW) infection was 4 % in cats and 28 % in dogs.

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Combining antigen and antibody testing led to an overall 19 % positive cats.

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Prevalence did not differ between dogs and cats with added feline antibody testing.

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Dirofilaria repens microfilariae were identified in one dog and one cat.

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Acanthocheilonema reconditum microfilariae were identified in four dogs.

The cornerstones of diagnosis of heartworm (HW) in dogs are the detection of circulating antigen from adult female Dirofilaria immitis or the visualization of microfilariae in whole blood. These tests are less sensitive in cats because of the feline immune response leading to low numbers of adult worms, but heartworm antibody tests are also licensed for use in cats. HW antibodies in cats are detectable when there has at least been larval development in the tissues, but positive antibody tests cannot distinguish between current and previous larval infections; thus, cats with positive antibody test results are considered currently or previously infected with D. immitis. The aim of the present study was to use multiple HW diagnostic modalities to maximize detection of infection in dogs and cats at high risk of infection and to compare infection prevalence between these two hosts. Blood samples collected from 100 stray dogs and 100 stray cats at Florida animal shelters were tested for HW antigen (before and after heat treatment) and microfilariae; cats were also tested for HW antibody. Dogs were significantly (P = 0.0001) more likely to be diagnosed with adult HW infection (28 %; 95 % CI: 20.1–37.6%) when compared with cats (4 %; 95 % CI: 1.6–10.2%) on the basis of positive antigen and microfilariae test results. Cats with current or previous adult, immature adult, or larval HW infections comprised 19 % (95 % CI: 12.4%–27.9%) of the feline population, which was not significantly different (P = 0.1) from the prevalence of adult D. immitis infection in dogs. Testing unprotected cats for heartworm antibodies demonstrated a similar, high risk of infection to the matched unprotected dog population in Florida, which supports the use of HW preventives in cats in areas where HW transmission occurs.

Survey of Dirofilaria immitis antigen and antibodies to Leishmania infantum and Toxoplasma gondii in cats from Madeira Island, Portugal

BACKGROUND

Dirofilaria immitis, Leishmania infantum and Toxoplasma gondii are zoonotic parasites which can affect domestic cats. Considering the lack of published data from the local feline population, this study aimed to assess infection with or exposure to these pathogens in cats from Madeira Island, Portugal.

METHODS

One hundred and forty-one domestic cats (77 males and 64 females; median age: 2 years) were sampled at a veterinary medical centre in Funchal, from September 2018 to January 2019. Serum samples were tested for D. immitis antigen, with an enzyme-linked immunosorbent assay kit, and for antibodies to Leishmania spp. or to T. gondii, with the direct agglutination test and the modified agglutination test, respectively.

RESULTS

Five cats (3.5%; 95% confidence interval, CI: 1.2-8.1) were positive to D. immitis; no cats were seropositive to Leishmania spp. (0%; 95% CI: 0-2.6%); and 43 cats (30.5%; 95% CI: 23.0-38.8%) were seropositive to T. gondii. Prevalence of the D. immitis antigen was significantly different between cats that received ectoparasiticides and those which did not (0 vs 12.2%; P = 0.009). Prevalence of antibodies to T. gondii was significantly different between juvenile and adult cats (12.8 vs 38.0%; P = 0.007). There were two cats concurrently positive to D. immitis and T. gondii, but no statistical association between these two dependent variables was found (P = 0.641).

CONCLUSIONS

To our knowledge, this is the first report of the presence of parasites D. immitis and T. gondii in the feline population of Madeira Island. Knowledge on the epidemiological situation of these and other zoonotic pathogens should raise awareness, both at the veterinary medical and public health levels, and contribute to promoting prevention and control.

First Report on Clinical Feline Heartworm (Dirofilaria Immitis) Infection in Romania

Dirofilaria immitis (Nematoda: Filarioidea) is the causative agent of heartworm disease (HWD), a severe and potentially fatal condition in dogs. Although cats are considered more resistant to infection than dogs, they are also susceptible to heartworm infection. Moreover, the clinical importance of feline dirofilariosis has increased in recent years, especially in heartworm endemic areas. In contrast to dog, definitive antemortem diagnosis of heartworm infection in cat is difficult to achieve and a combination of testing methods must be used for clinical confirmation. Here we describe a clinical case of heartworm infection in a 12-year-old male mixed breed cat, originated from Southern Romania, which was referred to a veterinary clinic with a history of vomiting and clinical signs of respiratory distress. The thoracic radiograph showed a diffuse bronchointerstitial pattern of the pulmonary parenchyma. The serological test for D. immitis circulating antibody was positive and heartworms were visualized by echocardiography in the main pulmonary artery. In conclusion, the present study clearly shows that cats are at risk for D. immitis infection in heartworm-endemic areas in Romania. Additionally, the findings highlight the urgent need for increased awareness among veterinary practitioners of the existence of feline heartworm diseases and for adequate prophylactic measures to be applied. To our knowledge, this is the first report on clinical evolution and radiographic and echocardiographic features of a naturally heartworm-infected cat in Romania.

Efficacy and safety of a new topical formulation containing selamectin and sarolaner in the prevention of heartworm disease and the treatment of roundworm infection in cats presented as veterinary patients in Japan

The efficacy and safety of a new topical formulation containing selamectin plus sarolaner (Revolution® Plus / Stronghold® Plus, Zoetis) was evaluated for the prevention of heartworm (Dirofilaria immitis) disease and the treatment of roundworm infection in cats enrolled as veterinary patients in two field studies conducted in Japan. In the heartworm field study, 91 cats negative for D. immitis antigen and anti-D. immitis antibody were enrolled and received 9 monthly topical treatments with selamectin plus sarolaner during the period of April to December 2015. Efficacy was assessed by testing post-treatment blood samples collected 8, 12, and 15 months after initiation of treatment for the presence of D. immitis antigen and anti-D. immitis antibody. Eighty-seven cats completed the entire study and were included in the determination of efficacy. No D. immitis antigen or anti-D. immitis antibody were detected in any of the post-treatment samples. In the roundworm field study, completed in the period from April to November 2015, 64 cats with ≥100 roundworm eggs per gram (EPG) of feces were enrolled and allocated randomly in a 1:1 ratio, to receive either selamectin plus sarolaner or emodepside plus praziquantel (Profender®, Bayer). Treatments were administered topically on Days 0 and 30, and efficacy was assessed by fecal EPG counts conducted on Days 14, 30, and 60. All cats completed the entire study. At enrollment, all cats were infected with Toxocara cati. Compared to pre-treatment, geometric mean T. cati EPG counts on Days 14, 30, and 60 were reduced by >99.9% in both treatment groups. There were no treatment-related adverse events in either study. Monthly topical administration of Revolution® Plus / Stronghold® Plus providing a minimum of 6 mg/kg selamectin and 1 mg/kg sarolaner was safe and effective in the prevention of heartworm disease and the treatment of roundworm infection in cats enrolled as veterinary patients in Japan.

Prevalence of heartworm infection in the feral cat population of Grand Cayman

Objectives

The aim of this study was to determine the presence and prevalence of heartworm infection in the feral cat population of Grand Cayman.

Methods

During the study period, feral cats were routinely trapped and euthanized for population control by the municipal animal shelter. Cats older than 6 months of age were obtained for post-mortem examination shortly after euthanasia. The heart, lungs, pulmonary vasculature, thoracic and abdominal cavities were examined for the presence, location and number of mature heartworms. Sections of caudal lung were evaluated histologically and serologic tests were performed to screen for additional evidence of heartworm exposure.

Results

Mature heartworms were identified in the pulmonary vasculature of 4/36 cats (11.1%). An additional nine cats showed histopathologic changes in the lungs consistent with heartworm exposure, and one cat had a positive antibody test.

Conclusions and relevance

The results indicate a minimum heartworm prevalence of 11.1% within this population of feral cats, consistent with published necropsy reports from other endemic localities. Considering the histopathologic changes observed in this group, the true prevalence is likely higher and underscores the importance of heartworm prevention for the companion cat population of the island.

Feline heartworm (Dirofilaria immitis) infection: first case report of serological diagnosis in Brazil, confirmed by molecular assay

The clinical importance of heartworm infection in cats has indeed increased in recent years. Dirofilaria immitis infection has been reported worldwide in cats and continues to be regularly diagnosed in endemic areas. The diagnosis can be overlooked easily, especially in Brazil, where there is not a specific feline immunodiagnostic test, forcing the veterinarians to use a test made for the canine host. In 2015, a 10-year-old female neutered cat was diagnosed with D. immitis using an antigen serological test, based on imunocromatography and designed for dogs. The modified Knott test was negative. As the disease progressed, the cat showed clinical signals of respiratory distress, such as dyspnoea and polypnea in addition to prostration and emaciation, and died a few weeks after the diagnosis. During necropsy, one adult nematode was found in the pulmonary artery. D. immitis infection was confirmed by molecular amplification, performed in the worm fragment. This is the first report of serological diagnosis of feline dirofilariasis in Brazil. A chemoprophylaxis routine in cats should be done, as is done in dogs from endemic areas.

Prime detection of Dirofilaria immitis: understanding the influence of blocked antigen on heartworm test performance

Detection of circulating antigen of Dirofilaria immitis has been a mainstay of identifying heartworm infection in clinical practice for the past three decades. Several validated commercial antigen tests have very good sensitivity, specificity, and positive predictive values, especially when used in patients for which heartworm infection is likely. In some dogs and cats infected with heartworm, antigen may not be available for detection although present in the patient sample; heat pretreatment of these samples reveals the antigen, changing the false negative to positive. This phenomenon was documented in the literature in the 1980s but subsequently overlooked by the heartworm research community for many years. In this review, we provide a summary of the current understanding of the role of heat reversal in diagnosing heartworm infection. This additional diagnostic step is most important for patients in which heartworm infection is likely, such as dogs or cats in an endemic area with an inconsistent history of heartworm preventive use, or dogs with a prior diagnosis of heartworm infection that were recently treated. To illustrate the concept, we share a summary of results from canine samples tested at the state veterinary diagnostic laboratory in Oklahoma, USA in 2017 by modified Knott test and by commercial antigen test before and after heat treatment of samples; in this sample set, heat treatment changed all D. immitis microfilaria-positive but antigen-negative samples to antigen-positive. Pet dogs with a history of consistent preventive use are unlikely to become positive with heat pretreatment; for that reason, routine pretreatment of all samples tested in a veterinary practice is not recommended. We also review known causes of false negative and false positive results on heartworm antigen tests that, although uncommon, can complicate accurate diagnosis in individual patients. Together, this review provides a primer to aid understanding of strategies that can enhance accurate diagnosis of heartworm infection in veterinary practice and clinical research.

Prevalence and epidemiology of canine and feline heartworm infection in Taiwan

Background

Heartworm, Dirofilaria immitis, has long been recognized in Taiwanese dogs but feline heartworm infection has been largely overlooked by veterinarians and pet owners. The main goal of this study was to determine the prevalence and epidemiology of canine and feline heartworm infection in Taiwan.

Methods

Household dogs and cats were selected from 103 veterinary hospitals in 13 cities throughout Taiwan. All animals were at least 1 year old, had received no heartworm prevention for more than 1 year, and had lived in the same city for at least 1 year. Client consent was obtained and an owner questionnaire was completed for each patient. Blood samples were collected from each canine patient and tested at each veterinary hospital for microfilariae and for circulating antigen. A positive result on either test was considered to confirm mature heartworm infection. Blood was collected from each feline patient and examined for microfilariae and a feline heartworm antigen/antibody test was performed. Descriptive statistics were used for heartworm prevalence. Multivariate logistic regression analysis was used to determine the relationships between heartworm infection and multiple risk factors.

Results

A total of 2064 household dogs and 616 household cats from 103 veterinary hospitals throughout Taiwan were included in the study. The overall prevalence of canine heartworm disease was 22.8% (471/2064). In heartworm-positive dogs, 63% were both microfilaria positive and antigen positive, 35% were microfilaria negative and antigen positive, and only 2% were microfilaria positive and antigen negative. In the comparison of different life style groups, outdoor dogs (N = 797) had significantly higher heartworm prevalence rate than indoor dogs (N = 1267; p = 0.000). The heartworm prevalence rate in dogs presented with dyspnea and cough was as high as 51%. The overall prevalence of antibody-positive cats was 6.7% (41/616) and the antigen-positive prevalence rate was 3.1% (19/616). In 41 antibody-positive cats, 6 of them were also antigen-positive. In 19 antigen-positive cats, 13 of them were antibody negative. In antibody-positive and antigen-negative cats, half had no clinical signs. In antigen-positive cats, 21% had no clinical signs and only 38% had classic heartworm clinical signs (dyspnea, cough, or gastrointestinal signs).

Conclusions

Our canine study showed that southern and eastern Taiwan have the highest heartworm prevalence. Dogs not receiving preventive and living outdoors or those that have either cough or dyspnea have a high incidence of heartworm infection. We also confirmed that feline heartworm exposure exists in most cities in Taiwan. The diagnosis of feline heartworm infection will remain challenging for clinicians, however, without a consistent relationship between the presence of heartworm infection and clinical signs and the vagaries of microfilaria and antigen/antibody testing.

Electronic supplementary material

The online version of this article (10.1186/s13071-017-2435-7) contains supplementary material, which is available to authorized users.

The progression of heartworm associated respiratory disease (HARD) in SPF cats 18 months after Dirofilaria immitis infection

BACKGROUND

Heartworm-associated respiratory disease (HARD) in cats is induced by the arrival and death of immature adult Dirofilaria immitis in the pulmonary system and is indistinguishable from mature adult heartworm infection.

METHODS

A controlled, blind research study investigated the long-term (18 months post infection, PI) consequences of the inflammatory response associated with the death of immature adult heartworms in cats. Three groups of cats, 10 per group, were infected with 100 third-stage (L3) larvae by subcutaneous injection. Group A cats were treated with selamectin (Revolution®; Zoetis) per label directions at 28 days PI and once monthly for 17 months. Group B cats were treated orally with ivermectin (Ivomec®; Merial) at 150 μg/kg) at 70 days PI, then every 2 weeks for 15 months. Group C cats were untreated PI. At baseline (Day 0) and on Days 70, 110, 168, 240, 309, 380, and 505 PI, peripheral blood, serum, bronchial lavage, and thoracic radiographic images were collected.

RESULTS

The selamectin-treated cats (Group A) and ivermectin-treated cats (Group B) were free of heartworms or heartworm fragments at necropsy. All cats became heartworm antibody positive at some time point in the study except for one cat in Group A. Only cats in Group C (all with adult heartworms) were heartworm antigen positive. The heartworm antibody titer for Group B was highest on Days 110 to 168 and then decreased over time and 50% were serologically antibody negative on Day 240. Eosinophilic bronchoalveolar lavage (BAL) cytology and peripheral eosinophilia were most pronounced on Day 110 in all cats. Randomly distributed myofibrocytes in the lungs of some Group A cats suggest that precardiac larval stages were affecting the lungs. Radiographs in Group B cats demonstrated partial resolution of the initial HARD reaction but chronic myofibrocyte proliferation was histologically evident 18 months after infection.

CONCLUSION

HARD was induced by immature adult worm infection with progressive improvement starting 6 to 8 months after infection but histologic lesions were evident in some cats 18 months after infection. The serologic antibody assay was negative in 50% of cats at 8 months and 100% of cats at 18 months post infection. Abnormal radiographic lung patterns continued in a subset of Group B cats for months after heartworm antibody serology and BAL cytology returned to normal.

Increased detection of Dirofilaria immitis antigen in cats after heat pretreatment of samples

Objectives

To determine whether pretreating diagnostic samples with heat increases the detection of Dirofilaria immitis antigen in adult cats, we evaluated feline serum and plasma samples collected in heartworm-endemic areas of the southern United States.

Methods

Commercial microtiter well assays for detection of D immitis antigen were used to evaluate serum or plasma samples from 385 shelter and free-roaming cats from the southcentral and southeastern United States before and after heat treatment; commercial antibody tests were performed on a subset of samples.

Results

Prior to sample heat treatment, 1/220 (0.5%) shelter cats and 4/165 (2.4%) free-roaming cats had detectable D immitis antigen. After heat pretreatment, the detection rate increased to 13/220 (5.9%) and 13/165 (7.9%), respectively. Antibody reactive to D immitis was significantly more common ( P <0.001) in the serum of cats that were antigen positive after heat treatment (10/13; 76.9%) than serum from cats that remained antigen negative after heat treatment (22/163; 13.5%).

Conclusions and relevance

Heat pretreatment of feline samples increased antigen detection by commercial assays for D immitis and improved overall concordance of antigen and antibody test results in antigen-positive samples in this population. Although further work to investigate the specificity of D immitis antigen assays when using pre-treated samples is warranted, this approach may be useful in the diagnosis of heartworm infection in individual cats and may increase the accuracy of surveys based on antigen detection.

Feline lower airway disease: A retrospective study of 22 naturally occurring cases from Greece

In this retrospective study of 22 cats with lower airway disease of either intermittent (23%) or persistent nature (77%), the Siamese breed (55%) was significantly over-represented. Females (68%) were slightly but not significantly over-represented. No significant association was found between the clinical stage of disease and the physical findings, thoracic radiographic changes or the response to treatment. Cough, the most common presenting complaint, was the only symptom detected in the cats with intermittent disease, yet the two most severely affected animals did not show it. Thoracic auscultation did not reveal any abnormality in 41% of the cats. Haematology revealed eosinophilia in 46% of the cats. A bronchial pattern was the most common radiographic abnormality (73%), followed by alveolar (32%) and interstitial patterns (23%). Interestingly, thoracic radiographs were normal in 23% of the cats. The combination of short-term corticosteroids and bronchodilators resulted in complete and long-term remission of symptoms in nine cats, while the other 11 required ongoing medication because of relatively frequent relapses. One of the remaining two cats died during an asthmatic crisis, while the other was lost to follow up.

Dirofilaria immitis exposure status in client-owned cats with or without lower airway/lung-associated signs: case-control study in a canine heartworm-endemic area

Objectives Heartworm-associated respiratory disease (HARD) is a recently recognised pathological manifestation in cats caused by Dirofilaria immitis exposure. This study aimed to estimate the percentage of cats at risk of developing HARD in a heartworm-endemic area (Taipei, Taiwan), and to test the correlation of heartworm exposure and the presence of lower airway/lung clinical signs (LA/L signs). Methods This was a prospective case-control study. The study design called for the enrolment of at least 80 cats with LA/L signs and at least 80 cats without such clinical signs in a 1 year period. The D immitis antibody seroprevalence of the two cohorts was compared. Results From February 2014 to January 2015, 187 client-owned cats were prospectively enrolled: 83 clinical cases with LA/L signs and 104 cats without such signs. Antibody seropositivity was approximately twice as frequent in cats with LA/L signs (13.3%) than in cats without signs (7.8%) (odds ratio [OR] 1.814); nevertheless, no statistically significant difference between the two cohorts ( P = 0.22) was found. We used 41 frozen samples from free-roaming cats to examine the possibility of different exposure rates to mosquito bites between client-owned cats and stray cats, finding the seroprevalence to be 7.5% in free-roaming cats - a result not statistically different to that in client-owned cats ( P = 0.60). Outdoor access was a significant risk factor for heartworm exposure in client-owned cats (OR 3.748; P = 0.03); however, living entirely indoors did not provide complete protection from exposure/infection. Conclusions and relevance Our results did not show statistically significant differences in antibody seroprevalence between cats with and without LA/L signs. LA/L signs were not always present under conditions of natural exposure. However, exposure to D immitis is not rare among client-owned cats, suggesting that heartworm prophylactics should be a part of routine care in all cats living in areas endemic for canine heartworm.

Seroprevalence of heartworm (Dirofilaria immitis) in feline and canine hosts from central and northern Portugal

Dirofilaria immitis is endemic in Portugal. Several studies have reported the presence of canine heartworm disease, although no previous studies on feline infections have been published. The aim of this study was to determine the prevalence of D. immitis in cats and dogs from central and northern Portugal. Blood samples from 434 cats were tested for circulating anti-D. immitis and anti-Wolbachia antibodies. Furthermore, 386 dogs were tested for circulating D. immitis antigens. Overall feline seroprevalence was 15%, while canine prevalence was 2.1%. The highest feline seroprevalences of 18.7% and 17.6% were found in Aveiro and Viseu, respectively, while the highest canine prevalences of 8.8% and 6.8% were found in Coimbra and Aveiro, respectively. Cats and dogs showing respiratory signs presented higher prevalences of 24.4% and 17%, respectively, while 50% of cats with gastrointestinal signs were seropositive. The present study confirms the seropositivity of D. immitis in the feline population in central and northern Portugal, and suggests the importance of including heartworm disease in the list of differential diagnoses of cats and dogs showing clinical signs compatible with the 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.

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.

Heartworm disease in animals and humans

Heartworm disease due to Dirofilaria immitis continues to cause severe disease and even death in dogs and other animals in many parts of the world, even though safe, highly effective and convenient preventatives have been available for the past two decades. Moreover, the parasite and vector mosquitoes continue to spread into areas where they have not been reported previously. Heartworm societies have been established in the USA and Japan and the First European Dirofilaria Days (FEDD) Conference was held in Zagreb, Croatia, in February of 2007. These organizations promote awareness, encourage research and provide updated guidelines for the diagnosis, treatment and prevention of heartworm disease. The chapter begins with a review of the biology and life cycle of the parasite. It continues with the prevalence and distribution of the disease in domestic and wild animals, with emphasis on more recent data on the spreading of the disease and the use of molecular biology techniques in vector studies. The section on pathogenesis and immunology also includes a discussion of the current knowledge of the potential role of the Wolbachia endosymbiont in inflammatory and immune responses to D. immitis infection, diagnostic use of specific immune responses to the bacteria, immunomodulatory activity and antibiotic treatment of infected animals. Canine, feline and ferret heartworm disease are updated with regard to the clinical presentation, diagnosis, prevention, therapy and management of the disease, with special emphasis on the recently described Heartworm Associated Respiratory Disease (HARD) Syndrome in cats. The section devoted to heartworm infection in humans also includes notes on other epizootic filariae, particularly D. repens in humans in Europe. The chapter concludes with a discussion on emerging strategies in heartworm treatment and control, highlighting the potential role of tetracycline antibiotics in adulticidal therapy.

Feline heartworm disease: A clinical review

Feline heartworm disease is caused by the filarial nematode Dirofilaria immitis, and is transmitted by mosquitoes in heartworm-endemic areas worldwide. While dogs are the definitive hosts for this parasite, cats can also be infected, and the overall prevalence in cats is between 5% and 10% of that in dogs in any given area. The spectrum of feline presentations varies from asymptomatic infections to chronic respiratory signs, sometimes accompanied by chronic vomiting to acute death with no premonitory signs. Ante-mortem diagnosis can be challenging and relies on a combination of tests, including antigen and antibody serology, thoracic radiography and echocardiography. As treatment with heartworm adulticidal drugs can be life-threatening and heartworm infection in cats is often self-limiting, infected cats are frequently managed with supportive treatment (corticosteroids, bronchodilators, and anti-emetics). Surgical removal of filariae using extraction devices may be considered in some acute cases where immediate curative treatment is necessary, but filarial breakage during the procedure may result in an acute fatal shock-like reaction. Necropsy findings are mainly pulmonary and include muscular hypertrophy of the pulmonary arteries and arterioles on histopathology. A number of safe and effective macrocytic lactone drugs are available for prophylaxis in cats. These drugs can kill a range of larval and adult life-cycle stage heartworms, which may be advantageous in cases of owner compliance failure or when heartworm infection status is undetermined at the time prophylaxis is commenced. An index of suspicion for feline heartworm disease is warranted in unprotected cats with respiratory signs, and perhaps chronic vomiting, in areas where canine heartworm disease is endemic. Many cats, once diagnosed and with appropriate supportive care and monitoring, will resolve their infection and be free of clinical signs.

Seroprevalence ofDirofilaria immitis, feline leukemia virus, and feline immunodeficiency virus infection among dogs and cats exported from the 2005 Gulf Coast hurricane disaster area

OBJECTIVE

To determine seroprevalence of dirofilariasis in dogs and seroprevalences of dirofilariasis, FeLV infection, and FIV infection in cats exported from the Gulf Coast region following the 2005 hurricanes.

DESIGN

Seroprevalence survey.

ANIMALS

1,958 dogs and 1,289 cats exported from Louisiana, Mississippi, and Texas between August 20 and December 31, 2005.

PROCEDURES

141 animal welfare groups in 37 states and Alberta, Canada, reported results of serologic testing. Risk factors for infection, including age, sex, neuter status, breed, and state of rescue, were examined by means of univariate and multivariate logistic regression.

RESULTS

Seroprevalence of dirofilariasis in dogs was 48.8%. Sexually intact dogs were 1.6 times as likely to have dirofilariasis as were neutered dogs, dogs in the ancient breed group were 2.2 times as likely and dogs in the guarding breed group were 1.7 times as likely to have dirofilariasis as were dogs in the herding breed group, and dogs from Mississippi were significantly less likely to have dirofilariasis than were dogs from Texas. Seroprevalences of dirofilariasis, FeLV infection, and FIV infection in cats were 4.0%, 2.6%, and 3.6%, respectively. Seroprevalence of FIV infection was significantly higher in adult cats than in juveniles and in males than in females.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggest that dogs and cats exported from the 2005 Gulf Coast hurricane disaster area had disease rates similar to those for animals in the region prior to the hurricanes.

Pulmonary arterial disease in cats seropositive for Dirofilaria immitis but lacking adult heartworms in the heart and lungs

OBJECTIVE

To determine the prevalence and severity of pulmonary arterial lesions in cats seropositive for heartworms (Dirofilaria immitis) but lacking adult heartworms in the heart and lungs during necropsy.

ANIMALS

630 adult cats from an animal control shelter in Florida.

PROCEDURE

Cats were tested for adult heartworms in the heart and pulmonary arteries and antibody against heartworms in the serum. Histologic examination was conducted on the right caudal lung lobe of 24 heartworm- and antibody-positive cats; 24 heartworm-negative and antibody-positive cats; and 24 heartworm-, antibody-, and antigen-negative cats. Wall areas of 10 small to medium-sized pulmonary arteries of each cat were measured and expressed as a proportion of total cross-sectional area.

RESULTS

Heartworm infection or seropositive status was significantly and strongly associated with seventy of medial hypertrophy of pulmonary arterial walls. Heartworm- and antibody-positive cats and heartworm-negative and antibody-positive cats had a significant increase in wall thickness, compared with wall thickness for heartworm- and antibody-negative cats. Heartworm- and antibody-positive cats had the most severe hypertrophy. The proportion with occlusive medial hypertrophy was significantly higher in heartworm- and antibody-positive cats (19/24 [79%]) and heartworm-negative and antibody-positive cats (12/24 [50%]), compared with heartworm- and antibody-negative cats (3/24 [13%]).

CONCLUSIONS AND CLINICAL RELEVANCE

Cats with serologic evidence of exposure to heartworms, including those without adult heartworms in the lungs and heart, have a greater prevalence of pulmonary arterial lesions than heartworm-negative cats without serologic evidence of exposure. Additional studies are needed to define the pathogenesis, specificity, and clinical importance of these lesions.

Prevalence of naturally occurring Dirofilaria immitis infection among nondomestic cats housed in an area in which heartworms are endemic

OBJECTIVE

To determine prevalences of heartworm exposure (ie, positive heartworm antibody test results) and heartworm infection (ie, positive heartworm antigen test results or identification of mature heartworms at necropsy) among nondomestic cats housed in an area in rural North Carolina where Dirofilaria immitis is known to be endemic and among nondomestic cats housed in areas with a low prevalence of dirofilariasis or in an area considered to be free from heartworms.

DESIGN

Cross-sectional prevalence survey.

ANIMALS

97 nondomestic cats in North Carolina (study population) and 29 nondomestic cats in Colorado; Queensland, Australia; or Auckland, New Zealand (control population).

PROCEDURE

Results of serologic tests and postmortem examinations were reviewed.

RESULTS

Results of heartworm antibody tests were positive for 57 of 75 (76%) study cats and 1 of 29 (3%) control cats. Male study cats had a significantly higher risk of heartworm exposure than did female study cats (relative risk, 1.3). Results of heartworm antigen tests were negative for all 47 study cats and 16 control cats that were tested. Postmortem examinations were performed on 21 study cats, and 1 (5%) was found to be infected with heartworms.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggested that nondomestic cats housed outdoors in the southeastern United States are at risk for heartworm exposure and infection, with male cats having a greater risk of exposure than female cats.

Prevalence of infectious diseases in feral cats in Northern Florida

Objectives of this study were to determine prevalence of infection in feral cats in Northern Florida with a select group of infectious organisms and to determine risk factors for infection. Blood samples or sera from 553 cats were tested with a panel of antibody, antigen or PCR assays. Male cats were at higher risk for FIV, Mycoplasma haemofelis, and M. haemominutum. Infection with either FeLV or FIV was associated with increased risk for coinfection with the other retrovirus, M. haemofelis, or M. haemominutum. Bartonella henselae had the highest prevalence and was the only organism that did not have any associated risk for coinfection with other organisms. Feral cats in this study had similar or lower prevalence rates of infections than those published for pet cats in the United States. Thus, feral cats assessed in this study appear to be of no greater risk to human beings or other cats than pet cats.

Comparison of Serological Tests for the Detection of Natural Heartworm Infection in Cats

Serological tests were performed on 380 cats with necropsy-confirmed heartworm status 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.

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.

Dirofilaria immitis infection of a snow leopard (Uncia uncia) in a Japanese zoo with mitochondrial DNA analysis

Three dog heartworms (Dirofilaria immitis) were detected in the lumen of the right cardiac ventriculus and of the pulmonary artery of a captive female snow leopard (Uncia uncia) that died of pancreatic carcinoma at a zoo in Japan. Neither clinical respiratory nor circulatory symptoms caused by the heartworm infection were observed. The filarial worms were identified as D. immitis from the morphologic characteristics of the esophagus, the presence of faint longitudinal ridges on the cuticular surface, the situation of vulva posterior to the esophagus, and the measurements of the body. The heartworms from the snow leopard were identical to that of D. immitis from dogs in the sequence of the cytochrome oxidase I region in the mitochondrial DNA. This host record is the first of D. immitis in U. uncia.

Two cases of cutaneous nodular dirofilariasis in the cat

Cutaneous nodular dirofilariasis is occasionally reported in dogs but is rare in cats. This report describes two cases of cutaneous nodular lesions due to Dirofilaria immitis adult parasites in domestic shorthaired cats living in an endemic area in northern Italy.

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.

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.