Investigation of Caval Syndrome in Dogs Experimentally Infected With Dirofilaria immitis

Nine of 16 dogs inoculated with 200 infective heartworm larvae developed caval syndrome (CS) of heartworm disease (HWD). There was no difference between dogs that did and did not develop CS with regard to total heartworm burden, burden relative to body weight, or female heartworm burden, indicating that factors other than worm mass are involved in the pathogenesis of CS. Male dogs were twice as frequently affected as females, although this finding was not statistically significant. Dogs afflicted with CS exhibited radiographic, pathologic, and hemodynamic evidence of chronic HWD. In a model of single heartworm exposure, these findings strongly support the theory that CS develops due to retrograde migration of adult worms from the pulmonary arteries and right ventricle to the right atrium and venae cavae. Pulmonary artery pressures were dramatically and significantly greater in dogs with CS (60 +/- 18 torr) as compared to non-CS (30 +/- 4 torr) dogs with equal worm burdens.     

Improvement in pulmonary arterial lesions after heartworm removal using flexible alligator forceps

Improvement of pulmonary arterial lesions after heartworm removal using flexible alligator forceps was investigated by measuring pulmonary arterial pressure (PAP), and by angiographic and histopathological examinations in 11 dogs. PAP obtained immediately after worm removal corresponded well with angiographic abnormalities. In 2 dogs, high PAP immediately after worm removal fell gradually by 12 weeks, and obstructions on angiogram were resolved at 4 to 12 weeks. In 4 dogs, slightly high PAP fell to the normal range at 4 weeks, and angiographic abnormalities were considerably reduced at 4 to 12 weeks. In 5 dogs, PAP returned to normal range immediately after worm removal, and angiographic changes almost disappeared at 4 to 8 weeks. On biopsy immediately after worm removal, samples of the main pulmonary arteries showed severe intimal proliferations with villous or papillary protrusion into the lumen. Autopsy at 12 to 20 weeks indicated that the intimal protrusions were remarkably reduced as compared with the biopsy samples in all cases. However, villous intimal protrusions were seen in the caudal lobar arteries in cases with remaining alive worms. New vessels seemed to develop into thromboemboli with time. From these findings, it is clear that the pulmonary arterial lesions improved after heartworm removal, and the clinical signs disappeared following the improvement in hemodynamics. Aspirin therapy (5 mg/kg/day) for 4 weeks after worm removal in 5 dogs did not improve the intimal lesions as compared to 3 control dogs.     

Relationship between pulmonary arterial pressure and pulmonary thromboembolism associated with dead worms in canine heartworm disease.

To examine effects of thromboemboli due to dead worms on pulmonary arterial pressure (PAP), 20 to 50 dead heartworms were inserted into the pulmonary arteries of 4 heartworm uninfected dogs (uninfected group) and 11 dogs infected with heartworms (infected group). In the uninfected group, the mean PAP rose 1 week after worm insertion (10.9 to 166. mmHg), but it recovered by the 4th week. Clinical signs, hemodynamics and blood gas findings also deteriorated at the 1st week, but recovered at the 4th week. Angiographic and pathological findings indicated that blood flow recovered through the spaces between thromboemboli and vessel walls at the 4th week. The infected dogs were divided into three groups. In the infected-I group (5 dogs), the intimal lesions of the pulmonary arteries were slight, and clinical and laboratory findings showed changes similar to those of the uninfected group. In the infected-II group (4 dogs), the pulmonary arterial lesions were severe and the mean PAP was higher (25.7 mmHg) than in the uninfected group before worm insertion. An increase in PAP (34.1 mmHg) and worsening of clinical and laboratory findings were noticed till the 4th week. Thromboemboli adhered extensively to the vessel walls. Two dogs in the infected-III group died of severe dyspnea on the 9th and 10th day, and the mean PAP rose remarkably at the 1st week (from 19.4 to 28.2 mmHg). Severe pulmonary parenchymal lesions with edema or perforation were observed. From the above results, it was clarified that effects of dead worms on PAP and clinical signs depended on the severity of pulmonary arterial lesions before worm insertion.(ABSTRACT TRUNCATED AT 250 WORDS)     

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.     

Contribution of live heartworms harboring in pulmonary arteries to pulmonary hypertension in dogs with dirofilariasis

To investigate whether adult heartworms harboring in the pulmonary arteries contribute to pulmonary hypertension, we determined the cardio-pulmonary values immediately before and after removal of heartworms from the pulmonary arteries and before and after insertion of live worms in their place. In 10 heartworm-infected dogs, 8 to 46 worms were removed. The mean pulmonary arterial pressure fell significantly from 24.5 +/- 7.9 mmHg to 16.3 +/- 4.9 mmHg (p less than 0.01) immediately after removal. The right cardiac output decreased in 7 of the 10 cases. The total pulmonary resistance and right ventricular stroke work index also decreased. At 24 hours after removal, live heartworms were put back into the pulmonary arteries of their host dog. The mean pulmonary arterial pressure elevated significantly (p less than 0.01) immediately after insertion. The right cardiac output further decreased in 7 of the 10 dogs, and the total pulmonary resistance and right ventricular stroke work index increased. Separate from this, 12 to 42 heartworms were transplanted into the pulmonary arteries of 5 heartworm-free dogs. Immediately after transplantation, the pulmonary arterial pressure did not show any significant change. However, the stroke volume decreased, and the total pulmonary resistance increased. These facts suggest a contribution of live heartworms to the pulmonary hypertension, although there is a complicated interaction among the presence of heartworms, the pulmonary lesions and the pulmonary hypertension.     

Contamination of dog hair with eggs of Toxocara canis

Toxocara canis, the common intestinal nematode of dogs and foxes, is the parasite responsible for human toxocarosis. It has recently been shown that dogs may harbour eggs of the parasite in their fur. To further investigate this claim a population of 100 stray dogs was examined to establish the prevalence and intensity of adult toxocaral worm infection in the intestines and eggs harboured in the hair. A novel method of washing the eggs from the hair was used. Sixty-seven percent of dogs were found to have T. canis eggs on their hair with a mean egg retrieval of nearly 584 eggs per gram from positive dogs. The age of the dog was found to be the only significant factor to influence the prevalence and intensity of eggs, with 95% of all the eggs recovered found on puppies. Thirty-nine percent of dogs were found to have adult T. canis worms in their intestine, although a significantly higher percentage of puppies (80%) were infected with worms than adults (22.5%). Puppies also had more worms per infection than adults and have a strong positive correlation between egg and worms numbers whereas adults did not. These studies show that stray dogs, particularly puppies, potentially harbour considerable numbers of eggs on their hair, at densities far higher than those reported in the soil or the general environment.     

Frequency of pulmonary mineralization and hypoxemia in 21 dogs with pituitary-dependent hyperadrenocorticism

The purpose of this study was to determine the frequency of hypoxemia and pulmonary mineralization using ^99mTc-methylene diphosphonate (^99mTc-MDP) in dogs with pituitary-dependent hyperadrenocorticism (PDH). Twenty-one dogs with PDH were pro-spectively evaluated using thoracic radiography, arterial blood gas analysis, and bone phase and pulmonary perfusion scintigraphy (using ^99mTc-macro-aggregated albumin [^99mTc-MAA]). The radiographs and bone and perfusion studies were evaluated subjectively. An averaged quantitative count density ratio was calculated between the thorax and cranial thoraco-lumbar vertebrae from lateral thoracic ^99mTc-MDP images. Thoracic: vertebral ratios were calculated using ^99mTc-MDP studies from 21 control dogs. The thoracic: vertebral ratios were compared between the 2 groups (PDH and control). The mean age (±SD) of the 21 PDH dogs was 10.2 (±3) years, whereas the mean age of the control group was 9.8 (±3) years. Seven of the 21 dogs with PDH were hypoxemic (denned as an arterial partial pressure of oxygen [PaO₂] <80 mm Hg) with an average PaO₂ (±SD) of 62 (±15) mm Hg. Of the 7 hypoxemic dogs, 2 were found to have pulmonary mineralization based on bone scintigraphic images. Pulmonary perfusion abnormalities were not identified using ^99mTc-MAA in any of the 21 PDH dogs. Six PDH dogs had an abnormal interstitial pulmonary pattern and 5 of these dogs were hypoxemic. The average quantitative thoracic: vertebral ratio was not significantly different between the PDH and control dogs (0.5 ± 0.4 versus 0.4 ± 0.1, P = .16). Causes of hypoxemia other than pulmonary thromboembolism should be considered in dogs with PDH. Pulmonary mineralization may contribute to hypoxemia in dogs with PDH.     

棘球蚴病综合防治技术推广应用

１９９６ —１９９８ 年在海北州３ 县５ 场进行棘球蚴病综合防治技术推广,对项目区２１ 万只犬应用吡喹酮药物采取“犬犬投药、季节驱虫”的模式,连续三年累计驱虫达３４８３ 万只（ 次） ,平均驱虫密度达９５ ％ ,犬细粒棘球绦虫感染率由综防前的６２０７ ％ 下降到零;１ ～３ 岁幼年羊棘球蚴感染率由综防前的３６３１ ％ 、４００６ ％ 和５７８６ ％ 分别下降到７８０ ％ 、１０１６ ％ 、１３４３ ％ ;幼年羊多头蚴感染率由综防前的４２９ ％ 下降到０３２ ％ ;１ ～３ 岁牛棘球蚴由综防前的１９４０ ％ 、４２６１ ％ 和５９２６ ％ 分别下降到零和２４３ ％ 、５６６ ％ ,效果明显、经济效益显著。     

Pathophysiologic mechanism of cardiac dysfunction in experimentally induced heartworm caval syndrome in dogs: an echocardiographic study

In dogs with experimentally induced heartworm infection, the onset of caval syndrome (CS) was characterized by a murmur, loudest over the tricuspid valve, and a large worm mass in the right ventricular lumen detectable during diastole by use of M-mode echocardiography. Two-dimensional echocardiography indicated that the worm mass was located in the right atrium and venae cavae and was "flowing" into the right ventricle during rapid diastolic filling. Paradoxical septal motion and vigorous right ventricular cranial wall motion also were observed. Other echocardiographic changes included decreased size of the left atrium and ventricle, aortic root, and ratio of left-to-right ventricular diastolic luminal diameter, compared with values obtained 6 months after experimentally induced heartworm infection. Right ventricular end diastolic diameter increased considerably. Most echocardiographic indices of left ventricular function (fractional shortening, velocity of circumferential fiber shortening, ejection fraction, and preejection period) were not altered appreciably, but estimates of cardiac index and stroke volume were markedly decreased. Electrocardiography revealed ventricular and supraventricular premature complexes in 7 of the 8 dogs studied, evidence of right ventricular enlargement in 6 of the 8 dogs studied, and increased mean heart rate, compared with that measured 6 months after inoculation of infective larvae, before the onset of CS. Cardiac catheterization was performed in 3 days at the onset of CS. Severe pulmonary arterial and right ventricular hypertension and decreased cardiac index (compared with values obtained before inoculation) were observed. Evidence of right ventricular inflow obstruction was not detected. Mean aortic blood pressure decreased with the onset of CS, but right ventricular end diastolic pressure increased.(ABSTRACT TRUNCATED AT 250 WORDS)     

Pathological findings in dogs naturally infected with Angiostrongylus vasorum in Newfoundland and Labrador, Canada.

Fifty-six dogs from St. John's, Newfoundland, Canada, were evaluated for Angiostrongylus vasorum infection. Small numbers of nematodes were found within pulmonary arteries of 6 dogs. Larvae were identified in fecal samples in 2 of 6 dogs. All 6 dogs had multifocal granulomatous pneumonia and sometimes foci of chronic thrombosis, which varied from very mild to severe. One dog had extensive pulmonary lesions resulting in cor pulmonale. Right heart failure was characterized by right ventricular hypertrophy, hepatic congestion, ascites, and hydrothorax. Microscopically, in most cases, eggs, larvae, and sometimes intravascular adults, were present within lung tissue sections. Small foci of granulomatous inflammation with and without larvae were present in kidney and brain in 4 dogs. An additional dog, diagnosed antemortem with angiostrongylosis via fecal examination, was also examined. Pathological findings consisted of severe pyogranulomatous interstitial pneumonia with myriad eggs, larvae, and numerous intravascular pulmonary adult nematodes with extensive arterial thrombosis. Five hundred and seventy-two adult worms were removed from pulmonary arteries. Foci of granulomatous inflammation, often associated with larvae and/or eggs, were present in tracheobronchial lymph nodes, adrenal gland, brain, and kidneys. Severe seizuring noted antemortem was attributed to several large, discrete areas of acute hemorrhagic infarction within the cerebrum and cerebellum. Natural A. vasorum infection in domestic dogs in eastern Newfoundland causes lung pathology of variable severity, which in some cases, may progress to cor pulmonale and which may be associated with extrapulmonary lesions and clinical signs.     

Cardiopulmonary function values before and after heartworm removal in dogs with caval syndrome

Cardiopulmonary function values were determined before and after surgical removal of adult heartworms in 25 dogs with spontaneous and 4 dogs with drug-induced caval syndrome (CS). Fifteen dogs with spontaneous CS (recovery group) and 4 dogs with drug-induced CS (drug-induced CS group) recovered after removal, and 10 dogs with spontaneous CS were euthanatized or died (nonsurviving group). Before heartworm removal, injected radiographic contrast medium was regurgitated from the right ventricle to the right atrium. Mean pulmonary arterial pressure and total pulmonary resistance were not statistically different between the recovery and nonsurviving groups of dogs, but the end-diastolic right ventricular pressure (mean +/- SD, 6.9 +/- 9.1 mm of Hg) and the a (8.7 +/- 9.2 mm of Hg)- and v (6.3 +/- 8.5 mm of Hg)-waves of the right atrial pressure curve in the recovery group were less, respectively, than the end-diastolic right ventricular pressure (17.3 +/- 6.0 mm of Hg) and the a (15.8 +/- 6.1 mm of Hg)- and v (21.4 +/- 6.9 mm of Hg)-waves in dogs of the nonsurviving group. After heartworm removal, contrast medium regurgitation disappeared, and cardiac output of the right ventricle increased in dogs of the recovery (from 2.08 +/- 0.72 to 2.38 +/- 0.68 L/min; P less than 0.05) and drug-induced CS (from 1.42 +/- 0.19 to 1.88 +/- 0.26 L/min, P less than 0.05) groups. However, regurgitation remained, and cardiac output did not increase in some dogs of the nonsurviving group.(ABSTRACT TRUNCATED AT 250 WORDS)     

Acute and Short-Term Hemodynamic,Echocardiography, and Clinical Effects of Enalapril Maleate in Dogs With Naturally Acquired Heart Failure: Results of the Invasive Multicenter PROspective Veterinary Evaluation of Enalapril Study: The IMPROVE Study Group

The efficacy of enalapril maleate in dogs with naturally acquired class III or class IV heart failure was evaluated in a multicenter study. Fifty-eight dogs with dilated cardiomyopathy (35 dogs), mitral regurgitation (22 dogs), or aortic regurgitation (1 dog) receiving conventional therapy for heart failure (furosemide with or without digoxin) were included in a randomized double-blind study. Thirty-one dogs received enalapril tablets PO at approximately 0.5 mg/kg body weight bid, and 27 dogs received placebo tablets PO bid. Physical, electrocardiographic, hemodynamic, echocardiographic, radiographic, and clinical examinations were performed on each dog before treatment and at the end of the approximately 21-day study. After treatment on day 0, the enalapril-treated dogs had significantly (P < .05) lower heart rate, mean systemic arterial blood pressure, and mean pulmonary arterial blood pressure than the placebo-treated dogs. Pulmonary capillary wedge pressure was marginally decreased (P= .0567) in the enalapril-treated dogs. When compared with those in the placebo-treated dogs, scores for pulmonary edema were significantly (P= .05) decreased on day 2 in the enalapril-treated dogs. At the end of the study, enalapriltreated dogs had significantly (P= .05) greater decreases in class of heart failure, pulmonary edema score, and mobility score relative to baseline, and had significantly (P= .05) better overall evaluation scores when compared with the placebo-treated dogs. This study shows the beneficial hemodynamic and clinical effects of adding enalapril to conventional therapy for dogs with heart failure.     

Successful transcatheter retrieval of embolized Amplatz Canine Duct Occluders in two dogs

Transcatheter occlusion of patent ductus arteriosus (PDA) using an Amplatz® Canine Duct Occluder (ACDO) is routinely performed in dogs. Pulmonary embolization of the device is a rarely reported complication of this procedure. We report here the first two cases of successful transcatheter retrieval of an embolized ACDO. An 8-month-old, 21-kg, German shepherd (case 1) was referred for pulmonary edema secondary to a large PDA with left-to-right shunting. After medical stabilization, an emergency procedure for PDA closure was recommended. An 8-mm ACDO was deployed under general anesthesia. The device was released after confirming its stability with a gentle tug test but migrated into the pulmonary trunk. A 10-mm ACDO was subsequently successfully deployed and released. Vascular access was then obtained from the right jugular vein so that a vascular snare could be used to capture the ACDO waist and pull it back toward the right ventricle and then the right atrium. It was then removed through the jugular vein. The dog recovered uneventfully and was discharged after confirmation of complete ductal occlusion. The same complication occurred in a second case (case 2, asymptomatic 6-month-old, 7.9-kg, cocker spaniel), and a similar procedure was used to successfully retrieve the embolized device. Both dogs are still doing well 9 and 21 months, respectively, after the procedure. These cases illustrate that transcatheter retrieval of ACDO devices embolized in the pulmonary artery using vascular snares is technically feasible in the dog.     

AORTIC AND CARDIAC MINERALIZATION IN THE DOG

Aortic and cardiac mineralization was found in 21 of 3443 (0.61%) canine thoracic radiographs. In none of 786 feline thoracic radiographs reviewed were such lesions present. Mineralizations were superimposed on the ascending aorta (19 dogs) or on the caudal cardiac silhouette (2 dogs). In 2 of 4 dogs mineralization was identified echocardiographically dorsal to the aortic valve in close proximity to coronary arteries. Computed tomography confirmed mineralization of the aortic arch and root in 2 of 2 dogs. Necropsy and histopathologic examination in 1 dog revealed multiple nodular aortic tunica media calcifications with adjacent areas of degeneration. Lesions were significantly overrepresented in older dogs and in Rottweilers, and regarded as dystrophic calcification, caused either by age-related degenerative changes or chronic disease-related processes. There was no evidence of clinical significance attributed to the mineralization in any dog. Aortic and cardiac mineralization should be recognized as an incidental, non-significant finding in dogs of advanced age and differentiated from pleural and pulmonary structures.     

Treatment by digital amputation of subungual squamous cell carcinoma in dogs: 21 cases (1987-1988)

Malignant digital tumors were diagnosed in 62 dogs during a 1-year period. Twenty-one (33.9%) of the dogs had subungual squamous cell carcinoma. Each of these dogs had involvement of single digits. Sixteen (76.2%) of the dogs with squamous cell carcinoma were large-breed dogs, and 15 (71.4%) had predominantly black coats. Labrador Retrievers (n = 5, 23.8%) and Standard Poodles (n = 3, 14.3%) were the most commonly represented purebreeds. None of the dogs had evidence of metastases prior to treatment. All 21 tumors were treated by amputation of the involved digit. Histologic evidence of neoplastic bone invasion was found in 15 of the 21 amputated digits (71.4%). Local tumor recurrences were not observed. Only 1 dog developed documented metastatic disease; this dog was euthanatized because of pulmonary metastases 5 months after surgery. At the time of this report, 9 dogs (42.9%) were alive with no evidence of disease (median, 26 months after surgery), and 11 dogs (52.4%) had died or were euthanatized (median, 20 months after surgery). The cause of death in 7 dogs was known to be unrelated to squamous cell carcinoma, and the cause of death in 4 dogs was unknown. The 1-year and 2-year survival rates were 76.2% and 42.9%, respectively.     

Infectivity of Ancylostoma caninum in dogs by different routes of inoculation

Infectivity of A. caninum in dogs inoculated with 500 larvae by different routes (percutaneous, subcutaneous, intravenous, per os, through a stomach tube and foot pad) was studied by ascertaining the worm burden at necropsy 21-27 days post-infection. Infection through foot-pads yielded the maximum number of worms. The percentage of worm establishment using foot-pad inoculation was 73.8%, followed by subcutaneous (49.0%), percutaneous (45.0%) and per os (35.0%) routes. These results show that active penetration of the larvae through skin and particularly foot-pad is the most favourable mode of infection of dogs.     

Studies on schistosomiasis. 8. The influence of age on the susceptibility of sheep to infestation with Schistosoma mattheei.

Twenty-eight Dorper wethers, allocated according to age into 4 groups of 7 animals each, and 1 group of 7 Merino wethers, were compared for susceptibility to Schistosoma mattheei infestation. The group mean ages of the Dorper sheep varied from 5-61 months and their live mass from 25-66 kg, while the Merinos were 8 months old and had a mean mass of 19 kg. Despite the marked differences in the age and live mass of the Dorper sheep and the inclusion of 2 breeds in the experiment, no statistically significant differences were found in cercariae which failed to penetrate the sheep the mean percentage development of cercariae to adult worms, worm distribution in the mesenteric and gastric radicles of the portal vein and the pulmonary arterial system, and worms not removed by perfusion. Significant differences between groups (5% significance level) were found, however, in the number of worms recovered from the hepatic portal system, and in the worm sex ratio. On 3 occasions the total number of eggs excreted per female schistosome in the mesentery per 24 hours differed significantly between groups, but each time a different group or groups of sheep were responsible for the variation which was probably due, therefore, not to the age or breed of the sheep, but to daily variations in individuals. Highly significant differences occurred in the infectivity of the 6 cercarial pools used for infestation in spite of standardized collection and handling of the cercariae. Possible reasons for this are discussed and a solution suggested. Frequent egg counts (5 per sheep per week) were done during the first 25 days of patency, until the sheep were slaughtered. Schistosome ova were detected in the faeces of only 1/18 sheep examined on Day +43 after infestation, and 3/17 on Day +44, whereafter this increased rapidly to 15/34 on Day +45, 25/33 on Day +46, etc. A highly significant correlation was found between the total worm egg excretion in the faeces of the sheep per day and the numbers of female schistosomes in the mesentery, especially shortly after the onset of egg production.     

Effects of doxycycline on early infections of Dirofilaria immitis in dogs

The antifilarial effects of tetracycline drugs were first demonstrated when they were found to be highly effective against L(3) and L(4) of Brugia pahangi and Litomosoides sigmodontis in rodent models. Tetracyclines are also now known to have activity against microfilariae and adult Dirofilaria immitis, but assessment of their activity against larval and juvenile heartworms has not been reported previously. This study assessed the effects of doxycycline administered orally at 10mg/kg twice daily for 30-day periods at selected times during the early part of the life cycle of D. immitis in dogs with dual infections of D. immitis and B. pahangi. Twenty beagles were randomly allocated by weight to four groups of five dogs each. On Day 0, each dog was given 50 D. immitis L(3) and 200 B. pahangi L(3) by SC injection. Dogs received doxycycline on Days 0-29 (Group 1); Days 40-69 (Group 2); or Days 65-94 (Group 3). Group 4 served as untreated controls. Blood samples were collected for microfilariae counting and antigen testing. Necropsy for collection of adult heartworms and selected tissues were performed Days 218-222. Heartworms recovered were examined by immunohistology, conventional microscopy/transmission electron microscopy, and molecular biology techniques. No live heartworms were recovered from dogs in Group 1; dogs in Group 2 had 0 to 2 live worms (98.4% efficacy), and dogs in Group 3 had 0-36 live worms (69.6% efficacy). All control dogs had live adult heartworms (25-41). The live worms recovered from dogs in Groups 2 and 3 were less developed and smaller that worms from control dogs. Microfilariae were not detected in any dogs in Groups 1 and 2; one dog in Group 3 had 1 microfilariae/ml at necropsy. All control dogs had microfilariae at necropsy. One dog in Group 1 was antigen positive at one sampling (Day 166). One dog in Group 2 was antigen positive Days 196 and 218-222 and three dogs in Group 3 were antigen positive at one or more samplings All five control dogs were antigen positive at all three sampling times. These findings suggest that doxycycline at 10mg/kg orally twice daily for 30 days has efficacy against migrating tissue-phase larvae and juvenile worms and will delay or restrict microfilarial production.     

Clinical and Pathological Features of Aortic Thromboembolism in 36 Dogs

Thirty-six dogs with aortic thromboembolism were identified in a retrospective study conducted using case material from the small animal necropsy service of the University of Pennsylvania, from 1977 through 1992. No age, breed, or sex predisposition was found. Thirty dogs presented with primary complaints referable to the aortic thromboembolus and the duration of signs varied from hours to months. In 16 dogs, the presence of the thromboembolus was confirmed antemortem by ultrasound or angiography. Coagulograms were performed in 11 animals, and were consistent with consumptive hemostatic disorders in 8. The aortic occlusions were determined to be emboli in 11 dogs, associated with cardiac disease (9 dogs) and neoplastic emboli (2 dogs). In 18 dogs, the aortic occlusions were determined to be caused by primary aortic thrombi. Nine of these dogs had renal disease and four dogs had severe atherosclerosis associated with thyroid disease. In seven dogs, it could not determined if the aortic occlusions were due to primary aortic thrombi or due to emboli. In 25 dogs, the aorta was the only vessel occluded; but in 11 dogs, thrombi were identified in vessels outside of the systemic arterial system. In 9 dogs, the pulmonary arteries contained thromboemboli; one dog had thrombi in the portal vein and pulmonary arteries, and one dog a cranial vena caval thrombus. Nine of 11 dogs with multiple vascular thrombi, as well as some of the dogs with primary aortic thrombi, may have had either a propensity for thrombosis (a hypercoagulable state) or an inability to lyse thrombi (a hypothrombolytic state).     

Postadulticide pulmonary hypertension of canine heartworm disease: successful treatment with oxygen and failure of antihistamines

Postadulticide pulmonary hypertension mechanisms and treatment with antihistamines and supplemental oxygen were studied in eight dogs with heartworm disease. To ensure severe postadulticide thromboembolism, additional heartworms (either 20 or 40 into 4 dogs each) were transplanted into naturally infected dogs before thiacetarsamide treatment. During pentobarbital anesthesia, 2 pulmonary hemodynamic studies were conducted on each dog with a sequence of baseline, hypoxia with FlO2 = 10%, hyperoxia with FlO2 = 100%, a second baseline, treatment with either diphenhydramine (D) or cimetidine (C), and another hypoxia. All dogs were pulmonary hypertensive, with each dog having a mean pulmonary arterial pressure (PPA) greater than 20 mm of Hg. Mean PPA increased from baseline conditions (25.0 +/- 4.5 SD for D and 24.3 +/- 4.4 for C) to hypoxia (28.5 +/- 4.7 for D and 28.4 +/- 3.7 for C), and decreased during hyperoxia (16.9 +/- 3.0 for D and 17.4 +/- 3.0 for C), respectively. Neither antihistamine reduced PPA at normoxia. The degree of pulmonary hypertension when breathing room air increased even more during hypoxia, and this increase was not attenuated by either antihistamine. Histamine did not appear to mediate pulmonary hypertension during postadulticide thromboembolism, nor to modify the hypoxia-mediated pulmonary hypertension at this disease stage. Because baseline PO2 was low (66.6 +/- 11.7 mm of Hg for D and 69.4 +/- 14.2 for C) and because PPA decreased during administration of oxygen, the pulmonary hypertension was mostly hypoxia-induced. In addition to the arterial lesions, much of the pulmonary hypertensive mechanism was an active and reversible vasoconstriction in response to hypoxia caused by the secondary lung disease.(ABSTRACT TRUNCATED AT 250 WORDS)