Heartworm-infected Dogs Research Articles

Clinical studies on canine dirofilarial hemoglobinuria: changes in right heart hemodynamics inducing heartworm migration from pulmonary artery.

In ordef to examine the changes in hemodynamics inducing heartworm migration from the pulmonary artery, the pressures of the right ventricle and pulmonary artery and right cardiac output were measured after administration of 1.5mg/kg body weight of milbemycin D (Milbe) in 6 heartworm-infected dogs under general anesthesia. The heartworms migrated from the pulmonary artery to the tricuspid valve orifice and right atrium from 50 to 105 min after Milbe administration in 4 of the dogs. After Milbe administration, heart rate increased transiently, then subsequently decreased. Systolic right ventricular and mean pulmonary pressures did not show uniform changes in heartworm-migration cases. The right cardiac output decreased clearly before heartworm migration in all such cases. Stroke volume (right cardiac output/heart rate), cardiac index (right cardiac output/kg body weight) and stroke index (stroke volume/kg body weight) also decreased in heartworm-migration cases. The heartworm migration from the pulmonary artery towards the right atrium may be associated with the decreases of blood flow volume and velocity in the right heart.

Canine dirofilarial hemoglobinuria: changes in right heart hemodynamics and heartworm migration from pulmonary artery towards right atrium following beta 1-blocker administration.

In order to investigate whether heartworm migration was induced or not, metoprolol, an anti-hypertensive agent with a cardioselective β-adrenoceptor blocking action (β1-blocker), was administered to heartworm-infected dogs under general anesthesia. After about 8mg/kg body weight of metoprolol administration, heart rate and right cardiac output reduced significantly in all 6 dogs. Heartworms migrated from the pulmonary artery to the right atrium in 5 dogs, and hurdled the pulmonary valve transiently in 1 dog on two-dimensional echocardiogram. However, the worms returned to the pulmonary artery in a short time in 4 cases. The pressures at the right ventricle and the pulmonary artery and stroke volume did not show uniform changes after the administration. It was considered that the decrease of heart rate and cardiac output, namely, decreased blood flow volume and velocity at the pulmonary artery by metoprolol administration induced the heartworm migration in the direction opposite blood flow.

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°C than other dogs with heartworm disease and the noninfected dogs. The number of positive Coombs' reactions at 4°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.

RIGHT HEART ENLARGEMENT IN HEARTWORM‐INFECTED DOGS

Radiographically, the size of the right ventricle of 54 heartworm‐infected dogs was graded subjectively as normal, 1 +, 2 +, and 3 + and served to classify the dogs into groups A, B, C, and D. With M‐mode echocardiograms, right ventricular enlargement ratios (RVE ratios) were determined for each dog by dividing the measured right ventricular internal diastolic dimension (RVIDd) by the expected RVIDd of a normal dog of the same body weight. The normal RVIDd relation to body weight was derived from 25 healthy heartworm‐free control dogs. These two variables were linearly related with a correlation coefficient r2= 0.59. Means and standard deviations of the RVE ratio were calculated for each group. Despite wide ranges and considerable overlap, the ratio was significantly different (t‐test, p < 0.005) between groups with the exception of groups A and B, and C and D. The incidence of electrocardiographic signs of right ventricular hypertrophy was also determined for each group; it was 38% in group C and 62% in group D. From this data, it was concluded that M‐mode echocardiography is a very sensitive technique for the documentation of right ventricular dilatation in heartworm‐infected dogs, correlating with radiographic impressions of right ventricular enlargement.

Blood cellular and biochemical studies in canine dirofilariasis.

Haematological studies in heartworm-infected dogs revealed low haemoglobin concentration, increased erythrocyte sedimentation rate and a marked increase in lymphocyte percentage. Biochemical analysis of serum of dogs infected with heartworm showed increases in serum total bilirubin, serum globulin, chloride, phosphorus, serum glutamic oxaloacetic transaminase and serum glutamic pyruvic transaminase values and a decrease in albumin content.

Cardiopulmonary Changes in Heartworm-Infected Dogs after a 32-Month Interval

To characterise physiologically progressive cardiovascular changes in heartworm-infected dogs not in congestive heart failure, 2 sets of physiological parameters were determined on 10 dogs at approximately a 3-year interval. The results of the electrocardiograms indicate a tendency for a clockwise rotation of the mean electrical axis, from 69° to 87°, over this period. The QRS interval (p

Fleas as Acceptable Intermediate Hosts of the Do Heartworm, Dirofilaria immitis.

The method of natural transmission of the dog heartworm, Dirofilaria immitis, is still incompletely elucidated. The larvae of this parasite have been shown to develop in many species of mosquitoes and, thus, mosquitoes have been believed to be incriminated in the natural transmission, but substantial proof of this is lacking. The possibility that other blood-sucking arthropods serve as transmitters was overlooked until 1921, when Breinl reported finding the micro-filarial embryos of Dirofilaria immitis in the fleas, Ctenocephalides canis and Ctenocephalides felis, collected from heartworm infected dogs in Australia. He also observed the advanced stages of development of this parasite in the Malpighian tubules of the fleas and the infective stage larvae in the hemocelic cavity. Recently, Brown has observed the microfilariae and partially developed larvae of this parasite in Ctenocephalides canis collected from heartworm-infected dogs in the eastern United States. In November of 1938, the writer, in examining dogs for heart-worm infection in New Orleans, observed the typical microfilariae of Dirofilaria immitis in Ctenocephalides canis. The early developmental stages and the infective larvae were also seen in the hemocelic cavity of fleas collected from a dog having a heavy infection. On other dogs harboring Dirofilaria immitis Ctenocephalides felis and Pulex irritans were found similarly infected. The female fleas of the 3 species were much more frequently infected and were more heavily infected with all the larval stages of the parasite than were the males. From some dogs infected with heartworm as many as 100% of the female fleas examined contained one or more infective-stage larvae and many of the earlier stages of development. The males harbored these stages only in small numbers and rarely contained the infective stage larvae.