Research progress on diagnosis and control technology of canine heartworm disease

Research progress on diagnosis and control technology of canine heartworm disease

Research progress on diagnosis and control technology of canine heartworm disease


Canine filariasis, also known as canine heartworm disease (Dofilara immitis), commonly known as "dog heartworm disease", is a parasitic infection of the right ventricle and pulmonary artery of dogs by adult heartworms.

According to reports, the infection rate of canine heartworm in the United States, Germany, Australia, Japan, Singapore, and Taiwan is 40-60%, and it is used as the main quarantine item for import and export.

I. Diagnostic techniques

The diagnosis of canine heartworm disease mainly depends on the observation of clinical symptoms, combined with the examination of microfilaria in the peripheral blood.

Diagnosis can also be confirmed by necropsy of the dog after death, observing its pathological changes or finding heartworm worms in the right ventricle and pulmonary artery of the dog.

1. Observation of clinical symptoms

In the early stage, the dogs did not show clinical symptoms, but with the development of the disease, they developed sudden cough after exercise, weight loss, and intolerance to exercise.

2. Pathological necropsy changes

Adult parasites in the pulmonary artery and right atrium block blood flow, so that the heart can not push out the normal blood supply collective needs, resulting in cardiac hypertrophy and expansion, myocardial fibers gradually lose their contractility.

3. Observation of Microfilariae

3.1 Blood smear method

Take 2 drops of peripheral blood and place them on a glass slide to make a thick drop piece, and observe the active microfilariae directly under the microscope.

3.2 Centrifugal collection method

Collect 1ml of venous blood in a test tube, add 9ml of 2% formaldehyde, or 5ml of 7% acetic acid, or add 5ml of 1% dilute hydrochloric acid, mix well, and lyse the red blood cells.

3.3 Filtration method

Collect 1ml of blood and add 5ml of 2.5% sodium citrate, pour it into a 300-mesh sieve and filter.

The filtration method is the most direct way to observe the worms. The cells in the anticoagulant can be filtered out through the sieve, and only the worms can stay in the filter grid, which is easy to find under the low magnification microscope.

4. Auscultation

4.1 Cardiac auscultation

When right heart enlargement and vena cava syndrome occur, systolic murmur or tricuspid valve regurgitation sound can be found on auscultation due to parasite interference with blood flow and tricuspid atresia; about 90% of heartworms with vena cava syndrome

4.2 Lung auscultation

When the dog inhales, a mild to obvious split murmur can occasionally be heard, and the dog will cause systemic clinical symptoms due to right-sided stasis heart failure: jugular vein pulsation/dilation, hepatomegaly and ascites, pleural effusion accumulation in the pleural cavity,

5. Thoracic X-ray examination and evaluation

Heartworm-infected sick animals are usually photographed by chest X-ray in a back-to-abdominal mode, so that more diagnostic thoracic X-rays can be obtained.

5.1 At the beginning of the course of the disease, the pulmonary arterioles around the pulmonary lobes had slight inconspicuous dilation, and these dilated arterioles showed linear opaque images on the X-ray film.

5.2 In the middle of the disease course, the interstitial density of the pulmonary lobes increased, and the diameters of the arterioles of the pulmonary arteriole plexus gradually changed and lost the original homogeneity.

5.3 At the end of the disease course, the pulmonary artery and the right heart were obviously dilated.

6. Electrocardiogram

In patients with chronic severe pulmonary arterial hypertension, the right ventricular hypertrophy of sick dogs is often seen on electrocardiogram.

7. Heart Ultrasonography

The right atrium and right ventricle were dilated and enlarged, and the tricuspid papillary muscle hypertrophy was detected in most dogs.

8. Hematology test

In cases of heartworm infection, cytopenias are often seen in hematological examinations. In severe cases, the hematocrit is reduced to 10%, and the plasma albumin content is reduced.

9. Immunological diagnosis

The established enzyme-linked immunosorbent assay and brief fluorescent antibody test have been used in the epidemiological investigation of this disease.

10. Molecular biological diagnosis

The detection method using PCR has high sensitivity and specificity.

2. Prevention and control

1. Drug prevention and treatment

There are many control drugs for canine heartworm, which can be divided into three categories: microfilaria killing, adult killing and preventive drugs. Because of the high toxicity of the drugs, the body must excrete the drugs as soon as possible after the drug is administered, otherwise it will endanger other organs.

2. Surgery

When the number of adult parasites is large, the intimal lesions of the pulmonary artery are significant, and the renal function is low and it is not suitable for drug treatment, surgical treatment can be used, especially for dogs with acute heartworm disease, timely surgical removal of the parasites can be cured.

3. Integrated control

3.1 According to the epidemiological characteristics of this disease, mosquitoes are the intermediate host of canine heartworm disease, and canine heartworm disease is transmitted through mosquito bites.

3.2 Bring the dog to the animal hospital for antigen detection of adult heartworms every six months, and according to the requirements of the veterinarian, during the mosquito active season, use the continuous administration method and the brief administration method to oral prophylaxis for dogs under 6 months old

3.3 Regarding the anti-insect vaccine, some people have developed the anti-microfilaria chitinic acid vaccine. Immunizing gerbils with this vaccine can protect the gerbils from being infected by microfilariae.

Three. Conclusion

Canine heartworm disease is widely distributed in Asia, Oceania, Africa, America and other areas with more mosquitoes. It is widely distributed in my country. Epidemiological survey results in some areas show that the infection rate of canine heartworm is more than 40%.