Canine filariasis, also known as polyfilariasis immunity, is commonly known as "canine heart disease". It is a parasitic nematodiasis caused by adult canine filariasis parasitic in the right ventricle and pulmonary artery of dogs, resulting in damage to the circulatory system, respiratory system and urinary system of dogs. Microfilaria is a larva produced by female insects, which enters and parasitizes the peripheral blood circulation of sick dogs. When mosquitoes and other intermediate hosts suck blood, microfilaria enter mosquitoes and develop into invasive larvae. Dogs can be infected when bitten by microfilaria-positive mosquitoes. The disease is widely distributed in Asia, Oceania, the Middle East, Africa, southern Europe and America.
Data show that the infection rate of heartworm in the United States, Germany, Australia, Japan, Singapore and Taiwan Province Province is 40-60%, which is the main quarantine item for import and export. In the early 1990s, the disease was prevalent among dogs in China, and police dogs in Heilongjiang, Shenyang, Nanjing, Zhejiang, Guangzhou, Yunnan, Chongqing and other places were infected one after another, but it was rarely reported in recent years. This disease is a parasitic disease of people and animals. In recent ten years, cases of human infection have been found in the United States, Japan, Taiwan Province Province and other places. 1993 held international conferences on filariasis in Europe and the United States respectively, suggesting that the importance of filariasis as a zoonotic disease has been paid more and more attention. With the rapid economic growth and the improvement of people's living standards in China, more and more people keep pet dogs, especially in large and medium-sized cities. The close contact between humans and dogs provides the possibility for the spread of diseases. In this paper, the research progress of diagnosis and control technology of canine cardiac filariasis is summarized as follows:
I. Diagnostic techniques
The diagnosis of canine cardiofilariasis mainly depends on the observation of clinical symptoms and the examination of microfilaria in peripheral blood. If there are characteristic skin lesions, the diagnosis can be made by taking blood from the lesion center and checking congestion filariasis. In addition, commercial reagents can be used for antigen detection. In addition to the above two commonly used diagnostic methods, it can also be combined with other diagnostic techniques such as chest X-ray photography and electrocardiogram to improve the diagnostic rate, and can also be used to evaluate the condition of sick dogs.
After the death of a sick dog, the pathological changes can be observed by autopsy, or worms can be found in the right ventricle and pulmonary artery of the sick dog, and a diagnosis can also be made.
1. Observation of clinical symptoms
Early sick dogs do not show clinical symptoms. With the development of the disease, they have symptoms such as sudden cough, weight loss and intolerance to exercise after exercise. When parasites spread to pulmonary intima hyperplasia, dyspnea, ascites, edema of limbs, pleural effusion, pericardial effusion and pulmonary edema occur. When combined with acute vena cava syndrome, symptoms such as hemoglobinuria, anemia, jaundice and uremia suddenly appear.
2. Pathological autopsy changes
Adults parasitize the pulmonary artery and the right atrium, blocking the blood flow, making the heart unable to push out the normal blood supply, leading to the hypertrophy and expansion of the heart, and the myocardial fibers gradually lose their contractility. In addition, worms constantly mechanically stimulate the endocardium, making the smooth endocardium rough and uneven, and easily forming tiny thrombus into the blood stream, causing microvascular embolism and leading to ischemic necrosis. Microfilaria can block venules, leading to circulatory disorder.
3. Observation of microfilaria
3. 1 blood smear method
Two drops of peripheral blood were placed on a glass slide to make thick drops, and the active microfilaria was directly observed under a microscope. Or, after the blood tablet is dried, red blood cells are dissolved with distilled water, and they are examined by a microscope when wet. You can also dry the blood slices, fix them with formaldehyde, and examine them under a microscope after Giemsa staining.
3.2 Centrifugal insect collection method
Take 1 ml venous blood in a test tube, add 9 ml of 2% formaldehyde, 5 ml of 7% acetic acid or 5 ml of 1% dilute hydrochloric acid, mix well and dissolve red blood cells. Centrifuge at 2500r/min for 20min, discard the supernatant, smear the precipitate for microscopic examination, or mix it with 0. 1% methylene blue solution after smear, and add cover glass for microscopic examination.
3.3 filtration method
Collect blood 1 ml, add 5 ml of 2.5% sodium citrate, pour it into a 300-mesh sieve and filter. Dip the blood on the back of the screen with qualitative filter paper and examine it directly under the microscope.
Filtering is the most direct way to observe worms. Cells in anticoagulation can be filtered through the screen, and only worms can stay in the mesh of the screen, which is easy to find at low magnification. Dilute hydrochloric acid and acetic acid are suitable for centrifugal collection of worms to dissolve red blood cells. Formaldehyde will make the sediment turbid and difficult to pick up. This method is best examined by microscope after dyeing, and the worm body is more obvious.
auscultate
4. 1 cardiac auscultation
Systolic murmur or tricuspid regurgitation sound can be found during auscultation when the right heart is dilated and vena cava syndrome, because insects interfere with blood flow and tricuspid valve insufficiency; About 90% of dogs with heartworm and vena cava syndrome can hear obvious tricuspid regurgitation sound when auscultating the heart; Due to the influence of pulmonary hypertension and valve insufficiency caused by pulmonary artery ring dilatation, pulmonary artery blood flows reversely, so diastolic murmurs can be heard during auscultation; Due to the influence of pulmonary hypertension, the second heart sound splits the heart murmur.
4.2 auscultation of lung
When the sick dog inhales, he can occasionally hear a slight to obvious split-like noise. Sick dogs will have systemic clinical symptoms due to heart failure with blood stasis on the right side: jugular vein pulsation/dilation, hepatomegaly ascites, pleural effusion, vague lung sounds and heart sounds during auscultation, even disappearing in severe cases, gradually losing weight, galloping rhythm during heart auscultation, and obvious enhancement of the third heart sound.
5. Chest X-ray examination and evaluation
In general, the sick animals infected with heartworm usually take chest X-rays by back-to-abdomen photography, so that more diagnostic chest X-rays can be obtained. According to the course of the disease, there will be different changes on the X-ray film.
5. 1 At the early stage of the disease, the pulmonary arterioles around the lung lobe were slightly dilated, and these dilated arterioles showed linear opaque images on X-ray films.
5.2 In the middle of the course of disease, it can be seen that the interstitial density of lung leaves increases, and the diameter between arterioles of pulmonary arteriole cluster changes gradually, losing its original uniformity.
5.3 At the end of the course, pulmonary artery and right heart were obviously dilated. In addition, the increase of lung lobe tissue density around hilum makes the influence of normal blood vessels in lung disappear, and this change of lung tissue is a characteristic lesion of eosinophilic pneumonia. If you see a stained lung parenchymal lesion on the X-ray film, it means that local granuloma has formed in the lesion area, and the main artery in the lung lobe is embolized.
6. Electrocardiogram
Electrocardiogram in chronic cases of severe pulmonary hypertension, it is often seen that the right ventricle of sick dogs is obviously enlarged. In addition, it can be found that sick dogs are often complicated with atrial fibrillation and sudden or persistent ventricular tachycardia.
? 7. Echocardiography
Hypertrophy of papillary muscles of right atrium, right ventricle and tricuspid valve can be detected in most sick dogs. In addition, in some cases with pulmonary hypertension or chronic heart failure, it is often found that the interventricular septum of sick animals has unreasonable movements. In addition, the suspicious cases of chronic heart failure can be diagnosed by the presence or absence of vena cava syndrome.
8. Hematological examination
Cases infected with heartworm often appear cytopenia in hematological examination. In severe cases, the hematocrit decreased to 65438 00%, and the plasma albumin content decreased. When the liver is necrotic or congested, the liver function index will increase. The blood life test shows that the serum alanine aminotransferase is increased (the normal value is 40, and the prognosis is poor when it reaches 80), and the serum urea nitrogen is increased to14 ~ 21mmol/L. Urine tests show proteinuria, hemoglobinuria and hyperbilirubinemia.
9. Immunological diagnosis
The established enzyme-linked immunosorbent assay (ELISA) and fluorescent antibody test have been used in the epidemiological investigation of the disease. However, only dogs infected with female adults can be detected by serological examination with antigens made from female adults. When the infection degree is light (for example, when there are less than five adult dogs), the result may also be negative. Dogs successfully infected by males alone are negative.
10. Molecular biological diagnosis
PCR detection method has high sensitivity and specificity. PCR detection can identify the genetic material of filariasis in blood samples. The test results are not affected by age and early infection of heartworm, and early infection can be confirmed in 24 hours. The sample size of PCR detection method is very small, and it can be detected as long as there are two heartworm cells. Therefore, it has a good application prospect in the diagnosis of canine cardiac filariasis.
Second, prevention and control.
1. Drug control
There are many drugs to prevent and treat canine cardiofilariasis, including killing microfilaria, killing adults and preventive medication. Because they are very toxic, the human body must excrete them as soon as possible after taking drugs, otherwise it will endanger other organs. Because heartworm is parasitic on pulmonary artery, it is easy to be complicated with interstitial pneumonia, and it often shows dry cough or hemoptysis after taking medicine. Cardiofilariasis is eliminated by human immune system, so it often shows listlessness and poor appetite after taking medicine. Therefore, in the process of drug treatment, we should pay attention to the observation and nursing of sick dogs, limit their strenuous exercise and give symptomatic treatment.
2. Surgical therapy
When there are a large number of adult parasites, pulmonary intimal lesions are obvious, renal function is low, and it is not suitable for drug treatment. Surgical treatment can be used, especially for dogs with acute filariasis. Only when the worms are removed in time can there be hope for treatment. There are two surgical treatments: ventriculectomy and phlebotomy.
? 3. Comprehensive prevention and control
3. 1 According to the epidemiological characteristics of the disease, mosquitoes are the intermediate hosts of canine cardiofilariasis, which is spread by mosquito bites. Therefore, it is an important aspect to prevent this disease to strengthen the cleanliness and sanitation in the kennel, disinfect it regularly and prevent mosquito breeding. If mosquitoes appear in the season, it is necessary to remove the accumulated water and weeds around the house, turn open ditches into underground ditches, raise fish in rice fields and pools, and eliminate mosquito larvae. Mosquito adults are killed by drugs and smoking. When mosquitoes are active at night, keep the dog in a house with screens and screen doors.
3.2 Take the dog to the animal hospital to detect the antigen of adult heartworm once every six months, and according to the requirements of the veterinarian, in the mosquito activity season, take the preventive medicine orally to the dog under 6 months to kill the third stage larvae that have invaded the dog and have not yet matured or moved into the heart.
3.3 Regarding the anti-insect vaccine, a chitin acid vaccine against microfilaria has been developed, which can protect gerbils from microfilaria infection by immunizing them. However, this vaccine is ineffective in microfilaremia.
Third, the conclusion
Canine heartworm is widely distributed in Asia, Oceania, Africa, America and other areas with more mosquitoes, and is also widely distributed in China. The results of epidemiological investigation in some areas show that the infection rate of heartworm in dogs is above 40%. However, the treatment effect of the disease is not ideal, and there is no mature vaccine to prevent it. Therefore, it is of far-reaching significance to analyze the immune mechanism of canine heartworm from the perspective of immunology and establish a specific and sensitive immune diagnosis method for early diagnosis of canine heartworm. At the same time, the key to prevent this disease is to take preventive measures as soon as possible after early diagnosis, cut off the source of infection and transmission route, treat or eliminate heartworm positive dogs, establish healthy dogs and prevent mosquito bites. Doing a good job in the prevention and treatment of canine cardiac filariasis can not only improve the health level of dogs and reduce the cost of feeding, but also protect human health.