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Filariasis

enero 12, 2021

 

There filariasis it’s a dangerous one parasitic dog disease, but not only that, which can have lethal consequences. From an epidemiological point of view, however, the dog is the most sensitive host among the different species of receptive hosts.

This disease is caused by a nematode, the filaria, and the transmission occurs through vector insects, and in particular through the bite of mosquitoes of the genus Aedes, Anopheles, Culex. By means of the vector then, heartworm is transmitted from a sick animal to a healthy animal. In this case, therefore, the mosquito plays the role of intermediate host as the parasite inside the latter continues its development. There Filariasis can be of two types: subcutaneous filariasis, mainly sustained by dirifilaria repens, or cardiopulmonary filariasis, whose causative agent is dirofilaria immitis.

Subcutaneous filariasis in particular is caused by nematodes which, in the adult form, are localized in the subcutaneous tissues of dogs, cats and humans. Man, in fact, can contract the disease (zoonosis). The presence of subcutaneous nodules will then be checked.

Heartworm disease, on the other hand, is the most severe form and heartworm immitis is also known as dog cardiopulmonary worm. The larvae of this nematode enter the circulatory system and once they have become adult worms, they are primarily localized in the pulmonary arterial system of the definitive host (dog, fox, canids and occasionally also in cats, wild felids and ferrets) until they settle in close proximity to the heart and lungs, reaching the ventricle right, right atrium, caudal vena cava and pulmonary artery.

There presence and permanence of the nematode at these levels it generates cardiocirculatory alterations, caused by the obstruction of the blood flow, which can lead to heart failure. Furthermore, the permanence of nematodes in activity can cause the appearance of endocarditis affecting the heart valves, pulmonary thrombus embolism, and a number of other conditions that aggravate the health of our friend. The disease, however, will have a silent onset from the clinical-symptomatological point of view, because the parasite needs time to grow and evolve, before it becomes manifest.

Once this maturation has occurred, symptoms such as: apathy, syncope, ascites, deterioration of physical conditions, chronic cough, hemoptysis, tachypnea and fatigue, rapid and unjustified weight loss will occur. Generally speaking, in in dogs less than one year of age, it is rare to observe manifest clinical forms. The pathology is transmitted through the bite of the mosquito which, by carrying out its blood meal on an animal infested with heartworm, will also take on some microfilariae together with its blood. These will come later transmitted by the same mosquito to the next blood meal performed on a healthy animal. In this new host, the microfilariae thus introduced will begin to grow and move towards the heart where, having become adult parasites, they will be able to start their reproductive cycle, producing in turn other microfilariae.

This pathology is more widespread in northern Italy, in warm temperate, tropical and more marshy areas, but is rapidly spreading to the rest of the country, constituting a concrete possibility of threat also in the central-southern regions. The period of greatest danger is subordinated to the period of maximum activity of the vectors, therefore of mosquitoes, and coincides with the period from February to November with an intense peak in the summer months.

To be able to effectively combat the heartworm danger, it will be necessary to adopt prophylactic and preventive measures recommended and set by the veterinarian or in any case aiming for an early diagnosis.

From a diagnostic point of view, the doctor will be able to use a wide range of procedures. First of all it will be essential to appreciate and recognize the typical clinical symptoms of a cardiovascular insufficiency; together with this there will be a rapid blood test, a direct examination that aims at the microscopic search and identification of microfilariae in the blood, chest X-ray that will allow to appreciate any pulmonary thickening or right ventricular hypertrophy, echocardiography, antigen tests, etc. It will be the doctor who, based on his observation and the detection of clinical symptoms, will decide the most appropriate instrumental examination for the specific need. But, precisely because of the usually fatal outcome of the pathology and given the difficulty of a decisive intervention, relying on preventive prophylaxis is the most effective means of fighting against heartworm. It will be the vet, according to particular epidemiological condition and needs, to choose the most appropriate prophylactic instrument and to establish the timing of the protocol. In fact, drugs to be administered orally, or injectable drugs, may be prescribed, always in the face of an assessment of the absence of the parasite.

Prophylaxis plays a central role especially if we consider the difficulty of setting up a resolutive therapy in the case of overt pathology. In fact, this therapy will be set only if the doctor deems it appropriate and must be undertaken only after a clinical examination of the animal and a careful evaluation of cardiopulmonary function, kidney and liver of the subject, since the therapy itself, if effective, inevitably causes embolism phenomena. These cardiopulmonary risks associated with therapy are due to the particular aptitude of these nematodes to gather in balls, and this will therefore make it essential to evaluate the lung radiologically, in order to determine the extent of the parasitic load.

In fact, in subjects with pulmonary alterations or in which they harbor a high number of adult parasites, a therapy with adulticidal drugs which will then kill the ball of nematodes, could generate the risk of thromboembolism and the consequences of parasite death could be fatal. Therefore, if the doctor decides to set up a therapy, following the adulticide treatment, it will be appropriate to reduce the activity of our friend for a period ranging from 2 to 6 weeks. Following elimination of adult parasites in dogs with severe abnormal heart function, it may be necessary to undertake supportive therapy to relieve heart failure.

It should also be emphasized that an already debilitated animal is more frequently subject to infection by other parasites living in the same environment. In fact it is always useful to verify that a subject suffering from filariasis is not also a vehicle and carrier of leishmania or other diseases transmitted by ticks. In any case, the prevention and proper management of our friend can be decisive in ensuring optimal health and improving his life expectancy.

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