Filaria or Filariasis is a parasitic disease that often affects dogs in a severe and even fatal way. In recent years, cases of the disease have steadily increased in number and geographical areas. How can this disease be transmitted, the difference between the various forms, and how can we protect our four-legged friends? In this article, we will give you a complete guide about heartworm prevention for dogs.
In general, Filariasis is transmitted by mosquitoes, vector insects. And can manifest itself in different forms according to the type of parasite that lurks. The primary forms are heartworm disease, Dirofilaria immitis, and cutaneous Filariasis, Dirofilaria repens. Both create nematodes belonging to the heartworm genus, commonly called or identified as roundworms due to their shape.
Heartworm prevention for dogs
The first has severe consequences for our animals. With heartworm prevention for dogs immitis, in fact, the larvae enter the circulatory system. Once they become adults, they move into the great vessels and heart chambers with harmful consequences. For the heart and breathing’s proper functioning.
These worms are usually whitish in color. They can reach dimensions ranging from 12 cm up to and over 30 cm. The adult male has a length of 20 cm with a diameter from 700 to 900 mm. On the other hand, the female can exceed 30 cm with a diameter ranging from 1 to 1.3 mm and is larviparous or lays larvae.
The least severe but always harmful form of heartworm is Dirofilaria repens, which occurs subcutaneously. In this case, the parasites settle under the dog’s skin and form nodules and even ulcers. The male reaches lengths ranging from 5 to 7 cm with a diameter of 300 micrometers and more (μm).
Simultaneously, the female gets lengths between 14 and 17 cm with a diameter from 420 to 460 micrometers. Also, in this case, damage to the blood circulation and consequently to the various organs can occur, thus undermining the dog’s health.
Heartworm disease: what happens
The main cause of heartworm or filariasis is a mosquito bite. Even though the most feared and dangerous is considered the tiger mosquito. In Italy, the greatest spread of mosquitoes is in the north and the center, mainly in swampy and humid areas but in recent years. With climate change and the arrival of the tiger mosquito in Europe. The spread of these insects also has generalized to include large areas of Sardinia, Sicily, and the South. That allow it to lay eggs continuously and spread massively and over a long time the year.
The mosquito not only acts as a biological vector by transporting the parasite from one sick dog to another but, more importantly, it allows the parasite itself to develop internally, thus increasing the risk and danger.
Parasites of the opposite sex are present in the heart of the sick dog. Through the eggs that hatch, the female expels microfilariae, which end up in the blood, and when a mosquito bites the sick dog along with the blood, it also sucks the microfilariae. These begin to mature already inside the mosquito, and within a maximum of 30 days, they become infesting larvae. After this time, if the mosquito bites another dog, it can transmit heartworm. In the new dog, the larvae take a few months to grow, become adult parasites, and above all, reach the heart and lungs and then cause serious and often fatal damage.
The entire cycle of transmission and evolution of the disease requires time. Before the onset of symptoms, it is possible to carry out tests and thus be able to prevent the aggravation of our dog with adequate care.
Subcutaneous filariasis: Heartworm Prevention For Dogs
The cycle, evolution, and timing of cutaneous filariasis or repens are very similar to cardiopulmonary filariasis. They differ in position, which in this case is just under the skin, in symptoms, and diagnosis. Parasites under the skin cause skin conditions, including nodules, dermatitis, and granulomas, often causing excessive itching in the animal. The nodules, if subjected to stimuli, tend to change and extend. Also, in this case, the dog tends not to eat and be depressed and often absent with difficulty moving.
When we observe changes in the habits of our four-legged friends or particular symptoms, the first fundamental rule is always the same. Don’t rush to conclusions and consult your vet. Being good observers and not underestimating any symptoms is essential for our animals’ health. As well as being able to report the symptoms to an expert. The professional does not underestimate the dog’s signals and uses tools and analyzes capable of diagnosing the presence of heartworm or not.
Accumulation of fluid in the abdomen or ascites, lack of stimulation of the hunger, depression and mood changes, and severe cases loss of consciousness or syncope. As already mentioned, in the case of subcutaneous heartworm, the presence of nodules and skin abrasions and, in some cases, even damage to the eyes can be symptoms related to this disease.
The therapy, which must be performed under the veterinarian’s prescription and control, is mainly based on drugs capable of killing the already adult parasites that cause the problems. First of all, it is essential to proceed with identifying parasites through analyses (radiological, ultrasound, tests, etc …) and with the correct diagnosis. Therapy is the result of a diagnosis that identifies the level of risk and considers the health and age of the dog as a whole.
Heartworm Symptoms in Dogs: Heartworm Prevention For Dogs
At first, some subjects may present absolutely asymptomatic. Others who present mild symptoms such as:
- occasional cough
- greater fatigue.
- Progressively, the following can occur:
- progressive weight loss
- strong cough
- severe breathing difficulties
- intolerance to effort
- right congestive heart failure
- pulmonary hypertension
- peripheral edema.
Acute signs may arise suddenly following thromboembolism secondary to the spontaneous death of the worms. In many cases and the presence of subcutaneous parasites, it is possible to intervene surgically with non-invasive techniques or through chemotherapy treatments. The therapies are in oral, slow-release injectable, or spot-on formulations such as pipettes.
Vena cava syndrome
In dogs in which the filarial adult partially obstructs blood flow through the tricuspid valve by interfering with the closing of the valve itself, one speaks of superior vena cava syndrome.
In these patients, the symptoms are:
- sudden onset of severe lethargy
- respiratory difficulties
- pale mucous membranes
In these patients, it is necessary to intervene quickly by surgery to remove the adult heartworms. Otherwise, the outcome is fatal in a few days.
How to recognize filariasis?
Two types of blood tests are available for the diagnosis of heartworm disease.
- Look for circulating microfilariae
- search for antigens of adult females.
The search for microfilariae can be carried out:
- using fresh blood preparations: the test is easy to perform but with low sensitivity
- blood concentration test (Knott test or filtration).
However, in the absence of this finding, it is not possible to exclude heartworm infestation because there are 30% of cases that present adult worms without microfilariae in circulation.
- It is important to remember that circulating microfilariae does not correlate with the number of adult worms.
In some cases, observing the microfilariae characteristics, it is possible to differentiate between D. immitis or D. repens. More often, it is necessary to resort to specific tests (histochemical staining and PCR).
To detect adult worms instead, some tests look for the antigens of adult females. These tests can be done in the clinic but are usually positive 6-8 months after the infestation occurs. The sensitivity of these tests is very high, but they can be falsely negative in the case of a small number of adults or the presence of only adult males.
Further diagnostic tests are useful to determine the severity of the disease :
- chest x-rays
- hematological tests
- to stage the disease and then treat it better.
Preventive Treatment: Heartworm Prevention For Dogs
A safe and effective method to prevent the dog from becoming sick with Filaria is to constantly treat the animal with substances that do not allow adult parasite development. Heartworm prevention for dogs. This ” microfilaricide therapy ” is not a vaccination. Still, treatment on the infested host (dog) against the larval forms L3 and L4 of the Filaria, to prevent them from becoming adult and causing the disease.
Since the transmission of the parasite is limited to the warm months, as mosquitoes appear in spring and disappear in autumn, our animals’ preventive treatment should go from April to November. Therapy can be started already in animals that are 6-8 weeks of age.
In Italy, various products act on the larval stages (L3-L4) of the parasite, causing its death. Being substances that act on the larval stages of the Filaria before L5, they are effective up to the 50th -55th day from the onset of the infestation (penetration of the Filaria in the definitive host).
The drugs available are
- The milbemycin oxime (Interceptor® FLAVOR; MILBEMAX® DOGS) given every 30 days for oral, beginning within 1 month after the onset of mosquitoes and ending with the last tablet within 30 days of their disappearance;
- the selamectin (STRONGHOLD), applied every month, in spot-on solution, on the skin at the base of the neck, with the first application within one month from the appearance of mosquitoes and the latest within 1 month of their disappearance;
- The Moxidectin, you can find:
- in a spot-on solution (ADVOCATE®), to be applied at least one month before the expected appearance of mosquitoes, then monthly up to 30 days after the disappearance of the insects;
- in the form of oral tablets (GUARDIAN®), which begin to be given within one month of the appearance of the intermediate hosts (mosquitoes), and continue, every month, until the month following their disappearance;
- injectable solution (GUARDIAN®SR), which, once injected subcutaneously, within 30 days of the appearance of mosquitoes, has an efficacy that lasts for the entire season of risk of the Filaria;
- Ivermectin (CARDOTEK-30®; CARDOTEK-30®PLUS), in the form of chewable tablets, begins to be administered every 30 days, within one month from the first exposure to mosquitoes, ending with the last dose within one month since the last exhibition.
Treatment of the dog sick with Filaria
It has already been said several times that heartworm disease is a subtle disease, as it manifests itself clinically long after the parasite has penetrated our animal.
For this purpose, it is advisable to perform – in dogs that have never undergone preventive prophylaxis (measures are taken to prevent the disease) or in dogs that are suspected of having been “discovered” (unprotected) for a certain time (i.e., for which the administration of the drugs in the indicated times was not followed correctly) – a test for the search for antigens (parasite substances) of the Filaria. This examination, straightforward and not at all invasive or painful for our dog, is performed by the vet for a few tens of euros.
Prevention and Prophylaxis
heartworm prevention for dogs is often underestimated for its serious consequences and its frequency in the area. The climate changes we are subjected to do not bode well for the future. Estimates predict an increasing spread of harmful insects and forms of heartworm. Furthermore, the diagnosis is not always simple. At times, it can be expensive and in many cases not possible. This makes prophylaxis the only action that is always effective.
Proper prevention also provides for the possibility of test blood in the clinic. The test becomes necessary when you are not up to date with annual prophylaxis or are not sure that you have always performed the prophylaxis correctly in the past. There are also other forms of parasitic diseases such as Leishmaniasis, transmitted through the bite of sandflies. Symptoms can be different and of various kinds: from weight loss to dog nosebleeds to the presence of enlarged lymph nodes.
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In conclusion: Heartworm Prevention For Dogs
Even before preventing parasites’ appearance, it is necessary to ensure a correct and adequate lifestyle for our dog. As? First of all, providing the dog with a healthy environment and minimizing mosquitoes’ presence, the main vehicles of the disease.
In the warm months, tiger mosquitoes can complete a development cycle in less than 10 days. This is why it is important to limit all situations that can favor reproduction and spread in our home’s vicinity. First of all, it is a good idea to remove any stagnant water. The saucers of our plants, for example, the gutters or external containers left full. Wherever the water stagnates, there is the possibility to favor the reproduction of mosquitoes. Equally important is carrying out an adequate disinfestation of the garden or outdoor spaces. And the maintenance holes also relying on professionals.
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