Dirofilariasis

Dirofilaria life cycle

The life cycle of Dirofilaria involves two hosts:

1. Mosquitoes: Mosquitoes act as intermediate vectors. When a mosquito bites an infected animal, it ingests parasite larvae called microfilariae, which circulate in the blood. These larvae develop inside the mosquito into an infective form (third instar larvae). The infected mosquito can then transmit the larvae to another host by biting it.
2. Mammals (definitive hosts): Once inside a mammal, the larvae migrate through the bloodstream to the heart and lungs, where they mature into adult worms. In dogs and cats, adult worms can cause serious health problems by clogging pulmonary arteries and heart chambers.

Clinical forms in animals

• Dogs: In dogs, Dirofilaria immitis causes the most severe form of the disease, known as cardiopulmonary dirofilariasis. Adult worms can grow up to 30 cm long and live for several years, causing damage to the heart, lungs and pulmonary arteries. Symptoms include coughing, fatigue, shortness of breath and, in advanced cases, heart failure and death.
• Cats: Although less common in cats, dirofilariasis can be severe, with symptoms including coughing, vomiting, difficulty breathing and weight loss. The inflammatory response in cats can be intense, even with a low parasite load, which can lead to an acute respiratory syndrome called HARD (Heartworm Associated Respiratory Disease).

Dirofilariasis in humans

In humans, Dirofilaria infection is rare and usually asymptomatic. However, when it does occur, it can manifest itself in the following ways:

• Pulmonary nodules: Dirofilaria immitis can migrate to the lungs and cause the formation of a nodule, which may be discovered incidentally on a chest X-ray. Although often benign, it may be mistaken for a malignant tumour until a biopsy is performed.

• Subcutaneous nodules: Dirofilaria repens tends to cause skin infections, manifesting as subcutaneous nodules on various parts of the body, especially the extremities and face. These nodules are usually painless and, in most cases, can be detected visually.

Diagnosis and treatment

• Diagnosis in animals: In dogs and cats, diagnosis is made by blood tests that detect adult worm antigens or microfilariae. Echocardiography and radiography may also be used to assess the presence and damage caused by the worms.

• Diagnosis in humans: In humans, dirofilariasis is often diagnosed after surgery or biopsy of a suspicious nodule. Identification of the parasite in the specimen confirms the diagnosis.

• Treatment: In dogs, treatment includes anti-parasitic drugs to eliminate adult worms and microfilariae, as well as treatments to control symptoms and cardiovascular complications. In advanced cases, surgery may be necessary to remove the worms. In cats, treatment is more complex due to the animal's sensitivity to anti-parasitic drugs; it focuses on symptom management.

In humans, dirofilariasis does not usually require deworming, as adult parasites do not reach full maturity in humans. Subcutaneous or pulmonary nodules are often surgically removed for diagnostic confirmation and resolution of the problem.

Prevention

Prevention of dirofilariasis in animals is essential and relies on:

• Preventive treatments: Preventive drugs are regularly administered to dogs and cats to kill Dirofilaria larvae before they can mature. These drugs are usually administered monthly.

• Mosquito control: Reducing exposure to mosquitoes is key to preventing infection. This includes using insect repellents, keeping pets indoors during peak mosquito activity, and eliminating areas of standing water where mosquitoes can breed.

Significance of the disease

Diarrhoea is a significant disease in veterinary medicine, especially in areas where mosquitoes are present throughout the year. Its management and prevention are essential for pet health. In humans, although the disease is rare, it is important that clinicians are aware of its existence to avoid misdiagnosis of pulmonary nodules or other symptoms.

In summary, dirofilariasis is a parasitic disease that mainly affects dogs and cats, with serious health consequences if left untreated. Prevention through deworming and mosquito control

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