Dirofilaria repens is a parasitic roundworm primarily recognized for infecting dogs. While commonly associated with canine health, this parasite can occasionally cross species barriers and infect humans, classifying it as a zoonotic disease. Human infection with Dirofilaria repens typically manifests as subcutaneous nodules or lesions, though other locations are possible. This article provides an overview of how this condition is managed in people.
Understanding Dirofilaria Repens Infection
Dirofilaria repens is a roundworm whose life cycle involves both a definitive host, usually a dog, and an intermediate host, a mosquito. Humans acquire the infection accidentally when bitten by an infected mosquito that has previously fed on an infected dog. Mosquitoes ingest microscopic larvae, known as microfilariae, from the dog’s blood. These microfilariae develop into infective larvae within the mosquito over 10 to 14 days.
When an infected mosquito bites a human, these infective larvae are deposited onto the skin and enter the bite wound. Once inside the human body, as humans are not natural hosts, the larvae usually fail to complete their full development into mature adult worms capable of reproduction. Instead, they migrate and become encapsulated, most commonly in the subcutaneous tissue. These form palpable nodules ranging from a few millimeters to several centimeters.
These nodules are often movable under the skin and may cause localized itching, redness, or discomfort. While subcutaneous locations are most frequent, Dirofilaria repens worms can also be found in other sites, including around the eye, breast tissue, or even internal organs, though less common.
Identifying the Infection
Diagnosing Dirofilaria repens infection in humans often begins when an individual notices a suspicious nodule or lump under their skin. A physical examination by a healthcare provider is usually the first step, assessing the nodule’s location, size, consistency, and any associated symptoms.
To further characterize or locate nodules that might be deeper or less apparent, imaging techniques can be employed. Ultrasound is frequently used to visualize the subcutaneous tissue and can sometimes reveal the presence of a worm within the nodule, appearing as a tubular structure. Magnetic Resonance Imaging (MRI) may also be utilized for more complex or deeper-seated lesions, providing detailed anatomical information. These imaging studies help guide the diagnostic process by confirming the presence of a mass and aiding in its precise localization.
The definitive diagnosis of Dirofilaria repens infection typically relies on the surgical removal of the suspected nodule. Following excision, the tissue is sent for histopathological examination, where a pathologist microscopically analyzes thin sections of the tissue. This examination aims to identify the characteristic morphology of the adult Dirofilaria worm within the encapsulated lesion. In some instances, the worm itself might be extracted intact during surgery, allowing for direct macroscopic and microscopic identification.
Treatment Approaches
The primary and most effective treatment method for human Dirofilaria repens infection, particularly for subcutaneous and ocular nodules, is surgical excision. This procedure involves the complete removal of the worm along with the surrounding fibrous capsule or nodule. For most cases, this surgical intervention is considered curative, as it physically eliminates the parasite from the body. The procedure is generally minor, often performed under local anesthesia in an outpatient setting, depending on the nodule’s size and location.
During the surgery, the surgeon carefully isolates the nodule and excises it, ensuring that the entire worm is removed without fragmentation. Complete removal of the parasite alleviates symptoms and prevents further migration. Once the worm is removed, the associated inflammatory response subsides, leading to the resolution of the nodule and any discomfort it caused.
Medical therapy using anti-parasitic drugs is generally considered less effective for adult Dirofilaria repens worms in humans compared to surgical removal. This is largely because the adult worms often become encapsulated within a fibrous tissue mass, which can limit the penetration and efficacy of systemic medications. Drugs like diethylcarbamazine or albendazole, while effective against other filarial parasites, have shown limited success in eradicating encapsulated D. repens adult worms. These medications might be considered in rare circumstances, such as suspected disseminated infection or if surgical removal is not feasible. However, even in such scenarios, the effectiveness of drug therapy against the encapsulated adult worm remains uncertain. Surgical removal remains the preferred and most reliable treatment for human Dirofilaria repens infections.
After Treatment and Preventing Re-infection
Following surgical removal of a Dirofilaria repens nodule, post-operative care typically involves standard wound management. This includes keeping the surgical site clean and dry, monitoring for any signs of infection, and attending follow-up appointments to ensure proper healing. Pain relief medication may be prescribed if needed, though discomfort is usually minimal after such minor procedures. The prognosis for human Dirofilaria repens infections is generally very good after successful and complete surgical removal, with recurrence at the same site being rare.
Preventing future infections is an important consideration, as individuals remain susceptible to new mosquito bites carrying the parasite. Personal protection measures against mosquitoes are highly recommended. This includes using insect repellents containing DEET, picaridin, or oil of lemon eucalyptus when outdoors, especially during dusk and dawn when mosquitoes are most active. Wearing long-sleeved shirts and long pants can also provide a physical barrier against mosquito bites. Ensuring that window and door screens are intact and properly sealed helps prevent mosquitoes from entering homes.
Controlling Dirofilaria in the primary host population, specifically dogs, also plays a significant role in reducing the risk of human infection. Regular veterinary check-ups for pets, along with the consistent use of prescribed heartworm preventatives, which often also target D. repens microfilariae, can significantly reduce the reservoir of infection. Additionally, community-level mosquito control efforts, such as eliminating stagnant water sources where mosquitoes breed, contribute to lowering the overall mosquito population and thus the risk of transmission to both animals and humans.