Rapid Differentiation of Dirofilaria Species in Dogs and Cats and Its Clinical Application

The dirofilariosis infections in dogs and cats consist of various species, which can lead to single-species infections in some regions, while mixed infections are more common in others, particularly in Europe. This complexity poses challenges for clinical veterinarians when making differential diagnoses.

Dirofilaria worms can be categorized into Dirofilaria immitis and Dirofilaria repens based on the locations they infect in the body. Typically, adult D. immitis worms reside in the pulmonary arteries, whereas adult D. repens worms inhabit subcutaneous and intramuscular connective tissues. Once they reach maturity in these areas, they release the next generation of microfilariae into the bloodstream, which are then transmitted to other hosts through mosquito bites. However, there are numerous cases where adult filarial worms migrate to other tissues, such as the eyes and kidneys. This migration can complicate differential diagnoses with other nematodes that preferentially inhabit those sites, such as Loa loa, Dirofilaria immitis, and Acanthocheilonema reconditum, as distinguishing between them morphologically is often challenging.

an adult D. repens was found in the eye of a 5-year-old male Boxer from northwestern Romania

A commonly used rapid antigen test in veterinary clinics offers a convenient and cost-effective method for diagnosis. This test specifically detects unique antigens secreted by female worms in the blood. It generally exhibits higher sensitivity compared to blood smears and the gold standard "Modified Knott’s Test." However, neither the antigen test nor the Modified Knott’s Test can differentiate between various dirofilaria species and other nematodes. Most commercially available test kits primarily target D. immitis and are not suitable for the equally prevalent D. repens, potentially leading to misdiagnoses in cases of either mixed or single infections.

blood smears reveal alive microfilariae

observations from the Modified Knott’s Test can show concentrated microfilariae

Consequently, veterinarians often need to conduct further tissue sampling for laboratory testing based on the infected areas and suspected life history of the parasites. In third-party clinical testing laboratories, these samples can undergo qPCR methods for species identification, and IHC tissue slides can be utilized to localize and identify the parasites at the lesions.

Is there a way to identify D. immitis and D. repens in-house? Recently, in regions where these two dirofilaria species are prevalent, such as Hungary, veterinarians have begun using a portable molecular device called MiniDock for the identification of D. immitis and D. repens.

In cases of suspected infections diagnosed in-house, MiniDock has garnered high praise from practitioners for its sensitivity

Patients can access results through a mobile app after their initial visit, and a PDF report can also be generated via computer software.

The operation of MiniDock is straightforward and does not require complex laboratory instruments. This technology, along with the RHAM principle, boasts sensitivity and specificity comparable to qPCR, allowing for efficient differentiation between D. immitis and D. repens.

Dirofilaria worms rely on mosquitoes as their hosts, and the impact of climate change in the 21st century has affected mosquito ecosystems. For instance, in 2007, the first reported case of indigenous Dirofilaria infection in Hungary was documented. By 2011, the incidence of heartworm cases was still limited to a small area of the Great Hungarian Plain. However, since 2012, there has been a significant increase in both the number of cases and the geographic spread of the parasite. A retrospective study indicates that much of Hungary has become an endemic area for heartworm, with infection rates rising dramatically over the past 12 years. Researchers, including Zoltán Széll, suggest that warming temperatures in Hungary may be a key reason for the emergence and rapid spread of Dirofilaria infections. Another global review has similarly noted that over the last 20 years, the geographic range of canine heartworm infections has substantially increased. In Europe, many hidden and subclinical infections persist due to a lack of suitable diagnostic methods, necessitating a rapid update of knowledge regarding parasitic diseases in the last two decades. Moving forward, we need convenient and sensitive diagnostic methods to differentiate these complex infections to provide better therapeutic options for pets.