Abstract
Subcutaneous dirofilariosis is a zoonotic disease emerging throughout Europe caused by the filarial nematode Dirofilaria repens. Despite its increasing prevalence, there is a large gap in knowledge of the impact of the parasite on the host. Currently classified as being non-pathogenic, recent evidence suggests that skin dirofilariosis is associated with dermatological conditions including concomitant pruritus, neoplastic processes, inflammation, and even blindness in dogs and humans. The aim of this study was to determine if natural canine D. repens infection leads to biological changes in the canine host. In a real-life veterinary clinic setting, animals are often presented to clinicians for unrelated issues, and D. repens is incidentally identified during inspection. As such, we compared hematological and biochemical parameters of 218 uninfected and 197 dogs naturally infected with D. repens. Interestingly, animals infected with D. repens had lower numbers of lymphocytes (p < 0.001), red blood cells (p < 0.001), and thrombocytes (p = 0.025), decreased hematocrit (p < 0.001), and increased alkaline phosphatase (p = 0.016) and creatinine activity (p = 0.023) compared to uninfected dogs. We further selected a subpopulation of 214 dogs having prima facie hematological and biochemical results within normal reference ranges to evaluate the effect of D. repens infections in seemingly healthy dogs. Among these patients, 93 dogs infected with D. repens had lower numbers of lymphocytes (p = 0.031), red blood cells (p = 0.025), and hematocrit (p = 0.002), higher glucose levels (p = 0.023), and border line elevated alkaline phosphatase levels (p = 0.054) compared to 121 uninfected animals. Despite being categorized as asymptomatic, we have observed hematological and biochemical changes associated with D. repens infections in dogs, and our data suggest that dirofilariosis may induce a state of chronic stress. These results link the presence of skin dirofilariosis to biological changes in the canine host, suggesting a mechanism for pathogenicity and shedding new light on the host–parasite relationship.
Highlights
Dirofilaria immitis and Dirofilaria repens are both filarial nematodes that have zoonotic potential and cause canine heartworm disease and skin dirofilariosis in dogs, respectively
Dogs infected with D. repens compared to uninfected individuals had significantly lower lymphocyte count (p < 0.001), red blood cell count (RBC) (p < 0.001), Ht (p = 0.001), and thrombocyte count (p = 0.025) and higher alkaline phosphatase (ALP) (p = 0.016) and creatinine (p = 0.023) activity (Table 2)
In order to determine if observed changes were present only in patients with abnormal blood test results, we decided to select a subpopulation of dogs having parameters within normal values, which we believe mainly represents the undiagnosed dogs infected with skin dirofilariosis in real-clinical practice
Summary
Dirofilaria immitis and Dirofilaria repens are both filarial nematodes that have zoonotic potential and cause canine heartworm disease and skin dirofilariosis in dogs, respectively. Despite its predominance throughout Europe and being the primary causative agent of human dirofilariasis, D. repens has received much less attention and study than D. immitis [1]. Dirofilariosis is a vector-borne disease transmitted by mosquitos. Mosquitos uptake microfilariae (Mf) circulating in the bloodstream of a definitive host during blood meals. After 2 weeks, Mf develop into infective larvae and are injected into a new host when the mosquito takes another blood meal. The L3 larvae penetrate into subcutaneous tissue where they mature into adult skin filarial worms, copulate, and release Mf into the circulating bloodstream. Adult D. repens can survive and reproduce in a host for as long as 5–10 years [2] and may actively migrate within the host tissues during this period what considerably hampers their detection [3]
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