Dirofilariasis: Time to Re-draw Iran Distribution Map

Background: Dirofilaria spp. are arthropod-borne nematodes of global significance, causing heartworm disease in dogs and subcutaneous infections in humans. Recent shifts in climate and animal movement patterns are suspected to be altering the traditional boundaries of dirofilariasis, necessitating an update to its distribution maps. In Iran, the epidemiological picture is fragmented. Specifically, in Ilam Province—a region where known vector species like Culex are present—no investigation has been conducted to determine the prevalence of Dirofilaria in the local canine population. This study aims to address this data gap, providing essential findings that challenge current assumptions of the parasite's range. Objective: This study aimed to investigate the prevalence of Dirofilaria immitis (D. immitis) infection among different dog populations (stray, shepherd, and guard) in Ilam Province, western Iran, to address the current lack of epidemiological data in this at-risk region. Materials and Methods: Blood samples were collected from ۱۳۹ dogs, including shepherd dogs (n=۱۶), guard dogs (n=۲۰), and stray dogs (n=۱۰۳), across three climatic zones of Ilam Province encompassing the counties of Dehloran, Dareh Shahr, Ivan, Badreh, Sirvan, Ilam, Sarableh, and Chavar. The samples were examined for the presence of microfilariae and parasite DNA using the modified Knott’s test and polymerase chain reaction (PCR) assay, respectively, employing two pairs of specific primers. Results: Microfilariae of D. immitis (۳۴ microfilariae/mL of blood) were detected in one blood sample from Sirvan County using the modified Knott’s test. Molecular analysis identified three samples positive for D. immitis DNA: one from Dehloran and two from Sirvan, based on amplification of a ۱۵۵ bp fragment of the ITS locus. Discussion and Conclusion: The overall prevalence of D. immitis infection in Ilam Province was ۲.۶%. This rate is strikingly low compared with the high prevalence reported from northern provinces such as Gilan (over ۶۵%) and even the neighboring province of Kermanshah (۱۸%). These findings identify Ilam as an unexpected cold spot in the epidemiological map of dirofilariasis in Iran. Positive cases were detected in Dehloran, Sirvan, and Sarableh counties, which are characterized by mild winters. The observed low prevalence in Ilam, despite the presence of potential vectors, may be attributed to a combination of ecological and climatic factors (e.g., lower humidity compared to Gilan) and differences in dog population management. Meanwhile, recent reports of dirofilariasis expansion into northern European countries (such as the Scandinavian region), previously considered non-endemic, highlight the dynamic and evolving nature of the disease worldwide. The growing evidence of geographical spread challenges the current assumptions regarding the parasite’s distribution pattern both in Iran and across the Middle East and underscores the urgent need to reassess the global risk maps of dirofilariasis. Further studies aimed at determining the prevalence and identifying risk factors associated with D. immitis infection—as an important zoonotic disease—are essential throughout Iran. Such research can contribute significantly to the development of effective prevention and control strategies against filarial infections.

کلیدواژه ها:

canine heartworm ، microfilaria ، polymerase chain reaction ، modified Knott’s test ، unexpected cold spot