Dirofilariosis in the Americas: a more virulent Dirofilaria immitis?

Abstract

Dirofilarioses are widespread diseases caused by filarioid nematodes (superfamily Filarioidea) of the genus Dirofilaria, which are transmitted by a plethora of mosquito species. The principal agent of canine dirofilariosis in the Americas is Dirofilaria immitis, which may also occasionally infest humans, resulting in pulmonary nodules that may be confounded with malignant lung tumours. Because human cases of dirofilariosis by D. immitis are relatively frequent in the Americas and rare in Europe and other eastern countries, where Dirofilaria repens is the main causative agent, the existence of a more virulent strain of D. immitis in the Americas has been speculated. Recently, a case of human ocular infestation by Dirofilaria sp. was diagnosed in Pará State, northern Brazil, where canine heartworm dirofilariosis is endemic. The nematode was shown to be morphologically and phylogenetically related to D. immitis but it was genetically distinct from reference sequences, including those of D. immitis infesting dogs in the same geographical area. This finding raised questions regarding the aetiology of human dirofilariosis in the Americas, since information on the genetic makeup of filarioids infesting dogs and humans is meagre. Further studies would be needed to better characterize filarioids infesting dogs, wild animals, and humans in the Americas and to assess the existence of a more virulent D. immitis strain in this continent. Finally, the competence of different culicid species/strains from Europe and the Americas as vectors of Dirofilaria species should be investigated. Such studies would help us to understand possible variations in transmission patterns and even to predict possible scenarios that may emerge in the future, with the introduction of non-endemic Dirofilaria species/strains in free areas through importation of infested animals, vectors, or both.

Molecular Study of Dirofilaria immitis and Dirofilaria repens in Dogs from Tunisia

“…Moreover, the infective capacity of the parasite is different in dogs and humans. In the Old World, the latter can be modified in human by the vector (Dantas‐Torres and Otranto, ). The only published sequences of D. immitis from the Mediterranean region are from Turkey in mosquitoes () and dogs (); they showed a genetic similarity of 95 and 99%, respectively.…”

Survey of canine tick-borne diseases in Lábrea, Brazilian Amazon: ‘accidental’ findings of Dirofilaria immitis infection

“…Finally, D. immitis has been treated as a zoonotic agent, which can induce pulmonary, subcutaneous, or ocular lesions in humans (DANTAS-TORRES & OTRANTO, 2013). However, such zoonotic potential could be related to strain variation or vector species, conditions yet to be investigated (DANTAS-TORRES & OTRANTO, 2013). Further studies are needed to evaluate the zoonotic potential of D. immitis in the Purus River region, where the human filarial parasite Mansonella ozzardi (Manson) is also prevalent (MEDEIROS et al, 2009).…”

“…Further studies are warranted to verify the possible epidemiological conditions that make the Amazon region more favorable for higher incidence of canine heartworm infection. Finally, D. immitis has been treated as a zoonotic agent, which can induce pulmonary, subcutaneous, or ocular lesions in humans (DANTAS-TORRES & OTRANTO, 2013). However, such zoonotic potential could be related to strain variation or vector species, conditions yet to be investigated (DANTAS-TORRES & OTRANTO, 2013).…”

Dirofilaria repens in the Russian Federation: current epidemiology, diagnosis, and treatment from a federal reference center perspective

“…2 In European countries, D. repens is the main causative agent of human dirofilariasis. [3][4][5] Whereas only a few dozen cases were reported worldwide in the first half of the twentieth century, the number has gradually increased and reached 782 cases worldwide at the end of the last century. 6 Of importance, approximately 700 of these cases of human dirofilariasis have been described in two scientific reviews published from the Russian Federation.…”