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Dirofilaria immitis is a worldwide filarial nematode causing heartworm disease in dogs and cats. Several mosquito species, which are able to feed both on humans and animals, can transmit this parasite. Inflammatory progression of host tissues induced by parasites are mediated by several molecules, including nitric oxide (NO), which usually exerts deleterious effects on parasites and occasionally on the host. We analyze the in vitro effect of total D. immitis adult worm somatic antigens on naïve rat alveolar macrophage NO production and further separation of parasite proteins to define specific D. immitis somatic molecules influencing host cell NO secretion. Additionally, we address the possible influence of Wolbachia spp. on the in vitro production of NO by macrophages. Our results demonstrate that D. immitis adult worm soluble antigens are able to specifically induce NO production from host macrophages. Furthermore, we demonstrated that this effect is due to nematode antigens rather than to defined components (LPS and metabolic molecules) derived from its endosymbiont, Wolbachia spp. In addition, we were able to isolate and identify one of the parasite specific components from the DiSo extract, denominated DiID35.3 and putatively belonging to the Immunoglobulin Superfamily Protein (ISP) group, triggering NO release from macrophages in a dose-dependent and specific manner.

The seroprevalence of seasonal variation of human anti-Dirofilaria immitis IgE levels were studied in an area where specific IgM and IgG had been previously investigated. An antibody capture ELISA assay was used to detect specific IgE. The IgE seroprevalence observed in the whole population was 12.6%. No specific IgE was detected in atopic individuals or in sera from people suffering other helminthiases. The distribution of the IgE anti-D. immitis seroprevalence by age groups did not show differences. Females had significantly higher levels than males. This isotype of immunoglobulin peaks in July, decreasing sharply in October, and persisting at a level similar to that of a non exposed population during the rest of the year. No specific IgE were detected in subjects with pulmonary alterations related to the parasite, suggesting a possible relationship between the clinico-radiological status and the type of immunoglobulin synthesized in subjects infected by D. immitis.

Infection by Dirofilaria immitis is a rare cause of solitary pulmonary nodule. We describe the second case of transitory pulmonary nodule found by us in the course of a case-finding study, the third one reported in the literature. The detection of cases of transient pulmonary dirofilariotic nodules suggests that human infection is more prevalent than usually thought, and that this kind of manifestation is frequent in human dirofilariosis. Greater awareness is warranted in endemic areas.