Utility of adult antigens of Dirofilaria immitis for the early detection of dirofilariosis and for the evaluation of chemoprophylactic treatment in experimentally infected cats

Human and animal dirofilariasis: the emergence of a zoonotic mosaic

Dirofilariasis represents a zoonotic mosaic, which includes two main filarial species (Dirofilaria immitis and D. repens) that have adapted to canine, feline, and human hosts with distinct biological and clinical implications. At the same time, both D. immitis and D. repens are themselves hosts to symbiotic bacteria of the genus Wolbachia, the study of which has resulted in a profound shift in the understanding of filarial biology, the mechanisms of the pathologies that they produce in their hosts, and issues related to dirofilariasis treatment. Moreover, because dirofilariasis is a vector-borne transmitted disease, their distribution and infection rates have undergone significant modifications influenced by global climate change. Despite advances in our knowledge of D. immitis and D. repens and the pathologies that they inflict on different hosts, there are still many unknown aspects of dirofilariasis. This review is focused on human and animal dirofilariasis, including the basic morphology, biology, protein composition, and metabolism of Dirofilaria species; the climate and human behavioral factors that influence distribution dynamics; the disease pathology; the host-parasite relationship; the mechanisms involved in parasite survival; the immune response and pathogenesis; and the clinical management of human and animal infections.

Specific IgG antibody response against antigens of Dirofilaria immitis and its Wolbachia endosymbiont bacterium in cats with natural and experimental infections

Sera from three groups of cats under different experimental conditions were studied by ELISA to assess the host's immune response against synthetic peptides derived from Dirofilaria immitis (Dipp) and against the surface protein of its endosymbiont, Wolbachia (WSPr). In experimentally infected cats (Group 1), an increase of IgG antibody against both Dipp and WSPr was observed from 2 months post-infection until the end of the study, 6 months post-infection. In experimentally infected cats, treated against infective larvae (Group 2), anti-Dipp IgG decreased dramatically from 4 months post-infection (3 months post treatment), showing very low values till the end of the study (6.5 months from infection, 5.5 months from treatment), while anti-WSP IgG increased constantly till the end of the study. Of 49 outdoor, asymptomatic cats exposed to a high risk of natural infection (Group 3), 9 were positive for anti-Dipp IgG and for a validated, in-clinic commercial antibody diagnostic kit for cats. Two cats were also found positive for circulating antigens of adult female worm. Anti-WSPr IgG were found in five of nine anti-Dipp IgG-positive sera and from eight ELISADipp-negative sera. Our results confirm the strong IgG response in heartworm infected cats and demonstrate the involvement of the Wolbachia endosymbiont in the immune reaction to the parasite both in experimentally infected cats and in cats exposed to a high risk of natural infection.

Feline dirofilariosis: antibody response to antigenic fractions containing specific 20 to 30 kDa polypeptides from the adult Dirofilaria immitis somatic antigen

Fractions from the adult somatic antigen (SA) Dirofilaria immitis complex, containing polypeptides from 20 to 30kDa, previously identified as molecular markers of feline dirofilariosis are isolated by sequential application of gel filtration and anion exchange chromatography. Indirect enzyme-linked immunosorbent assays, employing these fractions (20-26kDa/ELISAF1 and 30kDa/ELISAF7) show multivalent diagnostic capacities: they were able to detect pre-patent infections 2 months after infection, infections in clinical phase, and the fall of antibodies after the worms were removed from the heart, or the application of a ivermectin treatment. The results obtained by the two tests correlated well, in spite of the fact that ELISAF1 was most useful to detect antibodies in sera from cats in the clinical phase, while ELISAF7 has more sensitivity for the early detection of the infections. Both ELISAs were useful in the detection of the decrease of antibodies after the worms were removed by surgery or pharmacological treatment.

Antigenic role of the endosymbionts of filarial nematodes: IgG response against the Wolbachia surface protein in cats infected with Dirofilaria immitis

Filarial nematodes harbour intracellular endosymbiotic bacteria, which have been assigned to the genus Wolbachia. These bacteria appear to play an important role in the pathogenesis of filarial diseases through their lipopolysaccharides. In view of the presence of Wolbachia endosymbionts in the body of filarial nematodes, one might also expect that proteins from these bacteria play an antigenic role in humans and animals affected by filariases. To test this hypothesis, we produced in recombinant form the surface protein WSP and a portion of the cell-cycle protein FTSZ from the Wolbachia of Dirofilaria immitis. Western immunoblot assays were then performed using cat sera to test the immunogenicity of these proteins. Sera were collected from owners' cats, which were either sero-negative or sero-positive for D. immitis and from cats before and after experimental infection with D. immitis. FTSZ was recognized in Western blots by sera from both positive and negative cats and from both uninfected and experimentally infected cats. WSP was recognized only by sera from positive cats and from cats experimentally infected with D. immitis; this protein was not recognized by sera from negative cats and from cats before experimental infection with D. immitis. The results of Western blot assays on WSP thus support the hypothesis that infection with filarial nematodes induces the production of antibodies against Wolbachia proteins.