Protective efficacy of a filarial surface antigen in experimental filariasis.

A water-insoluble, detergent-soluble, surface-associated glycoprotein, designated as Dssd1, was found to induce microfilaria clearance in Mastomys coucha implanted with Setaria digitata. Intraperitoneal implantation of adult female worms of S. digitata in M. coucha could induce microfilaraemia lasting about 165 days in circulation. Immunization of M. coucha with Dssd1 antigen either before or after implantation of worms resulted in a significant reduction in microfilaria density. Complete clearance of circulating microfilaria was achieved by immunization (before and after implantation) in animals by 95 and 105 days post-implantation, respectively, indicating the efficacy of Dssd1 antigen in the clearance of microfilaraemia in infected M. coucha.

Combined ivermectin and doxycycline treatment has microfilaricidal and adulticidal activity against Dirofilaria immitis in experimentally infected dogs.

There is still a pressing need for effective adulticide treatment for human and animal filarial infections. Like many filarial nematodes, Dirofilaria immitis, the causative agent of canine heartworm disease, harbours the bacterial endosymbiont Wolbachia, which has been shown to be essential for worm development, fecundity and survival. Here the authors report the effect of different treatment regimens in dogs experimentally infected with adult D. immitis on microfilariemia, antigenemia, worm recovery and Wolbachia content. Treatment with ivermectin (IVM; 6 microg/kg per os weekly) combined with doxycycline (DOXY; 10 mg/kg/day orally from Weeks 0-6, 10-12, 16-18, 22-26 and 28-34) resulted in a significantly faster decrease of circulating microfilariae and higher adulticidal activity compared with either IVM or DOXY alone. Quantitative PCR analysis of ftsZ (Wolbachia DNA) and 18S rDNA (nematode DNA) absolute copy numbers showed significant decreases in Wolbachia content compared with controls in worms recovered from DOXY-treated dogs that were not, however, associated with worm death. Worms from IVM/DOXY-treated dogs, on the other hand, had Wolbachia/nematode DNA ratios similar to those of control worms, suggesting a loss of both Wolbachia and nematode DNA as indicated by absolute copy number values. Histology and transmission electron microscopy of worms recovered from the IVM/DOXY combination group showed complete loss of uterine content in females and immunohistochemistry for Wolbachia was negative. Results indicate that the combination of these two drugs causes adult worm death. This could have important implications for control of human and animal filarial infections.

Antigenicity of a filarial protease from Setaria digitata in Wuchereria bancrofti infection.

A protease isolated from adult Setaria digitata revealed a single, 110-kDa band in a gelatin-impregnated, substrate gel. Analysis with specific inhibitors indicated it to be a metallo-protease. IgG from chronic filarial patients living in an area of Orissa, India, endemic for Wuchereria bancrofti was able to neutralize the proteolytic activity of this enzyme completely. IgG from asymptomatic microfilaraemics and endemic normals (asymptomatic amicrofilaraemics) only caused partial inhibition and IgG from non-endemic normals was ineffective. The generation of inhibitory antibodies appears to depend on the severity of filariasis. Evaluation of IgG-subclass response to the protease indicated the dominance of IgG4 antibodies in asymptomatic carriers and of IgG1 in those with chronic filariasis. The IgG3 response was minimal and the IgG2 responses were similar for each of the filarial groups. When IgG4-subclass serology using the protease antigen was assessed, 47 of 50 microfilaraemics, 20 of 50 endemic normals and 23 of 50 chronic patients but none of 20 non-endemic normals were found seropositive. Appreciable levels of specific IgE, which correlated with those of IgG4, were detected in all filarial groups. IgG4 was detected in 35 out of 70 children (aged < 12 years) who appeared amicrofilariaemic and 38 of 40 microfilaraemic children.

Antibodies to diethylcarbamazine potentiate the antifilarial activity of the drug.

The antifilarial drug diethylcarbamazine citrate (DEC) is known to mediate in vivo microfilaricidal activity in conjunction with the host immune system. In this study passive transfer of antibodies to DEC elicited by immunization with methyl piperazine carboxylic acid (MPCA) coupled to bovine serum albumin (BSA), was found to potentiate microfilaricidal activity of subcurative doses of DEC in Setaria digitata infected Mastomys coucha. Active immunization of microfilaraemic animals with MPCA-BSA followed by administration of subcurative doses of DEC also resulted in rapid clearance of microfilaraemia in both S. digitata and Brugia malayi infected M. coucha indicating the synergistic activity of DEC and the antibodies to the drug. Since some of the filarial antibodies are known to react with DEC, it is proposed that such antibodies may potentiate the microfilaricidal activity of the drug in vivo.