Evaluation of chemotherapy in experimental toxocarosis by determination of specific immune complexes

The kinetic profile of clinical and laboratory findings and treatment outcome of patients with toxocariasis

OBJECTIVES

Human toxocariasis is a widespread zoonosis for which a chemotherapy decision and therapy effectiveness are difficult to determine. We aimed to investigate the kinetic profile of clinical and laboratory findings and treatment outcome of patients with toxocariasis in Vietnam.

METHODS

The prospective study was conducted between October 2017 and June 2019. The diagnosis of toxocariasis was established based on clinical, laboratory (eosinophilia, raised IgE concentration) and serological (positive Toxocara IgG ELISA) evaluation as well as the exclusion of another helminthic co-infection. The patients were followed up after seven days, then one, three and six months after chemotherapy by thiabendazole.

RESULTS

The study involved 80 patients with a mean age of 41.6 ± 15.2 years of whom 58.8% were female. At three and six months after chemotherapy, most patients demonstrated resolution of clinical signs and symptoms, eosinophil count and IgE concentration but not in the proportion of IgG seropositivity. Skin lesions and eosinophilia resolved earlier than the other symptoms (one month after treatment). About four-fifths of the patients were "cured" after three and six months of follow-up; 33.8% showed side effects to thiabendazole therapy but no severe events were reported. The most common adverse reaction was neurologic symptoms followed by gastrointestinal or skin manifestations which lasted as long as 4 days.

CONCLUSIONS

In toxocariasis patients, cutaneous manifestations and eosinophilia resolve more rapidly than other clinical and laboratory findings while IgG titre has a very slow kinetic after therapy. Thiabendazole seems to be a potential alternative for the treatment of human toxocariasis.

Toxocara canis: Analysis of the kinetics of antigen release and antibody production in an in vivo model for the detection of past or present infection

Worldwide, Toxocara canis is an important zoonotic nematode of public health concern. This soil-transmitted helminth causes visceral larva and ocular larva migrans in paratenic hosts. The detection of T. canis larva migrans is complicated because current immunological tests detect only IgG antibodies, which can cross-react with antigens from other parasites and cannot distinguish between the past and present infection. Analysis of antigen release and antibody production could help improve the detection of larva migrans. Here, we report the kinetics of antigen release, IgM and IgG production in an in vivo model for the detection of past or present infection. We used four groups of seven mice: two groups infected orally with 50 or 100 embryonated eggs, and the other two infected intraperitoneally with 50 or 100 live larvae. We obtained blood samples at 0, 3, 7, and 14days and, then, every two weeks until day 140. Sandwich ELISA and indirect ELISA were performed for antigen capture and the detection of immunoglobulins, respectively. Mice inoculated with larvae developed an immune response faster than those inoculated with eggs. In all groups, antigen capture was positive starting at 3days until 140days post-inoculation (dpi). Detection of immunoglobulins was at 14 or 28dpi in mice inoculated with larvae or eggs, respectively. Negative IgM values were detected at days 98 and 112. The samples remained positive for IgG until the last day of the experiment. Data suggest that in mice inoculated with T canis eggs, some larvae did not hatch, others died or never reached the bloodstream. Based on our model, we propose that there is early infection when only antigens are present, and active larva migrans when antigen and immunoglobulins are detected, implying an immune response of the host against the antigen. Our study offers a view into the parasite-host relationship and enables us to infer if there are live larvae. Additionally, these findings provide a foundation for the diagnosis and differentiation of recent infection and active larva migrans.

EFFICACY OF NITAZOXANIDE AGAINST Toxocara canis: LARVAL RECOVERY AND HUMORAL IMMUNE RESPONSE IN EXPERIMENTALLY INFECTED MICE

The efficacy of nitazoxanide (NTZ) against toxocariasis was investigated in an experimental murine model and results were compared to those obtained using mebendazole. Sixty male BALB/c mice, aged six to eight weeks-old, were divided into groups of 10 each; fifty were orally infected with 300 larvaed eggs of T. canisand grouped as follows, G I: infected untreated mice; G II: infected mice treated with MBZ (15 mg/kg/day) 10 days postinfection (dpi); G III: infected mice treated with NTZ (20 mg/kg/day) 10 dpi; G IV: infected mice treated with MBZ 60 dpi; G V: infected mice treated with NTZ 60 dpi; GVI: control group comprising uninfected mice. Mice were bled via retro-orbital plexus on four occasions between 30 and 120 dpi. Sera were processed using the ELISA technique to detect IgG anti- Toxocaraantibodies. At 120 dpi, mice were sacrificed for larval recovery in the CNS, liver, lungs, kidneys, eyes and carcass. Results showed similar levels of anti- ToxocaraIgG antibodies among mice infected but not submitted to treatment and groups treated with MBZ or NTZ, 10 and 60 dpi. Larval recovery showed similar values in groups treated with NTZ and MBZ 10 dpi. MBZ showed better efficacy 60 dpi, with a 72.6% reduction in the parasite load compared with NTZ, which showed only 46.5% reduction. We conclude that administration of these anthelmintics did not modify the humoral response in experimental infection by T. canis. No parasitological cure was observed with either drug; however, a greater reduction in parasite load was achieved following treatment with MBZ.

Therapeutic battle against larval toxocariasis: are we still far behind?

Toxocariasis is a widespread zoonotic helminthic disease. Human infection is acquired by ingestion of embryonated eggs of Toxocara which reach the environment via stools of dogs and cats. In paratenic hosts, such as humans and mice, the hatched larvae migrate systematically in the body and could reach critical sites such as the eye and the central nervous system. The clinical expression of toxocariasis includes two main forms of varying intensity: visceral and ocular, as well as several organ-specific clinical manifestations. The issue of treatment is a matter of great controversy not only because of limited efficacy of anthelmintic drugs in terms of parasite eradication, but also because of doubts about the benefits of therapy as most Toxocara infections are self-limiting. Many animal studies were conducted employing different drugs and regimens, yet the results were variable and inconsistent. On the other hand, experience in human therapy is unfortunately limited due to paucity of clinical trials. Herein, the problems and pitfalls of treatment of toxocariasis are addressed, and new trends in therapy are discussed.

Western blot antibody determination in sera from patients diagnosed with Anisakis sensitization with different antigenic fractions of Anisakis simplex purified by affinity chromatography

Using Western blot techniques, the specificities of crude and purified (PAK and PAS) Anisakis simplex antigens were compared against 24 sera from patients diagnosed with Anisakis sensitization. All patients recognized a 60 kDa protein against the A. simplex crude extract, while 37.5% and 12.5% reacted with proteins of 40 and 25 kDa, respectively, when IgG was tested. In the case of IgE determination, 41.6% of sera were negative, while 12.5% and 20.8% appeared to cross-react against Toxocara canis and Ascaris suum, respectively. When the PAK antigen (A. simplex antigen purified by means of a column of IgG anti-A. simplex) was tested, immune recognition towards the 60, 40 and 25 kDa proteins increased in 83.3%, 16.7% and 4.2%, respectively, when the Ig antibodies were tested. In the case of the PAS antigen (PAK antigen purified by means of a column of IgG anti-A. suum), the reaction against the 40 and 25 kDa proteins increased to 45.8% and 25%, respectively, when Ig antibodies were used. Finally, when the EAS antigen (eluted from the anti-A. suum column after PAK purification) was tested, 83.3% of the assayed sera reacted against the 14 kDa protein, when the Ig antibodies, IgG and IgM immunoglobulins were measured. With the IgE determination, the reactions were observed in 41.7% of patients with proteins between 60 and 35 kDa against the PAS antigen. With the EAS antigen, reactive bands of 184, 84 and 14 kDa appeared. In conclusion, in the purification process of the A. simplex larval crude extract, the proteins implicated in cross-reactions with Ascaris and Toxocara were eliminated, with an important concentration of proteins responsible for the induction of specific responses.

Evaluation of follow-up of therapy with fenbendazole incorporated into stabilized liposomes and immunomodulator glucan in mice infected with Toxocara canis larvae

Anthelmintic activity of benzimidazole carbamate anthelmintics is low against dormant Toxocara canis larvae during late infections in paratenic hosts. The present study was conducted to examine the efficacy of pure fenbendazole, or drug incorporated into sterically stabilized liposomes (SL-FBZ) administered to T. canis-infected mice alone and after its co-administration with the immunomodulator (1-->3)-beta-D-glucan against larvae localized in muscles and brains. Therapy with either drug forms (in total 250 mg/kg in 10 doses) commenced on day 28 post-infection (p.i.) and the efficacy of treatment, examined on day 30 after the last dose of drug, was the highest in groups of mice treated with SL-FBZ in combination with glucan (89.5+/-5.8% in the muscles, 66.1+/-8.1% in brains). During 56 days of follow-up after termination of therapy, serum levels of anti-TES IgG antibodies, circulating IgG-TES immune complexes (CIC) as well as IgG antibodies to the most immunogenic part of recombinant myosin antigen of T. canis larvae were investigated. In contrast to anti-TES IgG antibodies, levels of CIC and anti-myosin antibodies were in the linear correlation with the efficacy of treatments beginning from day 38 post-therapy. We also showed that the serum levels of CIC as well as anti-myosin IgG antibodies seem to be the suitable serological markers for the monitoring of progress in larval destruction and TES resorption from the tissues.

Enzyme-linked immunosorbent assay and Western blot antibody determination in sera from patients diagnosed with different helminthic infections with Anisakis simplex antigen purified by affinity chromatography

An evaluation of the sensitivity and the specificity of the Anisakis simplex antigens purified by affinity chromatography was performed using sera from patients diagnosed with Anisakis sensitisation and sera from patients previously diagnosed with different helminthic infections. Only the sera of the patients diagnosed with Schistosoma mansoni or Onchocerca volvulus parasitic infections were negative against the A. simplex antigen and its purified fractions (PAK antigen: A. simplex antigen purified using columns prepared with anti-A. simplex rabbit IgG and PAS antigen: PAK antigen purified using columns prepared with anti-Ascaris suum rabbit IgG). However all the sera were positive against the A. suum antigen. In all the sera from the patients diagnosed with Anisakis sensitisation, the antibody levels detected using the purified antigens (PAK and PAS antigens) were lower than the observed using the A. simplex crude extract with the highest diminution in the case of the IgG. When these same sera were tested against the A. simplex crude extract by Western blot, several bands of high molecular masses were observed as well as, intense bands at 60 and/or 40 kDa. A concentration of these last proteins was observed in the PAK and the PAS antigens. When the sensitivity and the specificity determinations were performed, only seven of the 38 patients diagnosed of Anisakis sensitisation were positive, as well as, the sera from the patients diagnosed with parasitisms by Echinococcus granulosus or Fasciola hepatica.

Evaluation by ELISA of anisakis simplex larval antigen purified by affinity chromatography

In order to improve the specificity and sensitivity of the techniques for the human anisakidosis diagnosis, a method of affinity chromatography for the purification of species-specific antigens from Anisakis simplex third-stage larvae (L3) has been developed. New Zealand rabbits were immunized with A. simplex or Ascaris suum antigens or inoculated with Toxocara canis embryonated eggs. The IgG specific antibodies were isolated by means of protein A-Sepharose CL-4B beads columns. IgG anti-A. simplex and -A. suum were coupled to CNBr-activated Sepharose 4B. For the purification of the larval A. simplex antigens, these were loaded into the anti-A. simplex column and bound antigens eluted. For the elimination of the epitopes responsible for the cross-reactions, the A. simplex specific proteins were loaded into the anti-A. suum column. To prove the specificity of the isolated proteins, immunochemical analyses by polyacrylamide gel electrophoresis were carried out. Further, we studied the different responses by ELISA to the different antigenic preparations of A. simplex used, observing their capability of discriminating among the different antisera raised in rabbits (anti-A. simplex, anti-A. suum, anti-T. canis). The discriminatory capability with the anti-T. canis antisera was good using the larval A. simplex crude extract (CE) antigen. When larval A. simplex CE antigen was loaded into a CNBr-activated Sepharose 4B coupled to IgG from rabbits immunized with A. simplex CE antigen, its capability for discriminate between A. simplex and A. suum was improved, increasing in the case of T. canis. The best results were obtained using larval A. simplex CE antigen loaded into a CNBr-activated Sepharose 4B coupled to IgG from rabbits immunized with adult A. suum CE antigen. When we compared the different serum dilution and antigenic concentration, we selected the working serum dilution of (1/4)00 and 1 microg/ml of antigenic concentration.

Evaluation of mebendazole activity on experimental murine toxocariasis by immune complexes determination

The mebendazole action on experimental murine toxocariasis, using different formulations and vehicles, was studied by means of the detection of antibodies and immune complexes by ELISA. After inoculation with 1000 embryonated Toxocara canis eggs, BALB/c mice were submitted to the anthelmintic treatment as follows: group 1 (control without treatment); group 2 (mebendazole (MBZ), Lomper, Steve Laboratories, Barcelona, Spain, suspended in 1% sodium carboxymethylcellulose (CMC) at a dose of 100 mg/kg/day); group 3 (MBZ, pure compound suspended in 1% CMC at a dose of 100 mg/kg/day); group 4 (MBZ, pure compound suspended in water at a dose of 100 mg/kg/day); group 5 (MBZ, pure compound, formulated to a solid dispersion at 10% in polyethylene glycol 6000 (PEG) then dissolved in water at a dose of 100 mg/kg/day); group 6 (MBZ, pure compound, formulated to a solid dispersion at 10% in PEG then dissolved in water at a dose of 50 mg/kg/day); group 7 (MBZ, pure compound, formulated to a solid dispersion at 10% in PEG then dissolved in water at a dose of 25 mg/kg/day). The treatments were administered on days 5-7 post-inoculation (p.i.) inclusive. The dynamics of the production of the specific antibodies for both excretory-secretory (ES) antigen or crude extract showed a similar profile as compared to the control group. In groups 2 and 6, from the beginning of the treatment, values of immune complexes fell rapidly and were undetectable for the remainder of the experiment. Reductions of immune complex levels by the 4th-6th, 2nd-3rd and 2nd-5th weeks p.i. were observed from groups 3, 5 and 7, respectively. In the other groups, similar profiles as compared to the control group were observed in the dynamics of the specific immune complexes. The evaluation of chemotherapy by immunological methods is a valid technique for the efficiency of the treatment without the disadvantages of larval recovery from several digested tissues. Mebendazole, pure compound, formulated to a solid dispersion in PEG, then dissolved in water reduced immune complexes from the beginning of the treatment. The larval immobilization produced by MBZ should entail a reduction in their metabolic activity with a reduction in the production of excretory-secretory substances which are responsible for the formation of immune complexes. The rapid clearance of specific immune complexes together with a total larvae reduction would explain the decrease in specific immune complexes, which detection is a valid technique for monitoring the efficiency of treatment.

Persistence of immune response in human toxocariasis as measured by ELISA

The antibody titer was followed in a group of patients, clinically diagnosed with toxocariasis, during a 5 year period. We observed that larvae can survive for at least 5 years in humans. Antigenic stimulation was enough to keep high levels of immunoglobulins over this period. Antibody levels decreased slowly and this pattern is similar to that shown by animal models.