Toxocara infection in pigs. The use of indirect fluorescent antibody tests and an in vitro larval precipitate test for detecting specific antibodies

Immunolocalization of arginine kinase (AK) in Toxocara canis, Toxocara vitulorum, and Ascaris lumbricoides

Arginine kinase (AK) is a member of the phosphagen kinase family. AK plays a major role in cellular energy metabolism in invertebrates including nematodes. In the present study, we performed the direct immunofluorescence test to determine the immunolocalization of AK in different stages of the life cycle (eggs, larvae, and adult worms) of Toxocara canis, Toxocara vitulorum, and Ascaris lumbricoides. Our results indicated variable levels of expression of AK in different stages. Moreover, strong fluorescence was observed in cleaving eggs than in dormant eggs. The highest activity of the enzyme was observed in the fully developed eggs. This may be due to high expression of AK in embryonic development, which is associated with increased energy demand due to cleavage and cellular differentiation. Surprisingly, expression of AK is significantly higher in the middle part and posterior end compared to anterior end of the larvae. In addition, AK is highly concentrated in cellular and metabolically active parts of the body such as hypodermis, muscle, intestine, ovaries, oviducts, and uterus, while it is absent in noncellular areas like cuticle. The present study revealed the presence of AK in T. canis, A. lumbricoides, and T. vitulorum and that it plays a major role in energy metabolism of these nematodes. Interestingly, antiserum was prepared against the recombinant T. canis AK and reacts with the native AKs of T. canis, A. lumbricoides, and T. vitulorum. AK levels could vary in relation to maximum potential rates of ATP turnover, oxidative capacity, and energy output. Further studies on subcellular localization of AK in these important helminths provide new information for researchers to develop effective anthelmintics against the parasites of veterinary and of public health importance.

Cross-reactivity between Anisakis simplex sensitization and visceral larva migrans by Toxocara canis

The aim of this work was to study cross-reactivity in the diagnosis of two related ascaridosis. Nineteen patients diagnosed with recidivous acute urticaria (RAU) caused by Anisakis simplex and 26 patients diagnosed with visceral larva migrans (VLM) caused by Toxocara canis were studied employing commercial diagnostic kits and "in house" assay kits. Cross-reactivity observed was greater when using "in house" assay kits, suggesting that T. canis excretory-secretory antigens were not only recognized by antibodies from patients with RAU but with greater intensity compared to the A. simplex excretory-secretory antigens.

Serological responses to Ascaris suum adult worm antigens in Iberian finisher pigs

Adult Ascaris suum were dissected to obtain different worm components (body wall, body fluid, ovaries, uterus and oesophagus) which were used as antigens when testing 95 sera of naturally A. suum-infected Iberian pigs by enzyme-linked immunosorbent assay (ELISA) and Western blot (WB). Pigs with patent Ascaris infections had significantly lower ELISA optical density values than pigs without adult worms when using the body fluid and the body wall as antigens. A poor negative correlation was found between adult intestinal worm burden or eggs in faeces and specific antibody responses, measured by ELISA and WB using all antigens. By WB, the recognition of specific bands was variable, but three groups of bands with molecular weights of 97 kDa, 54-58 kDa and 42-44 kDa were generally recognized by sera from naturally infected pigs as well as from hyperimmunized pigs when using the five antigen extracts. The ELISA and WB techniques may be used for immunodiagnosis, using somatic adult worm antigens, to declare young pigs to be Ascaris-free but cannot be used for individual Ascaris-diagnosis in adult Iberian pigs.

Response to repeated inoculations with Ascaris suum eggs in pigs during the fattening period. II. Specific IgA, IgG, and IgM antibodies determined by enzyme-linked immunosorbent assay

Experimental trickle inoculations of pigs with low doses (2 x 25 eggs/week) and high doses (2 x 500 eggs/week) of Ascaris suum were followed by enzyme-linked immunosorbent assay (ELISA) during a 14-week period. Three antigens were employed for coating: hatching fluid of embryonated eggs, excretory/secretory antigens from in vitro-cultivated infective larvae (L2/L3-ES), and adult body fluid. Seroconversion times (week 2 for the high-dose group and week 4 for the low-dose group) were essentially identical for the three antigens. The assay employing L2/L3-ES, however, produced significantly higher readings. Specific serum antibody in the IgA and IgG classes showed very similar time courses in both groups. A weak and transient, specific IgM response was recorded in the high-dose group. Mean ELISA responses to L2/L3-ES did not differ significantly between the groups at the termination of the experiment. Specific antibody correlated weakly with the number of liver milk spots recorded at slaughter.

Toxocara canis: monoclonal antibodies to larval excretory-secretory antigens that bind with genus and species specificity to the cuticular surface of infective larvae

When maintained in culture, the infective-stage larvae of Toxocara canis produce a group of excretory-secretory antigens. Monoclonal antibodies to these antigens have been produced and partially characterized. Hybridomas were made using spleens from mice that had been given 250 embryonated eggs of T. canis followed by immunization with excretory-secretory antigens. Monoclonal antibodies were first screened against excretory-secretory antigens using an indirect enzyme-linked immunosorbent assay. Those antibodies positive in this assay were then screened against the surfaces of formalin-fixed, infective-stage larvae using an indirect fluorescent antibody assay. The two monoclonal antibodies showing fluorescence were also tested against the surfaces of infective-stage larvae of Toxocara cati, Baylisascaris procyonis, Toxascaris leonina, Ascaris suum, a Porrocaecum sp., and Dirofilaria immitis. One of these two antibodies bound to the surface of T. canis and T. cati while the other bound only to the surface of T. canis; neither were reactive with the other ascaridoid larvae or the larvae of D. immitis. Enzyme-linked immunoelectrotransfer blotting techniques were used to demonstrate that the cross-reactive antibody recognized antigens with molecular weights of about 200 kDa while the more specific monoclonal antibody recognized antigens with approximate molecular weights of 80 kDa. The specificity of these two antibodies for T. canis and T. cati should prove helpful in the development of more specific assays for the diagnosis of visceral and ocular larva migrans.

An in vivo model for the study of chemotaxis induced by schistosomula of Schistosoma mansoni

Peritoneal leucocytosis, with an increased percentage of eosinophils, was found in mice which had been infected with Schistosoma mansoni for 7 weeks or longer. Specific IgG against worm and egg antigens increased in peritoneal fluids and their corresponding sera respectively 5 and 7 weeks after infection. An intraperitoneal challenge with schistosomula elicited neutrophilia in all mice regardless of immune status, as well as infiltration of eosinophils and macrophages in infected mice. The secondary eosinophilia occurred in mice previously infected for 1 week or longer, whereas the infiltration of macrophages occurred only after worms from the primary infection had started laying eggs. Unlike the eosinophilia the macrophage response required infection with bisexual populations of cercariae. Injection of previously infected mice with Escherichia, Trichinella or Toxocara failed to increase the proportions of eosinophils and macrophages. Schistosomula-induced eosinophilia could be elicited in passively sensitized mice. Intraperitoneal injection of PBS extract of adult worms elicited eosinophilia in infected mice and neutrophilia in normal mice. Two chromatographic fractions induced eosinophilia and the third only neutrophilia. The relevance of these observations to host response to S. mansoni infections is discussed.

Characterization of surface and excretory-secretory antigens of Toxocara canis infective larvae

The surface antigens of Toxocara canis infective larvae have been identified by radio-iodination and compared with the excretory-secretory (ES) products released by the larvae in vitro. Common antigens, of molecular weight 32 000 and 120 000 are found on the larval surface, in the ES material and in culture supernatant following surface iodination of living T. canis larvae. The 120 000 antigens consist of three closely migrating bands in each of these preparations. However, one prominent ES component, of molecular weight 400 000, is not found on the larval surface. Additional molecules of 55 000 and 70 000 are present in the ES material, but while these may be discerned in surface preparations there appears to be more heterogeneity of surface molecules in this size range. Both sets of molecules are antigens to infected patients and experimental animals. A comparison of characterized human sera show that a radio-immunoprecipitation assay correlates with the established ELISA test (r = 0.89), and that all labelled molecules are antigenic to the infected host.

Antigens in perienteric fluid of Ascaris suum as detected through antibodies in pigs orally inoculated with fully embryonated eggs

Perienteric fluid (Pf) of adult Ascaris suum was fractionated by ammonium sulfate precipitation, gel filtration or DEAE--cellulose chromatography, and sucrose density gradient centrifugation. Anti-sera (anti-EE) from pigs which were inoculated orally with fully embryonated eggs (EE) of A. suum were used in an indirect radioimmunoassay (IRIA) to determine which fractions of Pf reacted positively in the analyses at the lowest protein concentration. These fractions were considered to contain more potent antigens. Comparative IRIA were performed employing antisera (anti-Pf) produced by injecting Pf into pigs. Six out of 35 fractions reacted positively at less than or equal to 0.2 micrograms protein when anti-EE was used in the IRIA. Twenty-two out of 35 fractions reacted positively at less than or equal to 0.2 micrograms protein when anti-Pf was used. Five of the 6 fractions reacting positively with anti-EE also reacted with anti-Pf. A 76000 dalton component appears to be one of the major proteins in the fractions which react positively with anti-EE while components from 10000-138000 daltons were present in the various fractions reacting positively with anti-Pf at less than or equal to 0.2 micrograms protein.

[Serological differentiation of Ascaris suum and Toxocara canis infections in pigs (author's transl)]

Groups of eight miniature pigs were infected either with 1,500 embryonated eggs each of Ascaris suum or Toxocara canis or with 1,000 eggs each of both nematodes. Sera were sampled before the infection as well as three and six weeks postinfection and then investigated in the ELISA on microtitre plates against antigens of various developmental stages. When extracts of adult Ascaris and Toxocara worms were used as antigens, distinct reactions were registered both in the infected and in the uninfected control groups. Antigens isolated from either embryonated eggs or larvae of both worms produced distinctly positive reactions with sera of the infected animals, including those pigs with heterologous infections but not with sera from uninfected controls. After saturation with heterologous antigens, the sera showed distinct antibody reactions against homologous antigen extracts and in this way infections with the two nematode species could be serologically differentiated.

A paper radioimmunosorbent test (PRIST) for the detection of larva-specific antibodies to Toxocara canis in human sera

A paper radioimmunosorbent test (PRIST) was shown to be sensitive and reproducible when used with excretory/secretory antigen of Toxocara canis second stage larvae. Whatman No. 50 filter paper (5 mm discs) gave the most consistent and clear results with antigen at a concentration of 100 micrograms/ml, and could be stored for up to 3 weeks in vacuo at -70 degrees C. Antigen coated discs were incubated with test sera at 1:10 dilution for 3 h at room temperature (21 degrees C), reacted with [125I]anti-human IgG for 1 h and counts determined in a gamma counter. Sera from patients with fascioliasis, taeniasis, schistosomiasis, oxyuriasis, trichinellosis and ancyclostomiasis gave counts similar to cord serum controls. Sera from patients with ascariasis gave counts of up to twice as great as controls, but sera from patients with toxicariasis produced counts of 7,000-13,000, a 4-6-fold increase.

Toxocariasis: serological diagnosis by enzyme immunoassay

An enzyme-immunoassay was developed to measure the concentration of serum antibody specific for the secretory antigens released by migrating toxocaral larvae. This technique was evaluated by testing sera from healthy UK adults, and from patients with and without toxocariasis. In 922 healthy adults, 2.6% were found to have elevated specific antibody levels. Elevated values were observed twice as frequently in males as in females but showed no significant regression with age between 20 and 65 years. Of 62 patients with non-toxocaral helminthic infections, all had antitoxocaral antibody levels within the range of values observed in healthy controls and had a mean level which was not significantly elevated. All of 13 patients with clinical toxocariasis had enzyme-linked immunosorbent assay (ELISA) antibody levels above the 100th percentiles of both the healthy population and the helminth-infected group and had a significantly high mean value (p less than 0.001) more than 12 times that of the healthy or infected controls. The high degree of sensitivity and specificity of the toxocariasis enzyme-immunoassay indicates that this new test should be useful in reference immunodiagnostic applications and in large-scale seroepidemiological surveys.