Prevalence of natural ovine fasciolosis shown by demonstrating the presence of serum circulating antigens

The prevalence of fasciolosis in sheep (Galicia, Northwest Spain) kept under field conditions was determined by using a sandwich-enzyme-linked immunosorbent assay (sELISA). Serum Fasciola hepatica circulating antigens were captured by means of a rabbit polyclonal IgG antibody to F. hepatica excretory/secretory products. Results were compared to those obtained by faecal sedimentation and an indirect ELISA (iELISA) and excretory/secretory antigens. Prevalences were 39.1% by sELISA, 30.4% by faecal sedimentation and 56% by iELISA; 83.3% of the sheep were positive to any one of the three tests. We observed that 59.5% of the sheep examined had active fasciolosis, 29.1% (117) had antigenaemia, 20.4% (82) passed eggs, and 40 (10%) were positive to both probes. We conclude that there is a high prevalence of fasciolosis in sheep from the studied region, and that the combination of sELISA and coprological sedimentation is extremely helpful for demonstrating current fasciolosis, so its application can be strongly recommended for epidemiological surveys.

Diagnosis of parasitic zoonoses by immunoenzymatic assays--analysis of cross-reactivity among the excretory/secretory antigens of Fasciola hepatica, Toxocara canis, and Ascaris suum

Several parasitic infections such fasciolosis, toxocariosis or ascariosis are important zoonoses. During the infection with Fasciola hepatica, Toxocara canis and Ascaris suum, an important intraorganic phase in their hosts takes place, releasing antigens responsible for a humoral immune response, which enables the diagnosis of that parasitosis. A study to identify the existence of cross-reactivity among the excretory/ secretory antigens of F. hepatica, T. canis and A. suum was developed. One group of Sprague-Dawley rats was infected with 20 metacercariae of F. hepatica and another group remained uninfected as control. By means of an Indirect-ELISA, the rat humoral immune response (IgG and IgM) against the excretory/secretory antigens of F. hepatica was analysed and measured for cross reactivity with T. canis and A. suum. IgM cross-reaction was mainly observed in the first 10 weeks post-infection. IgG cross-reaction was observed throughout the study, and was maximal at the 2-3 weeks and 3-6 weeks post-infection, which corresponds to the intraorganic migratory phase of these parasites. The western-blot showed that the rat IgG recognised three proteins of 190, 160 and 33 kDa in the antigens from F. hepatica, T. canis and A. suum. The existence of cross-reactivity among these antigens seems to demonstrate also the presence of structural similarities, such as tegumental proteins. These results should be consider when immunoassay probes are used in the diagnosis of parasitic infections.

Chronobiology of Oestrus ovis (Diptera: Oestridae) in Sardinia, Italy: guidelines to chemoprophylaxis

Oestrus ovis (Linné 1761) larvae are obligatory parasites of the nasal and sinus cavities of sheep and goats. Infestation is prevalent in hot and dry regions, such as Mediterranean countries. The current work was developed to establish the chronobiology of O. ovis in Sardinia, to determine the most suitable time for chemoprophylaxis. A survey was carried out during 1998, and sheep heads were collected monthly from local flocks. A total of 443 heads was examined, and the prevalence of oestrosis was 73.8%. We collected 2,691 larvae (mean = 6.07 +/- 9.52), and the intensity was greatest in November. The humoral immune response against the nasal bot fly was analyzed by means of an indirect-ELISA using second-instar O. ovis excretory and secretory antigens. A seasonal variation in the antibody levels was observed, increasing from April and peaked in June and in September. A significant correlation was observed between first instar intensity and the mean relative humidity (r2 = 0.120; P < 0.05), and between second-instar intensity and the mean temperature (r2 = 0.241; P < 0.05). Three periods in the chronobiology of O. ovis were defined: diapause (October-February), the active phase ofthe endogenous cycle (March-September) and the exit phase (May-September). Our results showed that treatment in October-November was suitable, because first instars were in diapause, preventing the development of first into second instars, and second into third instars.

Influence of age and breed on natural bovine fasciolosis in an endemic area (Galicia, NW Spain)

An analysis was undertaken of the effect of breed and age on bovine fasciolosis using antibody and antigen detection ELISAs. A total of 84.3% of the 1284 serum samples examined had positive antibody values and 20.4% exhibited antigenaemia. The seroprevalence of antibodies in crossbred cattle was higher than that in autochthonous Rubia Gallega, Friesian or Brown Swiss cows. The highest percentage antigenaemia occurred in the Brown Swiss cattle, but the breed differences were not statistically significant. Cattle aged 3-5 years had the highest antibody and circulating antigen prevalence and the age differences were significant. It was concluded that the apparent influence of breed was probably closely associated with the husbandry system. The autochthonous Rubia Gallega may be better adapted to fasciolosis as its percentage of antigenaemia was the lowest.

Time-course analysis of coproantigens in rats infected and challenged with Fasciola hepatica

The influence of a challenge infection during an acute or chronic primary infection on Fasciola hepatica-coproantigen kinetics was established in rats. Egg-output and IgG humoral responses were also established. Two primary-infected groups were reinfected at different periods, one 4 weeks after primary infection (w.p.i.) (acute phase) and the other 11 w.p.i. (chronic phase). Another group remained without reinfection as a control. Coproantigens were first detected in the group challenged on acute fascioliasis. The highest values of coproantigens were recorded in the group reinfected during acute fascioliasis and the lowest in the group challenged during chronic fascioliasis. The IgG responses to F. hepatica excretory/secretory antigens increased after reinfection. Neither the egg output nor the parasitic burden were significantly different among the three infected groups. Our results indicate that the time of challenge affects the kinetics of coproantigens. Thus, challenge during acute fascioliasis favours the migration of the juvenile flukes from the primary infection to the bile ducts, and is responsible for the earlier presence of coproantigens in these animals. The possible relationship between coproantigen detection and T1 and T2 tegumentary antigens is discussed.

Bronchopulmonary helminths of roe deer (Capreolus capreolus) in the northwest of Spain

From 1993 to 1995, 148 hunter killed roe deer (Capreolus capreolus L.) from game reserves in Lugo (northwestern Spain) were examined for lungworm infection. The overall prevalence of infection was high (66.2%). Infections were comprised to two species, Varestrongylus capreoli and Dictyocaulus noerneri with a prevalence of 62.0 and 18.2%, respectively. Significant differences in the prevalence and larval burdens in lungs and faecal samples were observed between different locations. The highest overall prevalence of lungworm infection was observed in the large reserve at Ancares (78%) in comparison to that in smaller reserves (61.7%). Considering that the species recorded in this study are highly host-specific, it is unlikely that roe deer represent a significant reservoir of lungworm transmissible to domestic ruminants in northwestern Spain.

Effect of fasciolicides on the antigenaemia in sheep naturally infected with Fasciola hepatica

A study was developed to evaluate the influence of triclabendazole (Fasinex) and netobimin (Hapasil) the antigenaemia in sheep naturally infected with Fasciola hepatica during 16 weeks. A sandwich-ELISA (enzyme-linked immunosorbent assay) using a rabbit polyclonal IgG antibody to F. hepatica antigens was employed and the data obtained were compared to those from coprological and indirect-ELISA techniques. Triclabendazole reduced the values of circulating antigens at weeks 2-4 post-treatment and faecal output at weeks 2-8 post-treatment, but antibodies showed positive values until the end of the study. Netobimin did not reduce circulating antigens of the trematode nor egg-excretion; and IgG antibodies did not decrease throughout the study.

Dynamics of the antibody response in cattle infested by Hypoderma (Diptera: Oestridae) after a treatment with injectable and pour-on ivermectin

The dynamics of the anti-Hypoderma antibody response after a treatment with injectable and pour-on ivermectin against first instars of Hypoderma sp. were determined in naturally infested cows. Cattle were randomly assigned to three groups: group 1, which served as an untreated control; group 2, treated with pour-on ivermectin at a dose of 500 microg/kg of body weight, and group 3, which received 200 microg/kg of body weight of ivermectin by subcutaneous injection. Both ivermectins showed total efficacy against L-1 of Hypoderma sp. In untreated control animals, grubs became detectable in the 2 mo after treatment. Indirect enzyme-linked immunosorbent assay (ELISA) showed a significant increase in group 3 antibody levels 1 mo after treatment, whereas in group 2 the increase was not significant. Following the peak of anitibody activity in group 3, antibody levels declined at a faster rate than in those treated topically. In both treated groups, cattle remained serologically positive for 4 mo after ivermectin treatment. Thus, serological surveillance programs for cattle grubs conducted during this posttreatment period will not be influenced by treatment with ivermectin. The persistence of antibody levels after larval destruction makes the indirect ELISA unsuitable for the prediction of the efficacy of treatment.

Use of a sandwich-enzyme-linked immunosorbent assay (SEA) for the diagnosis of natural Fasciola hepatica infection in cattle from Galicia (NW Spain)

An indirect-enzyme immune-linked immunosorbent assay (IEA) was compared to a sandwich-enzyme-linked immunosorbent assay (SEA) to diagnose fasciolosis in naturally infected cattle. By means of a rabbit polyclonal IgG antibody to F. hepatica antigens, captured circulating antigens were detected by an SEA technique. A total of 85.1% of the samples examined was considered positive by using the IEA-test, whereas this percentage was of 37.3% by the SEA test. Using the two enzymatic probes, only the 38.3% resulted positive to both immunoassay probes. Our data indicate that circulating antigen detection assay in combination with results of antibody detection may offer a more reliable diagnostic technique than classic coprologic ones, with results very appropriate for epidemiologic studies carried out on a wide area.

Assessment of a recombinant antigen versus natural hypodermin C for the serodiagnosis of hypodermosis in cattle

An indirect ELISA test using as antigen a recombinant parasite protein, hypodermin C, was developed to measure Hypoderma-specific antibodies in cattle sera and compared with natural hypodermin C. To evaluate the field efficacy of the ELISA test, 334 serum samples were collected from cows raised at farms in Galicia for a serological survey. Compared with an ELISA based on natural parasite antigen, the recombinant hypodermin C gave excellent results, with a sensitivity of 95.8% and a specificity of 95.7%. Considering the cut-off point, with the recombinant hypodermin C, 70.9% of the animals had positive levels of antibodies to Hypoderma and with natural hypodermin C, 73.6%. Recombinant hypodermin C appears to be a useful alternative to the natural parasite antigen for the serodiagnosis of Hypoderma sp in cattle.

Subclass profile of specific IgG antibodies in rats challenged during acute and chronic primary infection with Fasciola hepatica

The influence of a previous infection (acute and chronic) on the kinetics of the immune humoral response in rats challenged with Fasciola hepatica was studied. Two infected groups were reinfected at different times--one, at 4 weeks after primary infection (w.a.p.i.); and the other, at 11 w.a.p.i. Signs of reinfection were observed in the two challenged groups as evidenced by an increment in glutamate dehydrogenase and gamma-glutamyl transpeptidase activity after secondary infection. IgG subclass (IgG1, IgG2a, IgG2b, IgG2c) responses to F. hepatica excretory/secretory products (FhESP) differed, depending on the time of challenge infection, but no difference was observed between the reinfected groups. A predominance of the IgG1 subclass was noted in the group challenged at 4 w.a.p.i., and IgG2b and IgG2c were prominent in the group reinfected at 11 w.a.p.i. These results indicate that the presence of juvenile or adult flukes in the liver at the time of challenge seems to influence the immune response to a secondary infection.

IgG isotype specific immune response in rats infected with Fasciola hepatica

Antibody responses (IgG1, IgG2a, IgG2b, and IgG2c subclasses) against Fasciola hepatica L. in rats infected with metacercariae were analysed by ELISA. Animals of group 1 (R-1) remained infected throughout 21 weeks, and rats of group 2 (R-2) received a single oral dose of triclabendazole (Fasinex 10%, Ciba-Geigy) at 4 weeks after infection. Group C (R-C) consisted of rats left intact which served as uninfected controls. All IgG subclasses increased during the first weeks after infection, but when triclabendazole was administered IgG1 and IgG2b diminished markedly. IgG2c showed a different profile to the other antibodies evaluated, increasing earliest and decreasing profoundly from the 9-11th week after infection (w.a.i). The infected-untreated rats produced higher titres of antibodies than the rats of R-2, and these differences were statistically significant (p < 0.05) in all subclasses evaluated except in IgG2a titres.

Puberty and serum concentrations of ovarian steroids during prepuberal period in Friesian heifers artificially infected with Fasciola hepatica

An experiment was conducted to study the effect of fascioliasis on puberty in 13 Friesian heifers divided into a control group (n = 7) and an infected group (n = 6). At 4 m.o. of age each infected heifer received 600 metacercariae of F. hepatica. Blood samples were taken twice a week, at which time permanent heat mount detectors were checked, from 8 m.o. of age until 2 estruses were detected in all heifers. Serum concentrations of progesterone (P4) and estradiol-17 beta (E2) were assayed by ELISA and RIA, respectively. There was a significant delay in the onset of puberty in infected heifers compared with controls. All animals reached puberty at similar body weights but at different ages. First estrus was delayed by 39 d in infected compared with control animals. Serum concentrations of E2 were significantly higher in the infected group than the control group, while P4 concentrations were lower. Fascioliasis alters the serum concentration of E2, which in turn results in an abnormally low concentration of P4, probably due to underdeveloped or absent corpora lutea.

Subclasses of IgG in different aged rats with fasciolosis

The variations in antibody responses (total IgG and IgG1, IgG2a, IgG2b, and IgG2c subclasses) were studied in two groups of rats infected with metacercariae of the trematode Fasciola hepatica L. Animals of group 1 were 4 weeks old, and rats of group 2 were 13 weeks old. All IgG subclasses increased during the course of infection except IgG2c, which decreased. The younger rats reached more marked responses than the older, at least during the period of this trial. IgG1 and IgG2a antibodies reached the highest levels, and among these two, IgG2a response was slightly superior to IgG1.

Effect of early treatment with ivermectin and doramectin on the dynamics of antibody response in cattle naturally infested by Hypoderma lineatum and H. bovis

The field efficacy of two avermectins (ivermectin and doramectin) and the subsequent development of the antibody response were assessed in cows naturally infested with first-instar larvae (L-1) of Hypoderma sp. Twenty-eight Frisian cows were randomly divided into three groups while the first-instar larvae were still in migration: Group 1 (G-C) untreated control; Group 2 (G-Iv), treated with ivermectin injectable (0.2 mg kg-1 body weight) and Group 3 (G-Dor), which received doramectin injectable (0.2 mg kg-1 body weight). Serum antibody response was studied by an indirect ELISA test using, as antigen, the hypodermin C obtained from L-1 of H. lineatum. In treated animals no grubs were present on the back at any time during the trial, whereas a variable number of nodules were found in untreated animals. Both avermectins showed total efficacy against L-1 of Hypoderma sp., and there were no local or general reactions. In ivermectin-treated cattle serum antibody levels declined from one month p.t., while in those treated with doramectin they started to fall two weeks later, but no differences were found among both groups. On the other hand, G-C antibody levels progressively increased and remained high until December, when the first grubs became detectable on the back; after that, they began to decline. Early treatments against Hypoderma sp. have an influence on the results of ELISA, so they must be considered to determine the most suitable time for blood sampling.

Faecal egg output, contamination of pastures and serum pepsinogen concentrations in heifers with natural gastrointestinal nematode infections in north-west Spain

In 1988, 1989 and 1990 second year grazing heifers, naturally infected with gastrointestinal nematodes, were separated into two groups, one of which was treated orally with albendazole. In 1988 and 1989 treatment was administered immediately after parturition (February), and in 1990 during the last term of pregnancy (December). Both treated and control animals were grazed on separate plots in a rotational system. Maximum faecal egg counts were observed around parturition, except in 1990, when treatment was given at the end of gestation. The main genera identified were Cooperia, Trichostrongylus, Ostertagia and Oesophagostomum. The number of Ostertagia larvae in the treated groups increased from 1989 to 1990, while the others decreased. Pasture contamination with third stage larvae (L3) was lower on the plots grazed by treated heifers. Maximum numbers of L3 were found in autumn, at the end of winter, and at the beginning of spring. Mean serum pepsinogen concentrations were significantly higher in the untreated groups. This concurs with the pattern for L3 on pasture. The trial shows that if a single treatment against gastrointestinal nematodes is carried out, and the animals remain on contaminated pastures, the parasitic load tends to level out after 4-5 months under favourable climatic conditions. However, the percentages of nematode genera occurring in the new populations may differ from those in the original infection.

Relationship between the excretion of protostrongylid larvae in sheep in north-west Spain and climatic conditions

The relationship between different climatic factors (temperature, relative humidity and rainfall) and the pattern of lungworm larval excretion was studied in sheep under a continuous grazing pattern in North-west Spain, where the climate is intermediate between sub-humid Mediterranean with an Atlantic tendency and European Atlantic. Over a period of one year, 44 animals were sampled once a month at random from a flock of 80 Galician breed sheep, all over 4 years old. Faeces were taken directly from the rectum and the number of first stage larvae per gram of faeces was determined for each animal, and the species of Protostrongylidae (Nematoda) identified. Larval excretion was irregular during the study. The prevalence and intensity of infection were greater in the colder months (40.9%; x = 12.3 +/- 40.4) and less in the warmer months (21.9%; mean = 0.7 +/- 2.7). The species of Protostrongylidae identified and prevalences (%) were Neostrongylus linearis (71.5), Muellerius capillaris (18.8) and Cystocaulus ocreatus (9.7). Between November and March, with low temperatures, the prevalence and intensity of parasitism with N. linearis and M. capillaris were greater than in the months with high temperatures (May to September). Multiple linear regression analysis showed statistical correlation between temperature, relative humidity and rainfall considered together and the number of N. linearis larvae per gram of faeces. Linear regression showed a correlation between the temperature and the percentage of sheep that passed M. capillaris. In general, the prevalence and intensity of infection of the sheep with N. linearis, M. capillaris and C. ocreatus larvae decrease when the temperature increases and increase when the relative humidity and rainfall increases.