Toxocara canis infection in the paratenic host: a study on the chemosusceptibility of the somatic larvae in mice.

A research on formulation and dosage strategies of anthelmintics have been conducted in mice experimentally infected with eggs of Toxocara canis. Multidose treatments commenced at days 2, 14, 81, 87 and 123 postinfection. Results indicated no detectable difference in the chemosusceptibility of the migrating early infection larvae and the resting hypobiotic chronic infection larvae. Application of medicated dry food (pellets) may be a simple way of improving efficacy of treatment compared to oral drenching. The larvicidal potential of fenbendazole (FBZ), albendazole (ABZ), flubendazole (FUBZ), oxibendazole (OBZ) and ivermectin was assessed. Reductions of 84.2 to 99.7 or 88.8 to 100% of group mean larval counts were recorded after 20-30-day courses of feeding pellets containing FBZ at 6 g kg-1 or ABZ at 1.6 g kg-1 food, respectively. Efficacies of 57.8 to 88.2 or 81.1 to 32.0% were achieved by 20-day courses of feeding pellets medicated with FUBZ and OBZ at 1.6 g kg-1 or 6.0 g kg-1 food, respectively. Ivermectin at various dosing regimens showed only moderate larvicidal potential. Efficacy rates were not closely correlated with the amount of drug taken by the animals. The blood-brain barrier is permeable for the anthelmintics tested, and the brain of mice does not provide a site promoting survival of larvae.

World Association for the Advancement of Veterinary Parasitology (W.A.A.V.P.) second edition of guidelines for evaluating the efficacy of anthelmintics in ruminants (bovine, ovine, caprine)

The first edition of the W.A.A.V.P. anthelmintic guidelines for ruminants was published in 1982. Since then improved parasitological procedures have been developed, new therapeutic and prophylactic products have appeared requiring different test methods, and registration authorities are requesting more detailed record keeping and data validation. This second edition addresses these developments and fulfills the original goal of publishing guidelines for high quality, scientifically valid testing standards for trials that would be accepted as proof of efficacy by registration authorities regardless of country of origin. This second edition includes updated guidance on standard parasitological procedures, dose titration, dose confirmation and clinical trials, and provides guidelines for evaluating products for efficacy against anthelmintic resistant parasites, persistence of activity and prophylactic activity. Tests for efficacy against nematodes, trematodes and cestodes are included.

The heritability and specificity of responsiveness to infection with Haemonchus contortus in sheep.

High responder (HR) and low responder (LR) lines of sheep of the Hungarian Merino breed were selected by using faecal egg counts (epg) as parameter of responsiveness after double artificial Haemonchus contortus test infections. A total of 81 lambs born to assortative matings of HR rams with HR ewes and LR rams with LR ewes, as well as 28 control lambs from unselected parent sheep, were studied to estimate the heritability of responsiveness. A relatively high level of heritability (h2 = 0.49 +/- 0.17) was observed. A comparative assessment of responder classification carried out by two subsequent and distinct H. contortus and Trichostrongylus colubriformis infections revealed a remarkable degree of agreement: identical results in 69.7% and marginal differences in 23.2% of 99 animals. These results suggest that by selecting sheep for high responsiveness to a certain species of nematodes, one can also achieve a substantial improvement of resistance against a wide range of other nematode species.

The distribution of nematode egg counts and larval counts in grazing sheep and their implications for parasite control.

The frequency distribution of gastrointestinal nematode egg and lungworm larval counts was examined in 101 and 87 naturally infected ewes on two farms. The egg and larval outputs of the two flocks followed the negative binomial pattern of distribution (with k values below unity) at each time of sampling, which suggests highly overdispersed worm burdens. The results of the statistical analysis indicated that a relatively small part of the two flocks was responsible for the excretion of the majority of both gastrointestinal nematode eggs and Dictyocaulus filaria larvae. It is concluded that by eliminating "wormy" individuals of flocks either by selective breeding or by their selective anthelmintic treatment, effective control of parasite transmission can be achieved. Because of the phenomenon of nematode "clumping" it seems necessary to expand new methods for estimation of flock productivity caused by nematodes in livestock and to incorporate negative binomial parameter (k) in mathematical models of nematode population dynamics.

Is there a relationship between haemoglobin genotype and the innate resistance to experimental Haemonchus contortus infection in Merino lambs?

Responses to a single or repeated infection with 7000 infective larvae of Haemonchus contortus were studied in an experiment using a total of 106 3-month-old lambs with AA, AB or BB haemoglobin (Hb) genotypes. Results were assessed by faecal egg counts, adult worm counts, haematocrit values, haemoglobin concentrations, total serum protein and serum antibody IgG1 and IgA ELISA titres. None of these parameters showed a strong relationship to the Hb type. The prevalence of low responder (greater than 500 worms) and of high responder (less than 50 worms) animals in groups AA, AB and BB Hb types was 3.8 and 34.6, 20.6 and 35.2, 28.1 and 43.7%, respectively, suggesting that the responsiveness to nematode infection is under the control of gene(s) not closely linked with those determining the Hb genotype. Worm counts of a primary infection are more subject to variation than those of a secondary infection. There is a strong relationship between adult worm counts and faecal egg counts taken close to the time of slaughter. In living animals low and high responder discrimination can be based on individual faecal egg counts around 50 days after a secondary infection. Haematocrit values proved to be of little value in the low and high responder selection. In this regard neither Hb concentration nor total serum protein values are of practical significance. In 3-month-old lambs primary infection induced partial immunity which could prevent the establishment of a part of the secondary infection, irrespective of the presence or absence of the primary worm population. The development of immunity was not associated with an increase of serum IgG1 and IgA antibody levels. Specific antibody production was not influenced by Hb types. Mean antibody levels of low responder lambs showed no difference from those of high responders. Thus, serum IgG1 and IgA levels are of no predictive value in identifying lambs which are genetically resistant to Haemonchus infection.

Complement C2, C3, C4 and factor B allele distribution in the Gipsy population in Hungary.

Allotype frequencies of four complement proteins (C3, C2, factor B, and C4) were tested in 150 healthy Hungarian and 126 healthy Gipsy individuals living in Hungary. We observed significant differences between the two ethnic groups in the incidence of C3*F, Bf*F, C4A*Q0, C4A*3, C4B*1 and C4B*2 allotypes. Bf*F occurred more frequently among Gipsies, while frequencies for the other three allotypes was lower in this group than in Hungarians. The similarities in the allotype frequencies of C3 and Bf among Gipsy and Gaddis (India) populations supports the Indian origin of the former ethnic group.

Standardized nomenclature of animal parasitic diseases (SNOAPAD).

An expert committee, appointed by the Executive Committee of the World Association for the Advancement of Veterinary Parasitology (W.A.A.V.P.), presents its proposal for uniform and proper terminology to denominate animal parasitic diseases or infections. In principle, the disease name is constructed solely by the suffix -osis, which is added to the stem of the name of the parasite taxon, formed from the nominative of the taxa. Standardized nomenclature of animal parasitic diseases (SNOAPAD) is meant as a guideline for general use, to improve the clarity of scientific communication. It should be especially useful in promoting effective usage of computerized data retrieval services.

Screening of IgA deficiency by ELISA: population frequency in Hungary.

The probability of the development of an anaphylactic shock in IgA deficient patients following repeated blood transfusion or the administration of any other IgA containing preparation is high. Since these individuals usually show mild, if any, clinical symptoms, the detection of deficiency and/or sensitisation is very important. We have developed an ELISA system suitable for both the rapid mass screening of IgA deficiency and for the detection of anti-IgA already present in the serum. Applying these methods for screening of serum IgA deficiency in healthy Hungarian population resulted in a similar pattern to that reported for other countries. Interestingly, the prevalence of IgA deficiency among Gipsies living in Hungary was significantly higher. We could detect anti-IgA only in one of our IgA deficient patients.

Activity of luxabendazole against liver flukes, gastrointestinal roundworms, and lungworms in naturally infected sheep.

The anthelmintic potential of luxabendazole was investigated in sheep harboring mixed naturally acquired helminth infections. Results were assessed by comparing worm counts of the treated groups (seven animals each) on days 7-8 posttreatment with those of the nontreated control group, except for protostrongylid lungworms, for which the changes in pre- and posttreatment group mean larval counts/g feces were assessed for intensity effect. A single oral treatment at doses of 10.0 or 12.5 mg/kg body wt removed 97.6% of the adult Fasciola hepatica and 63.2%-83.8% of the Dicrocoelium dendriticum. Luxabendazole at 7.5, 10.0, and 12.5 mg/kg proved 100% effective in removing adult worms of the genera Haemonchus, Ostertagia, Trichostrongylus, Cooperia and Nematodirus as well as tissue-associated larval stages of gastrointestinal nematodes of the abomasal mucosa. The drug showed an intensity effect of 79.7%-87.6% against Strongyloides papillosus. Luxabendazole removed all Dictyocaulus filaria and reduced the fecal excretion of larvae of protostrongylid species (Protostrongylus rufescens, Neostrongylus linearis, Cystocaulus ocreatus, Muellerius capillaris) by 97.8%-99.6%. The efficacy of luxabendazole compared favorably with that of Diplin Kombi (oxyclozanide and levamisole), which was used as a reference drug.

The reversibility of intestinal immune expulsion effects on adult Nippostrongylus brasiliensis.

An attempt has been made to study the extent and nature of the damage occurring in adult Nippostrongylus brasiliensis undergoing immune expulsion from the rat. It was found that worms are not killed nor irreparably damaged when being rejected. On transfer into naive second recipient rats the rate of re-establishment of worms previously incubated in immune rat recipients for 4-17 hr was high (68-69%) and comparable to that shown by worms from normal recipient rats (48-56%). Similarly, worms taken on days 10, 11, and 12 of a primary infection, already passed to the distal half of the small intestine due to immune expulsion effects, on transfer into naive recipient rats re-established themselves well (rates varying from 62 to 80%) compared to those harvested from their normal habitat in the proximal half of the small intestine (rates varying from 44 to 87%). Worm damage is associated with decreased motility and impaired locomotion capacity. The phenomenon of mucosal trapping occurs during expulsion, but merely to the extent of some 30% of the worm population. It is suggested that in principle, worms subjected to immune expulsion are in a state of acute, transient metabolic crisis. The present results support the enteroallergic indirect mechanism for worm rejection.

A protease inhibitor of Nippostrongylus brasiliensis.

Somatic extracts of Nippostrongylus brasiliensis contain protease inhibitor(s) capable of inhibiting the activity of trypsin and chymotrypsin A and B. This inhibitor was partially purified by affinity chromatography. Its molecular weight is in the range of 9500-10 000. The inhibition of both trypsin and chymotrypsin depends on the same or closely adjacent active sites of the inhibitor molecule. The inhibitor is unaffected by heating, pH changes or urea, but is sensitive to 2-mercaptoethanol The formation of the enzyme-inhibitor complex is time-dependent. The complex does not dissociate with KC1. The inhibitor has no effect on the activity of elastase, subtilisin, pepsin, rennin, papain and collagenase.

[Immunological reactivity of the host as an environmental factor and its significance for the development of parasitism]. / Die immunologische Reaktivität des Wirtes als Umweltfaktor und ihre Bedeutung für die Entwicklung des Parasitismus.

Concepts--mainly of SPRENT (1959, 1963), DINEEN (1963) and DAMIAN (1964)--concerning the immunological aspects of the phylogeny of host-parasite associations and the function of immune processes in the host-parasite relationship are discussed. In the light of some recent findings an integrating interpretation of the available body of evidence is attempted. The significance of the immuno-selection pressure during the course of host-parasite coevolution is stressed and some of the consequences of this pressure seen in the existing host-parasite systems are pointed out.