الفهرس 
Host-parasite relationshipOnly 14 pages are availabe for public view
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Abstract
Under certain conditions larvae of many ascarid
nematodes become dormant during the histotropic phase of
their development. This phenomenon is often referred as arrested larval development. The stage at which development is inhibited differs in different species, and the mechanisms involved appear to be complex. According to generally accepted opinion, inhibited development of nematodes depends on external environmental factors and parasite-related factors. During Ascaris infection, acquired resistance is reflected by increased serological, hematological responses and decreased recovery of worms from lungs and small intestine (Eriksen, 1982). The aim of the present work was to investigate, under laboratory conditions and in the laboratory model system (Neoascaris vitulorum), the host-parasite relationship mechanisms. For such purpose some experiments were carried out to investigate: (1) the effect of the dosage level on the infectivity of the embryonated eggs and the migratory pattern of the larvae;(2) the effect of some commonly, used food additives on the infectivity and development of Ascaris larvae; (3) the effect of superimposed and challenge infection on the dynamics of the host-parasite relationship, including the immunological status of the host and (4) the baseline survival characteristics for the infective embryonated eggs of Neoascaris vitulorum. The series of experiments were carried out using adult outbred male and female albino rats. Effectiveness of infection and percentage of protection at postmorten and changes in total and differential leucocyte counts were studied. The sera and mucosal extracts of the small intestine were collected at postmortem. Total serum protein concentrations were estimated employing the method of Lowry et al. (1951). Electrophoreisis on 10% polyacrylamid gel, for quantitative evaluation of protein fractions in sera, was used. Antibodies were determined in antisera and intestinal mucosae with hemagglutinating and precipitating tests. The following results were obtained: 1. Postmortem examinations indicated that the effectiveness of infection was correlated with the dose size of infective eggs. The infectivity was inversely propotional to size of the infective dose. The infective eggs lost most of their ability to infect or to complete their migration when stressed on by some food additives. Also, the dissection results indicated aUself-cure” reaction, which is manifested by a decrease in larval recovery and an increase in the antibodies levels and the percentage of protection. Additionally, a significant increase in the percentage of protection (82,8%) was obtained after immunization and challenge on day 32 with 3000 embryonated eggs. Furthermore, combination of temperature and moisture showed no significant effect on the migratory pattern of -N. vitulorum, while only temperature had such effect. The 40•‹C temperature could be considered as a good stimulus for the migratory enhancement of larvae from liver and lungs to intestine. On
the other hand, the sudden chilling (15”C-4”C) and low temperature ( 4 • ‹ C ) induced larvae to remain two days longer in liver and three days or more in lungs. 2. Haematological studies revealed peripheral blood changes both in total and differential leucocyte counts after single, second and challenge infections. The embryonated eggs attenuated under condition of this study, as well as fresh embryonated eggs, did not differ in their pathogenicity in leucogram during the course of infection and the reinfection had a small effect on leucogram. 3. Hypoproteinemia occured in sera after single and challenge infections. The dysproteinemia in sera resulted from a hypoalbuminemia, hyper- oc, -B and - 3 - globul inemia. A marked increase in B and’2j- globulins levels was observed after challenge infection. 4. Local antibody responses were demnostrated in intestinal mucosal and the reactions were obtained with the tissue fluids in hemagglutination (after single and challenge infection) and precipitation tests (only after superimposed and challenge infection). Also, the results suggest a clear-cut relationship between increased level of antibodies and larval expulsion, or the degree of protection.