The interaction between Cooperia spp. and Ostertagia spp. (Nematoda: Trichostrongylidae) in cattle

anglais. In this study the presence of interaction between Cooperia oncophora and Ostertagia ostertagi, nematodes which parasitize the small intestine and the abomasum of cattle, respectively, has been investigated. Interaction is of epidemiological importance when it leads to a reduced worm burden or a lowered faecal egg output. As there were some indications that interaction between C. oncophora and O.ostertagi is immunologically, mediated experiments were carried out in which calves were given some degree of immunity by inoculation with one of both species. By means of challenge infections it was examined whether this immunity affected the heterologous species or not. The effect of concurrent infections was also investigated.During the experiments the course of infection was monitored by faecal egg counts. Other parasitological parameters, worm numbers, worm length, number of eggs in utero (indicating the fecundity and vulval flap development of O.ostertagi females, were determined post mortem. By making use of the Enzyme-Linked-ImmunoSorbent Assay (ELISA), the relative amount of serum IgG was measured to examine whether the interaction is immunologically mediated or not. Additionaly, the numbers of some effector cells were counted in tissue fragments of the small intestinal and abomasal mucosa.Experiment I concerned 48 calves that were divided into 4 groups of 12 calves each. One group was kept as non-infected controls whilst the other groups received a single dose of 50*10 3, 100*10 3or 200*10 3C. oncophora larvae, respectively. These primary infections were terminated by anthelmintic: treatment on day 35 p.i. One week later the 4 groups were split into 3 subgroups of 4 animals each. These subgroups were infected with 100*10 3C. oncophora larvae, 100*10 3O. ostertagi larvae or a mixture of both doses, respectively. All calves were slaughtered on day 33 post challenge infection for post mortem examinations. The aim of exp. 1 was to investigate whether the acquired immunity against C. oncophora influenced O. ostertagi or not and, if so, whether this influence depended on the primary inoculation level or not. From the results of exp. I could be concluded that some degree of immunity was present against C. oncophora. This could be demonstrated by the reduced worm burdens, worm fertility and worm length in primarily infected groups when compared to primary controls. The negative relation between serum IgG titre counts and the parasitological parameters indicated that the host's immune response was involved. This immunity against C. oncophora however, had marginal affects on a subsequent O. ostertagi infection. Only the length of the abomasal worms was significantly reduced by a previous C. oncophora infection. This length was also negatively influenced by concurrent infections.The design of exp. 2 was equal to the one of exp. 1 except that the primary infection was carried out with several doses of O. ostertagi larvae (25*10 3, 50*10 3or 100*10 3). The aim of this experiment was to examine whether a previous O. ostertagi infection affects a subsequent C. oncophora infection or not. The results of this experiment demonstrated that some degree of acquired immunity against O. ostertagi existed after priming. This resistance led to reduced fertility, stunted growth and inhibited development (vulval flap) of O. ostertagi , but did not negatively affect the worm numbers. Immunity directed to O. ostertagi had little influence on C. oncophora . Only the length of the small intestinal worm was reduced, but due to the small group sizes this reduction was statistically not significant.Therefore, it was decided to enlarge the groups sizes in exp. 3. In this experiment priming was performed with repeated (3 times a week during 30 days) small doses of 7*103 C. oncophora larvae (16 calves) or 7*103 O. ostertagi larvae (16 animals); a third equally sized group was kept as control. Repeated dosing was carried out to imitate the natural situation. After anthelmintic treatment all calves were challenged with 100*10 3larvae of both species. The results showed that resistance to homologous species was present in the homologous situation the worm numbers and the growth and the development of the worms were reduced. The fecundity was also negatively affected for O. ostertagi . Reciprocal cross resistance was found for the worm growth and the development whilst the fecundity of O. ostertagi was also lowered by C. oncophora priming.In the fourth experiment the repeatibility of the previous experiments was assessed. The calves were allotted to 3 groups of 12 animals each. The primary infection was equal to the one in exp. 3. After anthelmintic treatment the primary groups were split into 3 equally sized subgroups. These subgroups were challenged as in exp. 1 and 2. With regard to C. oncophora there seemed to be no effect of priming. This was merely due to a loss of worms from primarily non-infected calves. The results from O. ostertagi infections were about equal to the results obtained in exp. 3.A fifth experiment was carried out to come to a conclusion about the relation between the local responses in the gastrointestinal tract and the occurrence of interaction. Cannulas were placed in the small intestine and the abomasum of six calves. This made it possible to collect tissue fragments of the small intestinal and the abomasal mucosa. The infections were equal to the ones in exp. 3 except that the primarily non-infected calves were also kept as controls during the challenge period. Histological examinations of the tissue fragments revealed that several cell types were involved in the local reactions. The numbers of eosinophils and IgM-, IgG 2 - and IgA plasma cells increased during the primary and the challenge infection. No response of these cells was found in the non-infected organ during the primary infections. This indicates that a response in the abomasaI mucosa is not expressed at the small intestinal level and vice versa . After the mixed challenge a very rapid response was seen in both organs when compared to the primary infection. Whether these accelerated reactions were due to priming or not could not be unequivocally proven, because they might also originate from the size of the dose, the repeated versusthe single inoculation or the age of the host at the moment of inoculation.From the results of exp. 1 to 4 can be deduced that interaction between C.oncophora and O. ostertagi exists. This interaction is expressed in a stunted growth and development of worms, but it does not affect the worm burden or the faecal egg output.The fact that interaction was only found in a sequential infection model implies that the host's immune response is involved by mediation of this interaction. This is also obvious when the negative relation between parasitological parameters and heterologous antibody levels are considered. The mechanism by which immunoglobulines affect parasitic nematodes is not known, but since they have affinity to secretory/excretory antigens, it is possible that antibodies interfere with enzymes that are necessary for normal growth and development.In many parasite-host models interaction between nematode species is of epidemiological importance, because it has a negative or positive influence on the size of the worm population or the faecal egg count.The results from experiments described in this thesis do not imply that such importance is present in the C.oncophora-O. ostertagi -calf model. However, when parameters indicating growth and development of worms are used as parameters that measure resistance it should be considered that these parameters are influenced by a previous heterologous infection.

néerlandais; flamand. Dit onderzoek heeft zich toegespitst op de vraag of er een interactie bestaat tussen Cooperia oncophora en Ostertagia ostertagi, nematoden die parasiteren in respectievelijk de dunne darm en de lebmaag van het rund. Een interactie tussen beide soorten is van epidemiologisch belang, wanneer dit leidt tot een veranderde wormlast of ei-uitscheiding. Aanwijzingen dat de interactie tussen beide nematodensoorten via de immuun respons verloopt leidden tot experimenten, waarin aan kalveren de gelegenheid werd gegeven om immuniteit op te bouwen tegen een van beide soorten. Vervolgens werd nagegaan of deze immuniteit van invloed was op de andere soort. Ook de invloed die beide soorten op elkaar uitoefenen bij gelijktijdige aanwezigheid in dezelfde gastheer werd onderzocht