In the present study the behavior and pathogenicity of second-stage larvae of Toxocara canis were examined in different mouse strains with special emphasis on the major histocompatibility complex (MHC). Mice of the inbred strains BALB, C3H, C57BL, and DBA and the outbred strain NMRI were infected orally with 1000 second-stage larvae of T. canis. The clinical behavior of the animals; the numbers of larvae detected in the liver, lungs, brain, and musculature; the hematological and serological parameters; and histological sections were examined. In mice of the BALB strain, no death occurred during the entire period of the investigation and the pattern of body-weight development of infected and uninfected animals was almost identical. The highest larval counts in the brain of all strains were found in BALB mice. The percentage of eosinophils in the blood of BALB mice increased after the 8th week postinfection, whereas it decreased in the other strains. Histological and pathophysiological changes developed to a lesser extent in this strain than in the other strains. In mice of the strains C3H, C57BL, DBA, and NMRI, deaths occurred from the 4th week postinfection onward. The infected animals lost weight in comparison with the uninfected controls; the number of larvae found in the brains of infected mice of the above-mentioned strains were lower than those detected in the BALB strain. There is no evidence that mechanical damage caused by migrating larvae in the brain tissue is mainly responsible for symptoms of central nervous toxocariasis. Likewise, the assumption that the MHC is involved in the allergic-inflammatory response in the brain could not be proven: infected mice of the BALB and DBA strains reacted completely differently, although both are equipped with the same MHC haplotype.

During the seal epidemic in 1988 and the beginning of 1989, 115 common seals found dead on the shores of the Wadden Sea of Lower Saxony were investigated for the presence of nematodes. The lungworm Otostrongylus circumlitus RAILLIET 1899 was found in 26.1 % of the seals, the lungworm Parafilaroides gymnurus RAILLIET 1899 in 26.9 % and the heartworrn Dipetalonema spirocauda LEIDY 1858 in 32.2 % of the seals. In the digestive tract, two anisakid species were found, Pseudoterranova decipiens MOZGOVOI 1951 in 87.8 % and Contracaecum osculatum RUDOLPHI 1802 in 10.4 Yo of the seals. Statistical analysis revealed a negative correlation between age of the seals and prevalence and intensity of infestation with the two lungworm species and the heartworms. Adult seals were found not to be infected with Dipetalonema spirocauda and Parafilaroides gymnurus, whereas the prevalence of the two anisakid species increased with increasing age of the seals. Pseudoterranova decipiens was found more often in autumn and winter than in summer. This parasite was more prevalent and had higher worm counts in the eastern part of the Wadden Sea than in the western part. Parafilaroides gymnurus and Dipetalonema spirocauda were found more often in seals with smaller blubber thickness than in well fed seals.

Adult as well as preadult Toxocara canis isolated from the intestine of a beagle were incubated for 2, 4, and 14 h in medium containing either different concentrations of pyrantel pamoate (23.6, 236, and 2360 micrograms/ml medium) or tritiated pyrantel pamoate (2.36 micrograms/ml medium). These incubations were performed to study the effects of pyrantel pamoate on the morphology of the parasitic nematodes and to obtain information concerning the mode of uptake, the distribution, and the total amount of pyrantel pamoate ingested by T. canis. The results of the ultrastructure studies indicate that the intestine, hypodermis, and muscle cells are the organs that are predominantly affected by the drug. Additionally, it turned out that the duration of the treatment, i.e., the incubation time, was more important in determining the efficacy of pyrantel pamoate against T. canis than was the concentration itself. Autoradiography studies revealed that the adult worms ingest the drug orally, whereas preadults absorb pyrantel pamoate mainly through the whole body surface. Finally, measurements of the total amount of pyrantel pamoate taken up by T. canis indicated that adult worms can limit or even reduce the ingestion of pyrantel for more than 4 h, but then ingest large amounts of the drug. Preadult worms, however, absorb the drug more or less continuously during the first 14 h through the cuticula, albeit in lower concentrations than the adults. The different experiments elucidate differences in the uptake of pyrantel pamoate as well as in the total amount of drug ingested or absorbed by adult or preadult worms, leading to the assumption that repeated treatment with lower concentrations will be more effective than high concentrations given only once.

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Zusammenfassung Die vorliegenden Untersuchungen erfolgten mit der Zielsetzung, den Einfluß sich ausbildender und bestehender Immunität des Wirtes auf die Wanderung und Streuung der Larven von Toxocara canis im Hund zu erfassen. Dazu wurden in getrennten Versuchsreihen der Umfang und Ablauf der Larvenausscheidung mit der Milch und die Zahl somatischer Larven in verschiedenen Organen von Muttertieren nach Erst‐ und Reinfektion bei einmaliger wie auch fraktionierter Gabe von Infektionsstadien ermittelt. Begleitende hämatologische und serologische Untersuchungen sollten Hinweise auf Ort, Art und zeitlichen Ablauf der Immunreaktion im Tier geben. Es wurden u. a. folgende Ergebnisse erzielt: Nach Erstinfektion bei einmaliger Gabe der Infektionsstadien war die Larvenausscheidung mit der Milch und die Zahl somatischer Larven in peripheren Organen der Tiere signifikant größer als nach fraktionierter Erstinfektion oder nach Reinfektion. Von fraktioniert infizierten Tieren wurden signifikant weniger Larven mit der Milch eliminiert als von in gleicher Weise und Stärke erstmalig infizierten Hündinnen. Die Zahl somatischer Larven in peripheren Organen der Tiere differierte jedoch nach fraktionierter Erst‐ und Reinfektion nur unwesentlich. Bei allen Tieren kam es während der arttypischen Wanderung der Larven von Toxocara canis zu einem Aktivitätsanstieg der leberspezifischen Enzyme ALT und GLDH wie auch der Zahl eosinophiler Granulozyten. Ihre Werte waren nach Reinfektion weniger stark erhöht als nach Erstinfektion. Antikörper gegen Larven von Toxocara canis konnten mit dem IFAT und dem ELISA bei allen Hündinnen erst nach experimenteller Infektion nachgewiesen werden. Nach Reinfektion stiegen die Titer bei sämtlichen Tieren innerhalb von 14 Tagen um mindestens eine Stufe. Nach Reinfektion kam es bei allen Hündinnen zu katarrhalisch‐hämorrhagischer Enteritis und Inappetenz. Mit zeitlicher Verzögerung und in abgeschwächter Form traten solche Erscheinungen auch bei Tieren nach Erstinfektion bei fraktionierter Applikation der Infektionsstadien auf. Die erhobenen Befunde ließen in ihrer Gesamtheit vermuten, daß bei bestehender Immunität die Einwanderung der Larven von Toxocara canis in den Organismus durch am Darm ablaufende entzündlich‐allergische Prozesse begrenzt wird. Summary Studies on the migration and distribution of larvae of Toxocara canis Werner 1782 (Anisakidae) in the definitive host (Beagle) after primary and reinfection The objective of these studies was to investigate the developing and existing immunity of the host and its influence on the migration and spread of the larvae of Toxocara canis in the dog. Separate studies were made of the extent and course of larval excretion with the milk and the number of somatic larvae in various organs of the dam after initial and reinfection after single and also fractionated doses of the infective stage of the parasite. Accompanying histological and serological studies were made on the location, nature and time relations of the immune reaction in the host. The following are t...