The primary sites of Aujeszky's disease virus (ADV) multiplication in intranasally (i.n.) infected pigs were found to be in the nasopharyngeal, tracheal and pulmonary regions. From the second day post infection (DPI) onward ADV invaded the central nervous system and other organs. The virus was isolated from the nasopharyngeal region for at least 2 weeks. In serum ADV was present with low levels from DPI 1 to DPI 7. In pigs vaccinated with an inactivated vaccine and then challenged the distribution of ADV was rather similar to that in non-vaccinated animals, in spite of the presence of neutralizing antibodies. The virus titres in the organs generally were lower than in non-vaccinated animals up to DPI 7. Thereafter, titre differences were no longer significant. Virus was isolated from the tonsils and the lungs for at least 2 weeks. Interferon production in vaccinated infected pigs was significantly lower than in non-vaccinated infected pigs. Though multiplication and dissemination of ADV occurred, vaccinated pigs did not show clinical symptoms of Aujeszky's disease. Traces of ADV were detected in a small percentage of white blood cells (WBC) of non-vaccinated infected pigs. ADV was isolated from the lymphocyte-enriched and polymorphnuclear leukocyte-enriched fractions, but not from the monocyte-enriched fractions, apparently on account of the small cell number. Multiplication of ADV was demonstrated in cultured WBC from some of the vaccinated and non-vaccinated infected animals.

The appearance of cell-mediated immunity was studied in Aujeszky diseased pigs with the aid of the in vitro stimulation of sensitized lymphocytes. The first cell-mediated immunity reaction of lymphocytes occurred 4 days after infection. From day 7 to 35, the latest day tested, the reactions were most marked with lymphocytes from lymph nodes and spleen, whereas blood and thymus lymphocytes reacted less frequently; bone marrow lymphocytes showed no response. Reinfection did not considerably enhance lymphocyte reactivity. Humoral immunity was demonstrated a few days later than cell-mediated immunity. Neutralizing antibodies were first detected at day 7, reaching optimal titers at day 14. Complement fixing antibodies were detected from day 14 onward. Reinfection caused a very weak booster effect only on neutralizing antibody production. The sensitivity of the neutralization test could be enhanced up to sixfold by the addition of fresh guinea pig complement. It is concluded that cell-mediated immunity influences the early stage of infection with Aujeszky disease virus when humoral immunity is not yet demonstrable or yet rather low. Lymph nodes and spleen are apparently of special importance for the appearance of ADV-reactive lymphocytes.

Zusammenfassung Nach Impfung von 6–8 Wochen alten Ferkeln mit einer Aujeszkyvirus (AV)‐Vakzine, die aus Äthylenimin‐inaktivertem Virus und DEAE‐Dextran als Adjuvans bestand, konnten neutralisierende Antikörper zum ersten Mal eine Woche nach der Impfung nachgewiesen werden. Während des geprüften Zeitraumes (6 Wochen) waren die Titer relativ nieder und die Mittelwerte zeigten keinen signifikanten Anstieg oder Abfall. Im Gegensatz zur Antikörperbildung traten bei den vakzinierten Tieren nach intranasaler Testinfektion zeitlich bedingte Immunitätsunterschiede auf. Während die vakzinierten Tiere eine Woche und 2 Wochen post vacc. immun waren, konnte 3 Wochen post vacc. ein gewisses Nachlassen des Impfschutzes festgestellt werden. Dagegen war der Impfschutz 6 Wochen post vacc. wieder stark ausgeprägt. Letzteres dürfte damit im Zusammenhang stehen, daß nach dem Verhalten der infizierten nicht vakzinierten Kontrolltiere zu schließen, die natürliche Resistenz von Ferkeln gegen das AV mit zunehmendem Alter rasch ansteigt. Die Ergebnisse wurden im Hinblick auf die Impfprophylaxe gegen AV besprochen. Summary Early stages of immunity after vaccination of piglets with an inactivated Aujeszky virus vaccine Vaccination of 6–8 week old piglets with an Aujeszky virus (AV) vaccine, consisting of ethyleneimine‐inactivated virus and DEAE dextran as adjuvant, resulted in detectable neutralizing antibody levels one week later. The titres were rather low and the mean values showed no significant rise or decline during the test period (6 weeks). Contrary to antibody production the vaccinated animals showed differences in protection against intranasal challange infection depending on vaccination time elapsed. One week and 2 weeks post vacc. the vaccinated animals were immune, whereas 3 weeks post vacc. a partial reduction of protection could be found. However, protection was very good again after 6 weeks post vacc. This may be connected with the finding that natural resistance of pigs against AV rises with age, as was shown by the infection of non vaccinated control pigs. The results are discussed with regard to immune prophylaxis against AV. Résumé Stades précoces de l'immunité après une vaccination de porcelets avec un vaccin inactivé du virus de la maladie d'Aujeszky Des anticorps neutralisants sont apparus une semaine après la vaccination de porcelets âgés de 6–8 semaines avec un vaccin du virus de la maladie d'Aujeszky (AV) inactive par l'éthyleninine et avec DEAE‐dextran comme adjuvant. Les titres furent relativement bas durant le temps d'examination (6 semaines) et les valeurs moyennes ne présentèrent aucune élévation ou chute spécifique. Certaines différences d'immunité sont intervenues dans la formation d'anticorps chez des animaux vaccinés après une infection intranasale expérimentale. Alors que les animaux vaccinés étaient immunisés une et deux semaines après la vaccination, on a constaté une certaine faiblesse de la protection vaccinale après trois semaines. La protection fut à nouveau renforcée six semaines après la vaccinati...

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Summary The results of Aujeszky virus titrations in rabbits, rats, mice and pigs show that rabbits are apparently the most susceptible animals. Zusammenfassung Vergleich der Empfindlichkeit von Kaninchen, Ratten, Mäusen und Schweinen gegen eine Infektion mit Aujeszkyschem Virus Nach vergleichenden Titrationen von Aujeszkyschem Virus in Kaninchen, Ratten, Mäusen und Schweinen hat sich gezeigt, daß Kaninchen gegen das Aujeszkysche Virus am empfindlichsten sind.