The local immune response of newborn piglets to experimental infection with rotavirus was analyzed by means of coproantibodies, immune complexes, and the detection of rotavirus. Immune complexes appeared in the feces on day 4 after inoculation when the production of rotavirus began to decrease; they reached a peak when no rotavirus could be detected in the feces. The presence of free IgA and IgM antibodies to rotavirus could be demonstrated on day 7 when the immune complexes had already reached a maximum level. An enzyme-linked immunosorbent assay was used for all of the analyses.

Aynaud, J.M., Bernard, S., Bottreau, E., Lantier, I., Salmon, H. and Vannier, Ph., 1991. Induction of lactogenic immunity to transmissible gastroenteritis virus of swine using an attenuated coronavirus mutant able to survive in the physicochemical environment of the digestive tract. Vet. Microbiol., 26: 227-239.A transmissible gastroenteritis (TGE) coronavirus mutant (188-SG), selected as attenuated and resistant to acidity and proteases of the digestive tract of adult pigs, was used as vaccine ("Nouzilly strain") in sows to protect suckling piglets against a challenge exposure carried out with a highly virulent TGEV strain. The pregnant sows were immunized once (42-49 days before farrowing) or twice (42-49 and 7-15 days before farrowing) by the oral, intramuscular or conjunctival route with the 188-SG strain. Sows exposed to virulent TGEV in the field and experimentally infected sows (two oral inoculations during pregnancy) were used as positive controls leading to high protection. The neutralizing antibody response to vaccination and/or infection was studied in serum and milk. No protection against mortality was observed in the litters of ( 1 ) the nine seronegative, susceptible sows, with piglet mortality of 65/70, (2) the seven once orally vaccinated sows, with mortality of 44/54, (3) the seven sows vaccinated twice by the conjunctival route, with mortality of 55/76. Moderate protection was observed in ( 1 ) the eight sows vaccinated intramuscularly twice with piglet mortality of 36 / 90, ( 2 ) the seven orally and intramuscularly vaccinated sows with piglet mortality of 31 / 51. In contrast, improved protection was observed in ( 1 ) the 10 sows vaccinated twice orally, with piglet mortality of 23/95, (2) the four naturally infected sows with piglet mortality of 6/41, (3) the six sows experimentally infected with virulent TGEV with piglet mortality of 1/59. No correlation was found between neutralizing antibodies titers in serum and milk and protection rate of the piglets. The results indicate that relative protective lactogenic immunity against TGEV is induced only by repeated ingestion of the attenuated 188-SG strain of TGEV.

A serological survey made in France reveals a rather large diffusion of the Parvovirus among pig herds. 45

potential applications in the field of diagnosis and vaccination. The use of monoclonal antibodies in research and survey laboratories is now widespread concerning viruses of the classical and African swine fever, Aujeszky's disease, Transmissible gastroenteritis and is extending to bacteriology (Salmonella, Mycoplasma). Nucleic acid probes, presently used as research tools, might also be applied to routine detection of infectious agents. Genetic engineering has allowed the development of several new strategies for immunoprophylaxis : synthetic peptides, recombinant antigens, non-pathogenic live vectors, attenuation by gene deletion. So far, the only commercialised recombinant vaccine is against E. coli-enterotoxicosis in the piglet. Designing of recombinant attenuated strains of pseudorabies virus is in rapid progress. The possibility to differentiate vaccinated from infected animals will be one of the major advantages of the future vaccines.

Summary A low virulence strain of classical swine fever virus isolated from a natural outbreak was studied in experimentally infected weaned pigs. Individual susceptibility was prominent in the development of clinical signs and the severity of the disease among post‐weaning piglets. Duration of hyperthermia ranged from one to nineteen days; 40% of the animals died, but the survivors were only slightly affected in their final growth rate. Survivors did not excrete the virus for longer than 26 to 30 days after they were inoculated and the virus was not detected in the organs of the animals after euthanasia 60 days or more after infection. Zusammenfassung Experimentelle Untersuchungen mit einem schwach virulenten Schweinepeststamm: Individuelle Variation und horizontale Übertragung Ein schwach virulenter Stamm des klassischen Schweinepestvirus, bei einer natürlichen Erkrankung isoliert, wurde anhand experimenteller Infektionen untersucht. Die individuelle Empfänglichkeit kam in den klassischen Erscheinungen und der Schwere der Erkrankungen bei Ferkeln nach dem Absetzen zur Geltung. Die Fieberphase hielt zwischen einem und 19 Tagen an. 40% der Tiere verendeten, die Überlebenden jedoch waren in der Wachstumsentwicklung kaum beeinträchtigt. Überlebende Tiere schieden das Virus nicht länger als 26 bis 30 Tage nach der Infektion aus. Nach dem 60. Tag wurde bei getöteten Viren kein Virus mehr in den Organen nachgewiesen. Résumé Recherches expérimentales avec une souche faiblement virulente du virus de la peste porcine: Variation individuelle et transmission horizontale Une souche faiblement virulente du virus de la peste porcine classique isolée à partir d'une infection naturelle a été étudiée par infection expérimentale. La seminilité individuelle est apparue predominante dans la gravité de la maladie chez des procelets sevrés. La phase fièvreuse a duré entre 1 et 19 jours. La mortalité a atteint 40% des animaux; les survivants furent cependant peu atteints dans leur développement. Les animaux survivants n'ont pas excrété le virus au‐delà de 26 à 30 jours. Aucun virus n'a pu être mis en évidence dans les organes des animaux abatus après le 60e jour. Resumen Estudios experimentales con una estirpe de peste porcina débilmente virulenta: Variación individual y transmisión horizontal Una estirpe débilmente virulenta del virus de la peste porcina clásica, aislada en una enfermedad natural, se examinó a base de infecciones experimentales. La receptividad individual se puso de manifiesto con los síntomas clásicos y la gravedad de las dolencias en los lechones tras el destete. La fase febril persistió entre un y 19 días. Sucumbió el 40% de los animales, mas los supervivientes apenas sufrieron en el desarrollo de su crecimiento. Los animales que supervivieron no eliminaban el virus más allá que 26 hasta 30 días tras la infección. Después del día 60° ya no se localizó ningún virus en los órganos de los animales matados.