Observations on pathogenic organisms in the airborne state

Summary Increasing numbers of human and animal diseases have been shown to be disseminated by micro-organisms in aerial suspension. The viability of such airborne organisms declines progressively as the result of physical and other factors which are summarized in the text. Relative humidity strongly influenced viability in experimental studies, but strain differences also appear to play an important role in certain diseases. Laboratory results were confirmed by observations made in the field on poliomyelitis, smallpox, foot and mouth disease, rinderpest and Newcastle disease; it is probable that Marek's disease, avian infectious bronchitis and numerous other maladies spread in the same manner. Long range dissemination by airstreams may be influenced, to some extent, by the virulence of the causal agent and by the fall-out rate for particles of a size which is optimal for deposition at the predilection site of the specific organism. Furthermore, local geographical and climatic factors may greatly modify distributional patterns of airborne disease during major epidemics or epizootics: specific outbreaks are cited as examples.

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Sumario Se ha demostrado que un número criente de enfermedades tanto en el hombre como en los animales son diseminadas por micro-organismos que se encuentran en suspension en el aire. La viabilidad de tales micro-organismos en el aire declina en forma progresiva como resultado de factores fisicos y otros factores sumarizados en el texto. La humedad relativa influencia de manera especial la viabilidad en estudios experimentales, pero las diferencias entre las cepas tambien parece jugar un importante rol en algunas enfermedades. Resultados de laboratorio fueron confirmados por observaciones hechas en el campo sobre poliomielitis, viruela, fiebre aftosa, peste bovina y enfermedad de Newcastle; Es probable que la enfermedad de Marek. la bronquitis infecciosa aviar y otras numerosas enfermedades seandiseminadas de la misma manera. La diseminación a grandes distancias por corrientes de aire puede ser influenciada, hasta cierto punto, por la virulencia del agente causal y por la tasa de acentamiento para particulas de un tama?o, las cuales son óptimas para su acentamiento en el lugar de predilección del organismo específico. Mas aun, factores locales geográficos y climáticos pueden modificar grandemente los patrones de distribución de enfermedades diseminadas por el aire durante grandes epidemias ó epizootias: Se citan como ejemplos brotes específicos.

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Résumé Il a été démontré qu'un nombre croissant de maladies humaine et animale sont dísséminées par des microorganismes en suspension dans l'atmosphère. La viabilité de tels agents pathogènes décroit progressivement en fonction de l'influence des facteurs physiques et autres qui sont énumérés dans ce texte. L'humidité relative influence fortement cette possibilité de survie comme l'ont montré des études expérimentales, mais des différences de souches semblent aussi jouer un r?le important pour certaines maladies. Les résultats expérimentaux ont été confirmés par des observations faites sur le terrain à propos de la poliomyélite, la variole, la fièvre aphteuse, la peste bovine et la maladie de Newcastle; il est probable que la maladie de Marek, la bronchite infectieuse aviaire et de nombreuses autres infections se répandent de la même manière. La dissémination à longue distance par les courants aériens peut être influencée, dans une certaine mesure, par la virulence de l'agent causal et par le pourcentage de particules dont la taille est optimale pour leur arrivée au site d'élection du microorganisme spécifique. En outre, des facteurs géographique et climatique locaux peuvent grandement modifier le schéma épidémiologique des maladies disséminées par voie aérienne; des foyers spécifiques sont cités en example.

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Based on a paper presented at a Meeting of the Central Canada Veterinary Association on 9th December 1970.     

Hydrogen Evolution by Nitrogen-Fixing Anabaena cylindrica Cultures

Actively growing, nitrogen-fixing cultures of the blue-green alga Anabaena cylindrica can simultaneously evolve hydrogen and oxygen frolni water and light. Hydrogen evolution was strongly inhibited by N(2) but only slightly by CO or O(2), characteristics of the nitrogenase reaction in the heterocysts of Anabaena cylindrica. We suggest that this reaction has potential use in solar energy conversion.     

Dietary calcium-phosphorus ratios for growing pigs in relation to serum levels and bone development

Two experiments comprising a total of 80 Danish Landrace pigs in the period 20–90 kg live-weight were carried out to study the effect of dietary levels and ratios of Ca and P on serum values of Ca, inorg. P, and alkaline phosphatase and on the development of degenerative arthritis and atrophic rhinitis.In both experiments each kg feed (Table 1) was supplemented with 600 i. u. vitamin D₃ and 80 p. p. m. Zn.In the first experiment the Ca:P ratio was 1.2 and the amount of Ca increased from 0.48 % to 1.20 % without influencing daily gain, feed conversion, carcass performance (Table 2) or frequency of atrophic rhinitis (Table 3). The Ca:P ratio in scapula was 2.15. Only when the diet was supplemented with 1.20 % Ga and 1.00 % P the bone quality was histomorphologically adequate (Figs. 1–4).In the second experiment various Ca:P ratios (ranging from 0.1 to 3.0) were compared with the recommended level and ratio of 0.72 % Ga and 0.60 % P. Performance of pigs on the normal level was better than for the other pigs (Table 4). Clinically, various degrees of leg-weakness and -deformation occurred, most pronounced in the high Ca — low P group. Very little lameness and no convulsions were observed. Marked hypocalcemia was not found. Unilateral high Ca intake increased serum Ca significantly, and serum alkaline phosphatase slightly, and decreased serum P (Figs. 5–7). Advanced pericytic osteolysis, poor mineralization and generalized osteodystrophia fibrosa were found in the low Ca groups (Figs. 8–13). The groups showed no differences in frequency of atrophic rhinitis (Table 5), and rickets was not observed.The incidence of degenerative joint lesions was not increased in pigs on the unfavourable Ca:P ratios, and depended apparently more on litters than on diets.