Experimental transmission of intestinal coccidiosis to piglets: clinical, parasitological and pathological findings.

Twenty-eight piglets coming from a "specific pathogen free" herd were inoculated at three days of age with 50 000 or 100 000 sporulated oocysts of Isospora suis. Fecal samples were examined for oocyst shedding daily and several clinical parameters were recorded. Ten piglets were used as normal controls. Groups of piglets were euthanized from three days to 12 days postinoculation and routine necropsies were performed. Bacteriological, virological, parasitological and histopathological examinations were made on the intestinal tracts. The incubation period was four to five days. Clinical signs and microscopic intestinal lesions observed in the experimentally infected animals were similar to those reported in spontaneous cases of porcine neonatal coccidiosis. Lesions of villous atrophy in the small intestine seemed to result from the destruction of villous epithelial cells mainly during the peak of asexual reproduction which occurred around four to five days postinoculation. Intracellular coccidial organisms were difficult to find during the late atrophic and villous regrowth stages of the intestinal lesions. The prepatent period varied from four to seven days and the most common was five days. Eighty percent of the piglets kept alive more than four days postinoculation have shed oocysts. Piglets dosed with old sporulated oocysts (ten months old) shed many more oocysts than those infected with a fresh inoculum (less than two months old). The patent period was not determined precisely with the design of the experiment but some of the infected piglets shed oocysts for at least five days.     

The genetic control of antibody formation

Studies of the molecular biology of lymphoid cells have markedly increased our understanding of how millions of different antibodies can be synthesized by a single animal. To date, the most detailed understanding has been achieved for the mouse, primarily because of the relatively greater experimental availability of this species. These studies, as well as those involving other species, have shown that the complete genes for antibody polypeptide chains are assembled from disparate genetic elements which are originally widely separated in the genome. The assembly process itself, together with the coding information present in the germ line genetic elements, contributes to the diversity of structure (and thus combining specificities) shown by mature antibody molecules. Specifically, the diversity of structure characteristic of antibody variable regions is due to three distinct mechanisms: innate variability of germ line genes; mismatching of individual gene segments during their somatic rearrangement leading to junctional diversity; and somatic mutation in variable region genetic material during or after the rearrangement. These processes lead to the wide array of combining specificities that permit the humoral immune system of a mature animal to interact with essentially any non-self antigen which it encounters. Complex genetic rearrangements are also responsible for the class switching phenomenon long known to be characteristic of the humoral immune response. A form of homologous recombination between constant region genes, possibly mediated by specific "switching" enzymes, is now believed to be involved in this phenomenon. It is also currently believed that the restriction of gene rearrangement processes to one of the two possible chromosomes of a diploid pair in each cell is responsible for the phenomenon of allelic exclusion that has long been associated with the normal functioning of mammalian B-cells.     

EFFECT OF PARAQUAT ON MICROBIAL ACTIVITIES IN SOILS*

Summary. When paraquat was added to four different soils, nitrification was not appreciably affected but ammonification of soil organic-matter nitrogen was slightly retarded. Carbon dioxide evolution as well as oxygen consumption was used as an index of metabolic activity of soil micro-organisms and paraquat had a stimulatory effect at higher concentrations. Oxidation of added sulphur was slightly depressed. Paraquat decreased both the total mould and bacterial populations in Chehalis silt loam. After 30 days incubation the percentages of Streptomyces and Penicillia were markedly increased by most treatments but were little affected in Chehalis silt clay and Woodburn soils. Except for the temporary suppression of nitrification, paraquat had no significant influence on general microbial activities of importance to soil fertility. Some bimodal effects or toxicity inversions were observed with intermediate concentrations. Effet du paraquat sur les activités microbiennes dans les sols