Biomedical subjects
Publications and source records attributed to B L Patel.
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In Minnesota, efforts have been made over the past 10 years to eliminate turkey coronaviral enteritis (TCE, bluecomb) by controlled depopulation and decontamination with a rest period before restocking. In 1973, clinical observations indicated that bluecomb was restricted to one limited area in Minnesota. Five epiornithics occurred during late 1973 and 1974, involving 5 different farms in this limited geographic area. During 1975, 3 epiornithics of TCE were investigated, involving 185,000 turkeys in 17 flocks, of which approximately 17,000 died. Naturally infected turkeys representing 7 operations between 1973 and 1976 were examined by both the direct fluorescent antibody test and indirect fluorescent antibody test (IFAT). The direct fluorescent antibody test detected coronaviral antigen in intestinal tissues during the acute phase of the disease, and the IFAT was highly useful in detecting TCE serum antibodies of turkey flocks that had recovered and were potential carriers. Therefore, an IFAT surveillance program was instituted for replacement flocks on farms where clinical epiornithics of TCE had occurred in 1974 through 1976. Operation 5 involved TCE epiornithics over a 2-year period and illustrate the importance of complete depopulation with an intensive decontamination program.
Intestinal sections from both experimental and field cases of turkey coronaviral enteritis (TCE) were examined by scanning electron microscopy and light microscopy through 10 days after inoculation and by a direct fluorescent antibody test for TCE through 12 days. Serums were collected for an indirect fluorescent antibody test for TCE through 160 days after inoculation. Lesions observed with the scanning electron microscopy were catarrhal enteritis with hemorrhage per diapedesis, epithelial desquamation, and villous atrophy which developed and regressed within 6 days after inoculation. Light microscopy demonstrated similar lesions, except that villus-to-crypt ratios remained depressed 10 days. The direct fluorescent antibody test demonstrated the presence of coronaviral antigen throughout the sampling period, and serum antibodies to TCE were present until at least 160 days, when the experiment was terminated.
Frozen sections of intestine obtained from experimentally infected embryos were satisfactory as a suitable antigen in the indirect fluorescent antibody (IFA) test for detection of antibodies to turkey coronaviral enteritis (TCE). Antibodies were detected in infected turkeys at 14 days after infection and persisted for at least 107 days when the 1st experiment was concluded. Antibodies were also detected in infected turkeys at 9 days after infection and persisted for at least 160 days when the 2nd experiment was terminated. The IFA test may be of value as a rapid and economical screening method for TCE antibodies.
Turkey flocks recovering from natural and laboratory induced coronaviral enteritis developed lifelong immunity. Virus neutralization tests indicated that neutralization capacity of serums from recovered turkeys was low. One-way cross challenge test using turkeys inoculated with various bluecomb isolates revealed close antigenic relationship or antigenic identity among bluecomb isolates. The controlled application of intestinal preparations containing coronavirus as a vaccination procedure had value in developing active lasting immunity but it has limitations in areas that are attempting to eliminate the disease by a depopulation program. Killed vaccines injected parenterally did not produce a detectable immunity.
Intestinal tissues obtained from coronavirus-infected embryos and turkeys were examined by fluorescent antibody tissue section technique (FAT). Evidence of viral antigen was demonstrated in the cytoplasm of the intestinal epithelial cells covering the villi. Embryo intestines that were examined from 24 to 96 hours after inoculation were positive for immunofluorescence (IF), whereas bursa of Fabricius was negative. Poults hatched from infected embryos were examined at 2 days of age and were positive for IF. Coronaviral antigen was detected by FAT in the cytoplasm of intestinal epithelial cells of the jejunum, ileum, duodenum, and cecum in all turkeys that were examined from 24 hours to 28 days.
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The histopathology of fasting and bluecomb disease in one-day-old turkey poults inoculated with bluecomb disease coronavirus (BCDCV) was studied. Uninoculated fasting poults produced clinical signs similar to those observed in BCDCV-inoculated poults. No histological changes in the intestines were observed in the fasted poults whereas definite lesions were observed in the BCDCV-inoculated poults. The lesions did not differ significantly with whether they were fed or fasted. The severity of the lesions in the intestinal epithelium was in decreasing order in the jejunum, ileum, and cecum. The lesions first appeared 24 hours postinoculation (PI) and progressed through 96 hours PI, as marked shortening of the villi, loss of microvilli, granular appearance of the cytoplasm of epithelial cells with nuclear margination of chromatin, and accentuation of the nucleolus. Similar lesions were observed in the jejunum, ileum, and cecum of turkey embryos inoculated at 24 days old as well as poults from these embryos. Signs of healing were first seen at 120 hours PI. No histopathological changes were observed in the pancreas, brain, kidneys, liver, adrenal, and bursa of Fabricius. The intestinal lesions observed should be a useful histological technique for differentiating fasting from bluecomb disease in turkey poults.