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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.

Studies on local immunity to transmissible coronaviral enteritis of turkeys (bluecomb) was made. Intestinal secretions and bile from affected birds contained secretory immunoglobulins against coronaviral antigen throughout the 6 months' duration of the experiment. Attempts to purify and to characterize the globulins in intestinal secretions and bile of the affected birds were made, using the techniques of gel filtration, DEAE chromatography, and immunoelectrophoresis. Class-specific anti-turkey IgA antiserum in the agar gel precipitin test further established the presence of IgA in the intestinal secretions and bile.

A double-antibody ELISA for the detection of coronaviruses in intestinal contents from turkey poults with diarrhea was developed. Antibodies were raised in rabbits and guinea pigs against a Minnesota isolate of turkey enteric coronavirus (TCV) propagated in embryonating turkey eggs and were purified by density-gradient centrifugation. The specificity of antisera was confirmed by hemagglutination-inhibition and immunoelectron microscopy. Absorption of anti-TCV hyperimmune sera with egg extracts or egg ovalbumin and the use of different dilution and blocking buffers influenced the sensitivity and specificity of the ELISA. Reciprocal cross-reactivity was detected among turkey, chicken, bovine, and murine coronaviruses. Antisera to the transmissible gastroenteritis virus of swine, the rabbit enteric coronavirus, or the human coronavirus strain 299E failed to react with TCV. The TCV cross-reacted only moderately with the avian infectious bronchitis virus and the hemagglutinating encephalomyelitis virus of swine. Investigations with samples from 47 commercial turkey flocks in Quebec with episodes of transmissible enteritis revealed that the ELISA was more sensitive than was electron microscopy for detection of TCV.

Studies on cell-mediated immune response in turkeys infected with turkey coronavirus (TCV) were made. A whole blood culture technique was developed for quantitatively evaluating in vitro lymphocyte reactivity to mitogens concanavalin A, phytohemagglutinin-P, and TCV antigen. The degree of blastogenesis was quantitated by the measurement of the uptake of the [125I]deoxyuridine in the presence of fluorodeoxyuridine. The stimulation indices were consistently higher in the infected birds compared with those in the noninfected controls, and they were statistically significant (P < 0.05). The detection of TCV specific responses indicated that cell-mediated immunity may be important in determining the immunity against turkey coronaviral enteritis. The whole blood lymphocyte transformation assay was emphasized as a convenient and useful in vitro indicator of cell-mediated immunity in TCV infection.

The present study concerns the production of specific secretory antibodies in turkeys orally inoculated with turkey coronavirus (TCV). Tissue localization of secretory antibodies in the intestines of recovered birds 4 and 5 months later was demonstrated by immunofluorescence technique. Intestinal sections were stained by sandwich method, using concentrated TCV antigen and anti-TCV conjugate. It was suggested that local synthesis of antibody might be responsible for life-long immunity seen in these birds after recovery from infection.