Winter dysentery caused by bovine coronavirus: no rule without an exception : diagnostics, clinical picture, epidemiology and herd immunityTråven, Madeleine
This study examines the strength of association between winter dysentery (WD) and bovine coronavirus (BCV), describes the clinical, epidemiological and serological features of the disease in Swedish dairy herds and investigates herd level immunity.
The significance of WD was determined by an interview study comprising 256 dairy herds in central Sweden. The prevalence and distribution of BCV antibodies in dairy herd bulk milk was assessed by a nation-wide survey in 2236 herds.
Isotype-capture ELISAs for BCV-specific IgM and IgA and an ELISA for BCV antigen were developed. Winter dysentery was experimentally reproduced in lactating, BCV seronegative cows with a virulent field strain o f BCV. BCV seronegative, colostrum-fed calves infected with the same BCV strain developed similar diarrhoea. However, the general condition was clearly less affected in the calves. The kinetics of the isotype-specific nasal and systemic antibody responses were followed for 6 to 22 months and very longlasting IgA responses were documented in milk, serum and nasal secretions. Also in naturally infected cows and calves, long-lasting IgA levels were recorded in milk and serum. Cows showed a longer duration of the systemic IgA response than calves.
Use of the BCV-specific IgM and IgA capture ELISAs in addition to the conventional IgGl antibody indirect ELISA detected significant milk or serum antibody responses in 90% of 236 cattle sampled in 38 WD outbreaks. IgM detection was particularly useful for diagnosing primary BCV infections in cattle where the acute samples were taken late. IgM detection can be used diagnostically in samples obtained on only one occasion, due to the comparatively short duration of high IgM levels after infection. An IgA titre increase in paired samples was particularly useful for diagnosing BCV reinfections. Both IgM and IgA detection diagnosed BCV in a higher proportion of the paired bulk milk samples (n=28) than IgGl.
The overall severity score of the WD outbreak and die decrease in milk yield were significantly associated with the herd BCV immunity level, expressed as time since the previous BCV infection.
One typical WD outbreak in south-eastern Sweden was not associated with BCV infection.
Keywordscattle; winter dysentery; bovine coronavirus; isotype-specific antibody response; isotype-capture ELISA; antibody survey; milk; bulk milk; experimental infection; herd immunity.
Published inActa Universitatis Agriculturae Sueciae. Veterinaria
2000, number: 79
Publisher: Swedish University of Agricultural Sciences
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