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A definition of bovine rotavirus virulence

Janice C. Bridger

AFRC Institute for Animal Health, Compton Laboratory, Compton, Newbury, Berkshire RG16 0NN, U.K.

Rotaviruses are accepted as enteric pathogens of calves but many natural infections are subclinical. In the present paper, the outcome of inoculation of gnotobiotic calves of three ages (the second day of life, the second week of life and calves aged 6 weeks and over) with doses of 10^5.0 to 10^6.5 TCID₅₀ was compared for three bovine rotavirus isolates (C3-160, 17/4 and 39/58). The clinical outcome of infection was dependent on both calf age and rotavirus isolate. Age-dependent resistance to infection was not found. By contrast, age-dependent resistance to disease was found with rotavirus isolates C3-160 and 17/4 but not with 39/58. All three isolates caused disease in calves inoculated on the second day of life but only one, 39/58, caused disease in the two older groups. Peak levels and duration of virus excretion were similar in clinically normal (10^{6.7 ± 1.08} TCID₅₀ per g of faeces for 4.6 ± 1.2 days) and diseased (10^{7.45 ± 0.94} TCID₅₀ per g of faeces for 5.3 ± 0.98 days) calves of all ages, but the onset of virus excretion occurred sooner in clinically affected calves (1.6 ± 0.63 days in clinically affected compared with 3.7 ± 1.5 days in clinically normal calves, P < 0.01). The present study confirmed the findings of an earlier study (Bridger & Pocock, 1986) which showed that bovine rotaviruses differ in virulence for calves in the second week of life and that older calves are susceptible to rotavirus infection and disease. In addition, the present study demonstrated for the first time, that differences in rotavirus virulence are not apparent with calves inoculated on the second day of life, an age which has been used commonly to assess rotavirus virulence. It is suggested that rotaviruses that cause disease in calves only on the second day of life should be described as of low virulence whereas those that cause disease in all ages should be described as virulent.

Present address: Department of Veterinary Pathology and Infectious Diseases, Royal Veterinary College, London NW1 0TU, U.K.

Received 26 November 1993; accepted 13 May 1994.

This article has been cited by other articles:

				J. C. Bridger, G. I. Tauscher, and U. Desselberger Viral Determinants of Rotavirus Pathogenicity in Pigs: Evidence that the Fourth Gene of a Porcine Rotavirus Confers Diarrhea in the Homologous Host J. Virol., August 1, 1998; 72(8): 6929 - 6931. [Abstract] [Full Text] [PDF]