Studies on the pathogenesis of rinderpest in experimental cattle I. Correlation of clinical signs, viraemia and virus excretion by various routes

Abstract

A total of twenty-five grade cattle were infected experimentally with a strain of rinderpest virus of moderately high virulence (RGK/1). Three methods of introduction of the virus were employed, i.e. subcutaneous or intranasal inoculation (14 animals) and housing in contact with reacting cattle (11 animals).A quantitative study of the viraemia and of virus excretion by the nasal, urinary and faecal routes, was made by the inoculation of primary calf kidney cultures. All virological data were related to the onset of pyrexia, the incubation period in inoculated animals being 3–5 days, while in those infected by contact it was 8–11 days. Viraemia preceded the first rise of temperature by as much as 2 days in inoculated animals and 1 day in the contact cases. All animals had viraemia by the 4th day of the disease, but thereafter the percentage of positives declined rapidly, reaching nil by the 9th day.The case mortality rate was 48 % with the majority of animals dying on the 7th to 10th days after reaction.Virus was detected in the nasal secretions of some animals on the 2nd day preceding pyrexia. The proportion of nasal excretors rose slowly to reach a maximum of 87·5 % on the 4th day and no positives were detected after the 9th day of fever. The titre of virus in nasal discharges reached high levels, often probably in the region of 105·0 to 106·0 TCD 50/ml.Urinary excretion of virus began on the 1st day of fever in about 25 % of animals; reaching a maximum of 62·5 % on the 7th day. No virus was recovered from the urine after the 8th day of the disease, the rapid decline in the excretor rate being only partially attributable to the death of severe cases. Urinary titres were relatively low; they seldom exceeded 102·0 TCD 50/ml.Virus was first recovered from the faeces on the 3rd day of pyrexia. Excretion by this route was not constantly associated with the development of diarrhoea, but the rapid decline which occurred in the excretor rate on the 8th and 9th days was undoubtedly attributable to the death of diarrhoeic individuals which took place at that time. The majority of faecal titres were in the approximate range of 103·0 to 104·0 TCD 50/g. but occasional samples attained ca. 106·0 TCD 50/g.It was calculated, from the clinical and virological data that cattle can excrete virus, at least by the nasal route, as much as 6 days before the appearance of pathognomonic clinical signs, i.e. oral necrosis and erosion.Our findings for rinderpest were compared with those of other investigators of this disease and also with the available information on canine distemper and human measles.We are very grateful for their able technical assistance to Messrs L. W. Rowe, C. S. Rampton and R. F. Staple. Particular thanks are due to Mr C. S. Rampton for his preparation of all the figures. We have received considerable and indispensable help from our junior laboratory staff, especially Mr Francis Ngugi Gachuhi and Mr Joash Adero.This paper is published by permission of Mr H. R. Binns, C.M.G., O.B.E., the Director of the East African Veterinary Research Organization.