Björn Sigurdsson

Cultivation of visna virus in tissue culture

The virus of Visna, a slow, demyelinating leucoencephalitis of sheep, has been cultivated in tissue culture. The cells employed are derived from the chorioid plexus of sheep. The virus causes characteristic cytopathic changes in the culture, so that the method may be used to detect virus activity and measure the activity of virus containing material. Virus which had undergone 3, 11, and 12 passages in TC was injected intracerebrally into sheep and found to produce typical Visna lesions. Neutralizing antibody has been detected in sera from a certain proportion of sheep affected with Visna. The rate of virus multiplication in tissue culture after inocula of varying size has been studied. Small inocula tend to give rise to a mild infection which persists in the culture for long periods of time without destroying more than a certain proportion of the cells. The possible relationship between this relatively stable balance between virus and cells and the extraordinarily slow progress of Visna in the CNS of sheep is discussed.

Adenomatosis of sheep's lungs; experimental transmission.

Infectious adenomatosis of sheeps lungs (Jaagsiekte) was transmitted to two out of four sheep using material from diseased lungs which had been kept frozen for 52 months. The infectious agent was sedimented twice in the ultracentrifuge in order to wash it of some soluble substances and in order to concentrate it slightly. The extract was inoculated directly into the lung, into the trachea and intranasally. The experiment was terminated after 14 months and at that time typical lesions were found, but they were of small size and seemed to be at an early stage.

The serological diagnosis of Johne's disease of sheep

Summary The results of a new diagnostic complement fixation test for Johnes disease among sheep are described. The antigen used was extracted from the infected intestinal mucosa. The study was carried out on an infected flock of 55 sheep. Out of 31 sheep found to be infected on slaughter, 30 had proved to be serologically positive, the remaining one not having been subjected to an adequate test. The sera from four more sheep in which no lesions could be found in the intestines, were also found to be strongly positive. One hundred and eighteen sheep from healthy areas were tested as controls. Four only of them showed serological reactions, which were very weak. Thirty-nine sheep of the experimental flock were also tested by means of the intradermal johnin test, using johnin PPD as described. Only about 50 per cent. of the infected sheep reacted to the various johnins used in the strengths mentioned in this paper.

A Disease of Icelandic: Cattle Characterised by Sudden Death

Summary “Bradadaudi,” a disease of cows, occurs in many widely separated areas in Iceland and the incidence varies from year to year in an entirely unexplained fashion. Affected animals die suddenly often without previous clinical symptoms. The disease reaches its peak during the spring and early summer. Cases frequently occur during or shortly after severe physical strain. On post-mortem examination gross macroscopic lesions are usually absent and conspicuous microscopic lesions are found only in the kidneys. These comprise small haemorrhages and a considerable exudation inside the nephron. The result of some feeding experiments and certain chemical analyses suggest, that the disease is not caused by hypocalcaemia, hypomagnesaemia, by a deficiency in ascorbic acid, nicotinic acid, panthothenic acid, pyridoxin, riboflavin or thiamin, nor by a deficiency in copper or cobalt. Clinically “Bradadaudi” is very similar to Falling Disease or Sudden Death of cattle in Australia which is believed to be caused by a deficiency of copper. The aetiology of the Icelandic disease has not yet been explained.