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Experimental Maedi Infection in Sheep

1. Detection of Virus, Clinical Course, Histopathology

Experimenten maedi infektion hos får. 1. Upptåckt av virus, klinisk bild, histopatologi.

Acta Veterinaria Scandinavica volume 21, pages 113–123 (1980)Cite this article

Abstract

Eight sheep were inoculated with Icelandic maedi strain M 88; 2 sheep served as control sheep and were in close contact with the inoculated ones. Four of the sheep were inoculated via the respiratory tract with 7×106 TGID50 of strain M88 and the other 4 intracerebrally with 5×105 TGID50 of the same strain.

Maedi M88 strain was isolated from peripheral blood leukocytes of all inoculated sheep. There was a striking difference between the 2 groups in the appearance of demonstrable viremia after inoculation. Viremia could be demonstrated in the intrapulmonarily inoculated sheep within 2–6 months but not until 8–11 months after inoculation in the intracerebrally inoculated ones. This finding is thought most probably to reflect a weak neurotropism of the strain used. After the first demonstration of viremia, maedi virus has been recovered quite reqularly in peripheral leukocytes of all intrapulmonarily inoculated sheep, but less regularly in the intracerebrally inoculated ones. Maedi virus was isolated from 1 of the uninoculated control sheep 15 months after inoculation.

The first clinical case with a clinical appearance suggesting combined involvement of maedi and visna was found among the intrapulmonarily inoculated sheep, 8% months after inoculation. Histopathological examination and virus isolation confirmed maedi. The cause of paraplegia could not be confirmed. No histopathological changes were found and no virus isolation was made from the central nervous system of this animal.

One of the intracerebrally inoculated sheep died suddenly without any observed clinical signs 11 months after inoculation. Histopathological examination revealed pulmonary lesions of maedi, but no visna lesions in the central nervous system, although maedi virus was isolated from various parts of brain.

None of the other experimental sheep displayed clinical signs of maedi or visna during the observation period of 18 months.

Sammanfattning

Åtta får inokulerades med en islåndsk maedi M88 stam, två oinokulerade får fungerade som kontroller och var i nåra kontakt med de inokulerade. Hålften av fåren inokulerades via luftvågarna med 7×106 TGID50 av M88 stammen och den andra hålften intracerebralt med 5×105 TCID50 av den samma stammen.

Maedi M88 stammen har isolerats från perifera blodleukocyter av alla inokulerade får. Skillnaden mellan de två grupperna betråffande påvisad viremi efter inokulationen var slående. Viremi demonstrerades i de intrapulmonalt inokulerade fåren inom 2–6 manader men i de intracerebralt inokulerade fåren först 8–11 månader efter inokulationen. Denna upptåckt reflekterar högst antagligen den anvånda stammens svaga neurotropism. Efter viremins första påvisande (till 16 månader efter inokulationen) har maediviruset åter isolerats ganska regelbundet i perifera blodleukocyter hos alla de intrapulmonalt inokulerade får och mindre regelbundet hos de intracerebralt inokulerade. Maedi virus isolerades från en av de oinokulerade kontrollfåren 15 månader efter inokulationen.

Det första kliniska fallet som såg ut som ett förenat falla av både maedi och visna hittades bland de intrapulmonalt inokulerade fåren 8½ månad efter inokulationen. Den histopatologiska undersökningen och virusisoleringen bekråftade maedi. Orsaken till paraplegin kunde inte bekråftas. Inga histopatologiska förändringar kunde påvisas och ingen virusisolering gjordes från detta fårs centralnervösa system.

Ett av de intracerebralt inokulerade fåren dog plötsligt utan att några kliniska tecken observerades elva månader efter inokulationen. Den histopatologiska undersökningen avslöjade lungföråndringar typiska för maedi men inga visnaföråndringar i dess centralnervösa system. Däremot isolerades maedi virus från olika delar av hjärnan.

Under en 18 månaders observationsperiod upptäckes inga kliniska symptom som tydde på maedi eller visna hos de andra försöksfåren.

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Authors and Affiliations

  1. Department of Microbiology and Epizootology, College of Veterinary Medicine, and the State Veterinary Medical Institute, Helsinki, Finland

    N. F. Friis, K. B. Pedersen & B. Bloch

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  1. N. F. Friis
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  2. K. B. Pedersen
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  3. B. Bloch
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This work was supported by the Finnish Academy.

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Friis, N., Pedersen, K. & Bloch, B. Experimental Maedi Infection in Sheep. Acta Vet Scand 21, 113–123 (1980). https://doi.org/10.1186/BF03546906

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Keywords

Acta Veterinaria Scandinavica

ISSN: 1751-0147