Abstract
Lambs born to 5 ewes in 3 successive years were studied for presence of maedi virus and its antibodies. In the middle of the first-year pregnancies the ewes and the only ram of the colony were inoculated with maedi virus. No antibodies or viraemia could be detected in the lambs at birth. After sucking colostrum, antibodies appeared in the lambs of the ewes which themselves were seropositive, and reached their peak in a few days. Maternal antibodies disappeared within 12 weeks in all the lambs. Neutralizing antibodies were demonstrated in the colostrum and their content declined rapidly after lambing. Virus was isolated from the milk of 2 ewes in the third year of the study
In the first year the spread of maedi virus was demonstrated to only 1 of the lambs, but in the other 2 years maedi virus was detected in tissues of half of the lambs sacrificed at 3–12 weeks of age. It was concluded that lambs born to chronically infected ewes are readily infected, indicating excretion of virus by ewes. The study yielded no information on the specific routes of transmission, except for the finding of the virus in milk of 2 ewes in the third year of the study. No evidence was obtained of transplacental transmission of maedi.
Keywords: maedi virus, transmission of virus, maternal antibodies
Sammanfattning
Lamm födda av fem tackor under tre på varanda följande r undersöktes med avseende på förekomsten aν maedi virus och dess antikroppar. Efter halva dräktighetstiden under det första ret inokulerades tackorna och den enda baggen i gruppen med maedi virus. Inga antikroppar eller viremi kunde pvisas hos lammen vid födelsen. Efter att ha ftt kolostrum kunde antikroppar pvisas hos lamm till de tackor som själva var seropositiva. Antikroppstitern hos lammen nådde sitt maximum inom några dagar. De maternala antikropparna försvann inom 12 veckor hos alla lammen. Neutraliserande antikroppar kunde påvisas i kolostrum och deras kvantitet sjönk snabt efter lammningen. Virus isolerades från mjölken av två tackor under det tredje året.
Under det första året kunde en spridning av maedi virus påvisas hos bara ett lamm, men under de två darpå följande aren kunde maedi virus redan påvisas i vävnaderna hos hälften av lammen som avlivades i en ålder av 3–12 veckor. Man kan sluta sig till att lamm födda av kroniskt infekterade tackor lätt kan bli infekterade, vilket tyder på att tackorna utsöndrar virus. Beträffande de spesifika överföringsvägarna kunde relevanta fakta inte erhållas i delta arbete, med undantag av upptäckten av virus i mjölken hos två tackor under det tredje året. Inga bevis för en transplacental transmission av maedi kunde erhållas
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Footnotes
This work was supported by grants from the Finnish Academy and the Finnish Veterinary Foundation.
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