Abstract
BackgroundThe Maedi-Visna (MV) lentivirus causes two slowly progressive eventually fatal diseases of sheep, Maedi, a progressive interstitial pneumonia, and Visna, a progressive demyelinating disease of the central nervous system. Other lentiviruses also cause fatal slow infections in their natural hosts, e.g. the HIV virus in humans. Results of experimental vaccination against any lentivirus where vaccinees are challenged by natural routes, may therefore be of general interest. From 1991–1998 experiments with formalin-inactivated whole Maedi-Visna virus vaccine were carried out in the Department of Microbiology at the University of Iceland. Western Blot tests showed good immune response to all major proteins of the virus. When aluminium hydroxide was added to the vaccine all vaccinees developed neutralizing antibodies to the vaccine strain at titers 1/8 – 1/256. After housing 5 twin pairs, one twin in each pair vaccinated, the other unvaccinated, with infected sheep for 4 years, all the unvaccinated twins became infected, but only 2 of their vaccinated siblings as confirmed by virus cultivation experiments on tissues from their lungs spleens lymph nodes and choroid plexuses.ResultsOne twin in each of 40 female twin pairs, born into a Maedi-Visna-infected sheep flock and kept under natural farming conditions in Cyprus, was vaccinated at birth, 3 weeks and 3 months, with formalin-inactivated whole Maedi-Visna lentivirus vaccine adjuvanted with aluminium hydroxide. 17 mothers of the twins were seronegative, 13 seroconverting and 10 had old infection. Of 17 vaccinees born to seronegative mothers 9 were uninfected at 28 months, but only 2 of their unvaccinated siblings. Of 13 unvaccinated twins born to seroconverting mothers, 12 caught infection during their first 10 weeks, but only 4 of their vaccinated siblings. Vaccination had no effects on 10 vaccinees born to mothers with long-standing Maedi-Visna infections and broad andibody response at birth of their lambs.ConclusionCompared with their unvaccinated siblings, natural infection was delayed in significant number of vaccinated twins born by seronegative and seroconverting mothers and vaccinated at birth, 3 weeks and 3 months with formalin inactivated whole MV vaccine adjuvanted with aluminium hydroxide. Maternal antibodies interfered with vaccination so early in life if the mother had old infection.
Highlights
The Maedi-Visna (MV) lentivirus causes two slowly progressive eventually fatal diseases of sheep, Maedi, a progressive interstitial pneumonia, and Visna, a progressive demyelinating disease of the central nervous system
Maedi, progressive interstitial pneumonia, and Visna, progressive demyelinating disease of the central nervous system, are two serious, slowly progressive and eventually fatal diseases of sheep caused by the same lentivirus infection, the Maedi-Visna (MV) virus infection [1,2,3]
Later in this study we found that 13 of the 30 mothers negative in the AGID test were positive in Western Blot (WB) tests against the vaccine strain of virus
Summary
The Maedi-Visna (MV) lentivirus causes two slowly progressive eventually fatal diseases of sheep, Maedi, a progressive interstitial pneumonia, and Visna, a progressive demyelinating disease of the central nervous system. Housing infected sheep with healthy flocks was the main mode of natural Maedi-Visna transmission from one farm to another in Iceland during the epidemic 1933–1952 [3] This route of transmission was chosen as the challenge in these experiments. After being housed with the infected sheep for 4 years, 5 unvaccinated twins in 5 twin pairs had become infected, but only 2 of their vaccinated siblings These results were confirmed by virus cultivation experiments on tissues from spleens, lymph nodes, lungs and choroid plexus from all 10 twins [5]. After these experiments it was tempting to test the effects of this vaccine in a naturally-infected sheep flock. The National Veterinary Services in Cyprus were introduced to these results, decided to participate in a field trial of the vaccine and found a place for the experiment on one very good sheep farm
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