Sheep-pox vaccine prepared from formaldehyde inactivated virus adsorbed to aluminium hydroxide gel

The aim of the study was to produce an efficacious formaldehyde inactivated, adsorbed vaccine from the Mongolian sheep-pox MH virus strain. Aluminium hydroxide gel prepared from AlCl3 X 6 H2O proved to be the most efficacious adsorbent among the gels prepared from different substances. Above 1.8% Al2O3 content the unadsorbed virus quantity was less than 1% of the original one. Using gel prepared from KAl(SO4)2 and AlCl3 X 6 H2O, respectively, the quantity of adsorbed virus was the same during the adsorption period from 10 min to 24 h. Intradermal inoculation of sheep proved more advantageous for virus production than subcutaneous inoculation. Three vaccines containing different quantities of antigen were prepared from virus propagated in sheep. The vaccine containing 19 800 ID50 inactivated virus did not protect the sheep even against a virus challenge of 25 ID50, while that of 67 000 ID50 content protected 50% of the animals infected with 125 to 287 ID50, and that of 395 000 ID50 content protected 100% of the animals against challenge with more than 100 000 ID50. More than 3 million sheep were inoculated in Mongolia with vaccines of 350 000 ID50 virus content in the last years. In the areas where vaccination has been introduced no sheep-pox epizootic has occurred.