Contagious agalactia of sheep and goats preliminary studies on vaccines

Abstract

Vaccines against contagious agalactia were tested for their ability to protect goats against challenge by subcutaneous inoculation of a strain of M. agalactiae of known infectivity. The results were assessed on clinical signs, and ante and post-mortern isolation of the challenge organism. They were expressed quantitatively by means of a scoring system. Serological response to vaccination was measured by complement fixation and growth inhibition tests. Of a number of vaccines prepared from formalin killed M. agalactiae those containing concentrated suspensions of mycoplasmata cells in oil adjuvants gave the best protection. A vaccine prepared from a cell suspension emulsified in oil and Falba gave better results than aluminium hydroxide vaccines prepared by the method of Popovici and De Simon (1966). Before challenge, most of the goats vaccinated with oil and Falba vaccine became reactors to the CF test, but none reacted to the GI test. None of the dead vaccines prevented infection after challenge, but the resulting disease was in some instances less severe than in unvaccinated control goats. A live vaccine, attenuated by 40 passes on selective agar, gave complete protection against the challenge inoculation. The vaccine strain could be differentiated from the challenge strain by bacteriological methods. Goats inoculated with the live vaccine had a small residual infection with the vaccine strain when killed 3 to 4 months after vaccination and later work has shown that it can produce clinical contagious agalactia in lactating sheep. Before challenge, all the goats inoculated with the live vaccine became reactors to both the CF and GI tests.