Prevalence and geographic origin of pigs with serological evidence of infection with Leptospira interrogans serovar pomona slaughtered in abattoirs in Victoria, Australia.

A set of 10,440 sera was collected from pigs slaughtered at Victorian abattoirs. These sera were subjected to the microscopic agglutination test for antibodies to Leptospira interrogans serovar pomona. Identification of the herd of origin was possible for 6511 pigs, and these were derived from 167 herds in Victoria (84% of sera), from 32 herds in New South Wales (8% of sera) and 29 herds in South Australia (8% of sera). The overall prevalence of titres of 512 and above was 3.7%. This was higher (5.3%) among pigs for which the property of origin was unknown than among pigs with identified properties of origin. Among the latter the prevalence was 2.7% (Victoria 0.6%, New South Wales 1.3%, South Australia 25.2%.) Most of the pigs with unknown properties of origin were derived from market groups and were probably typically from smaller herds. Within Victoria a comparison of results with the known pig populations of the 12 statistical divisions indicated that infection was spread throughout the State. Of the 228 identified herds of origin sampled, 32 (14%) had at least one pig with a high titre. However, this may underestimate the proportion of infected herds, as in many cases only a few serum samples were obtained. Of 73 herds from which 25 or more serum samples were obtained, serological evidence of infection was obtained in 18 herds (25%).