Known facts about the epidemiology of porcine proliferative enteropathy

Abstract

The amount of new information of the last seven years regarding Lawsonia intracellularis sensitivity to antimicrobial drugs, prevention/control based on treatment and vaccination, diagnosis and, finally, genome is amazing. Nevertheless, not much is known about the epidemiology of the disease, mainly regarding the source of infection, resistance of the bacteria in the environment and possible biological vectors that could spread the infection among farms. It was learned that as few as 1,000 to 10,000 bacteria are enough to induce infection and fecal shedding two to three weeks after inoculating susceptible pigs. It was also learned that L. intracellularis organisms can survive at least 14 days in infected feces at room temperature. Sow to piglet transmission is also speculated as a possible and reasonable method of transmission, however, detection of the bacteria in sow feces, quantification of these shed bacteria and evaluation of susceptibility of suckling piglets have never been done. There is no information in the literature regarding the importance of fomites such as boots and biological vectors for the transmission of L. intracellularis. Risk factors related to proliferative enteropathy have been published using retrospective and case control studies showing that transportation, feed change, significant temperature variation, pig flow and floor are all important aspects that have to be considered in order to reduce the pressure of infection. Nevertheless, even applying this knowledge in association to the use of efficient antimicrobials, there have been not many successful attempts to eradicate L. intracellularis from pig herds. It is clear that there is a lot missing about transmission and resistance of the bacteria in order to make a better and sufficient assessment of the relevant aspects of an eradication program.