Faecal shedding and serological study of Lawsonia intracellularis from two horse farms in Argentina

Lawsonia intracellularis (Li) is the causative agent of equine proliferative enteropathy (EPE), an endemic infection in pigs and an emerging concern in horses. EPE has been reported in North America, Europe, Australia and Brazil, and is more frequent in weaned foals. The antemortem diagnosis of EPE is based on the detection of Liespecific antibodies by serology and the molecular identification of DNA in feces by PCR. The aim of this work is to report an outbreak of EPE in two horse farms in Buenos Aires province. Serology tests were performed both in mares and weanlings (9-12 months) while PCR of faecal samples was performed only in weanlings. The DNA was extracted (ZR MiniPrep Zymo Research, USA) and the PCR was applied according to Jones et al. 1993. The indirect immunofluorescence was carried out according to Knittel et al. 1997. In farm one, sera from 32 mares and two foals with diarrhea and clinical signs were analyzed, while in farm two, sera from 14 mares and 15 foals were processed, where only one had chronic diarrhea and an antibiotic treatment. The results are shown in table 1. Total positive sera were 79% (50/63) and positive PCR in foals 12% (2/17). Besides, at least one animal was positive by PCR in each farm. The high percentage of seropositive animals may indicate previous exposure to Li. The seropositivity of mares implies subclinical infection, a situation of constant exposure or long term persistence of serum antibodies. In a foal with diarrhea and positive PCR may confirm the EPE. However, in a foal with diarrhea and negative PCR, the disease could not ruled out, because a negative result is expected in situations such as a prolonged course or antibiotic therapy. The detection of positive PCR animals without diarrhea, as observed in farm two, can be related to a subclinical infection, a common condition seen in swine. In conclusion, to our knowledge, this is the first description clinical and subclinical case of EPE with confirmed diagnosis by serology and fecal PCR in horses in Argentina. The EPE must be considered among the possible diagnoses in cases of enteritis in foals. Use of these tests may aid in detection of the disease allowing for early and specific treatment to improve the prognosis of affected horses.