High seroprevalence against Lawsonia intracellularis in horses living in Belgium

Lawsonia intracellularis (LI) is an obligate intracellular gram-negative rod causing equine proliferative enteropathy (EPE). Occasional cases of EPE in foals have been reported in Belgium, but the seroprevalence of equine LI in the country is unknown. The aim of this study was to determine the seroprevalence of LI in adult healthy horses in Belgium.
The target population included clinically healthy adult horses, housed in the same premises for the
previous 12 months. Serum samples from horses living throughout Belgium were collected and
analysed for specific IgG antibodies against LI using a blocking ELISA test. Results were expressed
as Percentage of Inhibition (PI). Samples that had a PI <20% were judged as negative, those
between 20 and 30% as inconclusive and those >30% were considered positive.
A total of 356 blood samples were analysed with 352 horses (98.8%) testing positive, 2 horses (0.
56%) testing negative and 2 horses (0.56%) showing inconclusive results. The high prevalence of
positive samples precluded any statistical analysis to test the impact of province of residence, age,
breed or gender on the results.
In conclusion, the large percentage of seropositive samples obtained in this study confirms a
widespread exposure of Belgian horses to LI. Seroconversion is rarely associated to clinical disease, but suggests that EPE should be part of the differential diagnosis in horses with compatible clinical signs (ill-thrift, hypoproteinemia, edema, and diarrhea). These results are in accordance with results of prevalence reported in neighbouring countries (The Netherlands, Germany), whilst other countries (Israel) report a much lower prevalence.