Epidemiological survey on farms with documented occurrence of equine proliferative enteropathy due to Lawsonia intracellularis.

PROLIFERATIVE enteropathy caused by the obligate intracellular organism Lawsonia intracellularis has been described in a number of domestic and wild animal species (Lawson and Gebhart 2000). In horses, the disease is known as equine proliferative enteropathy (EPE) and has been reported from North America (most American states and Canada), Europe (Great Britain, Belgium and Switzerland) and Australia (Lavoie and Drolet 2007). EPE commonly affects weanling foals at four to seven months of age and has a sporadic occurrence, although outbreaks on breeding farms have been reported (Lavoie and others 2000). Affected weanlings commonly show rapid weight loss, lethargy, depression, fever, subcutaneous oedema due to hypoproteinaemia, diarrhoea and colic. The epidemiology of EPE has remained poorly investigated and the transmission of infection in foals may occur through the ingestion of feed or water contaminated with L intracellularis-infected faeces from free-living or domestic animals (Lawson and Gebhart 2000, Lavoie and Drolet 2007). The objectives of this study were to determine the seroprevalence of L intracellularis in resident foals from two farms with documented cases of EPE, and to determine if subclinical foals contribute to the shedding of L intracellularis. The study was performed on two farms in California. The farms were selected based on one or more documented clinical case of EPE. All documented cases had clinical and clinicopathological findings compatible with EPE, a positive antibody titre to L intracellularis by immunoperoxidase mono layer antigen assay (IPMA) and positive faeces for L intracellularis by real-time PCR. Farm 1, a Percheron breeding farm with 190 resident horses housed on 20 acres, was visited one week following the diagnosis of EPE in a six-month-old filly (in December 2005). Farm 2, a thoroughbred breeding farm with 300 resident horses housed on 40 acres, was visited twice (in October and December 2006) following the diagnosis of five weanlings with EPE. The first visit on farm 2 occurred six weeks after the last of the five confirmed cases of EPE. During each visit, a physical examination was performed and blood and faecal samples were collected from each resident foal. The serum collected from the foals was used to determine the concentration of total solids using a refractometer, and to measure L intracellularis-specific antibodies by IPMA as reported by Guedes and others (2002). Faeces were processed for nucleic acid purification within 48 hours of collection. Phosphate-buffered saline (2 ml) was added to 2 g faeces in a conical tube. Each sample was vortexed for 10 seconds and centrifuged at 13,000 g for two minutes. Nucleic acid purification from 180 μl supernatant fluid was performed using an automated nucleic acid extraction system (CAS-1820 X-tractor Gene; Corbett Life Science) according to the manufacturer’s recommendations. The purified DNA was then analysed by real-time PCR using a previously validated assay targeting the 16S rRNA gene of L intracellularis (Feary and others 2007). Positive (DNA from cell-grown L intracellularis) and negative (L intracellularis-free DNA from faecal samples) DNA controls were used with each run. A total of 11 and 91 resident foals were sampled on farms 1 and 2, respectively. Sixty-five of the 91 foals from farm 2 were sampled a second time two months after the first collection. The previously diagnosed foals with EPE (one on farm 1 and five on farm 2) were among the sampled foals. The age of the resident foals at the first sampling ranged from 5·5 to 8·4 months (mean [sd] 7·1 [1·1] months) and from 4·7 to 9·3 months (7·6 [1·3] months), for farms 1 and 2, respectively. The population of foals comprised six colts and five fillies on farm 1, and 55 colts and 36 fillies on farm 2. On the day of sampling, all foals appeared in good health and none was showing clinical signs compatible with EPE. With the exception of the index case from farm 1 (56 g/l), all remaining foals from the same farm had solid serum concentrations in the reference range of 58 to 87 g/l, ranging from 58 to 67 g/l (mean [sd] 61 [4] g/l). The concentration of total solids of all resident foals from farm 2 was within reference limits and ranged from 58 to 72 g/l (mean [sd] 65 [3] g/l) in October and from 58 to 69 g/l (mean [sd] 66 [3] g/l) in December. Five of the 11 foals (45·5 per cent) from farm 1 had a positive titre (≥30) to L intracellularis by IPMA (Table 1). All seropositive foals, including the index case, had titres of 120. The serological data for farm 2 showed that 27 of 91 foals (29·7 per cent) and 22 of 65 foals (33·8 per cent) had a positive titre to L intracellularis in October and December, respectively (Table 1). The 27 seropositive foals from farm 2 that were tested in October had titres ranging from 30 to 1920 (Table 2), while the titres ranged from 30 to 240 for the 22 seropositive foals tested in December. The highest measured titre of 1920 belonged to a healthy eight-month-old thoroughbred colt with no prior history or signs of EPE. The titre of this foal decreased to 240 in December. From the 65 foals from farm 2 with dual serological results, 38 foals were seronegative (<30) for both sampling times, five foals became seronegative during the two-month period, six foals became seropositive, four foals kept the same titre, eight foals had a two-fold decrease in titre, two foals had a four-fold decrease in titre, one foal had an eight-fold decrease in titre, and one foal had a two-fold increase in titre (Table 2). The five previously diagnosed foals with EPE from farm 2 had titres ranging from 240 to 480 in October (three titres of 240 and two titres of 480). With the exception of one foal that kept the same Veterinary Record (2008) 163, 156-158