South African Equine Veterinary Association Congress 2015 Protea Hotel Stellenbosch
Figure 3. Transabdominal ultrasonographic image of
a weanling foal with severe hypoproteinemia and
thickened small intestinal walls consistent with
Lawsonia intracellularis infection
A retrospective study of 57 foals and weanlings with L. intracellularis infection revealed an age
of onset from 2 to 8 months of age. Further, a seasonal occurrence was noted with animals
affected from August through February but it was unclear whether this seasonality was due to
increased risk of exposure or was simply consistent with the age at which foals and weanlings are
most susceptible. 81% of the young horses had ventral oedema and all had moderate to severe
hypoalbuminemia (74% <2.0 g/dL [20 g/L]). Fever and diarrhoea were found in only 19% and
32% of affected patients, respectively.
Lawsonia intracellularis is a fastidious organism that cannot be cultured from faeces; thus, testing
of faeces by polymerase chain reaction (PCR) is pursued in an attempt to establish a definitive
diagnosis. However, both false-positive and false-negative PCR test results can occur as the
organism can pass through the intestinal tract without causing disease and intermittent shedding
of infected epithelial cells in a foal with clinical disease could leading to varying test results.
Consequently, an immunoperoxidase monolayer assay (IPMA) to detect antibodies in serum can
also be used to assess infection and an IPMA titre >60 is considered positive for L. intracellularis
infection. In the report of 57 cases, 38/51 horses tested positive by faecal PCR and 38/47 had a
positive serum IPMA titre. Only 26 foals had both positive faecal PCR and positive serum IPMA
results while 13 horses had a positive serum IPMA but a negative faecal PCR and nine horses had
a positive faecal PCR but a negative serum IPMA titre. In the same report the authors also tested
103 apparently healthy herd mates of the sick foals and found six with positive faecal PCR test
results and 34 with positive serum IPMA titers (both tests were not performed on all foals).
Cl